Turbo / Supercharging - Considerations

All things related to Engineering notably more performance from your Alfa Motor, Transplants, Fuelling & Ignition etc

Is this something people would enjoy?

Poll ended at Fri May 16, 2014 7:13 am

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Total votes: 9

buzzed
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Turbo / Supercharging - Considerations

Post by buzzed »

I thought I would start to share what I have learnt whilst designing and building my twin charge Alfetta. OK, so I have other threads that go into the detail, but the threads are large and, whilst a good read, are not a concise place to find information. To I will attempt to condense my knowledge here for others to benefit from. My hope, is that we will all do the same, on the areas we are most knowledgeable on. For me, that's engines, or more specifically, the modifications required to significantly increase the output. I will write the post over a week or two. and will try to break it into sections.

If people can post below what information would be really useful to them, I will try to incorporate it.

My background:
14 years as a mechanical engineer. Worked with GM designing body structures for various models. Spent 20 years modifying cars, generally focussed on turbo charging. I am not a mechanic, nor do I profess to be, although, I do my own work and have taught myself (like many others) enough to be dangerous . Any advise or suggestions I give here are personal opinion, backed by research, first hand experience, or gut feel (any combination ). Take my guidance at your own risk is what I am saying. Most of what I suggest may be track only solutions!

Righto, enough of that. The proposed topics (to be adjusted based on peoples interest)

[quote]Turbo or supercharging your engine.[/b]

Why do it?
OK guys (and gals), lets kick it off. I think this is the question that many of us skip over. Maybe you heard a turbo car go buy, or maybe you had a ride in a mates turbo/supercharged car and were hooked from then on. It's important (but not as much fun) to ask yourself why you want to head down the path in the first place. For two reasons, firstly, it's going to cost three times as much as you 'think' it will cost, and secondly, there are many ways to skin this cat, and if you don't get the right advise up front, you will either be unhappy with the end result, or end up putting your car up for sale as an 'unfinished project' and haemorrhaging cash :-).
I’ll tell you why I got into turbos and superchargers, and then we can talk about what might be a better approach .
I started off in a Fiat 128 3P (actually I finally bought one again...another story). It was to be fair, slow as a wet week, with a max speed of 140Km/hr fully wound out, but I loved it. I wrote that car off, so I bought the biggest engine car I could afford at the time to replace it with my paltry budget. Thank god this was not my first car, or I might never have fallen in love with cars at all. It was a Mitsubishi Sigma with a 2.6 Liter motor. I thought more liters equals more fun right?....how wrong could I be?! That was a hideous asthmatic 4 cylinder that refused to rev. I kicked it to the curb and purchased an Alfetta sedan...I was saved. I then did a bit of research and got interested in rotaries....maybe liters was not everything it was cracked up to be. Well I drove my 12a RX7 around for 12months and loved it....then a 13b turbo motor turned up for sale...hmmm. So I did my first engine swap. I knew stuff all about denotation and I drove that thing around hitting what I thought was the rev limiter, only to find out later the turbo was boost spiking after I put a 3inch exhaust on it which reduced back pressure to the turbo and allowed boost spikes to occur. Unknown to me I was regularly hitting 24+psi. Hats off to that motor, she never blew . I then uprated the turbo on the engine and ended up with over 245 KW at the wheels. The car screamed and was one fast street car. Even then, I wanted more Hp. Lesson number one..... you can NEVER have enough HP.
I have owned about 60 cars since then. You could say I am addicted.
OK, so back to the point, I ‘fell’ into turbo’s. I wanted more Hp and I was fascinated by the way the turbo extracted the Hp. I predominantly used the car as a street car with the occasional track day. These days I modify a car AFTER I work out what the hell I am going to do with it. This has taken me a long time to work out. You don’t modify cars without a purpose. If you do, you will end up driving them on the street, having the occasional drag race, spending most of your time avoiding speed humps and finally having your car impounded, and if you are an ‘enthusiastic’ driver, your licence taken for good measure. 99% of Society does not like the street car modifier....not one bit. I for one got tired of looking over my shoulder.
So here’s the rub, and it goes for all mods. Know the end use of the car. If it’s a road car, try to work within the rules, or at least know the rules....If you want to hit the track, build it to a set of rules, be it drags, circuit, hill climbs etc etc. Just remember, if you don’t build to a class, your car will be worth less at the end of it all, and you will be driving by yourself. The above even applies to those who don’t like to drive their cars so much as show them...there are still rules.
There are many different reasons to modify, no right or wrong way, but there are consequences for choosing one or the other, and if you go into it with your eyes open, the results will not be a surprise to you.
Lets talk about cost. If you head off aimlessly, without a goal in mind, a plan and a budget, by the time you work out what you really wanted, you will have p^$sed a lot of cash up against the wall. Oh....DO NOT get a loan for mods. Mods don’t make you money (almost always) and it sucks selling your car when you get bored or write it off or get it impounded or whatever, and you still have a loan to pay off....happens ALL the time...don’t be that person.
A great mate of mine (ex. Lambo engine builder actually) once said to me, you need a budget. When you get your pay-packet, 40% goes on living expenses, 30% goes to savings (for a house) and 30% goes on toys. It’s darn simple but I like the thinking. Don’t let your toys take over your life. Get yourself a sensible toy budget and stick to it.
So in summary, before you ask ‘how do I turbo a boxer’, first ask yourself ‘what’s my end use of the car, what’s it going to cost, and how long will it take me to save for it? It’s not the fun part, this planning business, but it sure makes for a much more rewarding package.
OK, I now feel like I have given responsible advise, and can get down to the good stuff . How!!

