First Look SuperTech Pistons (1.8l Dohc)
 

First Look
SuperTech Pistons

PN# P4-MA8350-N4

Bore Over Size Comp Ratio Volume CCs Head CCs

83.50mm +0.5mm 8.6:1 -4cc 50


Height Stroke Rod Length Pin Diam Weight

1.201"(30.5mm) 3.346" 5.228" 20mm 293g


Ring P/N Note
P4-MA8… GNH-8350


I have a set of factory sealed pistons for a turbo build on a 1.8l

https://www.miataturbo.net/attachmen...ine=1334706746

Open the box and this is what I see, pistons still sealed in there bag with wrist pins.

https://www.miataturbo.net/attachmen...ine=1334706746

I see a nice label on each piston with the pertinent info.
Part Number checks with what is on the box.
Proper bore size listed.
Piston weight listed at 278g
On all 4 pistons, We will see.
https://www.miataturbo.net/attachmen...ine=1334706746
On the Supertech website,
http://supertechperformance.com/cata...ection=pistons
They are listed to have a weight of 293g
15g difference between posted info and what is in the box.

Now to get them out of the packaging and give each a quick look over for any shipping damage.
Top looks good
https://www.miataturbo.net/attachmen...ine=1334706746
So do the bottoms and the ring lands.
https://www.miataturbo.net/attachmen...ine=1334706746

Now to weigh each one.

https://www.miataturbo.net/attachmen...ine=1334706746

Piston #1
https://www.miataturbo.net/attachmen...ine=1334706746
This piston was jumping between 279.0g and 279.1g

Piston #2
https://www.miataturbo.net/attachmen...ine=1334706746
278.8g

Piston #3
https://www.miataturbo.net/attachmen...ine=1334706746
278.3g

Piston #4
https://www.miataturbo.net/attachmen...ine=1334706746
This one bounced between 279.4g-279.5g

So piston #3 is the lightest at this point.

Next is to weigh the wrist pins.
As you saw in the above pic, the wrist pin was packaged with the piston.

Wrist pin #1
https://www.miataturbo.net/attachmen...ine=1334706746
98.7g

Wrist pin#2
https://www.miataturbo.net/attachmen...ine=1334706746
98.3g

Wrist pin #3
https://www.miataturbo.net/attachmen...ine=1334706746
98.4g

Wrist pin #4
Sorry, no pic
99.4g

The weight difference is rather wide for wrist pins.

Now , to weigh the combo and get the combined weight of the piston and wrist pin.

Combo #1
https://www.miataturbo.net/attachmen...ine=1334706746
377.8g
Combo #2
https://www.miataturbo.net/attachmen...ine=1334706746
377.2g
Combo #3
https://www.miataturbo.net/attachmen...ine=1334706746
376.6g
Combo #4

https://www.miataturbo.net/attachmen...ine=1334706746
378.8g

So we have a range of weight from 376.6g lightest to 378.8g heaviest.
The average weight is now 377.5g

Now since the wrist pins have such a variance of weight, I will swap them around some and see if I can get them closer.

Piston #1 with wrist pin #2
https://www.miataturbo.net/attachmen...ine=1334706746
377.4g

Piston #2 with wrist pin #1
https://www.miataturbo.net/attachmen...ine=1334706746
377.5

Piston #3 with wrist pin #4
https://www.miataturbo.net/attachmen...ine=1334706746
377.8g

Piston #4 with wrist pin #3
No pic, Sorry
377.9

Well, now this is a whole lot better, Now the weight difference from lightest to heaviest is .5g

Now to check the wrist pin clips and see how close they are.

https://www.miataturbo.net/attachmen...ine=1334706746

10 for 10 C clips weigh .8g each.

They can be hung on the rods at this point, But I want them closer.
My lightest now is 377.4g

With a touch on a belt sander, on the lip by the wrist pin boss, I will remove some weight.

https://www.miataturbo.net/attachmen...ine=1334706746
I buffed on 3 pistons to get a matched weight of 377.4g

Piston #2 needed .1g removed

Piston #3 needed .4g removed

Piston #4 needed the most removed with .5g

So you have an idea how much a gram weighs, Hold a dollar bill in your hand, That is 1g

A nickel weighs 5g

My over all opinion of the pistons is not too bad, the fit and fish looks good to the naked eye, but the out the box weights need to be checked.

