Carb Sizing

[Tongue Pirate]

If you are pushing on the rpms then yes. I ran a 454 at 40 over with a 600 double pumper & it ran better than a 750 because of the low end response it needed due to the large gearing in that car. If you like to putt around town & go out on leisurely cruises then keep the 600 on there.

[DAVID GAGNARD]

I think a lot depends on your engine build and the rpms you want it to run the best at.......

I have tried no less than 6 carbs (from 600 cfm to 770 cfm)(both vacum and double pumpers) on my 350 hp, 351-W over the years and a 20 year old Holley 600 double pumper I rebuilt gave the best results, both on the drag strip and on the street mpg wise....

My motor rarely sees anything above 5500rpms........most street driving/cruising done at or below 3000rpms and she still gets 23 mpg cruising on the interstate, the motor is in a 65 Mustang Fastback.......

David

[Tongue Pirate]

I refuse to sell my 600 dbl pumper cause i like it so much. well, not quite as much as the webers

[Pete Munroe]

You can ALWAYS spend more money later...like some of the fellas posted, what are your plans for the car? Street mainly?...keep the small carb for the torque.

I just had the opportunity to swap out my 750 dbl pmpr for a 650 dbl pmpr for the weekend.

(Hyde....care to swap out the Webers for a weekend?)

After an open track weekend at ButtonWillow raceway with the Pantera Club I would report:

the engine starts about the same, better?
seems to idle with less fumes
otherwise runs about the same/better? as with the 750.

The engine is 289/347, cam a mild roller, 224/228, TF heads, max rpm with the chip is 6000.

The 650 has 67's in the primaries/73 secondarys, the 750 has 73's/80's

There are not many points on a tight road track where you are at max RPM for more than a few seconds, and once I am at 6000, thats it...so more carb isn't going to help me rev higher. (could change the chip to 6500 but wear goes up with RPM so I would rather get lots of events on the engine rather than see the 500 RPM on my top speed)

For the street and a tight track, torque is better...for the drags HP is better.

You have the 600 carb in hand, RUN it...when you really need more to go drag racing or serious track, or get spanked BAD on the street...get the bigger carb and a dyno tune.

Above all, HAVE FUN, if you want braggin' rights...go ahead and get the big carb and dyno tune...see what the engine can do and frame the dyno sheet!

I would like to have dyno sheets for a range of carbs just out of curiousity...this stuff is Sooo much fun...

Pete

[Tongue Pirate]

Trade? You crazy?!!!

if you have the option have him dyno it with the 770 & he 600 YOu may find something in the results to sway you one way or the other.