milling 360 heads

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Snake

Snake

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I am sure this has been talk about a million times,but I take a lot of stock from everyones advice.My 915 340 J heades are in the hands of the machinest now.What I would like to know how much can be milled of my heades to bump up the comp.Thing is I dont want to run into any problims like milling my intake,or haveing to get new push rods.I would like to mill them and use my stock push rods and rockers and intake.My power plant is a 360.Thankssss.
 
Get a good cc first if you don't know the history on the heads. You may end up with 49cc heads like I did:)
 
what is and how is cc done.Thanks 63dartman.the last guy that had theaes heades witch he bought and never used them said they were milled,now he could of been pulling my leg because i was planning on installing on my 318,not now tho.
 
I have taken .060 off my J heads BUT you will run into mating problems with the front and rear seals and the intake. You can safely take off .030 without any real problems as long as you use good gaskets- but it won't raise the compression much -maybe .3 to .5 points. As for finding out if they have been cut before your machinist should be able to measure the head thickness and compare to stock specs.(measure from block surface to top of the valve cover gasket rail)
 
ive done .080 but the mech... shop did have to cut the intake. but it wasn't a big deal. all my stock rocker assembly still worked fine, but i did shim up my rocker shafts, which anyone could do. hope that helps...
 
You can mill .060 off those no problem, thick decks on j heads.

you will have to buy new push rods and mill the intake side of the heads to compensate, thats just the way it go's.

push rods might work but it all depends how much you change heights.

the shimming of the shafts depends on rocker tip/valve geometry.
 
90 plus but have to do intake side also or you cant get the intake to bolt up... my machinist told me the formula but i suffer from c.r.s.
 
well the j heads are at a different shop now being rebuilt.I think at this point no planssss on cuting the heads ,I dont want to play with anything but who knows.
 
Mill'em, don't be scared, you'll only need to really change PR length and cut intakes if go a lot.

340/360=it's .0048 per 1cc and .0095 off the intake face of the head or intake itself for every .0048 of the head....... and .0144 off the bottom of the intake for every .0095 off the intake face weather it be intake face of the head or the intake manifold.

I milled .040 of 1 and .020 off the other for my 410, better check'em!

FWIW 273/318 is a different formula-smaller chamber to work with.
 
.........Then have them angle milled, then u dont have 2 do anything with the intake side of the head or the intake.................if ur 360 is apart have them offset grind the crank, easiest way 2 more cubes and compression................kim...........
 
hi Kim my 360 bottom end is all built now,its at a different shop than the heads,different story there.i now have my 340 915 202 j heads being rebuilt.Thankssss for all the help om milling my heads guys,me thinks I will them as is.I soon will need that intake KIM if you still have it.I have a question on head gaskets if anyone wants to address it.I like the blue felpro ones whats the mim thickness I could use with out any fitment problims.I know the head builder likes the steel ones.Any thoughts.
 
I cut .100 off one and .095 off the other. Had to cut intake, used Hughes adjustable rockers. And it made a hugh performance difference. Oh and used Cometic.027 gaskets
 
oldkimmer said:
.........Then have them angle milled, then u dont have 2 do anything with the intake side of the head or the intake.................if ur 360 is apart have them offset grind the crank, easiest way 2 more cubes and compression................kim...........
Click to expand...

1wild&crazyguy said:
why do I not think that will work....
Click to expand...

Because you know very well that if you angle mill the head and change it's angle that the intake meets he'll have to mill the intake not only on the bottom but also the mating surface to the head with possible oil leakage from the attaching hardware.

This operation is best done with the whole engine at the shop so the machinest can take a good look at exactly what is being done and how much to cut on the intake at the new angle. After he sets it up in the machine, he'll have to cut the entire face down and not just a partial ethier.

the intake only has so much meat on the side so he must have it in hand with the engine assembled to a long block status. He'll also need to look at the heads and know exactly how much was cut and is left to calculate the new depth and angles present.

This operation is not cheap or quick and barley worth the expense.
 
.............OK Rumble, i have not had this done myself, but a couple guys i know have and claim that all that done was the heads not anything else........i never actually put much thought inti it..........ur explanations seems logical.........sorry to try and steer u wrong Don...................kim............
 
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