I recently posted my plans to build a mild 300. I asked for sources of pistons and got several ranging from Sealed Power 279P to V6 pistons. From what I can tell, the 279P are the stock pistons for the low compression (8:1) 300 (+0.050") or 350. The V6 pistons are for about 8:1 compression as well. The compression distance (CD) is all about the same as well, either 1.800" for V6 or 1.835" for the 300 or 350. All of these pistons claim a recessed top between 0.245" to 0.260", depending on the source. So, where is the compression coming from? Are the chambers on the 300 that much smaller that a low compression 350 or V6 piston will produce 10:1 compression ratio? What does the stock high compression piston look like? What is its recessed dimension? Incidentally, I have several sets of (used) stock, low compression 300 pistons. All of the recessed tops are about 0.145" to 0.155" with respect to the top flat on the circumference of the piston. So, what's the advertised recession measurement of 0.245" to 0.260" coming from? Two more points: 1. Can the center "nub" be removed from the piston? It looks like a detonation initiator. 2. What about the shroud around the spark plug hole in the head. Does that serve a purpose? Is there an advantage of removing it? Many thanks, Joe
Use a calculator such as this: https://diamondracing.net/p-10-compression-calculator.html One of the basic considerations is the piston compression height. A zero decked 300with stock heads will need some dish to run a 10.5 CR.With TA or Rover heads it will need nearly twice as much. Most SBB engines do not run squish.
Auto Tec will make whatever size piston in whatever comp. ratio you want. They’ll send you a sheet for your machinist to fill out. They’re forged and they’re reasonably priced, that’s what I have in my 350 GS
Sealed Power 340p are the higher compression stock replacement for 350. Seems to be out of stock in standard size and only available in .030 over.
If ordering custom pistons it is a perfect opportunity to spec out all the details. Get some squish, smaller lighter wrist pin, modern ring package, even use the inexpensive nascar take out rods. Of course the next step with the 300 is to use a 350 crank, and then maybe a roller cam so you can run modern oils. Really if you are going that far it almost doesn't make sense not to slap a set of TA/Rover heads on it. Then what? Maybe a Blower just for the fun of it? Hey, anybody interested in buying a 340 blower intake with a built in intercooler? I could probably be persuaded to sell... Just sayin, fella's gotta draw a line somewhere. Jim
There are not many higher compression pistons available for any of these engines. But it’s all about the dish size which you need to measure. .245-.260 dish is pretty large. But you need to look at depth of dish. Here is the 350 8.5 and 10 to 1 “rated” pistons. remember that compression distance and gaskets thickness can change compression.
Never seen these pistons before at Summit: BUICK DSS Racing 2-6243-3800 D.S.S. FX-Series Forged 2618 Alloy Pistons | Summit Racing Buick – DSS RACING PISTONS
They have more info on the second link, shows oversize. Nice compression height, your choice of 1.85 or 1.88. 15cc or 29cc dish. Reasonable price for forged pistons. Their website says other engine parts coming soon. Would really like some .001 under sized bearings.
1.880 compression distance. That must pop up thru gasket. By like .30 The other seems like a turbo piston.
The 15cc 1.85 shows 9.2 compression with 55cc head at .01 above deck in a 300. I have heard some 350's had abnormally high deck heights, maybe that was for the 1.88? The 29cc would be for Turbo application. Figured it out, they use a 6.35 aftermarket rod with the 1.88 pin height. Stock 350 rod should be 6.385.
Remember when Sealed Power made a 10.5 Hyper piston with valve reliefs for the 350. They were discontinued, but would'nt it be great if TA could make some like those.
In strength, inbetween cast and forged. Price inbetween too. Can run tighter tolerance to bore than forged. Perfect for street, non racing application.
Gents, Thanks for all the great suggestions. The decision will be between flat top 3.8 pistons with a 0.050" overbore or a set of Egge pistons "Stock high compression design" at 0.030" overbore. The real question is "For a relatively mild cam (low overlap) what should I aim for in static compression? I'm figuring on 10:25:1. Simple? Not so! My heads are measuring in at 51 cc (stock, before cleaning up). The factory spec is 57 and someone mentioned 55. Then the squish I've measured on two of my engines vary from 0.034" to 0.045". So, one cannot rely on factory tolerances. BTW, the factory high compression piston appears to have a 0.02" recess vs. a 0.156" recess on the low compression piston. I still don't know why all the piston specs out there are calling for 0.230"-0.245" recess. Maybe that was for the export pistons.
Maybe your heads have been milled? I think you mean the 82-87 3.0 V6 flat tops which would be .050 over. I know of no flat top 3.8 pistons. Keep us posted on your build.
Apparently Autotec is still made and sold through this outfit? "Racetec Pistons" in CA. They say all US made, but don't mention Buick on the catalog. I suppose if they make all custom that doesn't really matter. http://racetecpistons.com/wp-content/uploads/2019/11/RaceTec_Catalog.pdf
