Dual Carbs?
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Senior User
Joined: Feb 2004
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From: Redding, CA
Dual Carbs?
I was kicking around the idea of runnin twin 600cfm Holley carbs on my 460 big block 
. Anybody done anything like this? What are your impressions? Anything special I need to do to make it work? Oh, I will be rebuilding the engine and make it perform a lot better.
Thanx,
Red460
. Anybody done anything like this? What are your impressions? Anything special I need to do to make it work? Oh, I will be rebuilding the engine and make it perform a lot better.Thanx,
Red460
Thread Starter
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Senior User
Joined: Feb 2004
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From: Redding, CA
Wow thats something I didn't really think about. Basically what it comes down to is I was looking for a way to be different and have performance. So I think ill just swap it over to fuel injection.
Thanx for you help Brad.
Red460
Thanx for you help Brad.
Red460
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From: Normal, IL
Originally Posted by Brad Johnson
It would look nice but is not the best choice from a performance stanpoint. It would kill the intake charge velocity and punch a big hole in your low end and low rpm throttle response.
Brad
Brad
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Generally, I would agree about killing the low end, but, if the runner length is long enough, and he drops to 450 cfm carbs, he'd have very good throttle response, and a killer top end.
Brad
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From: Normal, IL
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Post Fiend
Joined: Mar 2004
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From: Union, Washington
If it was me, I'd stick a pair of Holly 390CFM carbs on it. I learned many years ago to use a lot of little holes instead of a few big ones. Ran a very warmed up 428SCJ with a short runner cross ram back in the early 70's. Used a pair of 600's first and was dead until above 4000 rpms. Changed to a couple of 450 cfm carbs and was better but still stumbled at the low end( below 2500rpms) if you didn't rev the more hard then dump the clutch. Change to 390 cfm carbs(vacuum secondarys) and was good all around and still turned 7200rpm's in the lights of the quarter mile.
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I'll be the opposition here. I ran dual Dominators on a stock 429 SCJ with headers in my #4000 Spoiler & picked up 60' times & ET, took some tuning. It's only going to take in as much as it needs & the last toy I just finished LOVED the 2 600 Holleys.
Mountain Pass
Joined: Apr 2004
Posts: 132
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From: Montana
I have to agree with bear 45/70. I think that smaller carbs are the way to go.
I witnessed a car once that was so cammed up that it would not idle. There was 850 cfm on top of the motor and if flooded everytime it was started. Was only good when coming out of the hole at high rpm's. Soon the 850 was swapped for a smaller (650 I think) carb. Ran much better and was just as respectable.
Bigger is not always better! The right carb for the right engine is the key. Some engines can take a bigger carb some can't. I am not sure you can compare Cj's and SCj's to a regular aspirated motor. Night and day otherwise they would not be differentiated in terms of the letters CJ and SCJ. Hope this helps.
I witnessed a car once that was so cammed up that it would not idle. There was 850 cfm on top of the motor and if flooded everytime it was started. Was only good when coming out of the hole at high rpm's. Soon the 850 was swapped for a smaller (650 I think) carb. Ran much better and was just as respectable.
Bigger is not always better! The right carb for the right engine is the key. Some engines can take a bigger carb some can't. I am not sure you can compare Cj's and SCj's to a regular aspirated motor. Night and day otherwise they would not be differentiated in terms of the letters CJ and SCJ. Hope this helps.
Post Fiend
Joined: Mar 2004
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From: Union, Washington
Back in the hey day of drag racing, the 60's and 70's, I had a Holley rep tell me at the Tulsa race in 1970 that the 800CFM double pumper carb was to much for my 428SCJ. Went back to the stock 735CFM and the car was quicker(ET) but slower(MPH). In drag racing ET is everything, top speed is for record books. Called the guy at Holley when I found a tri-power off a 406 that had 920CFM and he said "run it, a lot of little hole will work where a few big holes won't." Picked up almost a 10th of a second and 4 mph. I found over the years that he has been right way more often than not.
FE "Freakin Expensive"
Joined: Dec 2003
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From: Smith Mountain Lake, VA
Well I guess my memory is slipping at 50? I thought the only Difference in the cj and the scj was the cj ahd a hydraulic lift cam and the scj was mechanical a little more lift and duration..and the cj came stock with holley 750 with vac secs. and the scj had a holley 780?? I cant quite remember,,
Anyway I know big inch fords like CFM, I'am in the process of getting the parts together for my 460/521 build... and the cam will be somewhere in the 280 duration and about .650 lift for a street motor, and a ported victor,and a holley HP 950cfm carb.. and that will have all the HP and torque in at 6000rpm..
So they do like to breath and eat quite well....
Russ
Anyway I know big inch fords like CFM, I'am in the process of getting the parts together for my 460/521 build... and the cam will be somewhere in the 280 duration and about .650 lift for a street motor, and a ported victor,and a holley HP 950cfm carb.. and that will have all the HP and torque in at 6000rpm..
So they do like to breath and eat quite well....
Russ
