Proform main body identification

PolaraFury · Apr 29, 2021

I have a Proform main body with Holley float bowls on it. The metering blocks have 4780 stamped on top.

I was told it is an 850 but I was also told the engine was a fresh rebuild and that wasn’t true.

I am trying to figure out what cfm this thing is so I can get a rebuild kit for it.

Thanks for your time

vintage chromoly · Apr 29, 2021

I believe an 850 has 1.75” throttle bores.
A 750 has 1.6785” bores, if I’m not mistaken

33 IMP · Apr 29, 2021

4780 would be an 800 double pumper.
The best way to find out how much its supposed to flow, is measure the throttle blade size, and the venturi size.

PolaraFury · Apr 29, 2021

Do I measure them on the bottom side

33 IMP · Apr 29, 2021

You can measure the throttle blades from the bottom. You might have to take the base plate off to measure the venturi accurately from the bottom. I use a divider, once the base is off.

PolaraFury · Apr 29, 2021

33 IMP said:
4780 would be an 800 double pumper.
The best way to find out how much its supposed to flow, is measure the throttle blade size, and the venturi size.

Should the rear metering block also have idle circuit screws

33 IMP · Apr 29, 2021

Some do... some dont. Depends if the main body is drilled for secondary idle.
Im guessing a newer main body would be, the 4780 holley secondary metering plates probably arent.

Proform main body identification

PolaraFury

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vintage chromoly

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33 IMP

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PolaraFury

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33 IMP

FBBO Gold Member

PolaraFury

Well-Known Member

33 IMP

FBBO Gold Member

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