How is power made?
OK, You know you want to boost your engine. You want more power....but what are the variables that lead to more power?? Fuel has been so designed as to carry a lot of energy. The more fuel we can burn the more energy can be released. If your engine can hold together and flow enough, then it's happy days. There are your common street fuels, but of course there are also specialty fuels. To keep things simple we can talk about 98 octane fuel for now. So, to get ignition we need fuel+oxygen+spark. There is a ratio of oxygen to fuel required, it is called the stoichiometric ratio and is 14.7:1. That is, for complete combustion, we need 14.7 parts oxygen to one part fuel (mass..not volume). Righto, so we now know the ratio to mix fuel and oxygen, so it should become obvious that the more air we can shovel into the cylinder, the more fuel we can squirt in and the bigger the bang. So how to we get more in? If we open an intake valve on the engine and then draw the piston down the cylinder, we will pull in a cylinder full of oxygen and fuel, we then want to close the valve before the piston pumps it out of the cylinder (lets not get bogged down in valve tiing for now..maybe later :-)). This air entered the cylinder at atmospheric pressure, and depending on how high above sea level you are, will decide what pressure this is (that's right....you lose power as you climb a hill). So then if we want more in, all things being equal, we had better push the air/fuel mix in at a pressure higher that atmospheric pressure (force/unit area). Now is a good time to point out that atmospheric pressure at sea level is 14.7 pounds per square inch. Why? Well, if you looked at a one square inch footprint of a column of air to the top of the atmosphere (where psi=0) then it would weigh 14.7 pounds. Interesting when you think about it....or not.. what-evs.

Another thing to keep in mind is the pressure gauge in your car will typically give gauge pressure, that is, it is measuring the difference between atmospheric pressure and the pressure above which your intake is boosted to. So if you measure 14.7psi on you gauge, total pressure is actually 14.7+14.7=29.4psi. This is handy to remember, because superchargers and turbocharger graphs refer to pressure ratio. Pressure ratio is the ratio of absolute pressure to atmospheric pressure. In our example this would be (14.7+14.7)/14.7=2. That means 14.7 psi gauge is doubling the atmospheric pressure. It's a really handy number, intuitively, if someone has an NA engine making 100Hp, and they add a turbo or supercharger that provides 14.7psi gauge, then you would get PR=2, or expect twice as much air and fuel to be shoved in...and expect 2*100Hp = 200Hp. This assumes the rpm at which peak power is made is kept the same and that compression is 100% efficient. Think about this for a bit...I have just told you a very simple way to do a bullshit test on your mates claims :-p.

The main other thing to keep in mind about increasing pressure, is that it is not a 100% efficient process. Typically we are compressing with about 60-80% efficiency. Grab your bike pump and pump up a tyre, you'll notice the pump gets hot. The hotter air is the less dense it is for a given pressure. Take our cylinder moving down with Pressure ratio PR=2. We were shoving two times the air in at PR=2? Well yes, IF we did it at 100% adiabatic efficiency, but we have just said we are not. Make sure you have this clear in your mind....you can have 15psi at 10 degrees C and you can have 15psi at 200 degrees C. The latter will have less kilograms of our desired oxygen in it. Less dense means less oxygen, less oxygen means less fuel, less bang, less Hp...bugger. So the less we heat the air the better, which means the more efficient the turbo the better. But the best we can hope for is 80% efficient compression (roughly), so we still have hotter air, hotter than what? Hotter than the temperature of the day if you have set your intake up properly....hotter than your engine bay temp if you have not ;-). This is where intercooling comes in but we will get to this later.

