4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

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Rollbar1
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4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

Postby Rollbar1 » Mon May 23, 2016 12:41 pm

I have searched and turned up mostly CM info on the 350cfm carb and didn't find much in the finished dept of the Holly 350cfm for the 084 and was wondering if anyone has either used it, and if so the jetting etc.

I also have a few carbs here (MC-2100) that are two barrel and I think they are 270-300 cfm.

Just wondering if the 2bbl would be to much for the 084 with the original intake but modified for the carb to sit on top.

http://street2mud.com/webfiles/MC-2100% ... %20258.pdf

Thanks,
Jim

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Re: 4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

Postby pirate » Tue May 24, 2016 8:23 am

PM sent
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Re: 4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

Postby Rollbar1 » Tue May 24, 2016 9:06 am

Thank you very much,
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Re: 4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

Postby Rollbar1 » Thu May 26, 2016 5:59 pm

Last edited by Rollbar1 on Thu May 26, 2016 6:08 pm, edited 1 time in total.
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Re: 4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

Postby Rollbar1 » Thu May 26, 2016 6:05 pm

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Re: 4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

Postby jeepinocala1111 » Thu May 26, 2016 8:34 pm

Rollbar1 wrote:http://www.summitracing.com/popup/calcsandtools/cfm-calculator

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You cant go by that conversion it is for a car engine and does not work for an ac engine mine called for a 350 or smaller cfm carb I put an 500 holley ultra pro racing carb it makes my engine run so dam good I thank these forums every time I start it up for keeping me from buying a 350 cfm carb. :thumbleft:

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Re: 4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

Postby Rollbar1 » Thu May 26, 2016 11:24 pm

Ok thanks. I didn't know that. Thought CFM was the same.
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Re: 4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

Postby pirate » Fri May 27, 2016 7:18 am

Maybe you can explain why cfm is different. They are all internal combustion engines.
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Re: 4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

Postby Deano » Fri May 27, 2016 9:19 am

Rollbar1 wrote:Ok thanks. I didn't know that. Thought CFM was the same.
I believe that your presumption is correct. A cubic foot per minute = 1728 cubic inches per minute = 29.8 cubic inches per second. An engine is an air pump: CFMs is the measure of volume of the air moved.

pirate wrote:Maybe you can explain why cfm is different. They are all internal combustion engines.
I am interested in understanding this premise as well. A gallon of gasoline contains X amount of BTUs. X amount of BTUs will produce X amount of power. The significant variable in comparisons is the thermal or volumetric efficiency with which the given engine converts BTUs to usable power. This is why most CFM calculators will include that as a variable to be input before the calculation is done. It's my understanding that water cooled four stroke engines are among the most efficient.

Perhaps the decreased efficiency of a two stroke and/or an air cooled engine would require inflating the CFMs (and the gas contained therein) in order to get the same power output given the decreased efficiency ? :scratch: or :lol: ?

Here is some reading that you may find interesting . . .
especially the Brake Specific Fuel Consumption toward the end.
http://www.epi-eng.com/piston_engine_technology/thermal_efficiency.htm

Nothing against Summit, but you will find a number of calculators that may be of use to you here:
http://wallaceracing.com/Calculators.htm Specifically these:
http://wallaceracing.com/intakecfm.php and http://wallaceracing.com/calc-cfm-head.php

FWIW, I think his ground power is about 470 ci, my one Cadillac is 472 ci and they both run 500 CFM Holleys with good results. At 84 ci your engine is about 560% smaller, so that would equate to about 89 CFM by the same standard. This looks to be in the same neighborhood as these calculators are predicting.

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Why the predisposition to an automotive carb? There are far more similar sized engines running in motorcycles then there are in cars. Because that market is much more developed for that size engine, I would anticipate finding more numerous and efficient options. If it were me, and I was looking to carb that engine I would seriously consider a Keihen or a Mikuni Carb. The later being far more tunable, but also likely to be a bit more expensive to acquire.
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Re: 4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

Postby pirate » Fri May 27, 2016 10:32 am

Exactly.

FYI the 4a084 was a GPU(ground power unit) general purpose engine designed for the military. Although some have been refitted for use in aircraft that wasn't the original intent.
Last edited by pirate on Fri May 27, 2016 10:39 am, edited 1 time in total.
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Re: 4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

Postby glades cat » Fri May 27, 2016 10:38 am

Look at the Rochester single bbl "B" carb. They don't get much simpler that this.
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Re: 4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

Postby Rollbar1 » Fri May 27, 2016 1:39 pm

Thank you all and for the explanations/tips etc.
I have a Keihen on my HD 883 and it is a good carb.
I would have to see how that would flow etc.
I'll also check out the Rochester, forgot all about those.
Thanks, for the link CFM generator as well. I'm sure I can find something besides the VW carb.
Jim
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Re: 4a084-2 Barrel Carb (Holly/MC-2100) Conversion Question.

Postby Rollbar1 » Fri May 27, 2016 11:19 pm

So my blades came in today, and the max rpm for the blades are 3100rpm. (59x10*)
Here is the CFM rating when I punch in the 3100rpm on the program.

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