Re: [AMC-List] Update on surging 401

[Frank Swygert <farna@xxxxxxx>]

Well, we agree on the 600 cfm carb as being a good size for most 401s.
As I noted, you'd have to pull 7,000 rpm before a 401 needed 750 cfm.
I'm pretty sure a stock cam won't produce any useable power over 5,000. 
Many drag racers never turn their 401s up that much! Air flow is
dependent on rpm as well, but an engine has to be capable of pumping
that much air. Cam and such does limit capability, and a cam that will
allow that much flow at high rpm won't run well at low speeds. So we're 
both on the same page, more or less. 

On July 17, 2006 Savage, Peter wrote:

> Frank,
> 
> I disagree!  The engine can only pull as much air as the CI of the
engine allows.  This is
> somewhat dependent on camshaft, but overall with stock timing gear
the 401 will not need
> anything larger than the 600 CFM carb, even on the top end...
> 
> Peter
> 
> 
> -----Original Message-----
> From: amc-list-bounces@xxxxxxx [mailto:amc-list-bounces@xxxxxxx]On
Behalf Of Frank Swygert
> Sent: Sunday, July 16, 2006 11:34 PM
> To: amcrelay@xxxxxxxxxxxx
> Subject: Re: [AMC-List] Update on surging 401
> 
> 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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> 
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