Auto Racing: exhaust tuning, dual exhaust systems, bob sharpe

Question
QUESTION: hi - with respect to exhaust pipe tuning does a turbo charger interfere with the wave speed of the gases (not the particle speed) significantly enough to disrupt it (in other words act as a dampener) or do the waves still pass freely up and down the pipe?

ANSWER: Hi Daniel:

OK  I don't know much about this at all, partially because in my kind of racing only natural aspiration is allowed. We don't see turbos at all. However I have read a lot about what Nissan did in the 90's and seen pictures of engines built for Paul Newman, John Morton and others.  Plus my cam grinding guy here locally did all the work for Bob Sharpe back then.

What I have seen is that the exhaust system was of a tuned length up to the turbo - - -that is either one wave length, or perhaps some tricky fraction was used up TO the turbo- -  after that they just dumped it out the side.

On street cars it doesn't make enough difference to bother with.  As a matter of fact I tinkered around with tuned length ezhaust stuff for quite some time, and never saw any improvement on the stop watch at all.  Perhaps it exists on a dyno, or in the hands of a better driver.  I read all the stuff Smoky Yunic wrote, and some others that were around years before in hot rodding.  I s'pose the Formula One folks have their own mysterious ways of tuning lengths.  I know they have variabgle length intake runners, wierd to watch them work.

And if you are running anything other than a V-8, dual exhaust systems will slow you down.

ADmittedly that isn't much bit it's all I know !

Thanks for writing

Dan Liddy
Sarasota, Florida

---------- FOLLOW-UP ----------

QUESTION: Thanks! May I put one more idea past you?........if I were to have a tuned exhaust leading to a merge collector of whatever design then place a turbo further along the merge collector could I regulate the pressure in the merge collector chamber before the turbo and end up with a variable exhaust tuning system?

Many thanks!

Answer
Hi again:

If I'm not mistaken , the merge collector serves to put an end to wave motion - -or to create the vacuum desired at a point along the rev range to effect intake negative pressure. We used to run megaphones at the end of the secondary pipe for the same reason,  The primarys were of one cylinder volumn, and the secondary was two cylinder volumns on a four cylinder. The megaphone was intended to stop the wave motion at that point, and allow a huge pressure drop. The 12 culinder Ferraris brought tears to your eyes ! 12 cylinders, 4 megaphones, what a shriek they made !!

So to answer your question. You could probably create one effect or another by altering the internal size of the collection chamber, but that sounds like a lot of work to me. Or I s'pose you could put a series of baffles inside to alter the internal back pressure- - -again a lot of work but on a dyno it would be a help. On a race car it would be weight. We don't like weight.

I'm enjoying this , but I can't find much info in my library.  My engineering neighbor wont answer the bloody phone, and every thing he has in print is written in a language to which I've not been introduced !

Thanks for the glowing feed back !

Good luck !

Dan Liddy
Sarasota, Florida