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Re: 906 heads, home port vs. "Pro" job
[Re: ccdave]
#29400
08/31/06 09:26 PM
08/31/06 09:26 PM
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Joined: Jan 2003
Posts: 14,515
So. Burlington, Vt.
fast68plymouth
OP
I Live Here
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OP
I Live Here
Joined: Jan 2003
Posts: 14,515
So. Burlington, Vt.
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Quote:
What happened on the Intake side at .450? Flow went from 257.9 at .400 to 270 at .450, then back down to 265.9 at .500. Looks like turbulance starts at the .650 range so the rise in flow, than the dip between .400 and .500 seems odd.
lift----I/E
.100--69.5/56.3
.200-145.5/112.3
.300-208.5/158.4
.400-257.9/179.2
.450-270.7/187.1
.500-265.9/189.7
.550-269.1/194.9
.600-270.7/197.5
.650-267.5/201.4
.700-261.1/204.1
well....basically....this is the trade off for leaving the short turns final approach into the bowl fairly steep.
on this port, up to around .450 lift(it was actually around .470 lift where the "problem" occurs) the air column is being effeciently turned into the bowl, and the entire diameter of the valve is being taken advantage of.
when you try to get too much air over the short turn, the bottom of the air column has a hard time staying connected to the floor, and it starts skipping over the short turn, at which point the air column rides across the back of the valve, effectively shutting down the short turn side of the exit into the chamber.
this is why the flow drops as the valve is opened slightly beyond the point where the entire area of the valve is being utilized.
once you surpass that point, the effective curtain area is diminished, and the flow decreases.
then, if the port hasnt gone completely turbulent, the flow will continue to climb as the valve is opened, until you reach some other limitation in the port...which in this port, was again the short turn.
its this added height and steepness of the short turn on the 906/915 head that allows it to out-flow the later castings in the mid-lifts(when properly shaped to do so).
the newer castings just dont have enough short turn height and length to effeciently turn the air column in that lift range.
they generally start having the air column sliding over the back side of the valve at a little over .300 lift.
its very easy to hear when you're testing the head when the shift in flow from the whole valve area, to the partial area happens.
basically, if you kept lowering, and laying back the floor of the 906/915 intake port, it would start to get more and more like the later design castings.....meaning, you will generaly start to lose flow in the mid-lifts, and in doing so, hopefully delay the point at which the onset of turbulence happens.
this is the trade off.
actually, the next step from this point would be to start whittling down the guide boss, to make more room for the air column near the roof of the port, to try and minimize the congestion at the short turn floor.
this would gain you upwards or 6-10cfm.....although you might still end up having to tweek the short turn a bit more to get to a solid 280cfm.
when you're trying for the 290cfm range, and stable to .650 lift or more....the short turn will be layed back, and lowered quite a bit more than what i did here....and the guide boss needs to be more or less eliminated.
as far as a pic of the short turn....its the area you cant see thats critical.
you would need to have the head cut apart lengthwise through the intake port to see the shape of the short turn for a pic to be of any use at all.
the short turn is ported by "feel", and the results verified on the flow bench.
i checked the pushrod pinch width of these heads today. they varied from about .995 to as big as 1.025.
the one for this cylinder that was tested was 1.015.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
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Re: 906 heads, home port vs. "Pro" job
[Re: fast68plymouth]
#29401
08/31/06 09:48 PM
08/31/06 09:48 PM
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Joined: Jan 2003
Posts: 14,515
So. Burlington, Vt.
fast68plymouth
OP
I Live Here
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OP
I Live Here
Joined: Jan 2003
Posts: 14,515
So. Burlington, Vt.
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for comparison, here is a set of numbers from some 906's i ported last week. these are also going on a motor thats getting a mid-.500 lift flat tappet cam, so again, i didnt go for the "big number" at .700 lift. these also used a smaller than 2.14 intake valve, and a 1.74 exhaust valve. these got a fair amount of additional work compared to the reworked "home port" heads. the pushrod pinch was opened to 1.060, and the guide bosses were streamlined quite a bit, but i left as much of the bulkiness of the intake guide boss in the port as possible, and still get a decent number(yes, there is a reason for me leaving as much of the guide boss in the port as possible, and the smaller intake valve....but you guys will have to figure that one out for yourselves  ). the intake port opening is the same size as an OE valley pan gasket, and the exhaust port openings are barely any bigger than as cast(basically, just "squared up"). lift----I/E .100--69.2/51.9 .200-145.0/109.3 .300-210.3/150.0 .400-257.9/179.2 .450-274.7/188.4 .500-279.6/195.6 .550-282.0/203.4 .600-274.7/207.3 .650-274.7/209.3 .700-275.5/211.9
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
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Re: 906 heads, home port vs. "Pro" job
[Re: BradH]
#29406
09/01/06 10:23 AM
09/01/06 10:23 AM
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Joined: Jan 2003
Posts: 16,934
NC
440Jim
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 16,934
NC
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Quote:
lift----I/E
.100--69.2/51.9
.200-145.0/109.3
.300-210.3/150.0
.400-257.9/179.2
.450-274.7/188.4
.500-279.6/195.6
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Those are some good 906 iron heads.
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Re: 906 heads, home port vs. "Pro" job
[Re: 440Jim]
#29407
09/01/06 10:27 AM
09/01/06 10:27 AM
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Joined: May 2005
Posts: 6,446
NJ-USA
HPMike
master
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master
Joined: May 2005
Posts: 6,446
NJ-USA
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Re: 906 heads, home port vs. "Pro" job
[Re: Bob_Coomer]
#29409
09/01/06 12:27 PM
09/01/06 12:27 PM
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Joined: Dec 2003
Posts: 3,957
West Coast, CA
Troy
master
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master
Joined: Dec 2003
Posts: 3,957
West Coast, CA
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Hi Dwayne. Is there much of a difference between porting a Mopar Performance Stage V head over a 906/452? If equal time spent on a 906/452 and a Stage V head, how much CFM would you see different between the two heads?
BTW, Very good reading, Thank You.
....there is nothing like driving my 1968 Hemi Dart around town and having people looking at you like you're nuts!!
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Ron
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