Post from Rennlist - Piston Coatings
03-04-2002, 06:28 PM
#1
Rennlist Member
Thread Starter
Post from Rennlist - Piston Coatings
Hey all,
This topic has been discussed, but I have some more info/questions.
I was doing some more research into what aftermarket pistons could be used
in our 928 if we wanted boost, and wished not to bore the block. Well, our
choices are myriad, but we have to worry about those "Secret" coatings and
"special" pistons that are the only ones that will work in our "fairy
dust" treated blocks.
Back in Reality:
The pistons have to be coated with an iron substance so that they do not
score the aluminum in the bore. Aluminum on Aluminum (Aluminium for our UK
dwellers) is Bad karma. We all know that now, and it no longer a secret
(Maybe it never was, it took me a while to get a consensus). Mahl and
Kolbe-Schmidt have these pistons, but with the price of "Pieces of eight"
going well past 3k with a much needed cermaic coating on the top, it
started me thinking. <img src="graemlins/c.gif" border="0" alt="[ouch]" />
The reason the pistons need to be coated is because of the piston skirt,
and how it hits the bore. Well, if thats the issue, why can't we just do
this:
<a href="http://www.se-r.net/about/200sx/scc/june98/june11.jpg" target="_blank">http://www.se-r.net/about/200sx/scc/june98/june11.jpg</a>
That is a picture of the ceramic coating on the top of the piston, and
another coating on the side - A polymer coating that is something like
your non-stick frying pan coating. It is supposed to help the piston-bore
friction, and help you reach closer piston-bore clearances.
Now - you might say - Why trust coatings? Well - The iron on the mahl
pistons is a coating right?
Why not use this on a nice set of JE "Super dooper" forged pistons and
save, say 2-3k? And thats for 16 pistons.
They put these coatings on crank bearings, cams, and other HIGHLY stressed
wear surfaces. Would this not solve our "Special coating" problem, so that
we can use a stock block with whatever pistons we choose? If not, why not?
BTW - the Gold Substance on the top is Swain's "GoldCoat" and is a three
layer coating applied to stop the heat of the combustion process from
soaking into the piston. I am unsure on this one, as any engine I have
taken apart has had serious black carbon coatings on the piston tops. I
sorry that the carbon coating may not letthe gold coating work - unless it
is a materially blocks the heat, and does not reflect it.
Oh - and if you read through this, and you planning on responding, then
you can probably help me with this: How does one calculate bore/stroke
ratios, and what numbers are good or bad?
Thanks for reading,
Brendan Campion, intrepid reearcher, and breaker of non-secrets.
89S4
- and for a real treat, read this 24 page thread below that deals with a
low-cost (relative to motec) that is supposed to blow away the
competition. Supposedly. (Paste the whole line into your browser)
<a href="http://www.supraforums.com/showthread.php?s=4fb50b3f9d93acf6e50fd4748f06ecd5&threadid=10402&perpage =25&pagenumber=12" target="_blank">http://www.supraforums.com/showthread.php?s=4fb50b3f9d93acf6e50fd4748f06ecd5&threadid=10402&perpage =25&pagenumber=12</a>
This topic has been discussed, but I have some more info/questions.
I was doing some more research into what aftermarket pistons could be used
in our 928 if we wanted boost, and wished not to bore the block. Well, our
choices are myriad, but we have to worry about those "Secret" coatings and
"special" pistons that are the only ones that will work in our "fairy
dust" treated blocks.
Back in Reality:
The pistons have to be coated with an iron substance so that they do not
score the aluminum in the bore. Aluminum on Aluminum (Aluminium for our UK
dwellers) is Bad karma. We all know that now, and it no longer a secret
(Maybe it never was, it took me a while to get a consensus). Mahl and
Kolbe-Schmidt have these pistons, but with the price of "Pieces of eight"
going well past 3k with a much needed cermaic coating on the top, it
started me thinking. <img src="graemlins/c.gif" border="0" alt="[ouch]" />
The reason the pistons need to be coated is because of the piston skirt,
and how it hits the bore. Well, if thats the issue, why can't we just do
this:
<a href="http://www.se-r.net/about/200sx/scc/june98/june11.jpg" target="_blank">http://www.se-r.net/about/200sx/scc/june98/june11.jpg</a>
That is a picture of the ceramic coating on the top of the piston, and
another coating on the side - A polymer coating that is something like
your non-stick frying pan coating. It is supposed to help the piston-bore
friction, and help you reach closer piston-bore clearances.
