[gtobird]

It's been a long time since I purchased pistons. This time around, it's for a 68 400 that will be built to stock HO specs with the typical 068 grind cam and #16 heads. It will only be used on the street. I have this exact combination in another engine I built a while back with old school forged pistons and it runs great.

The question is which way to go for pistons? I'm of the philosophy of buying good quality stuff with a build it once and leave it alone mentality. I'm fine with spending a little more for peace of mind, but no point in buying big dollar stuff for racing use that the engine will never see.

So, what brand / type of material makes sense? I've been looking at the Speed Pro forged and KB Hypereutectic flat top pistons.

I appreciate your opinions.

Thanks
Old Joe

[mysticmissle]

Nothing wrong w those choices but there is some
Easy horse power in a customish piston w LS style ring pack for slightly more money, id throw some
Good rods in it too.
Paul k kre butler im sure could help with piston choice

[Half-Inch Stud]

Forged, Speedpro with a dish to get the iron 16s to 9.5:1

Check out Wallaceracing.com to practice Compression calcs.

[tom s]

Paul K has been helping me with pistons for a few years now.Tom

[JLMounce]

Honestly, if this is a street cruiser where getting every once of power out of the engine isn't desired or necessary, there's nothing wrong with the Speedpro stuff. It's older tech, but the TRW/Speedpro stuff is still good.

I'd go with the speedpro forged stuff at nearly the same price vs the KB hypereutectic stuff. Those things just don't like any amount of detonation which narrows your tuning window. The Speedpro's are known to take a beating.

If you were doing a stroker, I'd recommend the Mahle power pack pistons. Quality part and you get the 1mm, 1mm, 3mm ring pack. They only make off the shelf parts though in compression heights suitable for 4.25" stroke deals.

For a bit more, I run DSS FX pistons in my 465. I run their piston/ring combo which is a 1/16th, 1/16th, 3/16th ring size. I have great ring seal, no blowby and the pistons are dead quiet even when cold.

[John Milner]

I am not a big fan of the KB hypereutectic pistons if they have the strange wide gap between the top ring and 2nd ring. If they are that style, you had better pay very close attention to your ring gaps or you will break the top of the piston. I'm a TRW/Speed Pro forged piston fan for a street car. Yes they are a little heavy but they are plenty strong and don't break the bank.

[steve25]

Just to add this snippet, pistons with the stock size 5/64” 5/64” rings last a lot longer seal wise.
Yes, there’s more friction and hp loss above 5K, but so what on a street motor.

[performerrpm]

i like my ross pistons, which i think have went up ftom 699 to 750 but still nice pistons.

i have some forged icons i think are pretty nice pistons. either of these pistons are nicer and lighter than the trw forged i had in my 455....but i couldnt tell the diffetence in my gas pedal. i thought the kb hypers was a no go though.

[Bruce Meyer]

With your 16 heads the compression will be too high with flat top pistons. I would get dished pistons. Icon makes a good off the shelf forged dished piston.

[1969GTO]

Funny you should ask.
I am dropping my engine off to Paul Spotts of Spotts Performance in PA tomorrow 04/04/26.
I am having the same type of build done to my numbers matching 1968 GTO 400 engine.
I am using my YS block, 16 heads, original cast intake, QJet, distributor, crank shaft and rods.
The piston brand I don't remember but the compression will be knocked down to around 9.5.
I will also include RAM AIR Restorations exhaust manifolds and PYPES exhaust with an X pipe.
Contact Paul for more info on his builds.

[OG68]

Same here. '68 40 over WT. All stock parts, 068 cam, 16 heads measured at 71 cc. RA manifolds from Ames. I used ICON 14 cc dished pistons. CR came out to 9.65 with .039 head gasket.

[AG]

If it is a strictly street motor is really doesn't matter. I have cast pistons in my 455 in my '72 LeMans with a RAIV cam for the last twenty years and I beat on it. I have used KB hypers, ICON forged, TRW forged and custom Ross. Use the piston that makes sense for the application, I would recommend ICON if you want forged. Ross are over $1100 with rings and that's very expensive. I don't think your Hp goal needs a piston like that.

[tempest1964]

For my recent build I chose DSS 4032 pistons. They are forged, which gave me peace of mind for durability. And they are 4032 aluminum which has less expansion and more suited for street use. This allows for a tighter piston to bore set-up and creates less piston slap/noise on cold start-up. Sounds like a fun build for street. Good luck!

[blueghoast]

I'd go with TRW-Speed Pro and never look back
And don't buy dish pistons without CCing your heads first
Most of the 16's I've used are mostly in the upper 70 cc's
Your compression should be good as they are but still check.
You can probably use head gasket to get were you need to be.

GT

[OCMDGTO]

The 461 in my car now was previously a 400 w 16 heads and I ran Speed Pros at 9.5 compression. It ran great for 30k miles. That being said I am running Ross in the 467 and Mahle in the 461, both great. I would go for a quality forged lighter piston if I was you.

[mgarblik]

As stated, any forged piston is far better than the KB hyperutectic pistons. They are like glass and any detonation will likely damage them or crack them. I would see who has the pin height, dish, ring package you want to run and choose based on that and the costs/availability. Ross, DSS, IKON, Mahle, Sealed Power, Diamond and others all make good pistons. I personally like 2618 alloy the best. They are old school and WILL make some noise, especially cold. I like the sound and they are the most forgiving. 4032 alloy run tighter piston to bore and are virtually as quiet as cast. Either just fine for your application.

[Schurkey]

I have KB Hypers in multiple engines. Zero problems EXCEPT for mild piston slap when cold, that goes away after ten or fifteen seconds.

There is zero problem with ripping the top of the piston off if you're smart enough to follow the instructions (included with the pistons) for ring-gap. The top ring runs hot, expands more than usual, so the large gap isn't a problem, it's merely a difference. The KB Hypers tend to have modern design features, I actively LIKE the big gap between first and second rings. The ringpacks could use more-modern rings, though.

True enough, the Hypers do not respond as well to detonation as a proper forged piston.

[gtobird]

Thanks for all of your comments. I do appreciate hearing the logic behind each recommendation. Helps me make an informed choice.

[tjdjr]

Icon 14cc dished here also. Break-in went well with outer springs 2 weeks ago, going to add the inners this weekend. Same build as me 400 .030 over with #16 heads and melling spc-7 cam. sounds good on the run stand so far. I marked all the pushrods and they all were spinning nicely while running. Good Luck to you ! On a crazy note I thought i was going nuts trying to install the flex plate, I tried all the bolt holes trying to get them all lined up and the only way it would work is backwards ! I contacted PRW and sent them pics and the ring gear was welded incorrectly on the plate.. They sent out a replacement and paid shipping for the bad one to return.. Anyone else run into this?

[Tim Corcoran]

Hmmmmm Pontiac used cast pistons from the factory and I don't recall anyone having problems with cast pistons on a street car. They are plenty strong for street use and last a long time due to closer piston to bore clearance. And the rings last longer with a tight piston to bore as the piston isn't rocking as much.