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Holley 650cfm spreadbore for a 300?

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CoupeBoy
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Holley 650cfm spreadbore for a 300?

Post #1 by CoupeBoy » Fri Feb 05, 2016 11:08 am

I was cleaning shop last weekend, *trying* to organize my spare parts. And when I flipped over a Holley carb that I grabbed from Dad's house, I realized for the first time that it was a Spreadbore, not a squarebore.

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F-250Restorer seemed to have good luck with a straight quadrajet
QuadraJet on a 300 -- FordSix Forum

Has anybody else tried one of these?
Thoughts or opinions on what type of performance I can get out of this on a 300?

Thanks,
-ron

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Re: Holley 650cfm spreadbore for a 300?

Post #2 by bubba22349 » Fri Feb 05, 2016 11:13 am

Haven't used one on a 300 but I put one like that on my Father InLaws 1979 F150 (460 engine) it was a great working carb. :thumbup:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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Re: Holley 650cfm spreadbore for a 300?

Post #3 by CoupeBoy » Fri Feb 05, 2016 11:16 am

Those tiny primaries look promising for low RPM MPG.
And as a Holley, it should be very tunable.

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Re: Holley 650cfm spreadbore for a 300?

Post #4 by old jupiter » Fri Feb 05, 2016 12:00 pm

My notion is that a 4bbl of that size is what would ordinarily be used on a V-8 . . . a standard Detroit V-8 with a dual-plane manifold . . . which (disregarding the very small "balance" slot) in effect turns the 4bbl into a pair of 325cfm 2bbls, with any on cylinder drawing A/F from only one of those 2bbls. But if you put that same carb on something like a Clifford or Offy C manifold on a 240/300, each cylinder is drawing from the entire 650cfm. Seems like too much on a street machine, and evidently Detroit thought so too, which is why all Detroit V-8s had dual-plane manifolds. But if this carb was mounted on an Offy Dual-Port, or if you fabricated a divider and screwed it into the middle of your Clifford or OFFY C (so that half the carb feeds cylinders 1/2/3, and half feeds 4/5/6) then you've got what Detroit chose . . . . :hmmm:

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Re: Holley 650cfm spreadbore for a 300?

Post #5 by bubba22349 » Fri Feb 05, 2016 12:17 pm

Yes it was very tune able and got about 1 1/2 to 2 MPH better then original carb but of corse I also did some other mods to that truck. The back story was my father in law came to me and asked if I could get him a little more power out of the 460. His close friend another Contractor (and they both worked out of the same construction yard) he had a nearly identical 1978 F150 and they raced each other often. I went to work on it doing some simple internal and external mods in secret, tuned it, and kept the engine and truck looking almost totally stock on the outside. When it was done in the next "battle of the 460's" the when they lined up my father in law just walked away from his friends truck. His friend just couldn't understand being beat that bad so he sent his truck to the next door auto repair shop for a rebuild. Then he tried again but he still could never beat my father InLaws truck. :rolflmao:
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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Re: Holley 650cfm spreadbore for a 300?

Post #6 by CoupeBoy » Fri Feb 05, 2016 1:46 pm

old jupiter wrote:My notion is that a 4bbl of that size is what would ordinarily be used on a V-8 . . . a standard Detroit V-8 with a dual-plane manifold . . . which (disregarding the very small "balance" slot) in effect turns the 4bbl into a pair of 325cfm 2bbls
Comparing 2bbl to 4bbl carbs has always been a bit of voodoo for me, inconsistent testing procedures suck.
holley 390 vs 450 cfm 4 barrel carb. -- JeepsUnlimited.com wrote:"You can not directly compare the CFM rating between 2BBL’s and 4BBL’s as the test pressure that is used to measure the CFM is different between the two. The 4BBL is measured at a test pressure of 1.5 inches of Mercury (Hg) of pressure drop, while the 2BBL is rated at 3 inches HG. To convert the 2BBL into 4BBL use the following formula:
4BBL Flow = 2BBL Flow / 1.414.
So that 500 CFM 2BBL Carb actually flows 353.606 CFM on the 4BBL scale."
old jupiter wrote:with any on cylinder drawing A/F from only one of those 2bbls. But if you put that same carb on something like a Clifford or Offy C manifold on a 240/300, each cylinder is drawing from the entire 650cfm.
If I go with one, I was planning on starting to search for a DP like F-250Restorer used in his thread
old jupiter wrote:Seems like too much on a street machine, and evidently Detroit thought so too, which is why all Detroit V-8s had dual-plane manifolds. But if this carb was mounted on an Offy Dual-Port, or if you fabricated a divider and screwed it into the middle of your Clifford or OFFY C (so that half the carb feeds cylinders 1/2/3, and half feeds 4/5/6) then you've got what Detroit chose . . . . :hmmm:
Is this the same Detroint that decided an Autolite 1100 1bbl was sufficent for 300 cubic inches of i6? I take what they did with a grain of salt, bean counters and 'acceptable' performance with 'minimal customer issues or complaints'. Almost nothing they did was for all out performance or all out economy.

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Re: Holley 650cfm spreadbore for a 300?

Post #7 by Harte3 » Fri Feb 05, 2016 7:56 pm

"...each cylinder is drawing from the entire 650cfm. Seems like too much on a street machine,..."

Each cylinder and the whole engine for that matter are only drawing as much as they can use. One cannot force feed an engine with a bigger carb alone. At WOT with a properly set-up carb it will only draw as much as it can use and no more and will probably not be near the full capacity of the carb. According to Vizard the Wizard there is theoretically no such thing as a too-big carb. Having said that, I will not be trying a 1250 Dominator on my I6 any time soon...
'83 F150 300, 0.030 over, Offy DP, Holley 4160/1848-1 465 cfm, Comp Cam 260H. P/P head, EFI exhaust manifolds, Walker Y Pipe, Super Cat, Turbo muffler, Recurved DSII, Mallory HyFire 6a, ACCEL Super Stock Coil, Taylor 8mm Wires, EFI plugs.

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Re: Holley 650cfm spreadbore for a 300?

Post #8 by old jupiter » Sat Feb 06, 2016 12:35 am

Come on, Harte, you know I'm not talking about "force-feeding" anything but about having a good strong vacuum signal at the venturi(s), . . . which is why you said you aren't going to try to get your six to draw against a 1250 Dominator. As for your idea that, "At WOT with a properly set-up carb it will only draw as much as it can use and no more and will probably not be near the full capacity of the carb," maybe, but it seems to me that for WOT operation ideally you want the carb size that has the butterflies all the way open just as you hit the maximum power the engine can put out, to reduce pumping losses. If you had lots of time, a way to chose a carburetor (all else being equal) would be to keep trying bigger and bigger carbs while dynoing your engine until you get to a big enough carb that still has the secondaries partly closed when the engine is pulling its hardest . . . then go back to the previous carb size.

As to the different protocol for measuring 2bbls and 4bbls, yeah, and that makes my point more strongly. Whatever, I'm not saying that bigger carb can't be made to work at all, or that you shouldn't try it, I'm just GUESSING (repeat, repeat) that you'd get snappier throttle response, even given those small primaries, and better metering transitions all the way up the range, by having each cylinder draw on one side of the carb. As to not trusting Detroit, I might take your general point, but I don't think it applies very well to the V-8s, which were not the cheap economy engine option, but came in premium cars and performance versions . . . which still had dual-plane manifolds

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