Peter L Thanks! This day felt like payday to me, I've been working on the engine since October and finally all the work gave some actual results. And luckily it looks like the whole project was worth the effort too, I'm very happy with the performance already, and it's not even really all dialed in yet :)

Russ White Thanks! Unfortunately race season is already over but I hope to get some more testing done and get the kinks worked out before the end of spring so the engine will be ready for next season :)

Or glue them ;) I think I'll just use the rubbers :P

Thanks! The connecting rod is for a Rotax 800HO iirc, it has a 27 mm big end pin instead of 24, and 20 small end instead of 18.

@@Hollaendaren thank you

I've never had this problem with the rubbers off before, but both of them failing within an hour from each other is probably not a coincidence. I haven't used this type plug cap before either so that might be related. I'll just keep the rubbers on :) I always run without them because they can really get stuck onto the plug in the cold, but then again with the twin plugs I've never fouled a plug so I don't really have to remove plugs with the head being cold. The header starts at 43.0 mm, outlet is 28.0 mm and about 20 cm long. E-port effective diameter is around 46 mm now, going to be around 47 after I finish porting.

Yeah that pipe ratio is about 0.61 with 46 mm port, which is at the minimum being 0.6 But why is the header pipe smaller than the header diameter. Standard equations like Blair for example port to pipe ratio of 1.25 max for low BMEP engines and would put a port area diameter of 46 mm to header of 57.5 Or at minimum 46 mm header to 46 mm port for high BMEP engines. What are the port dimensions re width height and radius top and bottom ?

The standard formulas are starting to be a bit oldschool. The modern way of thinking is that the exhaust tract should taper down to around 75% of the E-port area, at least for narrow powerband applications. The theory being that you lose gas flow with a too large header because even if the gases are expanding, the exhaust port doesn't open all at once. I know the old way of thinking is taper to around 105% or more but this 75% thing definitely seems to work even if it seems a bit counterintuitive, because the engine really hauls ass :) In Engmod, a smaller header gives me a lot more peak HP (a lot more as in 10-20% more), while a larger diameter header gives a wider power band but lose out on top. As it's CVT I don't care too much if I get a narrow power band, it's mostly about peak HP. I'll send you an email with more porting details!

It follows the same theory if you want a very narrow power band. Keep in mind the calculations are for engines that have either a gearbox or like spring karts that need a wide power band and everything in between. We know that engines with a gearbox and some degree or power band will have a 1 to 1 port to pipe ratio, and the wider power band will go up to 1.25 Running a 0.92 port the pipe ratio will by the same theory give you a very narrow peak beyond what standard pipe and port to pipe ratio will cover. It doesn't deviate from the theory it's just the parameters and ratio used is outside the average values used. I look at the pics you sent (thanks for that) and got the same values from my own calculator based on the port area it shows and that uses straight Blair calculations from 1996. Id like to see that article you mentioned too..

Not me driving in the video ;)

Hollaendaren ja....that’s not fair