My desktop dyno says it's worth 10hp @ 6500 on my setup, but I want to know real world experiences.

Randy

 

With my set-up,I wish I would have kept the 52mm,but I went with a 58mm-I couldn't "feel" any difference-save your money for something else.

 

I actually believe it wontt gain a thing.52mm will supply enough air for a 383.You would lose velocity also.JMO

 

Thanks for the input guys. Anyone else with real world experiences?

Randy

 

ttt

 

For all NA cars I have seen a 52 will flow more then enough air. If you goto a 58 (as stated) you will loose air volocity which = less TQ and no additional HP. Last year durning some testing we lost 8 RWTQ and gained .5 RWHP - you make the call on if it was worth it

Car Specs

LT1/T56
ZZ-409 Cam
383/10.5:1 comp
AFR Heads

 

so the 58mm TB, you don't gain any hp compared to the 52? or is it you just don't gain anything and stick with the 52mm? I am curious, I figure the more air you are pumping into the intake, the better? some one explain this a little bit better to me...

 

Would you rather run your sprints breathing through a straw or through a megaphone?

The throttle body doesn't "pump" air into the engine, it's just in the path. If you just think of it as something in the "path" then it's a bit easier to understand.
You will see gains by going to a larger throttle body (bigger straw) if the current straw... I mean throttle body is a restriction.... if it's limiting volumetric efficiency the engine could theoretically make.
It's much the same as restrictor plate engines in Nascar, etc.. You increase the pumping losses and the engine is less efficient. See the other thread on throttle bodies, you may get something from the explanations given there.

-Mindgame

 

Changing the size of the components in the intake track doesn't necessarily increase air flow significantly. The only thing pushing air into the dropping piston is the "barometric" pressure of the outside air. As this air moves through the intake track, the pressure is "lost" as it goes through the filter, small diameter tubes, bends in the tube, sudden enlargements and contractions, and other obstructions (MAF, TB). Less mass (pounds) of air end up in the cylinder, because of the loss in pressure. You can reduce the pressure "loss" and maintain a higher pressure in the cylinders by eliminating the obstructions.

Put in a bigger filter, get a larger diameter flow tube, make the bends smooth, enlarge the MAF of the TB. But that only increases air flow if the component was a significant obstruction in the first place. If the throttle body is already of adequate size, the reduction in air flow pressure loss, from going to a larger unit provides improvements that show up as fractions of HP... not measureable improvements.

My engine was originally programmed in Alpha-N - a system that bases fuel flow ONLY on throttle position and RPM.... an alternative to speed-density or mass-air. For a 500HP 381, spinning in excess of 7,000rpm, the air flow max'd out at about 77% open throttle with a 58mm TB. In effect, once I got to 77% open throttle, the engine was getting ALL the air it could possibly use, and opening the blades further did absolutley nothing that could be measured. If you do the math, you will see that 77% open on a 58mm TB is less open area than a 100% open 52mm TB. I really don't need a 58mm TB for NA performance, proven on the engine dyno. It does provide performance improvements with my dry nitrous system, but that's another story.

I disagree with the statement that somehow reducing the velocity of the air through the TB causes a loss of low end torque. In a modern EFI system, and with the "plenum" design of the LT1 intake manifold, the TB is effectively "decoupled" from the intake runners to the extent that air velocity through the TB is not even seen at the intake runners.