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| Cam Speak https://slantsix.org/forum/viewtopic.php?t=34675 |
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| Author: | DadTruck [ Fri Apr 03, 2009 6:14 pm ] |
| Post subject: | Cam Speak |
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 |
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| Author: | Joshie225 [ Fri Apr 03, 2009 7:21 pm ] |
| Post subject: | |
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. |
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| Author: | DusterIdiot [ Fri Apr 03, 2009 9:05 pm ] |
| Post subject: | Lol... |
Quote: What a strange cam. 105° lobe centerline angle and ground 3° retarded
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 |
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| Author: | DadTruck [ Sat Apr 04, 2009 9:15 am ] |
| Post subject: | cam spec calculations |
Ok,, so how does one go from the valve opening / closing / duration numbers to the LSA and cam phasing?? thanks |
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| Author: | Joshie225 [ Sat Apr 04, 2009 9:32 am ] |
| Post subject: | |
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. |
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| Author: | DadTruck [ Sun Apr 05, 2009 2:13 pm ] |
| Post subject: | |
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. |
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| Author: | Al T [ Tue Apr 07, 2009 8:48 pm ] |
| Post subject: | Cam specs from valve events goes something like this . . . |
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' |
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| Author: | DadTruck [ Wed Apr 08, 2009 1:23 pm ] |
| Post subject: | |
Now that's what I'm talking about,,,great reply,,helped me comprehend relationships of the various cam aspects. thanks |
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