Well i went from being super excited, because i was finally going to find out the results of my heads and cam to extremely disappointed. I went to the dyno shop and my car only put down 318rwhp and 316.2 torque. I have AI heads and a 230/236. My friend just moments before put down 340 rwhp with just a 224/230. My friend ran datalogs on the car which he will try to post later today so maybe some of you guys could help me out. He also tuned it so the air fuel ratio was right on. I will post the Dyno sheets later too. The graph looks real smooth on the hp but it falls off at 5600-5700 which from what i've heard with this cam and heads it should pull to well pass six. The torque starts falling off big time at 5200. For a little back ground information when i first put the motor together i broke it in for 250 miles then took it to the track. It ran a 107mph with a friend in the car, and full tank of gas, babying the car shifting at 5500, with a 2.7 60' on street tires. I've taken it back recently with 1/2 of a tank gears riding by myself shifting at 6000 and the car only pulled about 105 mph. The track is notoriously bad but i think i lost some power or it might not of ever been there. I was hoping for about 110mph +. The car on the dyno would let out a little cloud of smoke at 5000rpms or so. I couldn't tell in the car what color it was, but it doesn't smoke all the time, or at idle so i don't think its white smoke (so it shouldn't be the motor). I've read up some and i saw that if you retard the timing by having the cam off a tooth your power band is moved down. Since my car falls on its face at 55-5700 that makes me think it could be the cam one tooth off. Me and a very experienced friend built the motor and both checked it but that doesn't mean it still couldn't be off. I hope to have the graph up and the datalogs up for you guys later but maybe with what i've said you guys can help me. Thanks Mike

 

Hmm... seems like your missing a cylinder, check all your wires & make sure the OPTI wasn't installed wrong, also what was your A/F? But that wouldn't do it.

Also, that cam doesn't pull past 6k k, around 6 she drops like a rock unless you got it on a 110 lsa with high lift (xer lobes) those ones seem to pull to 6500 or so.

Matt.

 

it could be down on a cylinder. There were a few car guys there and the all said "it didn't sound like it was down a cylinder." It doesn't vibrate or anything in 6th gear but it does have a little shake in the car around 2k if you just rev it up and hold it there. Also just FYI i never degreed the cam in. Its suppose to be a 230/236 on a 112 LSA. I was talking to one of my friends that has raced for years and he said probably almost %50 of his cams are off. So he is thinking we should degree it.

 

You can't degree LT1 cams, you can check to see if you're off but you can't keep it there, you'll have to get another cam if thats the case because the optispark will be off if you degree the cam, when LT1 guys was to advance/retard cam timing we have to get it ground into the cam.

What kind of lifters are you running? And what preload?

Matt.

 

who tuned your car you could be getting a lot of false knock mine was picking up 16 degrees and my cam fell on its face at 5900 also an 230/236 but i still dynoed 386rwhp. good luck

 

i am not getting any false knock. I was getting some on prior runs but we tuned it out. The car has a pcmforless tune on it that was tweaked by my friend. He managed to get an extra 15 rwhp out of his car on the dyno with the tune so he has an idea about what he's doing. Well i hope the cam was ground right from comp since i just can't move it one tooth if it was ground wrong. I'm running comp OEM replacement lifters because when i built the motor comp R's were impossible to find. We just adjusted them while the motor was running. We just backed them off until they clacked then tightened them until they quit and went a 1/4 turn after i think. It was a long time ago.

 

also my MAP was at 88 and i was told it should be 100 at WOT.

 

Sounds like a tuning issue v a mechanical issue.
I would reset the valves to 1/4 turn and get Bryan to look at the test sheets.Get him to retune if necessary.Make sure your whole CIA is in good shape to supply enough air.
How did you "tune out" the spark retard???If you didn't reburn the CPU to turn off the knock sensor that may be your problem.

 

Did you run a compression check? If so what was your results?

 

nope i haven't done a compression check yet. Its something on my list of things to check.

 

Check to make sure your throttle is opening 100%. I ran an Ultradyne 230/238 112 for a while, I called the chainsaw cam, in upper rpm's it would pull to the moon, definitely wouldn't fall off at 6000 rpm.

Do another WOT run, see if you pull more than 88 Kpa, It's too much air to be an intake restriction (ie. I doubt there's a shop towel clogging you airflow)

Keep in mind if something is very wrong with your exhaust it will lower manifold vacuum, why? Because the exhaust can't escape, so it slows the intake of fresh air. I'd slap it on the dyno again and try dropping part of the exhaust, if it makes the huge difference you know the cause.

Hope this helps,
-Christian

 

His problem is he has high manifold vacuum. I would look at the throttle body as others have suggested. Your car should be reading just about the same as your Barometric pressure when at WOT, if not then you have an intake restriction or the throttle body isn't opening all the way. What was your TPS voltage? Was it close to 5 volts like it's supposed to be?

-Dave C. '97 Z28

 

That hurts. Im guessing tuning at the most might get you 20hp. Did you replace all the goodies like lifters, headers, throttle body, injectors. Good luck.

 

I did not see it mentioned but do you have 30 lb injectors, 52 mm TB, 1 3/4 headers, etc?

stock TB, injectors and 1 5/8 headers will hurt the HP as well.

I agree, something is not right with the HP #'s you show and you probably need to fix/replace something and/or retune to get the #'s you are looking for.

I would re check teh valve adjustment as well. It is not un common for this to be off and the engin will NEVER run right until they are properly adjusted.

Good Luck

Lloyd Elliott
NightTrain66

 

Thanks Dave C, I meant high, was up too late typing ;^) You should see atmospheric pressure at WOT. I don't suppose you're at a really high elevation in Kansas are you? (joking, it was pretty flat last time I was out there, I'm sure there are mountains somewhere out there though.)

Find the source of the low MAP reading and you'll find your power.

Before you start throwing more mods at it, find out what's wrong. With those heads and cam a car with all stock externals would make more power, no question.

First check the intake plumbing and all vacuum hosing, make sure there aren't any shop towels stuck in there. How dirty is your air filter? Try pulling it and see if it's horribly clogged (can't imagine)

Make sure to adjust your valves properly, I do them one at a time, in order to 5/8 turns past zero lash. It's a bit slower than adjusting in batches, but I know it's done right.

If that doesn't get the airflow up try dropping the exhaust or pressure testing with copper tubing and a vacuum/ pressure guage to see if backpressure is > 1 psi.

Hope this helps, keep us posted with your progress.
-Christian