Supertech p/wall clearance
 

So what are you guys running for clearance? Seems like a lot of people run the .035 supertech says, but there are others (trackdayhooky, savington) that seem to run more clearance.

Lets hear some opinions. What should I run for an engine that will see a lot of track time and lots of HP... :D

Open it up, but be warned that the motor will not last as long and break-in procedure is absolutely critical to ward off excessive blowby. My clearances are right around .004".

How long are we talking here for engine longevity? And what kind of break in procedure would you reccomend? .004?

What I will most likely do is run the car N/A for break in. And have it trailered to the dyno from my place. Basically just turn it on at my place to make sure the car runs.

You say "open it up", but .004" < .035" ?!
What's your break in procedure?
What about piston slap on cold starts? How bad is that?

UMY enginee builder lauged when I said to go .004. He said there is no reason to and the engine will not last. It's currently with him and he is building it to .0025

I went with a loose bore on mine at the advice of my builder. I have no piston slap when cold, minimal blow-by, and I just ran 2-days at 5-hours of seat time with 250-280* oil temps and never once added oil.

My machinist told me to break-in by driving it to the track. He does a finish on the cylinder walls that supposedly minimized the need for break-in. I cruised up to 60-mph then hit over-run about 10-times and that's it. I ran 200whp for a week then up to 260whp and its stayed there for a while.

I hope you don't plan to track that car with .025" of wall clearance...but the builder probably knows more than me, Savingaids, my engine builder, and probably just about anyone tracking a turbo Miata.

0.0025" is tight, real tight. I'd run that on a NA motor but not something FI.

uHH

This dude's friend is smarter than you.

FWIW the alloy that Supertech uses in their piston has a different coefficient of thermal expansion (CTE) than the alloy that Wiseco uses in theirs (at least for Miatas).

As in Wiseco expands more, or less?

Uhhh. I think he meant .0035"

Wiseco expands more IIRC.

It's being built as a track car. And he knows that. I'm not too concerned because he warranties his work. If anything happens in regards to piston scoring, I can always be like "hey... see I said we should have gone with a larger bore"... And break in with him consists of like 5000kms of driving with a 4500RPM limit and 1000km check ups with a borescope to make sure everything is doing it's job. Or something along those lines... he went over it briefly with me.

I guess you're done asking questions and now you're telling us what you're doing? How much more reliable and stronger will your motor be than Savington's, thesnowboarder's, and mine? I guess this machinist knows something most don't since he insists on cutting the manufacturer's spec in half. What does he plan on checking with the bore scope? Lol @ oldschool break-in.

He sounds exactly like you did Hustler. You went from asking questions for 2...no 3 years about everything. To being an utmost expert on all things FI overnight with the only thing on your resume being installing a BEGI turbo kit.

So you and him should be able to see things eye to eye.

https://www.miataturbo.net/images_pb.../moderator.gif
do not piss me off.

Oh noes, I'm shaking in my boots....

Lol @ Virginians in boots.

Claiming to be an expert on precision machine work and making fun of someone for cutting the tolerance spec in half are two different things.

THREEEEEETHOUGHSANDFUCKINGMILESUNDER4500RPM??????? ?

That is the longest break in i have ever heard of.

what the fucking fuck???


i have never even heard of an oem break in close to that long. Ridiculous.

Does this idiot build lots of motors for "racecars" and does he warranty them?

I love this website.

I don't really care what others have done. I did my research and brought it forward to him when I dropped the engine off with the parts. I'm not an expert at building engines, and can only regurgitate what I see online. When I told him what others were running for clearance he basically laughed at me and said if I run the same the motor will not last very long. There's a reason I pay others to do things I don't know about... for their experience/skill/knowledge on the subject. And I'll take his word on what needs to be done over a few guys on the internet. I'm sure yours, Sav's and Snowboarders engines run great...

I want to know how this badass breaks-in motors for racecars. Does he make the owner strap the car to a dyno for 9-years?

