Sorry this is so long and choppy. I’ve copied and pasted it from two replies in the fuel and ignition forum.

I have been killing myself over this problem all summer and I finally got to a Dyno to prove what I was thinking. I am not making enough power up top and my mph across the finish line is a lot less than expected.

The dyno graphs and tables are posted on the following site. I haven't been able to figure out how to post them in this box yet. http://www.cardomain.com/ride/2408556/7 The dyno log I posted shows the peak TQs and peak HPs and their respsective AFRs. It also lists the degrees of timing advance. These advance values are what was programmed into the PCM. Datamaster logs however report them as being 4 degrees higher than what is programmed in (ex: 33 deg programmed reads 37 degrees in the logs).


I have a 3600 lb 1994 Camaro with an all-forged 355 with professionally ported heads and matched cam combo that should see 400+ RWHP and pull hard to 6800 rpm. It is a proven combo with many dyno sheets posted out there to prove it. The cam was degreed in by a respected engine assembler and it is on the correct centerline. I DO NOT think the heads/cam are the problem.

But I have a problem with my set-up. The launch seems fine. With 8” 4200 stall converter and TH-350 it yanks the tires 6" off the ground and carries them 5-6', but the 60' times are only a best of 1.69 seconds. Those times are indicative of 340 RWHP (I'm told).

I have a problem with the top end over 5000. On a typical 12.10 pass @ 111 mph, I'm in 3rd gear for 3.1 seconds and revving from 5500 to 5900 rpm (a really long time). Best of 11.87 @ 111, but times have dropped off over the last 10 runs to 12.20s, in better air. (oh by the way, it did this with 2 different trannys and two different TCs).

The car runs mechanically fine, no smoke, no detonation, no misses, just very lazy up top. Fuel pressure is fine (43 psi), injector duty cycle is 68% on 42# lucas injectors.

Everything ignition related has been changed (PCM, MSD billet opti, wires, plugs, MSD Digital 6, MSD coil). It is weak on stock ignition and on Digital 6 ignition.

On the dyno last week, I made 7 runs with timing between 28 & 37 degrees advanced and air fuel ratio between 12.2 and 14.0. The last MAF run (run #7) the AFR started at 12.6:1 @3200 and became slightly richer during the run to finish at 12.2:1 @ 6300.

All the runs were within 6 ft-lbs of torque and 13 hp of each other, which the Dyno operator could not believe and felt should not happen with that much timing and fuel variance. Max of 290 tq @ 5100 and 315 RWHP @6300.

Nothing we did to the timing or fuel changed the output more than 2-3%.
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I then made a run with a 100 shot of N20 because several of the mechanics present thought that maybe the torque converter was limiting the amount of power to the tranny due to all the runs being within 2-3% of each other. It increased 73 hp and 63 ft-lbs, so that was ruled out.
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I then made 7 runs in speed density mode with the filter/CAI/MAF/elbow removed because I thought the MAF might have been a restriction. I only gained 9 ft-lbs and 13 hp.

The last speed density run (run #13) started at 13.0:1 AFR @ 3200 rpm and finished at 12.7:1 AFR @ 6300. Max of 299 ft-lbs @5200 rpm and 328 RWHP @ 6300 rpm.

This leads me to believe it is not the injectors. If it were running out of fuel, it would not have gotten richer during the runs. There was no EXTERNAL air restriction (MAF, filter, etc) and the throttle blades were fully open. This can be seen in the speed density runs. But, it is only ingesting about 340 grams of air at 77 deg F which is around 770 cfm. (I don't have my formulas with me to get the exact number) the 58mm TB can flow 1050 cfm.

Air or ignition?
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One last thing:
My last set-up in the car (LT4 conversion w/ hot cam) was somewhat weaker than others with the same set-up (13.20's @ 104 mph compared to two guys running 12.40's and 12.50s respectively).

The only thing the same with the last combo and this one is the wiring harness. Both engine combos "weren't all there". I think it has to be in the harness. I have several connectors hanging unconnected ( ABS unit, air pump, CCP, EGR, reverse inhibit, skip-shift inhibit, wiper fluid, tranny VSS).

Could a lack of power to the ignition system hamper the hp that much? Like less than 12 volts to coil? etc.

If so, how and what can be checked?

Please, any ideas need to be brought up, mechanical, electrical, anything!!!

The more stupid it sounds, the better it will help!

Anything please!!

 

Im at work so im not able to view the graph but what it sounds like is a valvetrain problem. You didnt indicate what kind of valve springs you were using. You say everything is good until you get into the upper rpms ranges in which its falling off. Which tell me it could possibly be the valves floating.

