Originally Posted by
John_M_
Thats part of the reason, and why the cams can't be interchanged, if they could they would have the same part#... exhaust valves open early before bdc on the power stroke to blow down the cylinder combustion pressure before the piston starts the exhaust upstroke... thats done so the piston doesn't start to re-compress the expanding exhaust gases, which rob power from the next cylinder's combustion / power stroke., valve duration effects overlap and exhaust reversion / and induction standoff.... saito's known for their aggressive cam profiles, they mimic RW engine performance profiles why I was surprised the prototype shared the same valve timing for both cylinders
.
I only owned 4 saito's,. a .50GK, 1.30TD, 1.50s, and 1.80 NIB.... gave the 1.50s to a flying buddy, and sold the 1.80, I never had plans to used it, as I like the larger giant scale aircraft... I dislike the AAC's so I stopped purchasing saito... and they continue to disappoint with the 100TS having composite cam lobes.... otherwise they're nice performing engines.
Thanks John, helpful info.
Having a closer look at the 2 two cams yesterday it appears I was wrong, the lobe separation is the same, so close I can't see a difference without measuring. The cams do have different part numbers, true, but it may be only because the timing marks on the gears are in different places?
So, thinking on this further there is a difference between an even fire flat twin and this even fire IL twin.
On an even fire flat twin the right cylinder configuration is identical to a single cylinder engine i.e. the cam is turning the same direction and the ports are on the same side. The left cylinder has the cam turning the same direction but the ports are reversed. That's what dictates the need for two different cams, each having different lobe separation angles. That's what I'm hearing anyway. So:
The front cylinder of the even firing 200 IL twin is configured just as the left cylinder of a even firing flat twin i.e. cam rotating same direction as a single but with ports reversed. The rear cylinder (
when viewed from the rear of the engine) has the ports on the same side as a single HOWEVER, the cam is rotating backwards. This where things get confusing to me. Wouldn't the front and rear cylinders then use the same cam but get timed differently? The two cams I have appear to be just that, same cam profile but with different cam timing mark locations.
Sorry about the way I write, I'm not the best at communicating my thoughts.