Tri power CFM

[Ray G.]

Looking thru my Fact Book and 67 tech and judging guide, but cant find the CFM for these carbs. Anybody know?

[Ridge K.]

Re: Tri power CFM

Looking thru my Fact Book and 67 tech and judging guide, but cant find the CFM for these carbs. Anybody know?

Ray, in some publications I've seen a few different CFM ratings listed, but on Holley's website (Holley Performance Products), they list the center carburetor as being capable of flowing 350 CFM, and either outboard carburetors being capable of flowing 500 CFM.
I tend to think that the original manufacturer probably is the most correct source.
Hope this information is helpful, Ridge.

[Duke W.]

Re: Tri power CFM

Remember that 2-bbl carbs are rated at 3" Hg depression rather the the 1.5" used for 4-bbl carbs.

You can convert 3" flow to 1.5" by dividing by the square root of two.

I recall this discussion in the early days of the TDB and the equivalent 4-bbl flow of the trips system is 906 CFM.

Those discussions are probably still in the archives circa 2000.

Duke

[Ridge K.]

Re: Tri power CFM

Remember that 2-bbl carbs are rated at 3" Hg depression rather the the 1.5" used for 4-bbl carbs.

You can convert 3" flow to 1.5" by dividing by the square root of two.

I recall this discussion in the early days of the TDB and the equivalent 4-bbl flow of the trips system is 906 CFM.

Those discussions are probably still in the archives circa 2000.

Duke

I have heard the discussion of exactly what Duke is referring to. Here is a photograph of my original 1967 tri-,power carburetors, after restoration by Holley's in-house custom shop. In this pic, they are sitting on a NOS GM intake manifold from 1967.
I spoke to the technician directly, who performed the work on my carbs. I pushed him for Holley's testing results of exact CFM flow, for the three carbs. He would not divulge Holley's internal documentation, but stated that a figure of somewhere between 900 and 1,000 CFM, is a realistic, real world calculation. This would match up closely to Duke's reference.
That's as close as I can get.
p.s. I highly recommend the work performed at Holley's custom shop. As you can see in the pic, the plating is exactly as would be seen on new carburetors during the 1967 to 1969 tri-power era.

[Warren F.]

Re: Tri power CFM

The Corvette tri-power when calculated correctly is a 950 cfm rating. The Chrysler six-pak was rated at 1050 cfm.

[Duke W.]

Re: Tri power CFM

Please explain "correctly calculated".

Are the OE ratings of the Chryler six-pack configuration based on 2-bbl. flow at 3" Hg, or is it converted to 1.5".

It's always in the details.

Here is the original thread on the subject from 2000.

https://www.forums.ncrs.org/showthread.php?t=4352&highlight=carburetor&uid=2451

This thread quotes different flow rates for the end carbs - 500 vs. 466 CFM, both at 3" Hg.

If anyone wants to verify, I believe the Holley Web site includes flow rate for each list number with 2-bbls rated at 3" depression and 4-bbls at 1.5", which is "industry standard".


Duke

[Warren F.]

Re: Tri power CFM

Duke,

The "gross flow" is figured at the 2 bbl rating, which equates to around 1350 cfm for the six-pak configuration carb set-up.. The information came from Guide to Muscle Cars June 1986, two articles Holley Carb Supertuning and Chrysler's '69-'71 SIX-PAK in this issue.

[Duke W.]

Re: Tri power CFM

Using your data for the Chrysler system, 1350/1.414 = 955 CFM equivalent 4-bbl flow, not 1050.

Using Clem's data for the Corvette trips system:

(350 +2(466))/1.414 = 906.6 CFM equivalent 4-bbl flow.

Duke