Block Milling

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Problem Child

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The pistons I bought are gonna be fifty down in the hole. How far down can I mill the block to get more compression if I need it? Can anyone tell me what the compression will be with the following set up?

360 bored forty over
Magnum heads from 98 Durango ( will be surfaced and 2.02 valves installed
Felpro head gasket
Speed pro flat tops with four valve reliefs at fifty down in the hole

Is that all the info you need? Thanks guys.
 
Need to know what the pistons are,dished or domed and the cc of the dish or dome.Thickness of the head gasket compressed?What compression ratio do you want to run?What is the CC,s of the chamber of the head after you shaved the head?I will give some figures to my dyno and give you some ball park idea in a bit,Mrmopartech
 
I'm guessing 4 valve releifs is a flat top design. You can mill the block, but you are using the magnum heads. I'm not sure what the CCs are for them. With a std head (open chamber), and a thick head gasket, you'd be looking in the 9.5:1 range. IIRC, the Magnums are like 65cc? That sticks you at 10.5:1, using the .043 Fel Pro gasket. This is guessing the vavle pocket size at 6ccs. It sounds like you're where you want to be if they are true flat tops.
 
Sounds like I will have enough compression with the mag heads. The pistons are Speed Pro H405CP-40. Campbell Racing web site shows them with 63 cc heads at 9:22 Compression. The compression distance is 1.637, and they are a flat top with four valve reliefs. It doesn't say how much the reliefs are. I have seen write ups that say the Mag heads are 59 cc"s but I really don't know. I didthe math and came up with 10:65 but I used 14 cc for the valve reliefs, so I am probably wrong. Anyway, thanks for the help
 
If your pistons are .050" down in the hole, and you use a FP1008 gasket with .039" compressed thickness, then your quench distance would be nearly .080". That is not too good... in fact that is terrible. Everything I have read says you want your quench to be between .040" and .050" with the smaller number being better. I have heard some people are running as little as .025", but that is pretty risky. IMO, I would be trying to get some decent quench and not worry too much about the final compression ratio.
 
I have the KB107's in my 360 at zero deck and I am using a Fel-Pro .039 compressed thickness gasket with the magnum heads. These gaskets have a very large bore (4.180") so they add some head volume. Anyway, my calculated compression is 10.5 almost 10.6 to one. So far in the few hundred miles I have driven since first firing it up last Satruday I hae not had a hint of detonation. I can lug it right down to 1000rpm in 4th and still pull cleanly, not a hint of pinging. After some more miles I a going to give middle grade gas a try.
 
quench design is fairly new in the hot rod scene. if you are building an engine with quench in mind,that's another story. the magnum chambers are so much better on their own, that i dont think ther will be any issue. i agree, the compression will be a hair lower becuase of the gasket's bore size, but i think10.3-10.6:1 is about right.
 
FWIW, The machine shop that did my block work figured I would have less detonation problems with the ideal .040 quench with the magnum heads than I would at 9.5:1 with the orignal open chamber heads. So far I'd say he was right on.

Plus the throttle response at 10.5:1 is great! :)
 
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