Well, I just dyno'd my car today and was very disappointed, to say the least.
First run: 250hp/295 tq
Second run: 237hp/292 tq
Third run:230hp/286 tq

The only thing more disturbing than the actual result was the fact that I lost power on each run. I thought I would hit at least 280-300hp at the wheels, but fell waaaaaaaaaay short. Even the dyno tech was concerned at the loss of power for each consecutive run. By the third run, it was a struggle to get it to 5500. The only thing that I could think of that could cause this is a valvetrain problem. I have been experiencing quite a bit valvetrain noise and am thinking that my anti-pump up lifters are bleeding down too fast under load, reducing the valve lift. Is this possible? The noise gets worse when the engine warms up and oil begins to thin out.
With the combination of parts that I am now running, this thing should have pulled much stronger than it did.

355 ci
TRW forged flat top pistons
67cc S/R torquer heads(170cc intake runners)
Compression should be around 9:2.1- 9:5.1
Hooker 1-5/8 headers
Edelbrock Torquer II intake
Holley 650 DP
Cam: .480" lift/292 adv duration/230 @.05"

Now I must admit that I threw this engine together years ago when I was young and dumb. The Anti pump up lifters, though usually set with zero lash, have always been set at 1/4-1/2 turn of preload. In addition, I intalled these lifters on a new cam after having been run a short time on a milder cam(Remember, I was young then :bb )
Is it possible for a cam to go flat without the usual symptoms of poping and running rough?
What are your thoughts on all of this?

Tom

 

It sure sounds like you have a lifter/valve train problem. A new cam, springs and lifters sound like they are in order. The fall off in performance sure sounds like a tired valve train to me.
But there are probably other things that could cause a drop in performance as the car heats up. Are you sure that you were getting enough fuel to the engine? What was your Air/Fuel numbers like?

 

The heads are 1 year old and came with brand new springs, so they should be fine. I didn't bother with the A/F readings as I was only interested in the raw Hp/Tq fugures. The spark plugs show the proper color and there has never been any problems with detonation. I did discuss the fuel situation with the tech and he was fairly sure that was not an issue since it would rev up, but just not quickly. It just seems hard to believe that it could run so weak while running smoothly.
I must admit that it feels like it has much more torque at low speed than I thought it would, given the combination of parts that I have.

 

how hot did it run toward the end?

 

The first run was just under the 180 mark. The second run got a bit warmer at around 200. We let it cool for a few minutes before the third run which was about 190. Not at all hot enough to explain the drastic loss of power.

 

Dump some 20W50 oil in there and try again. If it is bleed down due to viscosity loss, that should solve it.

 

what fuel pump?
ignition system?

 

IMHO dyno runs are over rated. I prefer the 1/4mi et/trap speed evaluation. Its a true measurement of car,driver, in a real world situation. Who gives a crap what the dyno says. Run that beast and have fun.

 

Stock GM fuel pump. In my experience, a fuel starvation problem would cause symptoms similar to valve float. This is not something that seemed to be happening, but at this point I'm begining to wonder myself. I would be interested in hearing others experiences with fuel starvation. What symptoms have others had when using a fuel pump that does flow enough?

The ignition is a Mallory Unilite with MSD Blaster coil. This thing works well and I have never had any problems with misfiring. I run one of these in my streetrod with a different coil and it is perfect past 7800rpm.

 

