Ram pipes - full radius or not full radius

[Veesix75]

Subjective question to a degree but I will ask anyhow .

There are 2 types of ram pipe for carbs :

1 . Full radius where the tops are fully rolled over

2 . Trumpet type tops - as the name suggests more like a trumpet end, flared but not fully rolled over

What's the difference and which are better, and would I even notice on a non race engine?

Thanks...

[Alfasixnut]

I think there is a Tiny difference at maximum airflow in favour of the fully rolled over - BUT - it also depends upon the radius of the roll over, length of trumpet, type of flare etc. - so, on a road engine unnoticeable - decision more based on looks, cost and availability.....IMO

[Spacenut]

I think there is a Tiny difference at maximum airflow in favour of the fully rolled over

That's interesting. I always thought that the fully rolled tops was just a sop to modern safety legislation on sharp edges, but I guess the classic flared trumpet could cause some disruption to the incoming airflow...

Ultimately though, for a non-race engine, the difference in performance will be negligible. The difference in induction noise, on the other hand...

Lauren

[KevJTD]

guy croft has done a lot of research on the very subject, amazing how different radius ends make a big difference to flow.
his website makes for very interesting reading

[Veesix75]

I will take a read through, but the depth of pocket will probably dictate the answer. I found some trumpet type for half the price of full radius......

[Greencloverleaf pat]

Here's mine on my sud ti

[PETROLHEAD]

i think a large important factor is whether you are using them open, in which i would favour the full radius for a smooth entry into the trumpet, or from within a filter sock, airbox, cold air feed, at which i believe a half radius would be just fine.


in a slightly contradictory way, if i'm correct, the bls car uses full radius, short length carbon trumpets, from within their custom airbox.



personally, i think length has the biggest effect, but as a general rule, full radius is "probably" the better flowing in "most" environments, but, if the trumpets are to be used open maybe a half radius will prevent a little of the warm engine air below from being pulled in by creating a resistive edge for it to get around, rather than an all round flow encouraging shape


have i explained that at all reasonably well? lol!!!


half radius and taller is my own choice, but i only have my own theory to go on, and quite rightly i think Tim, on a stock motor, i'm not sure there will be acres between them either.




anyone deciphered the guy croft stuff yet?

[BS25]

Our are a specific intake length - valve to trumpet - we run spacers under the carbs to get the length correct given how deep the airbox could be to fit under the bonnet. The general guide seems to be short trumpets for torque, long for top end power. As others have said, on the road you'll probably not notice - though current thinking seems to be radiused encourages the air to accelerate in a bit quicker.

[PETROLHEAD]

aha!


some sound reasoning and theory at last! ha ha!


thank you bryan

[Spacenut]

Our are a specific intake length - valve to trumpet - we run spacers under the carbs to get the length correct given how deep the airbox could be to fit under the bonnet. The general guide seems to be short trumpets for torque, long for top end power. As others have said, on the road you'll probably not notice - though current thinking seems to be radiused encourages the air to accelerate in a bit quicker.

Hmm, interesting. I had always read that the opposite was true - that a longer intake tract was better for torque and a shorter one better for power. This seemed to be backed up by the cars from my youth, including my own Droop Snoot which had an experimental works intake manifold that was shorter than stock and certainly lifted the power peak. But now I am reading that carburettor engines respond to shorter intake tracts with improvements in both power and torque...

I guess the exhaust system design will also be a factor as well?

One thing I do know is that CanAm cars had so much surplus torque that they could afford to use different length intake trumpets for each cylinder, flattening the torque curve over the entire rpm range.

http://cdn05.motorsportretro.com/wp-con ... 4322_7.jpg

As to which cylinder was providing what torque at which specific rpm, I now have no idea

Lauren

[Veesix75]

It's for track days, but seeing as I am useless on corners, torque may still be better than top end .

Just to confuse further, what is 'short' and what is 'long'

[BS25]

Sorry, should have been specific, short on our engine for better torque (exhaust, inlet lengths, cams, etc taken into consideration). I agree, shorter for top end is very much the norm - we were surprised when the opposite proved to be the case.

