sach712003

My mods are in my sig here are my numbers
260 rwhp at 5000 rpm
290 rwtq at 4500 rpm

I think that something is killing my horsepower in the upper rpms because my horsepower should not peak so low. With the gm hot cam I should make power to about 6000 rpm. Any suggestions you guys have would be great. I think that I need long tube headers and 4 inch pipe. My air fuel ratio was right on so that was not the problem. It just think that there should be about 50 more hp in the motor somewhere.

AlkyIROC

Cam specs? Any head work? Compression ratio, fuel octane?

It could be any number of things. Even a plugged fuel filter or a weak pump can decrease HP.

TTA 1387

Definitely low for a HOT cam. I dynoed 324/324 at the wheels in my 96 WS6 with a HOT cam.

What heads? rockers? springs? how adjusted? cam degreed? what timing? Could be any number of things as stated above.

You don't need long tubes or a 4" exhaust with that cam. I ran stock manifolds and then dual cat headers and an SLP cat back. Its a pretty tame cam.

sach712003

It has about 9.5 to 1 compression. The heads are stock vortec heads. The timing is set at 18 degrees initial with 34 total. It is not being starved for fuel because the air fuel ratio is right on through out the rpm range. If it was being starved for fuel it would have leaned out and it did not. The cam was not degreed when I put it in so it could be that but I hope not.

AlkyIROC

Air/fuel has nothing to do with the amount of fuel the engine is getting. The carb is just metering it properly. Not enough fuel to the carb can have the effect of a lack of power. It's not just pressure but volume required to keep the float bowls filled.

I'm not up on SBC parts. What's the lift on a "hot cam"? I'm assuming you're using 1.5 rockers. What's the valves in the stock Vortec heads set up for? Typical stock SBC valve train don't like going above .500 lift.

TTA 1387

218/228 .525/.525 on a 112 assuming 1.6 rockers. I think is .494/.494 with 1.5. That's going from memory but I'm pretty sure that's it.

How did you set the rockers? Too tight and it won't make any power. Compression is a little low but shouldn't affect that much power.

What trans do you have? If auto, stall? Stalls skew the numbers a lot.

Does it really feel weak or are you just going by low dyno numbers? What does it run at the track? That would really give you "actual" numbers compared to "dyno" numbers.

sach712003

My transmission is the stock 700r4 and the converter is stock also. I am running 1.6 ratio gold roller rockers. I set them by starting the motor and with the engine running I adjusted each one until it stopped clicking then I went another 3/4 turn. As for the fuel pump its stock with a regulator for the carb. One end of the reg goes to the carb and the other to the return line. But if the carb wasnt getting enough fuel my car would run lean in the upper rpms and that was not the case so I dont think it is that. However I could be wrong. Other then the numbers it runs real good. I pull 14 inches of vaccuum at about 850 rpms. Throttle response is good and I did a compression test and got 180 psi. The only other thing that I can think of is that there is a crimp in the exhaust pipe right behind the cat. The exhaust is edelbrock TES to 3 inch all the way back, except for the crimp where it looks like something hit it.

daverr

iTrader: (1)

i had the same problem with my engines.My engine wouldnt rev past 5500 rpms.I went the dyno, A/F was fine.I put in a bigger fuel pump, it didnt fix it.So i went after the ignition ,i installed MSd ignition system(coil,module,wires,distributor).and that fixed my problem.now my engines revs easy to 7000(my rev limiter).
i also have a bigger cam than yours so it can also be your cam thats limiting your rpm range.

TTA 1387

I think your rockers are too tight. I would take up the lash and go 1/4 turn. It would produce a slight tick but nothing more than an injector noise. Maybe try that and see if it wakes it up in the upper rpm.

sach712003

I dont think its the ignition because I have an msd box a petronix coil and msd wires and cap. Could it be that the coil is petronix and the box is msd ignition. I checked the wiring to the coil and it was correct. I just dont understand why my peak torque is coming in at such a high rpm. It might just be that its choking in the upper rpms because of the crimp in the exhaust pipe behind the cat, its 3 inch pipe but probably lost at least 25% of its area. Do you think that could be my problem?

Ray87Z

Was it a Mustang Dyno? If so that could account for some of the lower numbers. However even if the numbers are low due to the dyno itself you still shouldn't be dropping power over 5000 rpm.

What was your A/F ratio, you say it's ok but perhaps you're misunderstanding it...

What valve springs do you have, the proper clearancing was done on the Vortecs to support the .525 lift of the Hotcam right? Could be floating the valves or other valvetrain problems that is killing the power over 5000rpm. I'm really leaning toward that...

Oh yeah, what brand/type of headers and which Edelbrock intake? If you're running the standard Performer you're leaving 15-20 hp on the table, try stepping up to the RPM...

Conv389drv

Good catch there. If those heads are stock untouched Vortecs, it is very likely to have some valvetrain problems with that much lift. The retainer could be contacting the top of the valve guide; I've read that stock vortecs can only take about .480 lift max.

When you go to readjust the valves, pull the pushrods one by one and roll them across a flat surface (thick plate of glass or good flat table). It'll show you pretty quick if any are bent.

Also, if you could post the graph of the dyno run, that could be useful. If the power falls off smoothly or stays flat, then it's likely a restriction. If it plummets, then it could be valve float.

GASGZLR

What elevation are you at? My car only dynoed at 330 to the wheels, but when I got dynoed at 7800 feet density altitude, it only pulled like 270 hp and 300-some foot punds of torque, but at 5800 rpm, and torque was flat across the board.

sach712003

The dyno that it was used was a mustang dyno and my horsepower does not drastically fall its more gradual. As for the heads they have been modified by scoggin-dickey for the LT4 springs, which are rated for lift up to .525. I know this is pushing since the cam has that exact lift but I would think that if valve float was my problem horsepower would have fallen dramatecilay and it didnt. From my peak horespower at 5000 rpm (258 hp) it only fell to 246 at 5500 rpm. I wouold think that if it was valvefloat it would have fallen more steeply.

I am thinking I might try a mechanical fuel pump since my car was origional a TBI and I am still useing the stock one. Also I dont know how I could be reading my a/f ratio wrong because I have a sheet which lists it at 40 rpm increments from 3000 grand to 5500 and it never got above 12.9


__________________
1989 Firebird rebuilt 350 bored .040 over vortec heads LT4 Hot cam headers exhaust Edelbrock manifold Holley 650 DP Roller Rockers 3.42 posi rearend girdle pulleys MSD 6A
solid bushings in the rear control arms and poly in the torque arm and track bar

sach712003

I am running a performer rpm intake edelbrock tes headers to a 3 inch catback. I am not sure of the elevation but I live in Omaha NE