I didn't even know supertech made pistons.

 

Those SuperTechs are made from a 4032 alloy which (from my limited understanding) isn't as resilient as the 2618.

 

Those look great Aaron! Sounds like it is almost time for a crank thread!

 

That would be a correct assessment, though there are plenty of pistons made out of 4032. One of the main thing is the difference in thermal expansion and how you need to build the motor (more clearance). I believe Wiseco uses 4032 in quite a few applications. I would assume (I am no metallurgist) that alot depends on what your overall build is going to be. Obviously a 9.5:1 piston that can stand 500whp is great in a 400whp motor, but not so hot in a 1000whp application

Mahle has some listed as well, I didnt go through and look at all the options for the pistons because I know some of the 9.5:1 are for 2.3's but there are 4 options so I'd think 2 of them are 2.0 apps-

http://www.racerwheel.com/under-the-...itsubishi.html

aaron

 

Oooo, thanks for that link on the Mahle pistons. I knew about the 8.5. Didn't know they made a 9.5 CR piston.

 

Great write up!

 

Any documentation on the higher compression spooling faster?

This was a common arguement in the honda world a few years back and was pretty much proven null...

I have tuned quite a few high compression turbo hondas (over 11:1, some over 12:1 ) and spool never really came on faster. I will admit transient response was much improved, but back to back 4th gear pulls no difference in spool.

No experience with a high compression 4g63 though

 

Actually, you're likely find more to support that if anything, the reverse is true.

 

i dont think compression affects spool - displacement does.

 

All the back to backs i've seen in the honda world spool remains consistent...

Although a back to back like this could have many variables arise..

 

I havent seen any support to show that spool is increased. As has been pointed out it seems that it might if anything lessen spool. To me there are 2 reasons for higher compression as I outlined in other threads. One is maximising the power for a given airflow value (i.e. stock turbo) and of course the other is fuel related. I suppose it comes down to the same thing, but if you have a fuel with a lower BTU value the increase in compression will regain some spool that would ordinarily be lost.

Most of my recent experimentation has been with E85/E98 and high compression and not race gas. What I know of gasoline and high compression/boost comes from rally which is airflow limited because of the restrictor. That creates its own special set of rules though anyway since ethanol increases spool by itself.

Pauls' motor is 10:1 and runs 44psi to make 1050whp this year on Import. Albeit this is with larger cams, a different head, and an AMS intake. 2007 it was 1014 @ 55psi on the same turbo at 9:1. Now there are probably many reasons (inlcuding the intake manifold change) but this year the boost was coming on about 600rpm earlier than it did before. As we change things around again for this season I will pay a little closer attention to what has gained us the most

 

Another thing that I forgot to mention is JE will make the pistons fairly inexpensive as well. All you have to do is order whatever bore at 9.5:1, and as Nick said its not rocket science for a stock rod, stockish bore piston.

 

CP also makes a 9.5:1 piston, FWIW..

 

Oh, I don't doubt CP, JE or Wiseco could give you anything you want. It's just I hadn't seen options from Mahle other than the 8.5 offering

 

I built a 10:1 in a 2G FWD DSM a couple years ago with a T67 and the car runs like a champ. Another friend did similar with a GT4088 and runs around on 91 octane without a problem. The cars don't really "spool" faster to a given boost level when looking at RPM, but the car sure does get up to that RPM a lot quicker.

On the 4G63, the reason to go 10:1 IMO is that it's a flat top piston. Run it with a tight deck height and a thin head gasket and it will make awesome power without even batting an eye at high boost on 91 octane. The piston is also a lot more resistant to carbon build up and the setups seem to like to be ran leaner then their lower compression couterparts. Toss in some good fuel and you have a pretty wicked little setup.

Cams and a good exhaust manifold make a huge difference on how resistant the motor will be to detonation on the high compression though. Match the high compression up to a larger cam/turbo setup and use a good divided manifold and you'll find the motor is quite resistant to detonation even on 91 octane.

Watch out though on some of the high compression domed pistons. A lot of the domed pistons are for N/A applications and often have a struted skirt design that is meant to make the piston as light as possible. These pistons don't have enough strength in the wrist pin area for a turbo motor though and things can get ugly real quick. This happened to a Honda friend that was running 12.5:1 on a T70 and 114 octane fuel. On the dyno it made sick power at lower boost (low 700s at like 20 PSI), didn't really improve peak power over the lower compression motor (780 peak), ran cooler, idled better. First time down the track where it saw sustained load and heat had piston parts all over the track. Inspection showed that the piston wrist pin area failed on 2 pistons and crack were all over the other 2 in the same areas.