Its a stock L98 with a 94 Vette LT1 cam. Engine was rebuilt about 30K ago. Installed the LT1 cam about 3 months ago while I cleaned, painted and installed all new gaskets. She is up and running great while in park. When driving, it just doesn't have the power it should and is running rich. Do I need my stock 350 prom reprogrammed? Timing is set at stock specs. The only thing thats not stock is the LT1 cam only. All the drivetrain is from a stock 91 Formula hardtop A/T 350. The TPI is speed density with an AUJP memcal. Thx.

I should add that its the most noticeable when you get your foot into. A stock 305 TPI car would have my lunch.


She has been drivable for the last 3 days. TV cable was adjusted today and its at 15, 25, 37-38 shift points at normal acceleration. To the floor kick down is slow also, it wines up.

Ideally I think you would want a better chip tune for the cam since you have speed density.They can be a lil picky about cam selection I noticed.Also trying giving it a lil more timing.Seems like the car is sluggish by your description.How is the throttle response if you blip it?She should rather crisp,smooth and no backfire or stumbling or hunting while idling

Id play with timing first..if not then look into having the chip tuned a lil more aggressive for the cam.Shouldnt need much at all.

I did another search and found a member here in Georgia that has a 91 GTA 350 with a LT1 cam. We talked on the phone and it sounds like I could be 1 tooth out on the distributor. Much easier to explain everything its doing and what work I've done to it, on the phone.

Throttle response is pretty good in park, even if you blip it. Response is not very good when driving it.

I'm going to adjust the timing and see if it makes a difference, if it does then I know its the dizzy is out a tooth.

He said that being just 1 tooth off, the car will run just like mine is. The ECM/Memcal can adjust and make it run OK if your 1 tooth off. Big loss of power though.

It is running rich and exhaust manifolds are getting too hot also. I could have cracked a manifold also running hot like it was. We will find out. I've only put 5 miles on it so far.

Yea sounds like it was a timing problem.When you do lock the timing in and it hits that sweet spot..man you will know it lol.The motor will purr and then plant you back when you stomp it.Hope it works out to be a simple fix for you

Exactly, its not throwing me back in the seat like I remember a great running 350 TPI did.

It purrs pretty nice in idle, its just when driving that most of the issues show up. A friend and I were very disappointed when we drove it and surprised. All that work and its not got much AS_ to it.

The guy I talked to really knew his shi_ and he is damn near 100% sure its the timing and he had the same problem before.

Well with the lt1 cam you might not make just as much torque off the line but midrange and upper rpm pull should be noticeable increase.I dont think it would be a huge hp increase ..more of a driver feel.A bit more a ecm tune wouldnt hurt either but id dial in your timing first and foremost.

I'm sending it out to have the fans lowered to 170. I'm looking into if its worth tuning the ECM. I believe you could get more out of a totally stock engine with a good ECM tune and mine with the LT1 cam. Right now I'm limited because of emissions. I can't get a title transfer and tags without a passing emissions test. I'm in the process of moving and where I'm moving to has no emissions.

Today I checked the timing and it was at 6 BTC so I bumped it up to 10 BTC and it runs A LOT better. It did put me back into my seat but I think it would run even better at 12 BTC.

I believe I'm 1 tooth off on the dizzy and I'm going to pull the Dizzy and get it right so I'm back in the correct 6-8 BTC.

I thought I did something wrong in the engine or somthing went bad inside. I'm sure glad it was just a timing issue.

Awesome.Glad to hear its a rather simple fix and she is starting to perform as expected.Also after you get the motor timed right..you might need to readjust the tps or iac and lower the idle back down a lil.Adding timing might make the rpm increase as she runs better.

I installed a new IAC last week and the TPS is new also. I adjusted both of them. I did plan on doing the IAC test again to make sure its set right. Rpms were slightly different but maybe 75 higher at most.


I did the remove and replace adjustments but didn't do the unplug the IAC and set and adjust timing with the idle screw on the T/B. I'm thinking of doing that but I can't find anything about doing the IAC adjustments when its cold or hot.

What is the correct order to adjust everything?

1. Base timing
2. IAC timing(hot or cold?)
3. TPS

buddy,

if you still run the combination, go with 14 degree timing, my stock 1990 GTA runs really fast with no problem at all.

I heard someone out there that tpis like more degree timing, and the 6 degree no not giving the real TPIs power.

I am in process of doing the same with my 1991 tpi vette.

I will let you know how the performance.

Thanks

That is too much advance for a cast-iron head TPI engine. You will be lucky if you don't cause enough detonation to kill your Vette engine running that much timing.

I would not advise giving your Vette (or any L98) that much initial timing advance. A '91 Vette has aluminum heads, which will take a lot more timing advance before detonation occurs, but the factory tune has already taken that into account and they run more advance in the tables (a lot more). On premium fuel, you might get away with that much advance, but I'd be willing to bet you've got some knock counts showing up pretty regularly at WOT with that much timing advance. You very well could cause some damage if you try to ramp the timing up that far. I would not go beyond 10 degrees BTDC (better use premium fuel even for that), until you have a chance to datalog the car and check for knock counts.

I seriously doubt that your distributor is one tooth off. That's an old wives tail from back in the day when the vacuum advance prevented the distributor from being turned very far to advance or retard timing. If you got the distributor off by a tooth, you didn't have enough room to turn it and adjust for the error. The window of adjustment on some of those things is pretty small. Our cars don't use a vacuum advance, so you basically could have the distributor as far off as you wanted to as long as you turned it far enough to get it back in spec. We're really only limited by where the spark plug wires will reach to. If you're timing light shows 6 degrees before top dead center, then that means the spark is firing 6 degrees before top dead center, regardless of how far you had to turn the dizzy to get there. Don't waste your time pulling that distributor back out and trying again, it won't help.

With a speed density car, I'd say you're going to need to get that chip tuned. They're a lot more sensitive to airflow modifications than MAF cars are, because they have no direct way to measure the amount of air coming in. If you plan on doing any modifications to the car in the future, you might as well get into chip burning now. It's easy and it'll save you a lot of money down the road, not to mention really help you get the most out of your mods. Also remember that by advancing the distributor to 10 degrees BTDC, you are effectively tricking the computer into advancing timing 4 degrees across the entire curve. Not nearly as effective as going into the table and raising timing however much it needs to be raised at the individual cell. You also have no idea where the engine will start pinging, because the knock sensor pulls timing and keeps it from being audible. You can get into bad trouble quick on a deal like that.

Sorry for the long post, just trying to save you some headache.

-cal30sniper

If you want an in-depth look of about what you can get away with in an Iron-headed L98 on premium fuel, look at this thread:

http://www.thirdgen.org/techboard/di...rk-please.html (Check My Work Please)

I spent a good deal of time in the fall working out a factory spark advance table that went as far as it could without any knock counts. Gained a nice gas mileage increase and a lot of throttle response/mid-range torque. Picked up about 45hp on the big end too.

-cal30sniper