Tim - ours are 55mm high. I don't think there are massive gains with a largely standard engine, most people run relatively short in flat fours. I remember a racer we were competing against in the late 90's who came out with a what he expected to be very torquey 1850 race engine - that ran very long trumpets - circa 150mm I would say. He really struggled to make it work until he went on to shorter trumpets and reported it was much better - it went better too! Probably a case of every engine is liable to be different.

Experimenting with the BMW M5 (5.0 V8) from the Ascari on the dyno was interesting - 90mm worked - anything more or less was worse! 520 bhp dropped to 510 bhp with a similar percentage drop in torque. The dyno and lots of parts is pretty much the only way to establish the reactions!

[Veesix75]

Thanks Bryan

150mm must have been a tight fit under a sud bonnet !

[rsfruitbat]

Hi All.

On my 1400 going back to a std plenum chamber gave an increase in torque over an extended straight inlet length that meant the air filters were just under the bonnet line.

The plenum has a longer inlet tract than the custome setup. So does cc also modify whats needed?

rsfruitbat

[PETROLHEAD]

I think there is the danger of info overload shortly!


Many different engines, even in our own boxer format, 8v, 16v, 1400 up to 1900 etc etc, and surely there can be no single answer?

The overall length in particular I should think will have effect on air speed, and therefore cylinder filling, but our engines are so different at head efficiency, there cannot be a single magic number.


Trial and error on a dyno would be the only true way to know, but that would mean a fortune in rampipes and dyno time, so I suspect the best you can do is go with the known theory, take a chance on somewhere in the middle of that, and if possible a notably different option both sides of it, so 3 sets of trumpets!



Or engineer an adjustable set???

[Alfasixnut]

I like trumpets!
And Shrew is quite correct in his assessment - but the length effect is not so much an airspeed thing (- that is more due to the diameter) but a resonance effect of the valve shutting and sending a pressure wave down the pipe which reflects at the open end to help fill the cylinder when it arrives back at the just opening valve.

[Alfasixnut]

Or engineer an adjustable set???[/quote]

That is not too difficult either

[Spacenut]

Or engineer an adjustable set???

I like that idea! How about a set of threaded 2-piece trumpets? Keep doing dyno pulls all day until you get the right length and then threadlock them in place!

Lauren

[Spacenut]

the length effect is a resonance effect of the valve shutting and sending a pressure wave down the pipe which reflects at the open end to help fill the cylinder when it arrives back at the just opening valve.

Aha! So it works in the same way as exhaust scavenging. Thanks Phil, that makes it much easier for me to visualise!

Lauren

[PETROLHEAD]

Nice Trumpet! (oooerr!)


were the radius tops taken from existing shorter rams Phil or made another way?



These are what ive come up with for my next phase of tune for the 16v sud. To keep it on fuel injection, dellorto 40mm throttle bodies, but ditch all the stock inlet plenum, air flow meter, and the ecu by using a stand alone management,

the Trumpets of Valhalla!

these taper from 45mm at the radius to a tight sleeve fit over the 40mm dellorto, and have about a 25-30mm range of height movemment to adjust the length to at least attempt to maximise with what ive got.


the throttle body itself will be machined with a 15 degree blend to almost nothing so it is stepless internally.

i'm hoping that the taper will go a small way to recreate the benefit that a carb has of a throttle choke, but with the added flexibility of remaining efi,


oh, and pretty much the noise of carbs too!

[Alfasixnut]

Thanks Lauren.
Shrew - yes the radius tops were cut off from the bases of the short ram pipes as I couldn't find any 6" ram pipes to buy for my next project.........Your work on that throttle body set up is most impressive.

[PETROLHEAD]

Thank you Phil


we can but try eh!

[Veesix75]

Well, this question was finally answered for me by a combination of eBay and wallet. I managed to drop onto some second hand full radius on ebay at a good price, and from someone just down the road which makes a nice change.

As you said shrew above - nice trumpet

[PETROLHEAD]

I'm great at justifying a bargain into the theory


i bet they're textbook perfect eh Tim?


glad you found something mate, and if theyre a proper thing, you'll be somewhere near i'm sure.

can you show us what you got yet or have you got to wait for the postie?