these are the correct graphsdigger wrote: ↑Sat Aug 08, 2020 11:28 pmhere 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
Low and medium lift Flow
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Re: Low and medium lift Flow
Re: Low and medium lift Flow
yeah, but the low lift proponents seem to like to do cam tests.....ptuomov wrote: ↑Sun Aug 09, 2020 12:37 am 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.
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Re: Low and medium lift Flow
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.
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.
Re: Low and medium lift Flow
“ 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?
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?
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Re: Low and medium lift Flow
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.
- 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.
Re: Low and medium lift Flow
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.
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.
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Re: Low and medium lift Flow
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.
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.
Re: Low and medium lift Flow
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.
Re: Low and medium lift Flow
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.