Dug out my '72 350 block and gave it a preliminary scrubbing. Interestingly enough, careful bore measurement shows virtually no wear- I plan to run it by the local automotive shop to confirm, but near as I can measure, just below the ring land might be 4.0575". An inch below that is 4.057" even.

Again, I want to confirm with better measuring equipment than I have, but I might be able to give it a quick hone to break the glaze, and drop in some stock-bore pistons. I could use the ones that came out- stock deep-dish cast, in good shape- since I'm not going for max power, but as I understand it, that with a thick gasket would likely only barely give me 8:1. Am I right on that?

I've found a number of stock-bore pistons available, but I'm wondering if anyone can recommend a specific good, budget set. Again, not shooting for max output, 250 to 300HP would be fine. (Still twice what I have now. )

Stock 7a heads, and presumably a thick modern gasket, though decking either head or block or both is by no means out of the question.

Thanks.
Doc.

 

Both Mahle and CP have Olds 350 pistons in a 4.065" hone to fit size, for good bores. I was going to use the Mahle but a couple of cylinders didn't clean up at that size. The Mahle have 10.2cc dish and the CP a 1.3cc dish. Possibly the old school Speedpro forged pistons which need .004" minimum piston to wall clearance might also work, if there is minimal wear.

 

I'd already looked at Mahle, given Cutlassefi's endorsements, and I'm hoping to hear him chime in, but I'm also given to understand that's one of the most expensive options. I just looked at Carrillo, thanks for the suggestion, but without digging into their custom options, it looks like the only Olds options were flattops with 10+ compression ratios?

I also looked at some Speed-Pro and Sealed Power stock-bores, but they apparently only come in flat-top. There's been a few others, but I haven't dug into them too deeply.

Yeah, I know I should just bore/hone- "do it right the first time" and all that - the low wear just gave me the idea I could get away without it, maybe save a few bucks.

Doc.

 

No piston options are affordable anymore unfortunately. Talk to Mark, he sells the pistons, pins which need honed to fit the rods and rings for less than anybody else. They sit about .020" below deck. Mine 350 deck was cut .016" and my pistons are about .003" below deck.The cheapest option is the 6cc Speedpro in .030" oversize and actually get any compression. But heavy, need double the piston to wall clearance, don't believe the .001" on the box or the .002" in the instructions. Old school 5/64" rings vs the Mahle 1mm rings, which do work just fine, multiple Olds builds, don't listen to T sirt salesmen. The DSS pistons sit in between, a slightly larger 12cc dish and a 1.5mm ring pack.

 

If you are looking for a stock replacement piston there is probably something available from Sealed Power or Silvolite. As far as performance goes the Speed Pros are good like o307 said but I have been finding lately that they have been doing away with a lot of their standard bore part numbers. I get it because there are very very few blocks that are still ok at standard bore.

 

I was actually considering just putting the stock pistons back in- I'm not kidding when I say my budget is tight- but one of them has a broken skirt. (Possibly the reason the engine was taken apart in the first place, though that's just a guess.)

Yeah, I know nothing's cheap these days, but I gathered the Mahle set would be $900+, and some of the other options more like $500-$600. And again, since this isn't a max-output situation, I figured a middle-of-the-road set would do me just fine.

Just looked at the DSS options- thanks for the suggestion. They indicate 10+ CR, with a 64cc head. I was given to understand my 7a heads had a 64, but a couple of older threads here have disputed that. I have no easy way of measuring them myself since the heads are bare, no valves. (Not sure what happened to them- the heads had been taken apart when I got the literal basket-case engine.)

Doc.

 

DSS have 2 different dish sizes, the 12cc would put you around 9 to 1. Your heads are probably more like 68cc, if they haven't been cut. The Mahle pistons includes rings in that price.

 

Silvolite has a stock replacement piston that would be around $250 a set. My warehouse does not have them in std but they might be available. Same with Sealed Power.

 

I take it those are the 24cc dish variety? If he is fine with 8 to 1 compression, it is definitely the cheapest way to go. Probably once the block is measured, it will probably require an overbore anyways.

 

Looking at the Silvolite cast piston p/n 332AP, it has a huge dish (0.215"), a compression distance of 1.596" as compared to the stock Olds 1.615" and claims a comp ratio of 7.9/1. Sealed Power's SpeedPro line of forged pistons show both a flat top L2320F and a shallow 0.076" dish L2321F both with a comp. distance of 1.612". Either one of those may suite your build as they are close to factory original piston weight and use the factory size ring pack as stated above by olds 307 and 403. I share his statement about insisting on a finished piston to wall clearance of 0.004" for those pistons. The SpeedPro was always an affordable piston, don't know what current pricing would be; check online sources like Jeg's, Summit, Speedway, etc. I used their L2320F piston (std. bore) many years ago when rebuilding an Olds "E" block and was very satisfied.

 

Thanks guys, that definitely gives me a few options to ponder. Doesn't look like the L2321F can be had in a standard bore- at least a quick search didn't show any.

I guess I find it a little odd this is a trickier question than I thought, but I suspect Bill's right in that there's not much demand for standard bores anymore...

Probably ought to just bite the bullet and get the Mahle 4.065" set. I either pay to have the block bored and honed, or just honed, and I suspect the shop will charge about the same either way.

Doc.

 

@cutlassefi

 

As noted, both of those are short on compression height and have huge dishes. If you’re gonna go with either of those brands, get the 68-70 flat top version as they are still short on compression height but don’t have a dish that would reduce compression even further.

 

Look on ebay: 350 OLDSMOBILE FORGED PISTONS LOW COMPRESSION STANDARD BORE L2345F

 

I believe those are a 18cc dish pistons. I bought a set of pistons and rods with a 330 crank years back. Better than a 24cc dish and only about the same as factory pistons, .025 to .030" below deck. The cheap cast pistons can be .040 or more below deck. That is getting into Dodge territory.

 

Look on ebay: SPEED PRO Forged Coated Flat Top Pistons Set/8 for Oldsmobile/Olds 350 W31 STD

 

If you get the SpeedPro flat top piston, L2320F, it is available in standard bore. Further, the deck is super thick on that piston so if necessary you could have a small dish machined in them to attain your desired compression ratio. Ya, I know, extra expense!

 

Yes, I have a set of these pistons with a 12cc dish milled into them. Bought for use in a 400E build that never happened.