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View Full Version : Piston quexchun,Forged or Hyper-u



RON S.
10-04-2005, 06:54 AM
I got a '94 that is in the process of a engine re-build.

After pulling a the heads for what seemed a routine blown head gasket,I saw that one of the pistons had a hole burn't thru it.

So,it is off to the machine shop for a thorough rebuild.
The question for those who've BTDT.is which type of pistons to use.

Hyper-u's are available I know.FedMog#H675CP + rings E4714.
But,they are pretty much the same as the stock ones,and I got one melted.

Are forged pistons the better choice for longetivity?I'm not really concerned about price.What I don't want is to have to go thru another re-build 2,3,or 4 years down the road.

Also,what brand names manufacture forged pistons for the SC,ie.Jahns,KB,TRW,Wiseco or any others?

And,lastly does anyone have any part#'s for any manufacturers?Just to save on all the phone calls asking.


Ron

XR7 Dave
10-04-2005, 08:46 AM
A melted piston is the result of an extreme lean condition that must be fixed. Forged pistons melt too as you know.

That being said, if you plan to run high boost or nitrous forged pistons are worthwhile. If not there maybe isn't much point. There can be many things that go wrong on these motors and pistons are only one of them.

A ceramic coating on the tops might be a big help if you are worried about melting one.

RON S.
10-04-2005, 09:07 AM
Dave,

What I'm intending here is a good rebuild,on the car.

I'm not really interested in drag racing or abusing the car.

I have had some expierience w/coatings.I used a place called Poly-Din performance several years back on 4cyl. 2.3l oval track mustang.

The Stuff does work to lower the friction level as well as oil & coolant temps.

I would just like the option of a forged piston,if any are readily available,and the who & where I can go to get them.

One extra note.The head gasket was leaking in the same cyl.as the burn't piston.When I had taken the head bolts loose,2 HB's on that cylinder were definately not torked to spec.

Ron

XR7 Dave
10-04-2005, 10:20 AM
Head bolts may have been insufficiently torqued, or it could have been that detonation stretched the bolts and they came loose. Either could have happened.

Anyway that doesn't matter now. There are several options for forged pistons. No one actually stocks a part number for SC's, but Ross, Diamond, Wiseco and maybe others will make a custom piston for you. The only thing is that in each case you have to specify exactly what you need and pay custom piston prices for them.

We recently worked out a deal with Wiseco to have all the data available to make things easier and a little cheaper. Shop around, and if you want email me about pricing and specific details on the Wiseco piston option.

[email protected]

BKB
10-04-2005, 02:44 PM
I like sticking with the stock type hyper pistons whenever possible. Because of there great expansion qualitys you can run a tighter piston wall clearance. This makes for a very quiet, emission frendly motor. Also the price is right. I would spend the money in other places like head studs, hone with torque plate, maybe new flow matched injectors. You need to find what caused this problem, pistons dont just melt for the hell of it.

sizemoremk
10-04-2005, 04:22 PM
Since it hasn't been mentioned in this thread, yuo may also want to be aware that if you go with the forge pistons, you can use 351W rods, I have Ross pistons and Cat H-beam rods going in the motor I'm building now. Dave Neibert of this site uses this combo also, and runs higher boost and 100ish shot of nitrous; he runs 11.6 ETs... So it is a proven combo. I'm sure others are using it too... I know you said this was not your goal, but just thought I'd make you aware. Custom pistons can be made for whatever rods you want obvuously, but if you are interested in this combo let us know and we'll get you the Ross job card number. This piston is for stock compression ratio with the 351w rods.

That said, XR7Dave has run 20 lbs of boost on a stock bottom end, so for stockish HP levels, the hypers are regarded as being sufficient as Dave said...
If I did not plan on using the juice, I would have used the hypers.

There is a very good thread in the members only performance section on this very topic, so you may want to think about being a paid member to see this, and several other very technical threads.

These two alone are worth the memership:

http://www.sccoa.com/forums/showthread.php?t=55471

http://www.sccoa.com/forums/showthread.php?t=54274


And as Mr. Dalke says, there is most likely some other reason you burned through the piston, so I would start looking for that problem ASAP; do you have any mods done to the car?

Also on the coatings, have you ever used these coatings on bearings???

I bought some coating products from www.techlinecoatings.com, and my machine shop scarred me into not coating the bearings... They sell the "ceramic-type" coatings for pistons tops and CCs, which I am goin to use; but I also bought their dry film lubricant for skirts and bearings, but the machine shop said they've had an experience with such a coating and it all flaked off and ruined a 302 in short order.... Have you any experience with such coatings?

68COUGAR
10-04-2005, 07:45 PM
I like.....stock type hyper pistons.....Because of there great expansion qualitys you can run a tighter piston wall clearance.....makes for a very quiet, emission frendly motor.
By GREAT EXPANSION do you mean that they expand a Lot, or do you mean that they expand a Little?

I know that todays forged pistons run MUCH tighter piston to wall tolerances that the old forged units from the '60's & 70's.

Can you explain why a tighter piston to wall tolerance makes less emissions?

68COUGAR

Mike8675309
10-04-2005, 09:22 PM
hyper pistons expand less allowing tighter piston wall clearances reducing piston slap when the motor is cold. Due to the high silicone content of hyper pistons they have noticably less wear on the cylinders than a typical forged piston. Such pistons are also better able to transfer heat evenly in the mass.

Yet still, for a motor intended to push over 400rwhp, or run nitros, i'd go forged. Hyper pistons are comparatively brittle compared to forged. So a lean cylinder with a hyper piston is more likely to have a catastrophic failure that creates more damage, then a forged piston. Nitros, or higher boost is going to dramatically increase the chance for some failure in the systems to create a lean condition.

If it's under 400rwhp.... go stock replacement unless you want to build for an uncertain future (i.e. you may be wanting something more later). The stock piston design is pretty decent. If anything is questionable it's the rods, but good bearings and good fasteners will help keep them together.

68COUGAR
10-05-2005, 11:42 AM
My personal theory is: I already now how to break parts. When I DO break them, I replace it with something stronger. It's more exensive initially, but at least I only have buy parts ONCE.

However, for a near stock SC, OEM parts are cheaper & will probably last the rest of the cars life.

68COUGAR

RON S.
10-05-2005, 01:51 PM
My personal theory is: I already now how to break parts. When I DO break them, I replace it with something stronger. It's more exensive initially, but at least I only have buy parts ONCE.

However, for a near stock SC, OEM parts are cheaper & will probably last the rest of the cars life.

68COUGAR

My thoughts are,to build up the bottom end,as it needs a re-do anyway.Then if at a later date I wanna add some bolt-on go fast goodies,I won't need to worry about the bottom ends strength holding up.


Ron

Mike8675309
10-05-2005, 10:49 PM
They key thing I used to keep in mind was that it was very difficult and expensive to go over 400rwhp. But with the advent of the Autorotor, snow system, and latest Magnum Powers higher efficiency blower, not to mention front mount intercoolers, making big power with bolt on's is becomeing very possible.

Thus my most recent change to looking for Forged pistons to support OVER 400 rwhp. Prior to that decision I would have lived with stock hyper pistons without a doubt. But at over 400rwhp, i'm more afraid of the rods than anything. And for decent priced new rods, that means new forged pistons.