Lighter wallet. I don't know if that will be an advantage, or not.

 

Not really needed. The piston geometry is (much) more important: compression height, valve pocket size, etc.

That being said, stock (or oversize) 5.0 forged replacements would be a safe choice for such an engine.

 

I went forged just to future-proof things. I haven’t added boost or nitrous yet, but it’s fun to know it’s an option.

 

I will give you some information and let you decide. I used to work at MAHLE. My job was testing the hardness and thickness of the anodized layer of pistons. I would cut samples from all types of pistons, from every manufacturer. I would make two parallel cuts with a disc cutter about a centimeter apart and two centimeters deep. I would then take a scewdriver and pop the sample out of the piston just to save time. I did this same procedure on all types even the Ford hypereutectic pistons. But when i would try this with the forged pistons the screwdriver would break before the sample would break out. Don't know about you but thats enough evidence for me never to buy anything else.

 

But what did that tell you about the hardness and thickness of the anodizing?

Or other characteristics that make a good piston?

Where you analyzing the materials or just tasked with sectioning them?

 

Forged pistons will give you a foundation to build whatever you want down the road. As BlakeTX stated "future proof". Some Forged pistons, like the DSS E series. are about the same price as the KB Hypers.

 

I had to laugh with Barts answer, because it is so correct, lighter wallet no appreciable gains. Standard rebuild for personal driving pleasure. Billions are spent in the after market on RACING parts, quite the scam. Like running racing oil, spark plugs, ignition systems etc. There is no reason to spend 500.00 to 1000.00 on pistons when a 200.00 set will give you many years of driving reliability. Choice is yours- Best of luck to you on your rebuild.

 

While I understand the greater point here, in my case, forged pistons were barely more expensive than stock. Maybe that pricing has changed drastically in the last few years, but the price was so close at the time, it was an absolute no-brainer to go forged.

 

For that matter, why run hypers?

 

For all the effort and expense of building a motor, good forged pistons, in comparison are a small cost.

Even if the motor isn't to be used for racing, forged pistons will buy you some "forgiveness" for mistakes like too much timing, running lean, bad fuel, etc. Needed? No. A good idea? Yes.

 

Forged pistons are not 'stronger' than hyper pistons. In terms of how much force they can handle before they are damaged, forged and hypereutectic pistons come out about the same. But forged pistons are more ductile, and less brittle.

Any kind of incident that exceeds the strength of a hyper piston will typically shatter it. With a forged piston, it will tend to deform first before catastrophic failure - and that means you have a chance to replace one piston instead of the whole engine, if you catch it. I've seen a forged piston on engine rebuild that had stamps of a wing nut all over its face before the nut managed to fly out the exhaust valve. The piston didn't care. Detonation will flat out explode a hyper piston on a hot build making good power.

If you're not making much power, then it probably doesn't matter.

 

Forged pistons are not 'stronger' than hyper pistons. In terms of how much force they can handle before they are damaged, forged and hypereutectic pistons come out about the same. But forged pistons are more ductile, and less brittle.

Any kind of incident that exceeds the strength of a hyper piston will typically shatter it. With a forged piston, it will tend to deform first before catastrophic failure - and that means you have a chance to replace one piston instead of the whole engine, if you catch it. I've seen a forged piston on engine rebuild that had stamps of a wing nut all over its face before the nut managed to fly out the exhaust valve. The piston didn't care. Detonation will flat out explode a hyper piston on a hot build making good power.

If you're not making much power, then it probably doesn't matter.

I second this ! I have a set of trickflow tw forged pistons that one piston was melted in the center of the valve reliefs from nitrous, ( got a hot spot, but was no hole in piston. It must have cooled down before a hole formed). Engine still ran strong with that deformation in piston, never knew it was there until it later got tore down. I firmly believe a hyper piston would never survive that, let alone continue performing under abuse !

 

I've been running forged pistons in my rebuilds since the early 80's, starting with the TRW's ordered through PAW! I had a set of Sealed Power forged pistons when the intake valve head broke off. The cylinder walls were destroyed, head damaged beyond repair, but the piston didn't shatter. I still have it and you can see where the broken stem of the valve gouged into the dome of the piston, and also how the whole thing bounced around until the engine shut down. The engine was running about 2000 rpm at the time (break in).

