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#1
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Quench style vs flat top pistons
Looking for feedback opinions/experience info?
For a 408 build for a street/strip combo to go in a 68 Dart Auto and all other components being the same (except gasket thickness or head CCs to attain 10.0:1CR, ), would it be performance wise better to go with quench style piston or Flat top - or doesn't it matter? thanks but waiting to be enlightened |
#2
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It would depend on the head type, open or closed chamber. The quench pop-up is used to get the correct distance from piston to head on open chamber heads. (.040 usually) With closed chamber heads this can be done with flat tops.
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#3
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To carry this a little farther. Keith Black, when doing the Hyper pistons, worked on and reported that a quench of .060 or less allowed one to run as I remember it a half point higher compression without detonation. I also feel from experience that the proper quench aids the combustion process so there for is worth some power. I build every engine with .040 to .055 quench.
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#4
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You can get closer than that. I like .038 to .028. I've run that to 8000 without a problem.
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#5
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Some "Rules of Thumb":
If you are using TRW type (high expansion) pistons, stock type rods(or Eagle, CAT,etc.), moderate RPM(8000 or less); you will be fine at .035" deck clearance with the Fel Pro .040" head gasket. Said another way, you can use a .090" quench on the piston. This would match the .090"-.100" recess in the head. the easy way to check it is to rotate the engine WITHOUT a head gasket. If it rotates OK, you are fine. If it doesn't rotate, you find where the obstruction is and remove it. Repeat this procedure for all 8 pistons. If you are using Low Expansion race pistons(JE, CP, Ross, etc.) and a real good steel rod(Crower, Oliver, Carillo billets, etc); you can go down to .025"(without gasket). You can go down closer than this; but, expect frequent teardowns. Eliminating the quench area in a standard Mopar head = HP, allows less ignition advance and increased compression. But, it sure requires some time to insure adequate clearance. |
#6
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I'm reasonably sure that the theoretical drawback of a quench dome piston, as compared to a closed head and a flat piston, is that the dome slows down flame travel.
Creates issues when attempting to optimize timing. If it's true or not, I have no idea. I think Don has some info/theories on this topic. |
#7
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There is only one advantage to running a pop up piston. To acheive the compression you want. If you can use the correct piston compression height. You will have a better combustion, flame travel and the piston will be lighter. Some of the TRW speed pro's are boat anchors for sure. As for running more compression without detnation. I think thats a load of bull. I dont know anyone who is running a dome piston, who is worried about what compression they can run or detnation problems. There all ready running race gas/high octane fuel right. I have not seen to many street racers with pop up pistons running 8.5:1 and cheap gas. What would be the point?
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68 Coronet 69 Super Bee......new 500 cid comin soon! 73 Duster witha missing 440/727 |
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