Recut domes in EAB heads

[petehoovie]

Originally Posted by cadillac512

I have a pair of EAB heads that have been milled at some point, and were too close to the pistons in my 260" Merc. I've been running a nice pair of lightly milled 8CM heads that have .035-.040 piston clearance (block is decked). I wanted to try the EAB's so after researching on the Barn I made a cutter like Ol' Ron did (Thank you!) from a file and an extra mag wheel lug nut. Made a drill press jig to radius it at 6" and sharpened it carefully by hand/eye on a bench grinder.

I took it to work this morning and mounted the heads on the Bridgeport Mill and set the speed to 60 rpm...slow as it goes. Wants to chatter a bit and everything needs to be VERY tight but it went well and did the job. The domes are now back to original diameter and depth is approx .040" deeper than when I started. Should put the clearance right back to where it is with the 8CM heads.

Many thanks to everyone who has done this and posted the info for us to learn from, with special thanks to Ron Holleran for the pics and info he posted.

In a week or so I'll see how this deal pans out!


P.S. I will sand out the grooves and dress down the center bump...just wanted to post this now.



Terry

[petehoovie]

Originally Posted by cadillac512

Here's a pic of Ol' Ron's setup for grinding the cutter radius...mine is the same but I used a drill press rather than a lathe. We both just swept the cutter over the stone back and forth by hand. Credit to Ron for this pic.

"Holding was a series of pipe fitting se t at the redius I wated the radius of the cutter. This was set for the Ross pistons which I think is 7" , but I'm not sure now. However the fixture is adjustable.
Gramos
PS that pic was taken over 20 years ago. I have allot of them on different projects. Ran out of Grand kids so it's hard for me to post pics and videos..
Gramps"

[38 coupe]

Originally Posted by cadillac512

I've run a few tanks of gas through it now, and where it previously delivered 16.5-17 mpg I am now seeing 18-18.7 mpg.
Terry

Thank you for the update. I find this very interesting, and per my memory is consistent with other back-to-back reports of modifying stock heads. Using the big flathead compression ratio file you increased compression from approximately 6.8 to 7.7 which is about 12%. You measured about 10% improvement in fuel economy. That improvement in fuel economy must come directly from improved power at the same part throttle.

The amount of improvement is much more than the normal theoretical improvement in power for a compression bump. I suspect this is because the theoretical compression benefits are not taking into account the improved combustion chamber dynamics that can be had in our ancient design side valve motors.