16v Carb Trumpets (Air horns)

[evanbottcher]

Hi folks,

I have an odd query - I've been interesting in what kind of trumpet (ram pipe) to fit on our carburettored 16v. There is a calculator here: Optimum Intake Runner Predictor Program that given an intake length will tell me which RPM ranges the harmonic benefits are. I think to make use of it, I need to know how long from the intake valve to the opening of the trumpet.

A quick measurement shows me from the port opening on the head (the face where my carb manifolds bolt up) to the top cover of the carbs is 195mm. That's the height of the manifolds and the carburettors together. I also need to measure the length of the intake tract within the head itself, to the valve face. This would have been much easier to measure before we put everything together...

Does anyone have a standard 16v head off the car and can measure that distance? I'd use a bit of wire in the shape of the tract, I guess. Or maybe someone already knows, roughly.

Also - if anyone has an opinion on the best length of trumpet, especially suppliers of trumpets , that would be much appreciated.

I was looking at something like this: http://www.ricambisport.it/ing/ricambi_ ... 143&id=164 (we run Dellorto DRLA 45s, apparently these will fit fine).

[PETROLHEAD]

Hi mate,

sadly i don't have as lose 16v head to measure for you, (thanks to an asshole member who refuses to send me my property back but thats another story!)

but i can say that those trumpets shown are notable longer than i expected to see.

calculations aside for a moment, i have some 45's and trumpets that i bought some time ago from BLS Automotive, taken from a previous set up race car, and they are considerably shorter.


I know their car has historically been dyno/rolling road set up and final tune, so i'd be pretty confident that they chose the optimum or very close for those carbs and their engine, without quite having one of every size to try for the absolute maximum.


I'll try to dig them out for you and show you what they used.

[Ted27sud]

Shrew, I still have two 16 valve heads lurking at the back of my garage complete with carb manifolds. I can't see that I will ever get around to doing anything on that project so if anyone wants them they can have them.

Shall I bring them to Cadwell next Monday? Let me know.

Cheers,

Ted

[evanbottcher]

The trumpets we're currently running are shown in this pic - I haven't measured them (car isn't with me tonight) but they are fairly short. Longer trumpets should improve torque lower in the rev range, something like 17 inches (430mm) of trumpet length would get the pulse improvement down to 7000rpm (http://www.bgsoflex.com/cgi-bin/intakeln.cgi?length=17).

Ted, can you measure the port to valve distance? I would send you lots of appreciation across the Internet...

[evanbottcher]

I also note that the original Trofeo Suds (the Autodelta kit) had curved trumpets on 44 IDF webers.

I definitely take on board what you're saying about the BLS setup though Shrew. Interested in other experiences as well if anyone can share? (or is willing!)

[PETROLHEAD]

Hi Ted, if you're sure you're ok with that, i'd love to take you up on that offer, and rest assured if you ever get the opportunity to go 16v again, i'll help with everything i can as always


Evan, the picture of what you're using currently is a lot closer to what BLS supplied me on the carbs, so i'm suspecting you maybe closer than you think?


The original trofeo's were still only small CC, and tuned to make the most of revs, so i suspect the longer trumpets may have been used to get some lower down tractability back?

[Ted27sud]

It will all be in the boot for next Monday, Shrew, including manifolds.

Ted

[PETROLHEAD]

Thank you Ted, you're a star!