pair of 950cfm on tunnel too much ? a set of 650 ?
#2041609
03/30/16 12:34 AM
03/30/16 12:34 AM
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Joined: May 2004
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Ste-Sophie, Quebec, Canada
Wedgeman
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Ste-Sophie, Quebec, Canada
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I was wondering if a pair of 950 cfm carbs would be too much to put
on a 408 ?
Indy heads
67 barracuda 2850 lbs w/o driver
10.9:1 cr
285*/293* duration solid roller
Dan
Last edited by Wedgeman; 03/30/16 11:56 PM.
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Re: pair of 950cfm on tunnel too much ?
[Re: Wedgeman]
#2041621
03/30/16 12:53 AM
03/30/16 12:53 AM
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Joined: Jan 2005
Posts: 4,243
Charlotte, North Carolina
sgcuda
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Charlotte, North Carolina
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Rumor has it that HP 950's don't quite flow 950 cfm. That being said, you might not have enough there for that size carbs. I'd like to see a set of old school 660 center squirters on your combo, myself. You could really use some more compression, too.
[image][/image]
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Re: pair of 950cfm on tunnel too much ?
[Re: Wedgeman]
#2041638
03/30/16 01:06 AM
03/30/16 01:06 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
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Master
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Romeo MI
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255*/263* @ .050
max rpm at 6700
Dan Since they dont flow 950 but at 6700 rpm you only need about 850 cfm.. but all that its gonna hurt is low end response... my 405ci turning 8200 needed 1050 cfm 
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Re: pair of 950cfm on tunnel too much ?
[Re: Wedgeman]
#2041671
03/30/16 02:06 AM
03/30/16 02:06 AM
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Joined: Jan 2003
Posts: 4,448
Phoenix, AZ
MoparBilly
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Phoenix, AZ
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If you have the carbs, I wouldn't be afraid to give it a try. We have twin 750s on a Weiand Hi-ram atop the 508 wedge in the Barnyard, and it's a real peach on the street, and strip.
"Livin' in a powder keg and givin' off sparks"
4 Street cars, 5 Race engines
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Re: pair of 950cfm on tunnel too much ?
[Re: Wedgeman]
#2041897
03/30/16 01:18 PM
03/30/16 01:18 PM
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Joined: Oct 2007
Posts: 4,213
New York
polyspheric
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New York
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I know, I know - "broken record", but still relevant.
If the engine is too small, or the carbs too large:
1. the carbs will flow less than their rating
2. WOT vacuum across the venturi may drop below the designed minimum of 1.5" Hg, and metering becomes shaky. WOT top end will be lean (usually a smaller HSAB is the cure, or aftermarket emulsion tube set).
If the engine is too large, or the carbs too small:
1. the carbs will flow more than their rating
2. WOT vacuum may not drop to the designed 1.5" Hg. WOT top end will be rich (larger HSAB, or aftermarket emulsion tube).
Boffin Emeritus
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Re: pair of 950cfm on tunnel too much ?
[Re: Wedgeman]
#2042622
03/31/16 11:57 AM
03/31/16 11:57 AM
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Joined: Jan 2003
Posts: 10,038
Frostbitefalls MN (Rocky&Bullw...
gregsdart
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I Live Here
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Frostbitefalls MN (Rocky&Bullw...
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What I don't like here is the motor is only 408 and a flat tappet cam that limits rpm. A call to a couple of good carb people ought to shed some light on what is best. I am betting their answers will be 650 cfm each or less.
If you do the math and figure out the lowest launch rpm, then calculate air demand, air demand should generate a certain minimum vacuum so the carbs can provide the right vaporization and be able to be tuned for a flat AFR.
Getting the max torque out of the motor at launch rpms will get you the best ET. Also a car spends a lot more time in the first half of each gear than the second half.
Last edited by gregsdart; 03/31/16 12:00 PM.
8.582, 160.18 mph best, 2905 lbs 549, indy 572-13, alky
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Re: pair of 950cfm on tunnel too much ?
[Re: gregsdart]
#2042852
03/31/16 06:01 PM
03/31/16 06:01 PM
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Joined: May 2004
Posts: 1,522
Ste-Sophie, Quebec, Canada
Wedgeman
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OP
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Joined: May 2004
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Ste-Sophie, Quebec, Canada
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What I don't like here is the motor is only 408 and a flat tappet cam that limits rpm. A call to a couple of good carb people ought to shed some light on what is best. I am betting their answers will be 650 cfm each or less.
If you do the math and figure out the lowest launch rpm, then calculate air demand, air demand should generate a certain minimum vacuum so the carbs can provide the right vaporization and be able to be tuned for a flat AFR.
Getting the max torque out of the motor at launch rpms will get you the best ET. Also a car spends a lot more time in the first half of each gear than the second half.
As mentioned, the cam is a solid roller...
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Re: pair of 950cfm on tunnel too much ?
[Re: Wedgeman]
#2043275
04/01/16 02:06 AM
04/01/16 02:06 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
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Master
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Romeo MI
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What I don't like here is the motor is only 408 and a flat tappet cam that limits rpm. A call to a couple of good carb people ought to shed some light on what is best. I am betting their answers will be 650 cfm each or less.
If you do the math and figure out the lowest launch rpm, then calculate air demand, air demand should generate a certain minimum vacuum so the carbs can provide the right vaporization and be able to be tuned for a flat AFR.
Getting the max torque out of the motor at launch rpms will get you the best ET. Also a car spends a lot more time in the first half of each gear than the second half.
As mentioned, the cam is a solid roller... As I said .. for your engine the air demand for the rpm will be somewhere near 850 cfm (without knowing a lot more of the engine) but 850 will be close.. if you are a trans brake car I would run them.. a foot brake car needs a quicker response to throttle up... myself I would try them.... I was gonna try either a single 1150 or a TR with 2 850s on my 405ci... 850s flow more than the 950s
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