Orion plugs or os p3

I think a P3 would be a little too hot for the stock shimming this engine comes with. By adding a shim it would work fine. Some guys locally are having trouble with a consistent tune on there Orion's. I think the Orion engines and this Optima come with a little too tight of piston to head clearance depending on elevation etc.
Shannon I added a shim to yours.

Rex

Cool, I was gonna try a #5 or even a p3 after the break in I did. Unfortunately our track is closed this week due to Tropical storm Darby.

I put a #5 in mine only idled 1 tank so far. Rex should i add a copper shim also?

I've been running Orion for a couple of months and in my opinion the engine runs much better with a P4 plug, idle is much better, and tuning is better. So I think the P4 plug is the way to go.

With a 5 it should be fine. I think you might like a shim added as it will just tune better and idle down better. A .1mm shim is all that is needed.

Rex

This things a rocket!

Very good engine, at cold engine with the P4's hard to take all these hot lap but once any worries now we have to make life testing, I roll with the nozzle 6.5 and 25% Rapicon

Hey Rex,
Any update on the engine you have been testing?

I have a Ronnefalk Orion here and it has too many shims 0.65 mm between piston and button..OS Speed S3 has 0.37 mm.....IMO the Orion is over shimmed which is causing heat and tune issues

How many shims are irrelevant. Distance between head and piston is not. I know you are aware of this but need to explain a bit better for the ones not so into engine as you, Max.

My engines runs best with a head clearnce of 0,6-0,7mm messured with a solderwire. Low (small number) head clarence usually gives an engine with ketchup effect, a tiny tuning window and ghost flameouts.

solder is a horribly inaccurate way to measure head clearance... impossible to get the solder to the true outer perimeter so it will always read higher then the true clearance actually is... OS makes the most reliable best running stock engines on the market today bar non, One of the reasons is they run a tight head with under 0.4 mm between the button and the piston.

No update, Neesh must be busy. Anyone else want to test one or have one they have already ran we can test?

Rex

Thanks Rex,
Have 2 to run in for next years racing here in Australia.
Will work them out as I go along.
Cheers,
Colin

Hey Max,
How would you measure head clearance?

What would you recommend as an upper and lower limit for shims? eg. .2 to .4?

Did you modify the orion so that it had .65 mm of shims?