75cc head with the same gasket.
notice how the chamber is pulled away from the gasket near the intake valve.
this does cost a little flow in the .300-.400 lift range, but doesnt seem to hurt the high lift flow at all.

here is that pad on the deck of an 84cc head

on the 75cc heads, its basically gone.

OOTB flow numbers, Edelbrock valve job, no modifications:

lift----I/E
.100--62.6/51.4
.200-122.0/100.4
.300-183.0/137.6
.400-230.3/166.6
.450-249.4/177.8
.500-261.8/185.2
.550-268.1/191.4
.600-274.8/195.1
.650-278.6/198.4
.700-282.3/201.3

while the low & mid-lift numbers are pretty weak OOTB, i will say that the high lift flow is as good as ive seen out of an OOTB Mopar RPM type head in a while.

re-cut seats, back cut valves, blend intake bowl and pushrod pinch area, basic clean up of entire exhaust port, but retain the OOTB port opening(for use with small tube headers or exhaust manifolds).
this is the same as what i do as a "stage I" job on the 84cc rpm head(no chamber work).

lift----I/E
.100--66.7/64.2
.200-129.3/109.1
.300-184.7/146.8
.400-235.6/177.8
.450-259.9/189.7
.500-271.1/198.4
.550-279.3/204.6
.600-284.2/208.8
.650-286.1/215.0
.700-286.1/217.0

same as above.....but with blended chamber:

lift----I/E
.100--69.6/60.7
.200-140.3/111.6
.300-204.9/147.5
.400-250.5/183.5
.450-264.4/198.4
.500-275.6/210.8
.550-283.1/218.2
.600-287.9/223.2
.650-287.9/228.1
.700-286.8/230.6


i have to say that this particular exhaust port seemed oddly good for that level of work. usually they are about 10 cfm lower in the upper lifts.

for comparison, here is an 84cc head with the stage I job(no chamber mods):

lift----I/E
.100--72.5/61.8
.200-148.1/117.8
.300-212.2/150.0
.400-250.5/178.5
.450-265.5/188.4
.500-275.6/198.4
.550-280.5/206.3
.600-282.3/213.2
.650-282.3/217.0
.700-282.3/220.7

basically, unless you can afford to lose some low and mid-lft flow, you're going to have to do some chamber clean-up work on the 75cc heads to keep that area of the flow curve on par with an 84cc head that doesnt have the chamber work.
while the 84cc head responds to a little chamber work as well, its not nearly as much of a differnce as what i saw with the 75cc head.

i see someone posted a pic of what i assume is the 75cc version of an RPM head with the chambers CNC'd.
i dont know how much of a cost increase that option is.......but its likely to be the best way to go.

Good comprehensive info as usual. Nice to see you back.

Do you think that chamber has enough of, for lack of a better description, that vortech shape to make a real difference in the flame travel?

Kevin

Brad,
the powdered mteal seats seem to hold up pretty well in most applications, especially street stuff.
i think they resist recession better than the ductile seats, but are more prone to fracturing when abused with very high spring loads.....and situations like valve float(high impact type loads).

over the last few years, RPM heads seem to have been supplied with Ferrea valves. i dont know who makes the valves for the E Street heads, but they dont look exactly the same, they have a different number on them.....and they dont say "Ferrea" on them.
the rest of the hardware(springs/cups/locks/seals) seems to be the same between the two heads.

and just because you know the comparison is going to be made.....(75cc chamber, std port opening, std rockers, etc)

std port EZ head:
OOTB

lift----I/E
.100--68.6/51.1
.200-134.6/94.2
.300-196.4/131.9
.400-239.3/166.6
.500-273.0/191.4
.550-282.3/198.8
.600-288.7/205.8
.650-293.6/213.7
.700-296.2/216.6

re-cut seats, back cut valves, blend intake and exhaust bowls, ported chamber, blend intake opening(this is my normal "stage I" for these heads).

lift----I/E
.100--74.8/58.9
.200-149.3/104.1
.300-206.6/142.6
.400-250.5/178.5
.500-289.8/207.0
.550-302.9/216.2
.600-308.5/223.2
.650-312.2/228.1
.700-314.9/233.1

the big thing with the EZ head is.....especially on a larger cube stroker......is that by just taking this level of prep and bringing the intake port opening out to MW size........you get another 20cfm + @ .600 lift, and 30cfm + @ .700 lift.

Now I'm curious where the head with the CNC'd chamber came from...

if i had to guess.....i'd say it's a 75cc version of the RPM head.