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

Post  CHARLIEB on April 2nd 2014, 7:10 pm

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.


Last edited by CHARLIEB on August 17th 2014, 10:10 am; edited 1 time in total
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Re: What size carburetor for max out street / strip 598ci pump gas motor

Post  dfree383 on April 2nd 2014, 7:13 pm

A 1450 should work fine on it IMO. Assuming you have some gear and a looser converter
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Re: What size carburetor for max out street / strip 598ci pump gas motor

Post  CHARLIEB on April 2nd 2014, 7:39 pm

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
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Re: What size carburetor for max out street / strip 598ci pump gas motor

Post  supervel45 on April 2nd 2014, 8:16 pm

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.

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Re: What size carburetor for max out street / strip 598ci pump gas motor

Post  dfree383 on April 2nd 2014, 8:45 pm

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
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Re: What size carburetor for max out street / strip 598ci pump gas motor

Post  CHARLIEB on April 2nd 2014, 9:39 pm

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.
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Re: What size carburetor for max out street / strip 598ci pump gas motor

Post  CHARLIEB on April 2nd 2014, 9:41 pm

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
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Re: What size carburetor for max out street / strip 598ci pump gas motor

Post  supervel45 on April 3rd 2014, 12:20 am

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.

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