Piston Advantages
 

Hey guys, I’m getting ready to put together a street cruiser 400. Approx compression is say 9:1, 3.55 geared and a TH350 with no stall. Car is used for cruising both city and some highway driving.

Is there an advantage in using one piston over another in this scenario between Speed Pro forged, KB Hypereutectic, or say Ross for this type of engine build? Will the weight savings be of benefit between these three options?

Thanks for your insight

Your first concern should be to step into the 1980s with a piston that does not use 5/64” wide (high friction ) compression rings.

Not following Steve, I don’t build engines for a living but assume that’s a dig on the KBs?

Having just completed an engine build, I had an idea of the piston I wanted, but ended up with a different piston because of build parameters. Depending on what parts you are using, you may be limited.

I ended up with DSS forged pistons. We wanted a Mahle that utilized a 1mm 1mm 3mm ring pack, but we couldn't get the correct compression height for a standard 455 4.21" stroke. If you can get the Mahle with the small ring pack, I think that's the piston to go with, but consult your builder.

I looked a bit and most of the KB stuff and the Speed Pro stuff still comes with the 5/64" ring lands.

That may limit you to pistons like Ross, DSS, Mahle etc.

I like to do as much of my own engine building as possible therefore TRW, Speed pro besides the weight and fat rings along with slotted skirt, press pin design are out of the question for me, if your in a pinch they fill the hole tho..

In the past i used Arias dont know if they are even in bizz anymore

my last build (433) got Auto Tech pistons from PK. pretty sweet units skinny rings slip fit pins drilled skirts

drilled skirts refers to area under oil rings TRW has a wide slot under ring better pistons have holes drilled here for oil migration and provide more skirt strength

Hey, is PK Paul K by chance?

Yes.

KB forged off the shelf since it’s a “street only” qualifier. Otherwise what the builder thinks is best.

Autotec 4032 alloy is what I used on my 434 build. You didn't specify if you need a dish or not, or what rings you want. The Autotec lets you spec anything you want for ring pack, ring placement, dish size and shape, pin placement, bore size, etc. If you can find a set of rings to fit the bore, Autotec can make the pistons to fit. Not sure who else does that.

I would not use a hypereutectic piston in anything. TRW forging is OK for a cruiser.

Auto tec from Paul K.Tom

I recently used Icon forged pistons from Kauffman.

Based on the options in the poll, I would bet there is a budget parameter here. Autotech has a good reputation for building what you need, but any custom piston isn’t necessarily going to be budget friendly.

I have been using Icon premium forged pistons on most of my 400/455 builds. Here are some of the benefits:
-They have a very good selection of both flat tops and dished
- They come std with a nice coating
-They use a 1/16, 1/16, 3/16 ring pack, not the most high performance, but very common with lots of options.
-They always seem to be the same size (diam) and weigh
Within one gram.
-Reasonable
No, I do not sell them, just have been very pleased.

My mild budget friendly build got the heavy, thick ring, press fit sealed power/trw forged pistons (no rings) for about $400. The higher performance larger budget build got DSS forged pistons (no rings) for just under $700.

Thank you Bill, this is the kind of information I’m looking for, I know nothing about ring packs weights etc so I am trying to learn. In a low compression street only cruiser is it worth nearly double the $ to go from Speed Pros or KBs? What are the gains?

Lack of knowledge of what is out there is why the poll does not contain all pistons. It is titled “advantages” which budget is always a consideration. Some of these pistons are twice as much as the old standards, but what do you gain in my application listed? Thanks for the reply Jason.

The ultimate street piston for a forged piston alloy should be a 4032 and not a 2618. The 4032 operates quieter, does not expand as much when hot, the piston to wall tolerances can be tighter, and the pistons will last longer. The ring lands will not wear as much either. The 2618 is stronger, more resiliant to deformation, and dissipates heat better. …not needed unless your past 600HP. The factory Speed pro forged are an alloy not far from being a 4032.