There is another reason we prefer a cooler charge. It's because fuel will self ignite at a certain temperature and pressure, increasing either past a certain point will see the mix self ignite (detonate). This is why we don’t just run 100psi on street fuel, it’s because the fuel/air mix will explode uncontrollably in the chamber because the spark decides the time is right...usually when the piston is still trying to come up the cylinder. So now you can see that the static pressure ratio of the cylinder must be matched to the boost that you run and the fuel that you intend to use.

In summary: We get more Hp by turbo or supercharging because it squeezes more air into the cylinder. More air allows more fuel to be added. More fuel means a bigger bang, which applies more torque to the crank and in turn the wheel. This increase in pressure comes with increase in temperature, which we want to minimise because it reduces the density and it also takes us closer to the detonation threshold.

What is the difference between Force, Toque and Power?


Above we have been talking about how to increase power for a given rpm. The end goal is to increase power...but where? We know there is a bang in our cylinder, but why does this make power? When the mixture is ignited, we get a sudden increase in pressure in the cylinder as the gas expands, we allow this to happen at the exact right time to maximise the beenfit of this on the piston. This effort on the piston is a force. The force applied, which is the bit we are interested in, is equal to the pressure multiplied by the area of the piston. The bigger the area of the piston for a given pressure, the larger the force....makes sense. We will come back to the fact our pressure is not constant, and therefore the force ever changing post ignition.

OK, so now the bang is converted to a force...next we talk about torque, the use of this force.


Most of you will know that Power=Torque multiplied by rpm. So let’s talk about that a little. Torque is a force applied at a distance from something, this is also called a moment arm. Examples of moment arms are levers...take for example a crow bar. Or try this, hold you are out straight and get your mate to push it near your shoulder, to keep it from moving, you have to apply a force equal to the force he is applying multiplied by the distance he is applying it at. If he then applies the force at your hand, with your arm remaining straight, you will have a great deal more trouble stopping you arm from moving. This is because he has now multiplied with force applied by a larger distance....he is not applying more force.
The explosion in the piston engine applies a force to the piston, in turn the conrod, in turn to the crank. But it does not do this at the center of the crank (hence is is called a crank!) it applies it at some distance (eccentricity) from the center of the shaft. The larger the eccentricity the larger the torque. The distance/eccentricity component of the torque is applied at some angle, but when we calculate torque, force acting at a distance must be determined such that the force is at 90 degrees to the distance used. To do this you first need to determine your coordinate system, that is which direction you call up, and then which way is left and right from up (at 90 deg). Great so now you know that the force applied to the crank needs to be multiplied by the distance from the crank, which is always changing, and it must be done such that the distance is 90 degrees to the force.....which it is not. In fact it is, at top dead center and bottom dead center, but the distance is zero and therefore the torque impacted on the shaft is zero. Everywhere else it is not at 90 degrees. What does this mean to us? It means that the force must be broken into its resultant vectors, you can take any force and brake it into a force triangle.
I don't want this to get bogged down with vectors, so it would suffice to say that when we take our force acting on the crank, and break it into its vectors to get one of the vectors (component of force) acting at 90 degrees to the crank (which we use to multiply by distance to get torque) we are left with a bit of left over force (more than a bit, half way through the power stroke we lose 45% when the moment arm is largest....but the pressure has greatly reduced at this point and so it is of less consequence than it might first appear). So what is this left over force good for? Well nothing, less than nothing. It's not a perfect machine right? This is a mechanical, structural, unavoidable compromise. This left over bit of force is going to try to load our bearings and bend our crank.

Luckily, engines are so arranged that there is an equal and opposite force on another cylinder, an equal distance from the longitudinal midpoint of the crank that balances this force out (actually torque, but I don't want to flip the reference plane on you and loose some people). The point is we lose some torque producing force, and the amount we lose is related to the number of degrees we are through the stroke. You should be able to see why the humble piston engine is actually not very good at converting energy from the fuel into usable power, it's actually only about 30-35% efficient at doing this.....yep, about 65-70% of the energy never makes it to the wheels. How sad.

