Lt1 exhaust on L98
12-09-2006, 05:35 PM
#2
Burning Brakes
I am getting ready to do that mod on my 86. I have an LT4 exhaust system including the cats. I managed to locate and get all of the hangers I will need. Most of those parts are discontinued items from the dealer. I think I will have to do some modifing to the flanges on the cats. I believe they are bigger then the L88 exhaust manafolds. I think I can use the old Y pipe and cut and weld the flanges from it to the cats.
12-09-2006, 05:36 PM
#3
Melting Slicks
Yes
Yes, all you need to do is use the LT1 hangars and all will be good. You may need to do a bit of adjusting to get perfect fit and alignment but it will work. It's a decent cheap upgrade for a L98 car(if you can get the LT1 exhaust for free)
12-09-2006, 08:20 PM
#4
Race Director
If you're doing this, change to the LT-1 exhaust manifolds too. I Know they're cast iron, but they flow ALOT better than the L-98 "headers". That is actually where most of the restriction is.
12-09-2006, 09:15 PM
#5
Burning Brakes
Aren't the ports a different shape on the LT1 manifolds as compared to the L98? If they are interchangable I have a set of the LT4 manifolds I got when I got the exhaust system. My car is an 86.
Last edited by PAINTER MAN; 12-09-2006 at 10:31 PM.
12-09-2006, 10:15 PM
#6
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I am doing the same with my '90 this winter. I have the exhaust, got it for free, and I have a line on some cats.
I would like to know more about Lt manifolds though. I hate to put a cast manifold on when I have stock tubular manifolds. Will the Lt manifolds realy be better?
I would like to know more about Lt manifolds though. I hate to put a cast manifold on when I have stock tubular manifolds. Will the Lt manifolds realy be better?
12-09-2006, 10:49 PM
#8
Originally Posted by zr1fred
If you're doing this, change to the LT-1 exhaust manifolds too. I Know they're cast iron, but they flow ALOT better than the L-98 "headers". That is actually where most of the restriction is.
12-10-2006, 10:46 AM
#9
Drifting
Best low buck mod I ever did on my old 91' vert. Kept the manifolds used high flow cats and an LT4 system I got for $40 bucks.
Here's the write up I did last year.
Hans
http://forums.corvetteforum.com/show...1257879&page=2
Here's the write up I did last year.
Hans
http://forums.corvetteforum.com/show...1257879&page=2
12-10-2006, 11:27 AM
#10
Race Director
Originally Posted by mikey whipreck
That's not true, they're both bad. Besides the L98 is a tubular manifold with a different exhaust port.
Last edited by zr1fred; 12-10-2006 at 11:30 AM.
12-10-2006, 12:19 PM
#11
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Indeed the stock L98 headers are restrictive:
-AIR tubes stick down into header tubes-cut them off
-EGR tube sticks down into header tube - cut it off
-header tube inside welds are messy-ported them out a bit
After all that work I did NOT see any gain in trap speed...
IMHO, the biggest restricitons in the L98 exhaust are with the waffle-bent front Y with its two pre-cats and the 20yr old main cat.
I'm sure the restrictions of the L98 exhaust is why the General went to dual exhausts for the 300chp LT1.
-AIR tubes stick down into header tubes-cut them off
-EGR tube sticks down into header tube - cut it off
-header tube inside welds are messy-ported them out a bit
After all that work I did NOT see any gain in trap speed...
IMHO, the biggest restricitons in the L98 exhaust are with the waffle-bent front Y with its two pre-cats and the 20yr old main cat.
I'm sure the restrictions of the L98 exhaust is why the General went to dual exhausts for the 300chp LT1.
Last edited by 65Z01; 12-10-2006 at 12:23 PM.
12-10-2006, 07:27 PM
#13
Drifting
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Originally Posted by PAINTER MAN
Aren't the ports a different shape on the LT1 manifolds as compared to the L98? If they are interchangable I have a set of the LT4 manifolds I got when I got the exhaust system. My car is an 86.
12-10-2006, 08:29 PM
#15
Drifting
Originally Posted by PAINTER MAN
So what I really want to know is, will the stock LT1/LT4 cats bolt up directly to the stock 86 exhaust manifolds without modification?
Bullet cats slid onto those and then onto the LT1/4 system which had to be shortened. Had the muffler shop mount and weld everything together. The system even passed emissions. If you do it with out the cats it's even cheaper.
Here's a pic when I was still thinking about using the original down pipes with gutted pre-cats. But you still get the idea. You can also see how wimpy the original system is.
Hans
12-10-2006, 08:56 PM
#16
Burning Brakes
On the LT1/LT4 system the cats are built right on the down pipes. The flanges that mount to the exhaust manifolds are part of the down pipes/cats. If the flanges were the same size, I would think they would bolt right up. If they are not the same size I was hoping to have new flanges installed before the LT1/LT4 cats and be able to attach to the exhaust manifolds.
12-10-2006, 09:00 PM
#17
Burning Brakes
Originally Posted by ccmano
No they won't... on the L98 you have the pre-cats built into the down pipes that come off the exhaust manifolds. You want to get those off there too. After looking at the situation I had a local muffler shop fab up some custom down pipes using the originals as templates. ($100)
Bullet cats slid onto those and then onto the LT1/4 system which had to be shortened. Had the muffler shop mount and weld everything together. The system even passed emissions. If you do it with out the cats it's even cheaper.
Here's a pic when I was still thinking about using the original down pipes with gutted pre-cats. But you still get the idea. You can also see how wimpy the original system is.
Hans
Bullet cats slid onto those and then onto the LT1/4 system which had to be shortened. Had the muffler shop mount and weld everything together. The system even passed emissions. If you do it with out the cats it's even cheaper.
Here's a pic when I was still thinking about using the original down pipes with gutted pre-cats. But you still get the idea. You can also see how wimpy the original system is.
Hans
I don't have my L98 system off of the car yet so I can't get a good look at the flanges to see the difference in size.