The thin 1/16 rings usually show gains of around 8 HP versus 5/16. The 1.5mm are closer to 10HP. Most the 1.5mm offerings have shorter skirts for less friction, and make more piston slap noise. Not all that friendly for street stuff. Modern pistons have skirt designs that offer advantages for friction. On a stock type street build it probably won’t change things much. On a max effort HP build the modern skirt design can be 30 or 40 HP.

On a stock street type build, having all the bells a whistles make you fell better. But if someone came in overnight and switched them out for old TRW slugs. I doubt you could honestly be able to tell until you went to a race track.

The engine I just finished we went with a custom piston, small ring package and short skirt design with a coating. One thing also done that I haven't experimented with before and really isn't talked about much is a longer rod setup. This is supposed to put less side load on the piston and provide a more stable piston at higher rpm with better ring control. It also does other things like more dwell time at TDC and stuff like that, which starts getting technical where discussions go on either side of the fence as to whether it's worthwhile. I was more interested in the stability aspect of it.

That makes some sense.

When costs are looked at, also look at if the piston is coming with a ring pack. As an example, my DSS pistons were a bit over $800.00, but came with the rings. The SpeedPro's may be around $400.00, but you're going to need to add rings to that, so the prices can start to narrow a little bit.

I will say that the previous engine build had the old TRW pistons in it. That engine still made great power even with a heavy piston and an old style ring pack.

I do think for a street only application where you may want quiet operation over anything else, a Hypereutectic piston is probably the best bet. You'd just have to know that if your plans for the car changed in the future, they may become a liability.

You guys still think Hyper pistons are a viable alternative? What about resistance to detonation and ring butting? Hyper pistons are high silicon content. They are dimensionally stable, but are brittle. Heavy detonation can crack them.
Some designs (particularly the KB hypers) tend to put a lot of heat in the top ring. In high power, nitrous or boosted engines, they tend to butt the top ring and tear the top of the piston off. They also cannot have dished milled in the top to lower compression. For a low compression, lesser than 400 HP builds, they would be an option. But if you get the bug for more HP, the hyper pistons quickly become a limiting factor to power production.

I used a set of Ross 2618 pistons in a long rod 400 nitrous street/strip motor. It ran for 10 years and about 15K miles. My only complaint was the piston slap when cold. Upon teardown, the pistons were good, even though the rings and bearings showed signs of being unhappy due to years of being run hard. The looser bore clearance makes some noise when cold and can shorten ring life. At least in 2004, the Ross pistons had limited options for customization. I sold those used Ross pistons to somebody here, they were still perfectly good.

Since I like to make the max power on pump gas and use nitrous, I have to use good pistons and rings. That 434 got the Autotec pistons and a $350 set of AP stainless LS style rings, torque plate honed, 6.8 BBC rods, the whole burrito. For a cruiser, the only pistons I would NEVER use would be a hypereutectic or the 8-eyebrow cast monster. Just be sure to consider the compression, camshaft choice, RPM range, gearing and risk of detonation with less expensive pistons and ring packs.

I don't use hypers in anything. Never had a noisy forged piston either so not sure what others have going on with that deal

Thanks, KBd would be a last resort for me. I’ll probably just go heavy Speed Pro

Icon forged if one will fit your desired CR. Otherwise it's custom piston and choose your favorite manufacturer, doesn't matter who that is since they are all over $1100 with rings (Ross, DSS etc).

That should be fine. A TRW piston with moly top ring, ductile iron 2nd and standard tension oil rings will be fine. I assume aftermarket 6.625 rods with press fit pin?

The next concern is compression. What heads are you using to get 9:1?

AutoTec 4032 alloys here in one build (slight domes, metric ring pack). Bought em from Shanon's 7 years ago when they were a smokin deal. Next set will be flattop AutoTecs from Paul K, once Don @ DCI has the mid 80cc chamber round port heads available.

The Icon IC890 have a decent quech, DSS and Ross for a 400 you have to deck the block to get a good quench. The DSS and Ross from Butler also all went to reversible pistons with the intake sized relief on both valves. They loose some compression against an icon. The IC890 icon for a street and strip 400 is a very nice piston.

