Which pistons should I buy?
 

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

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

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

Check out Wallaceracing.com to practice Compression calcs.

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

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.

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.

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.

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.

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.

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.

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.

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.

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!

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

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.

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.

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.

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

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?

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.

How clean-sounding does it run with 87 at WOT?

I had a cam bearing failure during the original engine break-in Stripped and cleaned block and rebuilt again.
Replaced the cam with a Crower and cylinder heads with Edelbrock D port 72s.

.040 over
4.160" bore
Stock ’N’ crank .020/.020
RPM 5140 I-Beam 6.625 press fit rods.
Icon C891-040 pistons 14cc dish
Hastings rings 4.160”, 2M644040, 1/16"x1/16"x3/16" Plasma Moly rings
Felpro 1016 .039" head gaskets
Edelbrock ‘D’ port heads; 72 cc, 2.11 intake, 1.66 exhaust
Crower 60242 Cam
Butler 60# ‘Pro’ oil pump
Crower ‘Cam Saver’ lifters
Butler Pushrods.
Melling Timing set with ‘Morse’ chain, Steel timing and crank gears
Crower Stainless Steel 1.5 full roller rockers
Stock cast iron intake
Stock Qjet built by Cliffs High Performance
Stock points distributor
Clevite 77 Main Bearings -.20
Clevite 77 Rod Bearings -.20
Powerbond Balancer PBO-PB1056ST

Engine is overbuilt for its intended usage. I know I could have installed flat top pistons and still be able to run on 91 but I've sank enough money and time into it already.

Second engine break-in went well and I currently have about 50 miles on it, so I don't know about 87. I'll probably not chance going that low.
But after I run a few tankfuls of 91, I'll start blending some 89 and see how it runs.

I would probably build it with Icon forged pistons. Built my 421 using dished Ross forged pistons and they were expensive at $750 over a decade ago.

I just had a 2276cc air cooled VW engine built for my pickup using Icon pistons and have another one in the works using Icon as well, they’re a little over $100 each for the 3.700” (94mm) size I’m using.

The Sealed Power / TRW pistons are great but I don’t care for the pressed wrist pins, the weight really isn’t the issue.

I’ve had engines with original factory cast pistons and they were fine. One was a low-12s / high-11s bracket race 455 so they do well no problem in performance street engines as well.

I use Icon pistons in about 75% of my engine builds for customers. which are 2618 alloy. The other 25% of the street engines I use DSS pistons with a 4032 alloy. Both are forged pistons with a good ring pack, 1/16, 1.16, 3/16., but the 4032 run a little quieter on start-up. Either one is commonly available, and will do the job. With your heads, #16's, I'd run a dished piston to reduce the compression ratio.

Surprised nobody has mentioned autotech pistons yet.

I just got an engine from Paul (65 -389) he really likes the Icons. We used ross in my 65 to get the dish right, but ICON and Ross are what he uses most.

The ross pistons were really nice , they were pricey but do it once. 25 cc dish to keep the compression down on my small chamber heads

The ross dished ones I just got were about $1200 with pins and rings. These are the semi custom ones where they cnc the dish you want from an instock blank

I used Autotec pistons for my 433 build and they are very nice pieces. Got them in 2019. I read that they were bought by private equity in 2023. Not sure if that affected price or quality.

I went with Ross on my last build.

I bought DSS off the shelf pistons for my upcoming 433 build. I would have to get custom pistons otherwise. Their CH distance put them at .005 in the hole on my decked block. Along with the 14 cc dish puts the cr at 9.9. Down from 10.1 in the 406 with speed pro and stock rods.

Have a set of Autotecs with slight domes for one of my 71 455 HO builds. Chose the AutoTecs for the tight wall clearance 4032 alloy &, the reasonable at the time upcharge for the slight domes. That was from Shannon's Engr years ago.

Once i can have my 72 T/A's block sonic tested, will choose a sizing for it's pistons. Will be another set of AutoTecs or possibly custom Icons, again w a slight dome.

DSS 455 040 18cc dish off the shelf piston and ring kit here. Block was squared and decked as per normal operation and got the thumbs up from my machine shop.

Through Paul I just got a set of custom 4.191 auto techs 4032 with a 1.501 CH. Little under 1100.00 with rings and floating pins.

I get Autotec from Paul K for all of my builds.No issue at all.Tom

Steve can you expand on this? First I head of the metric ring packs not lasting. I have heard of less parasitic drag.

Notes
1mm, 1mm, 3mm ring pack.
1/16th, 1/16th, 3/16th ring pack (1/16 = 1.5mm)
stock LS engines use a 1.5mm / 1.5mm / 3.0mm
Pontiac 400/428 (1967-1979): Generally uses 5/64", 5/64", 3/16" packs

Guys are seeing power gains with the new trick .7 mm ring packs. Lots of new tech in that area.
I used my Ross old school 1/6" ring pack pistons in my 461. But, I had Total Seal back cut some ported rings for less tension and used that flat wire spring steel for spacers under those rings. Everything turned out great, but a lot of work fitting it all. Never again, I will buy new pistons next time with metric rings.

I have to agree. All the pistons I broke (Back in when all I could afford was cast pistons) were from rods or valves failing first. However with part quality level we see today I'm not sure that holds true anymore.