06-06-2018, 09:03 AM
I'm going to guess the crank timing and TDC is the same across all 4, but only the factory knows for sure.
While a normal engine times the ign across all cyl a certain degree BTDC, changing the cam timing can change where optimal ign timing is set. But just like the cam timing being slightly mismatched, having the ign timing off a bit in either direction isn't a big deal- unless you advance enough to detonate (not pre-ignition).
You can rock most settings slightly- cam timing, ign timing, fueling rich or lean to little effect.
Heck, for all I know just by changing the duration and lift- therefor effecting the charge pressures, maybe overlap, scavenging, etc- it is possible the factory ign curve will no longer be optimal as is. I don't care- and wouldn't expect it to make a huge difference anyway.
There are soo many variables to engine design, operation, modifications, tuning. Luckily in modern computer designed engines as long as you don't stray far from what the factory designed not much of that matters in the real world. It is when you start pushing the limits that it really takes on a whole new world of complication.
Example- I am leaving the cam timing alone. I am not putting in huge cams. I am not raising the rev limiter.
So- I shouldn't have to worry about valve float, valve spring coil binding, piston pocket clearance, but stuff still changes- cams allow more air, which needs more fuel, but I am *possibly* also lowering my dynamic compression ratio at lower rpm (static will stay the same)..and might be increasing it up top due to scavenging and velocity. All depends on overlap which I admittedly haven't bothered to delve into.
I could spend a LOT of time doing all sorts of calculations and measurements, tearing my engine apart or buying pieces off Ebay for benchwork- but I've been doing that for decades and luckily have learned enough to know when it matters and when it doesn't.
This is by no means a race bike. There are plenty of bikes now if you want 200hp.
For what I am trying to achieve- just a more natural old school engine breathing before emissions and cats required very mild cams and lean fuel limiting both power generation and cooling purposes on our air cooled.... nothing extreme is needed.
I think 100whp will be broken though.
While a normal engine times the ign across all cyl a certain degree BTDC, changing the cam timing can change where optimal ign timing is set. But just like the cam timing being slightly mismatched, having the ign timing off a bit in either direction isn't a big deal- unless you advance enough to detonate (not pre-ignition).
You can rock most settings slightly- cam timing, ign timing, fueling rich or lean to little effect.
Heck, for all I know just by changing the duration and lift- therefor effecting the charge pressures, maybe overlap, scavenging, etc- it is possible the factory ign curve will no longer be optimal as is. I don't care- and wouldn't expect it to make a huge difference anyway.
There are soo many variables to engine design, operation, modifications, tuning. Luckily in modern computer designed engines as long as you don't stray far from what the factory designed not much of that matters in the real world. It is when you start pushing the limits that it really takes on a whole new world of complication.
Example- I am leaving the cam timing alone. I am not putting in huge cams. I am not raising the rev limiter.
So- I shouldn't have to worry about valve float, valve spring coil binding, piston pocket clearance, but stuff still changes- cams allow more air, which needs more fuel, but I am *possibly* also lowering my dynamic compression ratio at lower rpm (static will stay the same)..and might be increasing it up top due to scavenging and velocity. All depends on overlap which I admittedly haven't bothered to delve into.
I could spend a LOT of time doing all sorts of calculations and measurements, tearing my engine apart or buying pieces off Ebay for benchwork- but I've been doing that for decades and luckily have learned enough to know when it matters and when it doesn't.
This is by no means a race bike. There are plenty of bikes now if you want 200hp.
For what I am trying to achieve- just a more natural old school engine breathing before emissions and cats required very mild cams and lean fuel limiting both power generation and cooling purposes on our air cooled.... nothing extreme is needed.
I think 100whp will be broken though.