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By silent rick - 6 Years Ago
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my 57 292 is bored .050 over to 312 std size. i have a nice set set of ECZ-G heads ready to go. i've acquired a few intake combos for this build.
edelbrock 257 with dual 400cfm AFB's
edelbrock fm255 with dual teapots
highly polished offenhauser 6x2 with stromberg 97's
weiand 3x2 with strombergs.
something inside of me is telling me to sell all those intakes and carbs and join the big leagues and go with a 4-71 on top.
does anyone make a low compression piston for the ECZ-G heads? is there anything off the shelf or do i need to go the custom route?
will it be better to trade the heads for a set with larger combustion chambers?
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By Ted - 6 Years Ago
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You have several options but a shelf piston with a dish and without alterations is not one of them. Custom pistons with a dish are relatively easy and you get the advantage of going with a modern piston ring design. For a dish you can go several different directions which includes simply raising the pin height in a flat top piston, going with a combustion chamber specific dish, a “D’ shaped dish, or a reverse hemispherical dish. Diamond Pistons builds all the Y dished pistons that I use. If going the cylinder head route for lowering the compression ratio, then the 471 heads are approximately 13cc larger than the ‘G’ heads and in this case, some fine tuning of the static compression ration can be obtained by working with the piston deck heights.
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By charliemccraney - 6 Years Ago
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If you actually do need a dished piston, then it will have to be custom.
Your 292 may be low enough as it is. Assuming only a cleanup cut on the heads, 0 deck and flat top pistons, you should be around 8.8:1 at the most. If the pistons are in the hole, then that figure will be lower. You need to know these specs in order to calculate your current compression. Given that the bottom end work has already been done, if compression does need to be dropped, heads could be a more economical way to do it. Other things to consider are piston clearance and ring gaps - you may want to go back and revise those if you do go with a blower.
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By silent rick - 6 Years Ago
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thanks. i'd underdrive it for sure, looking for 4-6lbs of boost. i'm not too experienced with Y blocks.
i'll stick a finger in the water passage to see if the heads are posted. should i be concerned about the bottom end?
i'll get better rods from mummert. i'd rather lean to overkill rather than risk premature failure.
again, i'm only thinking about this at the moment. Ted sort of persuaded me against the 6x2. i'll admit he didn't have to do much persuading.
i thought i had settled on the 257 and AFB's
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By LordMrFord - 6 Years Ago
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Unposted heads are fine if not milled.
We grenaded stock bottom end with truck rods at somewhere 16 psi.
With unintercooled and supercharged engine I wouldnt go ever near that.
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By silent rick - 6 Years Ago
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4-6 lbs is all i'm looking for. still, better rods wouldn't hurt
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By LordMrFord - 6 Years Ago
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silent rick (10/11/2018)
4-6 lbs is all i'm looking for. still, better rods wouldn't hurt
Yes. With aftermarket rods and forged pistons you sleep better at nights.
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By miker - 6 Years Ago
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I ran a Paxton at 4lbs on a true 9:1 static motor for several years. Premium fuel and 2 degrees retard of regular timing starting at 1lb boost. The centrifugal didn’t make any boost under about 3000 rpm. I’ve got an OT engine that runs 7lbs on a factory stated ratio 9.4:1. It’s an Eaton unit, (Thunderbird and Buick used versions of them) fuel infected, all stock otherwise. It needed a lot of fuel enrichment (bigger pump and injectors, custom computer), but it works fine on premium. It makes almost full boost right off idle, like a 4-71 unit will. Probably a little more efficient with less heat generated than a 4-71.
So you’d be in the ballpark for a street motor and fairly low boost and probably just need some kind of retard under boost. Remember the vast majority of your driving is still part throttle cruise, or slight vacuum under easy acceleration. So you’ll want the timing to be optimal there too for throttle response and fuel economy. But it’s doable.
If you decide to build a race motor and run 10lbs or up, all this goes out the window. I’ve had 3 OT turbo cars that make 2 to 3 hp per cubic inch and run around 14 lbs boost. They are a whole different animal than something most of us could build based on a y block. Hollow heads excepted.
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