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long discussion with KTM tech department on the SX-F engines.
Huge power improvements by retiming the cams !
Lobe centres
· 103 inlet stk is around 107
· 105 exhaust stk is around 108
Now lets be very very clear here, there is no way I can validate or verify this, use at your own risk.
There is some variation in the stock cam settings from the factory and an engine with flat power delivery is often found to be out of spec on the cams (boy I sure hope so !!!)
Cams are pressed onto a taper and held with a retaining nut , no keyways, very easy to retime. KTM make a special tool that inserts into the crankcase (remove allen headed inspection bolt) that then engages into a recess in the crank to lock it at TDC, nice. Procedure is in the 450 SX-F dirtbike work shop manual.
Extreme care to be taken with the camshaft towers, these must be torqued to factory settings with a quality torque wrench and cams checked that they easily moved in end float.
Problems have occurred with excessive tightening leading to seized cams / ruined heads
Recommend KTM 505 setup. This information was provided based on a typical recent 505SX-F build with the emphasis on mid range muscle rather than top end shriek...............
Reliable 58 hp @ 9000 with strong over rev to 11,000
37 ft lbs at 7000 rpm
3 hp improvement over stock at 4000 rpm and stronger through out the power band from there after.
Stock Cams, Cam Shaft Lobe centres
· 103 inlet
· 105 exhaust
Full Akro exhaust, Akro head pipe SX-F type is the key to the gains. Good power also seen with full FMF systems.
Head work; mild port and clean up, porting is aimed at mid range torque improvement not top end increases.
41mm carb is plenty. Bigger only favours top end, emphasis on this build is mid range muscle
limited - minimal gains with CDI changes (Wolf or Vortex) tends to tame power down rather than add more power.
Unplugging the CDI brown wire, no to nominal change in peak power but slows acceleration in the low end - mid range - softens the hit. Marginally better in low traction greasy conditions.
13.5:1 compression. Machine 0.3mm ?? off base of cylinder to get 13.5:1 from stock piston. Apparently no problems with valve clearance with these engines. Minimum 98 octane race fuel. Would not go higher as detonation can be an issue inthe 2 wheelrs, quad with the higher loads will be more prone to deto risk
Recommend CP or Wossner pistons. CP 450 only at this stage. Wossner does both 450 and 505 pistons.
http://www.woessner-kolben.de/english/indexenglish.html
Piston change out 20 hours at pro level use, 10hrs desert racing with extended wide open throttle / hi ambient temperatures. High risk of piston cracking if engine life is pushed out past 20 hrs in fully built race engines / sustained high rpm usage.
Guess what I'm going to be doing in the new year..................
Huge power improvements by retiming the cams !
Lobe centres
· 103 inlet stk is around 107
· 105 exhaust stk is around 108
Now lets be very very clear here, there is no way I can validate or verify this, use at your own risk.
There is some variation in the stock cam settings from the factory and an engine with flat power delivery is often found to be out of spec on the cams (boy I sure hope so !!!)
Cams are pressed onto a taper and held with a retaining nut , no keyways, very easy to retime. KTM make a special tool that inserts into the crankcase (remove allen headed inspection bolt) that then engages into a recess in the crank to lock it at TDC, nice. Procedure is in the 450 SX-F dirtbike work shop manual.
Extreme care to be taken with the camshaft towers, these must be torqued to factory settings with a quality torque wrench and cams checked that they easily moved in end float.
Problems have occurred with excessive tightening leading to seized cams / ruined heads
Recommend KTM 505 setup. This information was provided based on a typical recent 505SX-F build with the emphasis on mid range muscle rather than top end shriek...............
Reliable 58 hp @ 9000 with strong over rev to 11,000
37 ft lbs at 7000 rpm
3 hp improvement over stock at 4000 rpm and stronger through out the power band from there after.
Stock Cams, Cam Shaft Lobe centres
· 103 inlet
· 105 exhaust
Full Akro exhaust, Akro head pipe SX-F type is the key to the gains. Good power also seen with full FMF systems.
Head work; mild port and clean up, porting is aimed at mid range torque improvement not top end increases.
41mm carb is plenty. Bigger only favours top end, emphasis on this build is mid range muscle
limited - minimal gains with CDI changes (Wolf or Vortex) tends to tame power down rather than add more power.
Unplugging the CDI brown wire, no to nominal change in peak power but slows acceleration in the low end - mid range - softens the hit. Marginally better in low traction greasy conditions.
13.5:1 compression. Machine 0.3mm ?? off base of cylinder to get 13.5:1 from stock piston. Apparently no problems with valve clearance with these engines. Minimum 98 octane race fuel. Would not go higher as detonation can be an issue inthe 2 wheelrs, quad with the higher loads will be more prone to deto risk
Recommend CP or Wossner pistons. CP 450 only at this stage. Wossner does both 450 and 505 pistons.
http://www.woessner-kolben.de/english/indexenglish.html
Piston change out 20 hours at pro level use, 10hrs desert racing with extended wide open throttle / hi ambient temperatures. High risk of piston cracking if engine life is pushed out past 20 hrs in fully built race engines / sustained high rpm usage.
Guess what I'm going to be doing in the new year..................