CArburetor?

[15wildea]

so I am rebuilding a ford 390 I hav a stage 2 comp cam in it and racing timing is a hollow 650 double pumper a good choice or is it too much haven't done anything to the heads.

[squirrel]

A hollow carb? like a Holley? damn phone spell check

650 double pumper is probably going to work pretty good. Of course, we don't have any idea about what the rest of the car or truck is like, so it's hard to say for sure. A 750 vacuum secondary might work better?

Things like what transmission, stall speed if it's an automatic, etc can have an effect on how big of a carb you can run.

[anotheridiot]

you can do that official cfm equation and probably need a 470. The general rule of thumb I heard is automatic likes vac secondaries, manuals like double pumpers. I need to learn alot more about carburetion, but you will probably get some good advice here as to what size jets to change to and which power valve if you are already too big. It would be nice to have that info when its on a table.

[milner351]

More info would be nice, but for a 390 my first choice would probably be a 750 vacuum secondary assuming it's an automatic trans.

The factory four barrels on the 428 were Holley and were 780 cfm if memory serves.

As Jim stated - it depends on a lot of factors, including intended RPM range.

[Beagle]

I like the vacuum secondary 750 idea if for no other reason that being pretty forgiving.

[Scott Liggett]

Vacuum secondary for street. Horse hockey!!
Vacuum secondary for automatic transmission. Bull pockey!!
Double pumpers for race only. Load of smelly crap!!
Double pumper for manual trans only. Mule mounds!!

Any one notice a pattern here with these statements? What they are really saying is that vacuum secondaries weenies who build pseudo hot rods with granny matic transmissions. AKA poseurs who can't operate a screwdriver. Double pumpers are for real hot rodders who build their own engines and who carry around a glass for reading spark plugs.

The truth is that you can drive a street car with an automatic with a double pumper as easily as driving the same car with a vacuum secondary. The people who can't set up a double pumper can't set up a vacuum secondary carb either.



For this 390, that 650 will work fine. It may run out of air in upper rpm range, but unlikely.

BTW, what is a "Stage 2 Comp Cam" and "Racing Timing"?

[Orange65]

650 DP will probably be a good carb for that engine. I had one on a 427 Chevy with a mild cam (.52's lift and small duration), stock peanut port heads, and a stock +1000 stall converter in a Chevy truck- the thing was a blast! A 750 vac secondary will probably get better mileage, but the 650, when tuned correctly, will give more throttle response and be more fun.

[yellomalibu]

I prefer a DP on a performance type of car. Stick or Auto, doesn't matter ... hell, I've actually never had a performance car with a stick.
Yes, there is a learning curve to tuning EITHER a DP or a VS carb properly.
I think the VS carbs are more forgiving to bolt it on and go - and that's probably why people like them.

[redneckjoe69]

i've been thinking of your statement above Scott. and while theres a lot of truth to it, if DPs are the best, why didnt every car manufacturer use them way back? probably because of gas usage? i agree though, most people dont know how to tune a carb. they'll buy a $400+ carb, but wont spend $20 on a book about tuning them.

[Beagle]

re-read it for the fiftieth time. I think I missed the point... if the point is "A properly tuned 650 double pumper should work fine" then, yeah, I'd go along with that.

[Scott Liggett]

i've been thinking of your statement above Scott. and while theres a lot of truth to it, if DPs are the best, why didnt every car manufacturer use them way back? probably because of gas usage? i agree though, most people dont know how to tune a carb. they'll buy a $400+ carb, but wont spend $20 on a book about tuning them.

The manufacturers also had emissions to deal with. Remember, that started in 1966.The same year the Holley and Quadrajet started showing up on cars. Why did a Hemi get crappy exhaust manifolds? These factory cars were also under warranty with conservative timing curves and carbs metered on the lean side. Performance dealerships and speed shops alike all advertised recurving distributors and rejetting carbs for more horsepower back then.

One more thing to think about. This is straight from Holley's carb rep. There is absolutely no difference between a 750 double pumpers and a 750 vacuum secondaries primary side. Not one thing. How the secondaries open is the only difference between the two carbs.. 99% of people who get crap mileage with a double pumper, screw it up trying to fix it, or too stupid to replace a blown power valve, are the same people who go buy a brand new carb, a vacuum secondary and put it on straight out of the box, which is the best place to start tuning on any carb bought.

[redneckjoe69]

yea, that makes sense.
personally i like my 750 VS on my auto. it runs better than FI. it was a junkyard $25 carb, but i went through it and tuned/modded it.
i think the point is, no matter what carb you choose, its worth tuning it properly. out of the box isnt going to be perfect for any motor.

[squirrel]

A 3310 works pretty nice if you put a softer spring in the secondary

[redneckjoe69]

this is a great addition to a 3310.

http://www.summitracing.com/parts/qft-63-1

[squirrel]

yeah, although this is all you really need

http://www.summitracing.com/parts/hly-20-13