Re: [AMC-List] Update on surging 401

[Frank Swygert <farna@xxxxxxx>]

Marty, the 600 will be fine on the 401 for normal street driving. The
smaller venturis (barrels) will improve low speed torque, so it will
feel better off the line and up to cruising speed. You'll lose some top 
end performance because the engine will enventually need more fuel/air
than the 600 can provide. 

Check this site out:
http://www.classictruckshop.com/garage/shopmathcfm1.asp

Using the calculator there, even at 100% volumetric efficiency the 401
only needs 580 cfm at 5,000 rpm. When you hit 80 I bet you were around
4,000 at the most. The calculator defaults to 90% VE, but 80% is more
like average for a factory stock engine. you might get close to 90 with 
a nice intake, headers, and free flowing exhaust system, but even then
85% is more like it. If you were drag dracing and turning the engine up 
to 7,000 rpm you'd need the 750 cfm carb -- the calc says 730 at 90%
VE. I think it defaults to 90 to give a little more carb than
absolutely necessary, it doesn't hurt to have a little more, but not a
lot. Most of the guys telling you 600 cfm isn't enough are racing their 
cars and want the higher rpm power. Street cars don't need it as they
rarely see over 3,000 rpm on a regular basis. 


On July 15, 2006 Marty Bricker wrote:

> Well, it appears that the problem was with the 750
> Carter .  I swapped it out with my 600 Edelbrock and
> it's running just great.
>   I purchased the 750 cause I was told the 600 would
> not be enough for the 401.  Where will I see a
> difference?  It seemed to pull great off the line up
> to 70-80 when I backed off.  I don't have any
> experience with an engine like this (304 was biggest I
> ever had before).  Thanks.
> Marty
> 
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