750 or 850 cfm?

-
6

69Chrgr

Charger/Cuda
Joined
Jan 29, 2007
Messages
421
Reaction score
17
Location
Midlothian, Texas
All right, another million dollar question:
Would I benefit by going from my 750 Quick Fuel D.P. to an 850 Quick Fuel D.P.? My 750 came from QF with 74 jets in front and 84 in the rear. Some folks have told me it's at the high end of the spectrum regarding jetting. Here is my combo:

408
Eagle Crank and Rods
Mopar M-1 Intake
Stock Eddy Heads
Hughes Roller 242 and 246 duration @ .050 lift w/matching valve springs
.555 and .565 gross lift
1.6 rollers
Forged Flat Tops
Approximately 11 to 1 comp.
Mech. Fuel pump
Dynamic 3800 Stall
Reverse Manual Valve Body
4.11 Gears w/powertrax locker

I just don't want to keep throwing money at it for no reason, however I would like to get in the lower 7's in the eighth and lower 11's in the quarter.

Thanks Again,
Darren
 
Your still running a mechanical fuel pump??..with that combo its time to step up to and electric pump and at least 3/8" fuel line front to rear..Quickfuel carbs.are'nt cheap so seeing as you already have the 750 get yourself a jet kit go to the track and experiment with the jetting...granted the 750 might be a little small for that combo but play with it before forking over another $650.00 for an 850...
 
If your 750 is too small for your combo, I have a 850 Mighty Demon that is too big for my combo that I would trade you.
 
Thanks 340 and DartSport. I think I'll stick with the 750 and see how well it works out.
340, I have 3/8 line, and a high performance Holley mech. pump. Do you think the mechanical pump is holding it back? Granted, I haven't even gone on all 4 barrels yet, I guess I'm over anxious. The QF came with 74 jets in front and 84's in back.
 
I think there would be a gain above 4000 rpm, but your 60' might drop a hair.
 
that 3/8 line is your bottle neck - I have seen a stroker a body pick up .6 with a 1/2 inch fule line and a holley fuel pump.

also the stroker will take as much plenum and carb you can throw at it. with that 3800 dynamic it will handle a bigger carb and you should not see any loss off the line with it.
 
69Chrgr said:
Thanks 340 and DartSport. I think I'll stick with the 750 and see how well it works out.
340, I have 3/8 line, and a high performance Holley mech. pump. Do you think the mechanical pump is holding it back? Granted, I haven't even gone on all 4 barrels yet, I guess I'm over anxious. The QF came with 74 jets in front and 84's in back.
Click to expand...

The quickest way to see if your pump can handle the engine, and probably cheapest, is plumb in a fuel pressure guage (you should have one anyway) and if the pump isn't meeting the demand with your foot in the carb you'll see it plain as day.

Terry
 
Dam, that's some good info guys. Obviously, I have some work to do. I wish other websites were this helpful and courteous. Looks like I'll work on the electric pump first. What kind and where should I find a gauge that I can plumb inside the car? I know it has to be electrical.

Thanks!
 
Thanks Ramcharger, looks like I need to drop some coin further on up the fuel system. I didn't think that I'd really need 1/2 inch line, but I'll start with the electric pump and new regulator. I have 3/8 AN fuel line right now in the whole fuel system.
 
340srule said:
You'll be just fine with 3/8" line,its been proven:-D:-D
Click to expand...

Have you tried a 1/2" line ? If not then you havent proven anything. Just because you run good with the 3/8" doesnt mean you wont run better with the 1/2.


AbodyJoe runs low 12s with a stock pump and 5-16 line with a mild 360 and 391 gears. Thats pretty good, Bet he would run quicker with a bigger line and better pump.

Its all about how fast you want to go and how much you feel like spending.
 
340srule said:
Really.. i've proven you can go 11.'0s with a "STREET" car..what are you running??...
Click to expand...

Thats not my point. I didnt say your car doesnt run good. Im just saying just because your running good with a 3/8 line doesnt mean you wouldnt pick up with a 1/2" line.

