Somewhere I heard 81's had the worst manifolds and try the 83's
Since I will have to have the motor gone thru I figured I would check,
I don't have a welder so I was hoping to find one someone had done or pay someone to do it.
1, the manifolds keep in heat better for spool and wont crack
2, the tubular headers flow better and the heat released is more but you pick up a ton of flow.
I believe 2, I ran 80 manifolds and switched to 85 GN tubes. Im wastegated to 7PSI and crept up to 9 on top of second gear. With the tubes it stays solid around 8PSI and doesnt so much creap but blows past the wastegate and has hit 14 on a few occasions. Good gas and generous timing retard kept it together I need to get the housing off and open the wastegate up, but being the CNC lathe is back in commision at work I was going to try my 87 GN comp. wheel in the 80 housing.
Ohh, and downpipes are limited. I built an aluminized 3 years ago and sold it to Mike on here. Built myself another stainless 2 piece to take the pipe off without taking the AC pump off. Heres my nice, polished example.
There is a 3rd school of thought....That narrow exhaust manifolds keep the exhaust velocity up and yield better spool up (at the sacrifice of top end). This might be better on a stock, street driven car. I've never tested any of this back to back. I think there might be something to experimenting with different up pipe diameters, since they are so easy to change. It sure looks like the 1980 up pipe is bigger than the 1981/83.
There's actually more schools of thought on manifold design than you can think. Ideally what you want is the cast manifold on the drivers side (keeps heat in) with a stepped crossover (2.125" for 3/4 length to 2.25") and then a tubular manifold with a 2.25" log, then up to a 2.5' up pipe. It keeps the heat in and as the exhaust moves along it allows for expansion and re-ignition on the passenger side so the turbo will spool better.
Dont like the pass side towards the up side feel it is very restrictive .Have thought about having extrude honed but afraid they will crack. They spool great but feel they restrict my head and cam combo on the top end on my app.And by the way merry christmas guys love all your input good bad and ugly