Clark455

Is there such a thing as a stock bore higher compression Olds 403 piston these days? The stock 403 pistons have such a silly deep dish that barely eeks out 8:1 compression. I remember back in the day when I owned Unlimited Racing in Detroit, we were sourcing some brand of cast piston with much less of a dish (higher compression). I used to love pumping up the 403's and swapping them in place of 350's but I can't remember if it was Zollner, Sylvolite, or what brand it was. I have been scouring the internet and catalogs for a higher compression stock bore 403 piston, and all I can find are better compression ratios on pistons only servicing an overbore currently available. The thing is that I do not need or want to overbore the already overly thin cylinder walls on this build - the cylinder walls are nice and clean, and still have some of the factory cross hatch in them - no need to overbore. I have a set of 69cc heads I'm putting on it, but that barely even gets it to 9.3:1 which is better, but I'm looking to pump this up to something better.

HMMM - uh oh - IDEA ??? I can't justify the expense of a custom made piston, but wonder if a .024" over piston could be diamond cut back down to a stock bore size? Maybe that wouldn't cost that much to do? But then the ring lands would have to be cut just a hair deeper too (or not?), hmmm, may have to contact UEM / Keith Black pistons to see if this is even possible. If a piston company won't bother to do it, maybe a good machinist with some precision equipment could wittle some material off? You know, I can actually picture that. I can't see where taking a few thou off the OD could hurt it any, or even change its weight by any real factor. Now the gears are turning in my head (sometimes that good, but sometimes, well...) I think I'd pay $150 to $175 comfortably to have a machinist put a perfect cut on some Keith Black Hypereutectics or similar. But would that take off any type of coating? I don't think so, but could be piston specific (as to whether it actually has a coating or not). I just thought of something though, in that all pistons aren't actually perfectly round, right? That might shoot this whole nifty idea right down...

WANTED TO BUY: STOCK BORE 403 OLDS PISTONS WITH HIGHER COMPRESSION / LESS OF A DISH THAN THE FACTORY PISTONS

Can be cast or forged, but must be for press on piston wrist pin use.

Let me know if anything like this exists!

Thank you kindly!

Paul

Paladin31

Mondello makes their 2230 403 piston in 30 & 40 over ?
makes me a little nervous in how much sidewall remains, perhaps they could turn a tad bore and you could sleeve & cut to stick with their flat top (with valve relief of course ) pistons
Brett

Paladin31

I HATE spellcheck, it looks like I am a 1st grader
bore & sleeve to standard size, have Mondello (or whomever) cut pistons to match
Brett

ROCKETMAN269V

Sleeving all 8 cylinders is NOT a good idea, both from a cost and, more importantly, a structural standpoint.

Paladin31

I agree Bob, the options aren’t great on the Siamese 403 design
I was thinking more in theory, but practicality has to be determining factor

thanks
Brett

ROCKETMAN269V

I kind of figured that you knew better, but some novice reading this might think "O boy, I can put eight sleeves in and I'm good to go".

Paladin31

Thanks Bob
i happen to have a 403 block that I’ve been thinking about doing up, and I had forgotten how much “meat” was left, seems like 100 thousands between two bores was max, or .050 each hole
what’s interesting though is mondello offers .040 oversized pistons, even running that much to me is like running on a razor blades edge….

mikeceli

I have not started on my 1979 Trans Am's 403 Build, yet, but I suspect I too will want a set of flat top, standard bore pistons.