Car surges on the dyno

[Phillip_L]

Hello,



I have been working on LS2 with a Kenne Bell blower. The motor is actually installed in a 1969 Camaro. Every time we dyno the car, it seems to surge on the dyno (bounce). The power curve looks like a sine wave going up and down about 30 hp through out the pull. My peak is around 540 hp at the rear wheels. The car can do more with a smaller pulley, but I need to clear this problem up first.

Has anyone seen this problem? The run sounds good and looks good on the scanner. The timing comes up and holds around 21 degrees. No knocking. The O2 sensors both look good through the entire pull. Talked to Tony W who had a similar problem. He felt the fuel was fluttering and the lines need to be revised. I just re-did the fuel lines again to try to address this issue and it did not help.

For fuel I am using a Stainless Steel tank
Bosh 040 intake pump
8an line from the tank to Summit in-line filter
8an line from the filter to an Areomotive “Y” block on the firewall
Two 6an lines out the Areomotive “Y” block to each areomotive fuel rail (one to each fuel rail)
Out of each fuel rail to a Aeromotive regulator (with two 6an inlet and 6 an return)
I then have a 6an return line back to the tank

[DJW32]

Phillip,
I have a few questions(these questions are for my general knowledge...I have no idea why your car is surging, sorry): What size blower pulley are you using? How many psi are you pushing? When or at what psi will you be happy? Are you shooting for a specfic number? Can you post your duno sheet? Good luck, I'm sure you'll figure out what's wrong...David

[Phillip_L]

I am running a 3.5" pulley are running about 7.5 psi. The car is already ridiculously fast. I have 9:1 pistons in the car so I am able to run a little more boost. I have two smaller pulleys from KB to try. I want to fix the surging problem first.

[rocketman]

Surge like it's trying to leave the dyno.Or the motor surge's.If the car is moving around on the dyno tighten the straps.Or it might be to tight on the rolls.I don't see any reason it does this,Doe sit drive fine on the street.

[derekf]

Do you have logging software running on the engine while you're on the dyno? You might be hitting some knock retard or similar.

[68sixspeed]

Stick or automatic? I've had several friends with aggressive motors with automatics that had wicked bad surging problems on a mustang chassis dyno (electro-magnetic type). -Dan

[WS6]

What is the smoothness setting on the graph of the dyno? Dynojet goes from 1-5 1 being not very smooth. It is not uncommon for a dyno graph set at 1 to be wavy. It should not be 30hp difference though. What could be causing that I am not sure. I just wanted to make sure you weren't expecting a perfectly smooth curve for your graph. A middle setting on the smoothness scale is pretty normal.

[Nine Ball]

Its not the Dynojet, his car bucks like a horse violently at higher rpm. My '69 did the same thing, it was related to the fuel system and some crappy fuel dampner spring on the Magnacharger rail. Removed that and plumbed it directly to the end of the rail and the problem went away.

Later on, I added a 2nd electrical fan to the car, and tapped into the hot wire that powered the fuel pump. Caused the same problem. I suspect your fuel pump voltage is dropping at higher rpm, probably need a heavier gauge wire to power it and have it come directly from the battery with it's own relay.

[camcojb]

Its not the Dynojet, his car bucks like a horse violently at higher rpm. My '69 did the same thing, it was related to the fuel system and some crappy fuel dampner spring on the Magnacharger rail. Removed that and plumbed it directly to the end of the rail and the problem went away.

Later on, I added a 2nd electrical fan to the car, and tapped into the hot wire that powered the fuel pump. Caused the same problem. I suspect your fuel pump voltage is dropping at higher rpm, probably need a heavier gauge wire to power it and have it come directly from the battery with it's own relay.

What is his fuel pressure doing at the rails? That will tell a lot and if you're right (which is likely) it should show up there.

Jody

[Nine Ball]

True, a fuel pressure gauge on my rail at the time would show the fluttering needle during the bucking.

Phillip, did you put a gauge on it at the rail?

[Phillip_L]

The fuel pressure looks good. I have a small oil filled gauge on the regulator. I am not sure if the oil hidding the dip, but the fuel pressure looks good the entire run.

[nitrorocket]

You should have at 60lb or larger injectors on that along with a good fuel system. What is the AFR doing?

[Nine Ball]

That's what I'd suggest also. 60# injectors and 58-60 psi steady throughout the entire rpm range. I'm betting it is your S&P wiring harness, those are designed for stock LS1 retro-fits, not 700 HP monsters with big fuel pumps ;)

Tony

[streetk14]

There are some guys here who have more experience with the LSX stuff than me, but maybe I can give you a few ideas.

First, is the surging only at higher rpm? If so, it does sound like a fuel delivery problem. Are you sure your pump and injectors are up to the task?

You might want to check voltage at your fuel pump if possible when the problem happens. Like some others have said, maybe you aren't getting proper voltage to the pump. You should have about 13.5 volts.

Along those same lines, maybe you should look into a boost a pump to help pump up voltage at the fuel pump during high demand. This could be an easy fix.

Let us know how it goes. I am also putting a blown LS1 into a first gen Camaro very soon, and am sure I will also have some gremlins to work out as well.


-Andy

[Phillip_L]

Sorry for the late update. I really have not felt like chasing the problem. The problem is still there.

Is there any chance this is due to axle wrap? Can this problem occur in 4th gear on a dyno or is axle wrap only caused by lauching?

[protour_chevelle]

Curious.... Your summit filter.. is it for carb or fuel injection? It could be bottle necking your fuel.... But you say you have steady and correct fuel pressure at the rails correct??

-Matt

[PhillipM]

Axle wrap could happen on a dyno but I don't see how that would apply to your specific problem of what sounds like a rythmetic like surge(ie a sine wave). Keep searching through your fuel and wiring.. I think that is where your problem lies.

[gEtyOpAPiOn]

stupid question hehe ...sd tunning or maf tunning ?

[SLED28]

Sounds like its an overly fat surge... What is the A/F ratio? The o2 sensor readings don't cut it...