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Old 12-01-2004, 13:50   #1 (permalink)
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carb understanding.

Ive been reading articles on carbs and tuning etc. Learning some before I get one.

But anyway.

I found this article on How 4 barrel carbs work. ARTICLE HERE

Within this article it quotes a formula for working out the CFM needed for %100 volumetric efficiency. The formula is as follows:

CID x max RPM / 3,456 = CFM

CID = 351
Whats the clevelands in xbgt's max rpm for this equation?
Divide that by 3,456 and you get your cfm figure.

This number determines what size carb you want.
Also, there is a choice between vacuum and mechanical secondaries. From what I read vacuum secondaries are better for everyday street use.

Then I just have to make a selection based on the above information to choose a brand?

Does all this sound right? Or am I not getting it?
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Old 12-01-2004, 14:36   #2 (permalink)
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Re: carb understanding.

if your going the vac sec.. i'd choose the elec choke model....
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Old 12-01-2004, 14:42   #3 (permalink)
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Re: carb understanding.

Ok. Why?

Is there any reason to go mechanical i dont know about?
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Old 12-01-2004, 14:59   #4 (permalink)
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Re: carb understanding.

it depends what use will have for it...

daily driven streeter/ occasional track use

Street/Strip

I'd use a vacuum secondary with electric choke for the street around 750cfm. Easier to live with... easy starting etc..

I'd go the mech sec if you were going to race it often, performance wise it would not be a major difference.
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Old 12-01-2004, 15:02   #5 (permalink)
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Re: carb understanding.

Yeah, im not interested in taking it to the track. It will totally be a street driven car just to enjoy driving it once a week on the weekend.

750cfm eh? What is the maximum rpm for the xb gt clevelands?
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Old 12-01-2004, 15:04   #6 (permalink)
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Re: carb understanding.

Very hard to get 100% volumetric efficiancy in a street engine. I believe that formula to be a little too conservative.
Your revs could be around 5500 for a fairly stock motor.
I would suggest a 650 cfm which would allow for the modifications you have spoken about in the past.
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Old 12-01-2004, 15:05   #7 (permalink)
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Re: carb understanding.

Because to use the above 750cfm carb, the max rpm for the engine would be around 7500rpm.

What Cfm is the stock carbi on xb gt's?
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Old 12-03-2004, 05:09   #8 (permalink)
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Re: carb understanding.

Quote:
Originally Posted by Black EX-R6
Because to use the above 750cfm carb, the max rpm for the engine would be around 7500rpm.

What Cfm is the stock carbi on xb gt's?
In the other thread, "blue eyes" said that the Autolite for your car would have been 605cfm but I suspect this may have been a typo and should read 650cfm
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Old 12-03-2004, 13:25   #9 (permalink)
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Re: carb understanding.

sorry, yeah that makes more sense. i got that from www.xbgt.info
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Old 12-03-2004, 13:58   #10 (permalink)
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Re: carb understanding.

Quote:
Originally Posted by blueyes
sorry, yeah that makes more sense. i got that from www.xbgt.info
There you go Black EF-R6 a web site to marvel at and you can hit the Contact button and ask them it the carby size is a typo
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