I have a 85 250r and it seems really fast compared to the other bikes I have ridden,but I was wondering how
it would compare to the trx250r that every body seems to compare ther atv's too. Does it have the same
engine or are they two totally different bikes? Any info would be appreciated

 

The 85/86 ATC 250R's has the same engine as the 86-89 TRX 250R's. There were some minor changes between the years(clutch, head, cylinder, piston) but almost all parts are interchangable. The ATC's have a little more compression due to a slightly thinner head gasket. I have an 87 TRX with my 86 ATC engine in it and have no problems.
All year engines bolt in any year frame ATC or TRX. The ATC's probabally are a little faster due to their lighter weight.
ERIC

 

I have an 88 250R, and an 86 ATC 250R. The 88 motor has a longer stroke, and the gearing is a little taller than the 86 motor. I race motocross on the quad, and ride in Glamis in the ATC. I decided to swap the motors. This worked out really well. The 86 motor has more bottom end, so it is great for MX. The 88 motor has more top, so it is awesome for the dunes.

 

The 88 does not have a longer stroke than any of the other ATC/TRX motors. The '87-'89 engines had a longer rod (by 5.0mm), but NOT a longer stroke. They all have a stroke of 72mm. And, the internal transmission gearing is higher in the ATC motors, not in the TRX motor.

 

OK, I stand corrected, I never claimed to be a mechanic. I guess the point was that the change worked out nicely because the 86 trike motor suited MX and the 88 TRX motor suited the desert.