Main goal: lower the engine oil temperature without using extra oil cooler. I believe that an oil cooler is fighting the symptoms instead of curing the disease. In the past I have ported a Moto Guzzi V50. The main goal was achieved. As a "bonus", the bike also got extra torque and power. Now I did the same with the TTR. To get to that result, I concentrate mainly on the exhaust gases. The idea it to get the hot gasses out of the engine as soon as possible to prevent them from heating up the cylinder head.
The engine: the bottom end of the engine is original TTR engine with 65.000km on the clock. The complete top end (cylinder, piston, cylinder head) is from a XT600 2KF from 1989 with 40.000km on the clock. The camshaft is standard, the CDI is standard, the compression is lowered, the carburetor is standard.
The modifications
Inlet:
- inlet valves from a Ducati 916 because of their slimmer profile
- replace air filter for a single layer TwinAir foam filter
- removed the snorkel from the air box
- enlarged the intake hole in the air box to maximum
Combustion chamber:
- removed all the high material between the valves
- removed material around the sunken exhaust valves (this is only in the 2KF-cylinder head, not in an original TTR cylinder head)
- removed squish edge around the exhaust valves
Exhaust:
- exhaust valves from Hyundai, 6mm valve stern (with 6mm valve stern guides from BMW), 25 degree back-cut on the valve dish
- exhaust valve seat inside material removed (see image) to 29.6mm diameter (OEM: 26,9mm diameter)
- removed material from exhaust port over the full length to 35mm diameter at the end (OEM: 30mm diameter)
- custom build exhaust system. Exhaust header made from stainless tube 38x1,5mm (OEM: 31x1,5mm) and link pipe from stainless tube 51x1,5mm (OEM: 41x1,5mm)
- exhaust silencer from Yamaha R1 2002 with the catalytic converter removed
The carburetor is tuned on a dyno meter. The results are 41bhp @ 6900rpm and 48Nm @ 5300rpm at the rear wheel
On this website there is a power diagram from a original TTR (with the CDI wire disconnected). That one has 35 bph and 42Nm (4.3kgm x 9,81). That is an increase of 6 bhp (17%) and 6 Nm (14%)
Unfortunately I did not measure the performance before the modification. To compare the results, I took the diagram from this website about the CDI disconnected wire. To compare, I have plotted the blue line on that diagram, and the results from my bike in a Excel diagram. Off course this is NOT a perfect comparison. Somehow on the original diagram the engine runs a maximum 7200rpm. On the dynometer my engine runs a maximum of 78000rpm. If I shift my diagram to a maximum of 7200rpm and put it in the same diagram as the original, this is the result:
Off course there is more power to win with a special cam shaft and Mikuni flat slide carburetors, but that stuff is expensive! The modifications that I made are reasonably affordable. Most of the stuff I could do myself in my garage with a welding machine and a good quality Dremel.
The main goal: lower the oil temperature! During the dyno testing the oil temperature did not go over 80 degree Celcius. Next summer on during offroad driving it will become clear if the engine really stays cool under every condition.
Extra goal: the Yamaha R1 exhaust silencer is extremely quiet!!!