Low and medium lift Flow

[digger]

Yes you input flow numbers and sizes of port throat, port entry and valve/seat sizes

Cool, It seems a bigger valve would be more prone to reversion on opening and a smaller port would be less prone to velocity lag but that is just an assumption on my part.

here is a comparison by taking the same engine and shrinking the entire inlet 1/8" including the valve and manifold (head flow is same so the Cd goes up)

port Mach No



mass flow

these are the correct graphs

[digger]

Isn’t the right experiment for simulations to increase and reduce the low lift flow map of the head and then see what happens to mass flow and power? The increase could be done either by increasing the area keeping the coefficient constant or increasing the coefficient keeping the area constant.

yeah, but the low lift proponents seem to like to do cam tests.....

[68corvette]

Simulations often do not have options for area/velocity change.
Like in the recent topic I made about AFR heads, the low lift flow did not change drastically, yet torque improved a lot:
viewtopic.php?f=1&t=60043

Its not just about the flow.

[ptuomov]

“ yeah, but the low lift proponents seem to like to do cam tests.....“

I don’t think one can separate the camshaft from the discussion of low lift flow. Does low low-lift flow and longer duration camshaft makes more torque and power below the peak power rpm than high low-lift flow and shorter duration camshaft? I think that’s the most relevant question, no?

[digger]

There are lots of permutations e.g

- a baseline flow curve
- reduced low lift flow but the same high lift flow
- reduces low lift flow but more high lift flow
- more low lift flow but same high lift flow
- more low lift flow but less high lift flow

If you have a valve that lifts 0.800” if the head is appropriately sized an extra 20cfm upto and including 50% lift (upto 0.400”) produces far less gains than 20cfm from 50% lift and up (0.400” upwards)



the better high lift flow head would allow a smaller cam to boost bottom end but match the low lift flow head up top.

[brentry]

Ls cammed 6.0 dyno test
799/706 both stock gm heads.
706 is 93% width or so and with a 45 angle,
the red circle tells the story . Obviously it does not flow well in reverse or forward at low lifts. And peaks at 218cfm or so with its 1.89 valve on my bench
799 peaks at 255cfm or so . With its 2.0 valve.
And normal looking factory vj. Much better flow thru the curve. 706 has about 0.35 more compression. On a cammed 5.3LS 706 is better everywhere
Cheap test. I had all the head data.

[digger]

can you post the full graph and the data for both the heads (flow, areas or volume)?

ive seen many tests where 706 comes out on top on the smaller size LS's mostly becasue the cross sectional areas are sufficient to meet the engines needs.

[CGT]

can you post the full graph and the data for both the heads (flow, areas or volume)?

ive seen many tests where 706 comes out on top on the smaller size LS's mostly becasue the cross sectional areas are sufficient to meet the engines needs.

Yeah which is kinda surprising because the 706/862 basically have no valve job from GM. The throat is too big for the valve size, and they are just a valve setting on a 45°seat with no bottom cut because there is no material there... Its like they used the seat insert from the castings that use a 2.00 intake valve, and threw the 1.89 valve on that seat.

[brentry]

Ya i will. I will have to find the data. Going from memory. I did flow both heads in reverse over a year ago before the 6.0 test was available.