Carburetor Question

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Joined
Apr 19, 2011
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Location
San Jose, CA
My Car
1971 M-code Grande
What size carb would a quench 351C 4V have come with from the

factory? If you do the math for a 351, 600 cfm is within range.

But the Cleveland is half 351 and half 429, how does that alter

the math? My current is a Holley 670, 80670 Avenger. The Boss 302

came with a 750, I think. It has been decided we don't need headers

so the next best option is the appropriate carb size for optimizing

this cars performance. We are going to stay with Holley's 4150 style

Avenger system and vacuum secondaries.

mike

 
The 4300D that my car came with is 750 cfm. I think all Q and R codes in 72 were that size.

 
Mike, The original would have been 600 cfm according to everything I've read back in the day and recently. The 670 should work well for what you are doing IF you got a good one. I've used two of these in the last several years. One good, the other was returned because there was no way to make it idle. Holley did an exchange. The carb on the Boss 302 was rated at 780 cfm. The only reason the 780 worked reasonably well on the B2 was it was vacuum secondaries with the purple spring causing the secondaries not to open fully, if at all, until way after the factory rev limiter engaged. Chuck

 
For what it is worth:

351 Cubic Inch

0.203 Cubic Feet( CI/(12x12x12) ) (About 1.6 gallons if fluid)

6000 RPM At Crank

3000 RPM At Intake(Crank RPM/2)(Lots of people forget this)

610 CFM ( CF x RPM)

0.8 Inefficiency Reduction Between Piston and Carb

487 Net CFM( CFM x Inefficiency )

302 Cubic Inch

0.175 Cubic Feet

6000 RPM At Crank

3000 RPM At Intake

524 CFM

0.8 Inefficiency Reduction Between Piston and Carb

419 Net CFM

429 Cubic Inch

0.248 Cubic Feet

6000 RPM At Crank

3000 RPM At Intake

744 CFM

0.8 Inefficiency Reduction Between Piston and Carb

595 Net CFM

 
What size carb would a quench 351C 4V have come with from the

factory? If you do the math for a 351, 600 cfm is within range.

But the Cleveland is half 351 and half 429, how does that alter

the math? My current is a Holley 670, 80670 Avenger. The Boss 302

came with a 750, I think. It has been decided we don't need headers

so the next best option is the appropriate carb size for optimizing

this cars performance. We are going to stay with Holley's 4150 style

Avenger system and vacuum secondaries.

mike
i still have my stock carb...Its a 4300D ..715cfm spread-bore ...i have a 1973 ..351 cobrajet 4v open chambered heads....Im pretty sure all 4300d's where 715cfm..Even the boss...But i cant say for sure...mine is.....and alot of sites state the same.

 
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The Boss 351 and the HO in 1972 both used a 715 CFM carb an Autolite 4300D. Over the counte a 780 CFM carb and intake combo was a common upgrade.

I'm running a 700 double pumper and It works very, very well, but I believe a 351 can use more maybe even 850 cfm with a solid lifter aggressive cam and a 7000 rpm redline, all of which are easy to do in a cleveland

A single intake valve flows 300 plus CFM at maximum lift which is 50 % more than other comparable sized v-8's, considering that the VE is either well over 100 or cylinder head flow is 50 % higher so the carb should be 50% bigger so a 650 may be fine on a 351 Windsor, but on a cleveland it will not allow maximum RPM's or power in my opinion

If I were starting from scratch I'd try a 750, but I think mine can use more than 50 CFM additional air flow

also keep in mind cfm ratings without a reference to inches of vacuum do not allow accurate comparison,

 
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The Boss 351 and the HO in 1972 both used a 715 CFM carb an Autolite 4300D.
Do you have a source for this? I am using BOSS 351 Ford Supplement and it lists the carb as 750.

Over the counte a 780 CFM carb and intake combo was a common upgrade.
This carb was a HOLLEY, and I have an NOS upgraded intake

Don't have the Holley...donations accepted.

 
I'm running a Holley 0-4779-3, 750cfm dp with mechanical secondaries and it's jetted way up. 75's primary, 84's secondary and it screams until I let off.

Was running a 4778, 700cfm,dp with mech sec. before I rebuilt the engine and it performed very well.

I'd say if you have a mild engine and you are going to run vacuum secondaries, then either your 670 jetted up and maybe nozzled up would be good, or bump to a 0-4118 725cfm and maybe jet it up a little if you have to.

I think the 750(3310) vac secondary may be a little heavy off the line. It would probably run fine, but just not perform to it's capacity. It's always better to be lean and go up, then visa versa.

 
What size carb would a quench 351C 4V have come with from the

factory?
So after 11 posts, what answer are you going with?
Keep the one I got. A Holley 670, vacuum secondaries, electric choke,

dual fuel lines but not double pumper.

mike

 
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