L98 Exhaust Options?

[mash2k]

After much review on this forum and a lot of thought, I have come down to three options for my 91 A4. It has the 3:07 rear, hi-flow main cat, and magnaflow SS catback. Other than a K&N the car is bone stock.

Option #1: LT 1 5/8 headers into 2 small cats to an Xpipe into duals. I am assuming that this would be purely custom work by a muffler shop.

Option #2: LT 1 5/8 headers into 2 1/2 in pipe to my hi-flow cat into my magnaflow SS catback.

Option #3: Bolt on 2 1/2 SS Y-pipe into my hi-flow cat into my magnaflow SS catback.

Immediate mods will be:

Cut Air filter lid
Remove frisbee
shift kit (which one?)
torque converter (stall ?)
possibly different gears (3:73 ?)

Initially, I will be doing mostly bolt-ons since my motor only has 75k. Down the road I will most likely have my heads ported and polished and the intake setup ported with a suitable cam when I do my rebuild or crate replacement.

What do you think and which option makes the most sense?!

 

[jwilliams]

Start with long tube headers designed for the L98. Cats are up to you. Does your state require them for smog? You can build a high flow fully smog legal exhaust for this car. As for mufflers, etc down wind of the cats or headers I have heard excellent things about the new Corsa system for the L98. Main thing is to use a set up designed for the L98. The LT1/LT5 motor has WAY different characterisitics than the L98.

I'm sure others will jump in with suggestions of what they've done.

 

[mash2k]

I do have to pass smog here in NE Ohio. If I go LT header, do I put aftermarket hi-flow cats right after the headers then back to x-pipe and mufflers?

I know the LT-1 has only 2 cats. I was trying to find out if that flows better than if I just use my one main cat or if it doesn't make that big of a difference. I also want to make sure it is legal to switch to a custom LT1 type exhaust with 2 cats. I just want to optimize HP, not make it sound overly loud. I would keep my magnaflows.

What do you think?

 

[Mad-Mic]

I do have to pass smog here in NE Ohio. If I go LT header, do I put aftermarket hi-flow cats right after the headers then back to x-pipe and mufflers?

I know the LT-1 has only 2 cats. I was trying to find out if that flows better than if I just use my one main cat or if it doesn't make that big of a difference. I also want to make sure it is legal to switch to a custom LT1 type exhaust with 2 cats. I just want to optimize HP, not make it sound overly loud. I would keep my magnaflows.

What do you think?

TPiS is your friend

gutted cats, 1 3/4" TPiS long tubes, chambered muffler eliminators.

http://www.corvettekillstories.com/photogallery/albums/Mad-Mic/Racing/Sweet_Sin.wmv

 

[Moonunit 451]

I used option #1 with Hooker 2151's, 3" RandomTech Metal Matrix Bullet cats, 3" Magnaflow X-pipe (pretty sure, could check) to Borla ZR1 2 3/4. Love it And ya it was custom, and not cheap, but if you know someone, well, it wouldn't be so bad.

 

[AdvancedAutoCC]

Option #1: LT 1 5/8 headers into 2 small cats to an Xpipe into duals. I am assuming that this would be purely custom work by a muffler shop.

Option #2: LT 1 5/8 headers into 2 1/2 in pipe to my hi-flow cat into my magnaflow SS catback.

Option #3: Bolt on 2 1/2 SS Y-pipe into my hi-flow cat into my magnaflow SS catback.

Immediate mods will be:

Cut Air filter lid
Remove frisbee
shift kit (which one?)
torque converter (stall ?)
possibly different gears (3:73 ?)

Initially, I will be doing mostly bolt-ons since my motor only has 75k. Down the road I will most likely have my heads ported and polished and the intake setup ported with a suitable cam when I do my rebuild or crate replacement.

What do you think and which option makes the most sense?!

Go with option #1 if you can find a competent shop to do it. My personal preference is Hooker for LT headers, but like everything else, everybody has their own opinion. PM me if you want info about high flow cats.

As to a shift kit, it's a pick 'em as you're basically just getting modified valve body plates and gaskets in the kit (not very romantic, just reality). Your best money spent in the drivetrain (even before a converter) is for gears. NOT cheap by any means, but well worth the expense. If you're planning any serious HP gains down the road, you would do well to investigate upgrading your diff to a D44 (again, NOT cheap!). Some guys have had good luck with the D36, but when you go over a 3.54 ratio, longevity can become an issue.

As to engine modifications, head porting, etc...think long and hard before doing anything..... and be brutally honest with yourself about money, time, etc., etc.. If you can't afford it, or can't justify spending the LARGE amount of money necessary to do engine work, then leave well enough alone.

Remember these words before laying a single wrench on your Vette:
Fail to plan....plan to fail.

Good luck, whatever you decide.

 

[mash2k]

Thanks guys, for all of the info and advice. I have thought long and hard about this and I am going to do the following:

B&M shift kit
2400 stall converter
1.6 roller rockers
remove "frisbee"
cut lid on intake
TB bypass
I will also ensure all sensors etc are working properly and that I have a good state of tune.



For exhaust, I will install a SS 2.5 inch mandrel bent catless front Y as a temporary measure. I will do this because that would make my entire exhaust stainless and because my vette never sees snow or salty roads, it will be in good shape when I sell it. With these bolt on mods I should see a nice little gain in fun factor.

In the meantime I will be planning my MAJOR engine buildup in which I plan to spend around 10k total. My engine only has 78k, runs great, and there are just other monetary priorities for the time being. I will hold off on Option #1 until I get my engine and do it in one shot. Once I exceed 100k on the motor, then the real performance fun will begin.

Again, I appreciate all the input and am much appreciative for all of your comments.

Mark