I guess it's time we get back to dyno results.
I summarized all dyno charts (most relevant) in a single excel file to be able to compare power and torque curve. The bluish curves have been obtained with the stock 411cc (78mm piston) engine, those yellow/orange/red with a 477/471cc (84/83.5mm, Indian made) and the green ones with a 443cc (81mm piston, Indian made). As usual credit for time, money and effort goes to
@Dool !
Let's analyze the data.
On a stock bike, it’s sufficient to remove all flow restrictions given by the stock air filter with the snorkel and the stock header pipe with cat converter and silencer (a DNA filter with open flange and a Delkevic exhaust pipe with free flowing silencer have been used) and add a more lift/ more duration camshaft (Himalayan-tools), using a simple FuelX to take care of fuel, to get to a gain (in percentages) of 24% in terms of power, although only 17% in terms of torque. This is because the higher “breathing” capacity of the engine is better suited to the higher RPM range!
The yellow curve shows a bike with only a bump in displacement to 477cc (and a red box unit for fuel), with aftermarket silencer and free flowing filter but with stock camshaft an exhaust pipe (with cat converter). Low RPMs torque is increased substantially but at medium to high RPMs, starting from 5000RPM, it starts to drop fast due to the insufficient ability of the system to get rid of exhaust gases, due to both cat restriction and insufficient time/lift of the valves.
It's sufficient to remove the cat converter in the exhaust pipe (using a Delkevic header) to gain between 1,5 and 2,5 hp along the curve, keeping all the other variables equal. At low RPM the torque is unaffected, in this case removing the cat converter has only benefits performance wise. Incidentally the maximum value for power is very similar between the orange and the dark blue curve, HOWEVER the driving perception is very different! Despite a comparable power gain (+24% blue vs +26% orange), the torque gain is doubled (+17% vs +34%) and it happens at lower (more usable) RPMs!
The red dotted line and the red continuous line represent basically the same configuration, specifically the orange configuration but with the addition of the Himalayan-tools camshaft. Both have been shown to underline the importance of map tuning, specially advance timing. Optimizing the map there are 1,5 to 2,5 hp of power to be gained and 1 to 4Nm of torque more, depending on the position on the curve.
In the case of the continuous red line, comparing to the stock bike, the gain is +38% powerwise and +48% torque wise, with a torque curve almost linear at 40Nm up until 5000/5500 RPMs! There are two months in terms of time between the two tests, during the first trial I was young and foolish!
The green line represents, finally, the maximum you could gain from a 443cc engine (Indian made) to which all possible improvements have been applied: all the other mods cited before plus bigger valves, ported head, bigger throttle body from a Continental GT535, airbox delete and a stage 2 camshaft from Hitchcock Motorcycle (the best performer overall according to our tests, so far...). The bike in this configuration runs without any loss of power up until the limiter at 8000RPM, with a torque curve (although lower than the previous case at 35-38Nm) nearly constant up to 6000RPMs! +37% of torque compared to the stock bike and almost +50% of power (ok, it’s +48%...).
Unfortunately we haven’t tested a similar configuration but with the 477/471 instead of the 443, but speculating a bit we should be on similar or slightly higher torque values w.r.t the red line, but extended up to 6000RPM, for an overall power of approx. 34hp. Anyhow this remains a speculation until when we’ll test it for real, if ever.
@Dool had a promising 500cc and the only dyno available shown impressive torque down low, but unfortunately the inlet manifold had an issue, hence the results above 5500 are rather useless (although around 32-33hp...)
In conclusion: if you’re fond of the red line zone, consider adding a camshaft and a dekat pipe (free flowing filter and aftermarket exhaust are taken for granted). If you want torque down low, instead, as the American use to say “there’s no replacement for displacement!”.
, my guess is Taiwan or China, this does not matter as long as they perform well.
