Since I was first learning how to work on cars I've heard the TPI engine was the best truck engine they never put in a truck. Most of the dyno graphs show that TPI has very large low end torque and basically falls on its face above 3500 rpm. So wouldn't it be an upgrade to just switch the tpi intake with a tbi? Probably no power gain but more of move the power into a more practical range for a sports car.

 

I'd say it falls on its face at 4500rpm but if you want it to run better upstairs then a manifold with shorter runners is what you're looking for. Factory TBI isn't really a performance setup out of the box but the runners are shorter. TBI as in a nice dual plane manifold and whatever you want to put on top of it would be a good choice for up to 6500rpm.

 

Pretty much what I was thinking with the dual plain reference.

 

Consider the ancient Chrysler "Long-Ram" intake manifolds. They peaked at 2,800 RPM, and they were even longer than TPI runners.

You don't need shorter runners as much as you need BIGGER runners. The cross-section isn't enough to support the airflow needed at higher RPM. I keep hearing that the TPI system was intended to build torque on 305s, but got used on 350s where the airflow demands were just too great.

I'm told that with proper tuning (which I have zero ability for) the TBI makes more power than the TPI; but I don't think it's due to runner length.

 

This is what a stock L98 puts down to the wheels:



Pulls ok out past 4k, but that's about it. You absolutely need shorter runners to move the torque peak up and get more top end performance. Every TPI style long runner setup is going to make the same graph shape, the largeness of the tube will just move the curve upwards. See also:

 

Very cool video. If you put cost vs performance a few of those intakes don't seem to be worth it.

 

They never mention what they did to tune the fuel curve, or the spark advance curve.