Ok, need help with high rpm power loss. I have a 245,000 mile 91 firebird. The engine finally died. I replaced the stock 350 engine with a recon rebuilt 350. Since performance parts are cheaper than stock, I bought these upgrades. Slp headers, catco dual converters, flowmaster 3" to dual 3" outlet catback exhaust, accel msd 6a ignition, hypertech chip, K&N filter, also purchased rebuilt trans from dealer. I have a new alternator, cap and rotor, accel 300+ 8.8mm wires, bosch platinum plugs, new smog pump, header wrap, new bosch O2 sensor, new temp sensors, fuel filter, new 3 core radiator, 160 thermostat for the chip, and I bought ads injectors, but have not installed them for fear they might make things worse, until i get that supercharger.

I have a gtech meter, and this is what i used to have before the new engine.
0-60 5.7sec
1/4mile 13.3sec
hp 270-300,(Depending on the 1-2 shift traction)
These were with the 8.8 wires, k&N and no muffler. ( the muffler broke off going over a rediclously high speed bump years ago. I've got trans pan holes before that way also.)
Now the specs are
0-60 7.8sec
1/4 17sec
200hp
I figure the performance mods should be at least a 50-70hp gain, not drop.

Then the car has been sitting for 2 years, I replaced the engine and trans and fluids, brakes and stuff. I broke the engine in for about 1000 miles, went slow never over 3,000rpm. All was good, then I started to drive it hard, noticed the car has solid low end power, but around 3,000 rpm the car has little power left. I took out chip and ignition, no change in performance. I tried replacing the est module in the distributor, no change. I've driven with the set timing connector disconnected, no change. (When I used to mess around, the car would do terrible with that connector unplugged. Now it doesn't seem to notice at all.) Timing is set at 6 degrees.
I've taken it to the dealer, there GM goodwrench service manager said in writing they would not work on my car because I had to many repairs.
I took it to local shop, the guy tried to tell me it was a truck engine, so I compared all casting numbers, it's not a truck engine. I took it back to him, he was pissed and did scan tests and pressure tests, and finally came up with the excuse it was the rev limiter, my car is supposed to have a rev limit at 4500 rpm, Knowing that the computer rev limit is about 6,200 I argued with him, got know where. No trouble codes are reported.

Power is fine to about 3,500rpm, In neutral I've noticed that it will go up to 5,000 rpm for a second and then bog down to 4,500 and stutter some at that rpm, like it really was a rev limit. Driving at 60, I can drop the car in second, the car is fine, but when I floor it, it slows down a lot to about 40, if I hold it all the way down. When I let off it, it picks up speed again.

I've also got a drop in mpg, I used to get 16city, 22hwy, now it's more like 14city 15 hwy.

I'm thinking fuel pump, pickup coil, injectors, fuel regulator. I don't really have money to replace anything else, I've put about $12,000 into this car, interior and drivetrain.

 

293,

What difference would it make if it were a truck engine? If the bore/stroke/rod lengths are the same, the ECM is from your car, not a truck. It will deliver fuel and curve spark accordingly. If the engine isn't a good match of parts, it should still run at higher RPM with light loads.

Have your checked the ignition system thoroughly? High RPM power loss is often ignition related. You could also have a fuel delivery problem, and the speed-density control scheme for your engine isn't helping. Still, you should be able to turn higher RPMs under no-load or light loading.

Incidentally, there is no rev-limiter in the stock programming on GM ECM/PROMs. The only limits are based on vehicle speed sensor inputs and only if the car was delivered with 15" tires. Fuel cut-off is either at 118 MPH of 254 MPH for "unlimited" cars.

Is the compression ratio on the engine at least 9.5:1? Are the head castings the same as your original? Are the valve sizes the same, or did you indeed get a truck engine with smaller valves/lower compression? Depending on the remanufacturer, you might have an older case and/or older heads that have smaller valves. You may have a completely mismatched engine. It might truly be a 350 CID, but the heads could be from a low-compression engine from the '70s with 76cc chambers. You might also have incorrect pistons for the head design. Worst of all, if you have no idea what the cam grind is like, you may be lucky to be getting 200 HP.

Many light trucks have camshafts with a high lift and extremely short duration to maximize vacuum and low-end torque for pulling loads. This would be great for anything up to about 3,500-4,000 RPM. Beyond that, the valves just don't allow enough air flow to support the engine at those speeds.

All that extra "bolt-on" intake and exhaust air flow isn't helping if you haven't engineered the components to fit within a complete system. If the cam doesn't support the package, you may never get the performance you want.

Your symptoms while driving make it sound as if you are very lean and/or have very weak spark that is getting blown out at higher RPMs, or you aren't moving air at higher RPMs.

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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0

 

I've replaced everything ignition wise, except the pickup coil and magnets. Thanks for getting back to me. I'm a bit drunk right now, so I hope this makes sense.

I've also noticed that my car will just stall out when the car is about 210 degrees. If I try to start it, it won't keep it self running at that temp. Not sure, so I'm sure the 2 symptoms are related. I have a good idea that it is the right type of engine, the cam grind is most likely an l98. The power curve feels familiar, and the head numbers don't match exactly, but the remanufacturer says it's 87-92. won't give me specs, but I'm sure it's something that supports the engine. I think the compression is not 9.75 like stock, but maybe 9.3 like older birds. Still that would not take 100hp away and 4,000+rpm. I think it must be something electric affected by heat. Right now I'm just going to save money and replace all the possible causes I can think of. Then I will have eliminated faulty parts from there, can't hurt unless i break something else(I'm on my 3rd starter and alternator, because of my stupidity). Fuel pumps are a bitch, with the crap I have to work with. I replaced one on my friends 89TA I'm thinking of ATI procharger d9b, 15-20 pounds of boost, I know they include a high pressure external pump, but if I replace the internal tank pump, Any suggestions? I also have no idea if the ADS $500 injectors I bought are going to negatively affect the stock normal intake. I know this is a hard to diagnose problem, but any help is appreciated, since 4 shops can't find the correct problem.