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By 63 Red Stake Bed - 18 Years Ago
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Does anyone know what a rough average would be on a 292 decl clearance? I am trying to come up with dynamic compression estimates & can't find any info. Does anyone know what average thickness for composit head gakets are? .010? .020? Kevin
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By Hoosier Hurricane - 18 Years Ago
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Kevin: You could expect the 292 deck clearance to be in the .020 to .030 range from the factory. The composite gaskets are more like .040 compressed. John
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By 63 Red Stake Bed - 18 Years Ago
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John, Thanks. So I am probably screwed if I am trying to get a decent dynamic above even 7 with a virgin deck 63 292 block with ecz-g's & composit gaskets & the intake closing @51 I think. I come up with dynamic of: Looks low to me. Do you think I should think about using domes? Kevin |
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By Ted - 18 Years Ago
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Kevin. Try using 61° for the value that the intake valve closes which will run the dynamic compression ratio even lower. That 61° number comes from the cam specs you posted on the other thread. Many of the aftemarket domed pistons for the Y will have a 10cc dome so you can also plug that value into the compression ratio calculator to get a better feel for both the static and revised dynamic compression ratios when using domed pistons. Are you using 292 or 312 rods in your engine?. If you’re using 292 rods, then use 6.324” for the rod length. That will also marginally lower the dynamic compression ratio.
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By 63 Red Stake Bed - 18 Years Ago
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Thanks Ted. Not sure where I got that rod length. I know this is probably a redundant question for this forum, but how much could safely be taken off the G heads? Do you know what the chambers end up at with Mummert's street port? My goal would still be to not have to replace pistons, Or deck it. I know using steel shim gaskets would help a pinch, but I worry about how good a seal I might get. Kevin
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By 46yblock - 18 Years Ago
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It sounds like your only 2 options for bumping compression is the steel gasket and head milling. I dont know how much can be removed from unposted heads, but according the Mummert's site .040 off of posted heads isnt a problem, unless your cam lift plus the head shave puts the valve onto the piston.
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By pcmenten - 18 Years Ago
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I think there's another reason why you'd be better off decking the block. It has to do with flame propagation, squish, and quench.
If I understand this correctly, the flame of combustion is 'quenched' or extinguished when it gets near to the surface of the head, piston and cylinder walls because the metal absorbs the heat and puts the flame out. So, the air/fuel mixture that gets trapped between the 'quench surface' of the head and the top of the piston does not get to burn until the piston pulls away from the head on its way back down the cylinder, or it explodes (pings) from combustion pressure.
With a .042" gasket and a piston that's .030" below the top of the block, you have about .072" of space that is holding air fuel mixture. I've heard that the optimum clearance is about .035", but people usually go for about .040", or the thickness of the head gasket.
By minimizing this area, the tendency to ping is reduced. Also, by concentrating the air fuel mixture in the combustion chamber, you reduce the distance the flame needs to travel to burn most of the mixture, so you reduce the amount of spark advance needed to 'time' the burn right. (This also leads to less pumping losses.)
Finally, the action of the piston squishing the mixture in the quench area causes that mixture to blow into the combustion chamber, which produces some turbulence that helps get a complete burn. This is one reason why people prefer the ECZ-G, ECZ-C, and the C1TE heads - they have more quench/squish area.
Short answer, you want to zero-deck your pistons to get the clearance to a minimum.
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By Hoosier Hurricane - 18 Years Ago
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Not to mention that decking the block say, .010 raises compression more than milling the head .010 because the area of the bore is larger than the area of the combustion chamber. John
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By 46yblock - 18 Years Ago
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I certainly agree with Paul and John regarding the decking, even though it has been ruled out for the time in your plans. Even with decking and some head milling, the reasonable top compression using flattops in a 3.81 bore 3.3 stroke 292 is in the realm of 9.25:1. Still not enough to go with a radical cam, but it would make your current E-4 work like it should.
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By 63 Red Stake Bed - 18 Years Ago
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Thanks for the feedback guys. I definetly have to be certain to get the details accounted for when I do this. I should focus on the t-5 first, & the engine second. 46, did you ever get your 301 running? Kevin
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By 46yblock - 18 Years Ago
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I wont put it into the truck until this winter. Kind of like you I keep tinkering on the books regarding compression. As it is now, and just taking the heads off the 305 cu. in. Y and putting them onto the new one, the compression is 8.92-8.94. If I take another cut on the heads and bring them to 68 cc, it ends up at 9.04. It no doubt isnt worth the cost, but it would be nice to know I broke the 9 barrier  .Mike
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By 63 Red Stake Bed - 18 Years Ago
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Yeah, it makes me jealous of my cousin's k code 289. Easy to build compression on those things! I wish I had the bucks to just take the bad motor from another truck I have & put a mummert 338 stroker kit in it! Then I could build it from the ground up as a 300+ hourse street killer! If only I had about 8 grand to drop on motor alone! Oh well, I guess once I get the trans in I can see how much It costs to do it each way & how much is available cash wise! The wife does want to get #2 kid on the way sometime in the next year or so, so I am sure that will make an impact! Kevin
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