Bog When Launching At The Track

347, AFR heads, Holley 650 vac secondaries, Performer RPM Cam, Edelbrock Performer intake, MSD, T5z, and 3.40 trac-lock.

I’ve been trying to launch at the track by dumping the clutch at 2000 RPM. The car launches great, and then it’s like time stands still it seems to freeze and then takes off again.

I had a real bad bog on the street in normal driving as well.

Here’s what I did:

Replaced accel pump cam with the green one (I think it’s the most aggressive one, but completely sure about that). This made it better on the street, but still bad.

Replaced the shooter with .035. This solved the issue on the street. I had hoped it solved it on the track as well. Saturday I found out is just as bad on the track.

Carb is stock other than that. It’s about 1 year old.

Here are some of my thoughts (tell me if you think I’m nuts).

1. Don’t think I have a vacuum leak, but if I plug the carb base port that connects to it, my idle goes down. I’m guessing that this is normal as now there’s less air getting into the intake. This also didn’t fix the problem.

2. I’m running Hoosier QTP drag slicks and I hook fairly well. Could it be that I’m just overwhelming the motor when I hook?

3. Vacuum leak someplace. But I really don’t see where. I’ve checked everything.

4. Before I fixed the bog on the street I had suspected that the secondaries are coming in too soon. I disconnected them and no dice. I haven’t tried disconnecting them at the track. I will do that this weekend.

5. Power valve dumping too much fuel?

6. My suspension is really stiff so the front end doesn’t lift much. So I don’t think it’s a float issue or fuel sloshing out the vent hole.

Other than that the car runs great: 12.9 @ 107 MPH. My 60’ time is bad: 2.0 (obviously).

Any thoughts or ideas you guys have would be greatly appreciated.

Do you notice any black smoke?

check your spark plugs

could also be a lean bog.....read the plugs

Try the RED Cam, you were going in the right direction with that pump shot idea, don't stray from that path.

I have Red in front and Blue in the rear. The Red is the most mellow shot, and the Blue is the second most mellow shot.

The Green Cam has the same lift as the Pink, but a shorter duration on the shot. (love this color selection)

Mine At launch the RPM's were great to 2200, then bog, then great, and it was the shot duration that was the issue. too long, richened the whole thing up.

I needed to make my accelerator shoot as small as possible to eliminate all bog.

The plugs look OK to me. Although maybe a little lighter tan than I'd expect (but I'm certainly not expert at reading them)

Also, no black smoke.

Mike66, do you mean make the duration short? This would mean that the same volume but a shorter duration?

You have to use some imagination when you look at these charts, but it will give you all the info about how they react under different conditions and rise of cam level amount.

You must read both specs together to get the 3D profile information...

The Red and Blue Cams have the least amount of shot and at the slowest rate of shot. They only squirt for the first 20 degrees of throttle opening, then they stop adding fuel. The pink ones, keep adding lots of fuel when it is not needed anymore. Trust me, it is enough to richen up your whole mixture for a good second or two.


Best...

So, Mike66, you think I'm too rich, correct?

At first I thought that too, but going richer (green cam, .035 shooters) made my on-the-street bog go away. (maybe there's no connection between my street-bog and my track-bog)

You still may be right. However, I'm wondering when I launch at 2500, I'm already at part throttle. So it would seem to me that part of the pump shot is already gone. Thus if I had too small of a shot, there would be nothing left when I finally did go to WOT.

But I think you're right, the issue is the pump shot.

(Oh, and nice touch with the color scheme!)

Are you running an aluminum flywheel?
What happens when you raise the launch RPM?
Do the tires initially spin on launch?
Do you have jet extensions in the rear bowls?
How much fuel in the tank?
What is the fuel pressure?
Where do you have your float level set?

My guess is you may be uncovering your rear jets. The initial pink cam on the carb should be very close. Most if the time a wrong pump cam will not cause the carb to stumble like you are describing. Most racers change the pump cam in order to sneek up on the best combination to lower their 60 ft times. In addition, your street manners and strip manners will not be comparable unless you are launching on the street with the same slicks. The load on the motor will be different with street tires vs slicks.

Steel billet flywheel.

I'm afraid to raise the rpm too high as I have an 8" rear end and I'd rather not break it. But I did start at 1000, went to 1500, then 2000, and finally 2500. Same result. I'm tempted to keep raising the ante but I'm a coward

No tire spin. It hooks really good.

No jet extensions, 1/2 tank. How do extension work, its seems like they'd make the problem worse?

Don't know the fuel pressure but I'll check it.
What should it be?

Its the new version of the Holley with the non-adjustable float level. So I assume its good.

My suspension is really tight. I built it with the street in mind. The car stays pretty flat. So I'd be surprised if its uncovering the jets. But I suppose its possible.

Great questions and info.

jet extensions keep the jets under fuel when your accelerating hard