408 Cfm
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Senior User
Joined: Jan 2004
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From: Illinois
408 Cfm
Hello,
This is my first time on this forum and I am amazed on how much info is on here. I recently finished a 351M to 408 conversion. It was fun and a lot of work. My question is, I had a 600 CFM Edelbrock performer on the 351 before I started. It ended up on my 408, my 408 has a higher compression ratio and an Edelbrock cam. I found a set of flat top Dynagear pistons bored 30 over, those were hard to find. Anyway, would the 408 peform any better with a 750 cfm or would it just be a waste of money. Thanks.
Sanders
This is my first time on this forum and I am amazed on how much info is on here. I recently finished a 351M to 408 conversion. It was fun and a lot of work. My question is, I had a 600 CFM Edelbrock performer on the 351 before I started. It ended up on my 408, my 408 has a higher compression ratio and an Edelbrock cam. I found a set of flat top Dynagear pistons bored 30 over, those were hard to find. Anyway, would the 408 peform any better with a 750 cfm or would it just be a waste of money. Thanks.
Sanders
Posting Legend
Joined: Sep 2001
Posts: 30,255
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The 600 will be just fine. The 750 will work but driveability and mileage will suffer. I use a 600 on my 400 and it will be going on my 408 also.
Rule of thumb for a street engine:
Cubes x 1.5 = Max CFM
408 x 1.5 = 612
Make sure you tune your carb with a A/F ratio sensor or by the seat of the pants drag race method shown in the carb manual.
Rule of thumb for a street engine:
Cubes x 1.5 = Max CFM
408 x 1.5 = 612
Make sure you tune your carb with a A/F ratio sensor or by the seat of the pants drag race method shown in the carb manual.
Postmaster
Joined: Aug 2001
Posts: 4,270
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From: Delaware
The 600 cfm Edelbrock Performer has smaller Primary Venturies than the 750 cfm, but the Secondary Venturies are the same size.
The 600 cfm carb should help the gas mileage and driveability, and only fall behind the 750 cfm carb at WOT.
In other words, unless you need to shave 0.1 seconds off your 1/4 mile ET, you are better off with the 600.
The 600 cfm carb should help the gas mileage and driveability, and only fall behind the 750 cfm carb at WOT.
In other words, unless you need to shave 0.1 seconds off your 1/4 mile ET, you are better off with the 600.
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Senior User
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From: Illinois
Thanks Danlee, that's kinda what I was thinking. I might later on change the jets and rods around a little to see if I can get a few more ponies.
74F100, you can get a 408 by taking a 351M installiing a 400 crank and pistons then boring it out .030 over.
Sanders
74F100, you can get a 408 by taking a 351M installiing a 400 crank and pistons then boring it out .030 over.
Sanders
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Joined: Apr 2003
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From: columbia
It all depends on your cam on how much cfm you need I'm planning to drop a comp 268h in my 400. 400 x 1.5 = 600 comp recomends 650 of greater.
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From: Normal, IL
Correct formula for finding cfm is:
(cu. in. x rpm x V.E.)/3456 = cfm
or in simpler terms:
408 x 5500 x .90 = 584.375 cfm
According to the formula, it only needs a 600. But Cleveland based engines, which we all know include 351M/400's, like larger cfm carburetors, just adjust your jetting and accelerator pump circuits accordingly. For good street and trail use a 600 is fine, but if you really want to ring it out above 6000, I highly recommend a 750-850 cfm carburetor.
(cu. in. x rpm x V.E.)/3456 = cfm
or in simpler terms:
408 x 5500 x .90 = 584.375 cfm
According to the formula, it only needs a 600. But Cleveland based engines, which we all know include 351M/400's, like larger cfm carburetors, just adjust your jetting and accelerator pump circuits accordingly. For good street and trail use a 600 is fine, but if you really want to ring it out above 6000, I highly recommend a 750-850 cfm carburetor.
