dmccain

iTrader: (2)

From what ive read the 350 and 5spd 305 TPI manifolds and y-pipe on these cars were the least restrictive . Hence the 25HP difference in auto vs manual 305 Speed density TPI cars. If they are that much better it would probably be a better fit and a good boost in power to an L03 engine rite? I was gona just probably wait and do headers once I get my 350 built but im thinking 350 manifolds and magnaflow y-pipe until then. Only thing im concerned with is once I used my 87 305 TPI manifolds on 350 Vortec heads and realized there was an extra bolt hole on the manifolds and I got an adapter for it but it gave me problems so I changed them out for headers. Will the 350 TPI manifolds have this issue?

dmccain

iTrader: (2)

Anyone have a good set to sell?

87Iroc5.0

iTrader: (4)

I have a good set of stock L98 exhaust Manifolds..complete with "AIR" tubing.

Kblakney

iTrader: (2)

I have a set I just removed from a 91 TPI 350.. complete exhaust and smog set up. PM me if interested.

Drew

iTrader: (58)

The HO manifolds are the same, 305 or 350 TPI. I'm assuming the extra hole you're talking about is the second threaded hole in the cylinder heads on #1 and #8 exhaust ports. All thirdgen V8 manifolds use the outside hole on #8, that some heads don't have drilled and tapped.

Also, it's not really that the manifolds are so much better, it's that the Y-pipe, catalytic converter, intermediate pipe, etc are all larger.

naf

iTrader: (7)

The vortec heads will not have the farthest bolt hole used by all third gen exhaust manifolds on the right side. The down sweep of the manifold spacing required this bolt hole relocation.

Several users, myself included, have used stock manifolds on vortec heads without the last bolt with no issues. A good, clean flat manifold surface is recommended.

305/350/L69 TPI manifolds were essentially the same. LU5/LG4/LO3 manifolds were smaller in diameter. The y-pipes are specific to the type of manifold. The better manifolds have a slightly longer down sweep on the right side and will not connect to the wrong y. All used an EFE or spacer between the right manifold and Y.

The biggest Y is from the L69 and early TPI. It is largest in diameter and beefier, but it's four bolt flange connection to the Cat limits cat-back exhaust selection. It would also be difficult to modify this Y for a different cat connection because it ovals prior to the cat.

The best option factory Y is from the later TPI cars. Modest weight, relatively large and 3" round connection to cat.

The LU4/LO3/LG4 Y should be avoided at all costs.

Drew

iTrader: (58)

Sorta. 90-up LB9 cars without the performance package (single cat cars) pretty much came with TBI manifolds, Y-pipe, catalytic converter, and intermediate pipe. Everything except the manifolds are the same part number. Chances are above average the only difference between the manifolds on later single cat LB9s and the L03 are the heat stove on the TBI manifolds.

dmccain

iTrader: (2)

From y-pipe back I have no cat and all 3in. So im looking for 350 manifolds and the larger matching y-pipe to mate up to it. Probably run this on my L03 til I do an engine swap later on.

naf

iTrader: (7)

I've heard that some of them were more restrictive but not seen any. I should also know better than to state a universal as only one instance is necessary to disprove.

The OP should look for a set of manifolds that go with the three inch Y. If you've got an LO3, you know what not to look for.