400 build questions
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From: Langley B.C.
400 build questions
got my 400 crank looks to be virgin=) next i need pistons. using stock 78 heads. seen the badger pistons. i read somewhere they were discontinued is this true or are they still being manufactured and are available? might anyone know of another drop in piston that will raise comp some. need to be able to run on pump gas. KB lists a 9.5:1 comp. piston for the 351C (76cc head). believe the part# is KB108 and has a comp. height of 1.67 and pin diameter of .9122. i know the rod would need to be bushed but could this piston work? Might someone know what my comp ratio would be with this one. I'm thinking i'd like to use comp cams 255or265deh. have an edelbrock intake and will get the matching timing set to the cam i get. Basically just lookin for more power and mileage. mostly being used for 4x4ing (33-36" tires and 3.50 gears np435) maybe a little towing and sometimes carrying a camper. pretty much looking for suggestions or any relavent info. moreso on the pistons than anything. I see tmi would be the best place to ask about pistons but its a weekend and i have to leave sunday night for a week or so for work. TIA
Postmaster
Joined: Aug 2001
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From: Delaware
With the 351C KB piston (1.67 CH) you will get about 9.37:1 CR. The Dynamic CR with a 255DEH cam will be about 8.1:1. This is in the 91 or higher Octane range. The 265DEH cam will bring the DCR down to about 7.8:1.
I assumed that the KB is a flattop piston with about 3cc valve relief. I think that it is KB177.
With the Badger piston The CR will be about 8.9:1. The DCR will be 7.66 with the 255DEH cam. This might run on 87 Octane, or 89 at the highest. With a 265DEH cam the DCR will be about 7.4:1.
I assumed that the KB is a flattop piston with about 3cc valve relief. I think that it is KB177.
With the Badger piston The CR will be about 8.9:1. The DCR will be 7.66 with the 255DEH cam. This might run on 87 Octane, or 89 at the highest. With a 265DEH cam the DCR will be about 7.4:1.
Elder User
Joined: Nov 2004
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From: So. California
I think that with 8.5:1 dynamic compression it should run without detonation on 91 octane everywhere with the exception it may or may not ping at the beach. I am no expert but I have done some studying on this matter.
Postmaster
Joined: Aug 2001
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From: Delaware
There is some data available that shows a Dynamic Compression Ratio of 8.5:1 is maximum for safe non-detonating operation on pump fuel (93 Octane). I assume that this figure is for a fast burning quench chamber. I think that the open chamber heads, with the piston down-the-hole that we deal with on these motors require some backing off of that number. My own experience with 8.2:1 DCR and 91 Octane tells me that this is close to the safe limit.
With modern alloy heads and fast burn chambers, these limits can be exceeded. I currently run such a setup with 8.2:1 DCR, and although I use 93 Octane, I can occasionally mix in 89 Octane. There is only $0.10/gal difference between grades, and at over $2.50/gal it is a fractional savings to run a lower grade.
With modern alloy heads and fast burn chambers, these limits can be exceeded. I currently run such a setup with 8.2:1 DCR, and although I use 93 Octane, I can occasionally mix in 89 Octane. There is only $0.10/gal difference between grades, and at over $2.50/gal it is a fractional savings to run a lower grade.
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