I was told to stick to 800 CFM or higher, not sure how true advice is.
I spoke to one guy who has his own site about mustang performances. he owns a 66 fastback with a 408 enfine running 950 CFm. Here is what he told me, let me know what you think. I was thinking about the avenger 670cfm but if you guys agree with him that I might only lose perfrmance then I'll have to get the avenger 770 CFM.
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I noticed that you have a dual plane intake (Performer RPM?). If that is the case, the rule of thumb is to run about 20% larger carb. The reason is that half the carb feeds half the engine where as a single plan allows the whole carb to feed the engine. I ran a 950 CFM on my 408W and made 454 rwhp. It was bout perfect for my setup. I would guess a 670 will cause you to lose performance. I am using a 750 cfm now, but that is because I am running a supercharger. I was referring to the intake manifold (Edelbrock Performer RPM). There are two designs for intake manifolds, the dual plane and single plane. The dual plane creates more low end torque and the single plane is for high rpm power. If you are running a dual plane intake manifold, then you don’t want a too small carb, you want a little larger carb. Most people don’t know this, so be careful when asking advice. greg.
I think a Holey speed demon is the ideal carb, if you are considering performance and reliability. If i had a 302 stroked to 347 then i think the speed demon 650cmf would work well, if your talking about a 351 stroked to 408, then a 750 should work just as well. it depends allot on the cam you will be running also. A big block is another matter all together, so 850 to 900 with a victor intake may be the ticket. i think what really needs to be discussed here is what carb is best for what application. A stock quadra jet is very dependable on a 302 application, but for performance the speed demon offers a good compromise between the two.
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DSS 331 stroker, AFR 185 heads, Performer rpm 2 intake, Accufab 75 mm race TB, 30lb injectors, 80 mm Pro-M mass air, Extreme energy cam 266.
Anderson ford power pipe the big one, Ford motor sport shorty headers, Bassani x pipe custom cat back with flows, World class T5, center force duel friction clutch.
Edelbrock Carb in the 600-650 range is plenty especially with a automatic trans. If it had a radical cam profile I'd step it up to 750 MAYBE, depending on how you drive the car. The advice that you got from the other site isn't real good advise. 800+ cfm is way over carbed for a street motor, it's a common mistake, every one tends to think bigger is better but when it comes to carbs that's just not the case. All you really need is 6-650 cfm on an engine that size. It will run better AND faster with a correct sized carb. 800 is way too much.
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1966 Fastback
1997 V6 Mustang
1998 GT
"Government is not the answer to our problems, government is the problem."
.I looked at the pictures, very nice looking Stang. I noticed that you have a dual plane intake (Performer RPM?). If that is the case, the rule of thumb is to run about 20% larger carb. The reason is that half the carb feeds half the engine where as a single plan allows the whole carb to feed the engine. I ran a 950 CFM on my 408W and made 454 rwhp. It was bout perfect for my setup. I would guess a 670 will cause you to lose performance. I am using a 750 cfm now, but that is because I am running a supercharger. There are two designs for intake manifolds, the dual plane and single plane. The dual plane creates more low end torque and the single plane is for high rpm power. If you are running a dual plane intake manifold, then you don’t want a too small carb, you want a little larger carb. Most people don’t know this, so be careful when asking advice
The guy stated what I quoted from him. He said by me having the dual plane manifold I neeed to stick to high CFM or I lose lots of power.
The guy who gave you the advice has no clue. It's all related to the engines total air flow, cyl. heads, cam, etc. Too big a carb will cause you to lose power and have no throttle response. A dual plane intake is fine for the street. A carb in the 650 to 700 cfm range is fine. Another thing to do is to drop the center divider in the intake 1/2" or run a 1/2" carb spacer. This will give you +12-15 hp.
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07 GT premium in Grabber Orange. 5spd. manual w/IUP, plenum cover,3.55's, Roush scoop, 14" antenna, C&L CAI, Bamachips 93 Predator tune, Steeda U/D pulleys, Hurst shifter, FRPP GTA's, CDC chin spoiler, CHE LCA, BMR panhard bar, Eibach Pro Kit. FRPP 17" black bullitts and 255R45 Firestones, Spydershaft aluminum driveshaft, MSD coils, D-Specs, Prothane motor mounts, BMR LCA brace, Steeda panhard brace, BMR adj. UCA, Webelectric sequentials, Mikronited FRPP 4.10's.
Looks like you have a pretty healthy 383ci 351W stroker. The "oversize with dual plane intakes" rule is valid, and all things considered, I'd be tempted to stay with your current carb and get it tuned well. Or, you could put 600cfm guts in a proform body. The prodorm bodies are much tougher/better/more HP than a regular holley and the way to go IMO.
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66 coupe 5.0/T5, home-brewed power 4 wheel disc setup, 350hp+, looks like it belongs in 1968
I do have a proform body on it but has holley ends. I guess I will keep it but have to find a good tuner. I might go to a stock or msd vacuum distributor over the non vacuum MSD one I currently have. I heard the vacuum distr. woul run more effient in fuel consumption
I might go to a stock or msd vacuum distributor over the non vacuum MSD one I currently have. I heard the vacuum distr. woul run more effient in fuel consumption
Yep, that's a good idea.
