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Author
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Topic: Squaring Carb
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Ken&Shell
Gearhead Posts: 614
From: Mocksville, NC
Registered: May 2000
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posted 10-22-2001 06:32 PM
   
Some of the guys at the track have started talking about squaring their carbs which another poster also mentioned. What is everyone's opinion on this? My buddies are saying it takes one more variable out in drag racing and I was wondering if any of you racers agreed with that?
Shell
ladyracer
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capri man
Gearhead Posts: 2689
From: doerun, ga.
Registered: Nov 2000
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posted 10-22-2001 06:47 PM
i assume you are talking about squareing the jets. that is a good starting point but only if you dont have a power valve in the front. again assuming you are talking about a holley. of course we all know what assuming will do for you! hee hee------------------
mike r
racing is real
everything else is just a game.
81 capri-7.56 @88mph 1/8
1.56 60 ft.
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Ken&Shell
Gearhead Posts: 614
From: Mocksville, NC
Registered: May 2000
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posted 10-22-2001 06:51 PM
quote:
Originally posted by capri man:
we all know what assuming will do for you! hee hee
All of your assumptions were correct darlin. It is a holley 750 without power valve and yes I meant squaring the jets. My next question of course is any recommendations on jet size. Shell
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capri man
Gearhead Posts: 2689
From: doerun, ga.
Registered: Nov 2000
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posted 10-22-2001 07:18 PM
ALEX!!!!! HEEEELP!!!!! assuming again that you are running a smallblock. i would start in the 81-84 range. just my opinion i could be wrong.------------------
mike r
racing is real
everything else is just a game.
81 capri-7.56 @88mph 1/8
1.56 60 ft. [This message has been edited by capri man (edited 10-22-2001).]
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Ken&Shell
Gearhead Posts: 614
From: Mocksville, NC
Registered: May 2000
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posted 10-22-2001 07:45 PM
MIke darlin you do a lot of assuming. I run a 351W with stock heads ported and polished. I run 7.30's in the 1/8th mile. What else you wanna know?Shell
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Dave_C
Gearhead Posts: 666
From: Gadsden, Al
Registered: Aug 99
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posted 10-22-2001 07:57 PM
For a track only car the square jetting does remove a variable. The mixture is the same from start to finish, no change by a pv opening or closing at a slightly different point.For reference: The 950 HP that I just installed: started out with 81 square, was lean. Jetted up to 85 square. Might be a touch rich, will back off to 84. I removed a 750 dp. The 750 worked well at 80-81 square or 73 square with 3.5 pv's front and rear. The 3.5 pv's made it idle cleaner and the numbers were low enough that they didn't affect the consistency very much. Later, David Cole
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Ken&Shell
Gearhead Posts: 614
From: Mocksville, NC
Registered: May 2000
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posted 10-22-2001 08:09 PM
OK, Carb lesson time.. What exactly does the power valve do and why use one or not use one?Shell
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capri man
Gearhead Posts: 2689
From: doerun, ga.
Registered: Nov 2000
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posted 10-22-2001 08:11 PM
The 750 worked well at 80-81 square per dave
see i toldja so, (well i was a litle high) but pretty close for a wild guess, huh? hee hee good luck
------------------
mike r
racing is real
everything else is just a game.
81 capri-7.56 @88mph 1/8
1.56 60 ft.
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steve'66
Gearhead Posts: 5659
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 10-22-2001 08:57 PM
Shell,The power valve opens at a set lower vacumm level to add more fuel to the mix. It's purpose is to add more fuel when a street car hits a hill and the engine's vacumm drops. This helps the car maintain the same speed.
But a race only car like yours doesn't need a power valve.  The power valve adds enough fuel to compensate for about 6 jet sizes. So with a front power valve, most people run a jet size 6-8 sizes smaller in the front than the rear.
With no power valve the jets should be the same all the way around or "squared" so all cylinders have the same air/fuel mix. Street cars also want to be leaner on the primaries so they can use less fuel for normal driving, then richen the mix up when they open up the secondaries. Make sense? SteveW
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capri man
Gearhead Posts: 2689
From: doerun, ga.
Registered: Nov 2000
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posted 10-22-2001 09:08 PM
yea, what he said!!!------------------
mike r
racing is real
everything else is just a game.