 

pAW, sure miss their annual catalogs, 3 to 4 inches thick.
And a 2 hour drive up to the store off Desoto in LA was always rewarded with a new funny car or dragster hanging from the ceiling. And all the eye candy, built motors on stands nest to the customer service lines!!!

 

Not needed. Lots of those blocks break with stock pistons.

 

thank you all for the replies. follow up question. What compression am i looking for on this build? 10.1?

 

That decision will be based mostly on your choice of camshafts. If you have lots of overlap then you will need higher static compression.

 

I have to agree the hype outweighs the facts. Assuming equal costs; unless you will (ever) exceed the rpm safe for HE pistons, they do run tighter and quieter, and were the most common choice of factory turbo engines. I have no issues and in-fact my preference is to run hyper (HE) pistons for their benefits, including in my boosted projects, but (and that's a big BUT), I will never let it wander into a poor tune or poor fuel, or build it to assume I will drop a part into it. You'll break your rings before you break the piston. Still trash. Never had a random failure, by now never expect to, and don't know anyone that had a performance-induced failure where it wouldn't have destroyed any piston type.

BTW - remember the old factory TV ads for detonation as "the sound of economy"?

 

in-fact my preference is to run hyper (HE) pistons for their benefits, including in my boosted projects, but (and that's a big BUT), I will never let it wander into a poor tune or poor fuel

I picked up a Procharger blower long ago, but never built a low compression forged short block so it sits on the shelf. I know people are boosting hyper piston motors (i.e. sloppy mechanics LS turbo builds). The peace of mind is in the tune, but how? Also, what percentage of power do you give up with lazy timing & lower boost?

 

Forged pistons a necessity for some builds...those that require extra resistance to detonation(note: higher resistance does not mean they are detonation proof...and even if they were other engine components are not) from things like boost, nitrous, or high compression. If you don't require forged pistons do not get them. The downside to forged pistons is that they require more piston-to-wall clearance...this means more piston slap and an engine that has higher wear than more conventional pistons. The are a necessary evil...they are not a goal in and of themselves.

 

The downside to forged pistons is that they require more piston-to-wall clearance...this means more piston slap and an engine that has higher wear than more conventional pistons. The are a necessary evil...they are not a goal in and of themselves.

You're correct that forged piston need more clearance than a cast piston due to thermal expansion. Forged piston do not lead to significant wear issues. If they did, OE's would not use them in some new cars.

From a tech contributor on a Corvette forum,



lars , 02-20-2020 12:49 AM
Tech Contributor
An aluminum piston doesn't cause an iron bore to wear... If the forged aluminum piston was rubbing and rocking that hard on the cylinder wall, the piston itself would wear out - not the iron cylinder wall.

The piston has no effect on cylinder wear. The wear on the cylinder comes from the rings dragging up and down the wall - not the piston. A block with forged pistons will last just as long as a block with cast pistons. If a little piston slop caused the block to wear out, then diesel engines should wear out every 20,000 miles...

Lars

 

In the OP's build, not needed. But as others have pointed out, not a bad idea if he decides to get into the horsepower game later on and do something like supercharging the engine (i.e nitrous, turbo, blower). I like to build my shortblocks more stout than I need them in case I decide to do something for more power out of my engine later . I'm glad I did this when I built the 351C in my first Mustang. I had put forged piston in it even though it was a low compression 350hp street engine. When I decided it would make a good candidate for nitrous, I knew my bottom end could handle being on the bottle.

 

Still not a good idea. If you ended up not putting nitrous on the car all you would have done is reduce longevity for no reason. Its far better to make a plan and stick to it all the way through. If you do make a major change like that later, you can always build a short block on the side and sell your original when you swap it out.

 

All this piston talk reminds me of dropping a couple valves.
Completely my fault but man does a Cleveland sound sweet going north of 6.5k rpm.
Till it doesn't I suppose.
This was the largest piece left of one of them. The other just had a valve embedded in it.

 

All this piston talk reminds me of dropping a couple valves.
Completely my fault but man does a Cleveland sound sweet going north of 6.5k rpm.
Till it doesn't I suppose.
This was the largest piece left of one of them. The other just had a valve embedded in it.

View attachment 855596

Ouch! That brings back bad memories from long ago.

 

As far as forged pistons needing larger P2W clearance, have a look at this. It's not nearly so bad for some alloys.

