Another mc2100 question

Another mc2100 question

ken98k

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Location
North Pole, Alaska
Vehicle(s)
{1980 cj-5, 258, t-176, d300 amc20 rear, D30}{1974 cj-5, 304, T-15, D20, D30 front, D44 rear}{1973 cj-5, 304, t-98,D20, amc20, D30}
{1990 yj 2.5L i-4 AX-5 NP231 Dana 30 front Dana 35c rear}
1996 XJ Cherokee 4.0 HO
{2000 silverado}
{1979 Cadillac Sedan DeVille}
I may be wrong but I beleive the 1.02 venturi is the next smaller size after 1.08
Would the 1.02 work on a 258?
 
From what I've read in my research into the MC2100 the 1.08 is ideal for the 258, but the 1.02 and the next size up(can't remember right now) do work on a stock 258 if you know how to tune them.
 
From what I've read in my research into the MC2100 the 1.08 is ideal for the 258, but the 1.02 and the next size up(can't remember right now) do work on a stock 258 if you know how to tune them.

My 74' CJ5 has the 304 with a 1.08 and runs great, (stock carb I think) so I thought a smaller v size might be a little better on a smaller motor.:confused:
 
There were a couple real good posts by elwoodblues on mc2100 that had cfm charts and best for what engines i will see if i can find it for you when i get to work. I believe the 1.08 is also what my 74 with 304 has, but also seem to remember the 258 ran great with it too according to the chart / my memory of reading...

Ill post you a link in a little bit...
 
I may be wrong but I beleive the 1.02 venturi is the next smaller size after 1.08. Would the 1.02 work on a 258?


Here's the chart JR74CJ5 was talking about;

venturi = CFM
.98 = 190
1.01 = 240
1.02 = 245
1.08 = 287
1.14 = 300
1.21 = 351
1.23 = 356
1.33 = 424

http://www.carburetion.com/Calc.asp If you follow this link to the CFM calculator, he get roughly 300 CFM needed for a 258. My 2¢, I think you'll starve your engine with a 1.02. I run a 1.14 and it runs well and still get's 15(ish) MPG.
 
Here's the chart JR74CJ5 was talking about;

venturi = CFM
.98 = 190
1.01 = 240
1.02 = 245
1.08 = 287
1.14 = 300
1.21 = 351
1.23 = 356
1.33 = 424

http://www.carburetion.com/Calc.asp If you follow this link to the CFM calculator, he get roughly 300 CFM needed for a 258. My 2¢, I think you'll starve your engine with a 1.02. I run a 1.14 and it runs well and still get's 15(ish) MPG.

Using that calculator I got 253 CMF when I input 4000 rpm,
 
Yeah Elwood, if you can help out on best way of using the calculator link, I'd also appreciate it... Like for instance, for the poster, do we put in the max RPM we run our engine at? Or max spec'ed rpm ok to run at? or on the stock, mildly built etc question, what would say 304 with a DUI distributor, msd streetfire ignition box and plugs gaped @ .050 be considered? still stock-ish, or mildly built? :D (that would be a slightly thread steeling question:cool:) but i basically mean per the calculator, what is stock - mild built gap etc...

:notworthy::notworthy::notworthy:

:chug:
 
CID x RPM / 3456 x VE% = CFM

CID= Cubic Inch Diameter
RPM= Maximum Engine RPM
VE%= Volumetric Efficiency


* Most engines are capable of achieving only about 80% VE (Volumetric Efficiency). A modified street engine with ported heads, headers, intake and carburetor can achieve about 85% VE. With extensive head and valve work and a new cam an engine may reach 95% or even more. It's normally not possible to achieve VE's over 100% without some form of forced induction.

** This represents the minimum CFM required, to support a certain cubic inch engine at the maximum RPM potential of that engine. The number represented by this equation does not account for obstructions such as air filters, or inaccurate CFM ratings found on some carburetors.


258 x 4500 / 3456 x 80% = 268.75

Using this formula and estimating that the typical max RPM for a 258 is 4500 and the VE to be roughly 80% we get a CFM of 268.75. It is also common that most CFM ratings on carburetors are overexagerated, sometimes up to 30% on some of the old Rochester carbs. This leads me to my conclusion that the 1.14 venturi MC2100 is the optimal carb for a 258, with the 1.08 being a close second.
 
What happened, I just blacked out 9.png
 
:poke:

:laugh:
 
Yes, but did I answer your questions? smileyvault-blink.png
 
Very well thank you (for me anyways)

((304 x 5000) / 3456)*.80= 351.851851851 CFM for me... So I should be using a 1.21 or 1.23

Correct? Thanks Teach... :notworthy:

But I am not the OP so let hear what he's got to say too... :chug:

Thanks again Elwood...

~JR
 
yeah man you did some good work, thanks haha
 

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