Fredbird

91 L98 Auto

Previous owner gave it a bit of a hard life.
I think I'm at the end of what I can do for her as far as care and feeding... I think I'm close to the point of Engine Rebuild. Runs decent, but lacking top end power.

Looking at Options/Best Practices from guys who have already done this. Not looking to make it a HotRod, but a nice running 91 Vette with a few performance upgrades.

Any blogs with good tips?

Also anyone in DFW area who knows of a good machine shop who won't take me for everything I'm worth to get heads and other machining done?

Other option is have wife's cousin (Mechanic) in Houston do it for me, but i would miss out on all the fun.

Not 100% sure what all I'm getting into. This would be my first rebuild, but am a relatively competent shade tree mechanic.

billschroeder5842

Fred,

You did not mention miles on your engine, condition, budget or goals so here goes as far a local contacts to start with...

As you know the L98 will be a lower end torque producer but fade at the higher end.

My first place to start would be the exhaust as the factory is pretty restrictive. You can take your car to Kinneys in Wautaga and Kirk can do magic. On my '89 he took out the pre cats and put in a performance catalysis. BIG difference. If you put on headers, BIGGER difference.

For top end work get in touch with Jim at Mid Cities Classics in Hurst. He does a bunch of the stuff that scares me and works on a few of the other local guys cars. If he can't do the work (he probably can) he will have the connections. He has been building Vettes for decades and knows what works and what does not.

As we are neighbors, give me a shout; I'm happy to stand in a garage, share a few beers and congratulate ourselves on how cool our cars are.

cardo0

First rebuild, well we all started somewhere. But it's hard to know if your motor is truly sick or just in need of some thoughtful care. Standard tests are compression and leakdown. Accurate milage record is helpful to. Driven daily with normal use the sbc can live for 350k mi. Now valve seal and cam lift start to deteriorate before 100k mi but the engine will continue to run on reduced power.

I guess what I'm saying is before you tear open the engine you should start with diagnostics and tune up. Check your compression and verify your timing curve just to get familiar with your sbc and it's installation.

IMHO a cylinder head remove and replace is easier than a cam swap. Once you master the top end then any problems there won't confuse you when rebuild a sbc bottom end.

Hope this can help.

Joe C

, although not sure about the 100K cam thing -- ??? without careful measurements, who really knows?

Fredbird

Yeah. Southlake. I'm right on the border of Southlake/TC. So very close.

Mileage - It's like asking a lady's age. Haha. 109,000 mi.
Previous owner was not very gentle.

Wanting to spend
This car is my hobby and so I am not wanting to spend incredible amounts, but I'm looking at sinking a few thousand into her.

billschroeder5842

With $2000 in mind, I'd do the exhaust. that will be 400 if you keep the stock muffler and cut the precats/catalysist, $600 if you cut the pre cats, catalysist and performance mufflers or 950ish if you do headers all the way back.

I'd spend a few bucks on a performance tune and double check your injectors. You could spend anywhere from 125 to 500 on this depending on what the guys (injectors?) find.

Save the rest as you will need it. Little nit noid things will pop up and you will go through it fast. Brakes, shocks, switches, ac will all com into play.

DGXR

If you are just looking for a strong running engine, there's no need to add performance parts. Just fix whatever is worn or broken. These motors are pretty strong from the factory and many owners are happy with them as-is. Maybe you will be too. Start with the compression and leak-down tests, and go from there. It might help to get a complete inspection by a competent mechanic -- maybe your wife's cousin can do this, or (even better) the two of you can inspect it together and you will get more intimately familiar with the Corvette.

Once you get it back to good health, drive it for a while and then decide if you want increased performance. As they say: "Speed costs money -- how fast do you want to spend?"

Whatever money you don't spend on performance parts, your 1991 will very likely provide other spending opportunities

GREGGPENN

109k still has some long life. Since you're competent, borrow a gauge from AutoZone and do a compression test. I suspect it's going to be fairly even.

As far as value (and since you might need springs/seals in the heads), you might consider a set of AFR180 Eliminators. For the price, it's not a bad upgrade. 195's are even better -- if you'd ever consider a stroker bottom-end.

The prior generation of AFRs is worth consideration (at the right price) too. Or...you could just replace seals/springs.

Replace the plenum/runner with large tubes and port to match. Another reasonable option is a FFI intake (First Fuel Injection) though you'd have to convert to a remote distributor setup. It would cost a couple hundred more but gain a TON of flow for a TPI. Or...a superram used. The exact intake kinda depends on deals out there and/or your exact goals for low/high powerband.

Set of Hedman's with exhaust from a local shop and see where you're at. If you get all/some stuff used, you can probably hit your $2k budget.

If/when you get into the bottom-end, you could/should consider a stroker kit and cam.

Purple92

I'd agree with Gregpenn & DGXR - start by doing a compression test / or a leakdown test. (While you have the plugs out I'd throw in a new set.) Once you figure out what the engine condition is - you'll know if a valve reface will be helpful - of if the you have more significant problems (if the compression reading comes up after putting a teaspoon of oil in the cylinder and rerunning the test - you probably have some ring sealing problems) or if the engine is mechanically "good".

Pulling the heads off is not that bad a job on a C4, but it will certainly take more than a day for a do-it-to-yourselfer.

As billschroeder5842 said - the L98's are torque makers, but they simply don't make lots of higher RPM power.

Bfenty

As billschroeder said, save a bit of money because you'll end up nickel and diming a bit on this car. There's not a lot that's truly expensive stuff on it but there's a lot of $30-$50 parts that are probably about to go bad on you, based on what you've said about the car. Injectors can get expensive too but I'd send your current ones to Jon at FIC to clean and refurbish if you're questioning them-it would most likely be under $200 and he does amazing work.

aklim

Let's start with what you HAVE to do. Make sure compression and leak down is good. My motor was having a lot of noise at 90k. Enough to make it hard to tune because of the knock retard from the sensor hearing noise. It was worn out. Check first.

GREGGPENN

The engine?

cv67

BlowerWorks

like !

aklim

Oh yes. Calms down the knock count by adding thick oil, and the leak down shows rings and heads

ChrisWhewell

Take your time and plan it, if you can afford to go into it, do both

aklim

Stroke and blow

GREGGPENN

Seemed obvious (to me) what you were saying, but your prior sentence could be interpreted multiple ways.