Run in stand/dyno build.

[Terry Keeley]

A little update, I've trimmed the wheel to 5" and am getting run times where I want them. Having some issues with vibration on the oiler at the coupler but I've isolated it now and will try it tomorrow.

I recently got the EngMod2T software and am digging into it, it's very detailed and will take some time to get ports mapped out and other data entered. Once done I'll run a simulation on this stock CMB 67 and compare it to the dyno, there are tweaks that can be done to match the two then it's supposed to be very good at simulating changes. I'll use it to design pipes etc. then try them on the dyno and finally in a boat.

At least that's the the plan.

 

[Steve White]

I gotta ask. Peak HP is at a lower RPM than I would have guessed. I'd be inclined to shorten up the pipe length and give it a go. Is the port timing optimal for the RPM range below 20K?

 

[Terry Keeley]

I gotta ask. Peak HP is at a lower RPM than I would have guessed. I'd be inclined to shorten up the pipe length and give it a go. Is the port timing optimal for the RPM range below 20K?

Ya, this pipe is long and the needle is rich, just giving the unit a shake down after some mods and getting a baseline.

 

[Terry Keeley]

Made some more pulls today, fixed the oiler issue and got a good base line for starting on the EngMod2T simulation software.

This thing is repeating very, very well, I actually got three runs back to back to back within 0.01 HP of each other. Most others were within 0.05 or 1% or so.

 

[Terry Keeley]

Got an AFR/Lambda sensor installed to help find the right needle easier between changes, seems to be working so far.

 

[LohringMiller]

I posted a lot more in another forum. Your results are the first that I know of measuring this. However, lambda measures oxygen in the exhaust. For gasoline at an ideal air/fuel ratio of 14.7:1 lambda is defined as 1. However, with oxygen containing fuels the air/fuel ratios are very different. Methanol's is 6.4/1 and nitromethane's is 1.7:1. How an oxygen sensor reacts to a mixture of these has not been tested as far as I know. I also believe that really rich mixtures don't lower power that much especially if you can raise the compression ratio.

Lohring Miller

 

[RaceMechaniX]

Years ago I had fantastic mentor who helped Yamaha develop their 2-stroke GP engines. He mentioned that measuring Lambda was not a useful data collection point for 2-strokes. EGT and CHT were far better indicators compared to lambda which was subjectable to fouling from 2-stroke oil.

 

[Norm Doerr]

BMEP is a good KPI to look at.