everyone that i talked to on this board tell me that the 305 tpi exhaust is the same as the tbi now for what i can tell you is mine is exactly the same as the 89 350 tpi iroc now i believe some of you guys are right because i seen the 87 305 ta and iroc both with the smaller system so can someone tell me if these were only put on 86;s

 

Really? What I've gathered is exactly the opposite. '86-'91 TPI single-cat all had the good stuff, TBI got nothing but the bad stuff.

 

How did '86 get the 350 tpi exhaust, when 350s weren't produced?

 

I believe the 305HO exhaust is the same size as the 350tpi.

JamesC

 

My expereince on this leads me to agree with James- the L-69 HO Carbureted motor had the 2 1/4 outlet manifolds and 2 1/4' primaries on the y-pipe leading to a 2 3/4" or 3" (not sure which, probably depends on year) stock cat. When they started making the TPI motors they all got this exhaust system (and then later, they came out with dual cats which still used the same manifolds, but a different dual-cat y-pipe).

The TBI motors got the carry-over 2" manifolds and y-pipe primaries off the LG-4 low output 305 carbureted motor along with it's tiny 2 1/4" cat.

What I DON'T know is when GM changed over from manioflds that used a "donut" gasket between the manifold and y-pipe to a flanged, gasketless junction. I know in 87 the TPI motors used the gasketless junction, but I don't know if they had that in 86. I'm pretty sure it happened sometime in the late 70s - early 80s, though.

 

My 85 IROC has the flanged, gasketless EFE valve on the pass side. No donut on the driver's side.

JamesC