 

They are comp bee hive springs. They have 650 miles on them and about 25-30 runs.

 

Buehler, Buehler...........anyone

TTT

 

A 355 at 7k rpm can only posibly ever intake around ~750 cfm - it is not an air problem, a 58mm tb is already more then enough for a near stock cube engine. Accufab had a nice little chart thing that showed the relationship between ci's and cfm's needed, but I do not have it bookmarked anymore.

Choking that much up top would seem to me to be valvetrain or head flow related, but you seem to have eliminated those two already.

Slow revving can be ignition related, but if it is not actually breaking up its going to be a PITA to hunt down.

What are your sensors reading at around the rpm range where it falls on its face? I had a dip right where my peak should have been that was costing me 10+ peak hp that ended up being the MAP sensor. Confused us for a bit until we traced the log, and found its voltage right at the dip dropped to like .4 when checked on the TechII. Yours doesnt seem nearly as obvious, but a trace of the "important" sensors at every rpm intervol may help get you in the right direction.

Sorry I couldnt be much help, you've got quite an interesting problem that is going to take some time to figure out.

 

I'm suspecting something in the electrical system of the car.

Or, the hot cam roller lifters from the last build are bleeding down not putting out the right lift.

Is that possible?

I talked to a guy who runs a 94 stocker that launches at 7000 and shifts at 7800 about valve float. After talking to him I'm pretty sure it's not floating the valves. The engine does not "FALL" on it's face or lose revs.

It just revs very slowly after 5000 in high gear (3rd - 1:1).

3.1 seconds in high gear from 5500 - 5900 rpm. 93 mph in 1/8th and 111 mph in 1/4.

Last combo with hot cam and M6 tranny was slower than average @ 13.20 @ 104.

No missing or rough running. No spikes in AFR. No vibrations when revving in neutral or park or with tranny brake on.

Just weak. The guy with the stocker seems to think the TC is preventing the motor from revving faster, like a water brake.

Any thoughts?

 

I would look at your transmission or your converter....only getting 73 rwhp out of a 100 shot does not jive...they typically put that out...and a tad more at the wheels. Also, the big red flag is only getting 63 rwtq...you should be getting almost 150 rwtq from a 100 shot of n2o.

I would be willing to bet that if your engine was on an engine dyno it would do what you wanted....so what is the difference?

I would not really look at your previous combo as a rule of thumb...some combo's just make less power for some people...even when it looks identical.

 

I'd like to know a little more about the heads/cam combo.

 

When you connected your TH-400 what did you do with the extra connectors?

My VSS is hijacked into the front VSS for speedo (until I get an A4 plug), my reverse inhibit and skip shift inhibitor are just hanging there.

I put a $20 skip shift resistor in at first, but it melted the resistor out of it.

So now it's just unplugged.

 

Did you get my PM regarding the timing/component issues?

 

Yes I got the PM. and I sent you a reply.

I will try to find TDC again and make a pointer and check the timing with the degreed balancer and a timing light. I'm pretty sure I'll have to work off of the bottom of the motor and use the 180 degree mark instead of 0.

I'll do all of this with the stock ignition, eliminating any retards that the MSD may be inhibiting.

If I don't find anything unusual, I'll have to tear it down and put a degree wheel on it and check all 8 cylinders since the assembler only degreed #1 and #8.

I'll aslo take all of this to Carl Rossler at Rossler racing transmissions to have him peruse over the info. He is a great guy to talk to and even came to my house before to change a governer on a Friday night with his wife in the car when my speedometer clip came loose and chewed up the nylon governor gear.

That may take care of the torque converter thoughts.

Thanks again for your help!

I need as many thoughts from as many people to figure this one out.

 

Ttt

 

To me it sounds like something in the valve train. Have you ever done a compression check?

I think you should look over the rockers, springs, studs, push rods, valve stems and the passages the push rods go thru. Either something is rubbing or isn't clearanced correctly or the push rods are not the correct length.

 

I've made an appointment to put it on an oscilloscope. I am also going to have him do a compression test becasue I am so flippin tired of working on this piece of crap, I don't have the energy.

TCI is going to take the TC back and look at it, and try a diffrent stator set-up.

I must have taken 80 pictures of the engine build, and I don't have one picture of the double roller timing chain set-up. I thought I might be able to see how the timing marks lined up, no help.

The pushrods are the correct length.

I have the blue-striped comp beehive springs though, could this be a problem?

 

Diameter, length and compression height are all things that must be considered before installation. At least check max lift allowed by the springs and compare that to your cams max lift with what ever rocker ratio you are using.