I've heard it said that 350 pistons are hard to come by. I've never looked. If they are readily available my advice would be to buy forged pistons. I've had issue with cast and will never use them in another motor I put together. Also, you have to know the exact dimensions of what you're going to put together before you purchase as far as compression ratios and such. There's a lot to be considered. Pin height, ring pack, valve relief, how far in the hole they will sit, deck height, chamber size of the heads you will be using, bore and stroke. Even your cam specs as far as opening and closing events. It's the difference of how much of your charge is bled off early or late. It all adds up.
Forged pistons for a 350 is a custom order $$$ In the long run it's easier to build a 400 with plenty piston choices.
This is pretty much fact.
Best forged piston value would be if you could find an NOS, or at least a good used set of TRW L2339F030 forged pistons. I found an NOS set a few years back, Never used 'em. Don't know if my engine guy still has 'em or not. Also have a set that are still in a 350 shortblock that came in a '69 Tempest drag car I bought. It got wet in a flood. So, I don't know if the pistons are still good or not.
I suppose it would be worth the time to inquire on all the Pontiac forums & FB pages, to see if you can locate some.
Unless you just insist on going with a 350, the difference in price of new forged pistons could just about pay for a decent 400 core block & crank.
As I've said on several Pontiac sites, the cheapest cast piston option I see is to use 318 Mopar pistons, They're a lot cheaper & have a taller pin height. Will need to have the rod pin holes honed out for the .984 Mopar pins, but will require less machine work on the block, which should more than pay for the pin fitting.
How good are the current cast pistons in a 350. I have no idea. This 350HO engine was built with 357P cast pistons & made 330hp. But, that don't tell you how long the cast pistons would last.
don't waste your money on custom pistons, I built plenty of engines with cast pistons and never an issue with a mostly street car, My last poncho 350 was an ho engine last year only issue was the ho pistons are not available so I just used the 2 barrel .030 piston and took .020 off the deck. cast pistons have no problem under 6000 rpm thats what the oem used. Dont get too wound on the pistons, make sure you have a good machinist that's more important, one thing I would suggest if your rods need to be reworked probably cheaper to buy a new set stronger than the factory and a bit cheaper than getting yours reworked.
don't waste your money on custom pistons, I built plenty of engines with cast pistons and never an issue with a mostly street car, My last poncho 350 was an ho engine last year only issue was the ho pistons are not available so I just used the 2 barrel .030 piston and took .020 off the deck. cast pistons have no problem under 6000 rpm thats what the oem used. Dont get too wound on the pistons, make sure you have a good machinist that's more important, one thing I would suggest if your rods need to be reworked probably cheaper to buy a new set stronger than the factory and a bit cheaper than getting yours reworked.
Sorry, but I just can't let this go.
(1) There were no such thing as 350HO pistons. All the Pontiac 350 pistons were the same, up thru about '73. They were cast & had 4 small valve reliefs. '74-'77 350 pistons had flat tops with no valve reliefs at all. If you have any verifiable proof that I'm wrong, please post your info.
(2) The cheapest forged Pontiac rods are now nearly $400 shipped.
Guessing that even with the new ARP rod bolts, which are less than $65, you can get a set of rods resized for $250 or less. If you've paid more than $400 to have some cast rods resized, please post this info, along with contact info for the shop that charged that much.
Yer right old school , after some digging it was the 350 pistons that we’re available at the time from sealed power the 357p series , I was buying my parts from Ace back in the day and we got to talking about the available options for a stock 350 ho build . Those pistons were all I could find and when I measured the deckheight they were .020 farther down in the hole , so I had the machine shop take that amount off , then I was .010 down just the same from gm
Found this also
One disadvantage of the 357P pistons is that they only have a 1.700" pin height. The pin height or compression distance, as it is sometimes called, is the distance from the center of the pin hole to the piston top. That means that quite a bit will have to be machined off the block decks, in order to achieve the desired zero deck height.
Yeah, for those who choose cast pistons, I usually recommend the Sealed Power 318 Mopar pistons. Their pin height is 1.720, which is is exactly what engine builder Paul Carter says the original 350 pistons had.
I've read that most pontiac engines came with the pistons at least .020 in the hole. Some say .023 was the norm. Anyhow, even with 318 pistons, some will still have to come off the deck, in order to get close to zero deck height, unless the block has already had quite a bit removed from the deck.
The rod pin holes will have to be honed out, slightly, to fit the .984 Mopar pins. But the cheaper price of the pistons, plus less deck machining, should more than pay for any charge for honing the pin holes.
The valve reliefs are slightly different. But, the reliefs in 350 pistons are very small. And, '74-up 350 pistons had no reliefs at all. So, unless you're gonna use some really small chamber heads and/or a high lift cam, there should be no valve to piston clearance problem.
Good info. Thanks. Plenty to think about. I look at it a couple way... one is that this car will be driven so little it could literally be generations before this ever gets done again. And god knows what will be available then? So making the investment for the best quality in a family heirloom and piece of history doesn't seem like too much to ask. I realize everyone isn't in that situation. The other side of the coin says because it won't be driven hard (well too much anyway), or a lot of miles, it probably is foolish to spend a lot of money on something like a forged piston. That mosey could be better spent on other parts. Just gotta decide I guess. You never know what you come across.
Rant time! I can't help but say how much it disappoints me every time somebody says "just build a 400, same cost blah blah" Well no crap! But guess what the car is 350. In this case an original numbers matching 350. Do the car some justice. Thousands of them were 350s and deserve some respect. We should be spending more time building great 350s and less time trashing them. Hell I don't even know if you can buy an aftermarket 69 350 hood anymore? I know the economics and HPs and all that say build a 400. I get it. But.. Won't be that long before original 350 cars WITH A 350 are rare AND your great grand kids will be looking for Poncho 350s in barns.
don't waste your money on custom pistons, I built plenty of engines with cast pistons and never an issue with a mostly street car, My last poncho 350 was an ho engine last year only issue was the ho pistons are not available so I just used the 2 barrel .030 piston and took .020 off the deck. cast pistons have no problem under 6000 rpm thats what the oem used. Dont get too wound on the pistons, make sure you have a good machinist that's more important, one thing I would suggest if your rods need to be reworked probably cheaper to buy a new set stronger than the factory and a bit cheaper than getting yours reworked.
Sorry, but I just can't let this go.
(1) There were no such thing as 350HO pistons. All the Pontiac 350 pistons were the same, up thru about '73. They were cast & had 4 small valve reliefs. '74-'77 350 pistons had flat tops with no valve reliefs at all. If you have any verifiable proof that I'm wrong, please post your info.
Hi oldskool,
I acquired a 68 350HO engine back in '81. It has Jahns aluminum pistons installed. No dome but has reliefs. What do you think of those pistons?
In my opinion it's not foolish to spend a little extra dough on better parts that are stronger and made to last. My personal experience with cast Pistons wasn't good so I will not make that mistake again. You may have better luck but how many times do you really want to pull that motor because the ring lands broke out from too high of compression or detonation that you didn't even hear. It's your money and your effort but it would be a shame to see that numbers matching block go to [censored] because of a few extra bucks that were deemed not worth it. Your motor. Do what you want. You asked.
I tend to agree with you Firebob. I usually don't spend the money until I can afford to do it right. And to me doing it right means the best I can get and or afford. That doesn't mean being ridiculous it means not cutting corners or taking a cheaper route to save a few bucks. I hope I only need to do this once! If I'm lucky enough to drive this things around the block a few times... maybe twice!