KB 107's

[71DartGuy]

Would there be any problems using these pistons in a Magnum block and having them set to zero deck? I know a lot of people are using this method with the older blocks and was curious wether or not it would work on a Magnum. Thanks

Mike

 

[rumblefish360]

I have not done this, but I don't see a problem in fitment myself. But with Magnum heads on top with there reduced chamber, street fuel could be a serious issue.

W/a 72cc head, they come in at 9.8-1.
A 63 Edel. cyl. head w/ a gasket sized @ 4.1 bore, .039 thick on that zero decked engine is 11.32 - 1.

How many cc's are the Magnum head?

 

[Coyote Jack]

With my magnum heads they come out at 10.58 to 1. Pump gas is not a problem but I have only tried mid-grade and premium.

Jack

 

[71DartGuy]

I'm thinking with a .040" quench from the gasket SHOULD be ok on 89 octane. The same method was used on the 400 HP 318 build up I read a while ago where they used the same heads. I guess the compression ratio would be a little higher with the larger cylinders though. Jack, are you running a magnum or LA block?

 

[dgc333]

I have a LA block with KB107's at zero deck and have magnum heads on the engine. Mine is 10.6:1 static compression and the cranking pressure is 180-190 psi. I run 89 octane all the time and recently tried 87. I get some detonation under hard acceleration when the rpm is below 2000 but otherwise it runs fine on 87. I am sticking with 89 for now but wouldn't hesitate to use 87 in a pinch.

The two sets of magnum heads I have checked both had 64 cc chambers and I use an 0.040" thick head gasket to get the 10.6:1 compression. The ability to use lower octane gas is going to be a function of the cam as well as the compression. The magnum heads make for a very detonation resistant engine when the pistons are at zero deck and you keep the quench at 0.040". A cam with more duration than the Comp XE268H that I am using may allow the use of 87 octane since the cranking pressure will be lower.

 

[Coyote Jack]

Mine is an LA block. I run a Comp Cams 280H. Total lift is .512, duration @50 is about 230 to 235 as the 1.6 rockers do increase the duration at the valve. Dave's and my engines are very similar with some little differences.

Jack