Your gonna loose power as it heats up, I don't think 20HP is quite withing the range of what can be expected though. It seems every time I've ever starved for fuel it would sputter and and want to backfire. Seems to me there should be some more tangible symtoms of fuel starvation. As to your dyno runs, If you add in the corrections for parasitic losses, it seems that you should be right around 300HP gross. Not too bad for a motor that appears to be pretty mild. SR torquers are ok but they're not much better than the factory fuellys from what I've heard. I had a set on my camaro and it wasn't any quicker than my vette with the stock 084's. I'm no expert, and god knows I've made my mistakes on cam and intake choices but it also looks like the cam/intake combo you have would be better suited for higher RPM applications. How high did you take the RPMs on the dyno? Something is definately wrong if it wont rev past 5500. The motor I had was almost a clone to yours exept I went with a 280 duration instead of a 292. It would rev to 6500 with no problem, and that was with a stock GM HEI and a big dual plane intake. I've flat lobed cams too and you should readily be able to tell when this is going on because it will shudder like it's missing and the valve train will be noisy. If this were an emissions car I'd say look for a clogged cat. Do a compression test and a leakdown to make sure everything is sealing right. Take off the valve covers and watch it run. Look for equal valve action. Drop in an HEI for comparison purposes. Try to eliminate each section (fuel, spark, mechanical) one piece at a time. Do you have a spare carb you could try? maybe the one you have is jetted all wrong. Hope this helps, let us know how it turns out.

 

I agree. This cam/intake combo should pull to 6000-6500 easily. While it will pull to 5500(even higher in lower gears), it seems to take forever to get from 4500 to 5500 in any gear past second. Although these heads are by no means comparable to some of the good aluminum heads on the market, they were designed to be better flowing than the heads used in early Z-28 and Vette LT-1's. Both of those engines ran to 6500 easily. One of the stronger qualities of these heads is the use of the 170cc runners(old fuelies were 160cc). This is supposed to keep low end torque strong(and it does feel strong down low), while still flowing more than enough to run past 6500. I may be wrong, but I would think these heads are capable of making 400hp gross, but probably not much more. Is this possible or am I expecting too much from these heads.

 

That's my fear of putting my car on a dyno, after really seeing what I have, it could cost me thousands for the number I'd really like to see :crazy: !

Hope you get your motor figured out easily .

 

You might be able to get 400 out of em, but 170cc runners may be a little small. Would be really good for torque. I had a 355 in my camaro, with the same head, pocket ported, I had a E-Performer, 600 carter AFB, headers, comp cams 280H. The only difference is that I had stock dished pistons which probably only gave me 8.5 to one. This motor was a real pig on the bottom end but would pull hard past 3500. I cant tell ya what you problem is though. Those heads should be good for at least 370 (LT-1).

 

either the cam is wiping or the fuel pump is too small.
Put a T and hook to a fuel pump gauge and tape it to the windshield. it will drop to zero by 5500 rpm if it is too small.(WOT)

my 72 had both, but not at the same time.

ran as you described both times.

 

When you strapped this thing down did you have a lot of halfshaft angle?

 

No. It sat pretty much like it always does under normal conditions. I am curious as to why you asked. Have you seen this type of thing create problems?

 

Those don't sound like bad numbers for that set up. I think if most of the guy's went out and dyno'ed they would see the were they are number wise. Then start the tuning process. You should be able to work 300 out of the set up with the right fuel mix. If the car dies out on the top end it's normally fat in mix. Two much secondaries. Did it scream going to 5000 or just bowww?

 

I guess I should have kicked out the extra $$$ needed to get the A/F ratio numbers. Then I would know for sure what I'm dealing with. They wanted an extra $35 to stuff the thing in the tailpipe, but it didn't seem worth it at the time. With only a 650DP running 76 jets in the secondaries and 68 in the primaries, I doubt that I'm running too rich, but at this point anything is possible. If anything, I was wondering if I should step up to a 700cfm.
On the dyno runs, it pulled steady, but slowly as if it was really working to get the RPMs up. There was no bogging of anykind.
The only bright side was the fact that it did make more RWHP than the car running a ZZ3 rated at 345hp, but even that one seemed to rev faster than mine. :confused:

 

I wish I knew. That motor should make alot of noise on the dyno. Gameshow Bob has about the same set up and he dyno'ed the same. He may of had alittle more torque. Good luck tuning. :cheers:

 

tsw71;

I think you'd find it very interesting to pull off a couple of valvesprings and take them to your nearest machine shop and have them checked out. If your cam and lifters are OK, that is.