KB quench domes milled off

[Marvin S]

I just talked to dale at hughes engines to get some pistons for my car. I told him I wanted the flat tops for closed chamber heads that sit .015 below deck which should have given 10.3 comp ratio. He talked me into getting the quench dome ones for open chamber heads and mill the domes off.Which should give me right at 9.5 comp ratio.They sit .025 below deck.Anyone have this same setup,if so how did it work for you.Thanks.

[rumblefish360]

What heads do you have now? Why change everything around?
10.3 for iron heads is pushing it. Closed chambered heads?

[Marvin S]

I will still be useing the original 915 heads. I talked to hughes again today and they said they where going to leave .020 of the dome on the piston.This should give me 9.5to1 or just a hair over.They said this should help combustion.

[tsteiner61]

I just finished putting together a 408 stroker with the KB quench dome pistons. (Part number KB-356). Just got it up and running last week. Sounds beautiful. Great power.

Trust the guys at Hughes, they know what they are talking about. I pieced together the parts from wherever I could, but if I could do it over I would just get the whole ball of wax from them. They have reasonable prices/knowledgeable people. They helped me pick out a real nice cam for my needs, too.

[dave571]

Being a skeptic by nature, I always question the math of others.

I entered your numbers into the kb-silvolite compression calculator.

I assuming from your profile, it's a 440 engine

78cc heads(typical volume of a 915 head)
0cc piston volume(no dome or valve reliefs, usually the case after milling)
4.350 bore(.030 over 440)
4.350 gasket bore
.025 deck clearance
3.75 inch stroke
and a .040" compostite gasket

hit calculate, and that comes out to 10.7 to 1. That's with no dome left on at all. Leave the dome on, and I don'y know how much that would addd to the piston head volume(and subsequently the compression) Might put you over 11:1

Wayyyyy more than you want with iron heads(even at 10.7)

I have talked to people at hughes before. What I find odd is that I talked to two people, and got two completely different stories. In fact, one was willing to make a cam recommendation to me without knowing the compression ratio of my engine.

Try the calculator if you like.

click on "calculators", at www.kb-silvolite.com

[jelsr]

The KB's have a large valve relief area cut completely across the piston and a little extra cut for the exhaust which makes them L or R sensitive. Probably in the 7cc range and should be included in the calculation.

[Marvin S]

Here are the numbers I put into the calc.Bore 4.360/.040 over. .5cc valve pocket in piston. 80cc head chamber I ccd them..039 thick gasket. .025 below deck. Just guessing about 3cc of dome left. I came up with 9.5. Maybee I done something wrong. Thanks for any imput guys.

[dave571]

I got 10.2

I put in
4.360 bore
4.360 gasket bore
80 cc head
4cc piston(jelsers 7cc - your 3cc of dome left)
.025 deck clearance
3.75 stroke
.039 gasket

I don't know where the difference is

[Marvin S]

I put it all in the calc again and came up with 10.2 also. One thing I did try was putting a + sym then a - sym in the deck hight part it seems to default to the + side if you dont put anything in it.The way it reads is + is below deck and - is above deck,seems backwards to me.I get 8.3 comp if I put a - in.Seems it ought to be higher.