As far as the website posted weight of 293g being off by appox 15g

The label weight of 278g being off by appox 1g

Supertech needs to update its website.

The label weight is close enough to work with.

What is your opinion of the sharp edge by the exhaust valves? I have seen several supertech pistons that were burned or melted there.

The ones I have in my hand have a slight champher on all the valve reliefs, and the reliefs do not extend into the edge of the piston like I have seen on some others.

Have pics or links to the melted pistons you speak of?

He means this:
Any comments on the intake "eyebrows" and how little meat there is to the edge?
They like to fail there. Granted this one probably detonated but...

https://www.miataturbo.net/attachmen...ine=1334716031

If you look at Pic #2 in this thread..
https://www.miataturbo.net/showthrea...349#post861349

A milder form, yes, but still the start of it.

If I need to hand touch up the valve reliefs, I will.
I will have to look into what the pistons are coated with.
I rather avoid a burnt piston from another form.


I would agree with too much inginion timing under boost,
With the commonly used tuning device of the board, Does it have an active role in ingtion retarding?

Or even a boost refrance that will pull timing? Think MSD 6BTM.

Also what are most you guys running for ring end gap?

Megasquirt ECU is popular here.

"roll in retard" - do you mean tip-in acceleration retard?

My AEM ECU FWIW has it.

How does ring end gap affect detonation?

Do not freak me out in this thread, please.

Jason, What I ment was does the knock sensor have an active role in pulling timing, based on the knock count the sensor picks up.

By the time your ear can hear the knock, it is too late.

Fae, That was an after thought question to see what the fourm tends to use.

I tend to like a tad wider ring gaps for a little padding insurance.

Most of the time cracked/busted ring lands are from the ring gap butting, then the ring flexes and breaks the land.

This happens from a lean condition, or a non-boosted engine going boosted.

Husler, I will try not to freak you out.
Just hug your teddy bear and all will be ok.

role vs. roll.

many of the ecus have active knock sensing. the megasquirt 3 is a work in progress. a few beta testers are running the knock code (e.g. me) but it's not mass-market.

Until I got the hardware to sense knock, I didn't know for sure if there was any. Now I know there is and I've addressed it by trimming fuel to each cylinder and backing off timing.

Even an active retard is still waiting for detonation to occur at some level before it pulls timing.

y8.. Sorry for the misuse of words.. I was I bit wore out last eve when I wrote this.

I am used to to reading about DSMLink, But what I know about ECU tuning would fit in a thimbel, and have room left over.

But what I have learned about link is that it can pull timing out as low as 1 or 2 counts.

I did not know if the setup that the Mazda was as sensitive or not.

Now on my Ford TC, I use a Vortec SC boost refrance ingnition box, it will remove 1-3* of timing per lb of boost to a total of 20*, The old EECIV does have a knock sensor, but is very crude in its use.

lemme ask a stupid question...
i have pistons that are also 83.5mm...
what's the clearance between piston and wall supposed to be?

Philly, What pistons? Cast? Forged?

Pistons come with the PTW clearance built into them.

But that tolerance can be changed depending on the build and use of the engine.

Most forged pistons want about .0035 PTW

But if we use a mazda BP-ZE engine for a base, Std Bore is 83mm/3.268"

Then add a .50mm/.020 over bore

The bore in the block will now be 83.50mm/3.288"

The forged piston should mic out appox 3.2845-3.2850

The pistons should have come with a spec/info sheet.

Looking at the info that Supertech has in the box they want .00276/.07mm

At the botom of the paper they have a disclaimer saying....

"Some applications may require more clearance. Correct piston installation is the responsibility of the customer."

So with that being said
Supertech pistons should measure out

3.288 - .00276 = 3.28524 call it 3.285

(I will post pics of the paperwork later)

How bad is it if you don't weight match the pistons and rods?

dgmorr.... hard to say, depends how bad off they are in the box.

If you look at the starting weights I had at first, then how he become closer with just swapping wrist pins around. To me they were rather far off.

The closer the balance the smoother the engine idles and revs

You ever see a break dancer do the worm? It's just like that....

What's your opinion about the supertechs? Some finishing work on them, match the weight and balance the rotating assy, think they're good to go? Any sort of finish on them from supertech?

Ok I just called Supertech, to find out about the coating on the pistons.

