bobl

The book Dennis Moore wrote on BBC marine engines has several cam profiles that they measured with duration listed from .004 to max lift. That may help you out too, if that's what you are looking for.

bobl

I just degreed the cam in a 502 I am building. It is a Howards grind #120266-12 236/242 and .635/.640 lift. This is lobe lift, not at the valve.I only did the intake for a comparison: .050=236 degrees, .100=207,. 200=158, .250=131, .300=100 As a comparison the old Crane 741 which was 234/242 and .610/.632 .050=234, .100=204, .200=154, .250=127, .300=93. Interesting to note that the Howard cam with .an additional 025 lift has 4 degrees more duration at .250 lift, 7 degrees more at .300 and it started with 2 degrees more at .050. The increased lift obviously makes for a more aggressive lobe, and that doesn't really show up in the specs. Hope this helps. I have the timing events written down also if anyone needs them.

Bob Lloyd

MILD THUNDER

iTrader: (3)

Think about it like this. Your office might be a 10 mile drive away. it might take you 10 minutes to get there. If your office moved to 15 miles away, the only way to get there in 10 minutes, is to drive faster.

Duration is time, lift is distance. More lift in same amount of time, equals a faster lobe. This is why cam companies , real cam companies, know that you have to stay within lift limits when working with shorter duration cams. Otherwise, it can become unstable and or hard on parts.

Rage

Sorry for the late response. I was traveling. Thanks for the interesting cam info Bob. What I am looking for is the measured lobe lift from the lobe base circle on BBC cams at every 2 degrees crank rotation/1 degree cam rotation. I asked for Cam Dr file (or what ever the in house measurement system was) lobe lift vs degrees rotation for various cam lobes I was considering from Crane, CompCam, Isky, Cam Motion. All said no way. My need is to evaluate valve train stability relative to valve toss (not resonant harmonics) with Performance Trends Engine Analyzer Pro software. I have hand measured the lobes of a number of cams. The lobe profile that the software auto generates from the cam card specs input is I guess OK for ball park HP but not valve train dynamics analysis. I compared valve train stability (loft) generated from the cam's cam card vs actual degreed cam lobe measurements on my previous engine's cam and the current cam. Big difference. So now I am interested in evaluating any BBC cam lobe for which I can get the actual measured lobe lift vs degrees rotation measurements to build some info on the range of ramp aggressiveness by cam mfg and lobe spec. Since my engine is now built and unavailable for cam measurements I purchased a set of V blocks off Ebay to measure additional cam lobes.

MILD THUNDER

iTrader: (3)

I now see where youre going with this, or at least think I do.

I have not used the perf trends software, but it sounds cool.

From your findings, is it safe to assume, the lobe with more lift, has shown there to be a higher likelihood of valve toss, generally speaking ?

Can you give us the specs of the cams you compared ?

MILD THUNDER

iTrader: (3)

I think that when the spread from .006 to .050 , begins to shrink degree wise, assuming the max lobe lift has not changed, the likelyhood of valve toss, grows. Or, when the .006 and .050 stays the same, but the lobe lift increases, the likelihood of valve toss, increases again as well.

But actually measuring the entire lobes profile, as you are doing, can give a much clearer picture of whats going on. I would think.

Of course whether or not valve toss /loft actually occurs, is probably more relative to the rest of the valvetrain setup. IE, spring, weight, rpm, and so on.

Rage

Yes to all in general.

If everything else in the valve train stays the same and the lobe base circle and duration stays the same then yes the max rpm w/o valve toss over the nose (do to valve train inertia not harmonic resonance instability) goes down as lift goes up. With a more aggressive lobe ramp valve toss can also occur on ramp up but recover before lobe nose at lower rpms.

Crane: 230*/236* @ 0.050", 292*/298* @0.004", .352"/.359" lift
CompCam: lobe# 3410B/3411B, 238*/244* @ 0.050", 292*/298* @0.006", .351"/.351" lift
Crane: 242*/240* @ 0.050", 304*/302* @0.004", .372"/.365" lift
CamMotion: 242*/240* @ 0.050", 304*/302* @0.004", .370"/.370" lift

Rage

Correction>>>>>CamMotion: 242*/240* @ 0.050", .370"/.370" lift

Rage

Is there anyone out there that will electronically measure a cam lobe vs degrees rotation (360 degrees) and provide an electronic file of the measurements in Cam Dr, Cam Pro Plus, S96, Andrews, Comp Cams, or Doctor Dr format?

bobl

OK Bill, just measured that cam every 2 degrees as you requested. Here's the short version: Beginning lift to 20 degrees the lift rose on average .002 every 2 degrees of crankshaft rotation, then .005 per 2 deg. up to 39 deg, .008 up to 51 deg, .009 up to 75 deg, .008 up to 81 deg, .007 up to 91 deg, .006 up to 101 deg, .005 up to 117, .003 up to 135 deg, .002 up to 145 deg, .001 up to 151 deg., 0 up to 162 then started closing at roughly the same rate. Hope this makes sense and can help you out. This is the exhaust lobe on the Howard cam which is 242.6 @ .050 and .640 lift, with a .377 lobe. Let me know if you need anything else. I still have the degree wheel attached.

Bob