the FSM specs for the stock hyd cam in this 83 D-150 are
intake opens BTC 6 deg
intake closes ABC 42 deg
exhaust opens BTC 36 deg
exhaust closes ATC 12 deg
valve overlap 18 deg
intake valve duration 228 deg
exhaust valve duration 228 deg
valve lift .378

1) knowing that, is it possible to mathematically back into to duration at 50 degrees,,and lob separation angle, for comparison to cams that I am considering? If so what are the formulas?
2) I think I remember seeing links to online tools that allow one to enter
engine parameters (cam, bore, ...) to predict performance,,where were those?

thanks

What a strange cam. 105° lobe centerline angle and ground 3° retarded.

There's no way to get the .050" tappet rise duration numbers without having the cam itself.

_________________
Joshua

Probably needed the tight LSA to keep the torque up, but had to retard it to hope it passed emissions... that happened a lot in those days...

My buddy just tore apart a 'smogger' Ford 460, while checking the engine he noticed that to get the big block to pass smog they retarded the cam in it 11 degrees...

-D.Idiot

Ok,, so how does one go from the valve opening / closing / duration numbers to the LSA and cam phasing??

thanks

I cheat and use DynoSim which is just a newer version of Desktop Dyno. I've also done it on paper, but it would be difficult to describe in words alone.

If you draw a line long enough to represent two crankshaft revolutions (720°) and mark both TDC and both BDC positions you can mark the valve timing events and find the duration and overlap pretty easily. Duration from valve events is easy to figure out on scratch paper. You add the valve opening point in degrees, 180° which is the difference between TDC and BDC, and the valve closing point.

Lobe centerline angle is harder because you have to find both the intake and exhaust centerlines to find the difference between them. With single pattern cams it's easy to see if the cam is ground straight up as the IVO will match the EVC and IVC will match the EVO.

_________________
Joshua

thanks

good tip, my thinking is that by charting out the events of the current cam and comparing those to what I am looking to purchase I'll have a better understanding of what I am installing.

Intake
6' before BTDC + 180 + 42' ABDC=228' duration
assuming a symetrical profile - the centerline is at half the duration (114') and adding this to the 6' BTDC gives an intake lobe centerline of 108' ATDC

Exhaust
36' BBDC + 180 + 12' ATDC = 228' duration
assuming a symetrical profile - the centerline is at half the duration (114') and subtracting this from the 12' ATDC gives an exhaust lobe centerline of 102 BTDC

Add intake centerline with exhaust centerline and divide by 2 gives LSA
(108+102)/2=105'

105 LSA-Intake centerline 108=-3'

_________________
Cheers!
Al T

Now that's what I'm talking about,,,great reply,,helped me comprehend relationships of the various cam aspects.


thanks