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Discussion Starter · #1 ·
I currently run a 600 cfm edlelbrock carb, but I have talked to several people who think I should go bigger (more cfm). I have a 10:1 compression 289 with edelbrock rpm heads, intake, 1 5/8 headers and a [email protected] cam. What do you think is the best cfm size for steet/strip duty? I have also run a holley 650dp but it didn't make much difference in power from the edelbrock. Is 750 too much carb?
 

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The most CFM you can pull is about 550 cfm.
D X 2 - 5%
Any larger is really a waste and distroys your bottom end response.
Smaller primaries are also a plus in that the response from them is faster.
Hence the AFB and Rochester primaries being small.
Vacume or Mechanical secondaries is a personal choice.
A well tuned mechanical is my preferance, but it takes a lot of tweaking to tune it correctly to your machine and uses.
Vacume secondaries are more suited to a daily driver where demands vary so much.
 

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Could use more info like what kind of intake,gears,car weight,type of trans etc.Generally a 600-650cfm works well on street/strip cars.
 

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Try a check with a vacuum gauge: Hook the vacuum line to a manifold vacuum source (not ported) and run the line inside the car to the vacuum gauge. Have someone read the gauge while you run up to redline through the gears (whatever your personal redline is). If the vacuum reading stays at zero or maybe goes to 1", your carb is big enough. If the vacuum reading climbs as you get near redline, the carb is acting as a restriction to airflow (or the air cleaner is the restriction).
 

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my Biggs 650DP is ten times better than the edelbrock I had previously run. I couldn't imagine a better performing carb on my 289. If you want it to run right be prepared to do some fine tuning. Out of the box my edelbrock ran waaaay to rich and idled like crap. The biggest pain was finding the right primary jet and metering rod combination that would work. I just gave up and bought a custom carb and it worked out great.
 

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the 600 is more than enough, but if it isnt calibrated and hasent been flowed how would you know if it works. send that 600 out to be modifed and calibrated to your combo. once its back on use a wideband to dial in the jetting if needed.
 

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A carb's CFM rating isn't "how much air it will flow", it is how much air it flows at a certain amount of manifold vacuum (1.5" Hg I believe). So if your engine "only needs 550cfm" and you put a 550 carb on it, you will be pulling 1.5" Hg, or about 0.74psi of vacuum. The more vacuum at WOT, the less dense air you get, and the less power you make. Now, this doesn't mean bigger is always better, but you gotta decide if you're willing to give up a little driveability for a little more top-end power. That being said, I just finished upgrading the stock 650dp on my 289 to a 750dp with the choke horn milled, and I've been driving it for about two weeks now and noticed no loss in street/part throttle performance, but it's MUCH stronger at about 1/2-2/3 throttle (just the primaries) and feels like it picked up WOT power as well, although I won't know how much 'till I get the jetting dialed in and take it to the track.
I think the 650dp when jetted right will make better power than your edelbrock 600, and even a 750dp would be fine, although you might notice a little loss in mileage. As others said, it also depends on if you're running an automatic or manual, heavy or light car, and tall or short rear end gears whether or not you'll really feel the difference.

_________________
'86 Bronco fullsize, 460, E4OD
'85 Ranger, 340hp 289, T5


<font size=-1>[ This Message was edited by: Motorhead on 3/28/06 1:33am ]</font>
 

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You can go bigger with a dual plane intake.
 

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what trans, gears, stall if auto, tire height? dp usually wants at least 4.10 gears and over 2ooo stall.
 

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Discussion Starter · #12 ·
I am running a t-5 trans with 3:50 gears and a 25" tall tire in a 66 mustang fastback. The intake is a dual plane rpm air gap, msd distributor, total timing set @37' let me know if more info will help.
Thanks for all of your help so far, this forum is great.
 

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I currently have a custom built Holley 850 dp with annular boosters on a mild 289 that likes to be shifted at only 6,000 rpm. The car picked up over 5 mph in the quarter mile over the previous tuned 625 Carter AFB. Better lowend, part throttle, and idle than the Carter. This carb only works because of the annular boosters and whatever tricks the guy did to it.

I would say you should be in good shape with a 650 dp and dog leg boosters. Annular boosters can allow you to go bigger while increasing lowend torque and top end horsepower.

It really depends on what your goals are for the car.


<font size=-1>[ This Message was edited by: 289nate on 3/28/06 3:59pm ]</font>
 

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I ran a Holley 500 CFM 2 BBl with a special ported intake and my 289 ran great (9.7:1, ported head, headers, Performer cam...)

Swapped in a 600 DP Holley recently and it did not run a smooth. I did give me better gas mileage. I probably need to increase the main jet size but I might go to a Performer carb.

I can't see going to a bigger carb... maybe even smaller might be better.
 
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