I'm getting one of these 2 carbs to replace the ailing q-jet. I'm kinda stuck on which one though. I thought I might post what I see as pros and cons and see what you guys think.

600 squarebore
PROS-new; simpler to work on
CONS-price; lower flow rate; less adjustable (metering plate on secondaries)

650 spreadbore
PROS-much cheaper; small primaries for MPG; more flow (more than the rated cfm, like 680)
CONS-may need rebuild; older technology

Everything else is similar/same.

My car is 98% street driven, so reliability and MPG are key. Would there be a major difference in performance? How about mileage? I'm leaning toward the spreadbore, so how hard is it to rebuild a holley vac. sec? Any opinions or advice is much appreciated. BTW, its holley all the way, not really considering any other one. Thanx

 

What engine? Auto or manual? Vacuum secondaries or DP?

 

I went from a newer 600 VS to an older spreadbore 650 DP...prolly the exact same 2 carbs you are talking about.

I only did it because I had a manual and 3.73's...and the VS carb was bogging on every shift.

is it the 6210 650 spreadbore? Thats what I have. They have a funky float bowl setup I don't like, and I don;t like spreadbores either. If I didn't have the stick..I would have stayed with the 600VS. You won't see much of a performance difference with only 50cfm difference.

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I agree, 50 cfm in a street car is nothing. A square bore has better fuel distribution. The 600 squarebore primaries are small enough to get the same mileage if both are tuned to maximum efficiency. The metering plate is usually about right and can be converted to a metering block with jets if needed. Go with the squarebore.

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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, current red metallic paint. Lots of other stuff...
82camaro