Now - you might say - Why trust coatings? Well - The iron on the mahl
pistons is a coating right?
Why not use this on a nice set of JE "Super dooper" forged pistons and
save, say 2-3k? And thats for 16 pistons.
They put these coatings on crank bearings, cams, and other HIGHLY stressed
wear surfaces. Would this not solve our "Special coating" problem, so that
we can use a stock block with whatever pistons we choose? If not, why not?
BTW - the Gold Substance on the top is Swain's "GoldCoat" and is a three
layer coating applied to stop the heat of the combustion process from
soaking into the piston. I am unsure on this one, as any engine I have
taken apart has had serious black carbon coatings on the piston tops. I
sorry that the carbon coating may not letthe gold coating work - unless it
is a materially blocks the heat, and does not reflect it.
Oh - and if you read through this, and you planning on responding, then
you can probably help me with this: How does one calculate bore/stroke
ratios, and what numbers are good or bad?
Thanks for reading,
Brendan Campion, intrepid reearcher, and breaker of non-secrets.
89S4
- and for a real treat, read this 24 page thread below that deals with a
low-cost (relative to motec) that is supposed to blow away the
competition. Supposedly. (Paste the whole line into your browser)
<a href="http://www.supraforums.com/showthread.php?s=4fb50b3f9d93acf6e50fd4748f06ecd5&threadid=10402&perpage =25&pagenumber=12" target="_blank">http://www.supraforums.com/showthread.php?s=4fb50b3f9d93acf6e50fd4748f06ecd5&threadid=10402&perpage =25&pagenumber=12</a>
03-04-2002, 10:58 PM
#2
The teflon coating on the piston skirts is a fairly comon thing on performance engine builds. I don't know if or how it would work with the 928 block though. The coating used on the tops of pistons is a ceramic material. It actually insulates, and doesn't just reflect heat. A carbon layer on top of it would probably just help insulate the piston top even better. The same type of coating is also used on valves and combustion chambers.
The bore/stroke ratio that's best really depends on what you'll be using the engine for. There is no one best ratio, just like there's no one best camshaft. You can have two engines with the same displacement, only one has a longer stroke and smaller bore, and the other has a larger bore with a shorter stroke. The one with the longer stroke will have more torque due to increased leverage on the crankshaft. It will also have a higher average piston speed at the same RPM than the other engine, because the piston has to travel further during each rotation. The engine with the shorter stroke and larger bore will make less torque because of less leverage on the crankshaft. The average piston speed will be lower, so it will probably be able to rev higher and make more high end horsepower. That's just a pretty general overview of the differences. There are probably all kinds of other things that would come into play in comparing those two engines. My personal preference? Longer stroke AND bigger bore.
The bore/stroke ratio that's best really depends on what you'll be using the engine for. There is no one best ratio, just like there's no one best camshaft. You can have two engines with the same displacement, only one has a longer stroke and smaller bore, and the other has a larger bore with a shorter stroke. The one with the longer stroke will have more torque due to increased leverage on the crankshaft. It will also have a higher average piston speed at the same RPM than the other engine, because the piston has to travel further during each rotation. The engine with the shorter stroke and larger bore will make less torque because of less leverage on the crankshaft. The average piston speed will be lower, so it will probably be able to rev higher and make more high end horsepower. That's just a pretty general overview of the differences. There are probably all kinds of other things that would come into play in comparing those two engines. My personal preference? Longer stroke AND bigger bore.
03-04-2002, 11:45 PM
#3
I think that the skirt coating have to be plenty
hard to resist the silicon crystals in the cyliner
walls scuffing it, thus iron or chrome.
We've discussed this before round here and I'll
offer up the same thing I did last time. I 've got
a set of Mahle replacement pistons here and they
are definatly coated;has to be chrome due to color.
Now this isn't like bumper chrome all shiny but
rather a dull finish and looks to be very thin.
From what I can tell the piston was cast, machined,coated,and the the dome/reliefs machined
again along with the space between the 2nd and the
oil ring.
I really don't think there's so much voodoo to
all of this chrome plating is readily available
and reasonably priced, I'd use the JE/chromed.
As far as boosting the engine, turbocharging seems to respond best to longer strokes;much torque to be had.
A search around the web for the guys running FWD
Chrysler turbo cars will give you alot of food for
thought, although our engines may be a bit on the
delicate side for that kind of abuse.
