I'm rebuilding a 66 225 Slant six I would like to know what is the best aftermarket Pistons to use if factory Originals cannot be found your help is greatly appreciated

There aren't too many aftermarket pistons to chose from... and most can be the same manufacturer and rebadged on the box... all of my mills from 9:1 up to 12:1 CR al have run fed mog sealed power flat top slugs... some people have run engine tech as well.

It used to be the best bang for the buck to buy a full rebuild kit from a place like Northern Auto Parts or Performance Automotive Warehouse, where you can get the slugs, rings, bearings, etc... all in one shot... price has gone up in recent years so they aren't as cheap any more (but at least its not like buying a kit for a 440 or Hemi though).

I wonder if we will ever reach the point where a long-rod rebuild becomes cheaper than a stock rebuild?

Performance application? How much compression and overbore do you want? How much do you want to spend?

Fed Mog, Sealed Power, Silvolite, Engine Tech are good names, assuming they are holding to their names... Might be good to get older stock pistons off Ebay?

Personally, for a peppy driver I would overbore 0.060" (you can go up to 0.100" later comfortably) and mill block or head to get 9:1 comp.

Lou

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Home of Slant6-powered fun machines since 1988

Only as long as cheap engine blocks can be had and the aftermarket still has parts available....at some time capitalism will take over and these aftermarket items will no longer be offered, and eventually when I retire we'll be looking through catalogs and specialty parts houses for rebuild parts like the guys trying to get parts for the old Lincoln V-12's....

I mostly agree with Lou, but am more conservative on my non-stocker builds... .040 overbore if the head and bores are matched right works fine to keep the 1.70/1.44 valves unshrouded, but as Lou points out .060 is better... when building the slant you will have to remember that overboring doesn't give extra displacement like the big bore V-8's, in fact on a standard 225 an overbore of .060 gives you a whole whopping 7 cid increase in displacement...so when applying some of the engine building planning and math look at if more from the perspective of 1) getting the head and valves to breathe better when matched to the correct cam, 2) increasing compression to make the best efficiency out of the build (again cam choice does play a part of this...and looking at the dynamic compression ratio will help get a solid street driver that can also be a good solid strip car, but not put you out at the gas pump.) 3) Make sure to look at the peak rpm for the cam and what you have for gears and transmission/torque convertor... the build needs to match or you will be applying bandaids and compromises to make it work right and not be entirely happy with what was accomplished.

Being a bit conservative so I actually start my builds at .040, so that way if it fails, I can go the .045 long rod for the next overbore or just get it overbored to .060 and try it again... that being said... .040 rings are not as easy to get as .030 or .060 (kind of like .080 rings were for a while)....
I had a hi-po engine fail at break in, and luckily I was able to pull it apart and just pay for the next overbore and resize another set of spare rods and hang a set of .060 pistons and that engine went on to race...and it's now back in my car with a different head and more compression...

I'd feel confident the aftermarket should cater to the slant for quite a while yet. Our Hemi 6 engines were produced in far smaller quantities than the slant and pistons are still available. Even the 245 Hemi which has a smaller bore than the more popular 265 can still be purchased from what Ive heard from local guys, I believe " Hypatec" is the brand name,yes they are off shore but there are no complaints and many guys run them in mild small blocks making moderate power... If we do alloy heads and Pistons for a relatively small production run engine like the Hemis I think the slant should be OK for a while yet. That being said I'm so impressed by the weight savings and piston design of the long rod engines I'd personally prefer that Scat or someone cranked out cheap I beam rods and run the 2.2 Pistons as an alternative.