What is not immediately evident is that as the piston moves down the cylinder, the pressure is reducing, and at the same time this is happening, the lever on our crank is also changing. When the piston is at the top of the cylinder, there is no lever arm. The rods journals are directly in line with the center of the

That is torque, Force*distance about a center. In the case of our engine, torque applied is clearly not consistent for all four strokes for one piston, indeed it is not consistent for one power stroke. As the gas expands, the pressure on the piston resides.

Options?

Lets consider the following options for boosting an engine, Strapping a turbo or a supercharger to a 1.5 boxer should be able to yield 200 crank Hp without trying too hard, so lets face it, either method will put a smile on the dial. Which option you choose comes largely down to how you like your torque delivered. Lets just be clear on our terminology. I will refer to supercharging as a boost adding device, driven mechanically by the crank. Turbochargers are driven by the energy from the exhaust gas exiting the head.

Does everyone here know the how the internals of the turbocharger and supercharger work? Probably but here goes for those who do not;

Supercharger: There are two common types of superchargers, ones that increase the pressure of the air charge inside the supercharger itself, and those that do not. Internal compression superchargers use two rotors that are so shaped that when spun in close proximity to one another, they form a volume of air that is sealed on all sides (mostly). As this volume moves from intake to exit of the supercharger, the volume reduces. If the volume has reduced, but the mass flow of air has not, it stands to reason that the air exits more closely packed together..and so an increase of pressure has occurred.

Turbochargers: these run a common shaft between a compressor wheel and a turbine wheel. The turbine wheel is placed in the exhaust gas flow. The flow has energy in the form of heat and kinetic energy (velocity). The flow is directed into the scroll of the turbine carefully constructed to increase and direct the velocity of the flow onto the blades of the turbine. The turbine responds by spinning up to incredible speeds. This spins the shaft and so to the compressor wheel. The compressor wheel operates in reverse to the turbine wheel. It takes airflow with low kinetic energy and imparts as much as possible to the flow. The airflow exits the compressor wheel and volute faster than the engine can ingest it, with the pressure rising as a consequence. At some point we want to stop the boost increasing either because the engine will detonate, or because the turbo would operate outside is safe/effective range. This regulation is the job of the waste gate. The waste gate bypass's the exhaust gas around the turbine wheel, which means the compressor wheel slows its speed, dropping the boost, the waste gate is then regulated by a pressure signal from the inlet manifold (or other spots depending on desired result).

The main options consist of:
Turbo's:
Single
Twin - parallel
Twin - sequential

Superchargers:
Roots
Screw
Centrifugal (Vortech etc)
Twin charging
Turbo blown supercharger(s)
Supercharger blown turbo charger(s)

to be continued.


How much Hp can I expect? (main variables in the equation)
Preparing the head
Preparing the block
Cooling - charge air (heat is not your friend)
Cooling - coolant
Drivetrain
Things people cock up
The fun bit - an example (twincharge explained) What worked? what did not?
Costs - how much will it cost me??
Useful formulas
Resources (books, links, forums)
Last edited by buzzed on Sun May 11, 2014 1:25 am, edited 5 times in total.

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AlfaCorseChris
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Re: Turbo / Supercharging - Considerations

Post by AlfaCorseChris »

Mike, I'm game mate, thanks for sharing all that knowledge with me :)

I just need to register that 75 first ;)
Then we can go through it on mine :)

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Re: Turbo / Supercharging - Considerations

Post by Fetta GTV »

Would it be best to turbo or supercharge a boxer motor?
Turbo and supercharger would be reasonably easy on a 16v but what about the 8v
I guess you would have to go to throttle bodies. Or you could go old school turbo and have a blow through system. Or use a single carb manifold and have a draw through supercharger setup. But these are very low tech set ups. What are the options?

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Re: Turbo / Supercharging - Considerations

Post by Johnboy »

I'm all ears on turboing a 16v 8-)
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buzzed
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Re: Turbo / Supercharging - Considerations

Post by buzzed »

Righto, first installment is done. See thread above.

Response to daves question:

Dave to your question on which is best to do, I think you will start to know my answer after reading up first update :-)....Tell me what you want to do with the car, what your budget is and I will tell you what 'I' think is best :-).

Supercharger vs turbo: It is interesting that manufacturers still use both. They both have their merits, and each can be used in various formats. Superchargers can be roots, screw, vortech and so on, Turbocharged can come in the form of variable vane, single, twin-series, twin parallel and so on. Then you have to decide on fuelling method...carbie (suck or blow) or fuel inject. Then of course there is twin charging, that is, using a supercharger and a turbocharger on the same engine. The goal of the twin charge being to take advantage of the good point of each.

