I looking to get a little more out of my 91 Vette. It is bone stock and has 40k on the clock.. Should i eliminate the cats and put on some muffler eliminators ?? Is there any sense in doing the tpi coolant bypass . Please guys im open to some and all suggestion. Does putting some gears in the rear make sense??

 

What is your goal?

Of course a cleaner exhaust will bring nice HP gains, i.e. no pre-cats, hi-flow/no cat, hi flow cat-back or true duals.

Some simple (~"free") mods will wake her up too:
-cut air intake lid with K&N filter
-160deg F. T-stat
-remove the "frisbee" from the front of the WP pulley.
-bump base timing a point or two.
-increase TPS to ~0.70 Vdc at idle
-remove spare & jack (50 lb loss ~5chp gain)

BTW, fine looking vert...

 

Thanks for the reply .. Sounds good and some low budget tips which i like .. I really dont want to dump a ton of money into it before i drive it a year or two and then i will probably do a nice roller motor for it .. The exhaust i will probably spend a couple dollars on being i will probably use it later on.. Thanks for the advice i will do exactly what you said..

 

Gears will make a noticeable difference that never gets old.

 

Something like a 3.54 will be a big improvement in acceleration. And it won't hurt the gas mileage very much. You didn't say what trans is in the car. Auto trans cars have a D36 diff whil the manual trans cars got the stronger D44 diff.

You didn't say if the car has to pass an emissions test. Headers and trues dual can certainly wake the car up, but you may have problems with emissions A good tune can help especially i you remove the cats. But exhaust improvements can also result in drone inside the car. An exhaust shop can remove the factory mufflers and add some straight pipe. Shouldn't cost a lot to do and it will give you a starting point for loudness.

 

x2 on emissions.

If you are not prone to getting sucked up in ET time slps, dyno # etc meaning realistic about imrprovements for the money...heres what Id do (doenst mean its right)
Gears...ones for verts usually suck

Wait for a deal on some aftermarket runners, leave the stock throttle body on.
Port the stock base as much as possible. You can get them on par with the aftermarkets, if youre real good a little better even .
Keep the duration on the cam @050 somewhere in the 2teens, around .500 lift+-
Port the stock heads, decent valve job & fresh springs. Neither costs a lot. Skip the big valves and quest for hero flow bench #s.

If you can get away with longtubes, definitely, add a true dual exh with stock type mufflers or dynomax/walker turbos or use a magnaflow resonator and muffler elims
Ive seen a friend use the LT1 DOugs shortie headers for the LT1 that had a CARB# and did a clean job adapting the smog tube. He got lucky and passed the visual out here...anythings better than the stock exh manifolds
(I hate cars that drone too much Keep em quiet or go uncorked.)
If not do a catback if youre not happy wiht the stock sound. 2.5"Y, 3" main.,

To get any more power you have to really spend a lot of money its not worth it. THen build up everything behind it.
I bet with the above stuff you will be deep in the 13s, smoke the tires when you want and most importantly stay together for along time.

Building for hp/rpm is expensive, building for tq isnt.

 

The car has an auto trans and the car don't have to pass an emission test here in NY just safety.. I will try a lot of the stuff you guys said .. First thing to cone off is the exhaust it us going to be straight pipe from front to back nothing in between . I question i have is no one makes a cold air hookup for the car rite ?? As in cold air intake and how about the heater hoses connected to the tbi can i eleminate that ?? Thats one of the stupidest things i have ever seen on a chevy..

 

To keep them from icing over if you lived in the Artic circle. Wont give you any power but if you want to bypass at least theres one less thing to leak-
Some cut the airlid for the intake, never saw any power gain over a decent quality paper filter. If you use a K and N go easy on the oil!

Exh will help but it will be loud. Guess if the tops down maybe it wont drone like an enclosed cabin would?

 

Timing might do something if the ECM doesn't detect detonation and retards the timing back. How does adjusting the TPS help? The 91 uses startup voltage as base. Most of the other stuff really doesn't do much by itself.

 

It certainly helps the placebo effect for the most part other than the timing, assuming it doesn't get removed when the ECM sees detonation. If you are getting anice motor, why bother with doing any of this stuff today? Spend the money to find the tuner that will retune it and go with that. When the motor comes, install and tune. I'd worry about the D36 if it is a manual and change that for a stronger one since you could break it. Rebuild the trans to stronger specs if you want to be ready for the new motor. Otherwise, just drive the car and be happy till then.

