If going to Methanol, do I need to raise the CFM as well?

patrickonb · Post by **patrickonb** » Wed Aug 10, 2022 1:58 pm

Hello Gang, I have another dumb question for y'all...

Building the 433 BBC, all info says I should use a carb in the 800-850 cfm range. If I decide to go
to Methanol or E85, and the fuel now needs to be doubled (or there about), do I then also need
to raise the CFM rating of the carb?

Thanks,
Patrick

mag2555 · Post by **mag2555** » Wed Aug 10, 2022 2:57 pm

No.
You could use bigger intake ports because since your now going to have twice as much fuel vapor taking up room that was air when running gas.
You could well use more lift also.

Elroy · Post by **Elroy** » Wed Aug 10, 2022 3:14 pm

In theory, i would think you could get away with a smaller carb on alcohol fuels.

Post by **CamKing** » Wed Aug 10, 2022 3:30 pm

No need to go bigger on carb, or ports.
When you switch to Methanol, it will lower the temp of the intake charge thru the carb, manifold and ports. The cooler charge will increase the air density, which more then makes up for the area lost to the added fuel.

patrickonb · Post by **patrickonb** » Wed Aug 10, 2022 8:45 pm

OK, thanks for the reply's, I appreciate it!

Patrick

Walter R. Malik · Post by **Walter R. Malik** » Wed Aug 10, 2022 9:29 pm

patrickonb wrote: ↑Wed Aug 10, 2022 1:58 pm Hello Gang, I have another dumb question for y'all...

Building the 433 BBC, all info says I should use a carb in the 800-850 cfm range. If I decide to go
to Methanol or E85, and the fuel now needs to be doubled (or there about), do I then also need
to raise the CFM rating of the carb?

Thanks,
Patrick

NO ... but, if you already are using a very large carb with gasoline, you may need to go to a smaller air flow rated carb because that large carb may not be able to flow enough fuel for its airflow rating, when using alcohol; even after being modified for alcohol.

patrickonb · Post by **patrickonb** » Wed Aug 10, 2022 11:30 pm

Walter R. Malik wrote: ↑Wed Aug 10, 2022 9:29 pm NO ... but, if you already are using a very large carb with gasoline, you may need to go to a smaller air flow rated carb because that large carb may not be able to flow enough fuel for its airflow rating, when using alcohol; even after being modified for alcohol.

Ahh yes, this does make sense!! Thank you.

Post by **Tom68** » Thu Aug 11, 2022 1:32 am

Walter R. Malik wrote: ↑Wed Aug 10, 2022 9:29 pm
patrickonb wrote: ↑Wed Aug 10, 2022 1:58 pm

Building the 433 BBC,

NO ... but, if you already are using a very large carb with gasoline, you may need to go to a smaller air flow rated carb because that large carb may not be able to flow enough fuel for its airflow rating, when using alcohol; even after being modified for alcohol.

433ci. 850cfm @ 20.4 inH20 would be a small carby if it's got good heads and a cam wouldn't it ?

Walter R. Malik · Post by **Walter R. Malik** » Thu Aug 11, 2022 9:39 am

Tom68 wrote: ↑Thu Aug 11, 2022 1:32 am
433ci. 850cfm @ 20.4 inH20 would be a small carby if it's got good heads and a cam wouldn't it ?

It is all about IF that carburetor is able to supply enough fuel for the amount of air it can flow.

gregsdart · Post by **gregsdart** » Fri Aug 12, 2022 11:21 am

What will the airflow be at launch, and also top end? You need a carb that will work at both ends. I would think an 850 to 950 cfm for a 750 hp build,,,,,,,

Alaskaracer · Post by **Alaskaracer** » Sat Aug 13, 2022 10:31 am

Not mentioned but noteworthy:

alky is nearly 50% by volume, oxygen. That's why you need to run roughly twice as much as gasoline. Methanol carbs tend to be smaller than gas on the same application so they have a bit stronger signal to the boosters, which helps pull the fuel. Carbs and methanol work, work well, but in my somewhat limited opinion, the best setup to run methanol is mfi. Simple, easy to tune, and much less headache than a carb......

prairiehotrodder · Post by **prairiehotrodder** » Sat Aug 13, 2022 10:35 am

Coloradoracer wrote: ↑Sat Aug 13, 2022 10:31 am Not mentioned but noteworthy:

alky is nearly 50% by volume, oxygen. That's why you need to run roughly twice as much as gasoline. Methanol carbs tend to be smaller than gas on the same application so they have a bit stronger signal to the boosters, which helps pull the fuel. Carbs and methanol work, work well, but in my somewhat limited opinion, the best setup to run methanol is mfi. Simple, easy to tune, and much less headache than a carb......

What kind of MFI do you like ?

Alaskaracer · Post by **Alaskaracer** » Sat Aug 13, 2022 4:24 pm

I run a Killerron's setup, and it's the best thing I ever did for my program. Enderle is also another huge one, and in wide use everywhere. Both work equally well.

Don Terrill’s Speed-Talk

If going to Methanol, do I need to raise the CFM as well?

If going to Methanol, do I need to raise the CFM as well?

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Re: If going to Methanol, do I need to raise the CFM as well?

Re: If going to Methanol, do I need to raise the CFM as well?

Re: If going to Methanol, do I need to raise the CFM as well?

Re: If going to Methanol, do I need to raise the CFM as well?

Re: If going to Methanol, do I need to raise the CFM as well?

Re: If going to Methanol, do I need to raise the CFM as well?