2618 Vs. 4032 Piston Material Differences | JE Pistons

Before a single machining operation is performed, the perfect aluminum alloy must be selected. 2618 and 4032, the two most prolific piston materials, have a

auto.jepistons.com

 

Mahle uses 4032 alloy in an awful lot of their OEM offerings for major manufacturers. When cold, hypers do fit tighter than forged pistons, but the design of modern skirts ameliorates any significant issues with piston slap. Once warm, they should be at the same clearances anyway. There's no issue with wear. The heavy TRW forged pistons used in stock 5.0 HO engines never had problems, and neither do modern high-quality forged units.

The ones I got were about 50 grams lighter than the best hypereutectic pistons I could find, and they were only $100 more in price for the set. Now prices have gone up a lot since then, but I bet the percentage of cost hasn't.

Lighter pistons and crank will not give you more horsepower, or increase your top speed. But they will most definitely improve reliability, and also improve the engine's ability to accelerate. At steady state or slow acceleration, there's no difference - but with rapid acceleration, it adds a lot of power. Less torque wasted accelerating parts of the rotating assembly.

If price is your only objective, then go with hyper, or even cast, if you're doing a stock build.

But if you plan to use a power adder, or make big power, the 'savings' you enjoy by going with hyper pistons is greatly outweighed by the potential problems later. Detonation when you're making 150 horsepower isn't a big deal. When you're putting down 400 horsepower, the first rattle you hear may well be your last.

I bought Mahle Powerpak pistons because of their light weight and excellent ring pack. I want this engine to last forever, and feel like these were a good choice to achieve that goal.

 

if you detonate forged pistons might hold up better and not crack

 

Ok. I’m more confused! Lol.
Can some one recommend a stock compression moderate priced forged piston?

Stock crank stock rods aftermarket cam with GT40p heads carbureted

 

Ok. I’m more confused! Lol.
Can some one recommend a stock compression moderate priced forged piston?

Stock crank stock rods aftermarket cam with GT40p heads carbureted

Speed Pro L2482F

 

Here are the specs.

 

No advantage whatsoever. Running forged in a weekend cruiser would be laughable, especially in a fairly stock, light build like yours. Hypers are plenty.

 

I'll put it a different way—if you have a set of pistons laying around, any type, use 'em. I wouldn't spend more on-purpose for this application, even if power adders come later. Forged or not, det at high power will crack your rings first, so the piston type isn't the issue. Don't let it det. Spend your money on tuning, tune stability and quality fuel.

Each type has pros and cons. Use what will do the job, or what makes you feel good if you don't know any better. You can't build it well enough to survive everything, so know the issues and avoid them instead. It's like watching the movie where they are running down the train tracks to get away from the train, and you're yelling at the TV for them to just step to the side.

 

Oh god I don't know how many years ago I read this post were a guy asked how good are $87 cast pistons? It was about 20 years ago. Anyway the guy threw together a cheap 5.0 motor using a set of cheap cast aluminum pistons and then threw a turbo on with a lot of boost. The block split in half and the pistons were perfect. So there you go. Strictly my thoughts as I'm not a engine builder. One of the big issues with cheap pistons I gather is that they juggle pin height to compensate for additional compression with the larger bore. The pin is located higher to lut the piston farther below deck height which results in poor quench. Possibly big valve reliefs or dish in addition.

So when the builder is building the engine, boring and honing for the most part is going to be the same between a cheap piston and a decent quality piston. In the grand scheme of things if a cheap set of pistons is $100 and a good set with anti friction coating and thin, low tention rings witha good deck height and so on is a couple hundred more, what's that in relation to the whole cost of the motor?

 

One of the big issues with cheap pistons I gather is that they juggle pin height to compensate for additional compression with the larger bore. The pin is located higher to lut the piston farther below deck height which results in poor quench. Possibly big valve reliefs or dish in addition.

True, the standard rebuilder pistons are often like that, with a compression height of 1.585 instead of 1.600. Others like the Sealed Power 273 Hypers have enormous valve pockets, also leading to compression loss.

 

The most important reason to run forged pistons is when your buddies are standing around the engine bay starring at your pretty new motor and one inevitably ask's "does it have forged pistons?", you can reply "yep" I'll never build another motor without using the Mahle power pack pistons with the tiny skirt and rings. The motor revs so fast!