I spoke with Willy, He told ne the coating is a dry lube coating to help oil absorbtion.
Also asked about removing the coating on the crown of the piston, by grinding to help remove sharp edges, He told me there will be no issue with doing that.

So yes you can polish the sharp edges on the supertech piston crowns.

Supertech Performance Inc
3550 Charter Park Drive
San Jose, CA 95136
(408) 448-2001
www.supertechperformance.com

What is your opion of piston coatings, top and skirts. Stuff like swain.

Do used coated pistons you see look better than uncoated?

whew...trying to wrap my head around all this...
mine are wiseco 83.5mm 8.5-8.8:1 forged pistons.
i didn't see a sheet with tolerances in the box.

Smooth right?

Just wondering for the DIY types. You see a lot of DIY budget builds with no mention of matching them.

Phillb From all the forged pistons I have seen, over 90% fall in the .003-.004, that includes Diamond, Wiseco, CP, JE.

Measure your skirt 90* to the wrist pin and see where they mic out. That will tell the tail.

Std bore + over bore - Piston measurement = PTW

dgmorr... the reason the DIY types do not weight match for the most part is they do not know that they should.

That is why I do these How tos/write ups, so the guys wanting to build an engine can do a bit better.

Good to know when the crowns look like this...https://www.miataturbo.net/attachmen...1&d=1334005195

Btw, any "smart" reason ST have lowered the outer edge 0.15mm?
For boosted apps trying to save the head gasket maybe...
In my 11:1 N/A application is just make the squish worse.
The compression height was also a good 0.5mm lower than stock (block decked 0.7mm to get the squish flush (and the lowered edge 0.15mm lower).

Niklas... so on yor dome piston the outer edge was dropped .006

The only reason I can think of to do that would be to give the flame front a path around the dome to help with air/fuel ignition.

Why the wrist pin was moved, I honestly can not say.

What part number are you working with?

"P4-M84-P10" according to their catalogue (84mm 11:1).

Well from what I can see posted on the website your compression height should be 1.201, the same as most of the others except PN# P4-MA84-CR9

And looks like a slight adjustment to increase the compression of the 8.6:1 piston

If the center line of the wrist pin to the crown flat does not measure out at that number, then they were machined wrong and should be sent back.

So if they are .50mm/.020 shorter then you shold see, 1.201 - .020 = 1.181

I am the proud owner of that piston. In addition to the rather obvious ringland damage, the center of that piston is dented straight down, presumably from preignition. (The root cause was determined to be inadequate intercooling.)

Here's what a normal 8.6:1 Supertech looks like:

https://www.miataturbo.net/attachmen...ine=1334781847

Here's that one:

https://www.miataturbo.net/attachmen...ine=1334781847

Complaining about how that piston failed at the sharp edges near the valve reliefs is like regretting the flammability of your polyester shirt while standing a few feet from the center of a military nuclear strike.

Sav... What were your AFRs when you did that?

I am impressed!

I would have said the dent in the crown came from high cylinder temps, for the simple reason that there is no splatter that is normaly seen with pre det. Like burning a hole in the center of the piston.

But no doubt you were getting ready to melt the center out of that slug.

A failed piston is a failed piston.

And for those who do not know, for every 1* drop in air inlet temps you drop 3* on the EGT

AFRs were ~11.5 give or take a couple of tenths. 100 octane. The failure happened at ACS Roval, so we were doing ~1:47 laps with about 35 continuous seconds of WOT in 5th and 6th per lap. Too much boost (21-22psi), too little intercooler for the conditions.

That was 2+ years ago as well. Lots has changed about the car since then (more injector, E85, different intake manifold/head, WAY more intercooler, less boost, more power).

I bet the move from gas to E85 gave the power curve a good raise.

Also you would have to about double the size of the injectors with the E85 set up

Did you ever take readings of the temp drop with the old IC and the new?

10% gain going from gas to E85 at the same boost level with no timing changes - 300whp at 14psi to 330whp at 14psi. All I did was add 20% to the fuel map and turn up the base pressure. Small timing/fuel changes were worth another 5whp, and the car ended up making 351whp at 17psi. That's all on an 8.6:1 motor - the next motor will get 11:1 pistons and a pile of boost.

