Thanks for the info. Good to know 150 grams savings is a 20% weight reduction. Nice! The important question is: Do the pistons have your name scribed on the bottom of them? Paul
Paul, no name on them. Just a job number. Not like anybody's ever going to see them. Swagon. There is no such thing as a 10 to 1 piston. You have to CC the chamber and piston dish. Then with the distance down the hole the piston sets with the gasket thickness and bore size you can calculate your actual compression ratio using one of the many online calculators. With the Buick 350 the chambers are so small that the slightest change makes a huge difference in compression. Switching from a steel shim head gasket ( .020") to a composition gasket (.045") is a difference of .025" (more math). That equals just over 1/2 point of compression. A stock piston or stock replacement can sit as much as .090" down the hole. Chamber size also varies quite a bit even chamber to chamber in the same head. Scott Brown sells 2 different dish size AutoTec pistons you can use to fine tune your compression once you know the other parameters. In my application I have 9.8 with custom dish Autotecs and a zero decked block.
How many CC's is the dish?? Deck height??Gasket thickness??? Head CC's??? What rods r u using??? And yes, I am nosey
TA Performance lists two advertised compression ratio options for cast 350 Pistons, 8.5 and 10.0. I'm assuming this indirectly refers to how much each is dished.
Brian, I would presume you are correct. FYI the only place I would put a cast piston is the trash. Put your money in the pistons and a sound short block.
Yes, different dish depth, but there is no such thing as a piston that will produce a specific SCR in any engine. The biggest variable is how far in the hole the piston ends up.
Agreed, just trying to point out why the original poster was referring to them as such. Kenne Bell noted their 350 piston options the same way, so it has been happening for some time.
Guess I'm squirrel turd. Thinking of running Super Stock so can't tell any specs and risk losing out on the big money. Yes that was a joke. 16 cc dish, .045 gasket with 3.9 opening. 3 845 bore, .005" below deck, cap screw rods. Chambers are 55cc.
lol Oh btw, hypers are cast too...we just call the OEM pistons 'cast' instead of calling them 'eutectic' due to the saturation level of silicon of 12-12.5% making them more durable and better resistant to detonation than the 'hyper-eutectic' pistons with their super-saturated levels of silicon of 16-18%, causing them to have higher rigidity and subsequent brittle nature with the 'glass nodes' throughout the aluminum. This is why they crack when subjected to sudden, hard shocks, not unlike glass itself. Or you can spend big money on solid aluminum slugs that were pressed and hammered into shape without being poured into a mold, a.k.a., forged pistons that tend to have a lower silicon content, higher expansion rate (which is why you have to install them loose in the cylinder wall to compensate for ambient operating expansion temperature, or they'll seize in the hole), loud/sloppy operation when cold (but who cares about that), increased oil consumption, more frequent oil change intervals, and can take one hell of a beating before getting cracks. Not sure how long they'll last mileage wise, but that's not a concern either in racing engines. So if you want to throw anything in the trash, let it be those busted up hypers. Good move on getting forged though, since who knows where the actual cranking PSI will sit and you can advance the timing all you want on high compression and 93 octane and the engine won't go south after repeated 5500+ RPM shifts without hearing all the bang/ping going on. Quiet mufflers FTW. BTW you should have had your name etched into the pistons. Like Paul said, it's worth at least 5 extra hp. I imagine from the weight savings of shaving the minuscule material out with the name etching. Maybe there's a math equation for that somewhere? hmm. lol It's funny when I read on here about people calling me the math guy. I've never used anything more complicated than 3rd grade arithmetic on here. But hey if that's advanced, then I dare not put any of the REAL math on here. :eek2: Gary
Correction. 16 cc dish, .045 gasket with 3.9 opening. 3 845 bore, .010" below deck, cap screw rods. Chambers are 55.5cc. Compression works out to about 9.9. Level 3 Crower back in set the same 6* retarded. Maybe Gary can see how that works out. Was trying to get down to 9.5 but didn't quite get there. So other than the bigger TA valves its back were it ran the 13.77. Except lighter pistons. Hope to fire it up Sunday. Plan to put it on a dyno before going back in the car. Pictures later.
