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  #11  
Old 08-13-2017
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DanR DanR is online now
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Thanks Mike for and excellent site.... Here is something I also found on their site that is interesting:

RPM and MPH Transmission Gear Ratio Calculator
Find out your RPM at cruising speed with or how much RPM the engine turns at any given speed.

Try it out - Mustangtek transmission ratio and shift point calculator

Simple way to get answers to all your questions

-
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  #12  
Old 08-13-2017
RootesRacer RootesRacer is offline
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Quote:
Originally Posted by Bill Blue View Post
Could you put all that into the context of the original question? i.e. if 800 cfm of DCOE's would be fine, does that mean a 500 Edelbrock would not be too large?

Bill
Bill, you modify the effective CFMs on DCOEs by changing the chokes (venturies).
A single 45 DCOE would then have a range of about 175 or so to 400+ CFMs.

A pair would therefore be from around 350 to 800 CFMs.

When you talk about 4 1.08" chokes making 480CFMs, thats more or less the same as running 2X45 DCOEs with 29mm chokes (29mm chokes are considered tiny even for 40s).

If the 4150/60, 4100 or the Edelbrock had replaceable chokes with a range for 26 to 40mm, then they would be equally adaptable for 250 to 800CFM.

Personally, 500 CFM seems way too much for a 7000 RPM 171 CID engine. 390 CFM even sounds a bit much to me...

Last edited by RootesRacer : 08-13-2017 at 10:32 AM.
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  #13  
Old 08-13-2017
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Quote:
Originally Posted by RootesRacer View Post
Personally, 500 CFM seems way too much for a 7000 RPM 171 CID engine. 390 CFM even sounds a bit much to me...

Jarrid hit an important nail on the head.

An old (and accurate) rule of thumb for 4-barrel carburetors on naturally aspirated street engines is 2 CFM per HP.

A more or less stock Ford 2.8 V6 might make 125 HP = 250 CFM.

A moderately modified Ford 2.8 V6 might make 150 HP = 300 CFM.

A highly modified Ford 2.8 V6 might make 175 HP = 350 CFM.

Anything less than a full race (not street) Ford 2.8 V6 simply does not need 400 CFM.

A carburetor that is too big does NOT make more power, but it does reduce throttle response / driveability and make tuning the carburetor more difficult.

Despite being too big, the Holley 390 is the only readily available game in town, so .....

Just my opinion, YMMV.
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Last edited by Barry : 08-13-2017 at 01:12 PM.
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  #14  
Old 08-13-2017
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Barry quoted "Jarrid hit an important nail on the head." +1

Best readily available option.

The ONLY issue that I have had with my 390 cfm Holley is that the installing mechanic did not properly adjust the slow speed idle (but then he was a track drag race guy and liked a very fast idle to avoid bogging down off the line).
By following the Holley instructions, I was able to get the slow idle down where it is tractable and the high lift cam lope is tolerable.
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  #15  
Old 08-13-2017
Fordtootsie Fordtootsie is offline
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Default carb size

I get a kick out of reading all the carb info.

I just through I would throw in by 2 cents. So here it is!!!

Assume perfect cam, no friction looses, 100 % eff no turbo or ram effect and 100% eff on everything....

a 171 cu in engine will ingest 247 cu ft per min at 5000 rev per min if I did the math correct.

John in Colorado
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  #16  
Old 08-13-2017
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Link to Holley Installation doc for 390 cfm carb, from Holley web site:
Carb overview:
https://www.holley.com/products/fuel...y/parts/0-8007

REPLACEMENT CARBURETOR - MODEL 4160
P/N 0-8007

Installation and adjustment Instructions:

http://documents.holley.com/199r8108-2rev4.pdf

My engine drove OK, but I was not satisfied with either the fast or slow idle, so I printed this doc and followed the tuning instructions for fast and slow idle and all was well. This was 3-4 years ago and it has worked well since.

I am not a mechanic and the above is all that I know about the M4160.
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  #17  
Old 08-13-2017
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Quote:
Originally Posted by Fordtootsie View Post
I get a kick out of reading all the carb info.

I just through I would throw in by 2 cents. So here it is!!!

Assume perfect cam, no friction looses, 100 % eff no turbo or ram effect and 100% eff on everything....

a 171 cu in engine will ingest 247 cu ft per min at 5000 rev per min if I did the math correct.

John in Colorado

John,

Absolutely correct @ 100% volumetric efficiency, but a good "performance" street engine probably has a VE of no more than 90% which changes the 247 CFM to 222 CFM.

Just my opinion, YMMV.
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  #18  
Old 08-13-2017
Fordtootsie Fordtootsie is offline
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Yep !!

Makes a Holley 390 cfm a little big.

John in Colorado
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  #19  
Old 08-13-2017
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Definitely too big, but the only readily available 4-barrel that is even close to the right size.

A 410 Carter in good condition would probably be a better choice, but good luck finding one.

FWIW, the 200 gross HP (probably about 175 net HP) 289 in the Mk-II Tiger used a 500 CFM Holley 2-barrel that worked very well. The 500 CFM rating is misleading; when tested the same way as a 4-barrel, the 500 CFM 2-barrel only flows about 350 CFM. The "mucho macho hot rod" factor would be missing, but it would probably work well for a "street performance" Ford 2.8 V6.

Just my opinion, YMMV.
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Last edited by Barry : 08-13-2017 at 06:11 PM.
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  #20  
Old 08-13-2017
todd reid todd reid is offline
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Default Carburation

I have read somewhere (maybe here) that across the pond in England, the popular carb upgrade is to replace the stock two barrel (where the barrels open in progression) with one where the barrels open simultaneously. If the Holley is oversized, maybe they are on to something - especially for a basically stock engine.

TR
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