Been looking for lost horsepower for 3 years. I have upgraded and added a lot to the car but never touched anything under the valve covers. The car only ran a 14.5 1/4 mile when I bought it so I figure it was putting out around 220 HP. I added a supercharger, headers and other bolt ons. According to the website it should have added at least 40% increase in HP making it 308. I am in the mid to high 13's which is very low for my setup. I should be putting out close to 400 if I had a done the mods to a brand new lt1 so I am missing around 50 or so horsepower from a stock setup. I replaced and checked everything like the opti, icm, plugs, wires, map, maf and on and on. Fuel pressure is perfect all the way to redline. My question is what could be going on in the valve train to cause such a big drop in power but have no obivious signs? I have done a compression test and it all was within specs so is there a way to tell or something else to do at this point? Thanks in advance.

 

Why do you think it's the valves? Did you ever scan it to see what the fuel trims or advance (or lack there of), is doing? I might be inclined to change springs but other than that, it should not have a problem.

When your running down the strip, what is your tranny set to?

How many burn outs have been done on the original POS limited slip diff?

I could go on and on and on......

 

If your running only mid 13's with 6psi of boost then something is wrong.

Any chance that your exhaust is clogged up(cats or muffler) and the engine can't breath?

I do completely agree that something is wrong.

 

Im looking for something the previous owner did or happened to him when he owned it. With 111,000 miles I doubt the horsepower would drop just because of the mileage so something happened and I have checked and rechecked everything external. The long term fuel trims looks to be running lean but the fuel pressure is right where it should be. I am thinking something like springs, push rods, rockers or something else might be bad or worn out.

(speedygonzales) When your running down the strip, what is your tranny set to?
I have no idea what you mean. The car shifts and the tires spin when shifting from 1st to 2nd around 6200 rpm.

(speedygonzales) How many burn outs have been done on the original POS limited slip diff?
Not many by me. Maybe has 10-15 track runs with very little if any burn outs.

ACE1252
Any chance that your exhaust is clogged up(cats or muffler) and the engine can't breath?
I have 3" exhaust going to a cutout and the cat is hi flow and pretty new.

 

You say your ET is in the mid/high 13s... what is your trap speed?

 

trap speed is 102.

 

according to your sig, you have a super charger with a stock cam? that might be part of the problem right there - ever think about get a new cam for it?

 

I really don't think the cam would lose that much power. I have bolt ons, last time at the track I was trapping 104 without going into the motor at all.

 

Let's do some basic checks,

Are you getting WOT at the butterflies and TPS

Size of throttle body

Air filter/maf/blow off placement. This is important. Air filter type, oiled/not oiled. maf function, tps function

Was car tuned with MSD in mind

Knock sensor to tight, giving false signals

fuel pressure, at idle vs under boost, is there a boost reference FPR

Valve adjustment/ to tight, to loose. You said you haven't removed the valve covers does not mean the previous didn't.

Stretched timing chain, degree the cam.

Transmission slip.

Just a few thougts to keep you busy.

Later

 

The datalog is showing 100% throttle so I assume it is working correctly. I have the biggest K&N filter that I could find and my maf is a new GM one and the mass airflow gm/sec reaches 360 when going wot. No fpr had the car tuned for the boost and have tightened the valves using Shoebox running engine method. As far as transmission slip how would you check that? I just noticed that on 1/3 of the rpm's after 60 mph the rpm will drop a little and then go back up. An example will be 4000/4150/4125/4150/4250/4175 and so on. Does this indicate anything that can be traced to a part or what it might be doing?

 

If I remember correctly you should get about 750 rpm drop between shifts at wot. Also this can be checked on a dyno so you can see the drops between shifts. Not sure what a shoe box method is for the valves, always willing to learn new things. Is your maf on the inlet side of the supercharger? And where is blow off in relation to the maf? Or does vent outside? Also is the msd distributor have the timing adjustment? Valve lash on stock lifters and cam are 0+1.25 turns on the rocker nut according to the manual.

One of the best things I did was port match my heads and intake for a smoother air flow. I did have to remove the heads for this, but well worth it. Already did the cam and other bolt on and am at 332hp/335tq.

Later

 

You might want to check if the converter in your trans is causing power loss. I'm not at all clear on the details, but I do remember guys with aftermarket converters losing quite a bit of power with the "wrong" converter.

I believe yours is stock, but maybe there's loss in the converter anyway due to the 110K+ miles... ???