After working around a lot of older guys in the industry and guys who have "lived a little" so to speak, I take everything that ANYONE says with a grain of salt. Keep an open mind. Don't listen to someone who is an "expert" just because they say so. Now on that note, if tons of guys are running with .004 (myself included) and havn't had any problems, (and honestly, no way in hell would I run a track car at half that spec either), I'd go with the known good, and not some spec that a so called expert pulled out of his ass. I work with "experts" and roll my eyes at shit that they do a lot of the time. Just think about what would happen if you ran a piston that is SUPPOSED to be run with .004, and you run it with half that, and it expands.
The "experts" at my job told me that my ES bushings would "make my car pull/cause play in my steering/control arms/was the cause for clunks when I step on the brake"
Thats my 2 cents.

Then delete this thread.
We know; I thought you didn't care about what others did?
Wow, lots of anomolies on this forum alone. I guess my days are numbered on this motor.
That makes two of us.
Then why did you make this thread again?
They do, and we all run a loose bore. I don't understand his logic of running a turbo track car "tight". Does he run cars that make less than say 175hp/L at .001"? Ironically, my machinist showed me 3-motors lying around where customers did a "tight bore" and letter added forced induction, and those same motors were in line for a bore and hone so they could try again. That convinced me to go loose as he suggested.

Is this guy going to warranty the labor, pistons, rods, valves, weld the head, and replace turbo if something goes south? Is he going to blame it on detonation? Is he going to insist that you didn't follow his absurd break-in?

Those are all vaild points. If the engine shits the bed I'll eat my words, but for now we'll see how it goes.

And it's not going to be turbo'd, it's going to be rotrex'd with water injection. Slightly less AIT than a turbo, and the WI will assist with keeping the motor cool as well. Also higher comp with lower boost... (10-12PSI).

I sustained <110*f IAT's in 95* heat last weekend in 30-minute sessions, with extreme humidity, so I doubt your IAT's are lower than a turbo car. "Lower boost" is irrelevant. Aren't cylinder temps at a given output are similar regardless of induction method?

I would consider lower boost to be relevant. Less air being forced into the combustion chamber = less compression of the air/gases = less heat.

I'm not too sure in regard to cyl temps, since I don't tune.

Last thing I have to say on this thread is I have also NEVER heard of an engine builder offering a warranty. Maybe for rare situations they might redo some work but in general, NO. You really think he will buy you new parts?

What the fuck is wrong with you? You are just being taken by this guy. I predict catastrophe and tragedy. And holy fuck, WI should not be your failsafe against your pistons expanding and seizing in the bore. Shit man, shit.

http://www.phuckpolitics.com/wp-cont...a_dumb--------

I never blindly trust what someone says based only on their "years of experience". I'm curious of the logic behind this three thousand mile break-in procedure. I doubt it stands to reason. If he or you can convince me, i'll eat my hat.

I think your hat is safe for today.

Supertech recommends .0028" wall clearance for their pistons, and that's considered extremely tight for a forged piston. Weisco recommends .004" or .005" for "heavy blower/nitrous use". .0025" is really, really tight, but hey, if your builder thinks he knows better than the folks that design pistons for a living, knock yourself out.

I might be able to get on board with tight wall clearances if the builder has had good luck with it using a certain piston or a certain motor, but once he recommends a 500km break-in my opinion quickly declines. Motor break-in is done and over with by the 50 mile mark - modern bearings need no break-in and if the rings haven't seated by the 50 mile mark they aren't going to seat at all. (I'm giving you the benefit of the doubt by assuming you meant 500km - if your builder wants a 5000km break-in period you should run screaming from his shop.)

This guy's website is horrible but his logic is exactly what i've heard over and over again from every expert i've ever had a "break-in" conversation with.

http://www.mototuneusa.com/break_in_secrets.htm

In short, you need to wear down the imperfections of the brand new rings to get a good seal against the cylinder bore. This is what that cross-hatch is for. If you do an easy break-in, you wear down the cross-hatch and not the rings which will screw you big time in the long run.

