Will lightened flywheel + 3" Exhaust = 50 hp
 

I have a street ported s4 NA motor with big exhaust ports, 49mm ITBs w/ 850 cc primaries and 1000 cc secondaries planted in a lightened FC. I have an RB header back to the stock Y-piping w/ stock mufflers. I also have the stock flywheel presently. The ECU is a Haltech e6x.

If I change up to a 3" straight exhaust and a flow-through muffler w/ a lightened flywheel, do you think I will gain another 50 hp? Presently dyno'd the car at 118 rear wheel hp. It pulls great in certain sections of the track, but blows down any long strait. I think I need at least another 50 hp to get the lap times I think the car should deliver.

I think you could find more power to the wheels somewhere in there but I don't think 50. I think you are way over fueled with those injectors. We use the stock injectors on street port engines making just over 200 at the wheels, about 235 at the shaft. And that is breathing through a stock S5 manifold.

Besides a good dyno tuning the stock mufflers could be killing power but as low as your numbers are I would maximize what you have.

^^So what combination of injectors would you recommend as the optimum setup with ITBs? 550s all around? I have to believe this has to breath better than a stock manifold. And, yes, I was expecting something in the vicinity of 200 hp to the wheels.

Your limits aren't the TB's it's the porting. The exhaust will be a huge step in the right direction. With the same ports and a Weber carb with 42mm venturis the engine should be able to make close to 250 at the shaft(250 for sure with S5 rotors). The Weber makes a little more power on top over the stock manifold just because of the length of the runners. So, your 49's aren't an issue. The stock injectors flow enough to feed 250hp with no problem, not even the turbo injectors are needed until then really.

Your trade off with the exhaust will be noise. We have a hard time getting under the SCCA db limit with a freeflowing exhaust. Usually two mufflers and some magic is needed.

^^Thanks for the input. I'll play around w/ some things, see if we can't get to that magic 200+ hp. It's got to be in there somewhere. I think at 200hp this thing could be pretty awesome with the rest of my setup.

JD to rescue = getgone (home pc)

Does anyone make a complete ITB setup?

118hp is like stock HP, i would try unhooking the mufflers and see what happens, and go from there.

I don't know what you consider "complete", but you can purchase an ITB from Tweakit or Fuji Racing. Both are high quality.

i would consider

lighweight flywheels do not put more hp to the wheels. I have before and after dyno's where the only change was from the RB steel flywheel to their aluminum one and a new clutch. I only say a .8whp increase and that isn't considered a gain due to changes in temperature and humidity between the days.

So just quicker revs?

Just quicker revs

a 800lb car with 100whp will accelerate faster than a 1000lb car w 100whp. same logic applies to drivetrain weight reduction such as flywheel, lighter wheels, aluminum driveshafts...

Working on that side of the equation as well, but need to get the HP optimized also.