double pumper versus vacuum secondaries

I am running a Holley 750 vs carb in my GT40. The engine is ford 302 with single plane intake and produces 400hp (dynoed). I do a few track days every year and was thinking of putting on a Holley 650 double pumper. Have any of you guys switched from vs to dp and what was your experience, other than higher fuel bills!.

650 DP is probabaly a better combination for track and unless you have put Jetting plates in the secondaries of the VS then the DP is far more tuneable.
As for that other thing called economy then the DP will probabaly be less economical as every time you stab the pedal you get 4 shots instead of 2. Really up to your driving habit as to how that works out.
If you are just looking for better tuneability of the carb then maybe putting jetting plates in the secondary may be the answer.
I have not looked very hard at them but there is also a number of aftermaket bodies for the Holley that give you better mixture alternatives and tuneability.

Personally I loved DPs before I started playing with injection.
If you end up with 650 DP then a good place to start for 302 is Primaries 68 Secondaries 70
650 (list 4777) is proabaly as big as you need. Go bigger and you lose bottom end. Unless you are doing 8000 RPM then you wont need to go bigger.
hope this helps ???

KB

I've run both and the two you are comparing is really not a straight across comparison. With the build you state, the 650 is probably a better carb cfm wise than the larger one. The DP is probably the better choice for the smaller engine with a manual gearbox. the VS is a little more forgiving, but really too much carb for the build you are running. I agree about the right foot enthusiasm and it's effect on gas mileage, but that's easily remedied with a little discretion. Initially you will likely wick it up more than you will after you get accustomed to the change in response. I have a 4777( I thought it was a 660 when I purchased it a few decades ago) that I ran on a 4 spd 351C 1970 'stang and liked it a lot. I think the VS is better suited for an auto equiped car.....unless you go manual valve body and want to row it....but why...if you want to row that's what a manual tranny is for.

+1 for the 650 DP. I had one on my 302-equipped GT350 clone, and it was simply perfect for that application. That carb originally lived on my 351C in my Pantera, and it worked great but ran out of puff at higher rpm (built motor with a cam). It moved to my 302 and lived a very happy life there for ten years. It has since been transferred to another Pantera with a stock high-compression 351C, and it utterly *transformed* that car, really waking it up and greatly improving bottom-end and midrange torque, with much better throttle response than the original stock vac secondary Motorcraft POS carb.

I think you'll be really happy with it on your GT40. They come jetted rather fat from the factory, so you may find some improvements in both performance and economy from leaning it out some.

Thanks for your input guys. I think I will try the 650 DP. My ford 302 develops maximum power at 65000rpm and maximum torque at 5800rpm, will 650 be enough cfm wise?

One suggestion; based on the quality of carburetors I've seen on my own cars, get a QuickFuels or ProForm (basically the same company) DP instead of a Holley. Two things to recommend them both over Holleys: everything is adjustable easily, and the quality is MUCH better; all the construction is billet and machined, they don't have internal leaks, and they are a lot easier to work on. They have really eaten Holley's lunch if you ask me.

I'd get a DP if you want throttle response. Sure, you'll use more fuel, but these aren't economy cars anyway. VS carbs have more lag in them, I think, as you wait for the vacuum to pull the secondaries open.