I get 9.91 SCR. Level 3 Buick 350 Crower cam, http://www.crower.com/camshafts/buick-350-compu-pro-hydraulic-cam-276-hdp.html I get 7.18 DCR with the cam at a 118 ICL (6* retarded)
Beat me to it Larry. I use that same calculator. The million dollar question here is: Crower says 4 degrees of advance has been 'ground into' the cam, making it a 108* ICL when 'lining up the dots' on a typical timing gear set. Retarding it 6* from this would put ICL at 114*, not 118*. Deja-vu yes? I believe you and I have had this same conversation once before some time back on cam installation. I don't fully recall the outcome though. Yes the cam has a 112 LSA, and putting the ICL at 118* would technically be the correct 6* retard, but according to Crower's valve timing events, this would actually be a full 10* retard from that position. So it matters then whether Steve put his ICL at 118* using a degreeing wheel, or put it 6* retard from the 'straight up' position on his timing gears, in which case ICL would be 114*, making the IVC point not 76*, but 72*, which increases his DCR to 7.45:1.
You guys are speaking in relative terms which can be very confusing. Please use absolute terms. Straight up is defined as having the ICL position the same as the LSA in terms of ATDC. If the LSA is 112* then the ICL is set at 112* ATDC. Anything after that point is defined as retarded and before is advanced. As far as built in advance, if a cam is installed with the timing marks lined up on the timing gears and the cam is actually at the correct position, it is time to drop all tools and head for the nearest casino. All cams should be checked for proper timing at installation and there should be total disregard for said ground in advance or any other timing. Here is the latest case in point. http://www.v8buick.com/showthread.p...p-guidance-for-a-newbie&p=2556652#post2556652 Also, I would not recommend a 350 cam be installed retarded. If need be straight up or 112* ATDC in this case should be it. Paul
Drop all tools and head for the nearest casino....golden humor Paul. lol Yes, it's quite the gamble when not using a degreeing wheel. I've heard of some real horror stories from people who trusted the cam manufacturer and their timing gears... To do it proper, yes, degree it. Lots of people go the easy way out and use a trusted brand name such as Crower to do it for them. Although you hear about the horror stories of the failures, you don't normally hear about all the successes because they're busy enjoying their car instead of seeking technical advice on this forum. Odds are it won't be spot-on unless you use the degreeing wheel and absolute calculations, but then odds are the compression ratio isn't spot-on either. Many will simply tune the variance out of it and call it good enough. For perfectionists and those who wish to milk every ounce of performance out of their machine, will likely be doing a degree wheel anyway. The point was though, whether Steve used a wheel to set it at 118, or the "114" setting (which could be off of course). The 'ground in advance' is referring to the cam sitting at 4* advance when lining up the dots, as opposed to the 'straight up' (0* advance/retard, or 112 LSA/112 ICL) when lining up the dots with other manufacturers (such as TA). Even if this is off a degree or two, it won't adversely affect things by much, as shown in the link you provided where his installation wasn't exactly spot on with a degreeing wheel, and was said to be good enough by you. The cam itself seemed to be off on its advertised specs too...which is one of the reasons I advise the use of OEM parts (but that's another story!). You're going to vary in timing with RPMs anyway due to timing chain flex and wear over time, up to 2-4* is common. The engine isn't going to run spot-on perfect from fresh to worn either. Constant tinkering and tuning will be required as time goes on, as is common with all performance machines. Lots of people enjoy this though. Some don't. Making the engine with built-in tolerance and expected variables within a certain spectrum is wise, unless you plan on professionally racing it. Some may view this as sloppy, others as safe. The OEM cams take this into consideration within its engineered intent, and is why the timing specs are so wide. Obviously I will (and have gotten) a lot of heat over this viewpoint. For professionals, I can see why this would get under your skin, so I sympathize. Anyway, my 2c. Just wanted to point it out, and thanks for your advice Paul. Gary