Turbos are quite popular at the moment, but in the case of the Sprint, a supercharged solution would be far more elegant from a packaging perspective. This is because a turbo solution will require all four exhausts to be collected to one point to feed into the turbocharger turbine housing. I can be done, and it's not that hard, but it's far from neat and gives a few cooling issues that need to be carefully thought out. Superchargers are likely to be cheaper to install on the boxer engine as well. With all this said, Subaru still stick to turbo charging, but note that they have increased torque through increasing capacity, and I suspect they avoid superchargers due to the slightly worse fuel economy. That said, these, days, superchargers are getting some very impressive efficiency numbers, and with the ability to declutch, are probably much of a muchness on fuel consumption. Anyway...I could care less about fuel economy to be quite frank.

The Alfa boxer engine is a nice, revvy engine, strapping a turbo to it will retain to a large degree this ability to rev. A supercharger will tend to have you swapping cogs earlier (unless it is Vortech, more on that later), but there is a lot to be said for instant torque as soon as you stomp the pedal (your gearbox may disagree..).

If I were building a hill climb car with lots of tight corners, I would lean toward the supercharger. If the course was more flowing, and I had a nice close ratio 6 speed box, I might lean toward a turbo for its higher power potential. If I were building a street car, I would choose a larger turbo for that nothing...nothing....everything feel :-), that's just me. For fun through the hills, supercharger.

Dave if I lived where you do, I reckon I would supercharger (plus intercool), especially seeing as you would probably just use the stock box, in this case, the supercharger generally allows for broader torque band which means gaps between gear ratios can be larger, and with no lag, there is no delay.

I am confident I could make a turbo or a supercharger work as well as each other with careful design of the system, so lot of it comes down to personal preference (and or class restrictions). What do you prefer and what matches your driving style.
The point is, it depends on what you want to do with the car.

Dave, as for how you fuel the setup, I really think that there is no sensible option outside of fuel injection. I am not saying it cannot be done with carbies, I am saying that few people will get carbies right, they have inherent limitations when boosted, and the consequence of getting it wrong is usually a blown head gasket (if you are a lucky), melted piston or cracked liner. Any of the above generally cost more that sorting the fuelling from the get go. On top of all that, fuel injection generally yields more area under the curve due to its higher degree of freedom when selecting fuelling points.

buzzed
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Re: Turbo / Supercharging - Considerations

Post by buzzed »

I've added a section on Force vs Torque vs Power. I think it is important for people to understand the difference. To maixmise power, you must understand how to first maximise force and torque. So breaking them down into basic building blocks helps collect together the variables we care about...then we can start talking about messing with them.

Pop quiz.....We care about force on the piston, and Force=Pressure*area. What affect does a domed piston versus a flat piston have on Force applied to the crank? A domed piston has more area...(assume compressed volume is the same for each).

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Re: Turbo / Supercharging - Considerations

Post by PETROLHEAD »

What a fantastic right up Mike, loving it lots!

I only hope when we get into it i was somewhere near right with my own design plan for a forced induction boxer engine, otherwise i'll fell a little silly! ha ha!


keep it coming mate, brilliant stuff.



(sorry for glossing over the pop quiz, i'm reading over it all again to make sure it sinks in instead!)
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Re: Turbo / Supercharging - Considerations

Post by Fetta GTV »

So a domed piston will give more force on the crank due to it's larger area.
But aren't domed pistons for high compression NA engines?
Turbo and a guess supercharged applications usually have flat top to reduce compression.
Can you use a domed piston but change the stroke to lower the compression so you can take advantage of the increased area but still have lower CR.
Or have you lost me already?

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Re: Turbo / Supercharging - Considerations

Post by buzzed »

So a domed piston will give more force on the crank due to it's larger area.
You would think so (this question tripped me up once). It is true that the area on which the pressure acts is larger than a flat top piston. BUT....remember how I said that pressure acts 'normal' to the surface? Did I explain normal? It means that the pressure in its vector form acts at 90 degree's to the surface of the piston surface. If the piston is flat, this 90degrees between the two sees the resulting force pointing striaght down the bore...cool, so Force=Pressure*Area, and it's ALL of the pressure vector. Now with the dome, the pressure vector does NOT point down the bore, but instead is perpendicular to the piston face at every point on the dome. That means that the force is not pointing straight down the bore but at some angle. You might recall fro abck at school, that to determine the component of the pressure vector that IS pointing down the bore, we convert the vector into its two components. The long and short of it is that on a dome, the resulting force =pressure*2*pie*radius, which is exactly thr same as a flat piston! So dome vs flat piston, geometrically at least, does diddly squate for power. What it does for combustion time, heat soak and squish area is another story.

