Hopefully everyone is having a good Monday!  We've been blessed with some warm weather in Minnesota, and I've been riding my 360 with the rt1mx top end.  

I recently put this rt1mx top end on the bike, it was swapped from an rt2mx top end.  I am using the rt1mx gyt pipe.  Anyway, im very content with the low end torque, and initially was pleased with the results.  Now im getting into some real issues.  For the record, ive moved the timing down to 2.3mm, it called for 2.9mm stock.  When it gets warmed up, running 91 octane no ethanol, I can hear detonation from time to time.  Regardless how much timing I pull out of it, it still does it.  I'm not looking to wreck the engine, and I'm not interested in running higher octane either.  

Yesterday I swapped my stock rt1b head onto it.  The "detonation" went away, but so did a good amount of torque, and it definitely took a solid 500 rpm off the peak rpm, and made it really burbly up top.  

I'm about ready to put this engine engine back to stock, but figured id get your opinions first.  I really like the rt2mx top end, but it NEEDS the rt2mx pipe to run right.  And the rt2mx pipe does not fit on my rt1 frame, with the fuel tank on..  I feel the time has come, I need to learn about designing 2 stroke pipes.  Anyone have a good option on where I should study that stuff?  Thank you!

94 RON from Sunoco or Mobil
Both 10% max ethanol

No matter how much timing you pull-out?
Makes no sense

and you want more perf.

Umm.

cliff

Rt head is low comp.
Low compression with a upped RPM band is low torque, automatically.
 

I think you need to measure your squish clearance with the original head on if it is pinging no matter the timing.

Sounds like it might be a little tight. If so, maybe a slightly thicker head gasket or even better a slightly thicker base gasket to add a bit more at the top.

Curious under what conditions you're hearing detonation?

Automan, yeah exactly how I put it.  It makes a noise that sounds kind of like spark knock.  But seeing as it doesn't go away by retarding the ignition timing, I have to assume it is a detonation issue.

Tinkicker, in my opinion it seems loose.  It doesn't even touch a piece of .080 solder.  Ive always been told tight squish is happier, so maybe that is a place to look.

Markt, it's in the lower rpm band that I can hear it, when i twist the throttle.  Its only briefly when i initially twist the throttle, at lower rpm.  If the rpms are up, or if I'm winding it out, I don't hear it.  It's not consistent like a spark knock.

Automan, to further elaborate, ive determined the exhaust port closing to be very similiar, if not the same, between a stock rt cylinder, and an rt1mx cylinder. That is why I decided to try it. The torque production is very similar to a stock enduro with the stock head, no surprise here. What really surprised me is how much the top end suffered. I actually thought it might stay the same, but it actually cut the peak power off by a solid 500 rpm.

If you have a genuine MX cylinder and an unmolested Enduro cylinder, the exhaust port timing is not the same. 

I agree you likely have too much squish clearance.  From what you said the clearance exceeds, you might as well not have a squish band at all.

Do you know of any way I could ID the cylinder?  The cylinder head has a 284 cast into it, and from what I've researched, that is a rt1mx head? My original rt1b head has a 275 cast into it.  Honestly I have questioned the cylinder, perhaps it's a 1970 rt1 jug without the compression release?

Well I'm gonna pull it back apart and do some actual measuring. I remember the port shapes looking bigger on the "rt1mx" cylinder. The only thing i measured was the exhaust port closing timing, and I compared it to an rt3 cylinder. I'll have to dig my rt1b cylinder out and measure that. Someone did a really good job cutting the fins to fit the rt1mx pipe, if it's not a rt1mx cylinder. It looks identical to any I can find in pictures.

RT1MX exhaust port should be about 2.4mm higher, which might not seem like much but even one mm can make a big difference. 

Transfers on the MX are about 2mm higher.

Your problem could simply be jetting...  might be going lean when you open the throttle.  When diagnosing, important to know the carb slide position when starting to open the throttle.  For example, if the "detonation" happens when the throttle is opened from almost closed, then a richer pilot and/or lower slide cutaway might be what you need.  If it happens when at half throttle initially, then raising the needle might help.

(Some Yamaha MX models seems to come with overly rich pilot circuits...  I've jetted the idle circuit "correctly" but using a smaller pilot jet than specified only to have issues like pinging or even stumbling when opening the throttle.)