The fuel setup is a Bosch 255HP, ID1000s@70psi of base pressure and a 1:1 boost reference. It's not quite as bad as double - the stoich ratio is 47% richer than gas, so I typically say gas x 1.5 for E85 fuel requirements to be on the safe side. Based on my math, this pump/injector setup will get me to ~425whp, and then I'll need to knock the base pressure up to ~90psi and run a dual-pump setup (likely a DW300 in the tank acting as a lift pump with a Bosch 044 in-line for pressure).

I never did get readings from the old (ebay core) to the new (Precision 600hp). With the new, in 100*F ambient temps, the IATs will fluctuate between 120*F and 130*F depending on the amount of time spent on throttle in 5th/6th. That's good enough for me.

Damn, The Id1000 are some nice injectors, I just read up on them a bit.

Flow 1015cc @43 psi

so you should be pushing them just around 1300 cc @ 70 psi
at 90psi that works out to almost 1500cc

I wonder what the fuel temps are at when racing.
How much head is being transfred to the fuel, and the heat from running thu the fuel lines.

Seems to me this would "thin out" the fuel being used

I can see a set up like that for drag, but not road racing.

What duty cycle are you sitting at?

Why not get some injectors in the 1500cc range and back down the fuel pressure?

Supertech Factory Info sheets
 

https://www.miataturbo.net/attachmen...ine=1334793807

https://www.miataturbo.net/attachmen...ine=1334793807

I lost all my logs long ago (haven't touched the tune on that car in ~2 years) but based on the map it's about 11ms actual PW (calc+dead) at redline, which works out to ~70% duty cycle at 7400rpm.

ID doesn't make an injector between 1000 and 2000cc, and the 2000cc/min units are close to $1000 for a set of 4. I don't need much more than what I have now - the boost levels to make 500whp on this motor will be close to 30psi so all I really need is a pump set that can move 1100-1200cc/min at ~100psi of rail pressure - no big deal :giggle:

Savington, I will admit you knowlage of fuel systems is beyond me.

Wouldn't it be fairly easy to add a second set of injectors on the bottom of your IM? If you're running 1kcc/min primary add a secondary 440cc? Not really sure what ECU you're running so that could be a roadblock..

Sav's our local guru. Tends to know pretty much everything about everything. And he has the most badass turbo'd BP here.

The series 1 AEM has enough spare injector drivers to do that, and the software will blend them properly, but that's a lot of extra failure points and similar cost (the injectors, plus the rail, plus fittings, etc) to adding an inline 044 to my current setup and spinning the FPR screw in a bit more.

Just don't ask me to bore my own engine block ;)

See, that's why I'm not an engineer- I tend to forget looking at ALL aspects of doing something. Adding more points of failure was never something I would've considered. Sounds like you've got a much more reliable plan! :cool:

Impressive.

Weren't there other Supertech pistons that also failed at the valve relief edge?

Any piston can fail under the right (wrong) conditions.

Go lean, too much advance, wrong tune, wrong octane, wrong PTW clearance,faulty sensor, the list can go on and on.

But to blame the edge of the piston to cause the failure is a bit out there.
What that shows is the weak point of the piston to fail.

Any piston will have a melting point.

Savington did say he had a small ebay IC when this happened, so being an armchair quaterback, the IC got heat soaked, the IAT went up, and that inturn brings up the combustion chamber temps, and that brings up EGT.

With the raised combustion chamber temps, that was just enough to cause the piston to fail.

Remember for every 1* IAT go up, EGT go up 3*

so even a 10* increase in IAT will cause a 30* in EGT, I do not know how much that would raise combustion temps.

I think the high IAT's didn't cause the failure in and of itself; it led to detonation.

Voodoo magic inside a motor, that's all I know.

Sav, do you remember what size that egay IC was? I think it's time for me to upgrade and I'm contemplating the Precision one you seem to like.

28x6x2.5 rings a bell, but it was mounted at a steep angle and not shrouded very well. The new one is 31x8x3.5, fully shrouded, stood straight up against the airflow. The 600hp core doesn't really fit in the car unless you've removed all of the stock plastics/shrouding, so buyer beware.

Our turbo kits will get the 350hp core, which is a 27x6x3.5. Should do the trick nicely.

I was going to say, the 350whp core should be alright for someone like myself with a mainly track day only car with a few TT's here and there? I will be doing some full shrouding. And coupled with the fact it's a Rotrex'd car I think the slightly smaller one should be ok?