Need some help. Searching for the right piston. The P heads are 60cc, and I want 9.6-9.7 compression, 9.5 is absolute minimum. Doing the calculations, even the smallest dish flat top is only going to give me about 9.1-9.2, stock bore 289, probably going to .030 over, but maybe not. If I can avoid shaving the heads, great, but will do it if that's the only way to get there. Arias has some that they claim to 9.5 but they also have a note on top of their lists that state block height of 8.190 at 0.00 piston deck height, i.e. as if you had shaved the block to get rid of the normal .016 deck height. Trw also has one that has a CH of 1.619(?) instead of the normal 1.6 or 1.605, L2288f, not sure, going on memory, looks like it's set up to zero deck. I can only get a little higher compression with zero deck. A net zero or maybe a couple cc dome would be about perfect but I can't find anything like that, flat tops with small dish or big domes only. So far the TRW or the Arias with some head shaving look like my best options. Going with the smallest cutouts I can find on flat tops will mean I'll look real closely at valve to piston clearance. Only interested in forged. My questions are as follows. 1. Any net zero or small, 2-3cc domes out there that I'm missing? 2. Pros-Cons of zero decking the piston? 3. Am I right about the TRW being set up specifially for zero decking or is it something else? 4. Anyone ever talk to Arias about how they spec the block height? 5. At zero deck the head gasket, approx .040, should give enough clearance for piston to head, have seen .035 minimum needed. True or false? 6. Does a -3cc dome really mean a 3cc dish as I have been assuming since they are spec'ing it on a flat top with cutouts. 7. Any other options to get up to 9.6-9.7. 8. Anyone have a formula or link for calculating dynamic compression? 9. The makers list 289 and 302 pistons, but aren't they interchangeable if CH is the same? Some are the same part numbers so do they just list twice to get the rod length and block heights in for different compresson ratios? Basic question is can I use any 302 piston with the right CH? 10. How much head shave for .5 increase in CR? I'll be able to make some calls tomorrow but any point of view is more information!!! Thanks.
7.) You can leave the block,and heads alone...run the T.R.W.s and run a Cometic M.L.S. (multi layered steel) head gasket. Mine are only .025 compressed thickness. My engine was already together and running when I decided to do a head swap. I plan to use the new heads (60 cc Victor jr.s) on a 393-408w later on ,so I did not want to have them milled any. I used the Cometic gaskets to help remedy the problem. These gaskets are expensive (aprox. $80.00 EACH) but you would have a hard time blowing one...and they can be re-used up to 5 times! www.cometic.com For compression calculators ,simply do an internet search for "compression calculators" and you`ll find several.
2.5cc Thanks guys. There's actually a picture of a 2.5cc dome on that compression calculator, now if I could just find one just like that for a 289 I'd be happy. That's static compression btw, which I have no trouble calculating. Looking for dynamic, but should be able to find it easy enough. The thinner gasket would definitely be easier and the cost is offset by not having to shave anything, not really expensive at all if I look at it that way. Although with a zero deck piston the clearance would be too small I imagine. With a flat top I need both, zero deck and still some reduction of the combustion chamber, or just a lot of combustion chamber reduction, which has it's own problems. Hoping to find that small dome.
check it out. http://cochise.uia.net/pkelley2/DynamicCR.html Finally had to log on to the windsor engine site, have seen you on there BMC, this is a great dynamic compression site. You actually have to download it, but worth it. Looks like I might just be buying some stock bigger dome pistons. I would guess not looking at this is why a lot of "over camming" (or "under compressing") happens. 'nother piece of the puzzle.
Interesting reading, I love theoretical stuff like this. Seems like a lot to go through for a street engine, though. I've always found it helpful to be aware of cylinder pressure values which also take into consideration cam specs and timing. And you can actually measure that with a compression tester.
Done. Maybe. I think I found the perfect piston. Keith Black forged 6.8 cc dome, leaves me a little room to play with gasket thickness and put it right where I want it. Have to make a phone call yet. They have a note, aftermarket heads only, Edelbrock style. Don't think there's anything about edelbrocks that would be weird, hoping they are only putting that in for the combustion chamber size, which is 60cc, exactly like our P's. My fingers are crossed anyway until I talk to them. This puts static compression right around 10:1 to 10.3:1, which would put my dynamic at right around 8 or a little less, should be good. This would explain why I keep seeing guys talking about 10:1 compression as safe for pump gas, they are running higher duration cams.
