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  #16 (permalink)  
Old 08-14-2007, 12:45 PM
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Quote:
Originally Posted by red65mustang
Not A T',
"actual" cfm on/thru a 383 cube motor (changes some but not alot with cam/etc)....

2,000rpm=163cfm
2500rpm=223cfm
3000rpm=286cfm

......5500=540cfm

I agree, time to try just the center carb...with 48* cruisin...for higher Hg

comment?:
at 13Hg, a carb is at the borderline for the gas not atomized by enough velocity, not suspended in the air for a good mix...
you will gain ALOT of velocity using only the center carb
red65mustang Wow now this is good information I have a mild comp cam sorry I don't remember the number but have them at home. Do you think changing to larger jets on the middle carb is the way to go or is there another way to achieve using the center carb only for cruse. I am out of adjustment on linkage with out giving up WOT

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Old 08-14-2007, 01:20 PM
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Not A T'

some Hg numbers from my mild/typical (250hp/320tq) 302 to use as a scale(?) for your motor.....

on a downshift 3rd to 2nd at 50mph no gas pedal....Hg reads 25-26"....(my rings and valves are sealing great...fresh build)....
at 3,000rpm in my garage just rev'in the motor in park....Hg reads 21....(motor friction, alternator, etc etc dropped it 5Hg)
at 3,000rpms/65mph/3400lbs....Hg reads 18....(wind/tires resistance, weight etc etc dropped it another 3Hg)
swap in "thicker rods" for leaner on the Edelbrock carb....65mph=20Hg...about 2mpg better than 18Hg @ 3,000
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Old 08-14-2007, 01:28 PM
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Quote:
Originally Posted by red65mustang
swap in "thicker rods" for leaner on the Edelbrock carb....65mph=20Hg...about 2mpg better than 18Hg @ 3,000
red65mustang not sure I understand the last statement can you elaborate some. Are you saying that leaner condition at cruse helped your vacuum and mileage? I was thinking that I need to go fatter on the center carb to finish getting off the secondary carbs?
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Old 08-14-2007, 01:35 PM
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first, when you find out "which" comp cam, use this link.....click on that cam graph to see all the details including carb idle Hg....higher is a little less fouling but 15Hg+ is fine

http://www.compcams.com/technical/DynoSheets/

second:
where the Heck is "Tech @ BG" when we need him!!!!
he is a well respected board member who works for Barry Grant....
sorry...I have no experience with their six shooter...
I'll send a pm to Tech @ BG and ask him to read this thread
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Old 08-14-2007, 01:47 PM
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Quote:
Originally Posted by red65mustang
first, when you find out "which" comp cam, use this link.....click on that cam graph to see all the details including carb idle Hg....higher is a little less fouling but 15Hg+ is fine

http://www.compcams.com/technical/DynoSheets/

second:
where the Heck is "Tech @ BG" when we need him!!!!
he is a well respected board member who works for Barry Grant....
sorry...I have no experience with their six shooter...
I'll send a pm to Tech @ BG and ask him to read this thread
it is the 268H cam.
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Old 08-14-2007, 01:52 PM
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because a motor is "loafing" at cruise, you can run a leaner mix for better mpg.....you've seen the statement:"only takes about 30-50hp to keep a car at 70mph"

every motor/car combo will have a lean burn limit A/F ratio...here's a guide attached...

for my car
to change the "jetting" on a Edelbrock, all you have to do is swap the rods to thicker with a given jet size, the rods extend thru the jet and make a bigger flow restriction....motor cfm is constant per given rpms.....less fuel thru the jets is leaner....
90% of my miles is in town, the thinner rods are alot more pedal responsive....I do put in the thicker rods for the 250 miles trip to my daughters....running leaner and a little hotter burns out all the crap in the cylinder heads
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Old 08-14-2007, 02:22 PM
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Quote:
Originally Posted by red65mustang
because a motor is "loafing" at cruise, you can run a leaner mix for better mpg.....you've seen the statement:"only takes about 30-50hp to keep a car at 70mph"

every motor/car combo will have a lean burn limit A/F ratio...here's a guide attached...

for my car
to change the "jetting" on a Edelbrock, all you have to do is swap the rods to thicker with a given jet size, the rods extend thru the jet and make a bigger flow restriction....motor cfm is constant per given rpms.....less fuel thru the jets is leaner....
90% of my miles is in town, the thinner rods are alot more pedal responsive....I do put in the thicker rods for the 250 miles trip to my daughters....running leaner and a little hotter burns out all the crap in the cylinder heads
So it is likely I am running rich at cruse and just can't tell by checking the plugs since I have not done as Frisco suggested and shut the car off and placed in neutral and coasted to a stop. I still don't understand how to get to my cruse speed of 65 MPH on center carb only with out providing more fuel from the center carb (larger jetting)
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Old 08-14-2007, 02:55 PM
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hooray! Tech @ BG arrived just in time....I defer to him!

"accellerating" normally from a stop sign, Hg will drop to 9-10 with alot of pedal....you want the other carbs to come in with more gas/richer for power

once the speed stabilizes at 65mph....you want to cruise on the center carb only jetted to about 15-16/1 A/F.....
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Old 08-14-2007, 02:58 PM
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First I'd say we need to jet down a little on the center carburetor (2 numbers) to help lean down the cruise a touch. From there I've got a few other thoughts that I'll let you know once we see what that does.
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Old 08-14-2007, 02:59 PM
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Quote:
Originally Posted by Tech @ BG
First I'd say we need to jet down a little on the center carburetor (2 numbers) to help lean down the cruise a touch. From there I've got a few other thoughts that I'll let you know once we see what that does.
Can you tell me which numbers come stock in the carb?
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Old 08-14-2007, 03:08 PM
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Quote:
Originally Posted by Not A T 25
Can you tell me which numbers come stock in the carb?
68'S I'd say to go down to 66's on the center carb...
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Old 08-14-2007, 03:22 PM
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Quote:
Originally Posted by Tech @ BG
68'S I'd say to go down to 66's on the center carb...
Thanks I will get a set ordered.
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