R
Ric
Guest
So after reading through the service manual for both bikes, I found that the 250 actually has a hotter cam grind than the 300. Both have the same 7mm lift, but the 250 has a duration of 280? while the 300 has 260?.
If I recall correctly, the 250 produced 27 hp at 10,000rpm(over 100hp/L). I've never seen power specs for the 300, but being a bigger engine with a milder cam profile I'd say it makes comparable power at considerably lower rpm. Understanding that I'm never gonna set records at the dragstrip with this thing, I do want it to perform well. So after doing some basic math - assuming 100%VE for simplicity's sake - I calculated that at 10,000rpm the 249cc engine moves roughly 43.9667600683cfm of air. Using the same parameters, I calculated that the 299cc engine would move the same amount of air at 8,327.7591973244rpm. If real-world calculations would be similar to these figures, then I am greatly tempted to drop some cabbage on a set of OEM 250 cams for the 300.
I totally get that the 250 likely struggled at lower rpm. That's to be expected with an overcammed engine. I also get that the compression ratio was markedly higher in the 250 than in the 300. I think some clever head millwork could close that gap. But considering that the 300's 9000-rpm redline is a bit conservative(it uses the same valvesprings as the 4V 750, which redlines at 9500rpm), an 8300-rpm peak airflow seems very useable. Especially since I have it properly tuned for the K&N pods and straight-flow mufflers on it, and it just doesn't pull at high rpm like it does at mid rpm. I'm okay with giving up some down low since the bike is already spooled up pretty high at cruising speed... almost as if it's already peaked out, making downshifts almost futile.
I kinda have a running theory that more cam doesn't always cost in low-end power so much as raise the power curve in the rpm range. In fact, I've seen cammed engines build more low-end power, and since the power curve moves higher in the rpm range the engine made MORE power there. The key is not to go over the top with your setup, and I find myself stoked to test this out on the bike.
So... am I crazy? Or might I be onto something here?
If I recall correctly, the 250 produced 27 hp at 10,000rpm(over 100hp/L). I've never seen power specs for the 300, but being a bigger engine with a milder cam profile I'd say it makes comparable power at considerably lower rpm. Understanding that I'm never gonna set records at the dragstrip with this thing, I do want it to perform well. So after doing some basic math - assuming 100%VE for simplicity's sake - I calculated that at 10,000rpm the 249cc engine moves roughly 43.9667600683cfm of air. Using the same parameters, I calculated that the 299cc engine would move the same amount of air at 8,327.7591973244rpm. If real-world calculations would be similar to these figures, then I am greatly tempted to drop some cabbage on a set of OEM 250 cams for the 300.
I totally get that the 250 likely struggled at lower rpm. That's to be expected with an overcammed engine. I also get that the compression ratio was markedly higher in the 250 than in the 300. I think some clever head millwork could close that gap. But considering that the 300's 9000-rpm redline is a bit conservative(it uses the same valvesprings as the 4V 750, which redlines at 9500rpm), an 8300-rpm peak airflow seems very useable. Especially since I have it properly tuned for the K&N pods and straight-flow mufflers on it, and it just doesn't pull at high rpm like it does at mid rpm. I'm okay with giving up some down low since the bike is already spooled up pretty high at cruising speed... almost as if it's already peaked out, making downshifts almost futile.
I kinda have a running theory that more cam doesn't always cost in low-end power so much as raise the power curve in the rpm range. In fact, I've seen cammed engines build more low-end power, and since the power curve moves higher in the rpm range the engine made MORE power there. The key is not to go over the top with your setup, and I find myself stoked to test this out on the bike.
So... am I crazy? Or might I be onto something here?
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