To me, even with a buget street build I would spend the money on the best short block build that you can and cheap out elsewhere. Meaning foged rods and the best bang for the buck piston. The short block is one place you cant easily go back and redo.
My researh has found Icon and Autotec hard to beat and way better then the old TRW as already stated.

These are the ones I meant by KB forged

Ported 7k3, zero decked

I agree!

Dennis

Just looked at a set of srp pistons, any reason they are designed with a 1.690 compression height?
Anyone using them,how much was taken off the block to get a zero deck?

I don't think the SpeedPro's are full floating. So also added would be the machine shop cost to put them on the rods.

No love for the KB hypereutectic pistons? Aside from the needed larger gap on upper ring, which may be missed during assembly how bad can they be in a street engine?
Anyone used and broke them and why did they brake?
I have a set in my 421 with 4.16" bore, so far so good.

Set up properly the KB Hypereutectic pistons work well. They run quiet, help the rings do their job due to the tight running clearance and keep heat in the combustion area..... Their down fall is they're detention intolerant and when they break you have catastrophic results.

I'm not an engine builder, but I built my current engine using the Speed Pro pistons. I consider the pressed in pin a major disadvantage. Just another thing a machine shop can mess up (they did mess up one of mine that had to be replaced).

The weight and rings were not a big factor for my street engine, but the hassle of worrying about a shop over heating the rods, or tweaking the pistons when pressing the pins isn't something I'd want to do again.

I bought a blown up 455 a couple years back. Had KB Hypereutectic pistons in it. Not sure of the whole story, that engine was a disaster, but to the point: top ring touched itself and popped off a chunk of the piston crown.

Happened to be a in a cylinder that already had a replacement sleeve. Cracked that sleeve. So now the block needs to be re-resleeved :/

Hardly the pistons fault if the mechanic is ignorant.

The guy did not follow KBs instructions.

I still remember being in the pits at Norwalk about 20 years ago and a guy pitted next to us "hit" his new 455 build with a shot of nitrous with disasterous results. He tore the engine down at the track since he was stuck there for the long weekend anyhow. Most of his new KB HT pistons were missing from the bores and piled up in the oil pan. They shattered like glass and left the rods and pins moving up and down in the bores void of any pistons on them.....NO THANKS!

I know that's an extreme scenario but it tells us that they have an elastic limit far below what you'd see from a decent forging, even the WAY too heavy TRW/Speed Pro forgings. Not a fan of those either because every set I've ran into ends up WAY to far down in the holes at TDC when I mocked them up required too much to be machined from the block to establish Zero Deck.

Anyhow, I've used Ross which are nice, and ICON, KB forgings. Since all my engines get forged rods and most will have the full floating option they fit the bill nicely. The modern alloys also allow for tight fitting compared to antiquated forgings from long ago. With a torque plate for final honing I set them at .002" here and have never had a single issue with that deal.

Even with all that said IF they made a nice flat top cast piston, even pressed pin I'd use them. Nearly all of my SBC builds get flat top cast pistons and they are fit really tight for minimal "rocking" in the bores, good ring seal and long life expectancy. The cast piston options for the 400's are absolutely pure bovine excrement and always have been. I still remember mocking up an engine I was hired to assemble decades ago using those pistons. They were WAY down in the holes at TDC and already taking over 15cc out of the squish area like using a dished piston. Team that up with a 4X or 6X-8 head in a 400 build and you'll have about as much compression as a Briggs and Stratton lawn mower engine, and left wondering why it doesn't idle or run for chit once placed in service......

It's not a bad choice, just be aware as Cliff mentions you'll have to shave a bit off the deck to get them at or near zero. I've used these pistons before in builds some 25+ years ago before we had all the nice choices we have now. Those engines are still together today, quiet as a mouse and running fine, but as mentioned, the blocks needed decked to get them up to the top.

That's not necessarily a bad thing as every single engine I've ever touched needs decked anyway simply because they are so far out of spec, and Pontiac is one of the worst with that deal. You'll find them lop sided many times having to take as much as .007-.0010 more material off one end compared to the other end to get them square. So it's not like it's the end of the world using the speed pros anyway. Probably my bigger gripe with them is the large tractor ring package they come with. That's pretty antiquated these days as smaller ring packs have proven themselves to be a better deal all around with better sealing abilities, lighter weight, less drag, all equals more HP.

