What size carburetor for max out street / strip 598ci pump gas motor
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What size carburetor for max out street / strip 598ci pump gas motor
Looking for some experienced and knowledgeable answers on what carburetor would be best for my build. This going to be a max out pump gas 604 cubic inch motor street / track vehicle. I have seen on pro system site stating this quote here.
I have an Quick fuel 1450 cfm some say its too big and when doing the match its shows to match the input formula. I don't know to go with the old formula or the new one here
I'm sure you remember this old formula:
CID x RPM x V.E. / 3456 = CFM
Well that formula is still being quoted by magazines and companies etc...but times have changed and carburetors are operating on almost immeasurable amounts of vacuum. 10 years ago a carburetor would require 10 inches of water to pull signal and shear fuel. Now they can can pull and shear fuel at only 3. Remember 20.4 inches of water (wet) is the cfm rating guide with reputable designers so we aren't looking to match cfm requirements with cfm ratings.
20.4 = 1.5 hg.
You can see that going from 10 inches of water as a requirement at launch to only 3 inches as a requirement really allows a serious increase in cfm size. This removal of restriction really pays off in cylinder head flow numbers and hp of course. Imagine altering this upstream restrictor when flowing your heads.
Because, most of you have specific application designs, a custom shop/unit is typically the plan.
In the future, use this calculation as a general rule on a modified carburetor:
CID x RPM x V.E. / 2820 = CFM
350 x 6600 x .9 / 2820 = 737 CFM
Now you'll be a little closer.
A .9 Volumetric Efficiency (V.E.) number represents a pretty good combination and a 1.1 V.E. number represents an all out assault on the engine blocks stress handling capabilities.
I have an Quick fuel 1450 cfm some say its too big and when doing the match its shows to match the input formula. I don't know to go with the old formula or the new one here
I'm sure you remember this old formula:
CID x RPM x V.E. / 3456 = CFM
Well that formula is still being quoted by magazines and companies etc...but times have changed and carburetors are operating on almost immeasurable amounts of vacuum. 10 years ago a carburetor would require 10 inches of water to pull signal and shear fuel. Now they can can pull and shear fuel at only 3. Remember 20.4 inches of water (wet) is the cfm rating guide with reputable designers so we aren't looking to match cfm requirements with cfm ratings.
20.4 = 1.5 hg.
You can see that going from 10 inches of water as a requirement at launch to only 3 inches as a requirement really allows a serious increase in cfm size. This removal of restriction really pays off in cylinder head flow numbers and hp of course. Imagine altering this upstream restrictor when flowing your heads.
Because, most of you have specific application designs, a custom shop/unit is typically the plan.
In the future, use this calculation as a general rule on a modified carburetor:
CID x RPM x V.E. / 2820 = CFM
350 x 6600 x .9 / 2820 = 737 CFM
Now you'll be a little closer.
A .9 Volumetric Efficiency (V.E.) number represents a pretty good combination and a 1.1 V.E. number represents an all out assault on the engine blocks stress handling capabilities.
Last edited by CHARLIEB on August 17th 2014, 10:10 am; edited 1 time in total
CHARLIEB- Posts : 145
Join date : 2012-05-20
Re: What size carburetor for max out street / strip 598ci pump gas motor
A 1450 should work fine on it IMO. Assuming you have some gear and a looser converter
dfree383- BBF CONTRIBUTOR
- Posts : 14851
Join date : 2009-07-09
Location : Home Wif Da Wife.....
Re: What size carburetor for max out street / strip 598ci pump gas motor
dfree383 wrote:A 1450 should work fine on it IMO. Assuming you have some gear and a looser converter
Thank you, Sounds great what gears would you think would go good with this combination three speed trans with 27 inch tires. I was thinking about 3.25 or 3.00 gears
CHARLIEB- Posts : 145
Join date : 2012-05-20
Re: What size carburetor for max out street / strip 598ci pump gas motor
I agree with Defree, if it matters. I have a little different take on your deal, than some people. I think you are going to have a serious problem getting any traction on the street with your setup, and probably at a well preped track too, with what you are trying to build. Like I have said before, You may want to take steps on your combo to remove low end Torque. Bigger Carbs do this and move the power band higher, along with cam selection. Sometimes too big makes sense and convention wisdom goes out the window.
supervel45- Posts : 4498
Join date : 2013-09-04
Re: What size carburetor for max out street / strip 598ci pump gas motor
With the short tires and 3 speed your in the ball park with the gearing
Watch you don't get the cam duration to big it will make low speed driving unpleasant
Watch you don't get the cam duration to big it will make low speed driving unpleasant
dfree383- BBF CONTRIBUTOR
- Posts : 14851
Join date : 2009-07-09
Location : Home Wif Da Wife.....
Re: What size carburetor for max out street / strip 598ci pump gas motor
dfree383 wrote:With the short tires and 3 speed your in the ball park with the gearing
Watch you don't get the cam duration to big it will make low speed driving unpleasant
Once again thank you for all your help.
CHARLIEB- Posts : 145
Join date : 2012-05-20
Re: What size carburetor for max out street / strip 598ci pump gas motor
supervel45 wrote:I agree with Defree, if it matters. I have a little different take on your deal, than some people. I think you are going to have a serious problem getting any traction on the street with your setup, and probably at a well preped track too, with what you are trying to build. Like I have said before, You may want to take steps on your combo to remove low end Torque. Bigger Carbs do this and move the power band higher, along with cam selection. Sometimes too big makes sense and convention wisdom goes out the window.
thank you for input and help with the information i was requiring
CHARLIEB- Posts : 145
Join date : 2012-05-20
Re: What size carburetor for max out street / strip 598ci pump gas motor
As for as the cam I don't mean go overboard either, but also pick a Lobe Seperation to move the powerband up and keep a some what smooth idle, and also where it is degreed in when installed, to work to your best advantage.
supervel45- Posts : 4498
Join date : 2013-09-04
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