What hapened to the other vector components in the horizontal plane? They cancelled the opposing horrizontal pressure component on the other side of the dome!
But aren't domed pistons for high compression NA engines?
Not necessarily, but lower compression typically eats away at the dome. It is important to retain as much squish as posible, but this is somethign most aftermarket pistons will fail to achieve as they will not be able to acheive the piston crown to piston dome clearances required to achieve true squish. We will get to this.
Can you use a domed piston but change the stroke to lower the compression so you can take advantage of the increased area but still have lower CR.
Nope. reducing stroke reduces literage....not generally a good idea.

Shrew, if any of it is not clear, ask questions. I can put pictures up, if someone will put me onto a good free mr quiggle program :-). If you can get this in your head, everything else we will talk about will make much more sense.

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PETROLHEAD
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Re: Turbo / Supercharging - Considerations

Post by PETROLHEAD »

I'm doing alright at the mo mate, keenly following, absorbing as much as poss.

Its nice to have the details explained rather than just the adopted norm of modifications, so i, like everyone else here i'm sure, is all ears! :D
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Re: Turbo / Supercharging - Considerations

Post by buzzed »

Cool, always hard to know how much to break things down, some people will not want to know the detail, and for some it might be too much?

It's all about the concepts, if you absorbe the concepts you have the tools to make your own choices and tweaks to your mods. As for your turbo scenario, Give me your engine configuration and we will work through it as the example.

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PETROLHEAD
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Re: Turbo / Supercharging - Considerations

Post by PETROLHEAD »

What details will you need Mike?

I'll get on it, but some specific engineering figures might be a little vague until others join in it has to be said! :?
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Re: Turbo / Supercharging - Considerations

Post by buzzed »

Just describe what you can Shrew.
Main ones are:
Engine type
Liters
planned rpm
Target Hp
Car model / weight
Use of car.
Prefered method of boosting, and why.

Thats more than enough.

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Re: Turbo / Supercharging - Considerations

Post by PETROLHEAD »

aah, ok.

I thought you were going to get all techno, with squish, lift and inlet throats etc!


so, to echo the sentiment of a few on here, i'll keep this in the realms of reality and reasonable budget.

engine type = flat four boxer
litres = 1712cc 16v
rpm - 7000/7500 max
target = approx 200bhp limited mainly by drivetrain weakness
model/weight = alfasud/800kilo
use = fast road/occasional track
preferred method = Turbo, flexibility of boost control and choices, budget of parts, (i considered the WRX - TD04 a good choice?)


because the stock motor is approximately 135bhp in healthy form, running a CR of something like 9.5/10-1, i thought the target of 180-200bhp would be achievable with a stock motor and low boost levels, 7/8psi added boost, with a pretty good expected reliability.

controlled by a full stand alone ecu too i might add.


am i a mile off?
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buzzed
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Re: Turbo / Supercharging - Considerations

Post by buzzed »

Cool Shrew, I think your sugegstion would net a good end result. I will work through your scenario with turbo and a supercharger comparison. With such low Hp target, I feel supercharging would be a better solution...same top power, more bottom end. Is that engine 200hp or wheel?

I could get technical on you, but with the target in mind, there is little need, you can do it blindfolded haha, but the key will be for min cost and max spread of torque agreed?

Your turbo choice is good bang for buck (L-13t), it's possible you could drop the turbine combo for even more low end repsonse and retain top end requirements. I'll sniff it out.

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Re: Turbo / Supercharging - Considerations

Post by AlfaCorseChris »

:feeling excited:

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Johnboy
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Re: Turbo / Supercharging - Considerations

Post by Johnboy »

This is sounding very interesting :D
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PETROLHEAD
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Re: Turbo / Supercharging - Considerations

Post by PETROLHEAD »

Thank you Mike, nice to know i was in the ballpark! ha ha!


There were other factors leading to my choice that may affect your engineering perspective.


The horsepower figure, whether wheels or crank really, has been set so low so that initially, i could use a stock motor, not lower the CR, or get into steel internals etc, so budgetary and simplicity for starters, but primarliy because there was little point aiming for more when the gearbox simply won't stand it.

So a tdo4 was a bit of a plan for the future too.