I'm very interested to see where this coating
research leads as well as anyone doing turbos as
I've been measuring and fitting for intercooler
and piping placement.
hard to resist the silicon crystals in the cyliner
walls scuffing it, thus iron or chrome.
We've discussed this before round here and I'll
offer up the same thing I did last time. I 've got
a set of Mahle replacement pistons here and they
are definatly coated;has to be chrome due to color.
Now this isn't like bumper chrome all shiny but
rather a dull finish and looks to be very thin.
From what I can tell the piston was cast, machined,coated,and the the dome/reliefs machined
again along with the space between the 2nd and the
oil ring.
I really don't think there's so much voodoo to
all of this chrome plating is readily available
and reasonably priced, I'd use the JE/chromed.
As far as boosting the engine, turbocharging seems to respond best to longer strokes;much torque to be had.
A search around the web for the guys running FWD
Chrysler turbo cars will give you alot of food for
thought, although our engines may be a bit on the
delicate side for that kind of abuse.
I'm very interested to see where this coating
research leads as well as anyone doing turbos as
I've been measuring and fitting for intercooler
and piping placement.
03-05-2002, 12:36 AM
#4
Brendan,
I think the engine builders that have discovered the correct piston coating for our engines have had to learn the hard way. Many want to recover their R&D costs by selling you their kit or pistons. Why do think Porsche, Mahle, or Kolbe-Schmidt doesn't advertise/publish the correct procedure to coat the pistons? Why the heck would you want to pay $3,000 for a set of pistons when you could get the same thing for $1,500 or less? In turn, if you could, you wouldn't need their pistons if you had all their R&D information.
I asked Mark, of F.A.S.T., why he sells his kits for sooooo much money? He said, " I'm recouping my R&D costs." I told him he was awfully proud of his knowledge, maybe too proud, for me to buy his bracket and an instruction manual for the price he's asking. I think I'll wing it for now. Who knows maybe I'll be lucky and nail it the first try?
Jim Nowak
I think the engine builders that have discovered the correct piston coating for our engines have had to learn the hard way. Many want to recover their R&D costs by selling you their kit or pistons. Why do think Porsche, Mahle, or Kolbe-Schmidt doesn't advertise/publish the correct procedure to coat the pistons? Why the heck would you want to pay $3,000 for a set of pistons when you could get the same thing for $1,500 or less? In turn, if you could, you wouldn't need their pistons if you had all their R&D information.
I asked Mark, of F.A.S.T., why he sells his kits for sooooo much money? He said, " I'm recouping my R&D costs." I told him he was awfully proud of his knowledge, maybe too proud, for me to buy his bracket and an instruction manual for the price he's asking. I think I'll wing it for now. Who knows maybe I'll be lucky and nail it the first try?
Jim Nowak
03-05-2002, 10:34 AM
#5
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Jim V, I would be curious as to where you are trying to mount an intercooler and what size. This has been something I and one other turbo 928 owner have been debating for some time. Lately I have really been leaning towards a rear mounted water/air unit in place of the stock air box assembly and possibly even a replacement intake with a built in cooler as well. Would mean a lot less plumbing since the turbos are mounted towards the back of the engine and their outlets point up as is.
As far as pistons, I did a decent amount of talking to PowerHaus and a few individuals. PH told me they knew of a place stateside that can do the proper coating, but never tried it because there is still an issue of heat expansion rates of the material used in say a JE or Ross piston.
PH is one of the places that recommends doing the ceramic coating to the piston on the crowns, skirts, and underneath. It's applied on top of the standard Mahle or K-S piston's
coating. Personally I think the route to go is just used 951 pistons that are still in great condition obviously. Marcus Hutchinson did this and just had to go to 2mm longer rods to prevent supper low compression. Seems places such as PH have realized a desire for used 951 pistons seeing as I first heard they are $50/ea from them and now they are saying about $190/ea plus rings at $35/ea, when they have them.
Some places/people also suggest sleeving the blocks instead and that it can handle a lot more power. From what little I looked into this, it still requires picking the right type of material for the sleeve due to the heat expansion issues.
Really if you keep detonation out of the car, you could run a stock 4.7 or 4.5 US spec motor with the lower compression they came with and boost. I know of a 1978 twin turbo 928 that was daily driven for 2 years making initially 8lbs of boost but later on 12lbs and it never had a motor issue. The issue it did have was constant heat issues and that heat leading to a timing belt that stretched a couple of inches, the turbos were front mounted so rather close to the timing belt.
