Got it. Makes sense. I wasn't sophisticated enough to even consider Duration. Combined with proper valve overlap so that escaping exhaust gases can help pull in the intake mixture, I see what you're saying. Always like to learn. Thanks!

 

Right. Marcelino's mod results in more valve overlap, though I don't think it's the increase in overlap that is the main factor. If anything, cams designed for best power at 4 to 8K rpm would have less overlap, or not more than the OEM setting. Marcelino's mod would be a compromise if I am right (read it as a better compromise as the OEM setting).

I expect it's the earlier intake valve closure that brings most of the benefits (52deg ABDC with Marcelino mod, versus 62deg OEM). Then, late exhaust opening also provides some benefit. As Marcelino said, the OEM setup is optimal for high rev engines (12K, more?). But the intake tract is tuned for 7Krpm, thus there is no point in having the cam timing optimized higher than that.

One word to put weight on my sayings: I am not a mechanic. Like TNC, I've been into engines for fun in the past (long time ago). But I am involved in engine electronics since more than five years. Also, I can apply the laws of physics to practical situations better than the average people, being a physicist in real life.

That being said, I would expect Marcelino's mod to be less effective on a big bore, unless one puts bigger valves. With a bigger bore, air velocity is greater at a given rpm, thus the same 62deg ABDC will be more adequate at 7k-8krpm, compared to the 250cc bore. That could explain the OEM setting, since our engine was born as a 300cc.

I am not sure if I made that clear, I am a physicist not a lecturer. Your comments are welcome

 

I am not sure if I made that clear, I am a physicist not a lecturer. Your comments are welcome[/QUOTE]

Vellly intellllestink. (Remember Sargent Shultz from Hogan's Heros?) Love hearing physics theory. Sometimes, reality makes us rethink theory until we get the theory correct. But, what you said makes sense to my limited knowledge mind. Thanks for taking the time...

 

It was born as a 250, 1993 through 1996 was 250 only. In 1997 Kawi put the bigger jug on it. Same cam spec's in both sizes.

Ride on
Brewster

 

I stand corrected. Do you know if the earlier version was a higher rev setup? For example, if it had more timing advance?

 

There are a few variables, year, engine size, and what countries the bike was going to.

250-D series
5 BTDC to 40 BTDC at 3000 rpm

250-E series
5 BTDC to 35 BTDC at 5000 rpm

300-A series
10 BTDC to 40 BTDC at 3000 rpm

Ride on
Brewster

 

Yeah, now that you mention it, I remember WestOz publishing some numbers in another post. They don't say much to me, other than our engine went through a very strange path along the years...

 

Thanks for bringing this to my attention. Been busy--so not much chance to study up on it yet. Got any suggestions for a good, reliable source of info?

 

Finally had an opportunity to go over it. Yep, I stand corrected. The offending post has just been edited. Mea culpa...

Thanks, ZW.