My 06 Tundra 300 isn't vintage, but I'm thinking I might get a little more help here with the motor.
While it's not the most likely candidate for modifying, I've been enjoying playing with my Tundra and it's keeping my brain cells active learning new stuff. Now I'm looking for a little help on the Rotax 277. Keep in mind this is a newer version with CDI.
I hadn't planned on engine work but the original exhaust rusted out and at $650 for OEM, thought I'd just get an aftermarket pipe..... and if doing that, might as well get it tuned for a higher rpm, which meant the engine would need a little porting as well... and of course might as well do some head work if I'm doing all that..... Funny how that works.
So, it's ported to 7,500 from 6,800 and .040 was removed from the head and .020 from the squish. This was done by Aaen Performance. There was improvement, but the timing was at about 6 degrees at 7,000 rpms and 16-18 was recommended with the increase in rpms, so after running it with no issues one winter, I sent the CDI out to get reprogrammed. I decided on 12 degrees at 7,500 rpms with was a little more conservative. I started running into what appears to be detonation issues on hard pulls, even with 93 octane. Damage to the very edge of the piston causing scoring and then seizing up. Nice thing about a single is it doesn't take much get it back running.
At first, I thought I needed to take a little off the squish to reduce compression, but after doing some reading, it seems that the squish is actually to much at .075. So now I'm thinking another .010-.015 off the head, but I'm concerned as the compression will be higher yet. I borrowed what I hope is an accurate compression gage and it reads 125 psi with the modded head and 110 with a stock head. Seems like 110 is about right stock, but I can't find info on that and 125 seems low for the modded head?
Any thoughts on all this?