Tony

Ok..whats the deal with the "factory" skirt coating on the stock pistons. Is the ENTIRE piston covered...is it dipped?...anodized? What?

How is it done at the factory?

Its obviously the biggest hurdle in running after market pistons in our engines with the alusil bore and one of the biggest voodoo subjects about this motor it seems.

When does this coating wear off?

DOES IT??

How do you know it has? Because at some point it has to. BS if it doesn't.

i've got a set of 951 pistons and there are areas on the skirts that definitely have a "different" color ...sheen...to them than the rest of the piston and other parts of the skirt. Is that worn coating?

So.....we have a coating on the skirt of the piston that in some cars is well over 150K miles. shouldn't it have worn off by now?
Some "damage" occurred?

apparently the objective is to not have similar metals, or i should say surfaces, rubbing on the skirt...cylinder wall contact area...CORRECT
(this shows you how much i know about this "science")

With todays technology, IMHO, i think it BS that a coating cant be found readily available that will work. Think of the money involved for some piston manufactures like JE that could provide us and others in the same situation (951s..BMWs..Jags) with a piston that will work

This "proprietary" coating thing is bizarre as well. Ok, you get a batch of pistons made and send them of to BFE somewhere, where some guy pulls the "Special Only Works In A 928 Motor" coating off the shelf and treats the pistons. I don't think so.

I d love a set of custom forged pistons to fit my application that will work in the infamous Alusil bore.

I just don't get it.
I find it all very mysterious.
And honestly very frustrating.

Venting a bit...and mainly puzzled!!

Chris

Hmmmmm, sure getting a bunch of replies here. Go try the 944/951 boards they seem to have a lot more experience.

Chris

BC

Tony - When I spoke to JE, they said that thier pistons wouldn't need a coating in the alusil bore. Now I think that may be a strech, but yesm this voodoo crap is useless to both customers and companies alike.

What about some JE pistons with skirts costed by www.swaintech.com or same? I stopped my research on this as I have sleeving planned, which will let me run JE without any coating if I want.

Mark Anderson

As far as I know (which can be little) all pistons are fully plated with either tin or iron. We took apart many high mileage motors which looked to have no plating left on the skirts and no apparent problems.

John.

It is a tin coating that is hard to replicate becauase of regulations surrounding the hazards of the process.

I looked inthe the Swain Tech stuff but it was 0.002" thick and that is more than the clearance you would run, or at least equal. No guarantees here and it sounded like a big risk.

Just plate the bores...just about every form of racing out there is now using Nikasil or some variation for performance engines. Formula 1, NASCAR, new carrera GT, 993TT, GT2, GT3, Aircraft engines and many industiral engines are all running Nikasil over aluminum. Best heat transfer and wear properties you will find. Best part... it is 1/2 the cost of sleeves. I see no reason to sleeve unless you want a larger bore, then you are into big machining and more $$$ and the integrity of the block is less than what it was when new.

BC

You paid 1000 dollars, right? (plus you had to ship your block - that should be factored in) - Sleeving is done locally, within reason, where ever you are.

LA Sleeve, and Darton both will do sleeves for between 75 and 100 dollars a hole. The machinging is between 800 and 1000 dollars for a V-8 block by people who know "how to do it" and have done it before.

So for between 1600 and 2000, compared to your 1000, I get to use bigger pistons, a material that will withstand boost pressure quite a bit better then the original bore. The integrity of the block is NOT LESS then what it was new. If you are talking about the side to side movement of the bore towers, it is about the same, if not a bit stiffer. You can solve this with a deck plate, and many 944 guys do just that.

Yes, Nikasil plating works for many PRODUCTION engines. Truth be told, I have heard of about as many "problems" with nikasil plating as I have with sleeving.

Just trying to keep the info on the level here.

Mark Anderson has had great luck with his nikasil plated block. Hopefully you will too. But when plans call for more bore then the stock walls can handle, then we have more options.

But Ductile Iron IS better for boost applications.

slate blue

I don't understand Brendon that you say ductile iron is better for boost applications. Aluminium has better heat transfer, I would just run more boost rather than chase the extra capacity if it had to come at the expense of sleeving. The nicasil is so far superior that it is not really even comparable. The wear rates are much lower especially in high power applications. Haven't you ever heard of how 500 hp odd chevy motors become 450 hp motors in about a year.

Nicasil oils better oilpholic I think the word is. It also has lower friction and expands and contracts at the same rate as the parent aluminium. Unlike the steel liners. Give me nicasil any day! Hope you change your mind before it is too late.

