Im in the process of attempting to replace a p/s exhaust manifold on a 305 TPI. However, the replacement manifold that I was sold does not seem to want to marry properly with the exhaust tubing coming from underneath. I've tried (unsuccessfully) in raising and lowering this engine at various positions in order to try and attempt to make this fit.
I was told that all the manifolds are interchangeable for chevy 305 for stock exhaust. This vehicle has the factory exhaust.
It seems to me, tho, that the lower end of the p/s manifold is tilted more at a 45 degree angle, as opposed to the angle of the exhaust pipe coming up from below (which is more or less straight).
Am I goin' crazy or is there a specific Chevy manifold that I need to use as a replacement for this car with this exhaust?
Any help would be appreciated since I have not been able to find any topics in the forums that seem to address this.

Thanks. (sorry for this long post)

 

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TPI manifolds are different than carb manifolds.
And I believe 85 was a one year deal(82-84 carb interchangable / 86-92 TPI interchangable). Maybe somebody else here can verify this.........hope this helps.

 

There were only 2 different manifolds for the V8's throughout the years, but they were different depending on what motor and gearing package they came on. Here is the breakdown.

2" outlet manifolds with single 2 1/4" y-pipe
82-87 305 LG4 (VIN H)
88-92 305 L03 (VIN E)
82-83 305 Crossfire
90-92 305 LB9 w/o G92 axle (VIN F)

2 1/4" outlet manifolds with single 3" y-pipe
83-86 305 L69 (VIN G)
85-89 305 LB9 (VIN F)
88 350 L98 (VIN 8)
89 350 L98 w/o G92 axle (VIN 8)

2 1/4" outlet manifolds with dual 2 1/4" cats
89 350 L98 w/G92 axle (VIN 8)
90-92 350 L98 (VIN 8)
89 305 LB9 w/G92 Axle (VIN F)
90-92 305 LB9 w/G92 (Vin F)

The manifolds from the single 3" cat and the dual 2.25" cats are interchangeable. On the passenger side manifold, some will have the heat riser butterfly valve, some will have a spacer, and some will just have a donut gasket. You most likely have the wrong manifold for your application. If you have the larger manifolds, then it may be worth it to get the larger y-pipe for some more performance.

 

So, 85 , 1st year with TPI(2.25 OUTLET) no air tubes, no butterfly valve.
85 with Carb-either 2" or 2.25 outlet,with butterfly valve and air tubes.
Either he has the wrong one, or possibly missing the spacer?????

 

They should all have AIR tubes in stock form. They may have been removed and bolts installed in place of the fittings. Only carburated cars got the butterfly valve. Some of the fuel injected cars got the spacer, which replaced the butterfly valve, and some just got a donut gasket with no spacer or valve. The angle of the outlet on the 2" vs. the 2.25" is different, so that is most likely the problem. Either the correct manifold needs to be used, or the corresponding y-pipe to the new manifold has to be used.

 

I swapped the LG4 exhaust manifolds to the L69. The difference in outlet, as noted above, required the correct y-pipe--which you can clearly see below.

JamesC

 

Did you notice any diffrence in power at all when you swapped manifolds and ypipe over James? I have the small mani/ypipe on my crossfire car and I was wondering if it's worth it to convert over.

 

If you have the parts at hand and the cost isn't prohibitive, I'd say do it. That said, the best choice is headers.

JamesC

 

wait a min, the l69s vin code is g? i thought it was the h code engine and the lg4 had the g code?

 

Vin H is the LG4; Vin G is the L69 (though the L69 is a "7" in 1983).

JamesC

 

i see , i never knew always figured that because it was the H O engine it would be H and the lG4 would be G i guess i've been looking at rebuild kits for lg4s when its not busy at work rather then for l69s lol now i know its g and not h thanks for good info