This is WHY L98 Guys May need Headers!!
Waka, Waka, Waka!
Joined: Jun 2002
Posts: 2,435
Likes: 2
From: Richmond Virginia
CI 4-6-8 & 10 Veteran
St. Jude Contributor
Re: This is WHY L98 Guys May need Headers!! (Bill's86Coupe)
Lots of great info and pic and wanted to say Thanks to all that replied and basically confirmed my "new" thoughts.
Burning Brakes
Joined: Jul 2002
Posts: 871
Likes: 0
From: Costa Mesa CA
Re: This is WHY L98 Guys May need Headers!! (Bill's86Coupe)
Yeah, when we replaced the head gaskets on my motor, my mechanic is an expert on porting small block Chevy's. He did the whole thing from the plenum to the exhaust ports. He said there is a gross mismatch between the heads and the base manifold. He had to do some serious grinding to get the ports to match. He said he spent 8 hours porting the heads and base manifold. I did the plenum myself. There's a big blockage there too that can be ground away.
We left the runners untouched as they are cheap enough to replace or until I get my spare set ported. You can cut the aluminum fins away from the MAF sensor with a jig saw as well. Every little bit helps.
Even with the cam change, the engine wouldn't rev past 4900-5000 rpm. Now with the extra flow, it pulls hard until 5200 or so when the tranny shifts and the tires break loose again. I can tell I need more fuel with all that increased air flow. Working on that.
The only thing that can be said favorably about the L98 exhaust manifolds is they are better than those old cast iron ones of yester-year.
FWIW,
BIG JIM
We left the runners untouched as they are cheap enough to replace or until I get my spare set ported. You can cut the aluminum fins away from the MAF sensor with a jig saw as well. Every little bit helps.
Even with the cam change, the engine wouldn't rev past 4900-5000 rpm. Now with the extra flow, it pulls hard until 5200 or so when the tranny shifts and the tires break loose again. I can tell I need more fuel with all that increased air flow. Working on that.
The only thing that can be said favorably about the L98 exhaust manifolds is they are better than those old cast iron ones of yester-year.
FWIW,
BIG JIM
Drifting
Joined: Mar 2001
Posts: 1,636
Likes: 3
From: Lafayette IN
Re: This is WHY L98 Guys May need Headers!! (Bill's86Coupe)
Hey Bill, good points.
I don't remember where I saw it, but recently (maybe on this forum), I ran across the method of slotting the manifold bolt holes vertically to actually create exhaust manifold to head interference (???where the offset actually helped build some power due to something or other...hehe??). I think one of Emmanuels or Vizzards books got into it--heck, mebbe someone that has posted in this thread was involved in the other thread.
Since you have a couple sets of manifolds, maybe you can test the theory out on our TPI engines :)
I don't remember where I saw it, but recently (maybe on this forum), I ran across the method of slotting the manifold bolt holes vertically to actually create exhaust manifold to head interference (???where the offset actually helped build some power due to something or other...hehe??). I think one of Emmanuels or Vizzards books got into it--heck, mebbe someone that has posted in this thread was involved in the other thread.
Since you have a couple sets of manifolds, maybe you can test the theory out on our TPI engines :)
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: This is WHY L98 Guys May need Headers!! (BIG JIM 54)
BIG JIM 54, if you feel you have a little low end torque to spare consider the siamese intake base. My L98 now pulls strongly well into the mid 5,000rpm range with stock heads, cam and headers.
Data shows you should gain about 15chp in going from a mandrel-bent front Y to FL headers.
Data shows you should gain about 15chp in going from a mandrel-bent front Y to FL headers.