Lagavulin

Aluminum does have better heat transfer, but it is nowhere as strong.

If one were to run a low boost application (..<= 8psi), then I would agree with you. However, if one were building an engine with running higher boost (.. > 14psi) in mind and have the money to do so, steel sleeves (..versus ductile iron) are the way to go as they are much more resistant to cylinder 'trumpeting' if and when a blast of detonation occurs.

So I disagree with your statement that 'The nicasil is so far superior that it is not really even comparable', and instead state that nicasil is inferior to steel from a strength standpoint in a high boost application.

If feasible, it's always better to bump up the NA power versus running more boost to achieve a target horsepower number.

No, not from any reputable sources when the engine is ran in the same state of tune.

BC

...Ductile Iron, or what many call "Centrifugally cast" sleeves are what IS being used in high boost applications. When someone takes a honda motor and sleeves it so that they can run 40psi of boost, they are not relying on the orginal aluminum engine bores. Ductile Iron, and other steel alloy materials are in use because they do not allow the form of ballooning that WILL happen to a 928's bore under boost. Once that bore moves, you lose headgasket seal, and your done.

Nikasil, if used properly, is a viable alternative to reboring an alusil blck and getting the bore back to orginal.

But I will be able to run LESS boost, while making MORE power, with MORE durability if I go the way I plan, which is to sleeve as FAR as I can go, possibly to 4.25 inches, use a 9:1 compression ratio, and get some big valve heads done. Some 86 32V cams will then top it off to AT LEAST 400 hp (thats very conservative), so then, when I add 14psi of boost and the fuel required, I will get 750 instead of 650, hypothetically. Lag can fill in the math.

When I spoke to the machine shops in the area about what www.lasleeve.com and www.dartonsleeves.com had to offer in the way of sleeves, I was specifically pointed towards the nodular iron sleeves, or another words the ductile iron. The reason for this is explained here:

http://www.dartonsleeves.com/main_fr.htm

As you can see, we have a high tensile strength, as well as a higth hardness rating. Higher, infact, then the Chromemoly sleeves that are sometimes suggested.

Further, as I mentioned, when a honda guy wants boost and 1000hp for draging, or whatever they get from 2 liters, they use these:
http://www.aebsracing.com/products.pl?product=tsleeves

And it is a proven fact by some that the aluminum bore tower WILL balloon as I stated, when subjected to boost. That level face on the top of the bore will not be level anymore.


Indeed Greg, I wanted to make sure you have not been recieving erroneous information from your own sources, as I do want everyone to have the same info I have, and more. This can only help us, and at the same time help our distributors.

Lizard928

thats funny, I thought they used stickers

BC

Yes, Sorry, 40psi of boost and some mugen stickers.


Thanks for the correction,

Lagavulin

Brendan, there is no need to go with 'big valve heads' with a supercharged 928. In 'Forced Induction Performance Tuning', there is a picture of a turbocharged BMW Formula 1 head, and the caption lists the valve sizes which are considerably smaller than an S4's. Save your money for something else on your project.

As for the 85-86 cams, I've heard the exhausts will work no problem, but the intakes will take a lot of machining to get them to fit into the S4 head.

BC

The big valve heads were a process that I was following with relation to what you said earlie r- to increase the power NA-wise before boost. You get more power with less boost in the long run by increasing t he efficiency of the engine. Also, since I am going to a larger bore, I will need more air flow to make the engine get to its potential NA. I don't have the page number right now, but A. Graham Bell states that a certain CC of bore volume will need a certain mm diameter of valve size (this is in his Naturally Aspirated book). I believe that it was 40mm intake valve for 700ccs, which would be my per-bore volume with 5.6L. I would actually be closer to 5.8 or more if I get to my full number of 4.25 for the bore.

You have a good point on the formula 1 head, and I have not sent my heads in yet for the work. I will do more thinking on this.

The 85-86 cams do need some work to fit, but with that work, it could still be consierably cheaper then finding GT cams and buying them for the horrible prices that they are currently at.

Can you figure the literage for a 107.95mm bore with stock stroke?

Thanks

Lagavulin

Keep in mind too those Formula 1 engines were putting out well over 1000hp from 1.0-1.5 Liters.

It would be interesting to find out how much the machining would cost since someone told me by the time you pay for the machining and the cams, you could have bought GT cams. I do not know how true that statement is.

Here's a link to figure out your displacement:

http://www.angelfire.com/fl/procrastination/motor.html

Tony

Ill start another thread on the 85-86 cams