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Old 07-27-2020, 08:33 PM
Randy Allen Randy Allen is offline
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Default E-Head 72cc Chamber

I have a Butler built 468 with 6X-4 heads ported to 256 cfm with a 238/244@.050 cam with Rhodes lifters that’s never been started because of a Pro-Touring build for a ‘77 Can Am. A buddy is building an 535 MR1 with high-ports and has some original round-port 72cc E-heads. My compression is roughly 10:5 and the horsepower simulation has it in the 495-505 range. Is it possible to open the chambers up on the 72cc E-heads to 87cc or more to reduce effective compression and then port the heads to flow 290-300 to get another ~50 horsepower?

If not, what round-port would you suggest and flowed to what cfm? I have no intention of going to a bigger cam as its a street car where a good idle and wide torque curve is important. I may occasionally road race or open road race (to 168 mph). It’s a 3.73 rear gear with a T-56 that will weight about 3750 when complete.

Thanks for your assistance.

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Old 07-27-2020, 08:48 PM
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leeklm leeklm is offline
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I cannot comment on your specific heads, but a couple of us are running the heads/cam seen in my signature, which is pretty close to 600hp & Tq at the crank.

Idles at 1k rpm with 14" of vacuum and drops about 200 rpm when in gear with an auto.

Great package with good street manners and good performance at the track. Attached is a rear wheel dyno sheet from last fall. This is through a TH400 and 9" rear with 3.50 gears

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Old 07-27-2020, 11:48 PM
Dragncar Dragncar is offline
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You could sand roll those heads with a good valve job and get 290-300cfm.

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Old 07-28-2020, 02:56 AM
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lust4speed lust4speed is offline
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Quote:
Originally Posted by Randy Allen View Post
...My compression is roughly 10:5...
Possibly 9.5 and not 10.5 with the 6X iron heads?

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Old 07-28-2020, 06:11 AM
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steve25 steve25 is online now
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In terms of getting some 300 cfm out of the E heads The main pinch point in those heads on the Intake is the neck down in roof height on back to the Intake flange starting at the crown of the short turn and how much the common wall head bolt boss sticks out into the port.

Unless you have a flow bench do not do anything in that massive 1.920" valve bowl other then a really light blend, like only removing .010" at most lest you drop off much needed low lift port velocity that these heads are short on!

Another thing, bo not polished out your rework with anything but a 80 grit roll at a slow speed other wise you will aggravate even more the not so great wet flow conditions these big port heads have out of the box!

In terms of dropping the compression with the 72 cc E heads the only way to do it accurately is to get your pistions dished unless you work with a shop to get a chamber maching program set up to rework the chamber on the spark plug side.

You could start off in the heads by first CCing them and then unshrouding the sides of the chamber ( the extreams of the Intake and Exh valves ) and then CCing again to see where you are.

With the way the 72 CC chambers are machined stock I find that I gain 3 CCs when I do that.

PS, I would say for sure that with your cid your going to need a good amount more then a 230/234 Cam to attain 168 mph!

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Last edited by steve25; 07-28-2020 at 06:37 AM.
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