If we bottom a design plan for reinforcing the drivetrain components without the need for a lottery win, then the td04 still has plenty of room left for more. It works well and remains cool at 250+ hp in the Subaru, so should have an easy life making in excess of 200hp if we get the chance to tweak further considering the above.


That was my reasoning behind it Mike, instead of turbo swapping in the future, that and the integrated wastegate making it a nice compact little unit, suitable (just!) for our engine bay room, or lack of!


I would have loved to go roller ball like the VF series, but i don't think we're ready for that yet, and not for a long time! ha ha!
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buzzed
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Re: Turbo / Supercharging - Considerations

Post by buzzed »

Fair enough, but you are bulding a compromise into your system, you have to remember that your engine has less gas flow that a subaru, you only hvae 1.7 liters. This wil reuslt in more lag for the same turbo. How thick are the liners on the Alfa 1.7 16v boxerwith stock pistons? Assume they are cast iron?

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Re: Turbo / Supercharging - Considerations

Post by PETROLHEAD »

I hear you Mike,

so you'd be an advocate for either a smaller spool happy turbo, or supercharging instead altogether, i get that.



as for the liners query, i can only assume you're leading us to a larger capacity scenario?

89mm pistons instead of the stock 87mm is quite a common mod, leaving us with approx 1830cc iirc (Johnboy is now on the edge of his seat!)

any more than 89mm, is almost certainly a gamble on remaining wall thickness.
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Johnboy
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Re: Turbo / Supercharging - Considerations

Post by Johnboy »

:lol: I just fell off it!
For if it's supercharging or turbo I'm happy , but as you say shrew . It's down to which doesn't require a lotto win! This is turning into a great thread . Even if it's making me go crossed :ugeek:
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Re: Turbo / Supercharging - Considerations

Post by buzzed »

so you'd be an advocate for either a smaller spool happy turbo, or supercharging instead altogether, i get that.
Not quite. I totally agree with your comment regarding leaving headroom for more Hp. I also get the need to maximise affect for the dollars spent. Here's the rub, you want to get the car on the road and enjoy it. I would guess that by the time you can afford a box (and sleeves) that will hold together for more Hp...you won't cry over buying a new turbo. So optomise for your limitations now, if 200 is safe, and 250 is borderline, slick with 200 and aim for a more responsive package. We have to get this number right though, there can be 20% loss between engine and wheel Hp so we need to be clear on the reference. I don't have a first hand feel for when these things let go and under what driving style, so you guys will need to guide me on this. I can make your engine make 500+Hp probably, but not much use if blows the lot appart haha!
as for the liners query, i can only assume you're leading us to a larger capacity scenario?
Nope, that would be too obvious haha. i asked because cranking up boost can split liners. For your 200Hp, I would not touch the liners, you want as much meat as possible. If you can go up 2mm but thats the limit, I would guess you have a wall of about 5-6mm. 3mm walls is pushing the friendship on factor Alfa liners, as I am sure you guys will have worked out.

The secret to happy days on a turbo engine is solid liners with o-ring to bite the headgasket and good fuel and spark control. Comp ratio as you say can probably remain standard, and use standard pistons for said power level, but you do run the risk of cracking a ring land on the piston eventually. My thinking would be don't even o-ring it, leave the engine unopened and run it till something lets go...might blow a headgasket, might crack a ring land. That way you avoid the cost that inevitably comes from opening an engine. It may sound crude, but it will mean your project gets on the road nice and fast, and reletively cheap.

For what it si worth Shrew, I don't mind a bit of lag personally, but only as much as is required to get the number up top. Make sure the turbo sits in the rhs of the efficiency map at max rpm and you will have a turbo that spends most of your dirvign life in the meat of the efficiency range, which for the street is perfect.

Hmmm, I should add nitrous to the list above...another good alternative, of course it's not legal on the road and you have to keep filling up a botte which is a pain.
Last edited by buzzed on Fri May 16, 2014 12:07 pm, edited 1 time in total.

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Re: Turbo / Supercharging - Considerations

Post by buzzed »

Can anyone supply a dyno chart for their non turbo 16valve setup? I would like to calibrate my model to the engine's efficiency, If I can get a curve showing rpm and power/torque I can do this. If you have a turbo map, even better. Just have to let me know if it is wheel or engine power, and I would prefer no bullshit dyno runs that have been meddled with :-). Will just make my end number more accurate.

Oh, and SHREW, which turbo? TDO4 13 or 15? I can check both of course, but just wondered which one you were interested in.
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TD04 - 13T
TD04 - 13T
TD04 - 15G
TD04 - 15G

buzzed
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Re: Turbo / Supercharging - Considerations

Post by buzzed »

Shrew,

I had a look at your setup.

