InfinityOlds

Good afternoon everyone,

I'm looking into piston options right now, specifically for the 330, and came across some past threads where those with 350s are running Chevy Pistons with the crank machined to accept the 2" rod journals.

I also came across Mopar 318 stroker kits and thought this might be a potential option - going with a .030 or .060 over 318 aftermarket forged stroker piston with 6.123" h-beam rods. Rod journals are 2.125, stroker pistons are available in a 1.46" length. Flat top pistons are available, as well as some other options. Prices for rods and pistons look reasonable.

Here's what I came up with:


Let me know what you guys think. It seems like this would be an easier path than boring the 330 to use Chevy pistons and changing the rod journal to 2" on the crank, and could be done for 350s as well, as the 360 pistons have an approx. 4" bore & the rods should work without machining the crank, unless I'm missing something.

InfinityOlds

Note: I'm only calling them "stroker" pistons because they're a shorter compression height than the typical 318 pistons.

Fun71

Lots of folks have used standard 350 pistons (4.057" diameter) in the 330 block. From what I have read, just sonic check the block to ensure there is sufficient cylinder wall thickness before boring the block.

Or, there are 330 pistons availabe from Egge, Kanter, SupercarsUnlimited, etc.

olds 307 and 403

Yes, some on here have offset ground the 330 crank with a sbc 350 piston and rod. The 1.56" compression height with a 6" long, 2" journal rod works with the 3.5" stroke 350. I plan on doing the same thing with a sbc 4.125" piston, since I have the 6" rod and stroked 330 crank. I looked at the Mopar rod, too narrow on the big end, I believe.

67OAI

Many 330 blocks have really thick cylinder walls and as stated above can be bored to 350 size (4.057"). If something like that is to your liking, Mark Remmel (CutlassEFI) has the stroker kits available and I think he has a piston in 4.065" available to go with it. Best to have your block sonic checked first! Another piston choice for the 330 is the Egge 4.00" bore flat top listed for the '65 to '67 400 CID Olds. Unfortunately that one is not a forged piston and is about 80 grams heavier than the 330 piston. Lighter is always better!

InfinityOlds

I'd seen the blocks can be bored out-- makes sense as the factory was configured for the same bore spacing. I'm planning a turbo build so I'd prefer the extra wall thickness over the cubes, but the piston availability aspects might push me towards a 350 bore (either chevy or Oldsmobile)

I haven't deep dived into the costs of buying short blocks, but I would think it might cost as much to bore the block to 4.057 as it would to pick up a 350 block to work with. Especially with the cost of the sonic-check baked in either way.

I was thinking it might be possible to get away with just a hone for the .030 over 318 pistons. A .013 clearance is too much to run the stock bore 318s. The .030 overs would be .0025 over, which I think would be good with just a hone.

I guess I'd have to get the block inspected to see whether the bore is in good enough condition for just a hone, and if not may as well bore to 4-4.057" where piston selection is better.

InfinityOlds

Yeah, I did see that the width is a little different on the big end. The big end width of the SCAT H-beams is .925, versus the .935-.937 of the stock Oldsmobile small block rods. I figured that was probably OK as far as having an extra .005" on each side, or that there might be a way to adjust for that, but I was worried about that! Is that extra play pretty much a deal-breaker?

Haven't looked into the other H-beam rods enough (false match led to this edit) but I'd imagine they've all got that same width at rod journal.

InfinityOlds

The Egge was about the only I'd found with specs listed for the 330. That's quite a bit heavier for that 4.00" piston! I think forged is the way to go if I'm going to use anything other than stock.

It seems like if I'm going to stick with this block boring it to 4.0 or 4.057 may be the way to go; or I may want to research picking up a 350 block that's already been sonic-checked.

I guess a final option is paying the extra money to have custom pistons made...

