First of all I'll write down the specs. It's a 1991 Trans Am with an L98. Short block is stock, 083 unported heads, 1 1/2 Hooker Long tubes, No cats, 3" exhaust with a Flowmaster 80 series, March pulleys, 24# injectors, AFPR, SuperRam intake with 52mm TB, compucam 2032 (214/220 270/276 .482/.496 with 1.6:1), 1.6:1 RR, Hypertech chip, NGK UR4 GP spark plugs.

Best run yielded 278.6 rwhp / 284 rwtq. Now the thing is that after 3500RPM the timing would go down to 30 degrees. I retarded the timing back to 6 initial degrees and the timing went down about 8 degrees again to around 25. Temperature was at 95 degrees and humidity at 50%.

I thought I might have some knocking since I have 215 psi of cranking pressure but at 6 degrees and 180 engine temp it seems unlikely. I used cheap a$$ 91 octane fuel but I'm still not sure if the sensor is reading false knock or if it's really knocking.

Oh, another thing... A/F ratio was at 11.7 which is very rich but when I brought the fuel pressure down to stock it leaned a little to 12.1 but lost 10rwhp in the process.

Anyone with this sort of problems? Or anyone with 215psi of cranking pressure or similar that might experience the same problem?

Thanks

 

What fuel pump do you have on it? Maybe the volume is not there for it. That could explain the leaning out but losing power.

 

Well, fuel pressure never dropped beyond the set point so I don't think that's the problem there.

 

I would suppect knock, as you leaned out the engine it knocked and pulled more timing and lost more power. To really very this you need to scan the car at WOT and see if it is pulling timing due to knock. The 11.7 AFR is rich and leaning it out to 12.5 should make more power if there is no knock.

 

yea like bjankuski said, there is probably something not right with the timing which is why it got worse when you leaned it out.
Also how old is your balancer. Its not uncommon for the outer ring to spin and throw off all the timing marks.

 

I agree with the leaning causing more knock. That's why I have to figure out what's causing it. I'll double check the balancer. Although I know for sure it's retarding because I can feel it as the engine "slows" down until redline. Timing was taken at WOT during the dyno pass. I am suspecting too hot spark plugs too. Will go down to something like a heat range 5 or maybe 6 (NGK heat range numbers) to see if I am having problems at higher rpms due to that. Figured that UR4 are too hot for the application. Any thoughts on this?

 

Will go to the dyno again on Friday. Got one step colder plugs, adjusted valves to minimize faux knock due to loose valves noise, will use good quality fuel plus timing and fuel pressure will be set to stock settings. Will see how it behaves and.set timing and fuel pressure accordingly. I'll post the results.

 

Ok so I did the tweaks I mentioned above and still got timing retard. I set the timing at 30 degrees of total advance so that no real know could happen and still got 8 to 10 degrees of.timing retard. Best numbers came in at 279rwhp and 307rwtq. Not bad for the mods i have.but still not getting the full advance and still at 11.7 af ratio

 

1" 1/2 longtube headers??? You should have bigger on it..

 

I know. That's why I think the numbers aren't bad, considering the mods. still having issues though. Next time I'll bypass the knock sensor and see how it behaves. Hopefully there will be no knock present

 

That's what I was going to suggest- bypass the KS (temporarily) and see if it's the cause of the problem or if it continues to happen.

When you get up over 200 PSI cranking compression things start to get dicey with pump gas and cast iron heads. I'm guessing this motor has flattops + stock (~64cc) heads which would put you around 10:1 with a small cam and that's the reason for the high cranking number.

 

Just noticed this.. Put your stock chip back in over this thing..

 

I thought about testing with the chip removed but didnt do it in the end. Now that you suggest it too i might then give it a try. Ill visit the dyno again with a switchable bypass for the ks and the pcm ready to test it with no chip. Thanks for the input guys. Btw, do u guys think the hp/tq numbers are ok?

 

Not NO chip, the STOCK chip. Some aftermarket "off the shelf" chips have junk programming in them.

 

With those mods you need a custom chip.

 

When i go to dyno I have club with his laptop doing a custom tune.
First I went I used 87 octane and with a 10.6:1 compression ratio and the timing set at 13* BTDC (didn't find that out until later) he wasn't able to tune because of it knocking. Also the knock sensor wasn't working correctly.
Anyway I got 326RWHP 360RWTQ.

Fixed all that went back with 91 octane fuel. I ran 352RWHP and 373RWTQ.

 

Thanks for the correction Damon. I mean factory chip.

PCM4LESS is on the to-do list. I've heard they do a decent job.

 

One other thing, did you degree the cam? I wouldn't think you should have that much with that cam.. I'm wondering if the cam is advanced a bit to much.

On the subject of tuning, find a local dyno and have a local person tune it. A mail order is just a guessing game. Don't waste your money on them.

 

Is it possible to tune it in real time with OBD1? About the cam timing well, my friend and I thought about that too but still have to buy a degree wheel to see if it's too advanced. We were thinking about just going back 4 degrees and see how it behaves but we agreed we should check the current installation first.

 

Yes it is, but people have tuned these without "real time" tuning for a long time. It's nice to have that option tho. If your having someone else tune it, you don't need to worry how they do it, just make sure they do a good job.

 

Still haven't been able to dyno again but bought a set of 1 5/8 long tubes, so that should free up 5-10hp perhaps?

 

I have had a Moates Autoprom for years now. By far the easiest way to tune an OBDI GM vehicle that uses flash chips. Just plug in the ribbon cable, hook up to the ALDL port, plug it into the serial port of your laptop and fire up TunerProRT. Load up a good ECM definition file and ADS file for the datastream and you can make ANY realtime change to your hearts content. Pop a flash chip into the unit when you are finished and burn it right on the spot. I love tuning the 89-92 TPI and 93-96 TBI engines with it as they have the 8192 baud data stream. The 160 streams are a tad slow for tuning although my initial tuning with the 7747 and 299 TBI ECMs were using TunerPro and WinALDL.