Using Dyno CFM reading for carb sizing

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F-BIRD'88
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Re: Using Dyno CFM reading for carb sizing

Post by F-BIRD'88 »

eric8 wrote: Fri Sep 03, 2021 8:54 pm
F-BIRD'88 wrote: Fri Sep 03, 2021 4:54 pm What was the power and torque difference between the Eddy 800 avs2 and the QF750?
I never dynoed it with the Eddy. Definitely could not tell any seat of the pants difference between the two though.
Very convoluted infirmation.
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Re: Using Dyno CFM reading for carb sizing

Post by Adger Smith »

I always complete my tuning with out the air turbine.
It seems to have an effect on carb metering and booster signal.
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Re: Using Dyno CFM reading for carb sizing

Post by In-Tech »

Adger Smith wrote: Sat Sep 04, 2021 12:11 am I always complete my tuning with out the air turbine.
It seems to have an effect on carb metering and booster signal.
Hi Adger,
A honeycomb element in the tract will help with that tremendously.
Heat is energy, energy is horsepower...but you gotta control the heat.
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Re: Using Dyno CFM reading for carb sizing

Post by Steve.k »

I’ve never seen a eddy carb perform as good as quickfuel.
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Re: Using Dyno CFM reading for carb sizing

Post by David Redszus »

eric8 wrote: Thu Sep 02, 2021 2:03 pm This seems like the most obvious metric for determining an engine’s true cfm needs, so it has me wondering. My mild 430 hp 383 SBC on a Superflo dyno had a cfm rating of 592 at 5,900 rpms. A 650 cfm carb should in fact be plenty, no? Just thinking out loud. Am I missing something?
A 383 cuin engine, running at 100%VE, will require a specific amount of air volume, depending on rpm.

5000rpm...554 cfm
6000........665
7000........776.

The air volume is dependent on whether the air contains fuel vapor or not. The air mass will depend on air density.
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Re: Using Dyno CFM reading for carb sizing

Post by CamKing »

eric8 wrote: Thu Sep 02, 2021 2:03 pm This seems like the most obvious metric for determining an engine’s true cfm needs, so it has me wondering. My mild 430 hp 383 SBC on a Superflo dyno had a cfm rating of 592 at 5,900 rpms. A 650 cfm carb should in fact be plenty, no? Just thinking out loud. Am I missing something?
CID x RPM / 3456 = CFM for 100%VE
383 x 5,900 / 3456 = 654 CFM.
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Re: Using Dyno CFM reading for carb sizing

Post by Stan Weiss »

Just a WAG as to what might be.

Stan

Code: Select all

_______STPPwr__STPTrq___BMEP_____Fuel___BSFC___UnCorr_UnCorr_Correct___A/F______Air
__RPM____CHP___Clb-ft____PSI___lbs/hr__lb/hph____HP___Torque__Factor__Ratio____SCFM____VE%
_5900___430.0___382.8__150.8___208.53__.4850___430.0___382.7__1.0001__13.00___591.9___90.6
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Re: Using Dyno CFM reading for carb sizing

Post by eric8 »

Stan Weiss wrote: Sat Sep 04, 2021 2:39 pm Just a WAG as to what might be.

Stan

Code: Select all

_______STPPwr__STPTrq___BMEP_____Fuel___BSFC___UnCorr_UnCorr_Correct___A/F______Air
__RPM____CHP___Clb-ft____PSI___lbs/hr__lb/hph____HP___Torque__Factor__Ratio____SCFM____VE%
_5900___430.0___382.8__150.8___208.53__.4850___430.0___382.7__1.0001__13.00___591.9___90.6
Sorry for the delay. Here’s the dyno sheet
B5F8D281-C76F-4288-A914-6D2D8A3FE171.jpeg
You do not have the required permissions to view the files attached to this post.
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Re: Using Dyno CFM reading for carb sizing

Post by David Redszus »

Stan Weiss wrote: Sat Sep 04, 2021 2:39 pm Just a WAG as to what might be.

Stan

Code: Select all

_______STPPwr__STPTrq___BMEP_____Fuel___BSFC___UnCorr_UnCorr_Correct___A/F______Air
__RPM____CHP___Clb-ft____PSI___lbs/hr__lb/hph____HP___Torque__Factor__Ratio____SCFM____VE%
_5900___430.0___382.8__150.8___208.53__.4850___430.0___382.7__1.0001__13.00___591.9___90.6
Stan,
When calculating carb CFM, what allowance is made for fuel vapor, if present?
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Re: Using Dyno CFM reading for carb sizing

Post by Stan Weiss »

David Redszus wrote: Tue Sep 07, 2021 7:53 pm
Stan Weiss wrote: Sat Sep 04, 2021 2:39 pm Just a WAG as to what might be.

Stan

Code: Select all

_______STPPwr__STPTrq___BMEP_____Fuel___BSFC___UnCorr_UnCorr_Correct___A/F______Air
__RPM____CHP___Clb-ft____PSI___lbs/hr__lb/hph____HP___Torque__Factor__Ratio____SCFM____VE%
_5900___430.0___382.8__150.8___208.53__.4850___430.0___382.7__1.0001__13.00___591.9___90.6
Stan,
When calculating carb CFM, what allowance is made for fuel vapor, if present?
David,
That CFM would be like what is measured by the dyno air turbine. When I do carb CFM calculations I ignore the fuel vapor.

Stan
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