As a offshoot to the thread about the as yet hypothetical direct drive V8 idea:
If I'm building an engine based on a common V8 there are literally hundreds, if not thousands of cam choices out there. I went down a rabbit hole the last couple of weeks and looked up everything there is on cams on the net.
The variables are of course: Duration, lift and lobe separation angle/overlap, advance/retard.
The internet and youtube is full of self-proclaimed gurus who think they know all the answers but there is very little consistency or scientific basis among their ideas. And nobody builds engines for this kind of low rpm/moderately high load application, they are all out there building monster hot rods. Some cam calculators out there give very weird numbers, so I'm not going there.
Using common rules of thumb I'd want something with low LSA, low to moderate duration and moderate lift. I've looked at literally hundreds of dyno charts and getting this wrong will easily throw away 20-30 hp. My goal is a healthy margin of 200hp, hopefully 230.
Interestingly, I looked up a few aircraft engine cams and got a few figures:
Gypsy Major, 6.1L -122hp @ 2550 - Duration 271/271/LSA 111, Lift unknown
Continental O-200 - 100hp@ 2700 - 259/259/112/Lift .041
Continental E-185 - 213hp@2575 - 255/250/111/Lift .482/.463
Most aircraft engines are pretty low compression compared to my 10.5:1, so maybe that affects cam choice too.
They seem to fall within a certain consistent range. The duration is longer than I would have expected. The LSAs are very typical.
I came across a lot of of engine builders on the net that had good results with very tight LSA but I've seen nothing much to explain why, just that dyno results seem to validate their use. I don't care about idle quality or vacuum , needless to say, as long as the thing doesn't quit on me on final! (A Merlin sounds very lumpy coming in to land.) Howard Cams got back to me and predictably said they didn't have anything on the shelf for that kind of application but what came closest was a 207/213/106/.450/.465. Curious that the duration is that much lower than regular airplane engines use. But even manufacturers sometimes just take a wild guess...
One more point is that I don't want any extreme lift cams, preferably nothing much over 0.50", for clearance reasons. I won't know how much exactly until I put the thing together and measure everything.
Any input? If you have ideas, please tell me the reasons for your choice; I'm open to suggestions. Or if you more numbers for existing aircraft engines, I'd like to see those too.
If I'm building an engine based on a common V8 there are literally hundreds, if not thousands of cam choices out there. I went down a rabbit hole the last couple of weeks and looked up everything there is on cams on the net.
The variables are of course: Duration, lift and lobe separation angle/overlap, advance/retard.
The internet and youtube is full of self-proclaimed gurus who think they know all the answers but there is very little consistency or scientific basis among their ideas. And nobody builds engines for this kind of low rpm/moderately high load application, they are all out there building monster hot rods. Some cam calculators out there give very weird numbers, so I'm not going there.
Using common rules of thumb I'd want something with low LSA, low to moderate duration and moderate lift. I've looked at literally hundreds of dyno charts and getting this wrong will easily throw away 20-30 hp. My goal is a healthy margin of 200hp, hopefully 230.
Interestingly, I looked up a few aircraft engine cams and got a few figures:
Gypsy Major, 6.1L -122hp @ 2550 - Duration 271/271/LSA 111, Lift unknown
Continental O-200 - 100hp@ 2700 - 259/259/112/Lift .041
Continental E-185 - 213hp@2575 - 255/250/111/Lift .482/.463
Most aircraft engines are pretty low compression compared to my 10.5:1, so maybe that affects cam choice too.
They seem to fall within a certain consistent range. The duration is longer than I would have expected. The LSAs are very typical.
I came across a lot of of engine builders on the net that had good results with very tight LSA but I've seen nothing much to explain why, just that dyno results seem to validate their use. I don't care about idle quality or vacuum , needless to say, as long as the thing doesn't quit on me on final! (A Merlin sounds very lumpy coming in to land.) Howard Cams got back to me and predictably said they didn't have anything on the shelf for that kind of application but what came closest was a 207/213/106/.450/.465. Curious that the duration is that much lower than regular airplane engines use. But even manufacturers sometimes just take a wild guess...
One more point is that I don't want any extreme lift cams, preferably nothing much over 0.50", for clearance reasons. I won't know how much exactly until I put the thing together and measure everything.
Any input? If you have ideas, please tell me the reasons for your choice; I'm open to suggestions. Or if you more numbers for existing aircraft engines, I'd like to see those too.
