[DeTomaso] REPLACMENT CARB ?

[Will Kooiman]

Here are 2 more data points.

Data Point #1:

I mention Hot Rod Engine Masters frequently.  They tested carburetor sizes in one episode.  They ran a 650,750,850,950, if I recall correctly.

They made nearly identical HP - until they didn't.  In other words, until your engine needs 750 cfm, the 650 and 750 made the same HP.  The larger carburetors only helped at the high end of the RPM scale.

Of course, that's exactly what you'd expect.  Their recommendation was a smaller carburetor will be more responsive, so basically you should choose the smallest carburetor that your engine needs.

Data Point #2:

I started with a 650DP on my mostly stock 351C.  It was my daily driver for several years.  Over about 5 years, I put around 30,000 miles on my car.  It averaged between 19-20 mpg.

After several engine upgrades (cam,heads,intake,exhaust), mpg dropped to about 18-19mpg.  I switched to a much larger carburetor, and I still got about 18-19mpg.  There was no difference at all.  I did this upgrade at about year 2, so most of my 18-19mpg was with lots of upgrades, and a big carburetor.

There is a difference between street carburetors and double pumpers, but that's because the DP carburetors are richer during cruise.  Their power valve circuits provide less gas, because they are intentionally jetted richer.

Switching from a 600cfm 1850 vacuum secondary to a 600cfm 4776 double pumper should result in a 1-2mpg drop in mpg, but switching from a 650DP to a 750DP should only result in worse throttle response - if your engine is too small.


On 1/26/22, 2:22 AM, "DeTomaso on behalf of Dennis Valdez via DeTomaso" <detomaso-bounces at server.detomasolist.com on behalf of detomaso at server.detomasolist.com> wrote:

    FWIW, I have a ‘74 with stock engine and intake.  Previous owner replaced the Motorcraft with an Edelbrock 650cfm Thunder Series 1806. The car runs very well with smooth acceleration and no flat spots. Stock air cleaner fits under the engine cover as well.  I have no complaints. 

    Best,

    Dennis Valdez

    > On Jan 25, 2022, at 8:31 AM, Larry Weston <lplugw at hotmail.com> wrote:
    > 
    >    most importantly, are you going to use the stock spread bore manifold
    >   or change out to a square bore manifold?
    >     __________________________________________________________________
    > 
    >   From: DeTomaso <detomaso-bounces at server.detomasolist.com> on behalf of
    >   Ken Green via DeTomaso <detomaso at server.detomasolist.com>
    >   Sent: Tuesday, January 25, 2022 11:28 AM
    >   To: Detomaso List <detomaso at server.detomasolist.com>; Ian Deffebach
    >   <flatbeds78 at yahoo.com>
    >   Subject: Re: [DeTomaso] REPLACMENT CARB ?
    > 
    >   Probably depends on use and the rest of the engine, original cam, etc.
    >       On Tuesday, January 25, 2022, 08:10:59 AM PST, Ian Deffebach via
    >   DeTomaso <detomaso at server.detomasolist.com> wrote:
    > 
    >      Do you know what the carb of choice is when replacing the original
    >     Motorcraft on a 74 ? Holley Avenger ? what CFM ? Model # ?
    >     Ian Deffebach
    >     Owner, Deffebach Trucking
    >     818-472-9655
    >     | "An asset based company."
    >     [7243690c-3537-43c1-be25-d8471a8633b7.png]
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