I was considering an upgrade for my sr90 and just wanted to see what emitters would be a direct swap without messing with the reflector.
Would the stock driver power an 6v mt-g2?
I recently moded one.
You won’t have much of use for stock driver because stock LED SST-90 is ~3.2V led but requires huge current, not sure but I think about 8A or so and you won’t find worthy replacement LED, you can have much better performances from XHP leds that are 6V so you will need new driver.
One of the problems is that stock driver is e-switch only and you won’t find 6V driver that is e-switch only and starts in OFF position (when you screw down the battery you want LED to be OFF and then when you press e-switch it powers ON and switches modes). I was not able to find 6V driver (for XHP50, XHP70 and MTG2) with this behaviour, they are either meant to be used with standard clicky switch or with both clicky + e-switch. I didn’t want to drill battery pack and add clicky switch (it would be hard but doable, next to battery status button) so I made my peace that I will have to unscrew battery pack every time I want to power it off.
About the LED, because of the unique mounting of sst-90 you will have to do some modification to be able to mount some other LED, you can check out pics in this post
I used FX-30 driver and wanted to use XHP70 with it but ended up using MTG2 because I had one on 25mm mcpcb because that made much easier mounting it under large reflector (stock screw holes for LED also fit perfectly for 25mm noctigon mcpcb) and centering reflector with slightly modified stock centering ring. Reflector hole is less than 20mm so if you want to use standard 20mm mcpcb you will have to sand it down I think about 2mm or so… There are some more modification needed to fit standard mcpcb in there, it’s not straight forward job…
What kind of beam do you want?
If you want a bit more throw you could use an XP-L2 with the stock driver. If you want a lot more throw you could use an XP-L V6 or W2 de-domed (XP-L2 will probably be ugly when de-domed) also with the stock driver. Both will reduce the size of the hotspot. If you have an older SR-90 the brightness will also increase. If you have a newer SR-90 brightness will be very similar.
The MT-G2 will throw much less compared the the SST-90 and the hotspot will be a little ugly because of the large smooth reflector.
There are LEDs that will work great at 8 amps like the XP-L if they have enough cooling 
That’s true but you really have to have a good sample, plus you might get a slightly more lumens but because smaller die of XML2/XPL will have more focused beam with less spill and you will percieve that as less output than stock SST-90 Also, this is a heavy light with huge reflector and plenty of heat sinking mass and plenty of cooling fins, it is as made for more powerful LEDs and I wanted noticeable step up from SST-90. XHP70 would be perfect in my book but because mounting MTG2 was easier for me I used that LED and got really good results.
Maybe he wants a really long distance beam?
An XP-L HI at 8 amps would be pretty incredible.
Hopefully texas ace can test a XP-L HI some time, he’s only done non-HI so far.
I’ve run mine at 6 amps just fine, so I would expect it to easily handle 8 without dying.
It would provide similar lumen output to the SST90 so the spill will still be bright, just a tighter beam for more throw.
I had a SR90 for a while. Other than being huge it was a really nice light. It would turn off streetlights from a pretty good distance. I would first try dedoming it and see if you like it. You’ll get mutch more throw and it’s really easy to do compared to most any domed led.
I would modify the driver to do 6A and pul an XPL Hi in ti
I might be doing a group buy on sbt-70 LEDs that will be a thrower
There is no need to reduce the current for XP-L (2)(HI) LEDs. Maybe down to 7A to get more runtime, but generally it shouldn’t be a problem.
The problem with LEDs like the XHP-70 is that the light has a very big smooth reflector. Quad-Die LEDs will get you a version pronounced donut-hole. The hotspot will resemble a circle.
I also wouldn’t use an XP-L HI. De-domed XP-Ls are brighter.
I would use a dedomed xp-l, either V6 or W2, running at 6 amps to keep it safe.
Take out two of cells and wire the remaining four in series, then put in an XHP35 HI.
This would most probably blow battery level gauge and render stock charger useless but you can use LD-51 instead, input is 6-8.4V but you have to change e-switch with regular clicky switch…
I just checked the tests to be sure. What I said is wring to some degree. 7A is pushing it with the XP-L (HI). 9A is too much.
The XP-L2 on the other hand has ni problem with 9A. So if you simply want to replace the LED, this option is easiest.
I also recommend first de-doming the SST-90 and testing that. De-doming these is really is easy.
When you dedome an LED you will get a lot less output, like 15-30% less, so all the lumen advantage of the XP-L will be gone.
The LED will also be unprotected without anything covering the phosphor and will probably die sooner than the HI equivalent.
The goal is for improvements all around, more throw, brighter spill etc…
oh and my stock battery pack is rebuilt with 26650’s
It’s very likely less than 30%, that would be extreme. See here.
De-Domed LEDs have been used for around 5 years now. I have not read a single report on phosphor degradation or LEDs failing just because they were de-domed. Never. The reason is basically always too much current or heat.
This of course doesn’t mean that it is not possible, but it seems rather unlikely. The only important consideration in my eyes is that the LED needs to be handled more carefully, but lots of people manage to do that.
Also, XP-Ls are not very expsenvie. If one dies it shouldn’t matter too much (if you own an SR-90…).
Really? You’ve never seen what happens when you touch the die of a dedomed LED?
But why would you ever do that? The OP wants to put it into a sealed light. Many people here do that all the time.
The stock light makes ~2200 lumens, right? Emitters like the XPL will give more throw, but they will give similar or less overall output. If you really want a lot of light, a direct drive XHP70 will give you ~7000lumens. If you slice the dome off nice and close the throw will be pretty good too. As mentioned above, it will make a donut hole beam to some extent.