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#1
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Max cut on “J” hea
What is the max. that a J head can be flat milled? Can you mill enough to remove the “open” portion of the open chamber? Trying to reach proper quench distance .038”-.040” with cast block & heads and steel rods. Will probably have to dish my “boat anchor” TRW pistons to achieve 93 octane compression ratio. Any idea of min. thickness for tops of pistons?
Thanks, |
#2
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be carfull!
If you know that you have "virgin" heads, I would not go more than .060". And there is a ratio of thickness that needs to come off the intake surface for every .010" taken off the head surface. Its like .014" for every .010" off the head surface. dont quote me on that figure.
Help me out Rumblefish! 5th |
#3
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LOL, Sooorrrry 5th, I can't help drag-n-cuda on this one.
I seen this thread earlier. I would have answered if I had known. I heard people taking huge amounts off, but I do not know the limit. Where is a safe amount to stop cutting? I don't know. The ratio? Ya mean for every .010 from the head to block surface , you remove .0095 from the intake face of the head. Milling the head surface that meets the block, for every.0048 removed is 1cc loss in the chamber. |
#4
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max recommended amount is .060. that will allegedly raise compression 1 full point ie. 10.0 to 11.0. once you go above that the rocker arms may need shimmed up or shorter pushrods will be required. are you running factory type pistons ?
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#5
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ohioDemon,
I pulled out another set of "j" heads today and looked at them. .060" would virtually if not completely eliminate the open chamber portion of the head. Yes, I'm running forged TRW's that are stock replacement type (10.2:1). I'm going to work thru the numbers and see what milling the piston tops will buy me for correcting quench and relieving some compression. drag-n |
#6
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are your pistons above the block deck ?. i'm thinking that 340's were .015 above the deck. you need to know this. if they are i may have a reasonably cheap solution for you.
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#7
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just a suggestion. Don't cut them heads. If you cut them that much you can never use em' on anything again. J heads are getting harder to find. And have a tendency to crack. Instead go with the KB190's they have the raise on the piston to close the chamber on the head.
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#8
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I had a J head that was cracked from the chamber outward toward the exhaust side of the head. I milled the junk head down enough to make closed chamber heads. It took close to .080ish to clear all four chambers. They were not all the same depth. Any how, the intake valve seat became very very close to being gone.
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#9
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ohioDemon - My pistons should be .008" above the deck, .018" for a blueprinted block. Assuming rods, stroke and pin heights are correct, the block could have another .010" removed from them.
dans76sport - I probably won't cut them anywhere near that much, but I trying to achieve .040" quench with about 10:1 compression for max power on 93 octane, no boost or mixing. There is not an off the shelf piston to do this. KB190's will be for the 372 version to come. I'm looking to modify heads for 372 combo, but also make 345 a little bit snappier. Thanks everyone, drag-n |
#10
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K-B makes a zero deck piston. I have them in my 360.
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#11
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rumblefish360,
By you signature, you have eddy heads. I assume they're the closed chamber ones, right? The flat tops would not get me proper quench with "j's" (open chambers), but the KB373's should and get me into the 9.5-10:1 range with correct quench. So I won't do any milling of my heads at this time, cause I won't need to when I go to the 3.58" stroke. I'll do a cam upgrade until this winter, when I can drop in the new crank, pistons and possibly rods. drag-n |
#12
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Both Edel. S/B heads are closed chambered. The 340 heads have a .060 (I think) relief for the pop up pistons that came stock on the 340. Thats it. So, yes.
I'm not familur (sp) with the KB373's piston. |
#13
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rumblefish360,
The .060" relief creates the "open chamber" like the stock Mopar heads of old. I measured 1 set of "j's" this weekend and the stock relief is also about .060" deep. KB373's set the quench distance to around .040", just what I will be looking for when I put in the new crank. Until then, I guess I leave the heads as is. I can still find many other places to spend money, new cam next. drag-n |
#14
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J heads
I am runnig a set of 915 "J" heads on my Dart. They have been milled .050 to get the chambers down to 63cc. I am also running the TRW forged piston 2316F. I did have to use the Mopar Performance shaft shims though. The engine has been running for four years with this combo with no problems. The car runs great. 7.60's @ 89 in the 1/8th.
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#15
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Darn Dart,
Thanks for the informative reply. You wouldn't happen to know the weights of the pistons, pin or both would you. It's difficult to find anyone with the older books. Also, what static compression ratio did this create. Thanks, drag-n |
#16
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According to TRW(Speed Pro) with a 63cc head and a .040 head gasket it will make a true 10.5:1 compression. One piston with pin and spirolocks weighs 888 grams. Very heavy piston, when you look at a comparible Chevy or Ford piston, they are much lighter.
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