badcoupe

When those of you who have went 2.8 or 3 liter raise your compression ratio any? Also has anyone ever heard of using NA pistons to do this on a stock bore motor? Just throwing some ideas around Thanks

Eyal 951

daniel 951 runs NA pistons on his 951 motor and upgraded turbo. I'm running slightly increased compression on a 2.5 bore, about 8.5:1 CR
~Eyal

AL951

Same here. Mill the head .050 for a new CR of 8.5:1. I would really wanted to go to a 9.5 to 9.8 CR, but I can't find anyone that can make the right pistons for ths application. The mayor problem, it seems is the piston special coating for it to work on the block. The only company that says that they can make it is Cosworth Ltd., But they can only produce 20 or more.

Regards,
AL

Eyal 951

Dude, 944 NA pistons will get you right there, and they'll be cheeaap!

Zero10

Yep, I'm building a motor for my 951 using N/A pistons. 100.5mm N/A pistons, 9.6:1 CR. I plan to run ~15psi of boost, and it should have an awesome torque curve, be quick to spool, and go like hell.

You could use the 10.something:1 pistons from a late N/A if you were really determined though

AL951

Thanks info guys!..................The problem is that they are cast not forged like those on the 951.

Regards,
AL

EdC

I always thought that a lower compression would allow more aggressive (higher) boost, and thus more power. Wouldn't raising compression a sizeable amount reduce power potential? Wouldn't more low rpm torgue be better accomplished by avoiding a large tiurbo, opting for a smaller turbo that hits harder at a lower rpm? Hey what do I know.

AL951

Zero10 I would be very intrested on how your project ends up. Please let us know your findings

Regards,
AL

Eyal 951

EdC, if you want to run 20-30 PSI, don't raise compression. The gains you see from being able ro trun 25PSI are far greater then 10:1 CR and 15 psi. But if your going to run 15 psi either way, and no more, then 10:1 on 15 PSI will yeild gains. I'm running 18 PSI on 8.5:1 with out any real problems.
~Eyal

theedge

Lower CR gives you more headroom for boost before running into detonation/knock/etc but less off boost power.

Higher CR gives more off boost power, but a lower threshold for boost before running into knock/etc. But, higher CR is another way of getting more power out of any engine. Porsches new engines run 11:1 or more of CR.

Its really a matter of what you want from the car...

AL951

Not necessary Edc, you could make lots of power with a high CR(9.0-10). The reason that they us a low compression pistons on older engines was because ignition timimg was still perty primitive and pre-ignition was a big problem. To control this they use this type of pistons.

Regards,
AL

RolexNJ

I'm running new Mahle 968T 8.0:1 CR pistons. I wanted this low of compression because I didn't want to ever be limited on higher boost levels to due a higher CR.

EdC: You are right about your comment too. A higher CR would impede you from running higher boost levels "safely". Some of the people I know of wanted higher CRs because they wanted a more responsive low end - N/A type. Not me, I want boost baby!

AL951

That is true Rolex, I want to do this because I want more power off boost.

Just think about this. Indy cars,(CART not IRL) run a CR of over 12:1 With a single turbo with methanol as fuel and no intercooler, and can produce 850 BHP from 2.65 L. All of this at a phenomenal 7 psi.

Regards,
AL

Ken From KLA Industries

You might send your questions about having pistons made to technical@klaindustries.net Tom has had some made with very good luck and we can get the proper coating put on the skirt.

Ken

AL951

Thanks ken, I will give him a try................Eyal How does it feel at 18 psi? Can you share with us?

Regards,
AL