Piston question, more info requested

[Bryan Tuvell 33ZX]

I am no motor head, what is the difference between Cast Aluminum Hypereutectic Pistons and Forged like my 502?
What is better???

Trying to get smart for a reason...
Thanks,
Bryan

[Woodsy]

Brian,

The major differences are weight and tolerances as they relate to to thermal expansion .While every motor builder has a preference, the real difference in the weight of the piston. The less piston weight, the less stress on the connecting rods and crankshaft. Usually, a lighter piston can equate into a higher piston speed, however, our marine engines are limited in rpm anyway.
Check this link out..

http://www.kb-silvolite.com/page11.htm

Hope this helps!!

Woodsy :D :D

[turbo2256]

Forged are stronger

[CDMA]

Blower, turbo or NOS forged is a must.

For anything else both have their merits. I looked into the Hypereutectic pistons for my 350 and almost went that route. The advantages are primarily, as Woodsy says, in the weight. The other aspect of them that can be beneficial is they expand less then forgings therefore can be fitted tighter in the cylinder. This leads to a quieter engine that tends to seal ever so slightly better. Basically hypereutectic pistons, in my mind, have severely narrowed the gap between traditional castings and forgings. Had I not realized due to my unpredictable nature anything was possible in the future ( blower , nos) I would have seriously thought about going the cast route.

Just my $.02

Chris

[RickSE]

Hypereutectic pistons also hold more heat in the piston tops, more than any other type. KB claims this aids in combustion.

A lot of people have been complaining lately about auto manufactures who use Hypereutectic pistons. The hyper pistons have a tendency to piston slap on start up until they get some heat in them, expanding enough to fit the cylinder bores correctly. A lot of people can’t understand why their new engine makes noise on startup and complain that the engine is defective. I guess these people never owned a 427 Corvette or LS6 Chevelle with forged pistons. Ford went so far as to coat all their piston skirts with Teflon to avoid customer complaints. GM has coated the pistons in the Corvette engines but seems to be conservatively evaluating coating the pistons in their truck/marine engines.

[turbo2256]

Without painting the back side of the piston top it can raise your oil temps though if it holds more heat....I have seen were the oil is fried on the back side of the piston

[MAXCAT]

Cast pistons are stronger than forgings, but that makes them brittle. That is why if they see any major detonation you wind up with a piston in pieces in the bottom of the oil pan. For this reason they are not as forgiving a a forged piston when it comes to blower motors. Forged pistons are less brittle than casting and can take more abuse from abnormal combustion events.

[Bryan Tuvell 33ZX]

Thanks so much guys, I REALLY appreciate the education you guys bring to the board. I am looking at the new Scorpion engines and the new 6.2 MX MPI Closed Cooling motors (320HP) and this is one area I am clueless, I have always read forged was the way to go and now on the new stock motors they are a new material.

I am VERY close on a deal but still think I CAN DO BETTER. Don't want to spill the beans on what I THINK I know and what I am going to do.
Hell I sure hope the bank likes me! I will be going from 6% to 6.99% now....

Insurance on an upgrade to twins 6.2's with State Farm (500 deductible) was $540 to $800 on 640HP, haven't ask about Scorpions yet.

Any input on the SCORPION motors vice 6.2's (I know more money)? Good bad or other???
Bryan

[Forrest]

Why can't I find insurance that cheap? frown

[RickSE]

I'd go with the 6.2L's. They're pretty close in power to the Scorpions and typically a lot less money. The only exception would be if you could get a good deal on a leftover Scorpion boat.

You probably already know this but the 6.2L is basically the same engine as the Scorpion. The Scorpion may have a different intake/fuel system and probably a different cam.

Merc. claims the 6.2L & Scorpion both have:
Forged-Steel Crank (Lunati)
Roller Cam
Hypereutectic Pistons
MEFI3 Fuel injection
Water Cooled Fuel System
70 Amp Alternator

Good Luck Bryan. What ever happened to Bob? Did he buy a boat? My dad backed out of giving him a quote (which I didn't agree with) and I never heard from him again.

[harbormaster]

Forrest, it because "they" only have a 3 month boating season... :D

[Rootsy]

yeah just 3 months of bad sledding is all... :D

[Bryan Tuvell 33ZX]

3 Month boating season???
We boat from March to November!
We are about to make the move but I have one issue with Donzi and emailed the top brass (Lee and Nick) tonight and will hope for a response so I can make a good decision.

For motors we want the upgraded 6.2 MX MPI Closed Cooling with the 555 ECM etc.
We are close on price but I received a lecture from the real mastermind of this house on a couple Donzi issues and to consider Cigarette and Active Thunder.
So who knows what a woman will tell her boat loving husband to do....
Like I always say, "I just ride the bus!"

