I don't know what the deal is with this car.

It makes 10lbs of boost, has a MSD -6AL with MSD coil NGK plugs gapped at .035

Its a automatic car

It just flat out will not make power between 4000 and 5200 rpm. the AFR stays between 11.5 and 12.0 and the advance has been pulled way back to 19 degrees with no change.

heres the dyno graph

 

are you positive that its not KR?

thats alot of hp to be missing out on!

 

what ecm are you using? any more details on the motor?

 

I agree with Marshall's suggestion. First I would turn off the KR in the PCM and then slowly advance the timing. Or else, just scan it to see itf it is pulling timing. Other possibilities - somehting in the intake collaping restricting airflow into the SC. Or, bad valve spring(s). Or weak spark (bad coil, plug wires, etc.)

Rich Krause

 

This is probably a dumb question, but do you feel the power loss on the street as well? Just thikning maybe somethin was up with the dyno, Im sure thats not it, but it would be dumb to overlook it.

 

Well, I tried the knock retard thing.. Locked the computer out.. and it still does it.

All I was getting in the first place was some transistional knock and it was nothing major (less than a degree)

I'm almost completely confident that its a blow out issue. I was talking with a buddy of mine whose getting his masters in motorsport engineering and floated the idea of Lots more boost under peak torque that your usual LT1 guy instead of makeing the same boost after this peak torque area and I told him its probally haveing a hard time firing threw the higher cyclendar pressures during this peak torque area.

The valve springs are all heathy and the car otherwize runs good.. It did the exact same thing with the last motor just sometimes worse than others.

I'm just going to bite the bullet and gap the plugs down to .025 (from .035) and see what that does.. One thing I've learned long ago is that give the car what it wants not what looks right.


PS.. I built the intake for this thing out of steel and a k&n i pulled off a suburban when I worked at the local dealer. So its freaking huge and theres no way it can collapse. (3.5 mandrel bent steel with a flaired to GM throttle body)

 

Well, going from the simple stuff first I'd try replacing the pugs, wires, etc. (assuming you haven't tried that a half dozen times already, which you probably have). After that I'd cast a suspicious eye towards the MSD box. THey don't usually get "weird" like that very often, but it does happen.

If this is an old generation small block with a distributor it's not a bad idea to have a complete, known-good one laying around for diagnostic work like this. I keep an old large-cap GM HEI distributor on my shelf for situations exactly like this on non-computer controlled engines.

If you can figure out a way to bypass the MSD temporarily (put it back to stock ignition configuration, for instance) and do some road tests you can quickly rule it in or out. No, it won't be adequate at high RPMs, but if the box is at fault you will notice an immediate improvement in the "problem RPM range." Enough that you can say- yep, I'm on the right track or nope, that's not it.

Also, get used to the idea of doing similar back-to-back testing by changing out the coil and other ignition components. The number of times I've traced an annoying problem like this down to something simple like a shot rotor or an ignition coil that's gone flaky is a lot.

The ignition you have should be plenty strong to keep the fires lit well over 6000 RPMs, so I'm not suggesting that the system is inadequate in any way- if it's functioning correctly.

 

let me ask you,

What gap do you run on your weiland? also how much boost...

umm.. I've tried new wires and such and the problem RPM is still there... well it won't even run at 4,000 without the MSD sounds like a rev limitor.

I agree.. I keep plenty of stuff like that around for diagnostic

 

Dang man, after seeing that video over on the speed density board you posted, I did'nt have a clue you were having troubles. Hopefully it works out, it's an incredible setup you've got going.

And FYI, I took my car to the shop finally. I'll keep you posted on that.

 

i remember watching the video you made of it on the street (from undergroundracing) and it looked like it pulled pretty good...or was that before the problem your having now?

 

its done this since the car has had nitrous really

2 motors, 2 different power adders, 2 differnet opti's, 2 diferent types of plugs, coils and wires.

You can hear it in the video.. and you can see it it in the tach.

 

I'm running a .040 gap on a dirt-cheap set of Autolite 3924 plugs and cheap parts-store no-name wires. Ignition is just an old junkyard HEI fortified with vitamin MSD and recurved by yours truly. Coil is likewise a cheap parts store stock replacement. Pulls strong right up to 6000 (a self-imposed rev limit- HP is still not quite topped out at that point). That's why I beleive your setup with better stuff in it should get the job done if it's working right.

Keep in mind I'm only pushing 5 PSI, though.

 

maybe that is it.. just that your at 5psi

i'm at 10psi

 

if you have some different pullies, try 5 or 8 psi or something like that...

 

I'm with Marshall- that's an easy one to test. Pulley down. Or just yank the belt off the blower for now and see how it runs N/A (if it's a centrifugal blower).