Just asking what compression ratio pistons you are using with pump fuel for a stock rebuild. I saw TA pistons are 10:1 is this too high ? I did read somewhere - I don't if it's true - that Egge are only ones manufacturing new cast pistons these days.
We'd have to ask Tom or Walt or somebody to weigh in here, but I don't think Egge is the only supplier of cast pistons. I do think that people are having trouble finding quality off-the-shelf pistons from any manufacturer, and we've certainly seen some specific complaints about Egge. Tom has worked with a piston manufacturer to come up with a fairly cost effective custom piston, and having seen them in person I can vouch - they are beautiful, its almost a shame to bury them in an engine! That said, all the heavy hitters here are not at all shy about spending the money on custom pistons, which has to say something about the standard market. The CR on my new motor will be 10:1, and I think Tom built John Codman's motor to 10:1 spec too - John, any detonation?
You can go as high as 10-1 with no problems with the combustion chamber design. Problem is is that one piston made to fit ALL applications will not cut it. Depending on ALL the variables you would be LUCKY to end up with 9.5. Even stock the best I've measured on a virgin, never before been apart since the factory was 9.75. Many are much less than that. Many times with off the shelf pistons many end up with closer to 8-1. Makes for a sluggish "Nail" with a poor quench/squish area. Just my thoughts. Tom T.
The compression ratio depends on what engine you are speaking of specifically and what year of manufacture. For instance, the 66 401/425 was rated at 10.25:1. But like Tom mentioned, he has found a virgin one to be that yet.
Replacement pistons are currently available from: Sealed Power/Federal Mogul, pn 69P UEM/Silvolite, pn 1717 EngineTech, pn P6004 Egge Machine, pn L2078 They do vary in dome height and compression height (piston pin location) between manufacturers, which will affect compression ratio. I agree the stock engine from Buick was somewhere around 9.8. To get to the 'advertised' 10.25 CR, they needed to be blueprinted to NHRA spec. For a performance build, custom pistons would be recommended. Diamond, Ross and RaceTec are a few options. Tom has some nice forgings avail via special order, built to your spec.
the Race-Tec are the way to go.you get your deck height right, plus light weight, stronger too, plus a real good price for forged pistons. use them on my 340 Buick. then Tom T. just got me a set for my 440 dodge with a D shaped dish for the closed chambered heads, saved 170 grams per piston.
Really good replacement pistons are available from Tom Telesco. My 425 (431) has a set of his 10:1 pistons and it is awesome. These are forged, and will probably last longer then I will. They can be manufactured in pretty much any compression ratio that you want. They are so pretty that I am thinking about ordering one more just for display. Not cheap, but you get what you pay for.
The forged pistons sound nice but I can't afford or justify them right now. I'm already well over budget on this rebuild. I did contact Russ Martin to order pistons but he is out of stock at the moment on .030" Any idea what make of piston he was offering ? I have read couple of negative comments on this site regarding Egge, but haven't come across Sealed Power or Silvolite or Engine Tech. Our regular fuel here is 91 RON unleaded, can get up to 98 but more expensive and not readily available.
Those are Kanter's. I had those. Good looking pistons, though pin height is lower than other stock repl. pistons. Silvolite aka Keith Black is up on Summit Racing, but I've never seen a pic of those.
vice versa, obviously! the lower the pin height (i.e. shorter piston), the bigger the distance between the piston top and the head.
yes, the lower you move the pin down the piston away from the top of the piston the more compression, say the stock pin height on a nail head is 1.93 and the stock piston is 50 thousand down the bore. if you want the top of the piston to be even with the top of the block you would need a 1.98 pin height.
Which NONE have. You must remember the quench/squish area. Stock they were barely good, except if you ended up with a short deck height from the factory, less than 10.08". Combined with a composite head gasket will yield about 8-1 on average with a QS area way excessive. If you factor in you also have to buy rings now the cost isn't as big a spread as mine come with rings. Just my thoughts.
Tom, do you measure the deck height on a bare block, with it assembled, or measure components and calculate it? I did a Google search and saw some different methods to measure a bare block.... such as using a straight edge in the crank bore, measure with calipers to the deck, and subtracting half the crank bore diameter..... Silvolite and Engine Tech pistons advertise the compression height as 1.912" with dome height of 0.370", and Sealed power has compression height of 1.905" and a 0.375" dome. Tough to determine compression ratio without knowing the dome VOLUME.
Just measure with calipers & you will end up with 8"+, then add 1/2 the main bore of the block. Blocks vary widely. Untouched virgin block decks have measured from 10.0065" to 10.0215". This is one of the things that make the pistons I'm selling attractive. They can be made to compliment ANY combo. That's why an off the shelf piston is a crap shot. Much too many VARIABLES. Tom T.
I agree, however, it's a little complicated way to say whether it's lower or higher pin height, since 1.93 is less than 1.98 pin height, which means one 1.93 has lower pin height, while 1.93 is heigher. I think we should start from the small con rod end to the top. Don't deck the block too much, always check piston top with placticine for clearance.
You should measure as much as you can. Better to measure the block with a caliper than a straightedge on the main. The width of a straightedge gives a bad measurement because of how it sits against the curvature of the main bore. The caliper has a thinner edge. If you have a suitable mic, a piece of round stock (precise) can sit against the main bore. Not real critical though. Check all 4 corners. Most home builders don't deal with the rods off the pistons, so it's a good idea to check the short block while assembled, from the piston top. If you don't have a bridge with an indicator or a depth mic, the caliper will do. Sadly, many shops that do the R&R on the rods don't measure them, and its difficult to see a bent one when hung on a piston because the depth of the skirt. I've seen a few come up short as much as .060" on other people's projects. Always a good idea to mock up the short block without rings. Check measured dome volume if concerned with compression. Better is to verify running clearance of valves to dome and valve reliefs. Not so much of a problem on a Nail, but many cast pistons vary in the valve relief area. Bottom of the piston will often indicate a # corresponding to a different mold. They don't cast them one at a time. From time to time you might find one that has an interference issue with the valve radially. Play-doh works good for that. Use light springs often found at the hardware store and a bit of ATF on the valve face. It's perfectly OK to fix issues with a die grinder on a budget build. Balance will not be affected with a little "massage". It takes quite a bit of material to even come up with a single gram. Don't leave a sharp edge or corner anywhere on the piston. As mentioned, the clearances are more important than the measured compression. Not much quench action on a Nail, but anything helps.
