Hi everyone, long time Vette lover and new member to the forum. I have a clean 1991 white L98 with 47k miles that is stock at this point. I don't want to change a lot, but am interested in picking up some "ponies" to increase acceleration.

I have heard that the most bang for my buck is changing the rear gears. Any thoughts from anyone on the above or any other worthwhile modifications for the L98. THANKS!

 

Click on "search" on the left side of the screen. It should return approximately 1 million results. :D

 

No gear changes for L98s :nono: Thats for LT1 guys.

It depends on your HP goals, and what transmission you have now.

 

Unless it's an auto with the 2.59 gears I wouldnt bother with gear changes. L98s dont have to have alot of gear. 3.07 is about optimal for an L98 auto and 3.33 for a 6 speed. Start on exhaust and intake and go from there. Headers [longtubes if possible] and a good catback will give a nice gain.

 

First of all congrats on your obvious good tastes in white '91 Vettes ;) :cool:

I have messed around with minor mods on my car and I believe that the biggest gains on a stock L98 will be found in exhaust modifications. First replace your front and rear y-pipes with bigger diameter (2.5") mandrel-bent pipes and opt for a front y-pipe w/out precats. Secondly, if your state allows, either hollow or replace your main cat with a test pipe. Then add the performance muffler of your choice (depends on your taste in sound) and you will have a killer exhaust system. With just these changes I dropped about .3 - .4 from my 1/4 mile time and I still have my stock exhaust manifolds so I imagine that the addition of headers would improve my times even more.

As far as the gear change goes you will not see the kind of improvement that the LT1 guys do from going to steeper gears. I think most will confer that the 3.07 rear is the optimal gear for the low RPM L98s. In my opinion you can even get away with the [cough, cough] 2.59 rear. With the 2.59 rear I managed as low as a 1.76 60' time and routinely cut about a 1.80. I have since switched to a 3.07 rear, but have yet to equal my 60' with the 2.59, although I think that is mostly due to traction. I think my times will eventually get better with the steeper rear, but I highly doubt I'll see much more than a tenth.

You'll also see nice gains from ditching the stock intake and going to an aftermarket (accel, tpis, etc) base with larger runners. I don't have times yet, but am in the process of switching to an accel base with ASM runners.

In any case, have fun with your car and feel confident that you'll receive plenty have helpful info here on the forum :cheers:

 

increase the size of the opening on the lid of your air filter box

add a stock size K&N air filter

remove the frisbee (metal disk bolted to the water pump) remove belt, unbolt frisbee, reinstall bolts using washers to take up the space the frisbee used to occupy

long tube headers (check local laws)

2.5" dual exhaust from a local muffler place. I used LT1 exhaust mounts. it can be tough to find room for the cats and dual exhaust when you use long tube headers and have an automatic.

Breathless Performance Products air pump eliminator kit (check local laws)

after that, it's cam, heads and intake. these should be decided on as a package.

i don't have an auto, but I believe a higher stall converter will help

 

Consider a set of March 'Power & Amp' underdrive pulleys.
Pay the premium for the aluminum ones and enjoy modest
additional savings in parasitic losses. Figure on a gain of
.10th or approx 10 hp

4425 - 3pc steel
4430 - 3pc alum

http://www.marchperf.com/pg10.html

You will need to get a shorter belt. March suggests
Dayco 506905, a better choice in my opinion is to
use Delco (6K905 - I think). GM dealers won't
have the Delco, you'll need to go to a Delco vendor.

Yes, this mod is controversial. With too much underdrive
there will be issues with inadequate charging for street-driven
cars. But with the right ratio, L98s like this one. Do a search
on Pulley in C4 Tech/Performance Archives to see for yourself.

 

Where did you here this ? For an L98, this is not true at all.

Headers, a free flowing Y pipe, & a catback exhaust will give you the best bolton performance.

Vic

 

My '91 auto came with the stock 2.59:1 rear gears. With all the mods. I have done so far I will say that changing the gears to 3.54:1 gave me the best SOTP (seat of the pants) performance increase. When you change the gears it feels like you just added 50 HP.

Good luck with your project,

 

(4th time trying to reply to this post. It keeps timing out)

Why do you say that? The SOTP diff between say 2.73 gears and 3.45's is like nite and day.

 

Of course its gonna feel different, but you are out of your powerband so fast that lesser cars can beat you in any race past 60 quite easily. Track ETs have proven that whatever gain you get before 60mph, you lose that and more past 60mph. (in an L98) The L98 does not need more, in stock form, than 3.07.

If you change the cam, or modify the intake, you may go a little lower, but even with the Superram its not necessary to go lower than 3.07.

 

That makes sense. Is there a diff then between having an AT or a ZF6? I mean will diff gears help one more than the other?

 

Yeah, with the A4, you only have 4 gears to play with and a lower rear will hurt gas mileage more, and since you do all your accel in 3 gears (usually) this loss of powerband is shown.

In a 6, you have more gears with diff ratios to play with, and a higher 1st gear ratio that makes the lower rear a plus. In an L98, you probably still dont want to go lower than 3.45 with the 6 (but i think 3.54 and 3.33 were optional). Plus, with the ZF6's 6th gear ratio, a lower rear will give you a real use for 6th gear on the hwy.

 

white 91's ROCK! Welcome and Good luck! :cool: :steering:

 

Welcome to the forum :hurray:

I don't have an A4, but I've driven many with the 3.07s and think they are about perfect for accelaration while maintaining good drivability. Lower gears in the Dana36 are available, but I haven't driven one with these, so can't opine.

1989 6-spds came with 3.54s very early in the production run. Somewhere around 1,000 6-spd cars, the switched to 3.33s. All L98 6-Spds from then had the 3.33s. There were no options. When the LT1s came out in 92, 6-spds all got 3.45s through 1996. I believe the 6spd L98s can handle 3.73s if they've got improved breathing. I'm going to try them next season, but they may be too much on a long straight. :flag

 

Hmmm...the RPO code on my '91 ZF6 coupe says 3.45's which I had heard was standard.

 

DarkHalo - you are sure right! I stand (humbly) corrected :bb Thank you.
I had a bad reference. I just verified this in my GM Parts CD. Here are the corrections for 6spd Vettes with RPO codes:

Early 89s had 3.54s (GH0). Mid 89 on had 3.33s (GT7).
In 1990 most were 3.33s, but 3.45s (GM3) were made an option (late?).
1991-1996 all had 3.45s (GM3).
:flag

 

I don't want to go crazy. I have the automatic decision and would like to increase acceleration. Thanks.

 

I agree, I love my white '91!!! Thanks for the tips.

 

Yeah, the person who told me has a '93 LT1. A different animal, I guess. I will reconsider the gear change idea.