Guessing game.

Build:

Lightly ported otherwise stock BP4W Head
1,900cc
NA8 Inlet manifold, ported cnc spacer to match port head
Absurdflow low mount style manifold 1.25" runners
GTX2976r 0.86
Full 3" straight through exhaust
8.6:1 forged bottom end
Boundary pump

Enough fuel, intercooler, intercooler piping, intake, gearbox, diff, clutch etc for 500whp

Premium Unleaded.

What do you all think?

What will be the limit, detonation or outright flow? Valve seat pressure? RPM?

Dann

 

350. Pump gas as the limiter.

 

I wouldn't waste your time with the NA8 manifold, not sure I've ever heard of it being an upgrade. Spend your time and money on converting a Honda short runner intake.

Hope you have a transmission solution in mind cause it'll make more than the 6 speed can take. BMW trans solution should be out some time this summer I would think.

 

I think 350 is a pretty good guess.

And it'll do that til the manifold separates from the turbo flange :P

Too soon?

 

300-350

 

327.59 whp.

The first limiter will be fuel. I am assuming pump gas. Get some E85 in that beast.

Then I would guess valve springs limiting RPM, or flow from the head/intake manifold.

 

I have no idea what pump fuel is like in Australia, but certainly here in the US, 91 or 92 octane would be the limit.

--Ian

 

340-350whp, detonation/EGT limited

 

I think it will make more than 350, but I agree that detonation will be the limiting factor.

Dann

 

I would guess 350-370whp on 93 with a perfect tune, if everything else is perfect as well. If you added some meth injection, I think you could add another 50-80whp depending on how much meth you spray. You would be octane limited is my guess, and I would highly recommend valve springs. If the exhaust valves float, it can cause hot exhaust gasses to dilute and raise the temps of your air/fuel mixture during the intake stroke, and that can quickly cause detonation.

 

Alright, the guy has decided he -does- want to go water meth and really lean on it.

Whats everyones experiences with valve springs, and would you bother with some small cams?

Dann

 

I don't have part numbers for you, but someone makes valves springs that have a changing diameter. Springs with a constant diameter have resonate frequencies that can cause problems. Running 2 or 3 different size springs together helps, but a spring with a varying diameter is the best solution, and I have read post/seen pics of them here. I'm going to swap to better springs next time my cylinder head is off for service. I haven't run aftermarket cams, so no experience. They are not cheap is all I've really found in my research.

 

^They are called beehive valvesprings.

There are also ovate (flat/oval cross section) valvesprings which have more spring rate than standard.

 

The easy button is just ST light doubles, about the cams, I think we will try without running new ones.

Hopefully we can just do ignition, water/meth and springs and just run 30-40 psi.


Dann