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66 coupe 5.0/T5, home-brewed power 4 wheel disc setup, 350hp+, looks like it belongs in 1968
I'd go with a 750, its goof proof. If you dont plan to wind it out though, beyond 5500 or so or plan to ever take it to the strip or engage in a stoplight mingle, I would go with around 700. If youre REALLY not in ANY way concerned about how fast the car would run the 1/4 mile or drag racing and just want to have fun you can go smaller and you will get even better throttle response, but I wouldn't even want to put anything as small as a 670 on that. A smaller carb will give better throttle response, but they suffocate the engine when the revs get up if its too small. Did resetting the timing fix the problem with the rough running?
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I like to let 'em stick with me for first and second, then I put the hurt on 'em when I chirp third ~
1967 Plymouth GTX, work in progress.
440 cubes (thats 7.2 litres for you modern guys)
375 horses
480 ft lbs of torque
MODS: Direct Connection Purple Shaft cam
well if that's thecase I migh as well just keep what I have on now. Unless, you think the upgrade of the proform main body would of automatic upgraded the 750 CFM holley to a 850-900 CFM by just adding the proform. Let me know b/c I'm not a guru of carb, still learning.
You're probably going too large on the carb you really only need something in the 650cfm range, anything more than that does nasty things to your motor like dumping to much gas in the cylinders and washing away needed oil which shortens engine life. When it comes to carbs Bigger is NOT better...or even faster in most cases. An oversized carb will kill your throttle response. Consider that the 289 Hi-po which had a pretty stout solid lifter cam came with a 600 cfm carb. OK so your motor is a bit bigger (but what are the specs on the cam?) lets compare motors that are similar is size to yours. The Hi-Po 390 Big Block came with a 600 cfm carb. The Boss 351 which is perhaps Fords most under appreciated motor came with a 715 cfm carb as did the 429 Cobra Jet engines, the Super CJ's came with 750 cfm carbs and the Boss 429 which had HUGE valves and pistons the size of basketballs came with only a 780 cfm carb. You really don't need a carb bigger than what topped a Boss. I don't know of any way to check cam specs with the cam installed in the car but if it has a reasonably normal idle all you need is a carb in the 600-650 range. If it has a very radical idle it may be able to handle a bit more but not THAT much more. Beware the urge to overcarb, along with over camming it's one of the two biggest mistake most people make with their cars.
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1966 Fastback
1997 V6 Mustang
1998 GT
"Government is not the answer to our problems, government is the problem."
preacher I think you were preachinh to 302boss for his advice lol
I might go withthe 670 avenger from holley like I was thinkign of doing. You made good points on the CFM sizes on thos engines. 670 CFM sounds like a good number and its not far from the 715 CFM from the 429 engine
Review 4 of 11
Price Paid: $350.00 from summit racing Year / Model Reviewed:
holley 3310 - 670cfm avenger Summary:
i've been adjusting carbs for 15 years on the road and seas. never had a problem with holley, until now! this 670 avenger is a poor carb for idle fuel control! wets plugs all the time at idle. Can't see extra fuel dripping in anywhere, from bowls, jets or power valve. i'm told that the plating on these carbs is because they failed the casting pourosity test! bad casting and charge premium to plate the carb! even the clear sight plugs react to fuel and fog over in the bowls to adjust the float level! give me a good brass plug to adjust it any day! And what's up with the poor quailty gaskets lately? tear way to often when rejetting. my trick has been to use Chapstick to coat the gaskets and prevent sticking to the bowls and body. still a bad paper gasket... and expensive to replace! tried to contact holley direct, the carb has a life warranty. foned and e-mailed, no help. Give me a Proform billet aluminum carb at 750 cfm any day! Makes my built baby 340 Challenger run with the big blocks! Yes 100 dollar premium price over the holley, but it's worth it! Holley's quality has suffered since being bought up by it's parent company.... they used to be the carb to beat. now they are getting beat... Strengths:
simple to dismantle and reassemble.. used to be easy to tune, but are finicky anymore.. quality suffering? Weaknesses:
idle fuel control poor! clear sight plugs for float fuel level adjustment fog and soften with exposure to fuel! poor quality gaskets.
to fuel! poor quality gaskets. Similar Products Used:
Proform 750 cfm carb with mechanical secondaries and billet machined metering blocks and main body. Awesome!
I was told to stick to 800 CFM or higher, not sure how true advice is. 
came with only a 780 cfm carb. You really don't need a carb bigger than what topped a Boss. I don't know of any way to check cam specs with the cam installed in the car but if it has a reasonably normal idle all you need is a carb in the 600-650 range. If it has a very radical idle it may be able to handle a bit more but not THAT much more. Beware the urge to overcarb, along with over camming it's one of the two biggest mistake most people make with their cars.
