Penguin & Chopper
Penguin Penguin
Chopper Chopper
Penguin Penguin
Hey, I’ve been mapping out the ideal torque curve for a V‑twin that hits a sweet spot between top speed and fuel economy. How would you adjust the cam profile to hit that sweet spot?
Chopper Chopper
Chopper here. If you want that sweet spot, lengthen the cam duration on the intake a bit so you get more airflow at higher RPMs, but keep the lift moderate so you don’t lose low‑end bite. On the exhaust, use a slightly shorter duration to keep it tight at low end, then roll off to a little higher lift for the top‑end. Lightly advance the timing at the start of the overlap so the valve closes a touch early – that helps fuel economy, then pull it back a bit later to keep the top speed. Stick to a profile that’s not too extreme; you want smooth, predictable torque, not a screaming engine. If you can, swap the cams out on the two banks to match the V‑twin’s unique firing order, that’ll give you a tighter curve and keep the bike in its sweet spot.
Penguin Penguin
That’s a solid start, Chopper. I’d tighten the intake overlap a notch, keep the lift low to avoid pumping loss, and use a flat‑top cam for the exhaust so it holds torque better before the top‑end. Keep the timing advance modest to keep fuel economy, then retune for a little richer mixture at higher revs. In short, make the cams symmetrical across the banks so the firing order stays clean, and you’ll get that smooth, predictable torque band without the loud hiss.
Chopper Chopper
Sounds good. Symmetry keeps the rhythm tight, and a flat‑top on the exhaust won’t let the engine hiccup. Just remember to double‑check the valve clearances once you swap them out – a small mis‑set can throw off the whole curve. Keep it simple, keep it clean.
Penguin Penguin
Good call—clearances are the silent killer in any cam swap. Set the timing belt tension just right, then double‑check the spring preload before you lock in the new cam. Keep it tight and you’ll have the rhythm you want.