InfinityOlds

Did a little research into this:

Interesting Article: https://www.enginelabs.com/engine-te...the-confusion/

"As an example, if on a small-block Chevy the side clearance on a pair of rods measures 0.023-inch and the stock Chevrolet spec is 0.008- to 0.013-inch, the additional clearance is not something to stress over. While the side clearance is out of spec, no damage will occur as a result unless this is a high-RPM engine where excessive lateral movement could cause problems."

Seems the extra side clearance on the MOPAR rods should probably be OK. On the extreme end some people are running "piston guided connecting rods", where they intentionally run a narrower rod for lower friction and remove the side play on the piston side with washers to remove any side clearance there.

olds 307 and 403

Hopefully, some of the experts chime in. Travato uses .008 to .012" on his builds, he claims stock rods have .009 to 013". Molnar and Speedmaster SBM rods have a .927" big end.

InfinityOlds

Agreed! I think it's an intriguing option, if possible. I think it would work out to about $1200 to buy pistons, rods, and have the engine honed, versus about $1500 to either bore to 4.057 or 4.00 (& machine crank), saving a little more money for the rest of the build.

Sounds like the build you're planning (4.125 pistons & 3.5 stroke) will result in about a 375ci & preserve the same oversquare ratio... should be a fun motor!

If a little play on the rods is OK & there are a lot of compression heights available in that piston diameter I suppose you could run a 5.7 or 5.8 H-beam rods (w/ Chevy Journals) & a machined big block crank offset to ~4" for a still over-square ~425 or so small-block...

olds 307 and 403

Yeah, we have to try and do what is realistic for our budget, I had to realize, my goals were unrealistic for my budget only took me 5 years. Hopefully it will work for you.

InfinityOlds

Thanks! I'm trying to use the "measure twice, cut once" approach. From other threads on here I've seen people seeking help with planning an ambitious build *after* they've bought pistons, and the general advice has been "you should have started with piston selection and built from there, you limited yourself by picking that and then asking for help". I need to sort out the transmission swap and some other things on the car first, so I've got a bit of time to figure things out before starting anything.

For the power levels I'd like to reach I'm taking the advice of folks here that I'll likely need/want forged rods and pistons. I haven't even decided yet if I want to build the 330 I've got, or pick up a short-block to build and then swap in. To some extent it'll just come down to garage space and cost. Getting another block would obviously have an up-front cost, but then I could take the motor in pieces for machining and not have to pay the machine shop to pull, disassemble, and re-assemble the motor, which would probably be as much money in labor as the entire bottom end set of parts! I could also sell the 330, which will have new valve springs and a 4bbl intake on it, or put that onto the stand and do a different build.

I think the biggest thing is not letting myself buy *anything* until I've got a firm start to finish plan & budget for the build. My head is still spinning at all the potential options and approaches.

olds 307 and 403

I hate my car not running. If that bothers you, like me, get a used 350 motor or block to build. Complete used and usually good running Olds 350's sell for well under $500 here. Yes, I bought the wrong parts for my needs and budget. I decided an overheating nightmare after spending thousands isn't the best plan, took me years to finally realize it. Any good condition 68 to 76 Olds 350 is a great engine to build. Just access things like antifreeze condition, that affects how much a block can be overbored and potential cooling issues. Good luck.

InfinityOlds

Great advice, thank you! I'm the same way about non-running vehicles, and my wife even more so, so I think that's probably the way to go to avoid multiple types of heartache over the next couple years. I'm a couple weeks away from having new valve springs (W-31s that I'm sure will be overkill) and seals in the 330 & I can finish putting it all back together to at least have a runner for next year.

I think I'll take your advice and get a 350 motor up on a stand this Spring, strip it down to the block and go from there. About the only thing I'm sure of right now is I'll be better off going with the Aluminum Edelbrock heads milled to height versus porting and machining Iron heads to run the bigger valves, which would probably run me just as much money in the end. The price point of those Aluminum heads is definitely painful on the wallet compared to everything else parts wise, though.

olds 307 and 403

Good plan, be patient. I have stumbled on good deals. I try to sell anything another member needs affordable enough they can actually use it. A lot on here do the same, keeps our obscure Oldsmobile's on the road.