My engine break in procedure:
1. Start engine, warm it up while watching for leaks.
2. As long as there are no oil leaks and no MAJOR coolant leaks, take it for a ripper around the neighborhood. Second gear works great for me. All the way to redline, then overrun all the way down to idle a few times. Some say to stay out of boost. I personally use boost to my advantage. The more combustion pushing the rings into the bore the better in my opinion. Lots of vacuum as well which is why you let it overrun from redline back to idle.
3. Go home and check for leaks again. Put all the shit back on that you never put on for the first drive (under-tray, etc.)

We should meet up and have a chat again sometime soon. I know i'm not an alleged "expert" and you probably aren't interested in any of my suggestions, but i've had 100% success on every engine i've built. If there was ever a problem with an engine i've put in a car, it wasn't anything related to my engine building. Unless you count not checking pistons/rings in my last motor that ended up having broken ring-lands before I even got my hands on it.

Wayne, your "that is what cross-hatch is for" statement doesn't make sense to me.

Why would lower cylinder pressures and less vacuum cause the rings OR the cross hatch to wear at a different rate than high pressure/vacuum? The only variable I can think of is that high pressure/vacuum generates more heat which um makes the rings more maleable????

This is true, I did a bunch of reading before I bought my pistons. Supertechs are 4032 alloy whereas most Wisecos, JE, CP and a bunch of others are 2618. The silicon content is much higher in 4032, so it doesn't expand as much as 2618. You can therefore run a bit tighter bore and get less piston slap on cold startup with 4032 so many people use that alloy for street cars. 2618 expands more and is a little softer so it can take a bit more abuse before it fails outright.

I went with Supertechs (4032) because there are several Miatas boosting around race tracks with them who haven't had any problems. I'm not going to be throwing such a shitload of boost at it and running at the ragged edge where 2618 becomes necessary. It's also a street car and I don't want to have to run .005"+ clearance on a motor that will see a bunch more cold starts than a dedicated track car does.

It also doesn't matter so much which forced induction method you use. Lower IATs from a more thermally efficient compressor, water injection, etc. allow you to safely make more power without knocking, but anything resembling a temperature low enough to keep your pistons from expanding is history once you light off the charge. You can't make power without making heat. It takes a specific amount of fuel to make a certain amount of power, and burning that specific amount of fuel creates a specific amount of heat in the combustion chamber. There's really no way around it. If we're both running around a track, you've got a rotrex and WI and I've got a conventional turbo with just an IC, if we're making the same power our pistons will be seeing all but identical temps. Significant expansion will occur, and if you run less than the piston manufacturer's minimum clearance spec you're a fucking moron.

Your used up Bubble-Yum sphincter notwithstanding, I've seen a specific number out of Savington (.004") but not from you. Are you running the same? If you don't know off the top of your head, look it up from the spec sheet you got from your machinist plsthxbai.

The reason is that increased pressure/vacuum pushes/pulls the rings against the cylinder bore with a greater force than just their "springiness". Thusly, the cross-hatch is able to wear the rough spots off of the rings more quickly. Supposedly over time the rings will wear the cross hatch down rather than shave the imperfections off of the rings so they are perfectly in match with the cylinder bore.

This is how I understand it anyway. Someone smarter than me will likely correct me. I'm no injuneer. But using this logic, it makes sense that breaking it in like a man will get those rings in shape rather quickly. I like to think of this as setting the pace for the type of life the engine will be living. I also have piece of mind in knowing that if anything horrible is going to go wrong, it'll go wrong in that first 20 miles of absolute abuse.

I think there is a bit of misunderstanding as to how I will break the engine in. I'm not going to baby the hell out of it for that long. I've broken in a few engines before as well as motorcycles, I know that you need a lot of engine braking/compression braking and accelerations through the gears, not staying int he same gear/RPM for long periods of time etc.. All I said was there will be an RPM limit for a predetermined time... that's it. And no boost until he gives me the go ahead. Which is fine considering he is the one building and tuning the engine.

Yes.

Sounds like he's building you a motor for NA use, not boosted or nitrous.

I'm just curious what this extra long time period of a low rev-limit is suppose to accomplish. If I hear some good reasoning i'll possibly stop taking my engines to redline within 15 minutes of the first start.

You know, just on a similar note, i've heard of people cutting open their oil filters after that first 50 or so miles. I still dont understand the point of this.