81 capri-7.56 @88mph 1/8
1.56 60 ft.
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bluestreek
Gearhead Posts: 1086
From: Athens,GA
Registered: Jul 2001
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posted 10-22-2001 10:39 PM
I like to square my 289 street carb and use a 4.5 power valve . That way it's there if I need it, but there has to be a pretty good load on the car before it begins to come in.. One thing I noticed with Holleys is the PV jets tend to be a little too large for stock 289/302 heads, so I like to tweak the two PV jets with different size wires, depending on the engine combinations. It works for me. 
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Moneymaker
Administrator Posts: 18704
From: Lyons, IL, USA
Registered: May 99
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posted 10-24-2001 11:37 AM
"Squaring" does not work on a SBF regardless of carb. The carbureted intake design does not lend itself to it. The rear cylinders are always leaner than the fronts. We run a 8 to 10 size variance front to rear on our stuff. Most street cars that I set up are at least 6 sizes different. ------------------
Alex Denysenko
Co-Administrator and Moderator
NHRA/IHRA/SRA member
NHRA and IHRA SS/LA National Record Holder '00 & '01
Fleet of FoMoCo products
Moneymaker Bio
US Class Nationals link
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Ken&Shell
Gearhead Posts: 614
From: Mocksville, NC
Registered: May 2000
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posted 10-24-2001 01:43 PM
Thanks for the lesson on power valve Steve. quote:
Originally posted by Moneymaker:
[BWe run a 8 to 10 size variance front to rear on our stuff. [/B]
Alex that is without power valve, right?
Shell
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Moneymaker
Administrator Posts: 18704
From: Lyons, IL, USA
Registered: May 99
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posted 10-24-2001 05:56 PM
Correct Shell. I do not use a power valve in MM, BUT..... I still never have gone quicker with ANY SBF using ANY carb with square jetting. Windsors by their inherit design need more fuel to th rear cylinders. Not even on my old Modified Production 351C tunnel ram twin 660 68 coupe. Even that thing had to have some stagger in it, but I blame old intake technology on that deal knowing what I know today. ------------------
Alex Denysenko
Co-Administrator and Moderator
NHRA/IHRA/SRA member
NHRA and IHRA SS/LA National Record Holder '00 & '01
Fleet of FoMoCo products
Moneymaker Bio
US Class Nationals link
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bluestreek
Gearhead Posts: 1086
From: Athens,GA
Registered: Jul 2001
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posted 10-24-2001 09:57 PM
quote:
Originally posted by Moneymaker:
"Squaring" does not work on a SBF regardless of carb. The carbureted intake design does not lend itself to it. The rear cylinders are always leaner than the fronts. We run a 8 to 10 size variance front to rear on our stuff. Most street cars that I set up are at least 6 sizes different.
For some reason mine seems to like it.. Maybe it has something to do with my highly modified intake plenum and 1" open spacer..?? My 650 DP works the best with 72 jets squared and 4.5 PV in front and back.. One other thing that you may not believe is my 289 pulls strong from 2000-7200 rpms with a little old 230 /.512" lift hyd. cam and open chamber heads. ( still has pressed in studs and rail rockers) .. If I could just figure out a way to keep the oil from slinging out of the dipstick tube. 
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Butch Jennings
Gearhead Posts: 534
From: California
Registered: Apr 2000
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posted 10-24-2001 10:14 PM
The Victor on my 460 seems to like the jetting squared up...86 jets with 4.5 power valves with a 1050 dominator.------------------
Butch
460 powered 1967 Comet Cyclone
10.271 @ 130.069
Butcher's Home Page
"Friends don't let friends drive Chevys"
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Moneymaker
Administrator Posts: 18704
From: Lyons, IL, USA
Registered: May 99
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posted 10-25-2001 12:37 AM
We have a 289 running around that pulls to 7500 RPM with a C7FE leMans cam in it. It is in a 65 fastback with an auto and runs 12.60's. Butch, I have always found that the 385 series engines like a lot of carburation and very little stagger if any. Especially with a dominator. ------------------
Alex Denysenko
Co-Administrator and Moderator
NHRA/IHRA/SRA member
NHRA and IHRA SS/LA National Record Holder '00 & '01
Fleet of FoMoCo products
Moneymaker Bio
US Class Nationals link
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