Motorcraft 2100 with 1.14 venturies on 258

[Bent]

Hello, I submitted this on another forum and got no response.

I'm in the process of converting from a Holley 2300 (350 CFM) to the Motorcraft 2100 on my AMC 258 i6 / 4.2l .

It seems like most people recommend the 1.08 venturi size for the AMC 258 i6 / 4.2l . I have a 1.08 and a 1.14. I assumed that the 1.14 was a larger carb based on the fact that it has larger venturies and flows more CFM. It's not! The 1.14 has smaller throttle bores t han the 1.08! Information on throttle bore size for these carbs is hard to find. But sitting next to each other it's obvious. It looks like the 1.02 and the 1.14 share a common bore size with different venturies. And, the 1.08 and the 1.21 share a common bore size. A smaller bore should increase air velocity through the carb and not just at the venture . This should improve low RPM torque and provide a stronger vacuum signal at the vacuum advance port.

I would like to hear from anyone that has run has run the 1.14 on a AMC 258 i6 / 4.2l . It's a 1978 AMC 258 i6 / 4.2l with a mild cam, HEI and a 1986 cylinder head. And no, I don't want to switch to a Weber. I believe annular discharge boosters are a better design for a low RPM motor.Thanks for any replies.

 

[jeremy5780]

Sorry I don't have any info for you, as I'm in the process of tracking down a 1.08 to rid my cj of it's cancer (HOLLEY carb) If you want to sell your 1.08 please send me a message. In the mean time email this guy and ask him your question Michael.ehrmann@hotmail.com he is who I have been talking to about my swap. He knows his stuff and will email you back very quickly!

 

[Dan77CJ7]

The formula below can be used to find your airflow requirement. It’s based on 100% volumetric
efficiency so any indicated airflow must be multiplied by the volumetric efficiency of your
particular engine. Use a carburetor with an airflow rating equal to or slightly smaller than the air
requirement of your engine.

Cubic In. Displacement X Maximum RPM = Maximum CFM
2 1728

Let’s take for example, a AMC 258 i6 / 4.2l C.I.D. I-6 which has a maximum RPM limit of 5000 RPM. It’s been
determined that this particular engine has a volumetric efficiency of 80%.

AMC 258 i6 / 4.2l Cubic Inches X 5000 RPM = 373 CFM
2 1728

373 X 80% = 298
According to our chart the engine’s airflow requirement is 373 C.F.M. at 100% volumetric
efficiency. At 80%, however, the C.F.M. requirement is 298 C.F.M. This engine would, therefore
require a 300 C.F.M. carburetor (or slightly smaller)



Note, the Motorcraft 2100/2150 series 2 barrel carburetor with 1.08 venturis is 287 CFM. This is a perfect
match for your AMC 258 i6 / 4.2l !!! Also remember for those who feel 287 CFM is “undersized” this is also based on turning
that engine at 5000 RPM. The less RPM requires, the smaller carb needed for max RPM capabilities. You will
find that the 1.08 venturis Motorcraft 2bbl is just about as perfect of a match as you can put together.


i got this info from Gronk its in the install guide.

 

[Dan77CJ7]

I was going to have Gronk do my install but he pretty much clipped my wings and told me i could do it, i emailed him about 5 times with minor questions, got back fast. i'm happy with my install, the smooth idle and nice throttle response from a stop is just what i wanted! the ram air is a nice touch got a lot of looks/questions at Sonic........

 

[Bent]

The formula below can be used to find your airflow requirement. It’s based on 100% volumetric
efficiency so any indicated airflow must be multiplied by the volumetric efficiency of your
particular engine. Use a carburetor with an airflow rating equal to or slightly smaller than the air
requirement of your engine.

Cubic In. Displacement X Maximum RPM = Maximum CFM
2 1728

Let’s take for example, a AMC 258 i6 / 4.2l C.I.D. I-6 which has a maximum RPM limit of 5000 RPM. It’s been
determined that this particular engine has a volumetric efficiency of 80%.

AMC 258 i6 / 4.2l Cubic Inches X 5000 RPM = 373 CFM
2 1728

373 X 80% = 298
According to our chart the engine’s airflow requirement is 373 C.F.M. at 100% volumetric
efficiency. At 80%, however, the C.F.M. requirement is 298 C.F.M. This engine would, therefore
require a 300 C.F.M. carburetor (or slightly smaller)



Note, the Motorcraft 2100/2150 series 2 barrel carburetor with 1.08 venturis is 287 CFM. This is a perfect
match for your AMC 258 i6 / 4.2l !!! Also remember for those who feel 287 CFM is “undersized” this is also based on turning
that engine at 5000 RPM. The less RPM requires, the smaller carb needed for max RPM capabilities. You will
find that the 1.08 venturis Motorcraft 2bbl is just about as perfect of a match as you can put together.


i got this info from Gronk its in the install guide.

CFM is how carbs are rated, so technically the 1.14 is a larger carb. There is a reason that the flow rating only increased 13 CFM with the normal venture size increase of .06 instead of 40-50 CFM increase like you see with the rest of the MC2100 when venture size is increased .06 or .07. The reason for only a 13 CFM increase is the smaller throttle bores. So if air speed is already higher through the carb because of the smaller throttle bores, you don't need a venturi as tight to produce a strong low pressure area. There is no such thing as a carb too big, only one that doesn't produce a strong enough low pressure signal for the jets.

I know people are having great success with 1.08 carb. But is throttle response simply a function of venturi size or is the throttle bore a factor. I have read that low RPM torque increased on the 260 v8 with the addition of the 1.14, but that was on the internet so...

Has anyone used both?

 

[johnnyreb]

hey Dan where did you get that cool airfilter set up?

 

[Bent]

Let me re-phrase my question:
The weber 38DGAS flows about 390 CFM.? The guys that can afford them report great results. The 350 CFM Holley 2300 that I have on the AMC 258 i6 / 4.2l now runs great until you uncover the power valve on a steep hill. So, the 13 CFM difference between the 1.08 and the 1.14 doesn't seem significant.

So if the difference between the two CFM ratings isn't significant, what other qualities do you use to choose between the two?

The one with the smaller throttle bores?
Or, the one with the larger throttle bores?
And why?

 

[rufus1138]

just a note, larger throttle bores will get you better gas mileage as they will have slightly less vacuum and pull less fuel.

 

[Bent]

just a note, larger throttle bores will get you better gas mileage as they will have slightly less vacuum and pull less fuel.

I was thinking that could be corrected with smaller jets

 

[Dan77CJ7]

Afford them? i wouldnt say that. the weber has been a great carb for some not all, most people i run into hated them with a white hot passion! if you want a hot race carb with ultra snappy throttle and a leaks like a screen door on.... never mind. when one re-shapes the wheel he must learn from his own built. good luck.

 

[Bent]

The results are in!

The 1.14 venturi carb runs good. It runs about like the Holley 2300. Good throttle response, Good low speed torque.

The 1.08 carb runs better. Great throttle response, great low speed torque! Now I just need to find one without a broken mounting flange.

What I learned from research is this: The throttle bore diameter is less important than the ratio between the throttle bore diameter and the venture diameter. The greater the difference, the better low RPM torque, less high RPM HP.

Venturi diameter/Throttle bore diameter
MC 2100
1.08/1.56= 69%
1.14/1.44= 79%
Holley 2300 (0-7448)
1.18/1.50= 79%

 

[superj]

I could never get my 1.14 to run without a not of hesitation.