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Supercharged Fuel problems

7K views 38 replies 12 participants last post by  drewbe 
#1 ·
First time posting, I have BDs 1071 blower with dual 1050 holleys. We have a magnafuel 500 pump with a bypass to the tank, we installed a magafuel regulator with the boost reference and the car pops and black smokes at the line, fuel pressure is set at 6.5 and at full throttle we get 13 psi of boost which is 19.5. I disconnect the boost reference, set the pressure to 8.5 and it launches, nothing hard, but then runs out of steam, it is looking for more fuel.

We tried to run a return line regualtor with boost reference and cap off the pump, it takes the regulator pressure (6.5) and makes this the line pressure, so now I am really out of fuel.

I have read some people do not run the boost reference but some do. Can help would be helpful.

thanks
 
#3 ·
It sounds like you have either some plumbing issues, or carburetion issues. You need to first check with Magnafuel to see how they want you to plumb the system. On a roots style supercharger you would not boost reference the fuel pressure regulator since the carburetors are above the supercharger and only see atmospheric pressure. Boost referencing is normally only done on carbureted applications when you vary the incoming air pressure to the carburetor such as in a turbo or centrifugal supercharged application. On an application like this normally you'd like to maintain between 6.5 and 7.5 psi through your entire run.
 
#10 ·
The guys are telling you correctly. Your carbs can't take 19psi of fuel pressure, that's why you were getting the black smoke and poor running engine. You may want to set your fuel pressure a little higher than 6.5 psi, do a little experimenting and see what works best. No boost reference needed.
 
#13 ·
Okay ran the car with 8 1/2 psi fuel pressue, no boost reference. Off the line the car never hit the wheelie bars, 1000ft mark it broke up. Checked the plugs lean. Added jet, still lean, added more jet, still lean. 92 primary 96 secondarys still lean. Now for the trick question, we have a base timing of 32degrees and have a boost retard for the timing that is set at 1 1/2 Does anyone run a MSD boost retard? Should we just throw it in the garbage and set the timing at 29degrees


thanks
 
#14 ·
Your Dominator can take 10PSI of fuel pressure, that's where we run our big nitrous motors. You have to confirm that fuel pressure is being maintained through the whole pass. Maybe you have but I might have missed it.

A good way to burn up a boosted motor is way too much timing. If your running 13 PSI I'd dial out at least that much timing under boost. 29, no matter what, is way too much in my opinion. Under boost the combustion process will be MUCH faster. 1.5 degress of timing taken out is not a heck of a lot.

I would assume your running decent heads if your base is 32.

Hopefully you plumbed this with -10 hose? We would normally run a bypass back to the cell from the reg versus deadhead the reg on an applicaton like this. But I think you first need to verify fuel pressure all the way down the track.
 
#15 ·
Thanks for the information. We have dart heads, #10 line throughout. We are going to verify fuel is constant on sunday. Just checked the rest of the plugs and they are all white on top and half way down light yellow.

Sorry for the confusion, we have the dial to take out 1 1/2 degress per pound of boost after 2 pounds. So thats a lot of timing out of the car.

thanks again
 
#19 ·
okay, here it is... 9 psi of pressure all the way down the track, retarded the timing 1degree after 5 pounds of boost for a total timing of 24, plugs came out white popping 100ft. we went up jet to 96 jets square, 26 degrees of timing at wot white plugs, popping 1000ft. no difference either way.

we thought maybe bad msd, replaced with new 7al2 box, same thing.

We made some calls to a couple of companies and blower shops, we were told it would be better to run a return line off the regulator than to run it off the pump. Any thoughts on this. I was told to go to 100+ jets as well. I thought this is way too much
 
#20 ·
drewbe,

On a drag race only application you shouldn't need a return line from the regulator. Have you flow checked your fuel system to see how much fuel volume its flowing yet? Where these carburetors calibrated to run on a blower? When you've gone up in jetting how did that affect the rest of the run?
 
#22 ·
How long did it take to flow a gallon of fuel through your regulator?

Did you 60' times change at all when you've made your jet changes?

How does it pull in first gear before you shift?
 
#25 ·
Hey when running a bypass install it as far away from the pump as possible.

I always plumb the fuel to feed the carbs then continue to the bypass valve. That way the carbs get uninterrupted fuel and the bypass is working off of pressure that is not influenced by any plumbing restrictions.

And look at the simple things like fuel tank vented well etc.
 
#26 ·
camaroman7d said:
The guys are telling you correctly. Your carbs can't take 19psi of fuel pressure, that's why you were getting the black smoke and poor running engine. You may want to set your fuel pressure a little higher than 6.5 psi, do a little experimenting and see what works best. No boost reference needed.
What kind of carbs? Carters and Edelbrocks will flood at pressures of 6.5 psi or greater. For these carbs, regulate to no more than 5.5 or 6.0 psi.

George
 
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