7 replies to this topic

[ozz1]

How many CFM does a standard 940 head produce? My piston demand is 126.4 CFM, what would I be looking at doing to achieve this?

[mini13]

At what pressure drop, vicars quotes std head as a tad over 90 cfm, a good ported head at about 130 and full race in the 140s

[Turbo Phil]

What depression and what valve lift ? A well modified 940 with a 35.7mm valve will get you into the 130+cfm [email protected]"+ lift tested at 28".

Phil.

Edited by Turbo Phil, 29 May 2017 - 10:29 PM.

[ozz1]

What depression and what valve lift ? A well modified 940 with a 35.7mm valve will get you into the 130+cfm [email protected]"+ lift tested at 28".
Phil.

Thanks Phil. What do you mean by depression? Lift is 0.394".

Being realistic of my skills...with some blending of the manifold locating step, basic polishing and some deshoruding to accommodate a 35.7mm valve, could I be nearing 120 cfm?

[ozz1]

At what pressure drop, vicars quotes std head as a tad over 90 cfm, a good ported head at about 130 and full race in the 140s

Cheers. What do you mean by pressure drop? Do you know where I might find flow rates for a std metro head? Google is proving pretty useless!

[nicklouse]

what they mean is the pressure difference between inlet and "cylinder" the greater the pressure drop the greater the flow. pressure is normally measured in inches of mercury hence the 28"

standard is as said circa 90 and no. you are up with some serious head work to get to 120.

[mini13]

by pressure drop i meant depression as Phil said,

 

the greatest improvements are to be had in the valve seat area, its only once youve sorted that, you need to look at the port. to do heads properly your looking at needing to do some pretty accurate machining, far mor cost and time effective IMO to outsource to someone like TurboPhil^^^ who has the kit and skils already.

 

best bet is get a copy of this, loads of info on heads and other stuff.

 

https://www.amazon.c...CH781PV9S8TEZHP

[Turbo Phil]

Test pressure/depression is the rise, measured in inches of H2o in a vertical manometer when using a flowbench. Tests are run at a certain pressure to give repeatable results and allow comparisons to be made. Common test pressures are 10, 25 and 28", with 28" generally being considered industry standard. When measuring CFM it is essential to know the test pressure used if you wish to compare your results with others, though a correction factor can be used to convert results at one test pressure to another if you do use a different pressure to somebody else.

Phil.

Edited by Turbo Phil, 30 May 2017 - 09:11 AM.