The price differences aren't really enough to even consider a decision maker in my opinion anyway, I'd just go with a nice modern forged full floating deal with a small ring package and call it a day.

A factory cast piston will run a tad longer than a hyper when tuning factors go off the rails since they are not as brittle.

This does not mean I would not use them in a build, but I would not use them in a short block that would be approaching or topping 400 Hp unless my wide open throttle tuning skills where very good.

To me Hyper’s are not a material to hone your tuning skills on, especially so with todays pump fuels.

I would sooner run a common 5/64” ring Speed pro piston and stuff far lighter wrist pins in them.

Also I need to mention because I forgot that total seal makes a shim to go from 5/64” rings to 1.2nm.
This changes things in a big way, and they claim a 12 Hp gain.
Taken with a grain of salt let’s say a solid 8 Hp gain.

It’s a bit of a learning curve to heat a rod for pressed pins.
I learned on 5 junk rods before I got the hang of it, but I gotta say that if a shop leaves this task to the lowly shop Gofer then the odd’s of taking the needed temper out of steel rods goes way up!

The best way to do that job right every time is with a Thermal gun.

Wow!

Unfortunately for them a lot of folks don’t know how much the timing needs to be backed down even with just a 150 Hp shot of that stuff!
If you don’t have a programmable ing box then that’s not easily done .

That's why KB does NOT recommend nitrous shot for the hypers.
But racers are racers, they will ALWAYS run their stuff until they break, one way or another.
(This is the "Street" section BTW).

I had them in a build that was done in '82. I asked the machinist to do a zero deck. I found out he did not and was glad for that as the pistons were .040 down. Swapped heads to a 6X-4 to alleviate detonation. Resulted in a CR of 7.6. Engine still ran ok . Swapped pistons to the heavy SpeedPro which brought the CR up to 8.2. Still not great but the engine runs much better.

Agree 100%

When you build engines for a living you don't want your customers having an issue. I've personally run KB Hypereutectic pistons in my own build and was happy with them. They were in a 1971 HO that ran bottom twelves on motor and high tens with spray. Never had an issue. May not be as good of a story with a 9:5 build and the guy gets a tank of 87 octane that's marked 93. The piston might launch into orbit before the driver here's any pinging.

KB hurt themselves when they first introduced those pistons. All their advertising was spent promoting the product and talking about how great they were. Little was ever mentioned about the increase in top ring gap needed and they never talked about them being octane intolerant. Folks were ripping the tops off those pistons more often than not due to using a standard ring gap. It took quite a while before they highlighted the ring gap issue and had advertisements make note of it also.

Thanks Kenth. Seems like every post goes to drag racing/max effort somehow somewhere, that’s why I posted the build of a 9ish:1 street cruiser. Sounds like KBs might be an option I’ve never considered. My builder is well versed on Pontiacs so I’d just have to reminds him about the clearance.
Do you know how much weight difference there is between the KBs and the Speed Pros?

Per the Speed Pro website: 589g/783g with pin

KB’s website does not list weights, from CNC motorsports website: 541g/704g with pin

https://www.drivparts.com/part-detai...rand_code=BHVW

https://uempistons.com/product/647/K...TM.030?sflag=0

My personal recommendation is to go with the speed pros. They were the go to for many years, I haven’t seen many examples on here of them failing. Multiple local machine shops have said the KB Hypers have issues even when you open the rings up to their specs. The shops said you wanna go REALLY big on the gaps

Of note: KB’s website says they sit 0.025” under the deck. Quite a bit of deck to trim off

In my opinion, it is hard to compare a hyper piston with a forged. But just for info here, I have a set of the KB 2618 forged pistons (+.030 428 piston with a dish) and they weigh 714.4 grams with pin and 567 grams without the pin.

I have used ICONs and Autotechs from PK. My understanding is the Autotechs are all 4032's while the Racetech's are 2618. No issues with either ICON or Autotech. Both were accurately machined and my current Autotech's are doing just fine. Thanks PK!