SPI vs. Wiseco Pistons

[Modman]

I agree run whatever you want.. but a cast piston is in no way more "dimensionally stable" (stronger) than a forged piston. I am new to the 2 stroke game and cannot comment on the reliability of wiseco vs stock argument, but have been building high horsepower small/big block engines for years and it is universally accepted that forged components are stronger and more durable than cast. This does not only apply to pistons but also connecting rods, cranks and pretty much anything that can be forged versus cast. It has to do with the stresses of the manufacturing process that the inherent strength is created, in fact certain parts can be further strengthened by "shot peening" them, (a process of adding stress into the metal by compressive force). Manufacturers like ski-doo do not use these processes as they are more expensive and the extra strength is deemed unnecessary for the application. Like everyone is saying.. run whatever you want but in my opinion a cast component is inferior to a forged one in terms of strength and ductility.

You're confusing "stronger" with "dimensionally stable". They are not the same thing. All the points you mention above are correct in terms of making a "stronger" piston (shot peening, manufacturing, etc). However, dimensionally stable refers to the ability of the piston to expand and contract evenly and uniformely throughout its dome and skirt and supporting material. Strength in a metal also comes with its composition (more silicon content in cast pistons typically) which leads to a low thermal expansion coefficient which is exploited for pistons, the high hardness of the silicon particles is selected for wear resistance. Thermal expansion is reduced substantially by silicon and wear resistance is usually better in hypereutectic alloys in which the hard silicon particles are well distributed either by phosphorus nucleation or by powder metallurgy fabrication. Increasing silicon content increases strength at the expense of ductility.

A cast piston has additional support and material cast into the raw blank when it is poured, meaning that areas that are thin and prone to heating faster and expanding quicker (potential for seizure) will have additional material cast into them or will have supporting points/material/lattice to ensure that this area expands and contracts evenly with the rest of the piston (heating predictability). This does not make it "stronger". Casting does produce a brittle piston, no doubt.

A forged piston cannot have this supporting work as it is pressed through a die to form its shape. Forging is a limited in this regard. The die can only have so much detail as the ingot is literally pounded into shape by male ram into a female die. The forging process is not able to produce as intricate support details in the pistons as casting, just simply due to the process. This is what makes it less dimensionally stable. You are correct in that forging produces a "stronger" piston, the material is much denser once the forging process is completed.

This is completely supported by the fact that Wiseco's need more clearance than cast pistons. If they were as stable as cast, you could get away with less clearance (similar to stock pistons) as they would not expand as much as they do. Instead, they need more clearance because they expand more and are not as "dimensionally stable". So you have to decide if you want "stronger" pistons or ones that are more "dimensionally stable". This is the age old question.

Run what you want, just make sure you heat them if they are Wiseco's.

 

[Slamnek]

I have been told to run stock doo pistons or Rk tech duel ring in my Rev. I used the Rk tech, 1600km and they run perfect. I do run wiesco in my CR250 and my buddies use them as well with no problems. I think weisco's are a decent piston but from what i have heard, they don't last too long. Thats just what i have been told, not speaking from experiance.

 

[maxwell]

speaking from experience here....you cant kill them

 

[mxz sledhead]

This may sound a little cheesee In my old 92 wildcat 700 I got this sled use.
big mistake I land up tear down the motor and found out some was in it already i one crome cly one steel clyinder so to make work i put 1 cast piston
1 forged it work and it still working after 8yrs. I wouldn't recommend it but it got me out of pinch

 

[joee]

First thing is first. There is only one factory that all these pistons are manufactured from. I use spi pistons in everything i rebulid and i rebuild around 10-20 sleds a year. My experience with the wiesco pistons is you have to gap at least 1-2 thousands more then recomended on the rings otherwise you are wasting your time. The t-moly teflon spi pistons are the one's that i use, i have done high performance triples, twins, and one lungers all with these pistons. The biggest difference between the 2 is around $80 per piston. Always, i mean always have your cylinders honed for you need a cross hatch in order for the rings to season properly and no matter what always let your machine warm up no matter what type pf pistons are in it, or what type of machine you are running. 15 minutes is usually what i idle either my 07 summit 600 ho sdi and my 2010 nytro xtx.

 

[Deez Nuts]

First thing is first. There is only one factory that all these pistons are manufactured from. I use spi pistons in everything i rebulid and i rebuild around 10-20 sleds a year. My experience with the wiesco pistons is you have to gap at least 1-2 thousands more then recomended on the rings otherwise you are wasting your time. The t-moly teflon spi pistons are the one's that i use, i have done high performance triples, twins, and one lungers all with these pistons. The biggest difference between the 2 is around $80 per piston. Always, i mean always have your cylinders honed for you need a cross hatch in order for the rings to season properly and no matter what always let your machine warm up no matter what type pf pistons are in it, or what type of machine you are running. 15 minutes is usually what i idle either my 07 summit 600 ho sdi and my 2010 nytro xtx.

I know this is a few years old, but I'm about to rebuild my sled engine and was wondering what grit hone you would use on a Nikasil coated cylinder? The finer the girt of a ball hone, the more expensive....just trying to get an cost estimate to do the job.

 

[Bernoff]

This thread is a couple years old just wondering if opinions are the same on the different pistons or have changed? Welcome your thoughts there Guys...

 

[moyiesledhead]

I've been using SPI's for many years very successfully in everything but my M1000. That engine did not like SPI's. Had to use OEM. Tried Wiseco's a few times through the years with no success at all in Nikasil cylinders. Seemed to work OK with the old school steel cylinders back in the day though.

 

[Lund]

I've been using SPI's for many years very successfully in everything but my M1000. That engine did not like SPI's. Had to use OEM. Tried Wiseco's a few times through the years with no success at all in Nikasil cylinders. Seemed to work OK with the old school steel cylinders back in the day though.

You are 100% correct with your statement. But Wiesco are IMO is a better design piston. The only way to use Wiesco piston's and avoiding issues is you need to have the cylinders matched to the pistons. The expansion rate of wiesco skirting is such that improperly matched piston and cylinders will cause problems.
Knowing this i have always used Weisco and when i do i send my cylinders in to my supplier Mongoose Machine. They will match the cylinders by re plating the Nikasil to the proper specs.
Failing to do so and if a tight budget needs to be fallow or cash conscious, then the SPI is a better option. No need to re chrome then but the draw back is the performance and durability is just not as good....
I have used SPI on quick out the door repairs with no issues.