Piston choice 460
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Freshman User
Joined: May 2005
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From: Lucan, ON
Piston choice 460
Am I right in thinking that if I go to a flat-top piston (with valve reliefs) on a 0.020 or 0.030 over-bore, with roughly 95cc D3VE heads and stock stroke on my 460, that I will get about 9.4:1 compression?
If so, I think that might be a good choice for performance street/strip?
Is it really worth it to "push" the compression ratio like this, or am I better to play it safe and try to aim for 9.0:1 tops like the machine shops are telling me?
I assume the block and head surfaces will be milled (just to be cleaned up, if nothing else) so I need to take that into account too .. although I don't think that will have a big bearing on it.
Thanks as always for the insight.
Rob.
If so, I think that might be a good choice for performance street/strip?
Is it really worth it to "push" the compression ratio like this, or am I better to play it safe and try to aim for 9.0:1 tops like the machine shops are telling me?
I assume the block and head surfaces will be milled (just to be cleaned up, if nothing else) so I need to take that into account too .. although I don't think that will have a big bearing on it.
Thanks as always for the insight.
Rob.
Elder User
Joined: Jun 2004
Posts: 800
Likes: 6
From: Edmonton, Alberta Canada
9.4:1 is a good choice. with the right cam choice you will still be able to use hi test pump gas. 9.5:1 by most accounts is about the upper limit with iron heads and proper cam.
with aluminum heads, you canusually get away with a little higher ratio, usually 10:1 due aluminum dispensing heat better.
i would stick with 9.4:1.
rgds
Mike
with aluminum heads, you canusually get away with a little higher ratio, usually 10:1 due aluminum dispensing heat better.
i would stick with 9.4:1.
rgds
Mike
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Joined: May 2005
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From: Lucan, ON
Thanks Mike.
One other factor I guess is zero deck height. Sounds like it is good practice to go for a zero deck height when doing the rebuild.
When I re-calculate based on zero deck height, a flat-top with valve reliefs (I used 4.2 cc Speed Pro) gives 9.6 which is starting to get a bit high perhaps on iron heads.
15cc dishes give 8.9 on zero deck-height by my calculation and would give a bit more (maybe 9.0) with usual head milling required in a rebuild?
I think those 15cc dish pistons (KB D-cup) must be the ones recommended by the machine shop I talked to then as they quotes me 8.9:1.
One other factor I guess is zero deck height. Sounds like it is good practice to go for a zero deck height when doing the rebuild.
When I re-calculate based on zero deck height, a flat-top with valve reliefs (I used 4.2 cc Speed Pro) gives 9.6 which is starting to get a bit high perhaps on iron heads.
15cc dishes give 8.9 on zero deck-height by my calculation and would give a bit more (maybe 9.0) with usual head milling required in a rebuild?
I think those 15cc dish pistons (KB D-cup) must be the ones recommended by the machine shop I talked to then as they quotes me 8.9:1.
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Joined: Mar 2007
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The exhaust ports are the real problem in the 385 heads. Don't think so? Just try stickin' your finger in the exhaust port. Lumpy & bumpy, ain't it? You will be money ahead with high compression pistons (read flat tops) and a modest port & polish job on the heads. Don't be wastin' your time and money lookin' for "early" small cc heads, and forget the CJ/SCJ stuff too as Ford Motorsport already offers an aluminum CJ head (M-6049-A429) While you're at it, get the chambers polished too. What those 95cc heads do offer is a large quench area to help fight preignition. What risk of preignition you face with 10:1 compression can be controlled by recurving the distributor and premium gasoline. Masquerading as a 320 H.P. weakling, the lowest compression ratio on the base 2V 429 was 10.5:1 -that was until 1972 anyway.
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Joined: Sep 2007
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I went through a similar decision last year. Like you, I have D3VE heads. With stock pistons, I had something less than 8:1 CR, not acceptable. The truck is primarily used for pulling trailers in excess of 8000 lbs, so 89 octane pump gas is a must. After crunching some numbers with my local machinist, we came up with using 89 and newer, fuel injected pistons and decking the head by .010". With this combo, we ended up with a 9.1:1 CR. Not to mention reasonably priced pistons. On top of this, I did some minor port and polish work on the heads. I found some really useful info at http://www.reincarnation-automotive.com/index_2.html If you join there site ($25 contribution), you get full access to porting tips. Since my cam runs out at 4500 RPM, I left the thermactor humps. I concluded that polishing the domes, port matching and smoothing out the exhaust ports were the best (and easiest) options. The only drawback that I'm experiencing is pre-ignition around 3000 RPMS, still working on that one. Hope this helps!
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