What pistons do you guys in finland use in your om603.96x engine tunded with the mynä-pump? I have this summer used the stock pistons for my "superturbo" engine with no good results. Every piston have cracked. The damage is about 4cm long in the middle,at the top of the piston. the boost have been set to about 1,6 - 1,7 bar.

Nowadays when the car is parked over the winter I,m going to replace the pistons with used ones, but with new pistonrings. Will the pistons break again? I can understand why the damage appears cause too high boost. Or is it too higt? Any recommendations?

The plans for my car this winter is to build a compressorsetup with the turbosetup. But is there something I should think about?

checkout my car
http://forum.savarturbo.se/viewtopic.php?t=11837

Hello, Original pistons of the turbo engine is good enough to get the engine running up to 400+ hp. Pistons of non turbo engines cause failures in turbo usage. Second-hand turbopistons are a good choise becase original turbopistons costs too much. There is and have been these pistons available in this forum with sensible price.

Obviously there should be large enough turbocharger to avoid problems caused of too high outlet manifold presure. You should have a gauge in the outlet manifold to ensure there is not too much pressure. Mynä-pump demands huge turbocharger to avoid problems.

Which turbo you have in your car ? Opening the link of your car demands login to the forum.

And a huge, i mean huge intercooler is must have in superturbo usage.

okey. I have a holset hx 40. And I have a quite large (megalarge) ic so that shoult not be a problem. And I forgt to mention that my engine is from the beginning a turboengine.
I have measured the exhaustpressure. I have had big problems as you said with the pressure. I have had almost the same exhaustpressure as the boostpressure before the turbo has spooled up. But after that the ex-pressure is sinking allitle bit .

But I have used the 48mm primearpipes to the mainfold and thinking its too much volume in the 48mm`rs. I mean, much volume= much exhaust before the pressure starts to spool the turbo.

And about the pistons, Is the non-turbo pistons the same as the turbo pistons? Im thinking about the compression.

Oh by the way, try this link. My car again. The engine as you can see from the picture in the white w201 is going to be used in the green/black one. That is also the intercooler I have used.
http://forum.savarturbo.se/viewtopic.php?t=11837

anton kirjoitti:And about the pistons, Is the non-turbo pistons the same as the turbo pistons? Im thinking about the compression.

Yes those are same as considered the compression ratio. At least no modification have been done so far while turbo piston are used in non turbo engine.

Actually i can not say what can cause the failure of pistons in this case, maybe a bit wrong injection timing, but i think it's better to wait response of real superturbo professionals (like Mauri H.). Original turboengines should not break pistons (in sensible use)...but while re-building the engine consider to add the exthaus temperature meter. It helps you to analyse if the temperature rises too much fro reason or other.

It should be ok if exhaustpressure lies below boostpressure + 0.5 Bar (at maximum).

How about the external oil cooler for the engine, it helps the oil squirters to cool pistons in the original turbo engine.

Am I reading correct that you are getting lower pre-turbo exhaust pressure than intake boost pressure?

While my turbo is currently the small KKK K26, I get exhaust pressures of 22-25psi when I have 14psi of boost.

I thought that drive pressure would always be higher than intake pressure.

RatMan kirjoitti:Am I reading correct that you are getting lower pre-turbo exhaust pressure than intake boost pressure?

While my turbo is currently the small KKK K26, I get exhaust pressures of 22-25psi when I have 14psi of boost.

I thought that drive pressure would always be higher than intake pressure.

With large enough turbo chargers, like hx40 is, it could be lower but not much. It depends obviously a bit about the wheel sizes but also other construction, like external wastegate. Small turbos have always too high exhaust pressure if lot of power is taken out and that cause turbo and engine failures in most cases.

If I dont remember wrong my hx is 63mm in and 65mm out.16housing. And Im using an 50mm external wastegate.

About the exhaust temperature, how hot should it be? Max?

anton kirjoitti:About the exhaust temperature, how hot should it be? Max?

Very good question, next please

ok, let's try to elaborate this. I do not have superturbo, neither i have no EGT meter installed. I only have tiny turbo and EGP(pressure) meter in my 4 sylinder Vito . What I have heard the temperatures have been up to 900+ degrees while full load. I think nobody can say what is the exact maximum value, becase it depends how well the pistons are able protect againts heat energy. The turbo pistons have a kind of coating, and i have considered to ask if there is opportunity to add an extra coating to increase terminal isolation to prevent the heat expansion of pistons. Installation of the EGT sensor can also cause some measuring error. But i think while driving with not full load you learn how the temperature behaves and if there happen something strange you will lift the pedal immediately before disaster.

If it rises up to 950 deg (e.g becase intercooler warms) i think you should let that ferrari drive off and slow down gently

For a pre-turbo Pyrometer, 1250*f is a safe limit. For post-turbo, 950*f is safe.

In an ideal world, you should have an EGT gauge for each cylinder to monitor the performance of individual cylinders. The best alternative location is where the exhaust collects before the turbo inlet.

Here is where mine is placed. You can see the brass fitting above the flange where I measure the turbo drive pressure.

anton kirjoitti: Every piston have cracked. The damage is about 4cm long in the middle,at the top of the piston. the boost have been set to about 1,6 - 1,7 bar.

It sounds like you have excessive cylinder pressures, most likely from combustion trying to push the piston down while the crankshaft is pushing it up. I would get a good set of factory pistons with tight ring grooves, ceramic coat them (it won't stop the cracking but it will make them run cooler) and retard the injection timing.
If you can find a shop that can measure cylinder pressures under load it would be worthwhile to have them set your timing on the dyno. This will not be cheap, the pressure sensor that they put in the glow plug hole costs about $1000 and has a very short life.

Hi! it looks like you are using far to wide primarys, it can not be bigger than hole in the head where from primarys start. In your case 38mm if I remember right.
In normal higway use constant speed like 55 mph ex temp normally stays under 350 C And not to be stay over 550 C in constand speed in acceleration it always goes higher like in my case 750 C

One more thing, are you sure using big enough lub-oil cooler

I have same kind of EGT readings as Petri K, except the extremes. Peak temperature has been always less than 600C. And more than 350C readings required full throttle pulls. EGT probe is located at 5th cylinder exhaust.