66E Conversion

Wiseco use to make 90mm pistons for this. They were custom. Back in mid 00’s many guys had gp1500’s. I had at least 5 or those pistons.
groupk Still has 87mm
also look at Polaris large bore sled pistons. the sledshop? Carl’s cycle too
 
To be clear I was questioning if a wideband would be helpful, efi could have big advantages, I suspect it could respond to quick changes in throttle position better than carbs, especially BIG carbs, and no worries about dribbling from vibration, super short intake tract, those seem like potential big advantages. No idea if that will actually work in reality. If you're not familiar with x-tau accel enrichment I would be looking into that.
 
I feel like a wide band o2 would be extremely helpful if it gave meaningful readings, for developing the base map, probably tune 0-100% throttle tied to a trailer in the water, cruising down the lake and out of water(won’t hit 100% here) and interpolate between those three lines to fill in your base fuel map, then I think you have to take it out and tune accel enrichment by riding it. I had not heard of x-tau enrichment but it sounds great, I think for a two stoke you will end up with a large x and long tau because fuel isn’t just stuck on the intake port wall, it has the whole crankcase and transfer port area to stick to. I didn’t get that deep into it but I’m hoping the mega squirt can just correlate throttle position to a map at a certain rpm(I think that’s how it handles alpha-n to begin with) and then derive mapdot from that for faster response.
I did message @tyler breitweser but he didn't offer up too much info
 
I feel like a wide band o2 would be extremely helpful if it gave meaningful readings, for developing the base map, probably tune 0-100% throttle tied to a trailer in the water, cruising down the lake and out of water(won’t hit 100% here) and interpolate between those three lines to fill in your base fuel map, then I think you have to take it out and tune accel enrichment by riding it. I had not heard of x-tau enrichment but it sounds great, I think for a two stoke you will end up with a large x and long tau because fuel isn’t just stuck on the intake port wall, it has the whole crankcase and transfer port area to stick to. I didn’t get that deep into it but I’m hoping the mega squirt can just correlate throttle position to a map at a certain rpm(I think that’s how it handles alpha-n to begin with) and then derive mapdot from that for faster response.
I did message @tyler breitweser but he didn't offer up too much info

It has been a while since I've had my nose in megasquirt, but I think you are spot on all around, and I'm pretty sure you can do exactly what you are describing.

A more sophisticated approach that I'm pretty sure megasquirt is capable of (but not 100% sure) is to take a "map" reading from the actual crankcase, and time it for the reading to be taken at a particular point in the stroke, probably just before transfer ports closing. No idea if that would actually work, but it makes sense to me. I think the way simpler Alpha-n is a better way to start off though. I think you can have compensation based on temp and "atmospheric" pressure with a pressure sensor inside the hull, which seems to me like a good idea.

Very cool project looking forward to seeing how it goes.
 
Yeah they mention phasing the map readings in the x-tau explanation, but it was unclear to me whether ms2/microsquirt was actually capable of that. That would be the coolest way to go about if it could I think
 
I'm pretty sure it can or the xtra code can. Once upon a time long long ago I was interested in putting a Microsquirt on a single cylinder dirt bike, the challenge with those is that there isn't really any plenum to take a map reading from, only the very short length of port between the throttle body and the intake valves which obviously has hugely varying pressure throughout the stroke. I remember reading about a guy who used Megasquirt on a similar motor and did the timing of the map reading thing in the intake port and timed it to read just before the intake valve closed. This is a little bit more complex on a four stroke because you need to know both the position of the crank fairly accurately, and you need to know which stroke you are on, so you either need a cam reference sensor or to do your position sensing on the camshaft, I was debating between trying to do that or just going Alpha-N but ended up never finishing the project. I think his project may have even lead to a modification of the extra code to allow choosing the timing of the map reading, but this was about 10 years ago so my memory is very hazy. Also no idea what sort of evolution the whole thing has had since then, but I doubt any capability was taken away.
 
Got a little progress on this project, Pump Installed and some motor assembly:

Clearance PVs
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Adapter Bearing:

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Laser Cut Cylinder Spacers:
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Other stuff:


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Layed up two hoods this weekend, The first one was way too flimsy at only 4 layers. The second one I used the rest of the carbon I had, making it 9 layers and an extra strip under where the pole pad will land. I would still like it thicker, but I think once I add a chamber for breathers it will stiffen it up to where I think it should last for a while.

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Inching along, cut some headshells, hopefully will cut some domes and double check squish on the cr500 pistons by the end of the week. they changed a bit since I posted the cad image, I figgured these cylinders have a thick enough flange to not need girdle studs , so might as well save that weight.


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What I found was a suspension bearing for a Kawasaki 4 wheeler, 92046-1290. It’s also listed other places as a ta202725 and sometimes as just a ta2025. I haven’t looked super hard but if you can find one with an oiling hole im sure that would be preferable. 20mm Id 27mm od 25mm thick
 
So, I did exactly what you did with the drive shaft. My boss at the time, a self made machinist, told me it would not work. Mark Ericson told me it would not work unless perfectly balanced. And still probably not. I had it trued to less than .001 of runout. It broke in less than 2 hours of riding. Trying to save you the hassle.

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So, I did exactly what you did with the drive shaft. My boss at the time, a self made machinist, told me it would not work. Mark Ericson told me it would not work unless perfectly balanced. And still probably not. I had it trued to less than .001 of runout. It broke in less than 2 hours of riding. Trying to save you the hassle.

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lol, well its in so I'll try it I guess. Although may be moving this project over to an eme hull thanks to my local used hull dealer @Rushford_Ripper and the amp will sit for a while longer, space may be a concern in the eme though hopefully I'll get some time to work on it this week or next
 
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