Replies to this message are sent to The Chevelle Mailing List
------------------------------------------------------------
again Rob,
i tend ta agree with ur thinkin........................
Rob Means
"be good,if not,be good at it
[EMAIL PROTECTED]
----- Original Message -----
From: "Rob Thorburn" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Wednesday, March 20, 2002 4:12 PM
Subject: Re: [Chevelle-List] Carb sizing
>
> Replies to this message are sent to The Chevelle Mailing List
> ------------------------------------------------------------
>
> Where this formula goes "off the tracks" so to speak, is that it assumes
> that the CFM rating is measured at the optimal amount of vacuum for the
> engine in question. It is not commonly known, but four barrels are CFM
> rated at 1.5 pounds of vacuum, and two barrels are CFM rated at three
pounds
> of vacuum. Now the real interesting part is: engines make optimum power
> closer to .5 pounds of vacuum.
> This formula cannot take vacuum into account. So is that 500 CFM for a two
> barrel or a four barrel? I would say a two barrel at three pounds of
> vacuum. That big block will trying to suck that carb into the manifold!
My
> experience has been, it is difficult to over-carburete a big block. My
> friend Ron and I put a 850 double pump on a smooth idle 396 in a truck and
> it drove just fine.
> For some reason, hot-rodders tend to be in disbelief at how Rat motors
> love fuel. They can't believe a big-block wants a really big Carburetor.
> They can't believe that Big-blocks need a HUGE fuel delivery system to NOT
> run out of fuel. They can't believe that Big-blocks want a dual three
inch
> exhaust system, and so on.
> Here's a better way to do the math: most people have cut there teeth on
> small blocks, lets use a small-block and compare it to a Big-block. Lets
> take a mild 327 small block with a 650 spread bore: We will cross
multiply
> to get the answer.
>
> 650 x
> ------ ----- = 650 times 396 divided by
327
> equals 787 CFM for a mild Big-block.
> 327 396
> So a 750 is the very smallest carb I would go with. And if you would like
> some tire smoke to go with that Big-block, you will need a bigger carb,
> bigger valves, bigger cam, and bigger exhaust (more compression)
>
> I like a racing mechicanal fuel pump with a regulator to go with that
Holley
> carb, and make sure you have at LEAST 3/8" fuel line!
>
> Don't let the small-block thinkers talk you down! You are building a RAT
!
>
> Rob
> '67 Malibu
> '67 El Camino (in a basket)
>
> ----- Original Message -----
> From: "John Nasta" <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Tuesday, March 19, 2002 2:21 PM
> Subject: RE: [Chevelle-List] Carb sizing
>
>
> >
> > Replies to this message are sent to The Chevelle Mailing List
> > ------------------------------------------------------------
> >
> > Yes, that is the correct carb if you want 80% volumetric efficiency. The
> > idea is to assume that you want 100% VE, and figure out what cfm carb
will
> > theoretically give you that.
> > -----Original Message-----
> > I've had essentially the same engine), at 5500 RPM (realistic[?]) x 396
> CID
> > x 80% (if lucky) / 3456 = a 500 cfm carb
> >
> >
> > -----------------------------------------------------
> > To Unsubscribe please visit www.chevelles.net/list.html
> > To start a new topic, send mail to: [EMAIL PROTECTED]
> >
> >
>
>
>
> -----------------------------------------------------
> To Unsubscribe please visit www.chevelles.net/list.html
> To start a new topic, send mail to: [EMAIL PROTECTED]
>
-----------------------------------------------------
To Unsubscribe please visit www.chevelles.net/list.html
To start a new topic, send mail to: [EMAIL PROTECTED]
