4 bbl type throttle body or 90 mm
 

My twin turbo setup (still in the making, of course) has the L92, GMPP 4bbl
intake manifold with the L92 heads.
I was going to run an intake elbow and then a 90mm, LS type of throttle body. Then I got to thinking that I could do a 4150 style throttle body with a "hat" on it for the Turbonetics 62-1 to feed into it. Is anyone running a 4150 style (based on a Holley carb) throttle body with a twin turbo setup? Any ideas, feedback, pics, comments would greatly be appreciated.

Well there are 4150 style throttle bodies out there that will far outflow a 90 mm throttle body thats for sure. However in a boosted application the difference between an adequately sized throttle body and a max effort larger one will show little on a dyno. The theory being that boost is a result of some sort of restriction. Take for example a D1 procharger(I choose a procharger so we know the same amount of air is being moved) : with the same size pulley on it it might make 10 lbs of boost with the 90 mm throttle body that flows 1000cfm and 8 lbs of boost with the 4150 throttle body that flows 1250cfm. However, both with make darn near the exact number on the dyno. The reason being the same amount of air is making it into the cylinders in the end. Now take into consideration the 90mm will have its limits to where its a restriction once you go above and beyond 1000 rwhp and I am also assuming both situations have an intake that can adequately take advantage of the flow of each respective throttle body. Another thing to consider is once you go to a 4150 throttle body you are pretty much stuck with a speed density tune which many consider to be the best for boost anyways but thats another debate in itself.

When you say "speed-density", is that better than a mass air-flow system? I hear alot of controversy surrounding the two in terms of performance. Which system has less sensors to fail? Which one will be the most adjustable? For my application, which would be the best? Thanks for your help...it is much appreciated!

Well its hard to say which one is better as there are people on both sides of the fence about this issue. Speed density is done without the Maf (mass air flow sensor) as you mentioned. To put it simply basicly the engine runs of set fuel tables rather than relying so heavily on the maf and compensating for outside conditions. Many consider the Maf a restiction once you start making alot of power since they only go up to 90mm (100 mm ones have been recently released). Really what it comes down to is the maf allows your car to adjust better for altitude and temperature etc. However with a good speed density tune especially in a boosted application like yours you may never know the difference. I suggest you check out the tuning section on LS1tech and read up on it and decide for yourself. You may also want to talk to some tuners you are considering because I am far from an expert on this topic. What kind of power are you looking to make?

the maf is a nice way to go until you max it out; that is not real hard to do with forced induction. At that point tuning becomes "tricking" the computer through the pe tables, and I do not like that at all. I always go speed density with forced inductions, just easier, less to go wrong, and runs just as smooth in my opinion if tuned properly.

On the throttle bodies, every time I've swapped from a 4 bbl style to a monoblade I've picked up throttle response, so now I just start out with monoblades. And 90mm is plenty, I've made well over 800 rwhp with a much smaller 75mm monoblade. Not much of a restriction when under pressure.

Jody

Again, thanks for your help, input and advice guys! My target hp goal is 1000-1200. I was told this is doable with with 408 cid, twin Turbonetics 62-1's, L92 heads, truck exhaust manifolds, 18psi boost, with good gas, yada, yada, yada. I just want to do it right the first time, since this is an expensive endeavor...no budget for mistakes or re-vamping. I have the GMPP 4-bbl intake, was considering a TPIS sheet-metal intake with a 90 or 100mm tb. I see alot of guys running the 4-bbl intake with an elbow and a 90mm tb. I'm concerned about flow from the elbow to the intake vs. a TPIS sheet-metal intake with a 90 or 100mm. Plus, the TPIS just looks killer!!! Especially with the TT set-up.

On a 408 with twin turbos 1000-1200 shouldn't be a problem as long as the motor is build fairly stout and I assume it is. You would be pushing something like an LS6 intake at those power levels but it certainly could be done there is a guy with a 71 chevelle around here making 1000 with an LS1 347 cubes and an ls6 intake. The advantage of a sheet metal intake over the GMPP piece would mainly be equal runner length and being able to design it for your specific setup (plenum volume runner length etc.) which is a definite advantage. Once again it won't be absolutely necessary to your build but it will affect the torque curve and and where power comes in at I would imagine. Perhaps your engine builder could shed a bit more light on this. On a side note, I agree the TPIS as well as the beck and I believe Nelson Racing Engines has one out now all are awesome looking intakes. If you do decide to do the intake elbow consider going with the wilson cast elbow as some people have trouble with the fabricated ones coming apart. Also, Camcojb makes a good point about maxing out the maf that I forgot to mention which i am sure you will have maxxed it out before you achieve your power goals.

Well right on, guys!!!! Again, I do appreciate ALL of your input, suggestions and feedback regarding this issue. You have been very helpful in so many ways. I'll keep you guys posted!