650 DP or 750 Vac secondaries? Which one?

[Badart]

I have both carbs and can't decide which one to use. Dart will be see street and strip. By no means a daily driver, but weekend cruiser.

I have both holley carbs and can't decide which one would be better for my combo. The 650 double pumper has no choke plate and will be a pain on cold starts and the 750 has automatic choke and vacuum secondaries. Here is my combo. I am wondering if the performance will be similar when tuned right?

360 Zero decked .030 KB107's
2.02 J heads with mild porting
Comp 284H
1.6 roller rockers
Eddy RPM
Hooker comp headers
3000 stall
3.91 gears

 

[rumblefish360]

750 would be my choice.

Yes, the performance would be similar. The difference , however super mall would be;

smaller carb, a bit better throttle response and torque would be better down low (But not where your making any power but the put put around town type)

More noticeable difference would be the 750 will have greater mid-range torque and high end HP, IMO, somewhere round 10 HP and lbs.

 

[Locomotion]

While I was only bracket racing years ago, I swapped between a 650 DP and 750 vacuum and, as noted, there was very little, if any difference at the drag strip. Switching to a 750 DP picked me up about a tenth on my particular combo over the other two. Can't say if I got each one "optimized", but they were all extensively tinkered with - jets, squirters, pump cams. I still tinker because any change to the car and engine can change the carb "tune-up".

A double pumper will launch the car harder IF you can get it tuned right. In my opinion, it is usually harder to tune a double pumper than a vacuum carb, especially if you don't have a lot of gear and converter. I don't think you do. So, in my opinion, the 750 vacuum should be an overall better performer with the vacuum secondaries.

With the 650, you can always test & tune at the track when you have the time, money and tuning parts.

 

[Salty Dog]

750 baby!

 

[sireland67]

750 vacuum is a really nice carb that is easy to tune and runs great on the street.
650 DP will also work but it will take more fine tuning to get it to hit just right.
Try them both and see which one works the best for your combination.

 

[RustyRatRod]

750