lobe seperation
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bsfc9
lobe seperation
would anyone care to comment on how engine CID effects camshaft lobe seperation angle selection?
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bill jones
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-If you are talking about big cube, racing only, normally aspirated and hi-compression and two valves per cylinder, then the way I see it is you need more cam than you can get and that requires basically as wide a lobe spread as you can buy just so you can get the valves to clear the pistons near TDC overlap.
-From what I've seen on the big chief 598's to 632's this is the primary problem, the engines always run faster with a larger cam and then trying to get it all to fit means you just can't run anything much less than about 115 lobe spread.
-But I've only been into about 5 of these engines so I'm no expert on any other reason.
-From what I've seen on the big chief 598's to 632's this is the primary problem, the engines always run faster with a larger cam and then trying to get it all to fit means you just can't run anything much less than about 115 lobe spread.
-But I've only been into about 5 of these engines so I'm no expert on any other reason.
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buddy rawls
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If you consider the displaced cylinder volume as a variable, and leave rpm, flow paths/cross-section, etc constant, then you will effectively have a stronger pull on the inlet path which will provide higher velocity flow. But will actually provide a tad less filling capability (given optimized valve events). If you look at the available inlet flow capability versus the cylinder pumping volume at equal rpms, this sort of leads to the set-up acting more restricted as the CID goes up. The typical trend in an increasingly restrictive inlet path would be to open the intake a tad earlier, and to delay the exh activity slightly. So LSA should decrease.
This is based on the valve events being optimized. IF the cam was not truly optimized for the scenario, then you can't make the assumption. Its possible that timing events (and associated LSA) were too narrow to begin with, and when you increased CID, the motor grew closer to the valve events. Lash tuning will give the hints as to which way the motor wants to go.
Buddy Rawls
This is based on the valve events being optimized. IF the cam was not truly optimized for the scenario, then you can't make the assumption. Its possible that timing events (and associated LSA) were too narrow to begin with, and when you increased CID, the motor grew closer to the valve events. Lash tuning will give the hints as to which way the motor wants to go.
Buddy Rawls
Buddy Rawls
Cross Section Engineering
Cross Section Engineering
IN MY EXPERIENCE WITH REGARDS TO LSA AND CID, IF I HAVE A GOOD FLOWING HEAD IN RELATION TO ENGINE SIZE, DON'T NEED TO GO OVERKILL ON DURATION BUT SPREAD OUT THE LSA, IMPROVES CYLINDER FILLING, BBC HIGH COMPRESSION NA MOTORS WAKEUP UP @ HIGHER RPM W/ WIDER LSA (114+), ALSO MOVES TORQUE BAND HIGHER ON THESE MOTORS. BIG CAMS LOVE BIG COMPRESSION,...LOW COMPRESSION AND YOU NEED TO TIGHTEN LSA...THIS AN EXCELENT SUBJECT FOR US MOTORHEADS...HOPE SOME OTHER GUYS REPLY...THANKS,..BOB
stand on it!
I look at LSA and beyond the clearance issues Mr Jones mentioned, I just see a way to place the opening and closing events. Whether one way is better than the other is all a matter of variables... some of which carry over into the intended use and car setup. Once you place the opening and closing points for optimal performance what's left to think about?
The IVC obviously has a big impact on the engine performance. Could mean low cylinder pressures at lower revs and perhaps a loss of torque in certain areas. So you definitely need to look at compression dynamically.
I'd just prefer hashing it all out with a program. Better yet, a program and a builder who has a lot of experience under his belt.
Regards,
Chuck
The IVC obviously has a big impact on the engine performance. Could mean low cylinder pressures at lower revs and perhaps a loss of torque in certain areas. So you definitely need to look at compression dynamically.
I'd just prefer hashing it all out with a program. Better yet, a program and a builder who has a lot of experience under his belt.
Regards,
Chuck
