Thread: 3.9 Hi comp pistons

Right, all has now been resolved.

Stuart (From Rovacraft in Perth) just rang with a price, thay are IN STOCK, and I have ordered the set. They are a stupid price, AE brand, including rings. Not sure I should reveal the $$ but, they ARE VERY COMPETITIVE. VERY.
Give them a buzz or PM Stu for $$$
Thanks Stu. And enjoy the Holidays.

JC

You could also try i think its JE or JP engineering in SA, they specialize in pitons etc and usually have them for rare vehicle or can turn up blanks to suit. My old man got some hi comp pistons for his 1928 Dodge 4 and 1928 Dodge six.

What is the minimum octane for high compression pistons?

95 or 98 octane RON?

I've got high comp pistons as well as increased compression ratio and was told only 98 octane

You could lower to say 9.0:1 by taking some material from the combustion chambers.
I am too tired to do the math now, but a couple of cc added to the combustion chamber would lower the CR possibly enough to use unleaded.
There is plenty of potential next to the inlet valve.
Regards Philip A

Originally Posted by PhilipA

You could lower to say 9.0:1 by taking some material from the combustion chambers.
I am too tired to do the math now, but a couple of cc added to the combustion chamber would lower the CR possibly enough to use unleaded.
There is plenty of potential next to the inlet valve.
Regards Philip A

Hi Phillip, I'm actually planning to run this on Premium, with quite a bit of spark advance using a Bruce Davis remapped 14CUX ECU I had in my 4.6 stroker.
I am running this ECU ATM in the tired old 3.9 low comp and it is quite a change from the standard one, and strangely dosen't use much more fuel...?!Nicer idle and pulls well from rest, running 12 to 14 deg adv at idle with a perforated adv diaphragm.

I will put it on LPG eventually, hence the 9.35 comp ratio, but am expecting a good driveable engine on PULP.

It's nice to have a V8 AND a diesel RRC!!

JC

Originally Posted by justinc

Hi Phillip, I'm actually planning to run this on Premium, with quite a bit of spark advance using a Bruce Davis remapped 14CUX ECU I had in my 4.6 stroker.
I am running this ECU ATM in the tired old 3.9 low comp and it is quite a change from the standard one, and strangely dosen't use much more fuel...?!Nicer idle and pulls well from rest, running 12 to 14 deg adv at idle with a perforated adv diaphragm.

I will put it on LPG eventually, hence the 9.35 comp ratio, but am expecting a good driveable engine on PULP.

It's nice to have a V8 AND a diesel RRC!!

JC

If you have bored it oversize that will increase Compression Ratio as well, don't go to far, are the pistons forged or cast? Regards Frank.

if you are just using standard pistons and want to up the comp ratio, get the heads machined ,and any half decent place engine shop will get it right ,and you only cc the heads when you are blueprinting to get all your com chambers the exact same,most commonly used on performance motors ,most manufacturers specs are pretty average