I will keep you guys posted. Who knows what we will have at AOTH III, maybe the same boat!!!
OR???? :D

FOR RICK S. DMAN2 is alive and well and about to own his 3rd Donzi I think... But then again, maybe not!!!
Bryan

[BigGrizzly]

Bryan,Hypereutectic pistons are a cheap decent piston, not for blower use. They are also known as claimer pistons,because of the use in claiming races. Forgings are by far the strongest pistons. Cast pistons are used for production engines because of the mass production capabilities and inexpensesive cost. In any case I am not a fan of the Hyper pistons because of the expansion rates and the fact that ring end gaps need to be larger. I won't use them in anything I build. Yet others have good luck with them but they are realtivly low hp per cubic inch motors.

Randy

[Formula Jr]

I was driving to Portland one day, where I get to hear The Motor Man on the radio - a treat for me. Well the discussion this day was on the Hyper or Forged Pistons. Well, The Motor Man was in the forged camp on this one for American Made Motors. High Torgue, low rpm motors. And he went right into the the whole torque/HP controversy. Said you could get 400 HP out of a weed eater for three seconds, if ya tried hard enough. :D

[Ranman]

Grizz, I will not claim to be an expert on this subject by any means, but I'm a bit surprized by your response since I've seen you and Lil Grizz talk about Mustangs in the past. It seems that I've read in many issues of Super Ford, 5.0 Mustang etc... that Hyper pistons work well in blower motors. I'm not saying that they are better than forged in the same application, or that they are the best for a marine application, but there are many a 5.0 Mustang out there running good HP nummbers with blowers that are very reliable.

[Forrest]

The link that Woodsy provided above is good straight-forward reading on Forged vs Hyperutectic[/URL] from a company that makes both. Also, click here (http://www.kb-silvolite.com/1toc.htm) for all whole bunch of info on hyperutectic pistons in general. I run T-6 heat treated hyperutectic pistons (KB) in all of my marine engines except for the 383 in my X-18. That 383 has the cheaper T-5 heat-treated (Silvolite Claimer (http://www.kb-silvolite.com/Claimer/Intro%20page.html)) hyperutectic pistons. They are quiet when the engine hot or cold since they fit in a very tight bore as compaired to the relitively loose bore in which a forged piston must fit. Proper ring gap is a must on these hyperutectic pistons otherwise you will have problems.

Unless you are into really big blower power, I don't think forged pistons are as necessary as the were in the past. Also, I sure wouldn't try to second guess why Merc decided to use hyperutectic over forged pistons in their expensive 6.2 engine. I bet you that they save $10 to $15 per hole by using hypertuectic pistons, but I'm also sure that Merc doesn't figure on doing very many warranty claims for piston failures in that engine either. That repair alone would indeed cost them much more than the $80 to $120 that they saved by using hyperutectic over forged pistons.

[Gearhead99]

Use the Forged pistons. They can handle the long WOT runs and some detonation much better then cast.

[Lil Grizz]

the 5.0 went to hyper pistons in late 92-93. before then they used cast pistons. The people you hear about running those big numbers with those pistons in their mustangs are only doing so because they are running the stock bottom end. The 5.0 is capable of holding together using the stock rotating assembly with a proper tune to around 450hp. Understand this is sketchy because some hold together while others do not. when these engines let go they do so in a very bad way(pistons, rods, crank snap to pieces). Some last a long time under those power levels while others dont even survive the break in period. Everyone I have ever discussed this issue with insisted on throwing away the stock pistons if you intend on making some real power. On my supercharged 98 DOHC Cobra the stock rods and pistons are the weak link but i still use them simply because the cost and effort to replace the internals of the shoehorned engine are the same as just buying a whole new long block equiped with the top of the line parts. I am just waiting till the engine pops to do any work to it. Same thing with my boat, im pretty much treating the 7.4 mpi as the disposable piece it is. Replacing all its weak links add up to building a totally new engine. If I had known ahead of time just low end the parts in a 7.4 are I might not have bought it. But I have it now and I am going out of my way to work with what little options I have for it.

[Ranman]

Lil Grizz, I pretty much concur with what you have said. Up here in Detroit, the 5.0 Mustang thing is huge. I used to run a sprayed '95 and have friends with built and blown Mustangs using the stock short block. I also have buddies that run all the way up to 1300 - 1400 HP turning mid 7 sec passes (obviously using dry sump race engines). Anyway, The built and blown friends both run in the 375 - 400 hp range and both have had turn key cars using the stock lowers. It was my understanding that the stock 5.0 short block was good for around 500hp which is pretty much what you have said. Beyond the 500hp even the block is weak and an A4 would be in order.

In any event, my point is that generally speaking, it doesn't matter too much how you make the power (blower, nitrous, or a good breathing motor) the stock 5.0's are good for over 400hp even with hyper pistons. Since I've seen sooo many turn key, reliable blown Mustangs running the stock short block, I think it is somewhat inaccurate to say hyper pistons are "not for blower use". Are they the best choice? Maybe not. Would you use them when building a brand new blower motor? Typically no. Can you run a blower with hyper pistons? Absolutly. Randy

[turbo2256]

Little Griz.
Another weak link in the 4.6 is the mains in the aluminum block allow the crank to walk. As for the 7.4 if buying a boat new for the cost of the upgrade to the magnum engine 8 to 10 k one can upgrade the 7.4 to a more powerful engine than the 500HP with good oval port heads and have bucks left over.