Intake manifold modifications

[C. Ludwig]

Originally Posted by NoDOHC

On my tired 6-port, I made peak power at 6200 (155 WHp) this was at 13.5:1

It made 140 Wlb-ft at 3200 rpm.

I am impressed with the 4-port power.

My 6-port experience was what led me to tune around the 13.5:1 region. However, I can believe that my polished intake runners, smoothed ports and polished rotors will require a little more fuel.

Doesn't really work that way. You're trying to provide just enough fuel so that every oxygen molecule has something latch on to. You'll hit peak efficiency when you use all of the oxygen molecules without wasting a bunch of fuel. Stoichiometric is the theoretical mixture at which all of the oxygen available find a fuel molecule to work with and all the fuel is burned up. You usually find max torque in the real world at a mixture on the fat side of stoich because in a combustion chamber things aren't ideal. A good intake system and combustion chamber will allow for proper mixing (tumble and/or swirl of the charge) and proper quench to keep the charge more or less packed into a homogeneous mixture near the plug. A good combustion chamber will also promote good flame propagation which helps to ensure the entire mixture is burned. If you need a mixture that is fatter then you've lost efficiency somewhere. It's possible you're seeing peak torque at that mixture but if you are something has changed to the detriment of efficiency. You're still not making more power than has been made with completely stock components so if it's taking more fuel you've erred somewhere.

Originally Posted by NoDOHC

Believe it or not, at 9,000 rpm in 4th gear, the rear wheels are actually going 180 mph - not that I have gone that fast, but the engine is running exactly 4,000 rpm at 80 mph (I have checked the speedometer and the rpm is from the Haltech).

I absolutely don't believe it. I spent a number of year racing these car in SCCA Club Racing. I know how fast the thing goes in 4th with a 4.10 rear gear. Even a gear calculator will tell you that you're well short of 190 mph. Just ran through one and it gives 150 for a 23" tire and 163 for a 25" tire. That's higher than I said before. Guess I was thinking 8k max rpm which was typical at most tracks we ran at. Unless you have a 30" tire on there you aren't seeing 190. They don't call them dreamometers for nothing.