2100 Motorcraft Carb Series CFM Ratings

[Fastatv]

I was discussing the CFM ratings with my gearhead neighbor this evening and he had discovered the Motorcraft 2100 CFM ratings on several of his websites and he shared this with me. Many of you may know this but, carb builder that I am, I didn't know. The number is stamped on the drivers side carb bowl...and in a circle. I hope I'm not appearing totally dumb here and again, I should have known this.....



Stamped No + CFM

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

 

[Peanut Butter]

The Hoursepower show last Sunday on PowerNation had an interesting formula for the amount of CFM to be used with an engine. This was just a guide line, and was most likely designed for big Hoursepower engines, but I thought that it was very interesting since I know very little about this stuff.

It was: cubic inches X max rpm ÷ 3456 = cfm needed

Plugging this into a stock I6 engine gives some interesting results. My conclusion was that a lot of people are putting way too big of a carburetor on their engines.

Along with this idea my curiosity. wonders about the install of a Offenhouser manifold with a 4 barrel carb. You alls thoughts?

 

[Fastatv]

The Hoursepower show last Sunday on PowerNation had an interesting formula for the amount of CFM to be used with an engine. This was just a guide line, and was most likely designed for big Hoursepower engines, but I thought that it was very interesting since I know very little about this stuff.

It was: cubic inches X max rpm ÷ 3456 = cfm needed

Plugging this into a stock I6 engine gives some interesting results. My conclusion was that a lot of people are putting way too big of a carburetor on their engines.

Along with this idea my curiosity. wonders about the install of a Offenhouser manifold with a 4 barrel carb. You alls thoughts?

Yes, many many folks think that a larger carb is going to increase their engines performance. About 1 million years ago , I used the above formula when installing new carbs on V-8 engined cars/trucks. But rarely did the owner go with what I said. If they had a SBC 350, with headers...they wanted a 750 CFM carb...I sold it to them.. when in reality they my have only needed a 500 CFM....600 max. Anyway, they wouldn't listen ( most ), and I just did what they asked and got paid....
What are you installing the Offy and 4BBL on?

 

[Peanut Butter]

What are you installing the Offy and 4BBL on?

Actually I'm not. Looked at it in the catalogs, but couldn't see the need for a 4 bbl on a straight 6. If I do anything, which is probably way in the future, it will be the fuel injection route. Right now the engine setup that I have will do for what I need. My other choice since I have a GM Turbo 400 Transmission would be to go the V8 route. That is the more likely of the two, but only because I would like to lengthen the Jeep and make a truck out of it. But I'm wishing in one hand and in the other right now.

 

[Woolyworm]

I've got either the 1.08 or the 1.14 on my AMC 304 and it loves it. You get a lot finer and better throttle response when sized correctly. I think most run the 1.08 on the 258s


Wooly

 

[Fastatv]

Here's a link for the same info, but a little more additional info. Second post after the link is opened. I would have placed this in my first post but didn't see an "edit" button...

Motorcraft 2100-2150 to 82 -258 adapter? - The AMC Forum - Page 2

 

[Fastatv]

I've got either the 1.08 or the 1.14 on my AMC 304 and it loves it. You get a lot finer and better throttle response when sized correctly. I think most run the 1.08 on the 258s


Wooly

I have the 1.08 on my 360 V8. It runs fairly well but if I do the calculating, my 360 turning 4200 rpm ( which is very rare however ) would require about 430 CFM. The 1.08 is 287 CFM....lol....yikes!
And yes, the 1.08 is probably great on the AMC 258 i6 / 4.2l ......requires 298 CFM at 4,000 RPM.
Wooly, if you ever have time, could you let me know which one you have....I'm just very curiuos.. :drool:

 

[Fastatv]

I can very much relate to this!

 

[Jimbos76cj]

I think the formula they use also accounts for only 80 something percent VE? better running motor may take a little more. I didn't see the show so Im guessing but most carb calculators don't figure it at 100% which they shouldn't.

 

[Posi]

I think the formula they use also accounts for only 80 something percent VE?

Volumetric Efficiency

 

[Woolyworm]

Mine is 1.08


Wooly

 

[Woolyworm]

A lot depends on what rpm you put in. If I run my AMC 304 at 3800 I should have 320 CFM to feed it. I've probably had it at 3800 or above for about 2 minutes of the 6 years I've owned it. The advantage of a smaller Venturi carb is faster air flow and better atomization which gives you better fuel mixture and better throttle response. At 1000 rpm my AMC 304 only calls for about 90 cfm. Easily delivered by the 1.08. This combined with my small tunnel 2psp intake creates really great throttle response and control. If I start running out of power at 3500 rpm that's probably a good thing vs throwing things out of my engine.


Wooly

 

[Peanut Butter]

If I start running out of power at 3500 rpm that's probably a good thing vs throwing things out of my engine. Wooly

I like that!

One side note for those not so educated (like me) (uneducated that is), There is a number at the base of the carburetor that you need to be able to get the correct rebuild kit.

3FCC

 

[Fastatv]

I will check mine.... I have built carbs for 35 years....but I learn every day. , I may go to garage and check it now! Does your number indicate 1973?
I checked mine....the number...exactly like yours....identical...3FCC...

 

[Peanut Butter]

I will check mine.... I have built carbs for 35 years....but I learn every day. , I may go to garage and check it now! Does your number indicate 1973?
I checked mine....the number...exactly like yours....identical...3FCC...

I cant begin to tell you how much I have learned from others on this forum!

I have no idea what the numbers mean literally, but there are three different set of numbers that correspond to different rebuild kits (one is C5ZF). I think the main difference is in the bottom gasket and a slightly different footprint. So I think you might be able to conclude that those were different versions made in different years.

Also in the "DOCs" section of this forum is a rebuild instruction sheet. http://www.jeep-cj.com/docs/non-specific-jeep-7/

 

[Fastatv]

Dang...:drool::drool:, I was going thru my old carbs that I have had for years...found a motorcraft 2100 1.23...8A BA, off of a 68 ford 390....356 CFM , and its complete! I'm afraid it will have to go on my 360......

 

[mriplaybass]

While just wasting time surfing for a V8 to put into a future 47 IHC hot rod truck that is just a future dream right now, I found this CFM calculator. Probably uses the same formula as was already posted, but pretty much just a plug and play calculator.
CFM Calculator