 

I would not do gears on a 91, L98 does not respond to that as well as the LT1 does. Instead, I would go with a higher stall TC, 2000-2400rpm, and then an additional tranny cooler.

The cold air setups for C4s leave much to be desired, I have the SLP, its not really doing much other than sounding cool.

Do the exhaust system first.

 

I like the TB coolant bypass as it makes life much simpler if you need to take off the TB and it keeps incoming air a bit cooler. This is a good one to do when you install the 160deg F. T-stat.

The TPS advance gave me crisper throttle response off idle.

Indeed one need be careful to not advance base timing too much. On my prior '88 I had a scan/monitor tool with which I verified there was no timing pull on a WOT pull.

 

About all that's good for. Ease of TB removal. I don't recall seeing how that makes any difference other than maybe a theoretical improvement. As for the TPS, I think they are round holes NOT slotted and the ECM uses initial start up voltage as baseline. If that is correct, any improvement might be in the head.

 

Good catch. Think I now recall that last L98 years did not use slotted holes for the TPS...

 

Yes and it was amusing to watch someone swear that the slotted ones made it better. I slotted mine too. Set it for 0.54V but told him it was higher. He swore that there was a huge response difference. 2 problems. I didn't set it higher and it didn't care until you went overboard. When I do see him, I always ask if slotting works. Last time he said "Fawk You".

 

100%

Exhaust is the biggest gain for a stockish L98. With my 91, I started with a cat-back and a front Y-pipe without pre-cats. I've done many exhaust combinations, through the years, as my mod list grew. I now have long tube headers, 2.5" duals with a X-pipe and Corsa mufflers with no cats. I've also tied a few different rear end ratios, starting with 2.59s, which I'm pretty sure you have in your vert. 2.59s really aren't that bad in an automatic, TPI car. With a 2500 stall TC and a set of DRs, I would normally see 60' times in the high 1.7x to the low 1.8x range with simple mods. I later added a 3.07 rear which got my 60' times pretty solidly in the low 1.7x range. A later change to 3.33s got me into the high 1.6x range on a good day, but slowed me down on the back end of the track. I think, in terms of 1/4 times, the 3.07 rear is pretty much proven, the best rear end ratio in an A4, TPI car, but you can easily get away with keeping the 2.59s. Steeper gears might get you out of the whole a little quicker, but will likely slow you down after 30 MPH, or so. Again, this is strictly based on TPI cars and 1/4 mile performance. If you're looking for a stoplight warrior, then you could probably get away with 3.54s, but be aware your car would be slower at the track (if that matters to you).

I'd also do the TB bypass. There's virtually no down side and it makes removing your TB a simple process. Not sure about performance gains, but it certainly can't hurt. My TB definitely felt cooler afterward.

 

Thanks for all the tips .. I will try a bunch of them the tpi bypass being first and the aircleaner with the lid then the exhaust.. No looking to go that fast with this motor just want reliability and a little more performance.. I will probably do a tune on it being ive seen this these cars get as much as a 50hp increase on a good tune.. I also have a gas station around the corner that sells e85 i was thinking about doing 4 to 16 gallon mix.?? Please give ne sone feedback on this ..

 

It probably will be as reliable as stock since you have pretty much stock. Only thing is if you are in sub zero conditions, your TB can freeze up or so the GM engineers thought. The little bit more performance, IDK if you will see it.

If you haven't done much, there isn't a real reason to tune unless you have money to waste. IDK about 50 just from tuning.

What are you trying to achieve? If you want to run E85 solid and get more power through advanced timing without detonation, you might have to change the injectors for that. Ethanol has less BTU so it has less energy to impart.

 

Like i said i would run a e85 mix 4 galloms and 16 super unleaded.. Here in ny super us 93 octane.. which with the calculator would bring the octane up to 95..

 

Indeed the TB "can" freeze up with the TB bypass. It happened to me but once in 18yrs and that was in -4deg F temps when I failed to let the engine warm up before hitting the highway.

Don't forget the real benefit of the 160deg T-stat. I've measured the HP gain at the strip, measured by increase in trap speed. To keep temps in the 160-170deg range in traffic you will need to coax the main fan to come on. You can do this by opening the front connector in the A/C pressure line or install a manual fan switch.

These simple mods, along with exhaust work, will make your Vette more enjoyable to drive though a too heavy foot will easily light 'em up on the street.