340 dyno chart thoughts
Just so someone doesn't come along and read this **** and actually THINK that LSA is a vacuum killer, and idle killer and all that silly ****, I'll spell it out one more ******* time.
The biggest killer of low speed torque, idle and vacuum is seat to seat duration. If you have a cam with 314 degrees of seat timing, but has an at .050 of 220 that cam has SLOW ramps. It will RPM to the moon with an LSA wide enough but it will RPM slow and be a pig. This is what GM did with the JUNK 30-30 cam that some GM guys think is the best thing since Pussy. Junk is junk.
Now, take that same 220 at .050 and make the seat timing 270. You can pull the LSA in a bit, it will still idle and have vacuum. Seat to seat duration is the biggest killer there is.
Oh, Gee. Don't you think maybe the reason why increasing duration screws up your idle might be because it increases overlap?
I mean, really. Take a step back and think about what "increase duration" means.
It means the lobes open earlier and close later.
If the exhaust is still closing while the intake is opening. that means more duration means they are both simultaneously open for more crank degrees and are also at higher lifts.
Newsflash, pretty much all street/strip cams have a positive overlap figure in degrees @ 0,050" lift. that means the valves are simultaneously open to 0.050" of lift or more for a certain number of degrees of the crankshaft.
Don't you think that is just a little more telling than how many degrees the valves are both open 0.006"? where they don't actually FLOW anything?
The next biggest killer, and just as important is the INTAKE VALVE CLOSING point. The later you close the intake , the shittier the idle and the lower the vacuum is. This is the number ONE killer of all things guys ***** about. Yet all the heros blame LSA when it isn't LSA that is causing the issue.
Soooooooo, if you take the same cam, and change the INTAKE CENTER LINE, you change the INTAKE VALVE CLOSING point.
I disagree. Let's use an example.
Cam 1, 230/230 on 105LSA IVC 40 ABDC
compared to
Cam 2, 230/230 on 115LSA IVC 50 ABDC
IF the first important thing is duration, we eliminated that by keeping them equal.
If the second most important thing is having an early IVC for a good idle with high manifold vacuum, why is it that Cam 2 has a LATER IVC but actually idles better and has more vacuum?
I'll give you a hint
Cam 1, EVC 10 ATDC. IVO 10 BTDC.
Cam 2, EVC 0 ATDC, IVO 0 BTDC.