Over the years most manufacturers have made lots of improvements to Cylinder port shapes. Most cylinders can actually flow worse, if you grind /polish the area,s from under the cylinder. If you take material away, you may decrease bottom to mid power, as this effects the primary compression ratio. This can be corrected with case stuffing. Without a good small Dyno, you may not realise whats happened. The curves in the transfer ports have now a more tighter curve, increasing the slug volume speed into the cylinder, KTM have pioneered this design which works really well, and yet the ports look small! High air speed is gained. Most surface finnishes on modern cylinders cannot be changed, to gain power. Even the exhaust expansion chamber inlet is now smaller than ever, on late model pipes, keeping air speed high. However, there is still work that can be done, port windows, chrome rough edges, and the whole exhaust port can be changed that yields good power improvements over most of the rev range. Cutting through the chrome is tricky, most engine porters now using some lubrication/cooling method, so as the chrome plating is not being effected by heat and vibration. Dyno testing with many cylinder port shapes, sizes, heights etc is done to make sure the power is gained. So before you grab that file, or porting tool, call and have a chat, we can hopefully save you some time.
Some engines 85cc 125cc 150cc 250cc need to use more stronger/robust type spark plugs.
If the engine has higher internal pressures, excessive crankcase stuffing, too high compression ratios, incorrect crankshaft balance factor, Detonation, engine frequency type vibrations/pulses can harden and weaken the earth electrode and it will FALL OFF causing expensive damage.
Some modern engines are already made high performance from the factory and pressures are really high and they need better spark plugs. Some 85cc and most larger 2 strokes will need these plugs. part number NGK R6918B-9 is one of the best choices. $60.00 each. Replaces BR9EIX or BR9EG or BR9EV or BR9ES etc. ( 9 ) is the heat range ,so you can buy 8,9,10 heat ranges normally.
Be careful, if the bike comes from the factory with a R6918 type plug,(like the current model Suzuki RM125) dont put a cheaper plug in as you will reduce performance and damage the engine.
In winter you always need to increase fuel supply. Approximately 5% richer.
Balance factor is different from sizes of engines. Change of the factor will change the power curve.
The new VP Roo Fueld makes combusion and mixing temperatures cooler. Good for 2 strokes! Must change jetting approx 6% richer. Best to increase compression too. Good for 4 strokes too.
Note: Race Fuel Above 100 – No point using it. Fuel testing will be done at Australian and FIM Wold Championships.
The benefits you can achieve by having components treated include:
HGS Exhaust. VHM Cylinder Head. 185-190 main jet. Ignition timing 1.1mm BTDC.
The European exhausts are the best tested on the dyno and at the track. The scalvini produced good power in the top end, and the engine needs to be tuned for this type of power, the pipe is thin and will get damaged easily , the damaged pipe will have a loss of power. Van Hasselt exhaust is specially designed for MX, best mid range power and easy to race , and the construction is good. the HGS has the best top end power out of all the pipes, but engine must be tuned to suit this for the rider. All pipes have more power than the stock pipe. USA pipes, euro pipes included. USA pipes crack alot. Euro pipes are stronger and make more power, but are not coated and rust easily. Most of the power increase comes form the pipe, not the silencer . The silencer does change the engine noise alot, but the dyno tests show no big power changes are made.
Some pistons on the compression side do not have a wear band-ring. You can order one from the rebound side and machine the piston to fit it so you have smoothness on compression (as it should be). Common SX65. Shivers have this as standard.
Note: Only use Mazzoochi Seals (a lot less drag).
Many different production types. Example: KTM Vertex is not the same piston as Vertex after-market type. Check weights!