ViribusUnits

How important are forged pistons to supercharged cars?

If you use a car, with say 15 pis of boost, and have it riged so there's no detonation, would cast postions be OK? Not that I'm trying to do so to my car, but...

I know forged pistions are stronger, and I even know why, the whole grain size thing. I just kinda wish I knew how much stronger. I'm tryin to get a hanndle on the whole issue.

Thanks.

Oh, btw, any one tryed 928developments.com's forged coated pistions? If that works, that could be cool. I just can't figure out the name of the coating. They're realy careful not to say it on their web site, but I haven't looked too hard yet eighter.

Thanks.

BrianG

Even cars with moderately high static compression ratios are using hypereutectic pistons now. That's a middle-step between cast and forged.

Any factor blown engine that I know of has forged pistons. Cast pistons simply don't cut the heat of a high performance environment.

In the old days, there was an issue of piston expansion as they came up to operating temperatures, so they had to be installed loose, and that made them noisy on startup...... something not appreciated in your mom's grocery-getter. I am given to understand that this has been sorted out.

Danno

The forged pistons will still expand more than the cast one. Piston-manufacturers specify larger clearance ranges for these pistons. However, this is assuming they're going into a cast-iron block.

An Alusil block will expand more than an iron block, making it OK to have narrow-clearances with forged pistons in these engines.

I saw a tidbit somewhere that Porsche used forged ALUSIL pistons in their boosted cars.. but I'm not sure where I picked that up. Gotta do so more research....

BTW, Andial just got in a batch of 104mm Mahle pistons with 8.0:1 compression for turbocharging...

ViribusUnits

Random question.

Anyone heard of a forged 96mm pistion for a Alusil block?

Thanks for the info so far.

twinturbo928

If you have the car dialed in, you can easily run sub 10 psi of boost on the stock lower end. I know, because I did this for MANY years on the Bastard.

As for forged pistons, well I would say go with them if you plan on going over 10 psig on the boost.

If i was in your shoes, I would have the block Nikasil plated and then go with a JE. Mahle has a facility here in the states, but customer service sucks. You would likely wait for months to get anything out of them.

I would not mess with any coated pistons on the old alusil, as most are unproven this far. I looked at the Developments pistons, but there was no time on them yet and it was not a risk I wanted to take. Those were also Wiseco pistons and I wanted a JE

RE on the clearances, the factory shark runs about 0.0016" between the pistons and the bore. My new JEs on the Nikasil will run about 0.00025", or about 8 to 9 tenths larger because of the turbocharging and the different thermal expansion. This was something I made certain was as close as possible but also as large as possible in the event of piston crown expansion under boost.

BWM has successfully given the Nikasil process a bad name, but I am pretty certain this was a result of a flaw in the process they used. Nikasil was used for MANY years on 911s and is still used to this day in the 911 twin turbo, GT2 and GT3. It is also used in the new Carrera GT V-10. If Porsche trusts it for their flagship street cars, no reason it won't work on the old alusil block.

Sleeving is going backwards in terms of technology. There you would have to run nearly 0.004" of clearance, making piston and ring life suffer.

If you are seriously considering boosting up that high, go with a good forged piston and then have your block Nikasil plated.

Contact me if you want to discuss the options. I'll be assembling my engine in the next week or so after the parts are balanced.

Blosk and pistons are waiting at home, but I am stuck in Chicago at a trade show. UGH! It is time to play!!!

ViribusUnits

The thing that intersted me about the developments pistion is the web site said that it had been in use for Mercadzes Bens for the last 5 years or so on Ausil type blocks, w/o problems.

My engineering class tells me that network polymers might just be able to do what we want them do. Network polymers like bakelite are typicaly realy good at dealing with high tempetures, and can have good wear propertys. This lends credibility to the 928 developments web sites claim.

If I can, I'd like to stay with a Alusil block, simply because I think it's an exelent feature of the 928. It's nearly wear proof! Cool, much better than the cast iron I'm rather used to. I know, I know, Nikasil is suppost to be just as good, and when I drive the car, theres no way I'll know, but well, I'm realy sold on the Alusil. When it comes to it, and
I realy have to pick, if Nikasil is the only reasonable way to do it, so be it.

The problem that I have is 928development.com is not very forth comeing about the process, who they intend to use, and what exactly they intend to do to the piston. I haven't call 'em yet, but if I was them, I'd have it pretty blazen on the web site.

I know I've said this before, but right now I'm just playing. I'm doing math, and checking what would do to be done to do X to my 928. How much money would it cost to do all of X, and how much time. Like most of us early 928ers, I'm looking for a bit more power to hanndle the new generation of Camaros, Mustanges, and yes, even imports. I figure I might as well plan when I have time and no money, rather than when I have money and no time!

In a maybe one to two years, the finances should be OK for me to buy a 924 Turbo, or a 944, or a Ford Ranger, or Chevy S 10, and then I can get my hands dirty with the 928. I'd like to stay with the 924 family, simply because it's so close to the 928, and I'm comfertable with my car. I have a feeling that real life will dictate a Ranger or F-150, or S 10 or Z.71 Oh well, we take what we can get, right?

Thanks.

twinturbo928

I looked into the polymeric coated piston like you are doing. No info other than "it works". I wanted to talk with the company, but that was not possible, because the name would not be realesed to me.

Call Devek and ask Marc about his experience with trying to coat a forged JE in an Alusil block. He no longer does these conversions because the coating process has had issues.

I know the boys in texas run some high boost on the S4 motors with the stock cast pistons.

I would just be cautious with it is all I am saying. Remember, you also have a higher compression than my car, and this invites more detonation. The 2 valve head arrangement is more prone to detonation than the 4 valve heads are.

As for the Alusil vs. Nikasil, well the Nikasil is a lot harder and will not score like the alusil will in the event of a problem...so I am told. It is so hard, the only way to cut it is with a diamond hone.

My pistons with Goetze (911) rings and wristpins were $1250.

Block Nikasil plating was $950 with delivery both ways to and from Wisconsin.

The good thing is I will have a like new bore with fresh rings, it should be a sweet setup when all is said and done. I'll be running a leak down on it before installation.

ViribusUnits

Very sweet.

Did you change your username recently? I seem to recall it being something diffrent.

I don't guess you tryed to deal through Mercades? If 928 development is so secretive that they won't talk, I might to to cut them out.

Thanks.

twinturbo928

Yes, it is typically under John, my first name. I am in Chicago on my laptop this week. Home tomorrow to pick up my normal identity!

When I asked for the coating manufacturer, the phone went silent and that is all I am sating on that topic.

I did not bother with MB. My block was scored anyway, so I repaired and upgraded it all in one step. the Nikasil is only 0.005" to 00.008" thick. You end up with a very hard, wear resistant surface with the ability to run really close wall clearances and you also get to keep that great heat transfer.

I saw sleeving as BAD and more bad...too risky and too many variables, some of the blocks have actuallly cracked in this configuration, plus you never have intimate contact, there is always some gap between the Aluminum and the iron.