If I was set on building a motor up, I would just go with Mahle pistons, no one can seem to present a reason not to other than cost. You can get custom Mahle pistons made as well, they run about $3k for a set of 8 with rings and wrist pins. From what I am seeing factory spec'd Mahles are a little more than that at somewhere around $3500. If I went custom, I would try to get a couple extra pistons just in case ever needed they would match the others, as far as I know you can buy the Mahles in sets of 4, not sure if they can be had in smaller batches.
As far as pistons, I did a decent amount of talking to PowerHaus and a few individuals. PH told me they knew of a place stateside that can do the proper coating, but never tried it because there is still an issue of heat expansion rates of the material used in say a JE or Ross piston.
PH is one of the places that recommends doing the ceramic coating to the piston on the crowns, skirts, and underneath. It's applied on top of the standard Mahle or K-S piston's
coating. Personally I think the route to go is just used 951 pistons that are still in great condition obviously. Marcus Hutchinson did this and just had to go to 2mm longer rods to prevent supper low compression. Seems places such as PH have realized a desire for used 951 pistons seeing as I first heard they are $50/ea from them and now they are saying about $190/ea plus rings at $35/ea, when they have them.
Some places/people also suggest sleeving the blocks instead and that it can handle a lot more power. From what little I looked into this, it still requires picking the right type of material for the sleeve due to the heat expansion issues.
Really if you keep detonation out of the car, you could run a stock 4.7 or 4.5 US spec motor with the lower compression they came with and boost. I know of a 1978 twin turbo 928 that was daily driven for 2 years making initially 8lbs of boost but later on 12lbs and it never had a motor issue. The issue it did have was constant heat issues and that heat leading to a timing belt that stretched a couple of inches, the turbos were front mounted so rather close to the timing belt.
If I was set on building a motor up, I would just go with Mahle pistons, no one can seem to present a reason not to other than cost. You can get custom Mahle pistons made as well, they run about $3k for a set of 8 with rings and wrist pins. From what I am seeing factory spec'd Mahles are a little more than that at somewhere around $3500. If I went custom, I would try to get a couple extra pistons just in case ever needed they would match the others, as far as I know you can buy the Mahles in sets of 4, not sure if they can be had in smaller batches.
03-05-2002, 03:26 PM
#6
Aaron,
The car in question is a '79 US so I'm not sure I
need to do anything piston-wise. I've heard of broken ring-lands and such on these but that's usually a sign of detonation which is so critical
on a boosted engine.As you've just stated others
have had no problems so stock pistons are probably fine.
My exp. with turbo cars is from FWD Dodge products;a Very stout engine that seems to be able
to take any boost(abuse) you give it.
What I'm going to try to do is use components from these engines as they a cheap available and
proven.
The intercooler from a Dodge Daytona is aprox. 12"x6"x4"; possibilities I've looked at for mounting a pair of these are in the grill or in place of the fog/driving lights. It would be a plumbing nightmare. The other thing I've thought
of is a custom radiator;narrower & deeper with one
I/C on each side or to trash the A/C and put them
there.
Lately I think the best solution would be to cut
in some ducts where the brake cooling ducts would
be on the S models and mount the I/Cs up behind the headlights, replace the fender liners with some metal ones venting the air into the wheelwell.
The turbos would be a pair of Garret TO3s from a
Dodge application again because of the built-in
wastegate and ready-made 2.5" exhaust mount.
The turbos are available in the wrecking yard for
about $30 ea. and rebuild kits are under $200.
Boost control would be handled by a stock Dodge
(again) control; staged boost which can be over-ridden and metering capabilities to 14 PSI.
Timing does not need to be on a curve with a boosted engine but rather in stages as found in a
(you geussed it) stock Dodge controller, the only
prob there would be converting the 928 distributer
to handle the Hall-Effect inards from the 4-cyl distributer.
Custom intake and exhaust (welded tube) would be
a must for turbo mounting and the need to mount the knock and charge air temp sensor on the intake side.
Sounds crazy huh? I figure I can put this together for under $1000 doing all the fab myself,
and be able to run up to 14 psi on a 928.
BTW just for compare there's a guy running 12.65
in the 1/4 mile with 25psi and a 2.5 L engine in
an '89 Dodge Mini-Van!
The car in question is a '79 US so I'm not sure I
need to do anything piston-wise. I've heard of broken ring-lands and such on these but that's usually a sign of detonation which is so critical
on a boosted engine.As you've just stated others
have had no problems so stock pistons are probably fine.