Humm. Where's the edelbrock plug? Since the dome is really kind of one sided I doubt this will be a problem, but I'll check. Did call KB today and they said yeah, note is only there for combustion chamber size. i.e., they aren't recommending it for 54 cc heads. BUT in one of life's little happy coincidences I went to talk to a local, long time, Ford only, drag builder, and he just happened to have a brand new, in the box, set of TRW L2249F's, 10.4 cc (solid) domes. Been in his shop for 12 years. I can get them for $250, Summit wants $456. He confirmed dynamic compression importance, fine with 10.3 static, with a good duration cam. Then in more of life's goodness went to talk to a great machinist/automation designer that does little piddly stuff for my wood shop, basically just for fun, and an ex circle track racer to boot. He'll set me up and let me cut them myself to whatever I want for basically nothing. I get a great machining lesson to boot. Can I get a Hallelujah? KB part number is KB736 if anyone is interested. About perfect for a 289 high duration build with aftermarket heads. If I hadn't blundered into heaven today I would definitely be buying them. For a 302 with this head, flat tops with head shaving would probably be the better way to go, better flame front, and you can set quench lovely too(with that cometec gasket mentioned above). If the plug placement proves to be a problem this is the way I'll go and live with shaving the intake too. Engine design is basically done and man am I one happy camper today!
Round and round. Well BMC the TRW is not possible, the dome is lumped right in the middle- .440 tall, the KB is what I'm going to end up doing, it's a broad based .150 tall dome. Will shave about .080 off the very top of the plug nipple and have plenty of room for piston clearance. Talked to a good engine machine shop about just going for flat tops and shaving everything and after he had talked himself through all that would need to be done he told me to just go with the KB. The flat tops could be done at the compression I want but it's just too much trouble. If I was willing to just throw money at it I'd probably do it, but the KB is a nice easy solution and I'm going to see what hp I end up going that route. I could always still do the flat tops later after I win the lottery. Done running my poor brain through the hoops for now.
answers Research finally managed to answer all of my questions that I had posed so here it is just in case someone needs it in the future. And thanks to Steven also. 1. Any net zero or small, 2-3cc domes out there that I'm missing? DON'T THINK SO. THE PRACTICE IS SHAVE A BIGGER (MAKE SURE IT'S SOLID) DOME. 2. Pros-Cons of zero decking the piston? IT'S NORMAL TO ADJUST THIS FROM ZERO TO THE STOCK SETTING OF .016, OR EVEN HAVE THE PISTON STICKING OUT A LITTLE, SETTING QUENCH AT .O35(or less) IS THE AIM. THE .O25 COMETEC GASKET WOULD USE A DECK HEIGHT OF .010 FOR .035 QUENCH. WHICH HAPPENS TO BE GOOD FOR PISTON TO HEAD CLEARANCE. 3. Am I right about the TRW being set up specifically for zero decking or is it something else? ENDED UP NOT CARING ABOUT THIS ONE, BUT IT COULD BE USEFUL. 4. Anyone ever talk to Arias about how they spec the block height? THEY DO SPEC ALL THEIR PISTON'S CR'S AT ZERO DECK. SO CAREFUL, IT MAKES CR LOOK HIGHER THAN YOU MAY END UP WITH. 5. At zero deck the head gasket, approx .040, should give enough clearance for piston to head, have seen .035 minimum needed. True or false? SORTA TRUE, BUT SOME BUILDERS GO SMALLER, I.E. THE PROS, WELL UNDER .035 SOMETIMES. 6. Does a -3cc dome really mean a 3cc dish as I have been assuming since they are spec'ing it on a flat top with cutouts. YES, BUT IT'S CONFUSING BECAUSE SOME DOMES ARE SPEC.ED AS POSITIVE CC'S, SOME AS NEGATIVE CC'S, POSITIVE ON THE PISTON, NEGATIVE IN THE COMBUSTION CHAMBER. I THINK THIS HAPPENS WITH DISHES SOMETIMES TOO, BUT IN REVERSE. 7. Any other options to get up to 9.6-9.7. THERE'S ALWAYS ANOTHER OPTION. LOL. NOW I'M GOING TO 10.3-10.4. 8. Anyone have a formula or link for calculating dynamic compression? SEE ABOVE, IT'S WORTH THE READ. 9. The makers list 289 and 302 pistons, but aren't they interchangeable if CH is the same? Some are the same part numbers so do they just list twice to get the rod length and block heights in for different compresson ratios? Basic question is can I use any 302 piston with the right CH? YEAH, AS LONG AS CH IS THE SAME, USE IT. MIGHT BE A RARE SKIRT LENGTH ISSUE JUST TO SCREW SOMEONE UP. HAVE TO CALCULATE THE CR IF ITS A DIFFERENT STROKE THOUGH. 10. How much head shave for .5 increase in CR? HAVE SEEN .007 EQUALS 1CC, NOT A HARD AND FAST RULE BASED ON COMBUSTION CHAMBER SHAPE BUT IT'S GOOD FOR GUESSTIMATING. USE A COMPRESSION CALCULATER AND PLAY WITH COMBUSTION CHAMBER CC'S AND THEN SEE HOW MUCH YOU HAVE TO SHAVE.
