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392 carb
SPF on order. Using Ford motorsports 392 stroker. Ford recommends a holley 750 cfm. but my experienced engine installer use's a holly 4150, 650 cfm. He think's the 750 is to much carb for the motor. He also recommends an upgrade to a speed demon 650. Who's right?
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Frank,
I'm using a custom built Holly 750 DP and loven it, no driveability problems. These engines breath pretty well and the carb seems to be a great match. Joe |
The 750 is the right size carb for your engine size, but may be too big to use it for your driving requirements/situation.
Your machinist is probably right in recommending a Demon 650 for street driving in the burbs where you live. It puts your powerband in the off-idle to 5000 RPM. For track use, take the 650 off, and install a 750. By all means, check out the Airflow Research web site and see what they did swapping out the crate SVO heads for a pair of AR 185's. |
Frank....
Jack21 is right on. Check my reply to another thread. http://www.clubcobra.com/forums/show...threadid=21852 Lew |
In the November issue of Muscle Mustang & Fast Fords, they put a Speed Demon 575 on their DSS built 393. This motor ran a 10.8 at 124 mph with a Holley 750 and a 10.82 @ 123 with the Speed Demon 575. Amazing - this is a 500 + hp engine. I have read in the past that single plane intake manifolds can make lots of horsepower with a small carb. So if you keep the Vic. Jr that comes with the motor, you should be fine with the 575. I run a 750 DP model number 9379 (the unit that comes recommeded by Ford for the crate engine) on my 351 and like it a lot. It does run a little fat at idle though.
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Frank...401k runs a 650 SD. When his 392 was stock he dynoed at 376 RW with a real wide power band. That equates in the 445-450 range. The 650 will give you a crisper throttle response in the low (2500-4000)to mid range. It will lower the power band slightly providing more tq (20) in the mid range. The 750 would come on with about 15+ more HP at the very top but if you get out of it by 6000-6200 the 650 may provide the best street performance.
Guys use both and it is more of a personal choice. Nick has found more folks at the Pit like the 650 over the 750. The Holley HP is another very nice 650 for about $500. . I ran a 650 Race Demon on a 450HP 351W. Throttle response was "very snappy" , I mean instant, everywhere. The car ran like heck and never ran out of carb with a 6200 shift chip. Go to www.prestage.com. Under "Car Math" then "Engine building" There is a carb formula there. Looks like a 392 needs 598 cfm at 6200 with 85% VE and 633 with 90%. The Demons actually wet flow a bit above 650. Jim Marotta |
650 demon carb
he may also be quoting from a recent article done by Hot rod mag, they used that 392 stroker with a Demon carb and made almost 500hp. i would be happy with the Demon or a modified holley stock holleys dont work well on heavily modded engines. either way sound like a great setup . enjoy.
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Carb size
In dyno tests with a friends SPF with a well built 408W, we had the opportunity to try 650 and 750 Demon's in the same afternoon. After optimizing the jetting in each carb, we found the 650 gave us 399hp at the rear wheels and the 750 405hp. Both run up to 6200rpm. We settled on the 650 as it seemed to give more throttle reponse and was much crisper throughout the range.
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I'd put a 750 on there, unless it's got really good top end, then it would get an 850. You will lose a tiny bit of throttle response down low, but pick some up on the top end. If you have a single plane intake, you can get away with the smaller carb more easily.
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Single plane intake may not fit under the closed hood of your car/engine combo. Take some measurements or ask somebody using same setup. 351W's are tall motors. CR motor - frame mounts needed to be dropped 3/4" - 7/8" just to use the Performer RPM.
On the street, you'll be happier with the Ede Perf RPM. |
Jack21 , i found that the height of the aircleaner was the biggest factor, my CR has the Performer RPM , and with the standard small 10 inch cleaner i had good clearence but when i went to the 12-14 oval 2 inch cleaner, the cleaner is close to the top hood scoop. no rubbing but if the cleaner is not down tight it will rub with the engine running. small wobble from the cam. from looking at the books, the spects for the new Air gap intake should be ok with the low style cleaner. but good luck on getting a Victor Jr under there.
will be happy to post pics if anyone want to see the beauty. |
Frank,
I have a 650 SD on my 392 stroker and I don't think I could find another carb that is as responsive. My Snake jumps to the touch. I will see you tomorrow at Snakepit and we will talk. Later......John |
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