Blow Through 408w - Massive Stumble

Posting this for a friend but leaving the names out for now.

This a very racy deal that is being setup for a certain class.

The car should run about 9.0 and is making about 1000 hp. Testing at the track it does a great tire boiling burnout, and things appear fine at that point. The car then seems to stage OK, and you can bring up the rpm while on the transbrake. When the brake is released the car moves a few feet and the engine flat dies. The data logging shows that it goes dead lean, i.e. 22:1. I don't see how it can be the pump shot or pump cam since the throttle is already to the floor and the car is on the transbrake. Any ideas?

Setup is a centrifigal blowing through a specially built 750 DP, Victor intake, fantastic heads, large solid roller cam, aluminum rods, etc.

The owner had the same problem when trying to run it prior to installing the blower, using the previous carb from the last naturally aspirated combo.

So to me the problem must be something that was common to both setups.

My vote would be the fuel system, pump, lines, pickup,etc

are there jet extenitions on the rear jets

What type of pump and what size line, sometimes it gets over looked that when a car leaves really hard the pump has to also over come the weight of the fuel in the line trying to be pushed back to the tank by g-force, you can also have pressure without much volume.

T.

One of my thoughts as well. Both carbs that he tried lack jet extensions so that could be an explanation. The car 60 foots in the 1.4 -1.5 range. I believe the fuel line is 5/8". The regulator is a return-style Aeromotive unit and it is boost-referenced.

Typically when the car restarts he'll stab it and run down the track about 1/2 way and it seems fine when he does that. But that's puzzling since if there is a fuel delivery problem it should go lean then as well.

Are you running a blow-thru carb. with hat?

If so who fixed the carb?

It's a CSU carb and a 4" hat on it. I don't recall the brand but it's cast aluminum.

I'm thinking it has to be a delivery issue, and the bowls are closer to empty after the burnout than we thought.

I think it's time to go through the system from the tank pickup forward and see if there's been some sort of mistake or oversight.

From what I gather, CSU carbs are well done, plus this thing did the same thing with another carb too. So I'm not convinced it's the carb itself.

We had a friend with a similar problem and it turned out "Boost references" were not supplying the right signal. He had vacumm running through a log and somehow he did not get the correc t signal to the fuel circuit. Good Luck.

Originally Posted by rcodemach1

It's a CSU carb and a 4" hat on it. I don't recall the brand but it's cast aluminum.

I'm thinking it has to be a delivery issue, and the bowls are closer to empty after the burnout than we thought.

I think it's time to go through the system from the tank pickup forward and see if there's been some sort of mistake or oversight.

From what I gather, CSU carbs are well done, plus this thing did the same thing with another carb too. So I'm not convinced it's the carb itself.

CSU is a great carb. along with C & S Specialties.
If you have around 1200 HP you will need the dual needle and seat bowls. Sounds like fuel delivery problem of some sort. You need a excellent pump and a bypass boost assisted regulator, not just regular regulator. I don't know much more to tell you.
I can get you a person's name to call @CSU. Give me a few days.

/

Originally Posted by rcodemach1

Posting this for a friend but leaving the names out for now.

This a very racy deal that is being setup for a certain class.

The car should run about 9.0 and is making about 1000 hp. Testing at the track it does a great tire boiling burnout, and things appear fine at that point. The car then seems to stage OK, and you can bring up the rpm while on the transbrake. When the brake is released the car moves a few feet and the engine flat dies. The data logging shows that it goes dead lean, i.e. 22:1. I don't see how it can be the pump shot or pump cam since the throttle is already to the floor and the car is on the transbrake. Any ideas?

Setup is a centrifigal blowing through a specially built 750 DP, Victor intake, fantastic heads, large solid roller cam, aluminum rods, etc.

The owner had the same problem when trying to run it prior to installing the blower, using the previous carb from the last naturally aspirated combo.

So to me the problem must be something that was common to both setups.

I am concerned about the last sentence.
Is this a blow thru. carb. ?????

Sounds just like you have a standard or natrually aspritaded carburetor. The blow off is working at idle and when you slap the throttle it goes lean and stumbles or shuts off.

You need a blow thru carb. especially built to blow thru applications. I would only purchase a CSU or C&S Specialties carb for blow thru... deffinately not a BG

The accelorator pump circuit won't be doing anything, if he already has it floored.

Probably need to stage at part throttle, so squirters can give a shot.

I'm guessing you do NOT have the lean problem when does the scenerio you describe as
"Typically when the car restarts he'll stab it and run down the track about 1/2 way and it seems fine when he does that." ??

Lee