I don't know either... but it's what's required to ensure he stands behind the motor.

It could just be to ensure that you aren't going to be fucking with your tune and causing detonation or something.

All this bologna makes me wanna just use stock pistons lol

What is stock piston/wall clearance? Just out of curiosity.

I think its like 0.0015-0.0020" or something very close to that.

Looking at the oil filter guts tells you if something is not good in the engine and saves a few parts.

How does he manage a 50000000km break-in on a racecar? Strap it to the dyno for several hours? Install the racecar motor in a street car for a month before the first race?

I'm running .004 according to my builder who just replied to my email.

Have you talked to other customers?

Irrelevant, cast pistons runs significantly tighter clearances than forged pistons.

Exactly Sav.... you would agree that is the concern. How much larger is his than stock? Not enough?

Just think about it for a sec, I'm not sure if he was implying that when he posed the question but thats how I took it.

It doesn't really matter how much larger it is vs. stock - you're drastically changing the design of the piston, which requires that you appropriately alter the environment that piston will be living in. Mazda could use unobtanium pistons that do not expand at all with heat, thus requiring a wall clearance that would approach zero - but it wouldn't matter at all if you're replacing them with Supertechs that require a minimum of .0028" wall clearance.

Internet wisdom agrees with you. Crosshatching is a very small series of peaks and valleys on the cylinder walls, and the piston ring has to smooth out the peaks in order to support itself while still leaving the valleys intact for lubrication purposes.

Full-blown abuse is not good, since it produces too much pressure and thus too much heat, which will glaze the walls - too little abuse will not produce enough pressure and the rings will glaze the walls as well.

The deceleration part is important as well since it draws oil up onto the walls, cooling the rings/walls and carrying away the small metal particles the ring is shaving off.

then why bother asking on here? You always ask for peoples opinions and then when you get them, you find a way to tell them they are wrong and you are right.

:bowrofl:

I have played the horsepower game for a lot of years, and have learned 2 things that are important.

Loose piston wall clearance makes horsepower, tight takes it away.

There are trade-offs, but loose usually wont squeak pistons.

I do hope with clearance as tight as Ocean wants, he at least uses deck plates to bore and hone, if not, I hope he has a warranty fund!

Very interesting thread. If I were you, just follow what supertech specifies or at least listen to the people on this thread. I came to know about SuperTech on this forum, so many members talk good about them. Why do it differently? If what you want is test a different route good as well. Have the balls to put pictures on how the engine looks when it cracks in half and shitty dyno charts.

Looking forward for a Miata part-out thread...

Holy shit, can some mod please delete the numbfuckskullery that is every single thing falcon has posted in this thread?


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As for the theory behind this stuff, I am still not really convinced.

Are rings softer than the cylinder or is it the other way around? Or are they the same? If they are same I'd think they'd wear at the same rate. I think this matters.

I might be wrong about this as well, but here is how I understand it. The rings are softer than the block. The cross hatch acts kind of like sand paper to create a tight seal on a microscopic level. But over time, the rings get work hardened from the heat and pressures. So you only have a limited window in which to do perform the seating. If you push the engine too hot too fast, the rings harden and will never seat. Same deal if you don't push it at all because you don't get the force to press the rings into the cylinders before they are hardened. Again, I could be quite wrong with my limited knowledge of materials sciences.

I'm interested in how this is turning out.

The spec sheet, that came with my supertech 85.5 9:1 pistons that I bought from emilio said this:

Application: Factor:
Street Performance 0.0045
Moderate turbo / Nitrous 0.0050
Drag/oval track 0.0055
Turbo/nitrous race only 0.0065

My builder and I decided to go with "Moderate turbo / Nitrous" 0.0050. He is not a miata guy, but does high HP subies and evos. I hope we didn't swing to far the other way. Well, thats if I ever get my motor back. I'll save this story for it's own thread. :(

I think too hard break-in could deform the honed peaks into the valleys while a softer break-in rips off the peaks into the oil gradually. I would go gradually harder on the throttle and revs with occasional blips up even higher in the rev range in neutral to eliminate the formation of ridges on the wall by incomplete conrod stretch.