Hell, Dwayne Porter went low 11s with a 5-16 line and a Holley blue pump. Doesnt mean its the way to go does it ?
 
340srule said:
You'll be just fine with 3/8" line,its been proven:-D:-D
Click to expand...

AdamR said:
Have you tried a 1/2" line ? If not then you havent proven anything. Just because you run good with the 3/8" doesnt mean you wont run better with the 1/2.


AbodyJoe runs low 12s with a stock pump and 5-16 line with a mild 360 and 391 gears. Thats pretty good, Bet he would run quicker with a bigger line and better pump.

Its all about how fast you want to go and how much you feel like spending.
Click to expand...

340srule said:
Really.. i've proven you can go 11.'0s with a "STREET" car..what are you running??...
Click to expand...

AdamR said:
Thats not my point. I didnt say your car doesnt run good. Im just saying just because your running good with a 3/8 line doesnt mean you wouldnt pick up with a 1/2" line.

Hell, Dwayne Porter went low 11s with a 5-16 line and a Holley blue pump. Doesnt mean its the way to go does it ?
Click to expand...

SOS... except with fuel delivery.

Running a mechanical pump, you really need to have a large feed line. Once fuel is under pressure, line size isn't as big of an issue. Getting it from the tank to pump IS the big issue. Think about running and inhaling through a straw. Larger the straw you use, the easier it is to fill the lungs.

Will a 5/16 or 3/8 line work and get fuel to the carb. Yes it will. Will it work to maximize the performance of your car compared to a 7/16 and up ID line... Probably not.

We've had more than a few cars that ran 5/16 or 3/8 lines. In every case except one, when lines were upgraded to a larger diameter, the cars picked up ET and MPH.

You might try to work a small electric pump into the system that is on a relay and not running all the time. I know some guys that drive all the time on a mechanical, then hit the switch to turn on an electric supplementing fuel to the front of a car.

In the case of fuel delivery, having volume in reserve is ALWAYS a good thing.

IMHO, Run the 850 on the stroker, they tend to eat up carb cfm like they do cam duration.
 
AdamR said:
Have you tried a 1/2" line ? If not then you havent proven anything. Just because you run good with the 3/8" doesnt mean you wont run better with the 1/2.

Its all about how fast you want to go and how much you feel like spending.
Click to expand...
Absolutely true and one of the most commonly overlooked areas of performance. Running great does not necessarily mean running at full potential. I personally know 2 guys who picked up a tenth or two and several MPH by going to ½" tubing from the tank, through the filter and pump, all the way up to the regulator. They thought they were fine with 3/8" too and were suprised at the result of switching. As you said, it is all about how much you want to spend. It that a big enough difference to justify the cost on a street car? Maybe, maybe not. On a car that is run alot? Probably. My car was at the other end of the scale when I bought it. It had two 7/8" lines (yes, heater hose size) from the tank to 2 pumps in the trunk, to a 1" line that went up to the front. Overkill to say the least, and definitely increased the time it took for the pumps to react when pressure dropped. I have ½" now.
 
Wow, very interesting. Looks like I'm WAY behind compare to everyone else. I obviously built more engine than the fuel system might be capable of. Hell, I can't wait to see what it runs like with the secondaries fully opened! Thanks a Million!!
 
It will like the 850

000_0130.jpg
[/IMG]
 
7172 duster said:
It will like the 850
Click to expand...

He will probably be OK with an 850 but you have to be careful. Over-carbing and over-camming are the two most common mistakes in this game. If you go with a carb that is even a little too big the air velocity will never be high enough to pull the max amount of fuel and your mixture will be too lean. If the carb is way too big you can use jets the size of a garden hose and you will still be too lean. An engine will usually run better with a carb that is slightly too small that has big jets than it will with a carb that is too big.
 
I remember reading an article in Hot Rod that had a formula for figuring out fuel line size, but I think I threw it out when I moved. Let me look around a bit.
 
You must log in or register to reply here.
-

Back
Top