600 vs 750 Holley

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Snake

Snake

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Right now I have a well tuned 600 vac sec Holley on my 360,I now have the 3310-2 750 vac sec ready for rebuild.What difference in performance can I expect going from the 600 to the 750,I know my gas mileage will be different tho.Share your opinions please.My build is 360 20 over,202 J heads rebuilt no porting,LD340 intake,MP cam 284-474, headers,2400 stall, 323 gear,727 with Trans go 2 shift kit.
 
I have 66 Cuda with 360 280H magnum cam edelbrock airgap intake. I had both 600 Holley and 3310 Holley on car. It runs better with 600 but was a lot quicker with 3310. The 600 is still on the car but I'm goin to try to tune 3310 on it when I get a another chance. For the street the 600 is better. IMHO
 
.............Hey Don.........u should see a pretty good performance improvement.........wont be much difference in mileage if u keep ur foot out of it.........kim........
 
oldkimmer said:
.............Hey Don.........u should see a pretty good performance improvement.........wont be much difference in mileage if u keep ur foot out of it.........kim........
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More power yes,mileage not to worried.Its all rebuilt now,I have 70 jets up front stock plate in the rear, 4.5 power valve,#31 nozzle,light spring for the secondary's, all blue gaskets.Maybe try it out just before I put the Dart away.Thanks again.
 
The 750cfm carb will give you a very slight low end performance loss, mid range should be slightly better, but the high end will be substantially stronger.
IMHO your motor was undercarbed. The 750 will be just what the doctor ordered.:toothy8:
 
A 750 will work better if you add a Quick Fuel vaccum secondary unit that if very adjustable.
 
The 750 will run even better if you throw alittle N2o at it lol.
 
IfItsGotWheels said:
The 750cfm carb will give you a very slight low end performance loss, mid range should be slightly better, but the high end will be substantially stronger.
IMHO your motor was undercarbed. The 750 will be just what the doctor ordered.:toothy8:
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I agree,she screamessss and throttle response from idle all the way up with the 600 is great but I know there's more to be had.It never endssssssssss
 
I pondered the exact same thing last year, Snake. After some schooling I switched from a 600 holley vs to a 750 holley dp. Let's just say your mileage will go down slightly but your smileage will definitely go up.:D
 
MoparLvr said:
I pondered the exact same thing last year, Snake. After some schooling I switched from a 600 holley vs to a 750 holley dp. Let's just say your mileage will go down slightly but your smileage will definitely go up.:D
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Thatsssssssssssss just what I want to here.:cheers::cheers::cheers::cheers::cheers:
 
Thermoquads used on stock 360's were way bigger then 600 I would tend to think your under-carbed too. Your using 70 jets now in the primaries and 3310's would normally have 76's. It's only 75 or so more primary cfm. I would think if the secondaries were well tuned and you drive the same you would see little difference in MPG in everyday driving. I ran a 3310 on my 70 roadrunner back in the 70's and could get 16.7 MPG on the highway with 383 /727 and 3.23 gearing.
 
furz4 said:
Thermoquads used on stock 360's were way bigger then 600 I would tend to think your under-carbed too. Your using 70 jets now in the primaries and 3310's would normally have 76's. It's only 75 or so more primary cfm. I would think if the secondaries were well tuned and you drive the same you would see little difference in MPG in everyday driving. I ran a 3310 on my 70 roadrunner back in the 70's and could get 16.7 MPG on the highway with 383 /727 and 3.23 gearing.
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Right now gas mileage sucks any way.
 
I have had 600, 670, 725 and 750 vacuum secondary carbs on my 360.

The throttle response and mid range performance with the 600 and 670 is far superior to the 725 Demon or the 3310 750. The 725 and 750 had a slight top end (above 4500 rpm) over the 600 but no advantage over the 670. The 600 and 670 get about 5mpg more than the 725 or 750.

If you have the 750 go ahead and give it a try but if your car is primarily a street car I bet you will be putting the 600 back on. FWIW, my Barracuda has run a best of 13.7 @ 102 mph in the 1/4 with a very traction limited 2.2 sec 60'. The 102 trap speed should push the car very close to the 12's if the traction issues were sorted out.

BTW, comparing a square bore Holley to a Spreadbore Thermoquad is an apple and oranges comparison. The Thermoquad has primary bores that are smaller even than the 600 and the secondaries are never fully utilized in a stock or near stock small block.
 
dgc333 said:
I have had 600, 670, 725 and 750 vacuum secondary carbs on my 360.

The throttle response and mid range performance with the 600 and 670 is far superior to the 725 Demon or the 3310 750. The 725 and 750 had a slight top end (above 4500 rpm) over the 600 but no advantage over the 670. The 600 and 670 get about 5mpg more than the 725 or 750.

If you have the 750 go ahead and give it a try but if your car is primarily a street car I bet you will be putting the 600 back on. FWIW, my Barracuda has run a best of 13.7 @ 102 mph in the 1/4 with a very traction limited 2.2 sec 60'. The 102 trap speed should push the car very close to the 12's if the traction issues were sorted out.

BTW, comparing a square bore Holley to a Spreadbore Thermoquad is an apple and oranges comparison. The Thermoquad has primary bores that are smaller even than the 600 and the secondaries are never fully utilized in a stock or near stock small block.
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Well said but my foot is into it almost all of the time even for a street car.
 
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