Target: 200Hp@engine
Stock max rpm: 5500
stock compression: 9.5:1 correct?
Allowable boost: 8psi (on 9.5:1 gives static compression ratio of approx 11.7:1 when boosted)

A factory MY97-98 WRX makes 155KW (aprox 208Hp)@engine at 5600 with 1994cc, almost 300cc more than you have. It runs 8:1 static compression and 13.5psi which is about 11.7:1 static compression when boosted. So our total static compression ratios make sense so far.

Scenario 1: Sensible boost
Intercooling reccomended, but perhaps not mandatory.
Comp: 9.5:1
5500rpm
8psi (reliable boost)
148Hp@ engine (approx)

Scenario 2: Max boost
intercooled!! water/methanol 50/50 perhaps as added safety.
Comp: 9.5:1
5500rpm
10psi (max boost for street fuel on this comp)
160Hp@ engine (approx)

Scenario 3: Maintain valumetric efficiency post 5500rpm
intercooled!! water/methanol 50/50 perhaps as added safety.
Comp: 9.5:1
7500rpm
10psi (max boost for street fuel on this comp)
211Hp@ engine (approx)

Scenario 4: My mad Alfasud
Fuel = toluene/98 octane mix
Engine capacity (2 liter with custom forged piston and crank)
Turbo Head work
intercooled!!
Lots of other support stuff...custom liners, crank, cams, etc.
Comp: 9.5:1
8500rpm
35psi
550Hp@ engine (approx)

Realistically, I think you could hope for Option 2:160 engine Hp on stock compression. If you can increase boost post 5500rpm to fill the torque curve and streth out the usable rpm, I think you can come darn close to wrx peak power, which in these cars would be pretty silly fun. It is worth noting that Option 1 nets you the same power to wieght ratio (what really matters) as a WRX. That is about as far as you would probably go without opening the engine. I suspect you would end up opneing the engine after a blown headgasket, and a decent tuner would eb required, but this goes without saying for all engine modding.

I've used TD04 for these calcs, but it matters little for this discussion, ultimate turbo choice will come down to mainting flow requirements with decent efficiency, and not keeping too much in reserve. Get it right, the result is mind blowing, get it wrong and it's a bit ho hum, and annoying between gears. I still maintain that for the flow we will need on this scenario, the turbo may be a little large still, as it is capable of some 250Hp, and realistically, we are hovering around 150-200 MAX.

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Re: Turbo / Supercharging - Considerations

Post by PETROLHEAD »

Hi Mike

great reading again. well done that man.

as for the TD04, i was actually considering the even smaller 11g for my 200hp engine target.

different markets may label, and certainly get different turbo's i know, and sadly i don't have a flow chart for it, but does that figure in the sums any more suitable?
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Re: Turbo / Supercharging - Considerations

Post by buzzed »

Without a flow chart it is hard to say. Indirectly you can make an assesment based on what it is strapped to. I also could not find a flow chart for it. I was thinking something like the CA18 Nissan turbo engine might be an option. They are old now though so most if not all are probably stuffed. Perhaps a turbo off a much newer model car to get the benefit of better turbo design. Try something like the turbo mini turbo, or other 1600-1800cc engines that produce your target Hp. Stay away from turbos that have the turbine glued on, overboosting these tends to see them end up in the exhaust somewhere near the first muffler :-).

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Re: Turbo / Supercharging - Considerations

Post by AlfaCorseChris »

Wow !!!

Now thats some great info there !

Mike, you are the turbo guru 8-)

I think the crank would be the most difficult and most expensive job of all

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Re: Turbo / Supercharging - Considerations

Post by buzzed »

Golf mark 4 ko3, ko3s and ko4 are are also good options. You could high flow the to3 with to4 internals as an upgrade. Those turbos must be 50 quid at a wrecker by now. The trick as always will be getting one that is not flogged out. Try to avoid the temptation of chinese turbos, a mate of mine in a garage found that 1 out of 3 were cactus, and I bet the others were not far behind....and thats from new.

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Re: Turbo / Supercharging - Considerations

Post by Alfasixnut »

Excellent thread...very good real world information - many thanks for sharing - even though I tend to just put in bigger engines for my entertainment! :lol:

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PETROLHEAD
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Re: Turbo / Supercharging - Considerations

Post by PETROLHEAD »

The American way eh Phil,


no substitute for cubes! :D :D :D
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