Could the difference be attributed to anything in particular? That seems like a major amount that would be observable by measurement (dimensions, air flow, etc).
What happens when the the carbs are swapped on those two engines?
Rotax have just released a new barrel to āimproveā parity.
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Are there any series that donāt do scrutineering? Like yours, for example, since itās bonkers vintage stuff? Are there any unlimited sprint races or is that all time attack for open tuning?
Thereās scrutineering, in may respects harsher if adherence to original homologations are important. Chassis have to be dated which can often be very tricky. I have learnt in my time with what people do in the retro scene, that anything is possible for modern classes in terms of scope.
But in other ways since you can actually tune the engine and machine ports etcā¦ the idea of ācheatingā because less possible. The scope of (legal) tuning is a lot more.
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Both were prepped the same out of the box, run in the same, and tested on the same day. Couldāve been carby-based as the tunes were slightly different, however even after a rebuild and dyno they were still performing differently, currently just using the slower one for testing and shakedowns and the quick one for the big races
If you run junior you can dremel the restricotor to be at 24mm from factory they are a little bit smaller then alowed. when i was new even scrutuneering said to me to file it down.
I noted that some gaskets like carb gasket and reed house gasket have a bit small or missplaced hole, so that it interupts with the holes in carb and reed house. what i do is i take that tool you use to do holes in your belt. set it on 3.5mm and just place it in the middle of existing hole, original hole is 3mm. i confirmed this with the scrutineers and thay said it was completly fine, beacuse you are just making an adjustemnt as it supposed to beā¦
You can also take a thinner oil in the gerbox, The original iame is a bit thick, I usually run a ATF oil like this one:
its also cheaper to buy. and it makes the resistance between the gears lighter, (thinner oil = lighter spinning) And i have ran it all this seasong with no problems
// Mike
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I know these arenāt legal but has anyone tried piston and/or combustion chamber coatings (Swain Coatings comes to mind)? Thermal coat the piston crown and combustion chamber, moly coat the piston skirt?
Also, what about reeds? Carbon reeds vs OEM, low vs high tension reeds?
Parasitic loss is the term you can use for this.
I wonder how much hp is lost due to the balance shaft in an X30.
Is there a way that someone is willing to dyno with and without the balance shaft?
I know itās illegal to run without it, but push start engines donāt have the balance shaft right?
Thanks for informingā:ok_hand: learn more new words here then in schoolā:sob:
There was a guy that ran a race with a drilled out balance shaft, he was faster is all that i can say
We havent dyno a x30 with modified balance bescuse its simply illegal,
After the guy had a drilled out balance shaft, when i won they took my whole engine appart to every screw. I was pretty happy at home putting it together beacuse they think me enginw was illegal
One quick question.
What piston to wall clearance do you guys go with? I think the X30 service manual is quite conservative on this.
Any thoughts?
I found 0.14mm to be right in the sweet spot, many reputable builders where running it
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Yep, but it is a guideline.
Iāve been running 0.14 for 3 years when I drove X30, no problem at all 
It is a common clearance, Grice engines is one of them for example
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Whatās the recommended replacement interval from Grice?
Generally larger clearances come at the expense of shorter running between services.
4-5h
And thatās was what I ran to, the coating went bad fasterš
But the people who run their engines generally put a new piston in after 2 races
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Whats the benefit of running larger clearences?
I was under the impression that thighter would decrease compression loss and make more power, with the risk of seazing the engine.
Larger clearence is for when you have higher temperature applications such as turbos.
Or do these builders recommend higher egt?
The compression is mostly down to the ring seal.
Higher clearance can reduce the frictional loss between the piston and cylinder wall. The downside is that you get more piston rocking which can lead to premature failureā¦. Ie if you run it for too long it can crack or even shatter.