Well today a friend of mine had an open dyno day at his speed shop. I decided to take a ride over and see what my 88 IROC could do on the dyno. After all was said and done the HP was 188 @ 3900 and the torque was 288 @ 3250. I guess I expected a little more from the HP number, the torque number isn't all that bad considering I haven't done much to the motor and all the addons were done before I purchased the car. I'm not sure which direction to take right now. Maybe some more work to the motor to get the HP number up to 250 or maybe I'll call it good and carry on with the cosmetic work as planned. I just needed a vent and maybe some suggestions. Thanks gang.

 

ummm...you didn't say anything about your combo...what size engine is it and what has been done?

 

it's a 5.7 TPI. As for what has been done I couldn't tell you. All I've done is a tune up and replaced the rear end and suspension. I just figured that the numbers would've been a little better considering that the car hauls @ss. I know the throttle body is stock as are the runners and it's got 24 pound injectors. The cam has been changed from stock to what I don't know. Other than that I've just driven the car for the past 3 summers.

 

i bet you if you put the stock injectors back in and wide-band tuned that bad boy for the cam that's in it that it'd run alot better...normally tpi system will run outta air before they run into lean conditions. also, does it have headers/full exhaust on it? you can't start putting more air in till you can get the stuff you have in the motor out.

 

Yeah it's got headers and a full exhaust. 3" from the collectors back. I'm gonna scan the dyno printout sometime today and post it.

 

Here is the printout.

 

something is wrong...that curve is as flat as a table...

 

Beats me.... I just drive the darn thing

 

I dyno'd mine this spring, made very similar numbers with a flat HP "curve". '89 Formula 350, TPI, stock internals with 125,000 miles. Ported plenum, custom tune, hooker 2055's, MagnaFow direct fit cat, Borla exhaust. My engine is tired, rings are no longer sealing well. Still pull 2.0x 60's, but only 14.7 1/4's in Houston.

Won't let me upload the dyno scan again, already posted here.

https://www.thirdgen.org/forums/sout...day-5-a-3.html

 

This forum is for Power Adders. Not to be confused with "Adding Power." Which is in the end, what were all trying to do. Here is a list of what could possibly be wrong, you need to check all these things to confirm they are in order. A badass engine thats not well tuned will be a dog.

How your car fell flat on its face, I would suspect valvesprings are shot. I went a year trying to diagnose a performance problem with my L98 only to find the springs were shot. I could literally compress them in my hand. I switched out to Comp Cam 981 springs and LT4 Retainers. Less than $100 for both things and it picked up ALOT of power. I would almost change that without looking at the rest. It just screams that to me.

If that doesnt fix it.....

You need to find out what cam you have. What could possibly be happening is that the cam needs some RPM's to start creating power and the TPI manifold cannot deliver that amount of air the cam needs at high RPM's to develop the power.

I would also try doing a compression check. The engine could just be tired.

Check timing. With the (cant remember the name, someone please fill in the blank) unplugged you should have 6* stock. I bumped mine to 8* with good results. I can run it on 89 octane just fine.

Fuel pressure, stock is something like 43.5psi. Thats where mine is set. Seemed to be the best comprimise between economy and performance. From looking at your A/F, it looks to be right on, if anything a tad lean. But its not going to short you 40hp. Maybe 5 at most.

 

Uh, what does this have to do with a Nitrous, Turbo, or Supercharger?

 

Yeah I really should get the car tuned and look at the compression and springs. I just haven't had the time to get dirty and dig into the motor a little. The flat curve really threw me off, it just looked so blah like the car was tired but it doesn't burn any oil, it runs very strong, and it takes off like a bat out of hell whenever I mash the gas. Before I saw someone else with the same problem I thought that the dyno gave me a false reading.

 

Not a thing, should be in the Tech / General Engine forum.

Mods, make a move?

 

Valve springs are worn out and floating the valves at over 3500 rpms.

 

Well from the looks of your printout, your motor somehow isnt moving enough air. look how your hp curve is so flat across all the rpms. that means the motor reaches its full potential early on and cannot surpass this even with more rpm. even with a bone stock motor i would expect more of a sloped powerband. check your valvetrain as others have said, i suspect the culprit lies either there, or maybe we have a ECM/Injection problem on our hands?

 

Thanks gang. Really helped a lot. I'll be looking at the valvetrain asap and taking care of the problem. As for the ECM, I'll be having a new prom burned for my new throttle body and a few other minor changes I'll be making when the car is tuned properly. Again thank you.

 

Yea, something is wrong… judging from the fact that your a/f stays reasonable, I’m guessing that you’ve got a restriction preventing you from getting more then that 18xHP worth of air in there. Valve spring float should be fairly obvious, the car would run like crap past that rpm and power would actually drop, rather then stay flat. Timing should do something similar also.

 

Actually, its sorta not obvious. Mine pulled hard and slowly stopped pulling all the way to redline.

 

i thinkn it was HOT ROD magazine was doing a build up on a TPI firebird and had a really flat dyno sheet ended up being a bad tourque converter that wasnt locking up or something like that just a couple months ago ik think

 

Well gang here's the latest and greatest. I did a full tuneup on the car. Changed the valve springs and checked things over. The car is running much better anyways. I'm not going to be able to get back to the shop for another month or so since I'll be on vacation but as soon as I get back I'm putting her back on the dyno for another pull and I'll adjust things from there. Thanks to everyone that had input, it all helped a lot.

 

Take one of your old valve springs to a machine shop and ask them to test it for you.

 

Also mabye check your ignition system. RPM related problems often lie there.