My exp. with turbo cars is from FWD Dodge products;a Very stout engine that seems to be able
to take any boost(abuse) you give it.
What I'm going to try to do is use components from these engines as they a cheap available and
proven.
The intercooler from a Dodge Daytona is aprox. 12"x6"x4"; possibilities I've looked at for mounting a pair of these are in the grill or in place of the fog/driving lights. It would be a plumbing nightmare. The other thing I've thought
of is a custom radiator;narrower & deeper with one
I/C on each side or to trash the A/C and put them
there.
Lately I think the best solution would be to cut
in some ducts where the brake cooling ducts would
be on the S models and mount the I/Cs up behind the headlights, replace the fender liners with some metal ones venting the air into the wheelwell.
The turbos would be a pair of Garret TO3s from a
Dodge application again because of the built-in
wastegate and ready-made 2.5" exhaust mount.
The turbos are available in the wrecking yard for
about $30 ea. and rebuild kits are under $200.
Boost control would be handled by a stock Dodge
(again) control; staged boost which can be over-ridden and metering capabilities to 14 PSI.
Timing does not need to be on a curve with a boosted engine but rather in stages as found in a
(you geussed it) stock Dodge controller, the only
prob there would be converting the 928 distributer
to handle the Hall-Effect inards from the 4-cyl distributer.
Custom intake and exhaust (welded tube) would be
a must for turbo mounting and the need to mount the knock and charge air temp sensor on the intake side.
Sounds crazy huh? I figure I can put this together for under $1000 doing all the fab myself,
and be able to run up to 14 psi on a 928.
BTW just for compare there's a guy running 12.65
in the 1/4 mile with 25psi and a 2.5 L engine in
an '89 Dodge Mini-Van!
03-05-2002, 03:32 PM
#7
Just a follow-up to my last post;
The 928 guys save one swear it won't work,
the Dodge turbo guy swear it will and be easy, but
wonder why I want to do it to "that crate".
Oh well.
BTW does anyone know why my posts are always such
a mess?? screen res.? illiteracy??
The 928 guys save one swear it won't work,
the Dodge turbo guy swear it will and be easy, but
wonder why I want to do it to "that crate".
Oh well.
BTW does anyone know why my posts are always such
a mess?? screen res.? illiteracy??
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03-05-2002, 05:02 PM
#8
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Jim V, I have headers and outlet piping already designed and built and to use T3 turbos, commonly found on such cars as a Turbo Coupe and I might be wrong but I think a LeBaron had them. They do not have integrated wastegates, I used a pair of Delta II turbonetics wastegates. Also have all of the oiling system built and a scavange pump along with a oil catch tank. The 78 I mentioned did a custom radiator and still had heat issues, he even did not have great cooling without the turbos on the car and that radiator. A lot of the people I have talked to are under the firm belief of staying with a good working stock radiator if at all possible, then some say if anything go to the Devek piece. The original intent of my setup was to go to an air-air intercooler mounted up front, even modified a stock intake so that the TB could be fed from the front instead of the rear. However the more and more I ponder on this setup, I keep trying to find a feasible way to not go that route. Reason being about the only way to go to that front mount IC is under the radiator support and then you have a nightmare of a ground clearance problem, then you also have the nightmare of the IC blocking needed air to other systems and heat soaking into the radiator.
It is a lot of work to build all of those pieces, just not any room in these engine bays. Hope you are one heck of a frabicator.
It is a lot of work to build all of those pieces, just not any room in these engine bays. Hope you are one heck of a frabicator.
03-05-2002, 07:19 PM
#9
Another option for the I/C would be to put
a fan on it. There was a guy who used a Ford
powerstroke I/C who did this because he didn't
want to lose his A/C.
Still on the 928 I don't know where except maybe
a big louvered vent in the hood.
My project is still in the "one day I'd like to"
stage, still have another 928 I'm trying to do a restore on and moving this summer-bleh.
a fan on it. There was a guy who used a Ford
powerstroke I/C who did this because he didn't
want to lose his A/C.
Still on the 928 I don't know where except maybe
a big louvered vent in the hood.
My project is still in the "one day I'd like to"
stage, still have another 928 I'm trying to do a restore on and moving this summer-bleh.
03-05-2002, 10:48 PM
#10
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The fan idea was tried actually on the same 78 I mentioned. Meant doing away with the AC condensor fan, sitting the IC back a little and had a fan in from of the IC. Then tried a whole slew of different fans on the engine side of the radiator.
