We know log manifolds increases backpressure and exhaust gas reversion compared to tubular manifolds. They also have high heat retention and low exhaust volume between the exhaust ports and the turbo. This significantly impacts the characterstics of the resulting engine/turbo package.

Turbo experts: would the type of exhaust manifold impact your turbine selection, keeping all other variables equal?

Example: Let`s say we have a stock F20C engine, and our target is 400whp on 93 oct. Compressor sizing calculations would lead us to a 48-55 lbs/in capable turbo. Typical suspects would be GT3071-GTX3071-GT3076, for which you have .63 ar, .82 ar and 1.06 ar turbine trim options. Would it make a difference which type of manifold you were using on your turbine trim selection? Maybe you could choose the .63ar for the tubular to increase midrange performance, and .82ar for the log to diminish reversion and increase top end performance?

I searched long and hard for this with no results. Not trying to start a log vs tubular war, I think we all know the advantages/disadvantages, and logs can definetly make power, Mercedes dominated 2014 turbo-F1 season with one.

 

It was also the main reason they dominated last year too; everyone else was stuck with their tubular manifold designs, mercedes went another route and it payed off big time.

I've seen the cars with big numbers attached to using a log, though can't seem to recall quite as many graphs as others...One problem I find with your questions is that:

A) Using the tubular manifolds and equal length headers such as with topmounts, should net you some extra top end torque thanks to less back-pressure on engine = better breathing and more torque. Logs will fight you to do that (depending on power band placement/revs etc)

B) A long-ago active member on TI by the name of 'Michael Delaney' would put it like this: don't heavily miss-match different components of your setup in order to try to get the best of both worlds; specializing in one area for your power band is what helps the most (Note, this was talking all motor setups). With turbine/manifold suggestions TheShodan usually always advocates for tubular log/mini ram for nearly any street setup all the way through 500whp, and most of the time .63ar.

I did see this build mixing a .48ar turbine and a ramhorn from Evans tuning with great results : 1992 Acura Integra GSR - 440whp/310tq - Hondata S300 - Dyno Graph


Edit: Sorry for being redundant on A), I just wanted to emphasize that tubular manifolds with large a/r turbines definitely have their places.

 

I think you need to decide whats more important quick spool vs topend power, but basically yes you do match your manifold to your turbine, larger manifold = larger turbo

I wouldnt sugest putting an overy large turbo on a log manifold, just as I wouldnt put a small t28 on a ram/topmount
same goes for the exhaust A/r, and you do need to look at the big picture as all 3 items make an influence

small manifold aka log = better response less top end
ram/topmount = better topend


This is backwords, you would typically use the higher A/r on a tublar manifold especially when focusing on topend power, and the smaller A/R would be suited for the log manifold when shooting for low end power

 

That Delaney quote makes a lot of sense. And thanks for sharing Shodan`s usual recommendation. He did choose a significantly bigger 65mm turbine wheel for his 53 lbs/in "Hunter" turbo (compared to the 60mm 3071 and 3076 exhaust wheels) so maybe he sees some value in the .82ar if using a 3076? Although of course, it would be a bandaid to correct the original mismatch.


Sure, that would be "focusing on your strong points" as Geis quoted, and maybe it`s the correct path. Going the other way trying to improve your weaknesses with turbine A/R selection might be dumb. I just haven`t found any empirical evidence, most people (maybe rightly so) just go for the "typical" or more used setups.

 

The Hunter is .63 ar, and so should any gt30. Although you would have to ask TheShodan for the specifics, the hunter is an extremely responsive turbo.

 

Ive seen shodan post that using a small turbo on a ram horn trying to get the best of both worlds was an extremely bad idea which pretty much goes back to the Delaney quote.

so yeaah basically I would say its more about focusing on strong points rather then weaker ones. its always a trade off so depends on what you are looking for.

I think your better off in choosing the correct turbo and enhancing those characteristics with the manifold and or a/r then trying to fix any drawback it may have with manifold or a/r selection.