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[dave brode]

All,

Being a car guy, it seems absurd that cams are advertised with no seat timing specs. It would be quite rare to see car engine cam advertised without the seat timing being listed. Do they think that too many numbers would overwhelm the common man's brain? 

Andrews, oddly, [to me] lists duration at .020". That tell a little story, but still doesn't tell us all that much about the ramps. The .020" rise numbers are normally used for solid cams in the car world, and .006" rise is what's used for hydraulic grinds.

I chuckle what I read a fellow claiming that "this" cam is close to "that" cam, as he compared the .053" rise numbers. The seat timing could vary by a huge amount...

I have asked several cam grinders for seat timing info. To this point, only Zippers has supplied me any info. [thanks Pete]

I remember 20 yrs ago, it was rare to even see LSA and/or L/C listed for HD cams. It's not like one can't calculate it. At least that has changed in some cases. 

Dave
p.s. - I'd bet big $ that some racers aren't using solid grinds in the TCs, but I haven't seen any. I do remember, before S&S buy-out, when Crane had a drop in solid lifter for the '87 up chev/HD.  Some of the hyd grinds that are listed for TCs would be seen as being absurd in the car world.

[HD Street Performance]

Solids have been tried by Bonneville efforts in a TC. Ironically they grow less than an evo, all things considered including pushrod growth

[dave brode]

I remember from HTT, someone heated parts in an oven and the difference in cyl vs p-rod growth was small. Less than scientific but interesting.

[MCE]

Published specs are almost meaningless (almost). It's a general guideline at best.

One would have to plot the lobe's lift vs. degrees to do any meaningful comparisons.
I haven't found a cam maker that will provide cam-pro files. You have to buy the
cam and get the data yourself.

"Advertised" means it's just like any other advertisement.   

[dave brode]

Matt,

I agree that merely having some sort of seat timing in addition to the .053" timing isn't like you cam doctored it [or used a wheel and your brain], but it would still give some idea of the opening and closing ramp designs, in general. I'd like to know what's happening at less than .053" rise and make my own decisions.

Imo, just because they don't supply us with more doesn't mean we should just accept that. Most major car cam companies publish duration at .006" [hyd only] .020", .050" and .200" in their lobe listings.  Some will give you more than that if you ask.


Thanks

Dave
p.s. - and what's with the .053" number vs .050"? Anyone know why that became the std? Curious.....
 

[dave brode]

Matt,

I admit that I realize that the end results might be better if I became a "here's my credit card" guy. LOL

Dave

[MCE]

Matt,

I agree that merely having some sort of seat timing in addition to the .053" timing isn't like you cam doctored it [or used a wheel and your brain], but it would still give some idea of the opening and closing ramp designs, in general. I'd like to know what's happening at less than .053" rise and make my own decisions.

Imo, just because they don't supply us with more doesn't mean we should just accept that. Most major car cam companies publish duration at .006" [hyd only] .020", .050" and .200" in their lobe listings.  Some will give you more than that if you ask.


Thanks

Dave
p.s. - and what's with the .053" number vs .050"? Anyone know why that became the std? Curious.....

None (that I know of) will give you the actual lobe data files. As far as 'what's happening below .053"?
Not much. That's why they (somewhat) standardized the .050/.053" measurement. (the .003 difference
is almost insignificant imo)

But that still doesn't tell you enough to make any kind of real comparison. You could run Three cams with
identical .053 durations and lifts and get Three completely different sets of results.

It's the area under the curve that we're mostly interested in. That translates into the valve curtain area that's
presented to the cylinder. Then, there's that area at 'x' degrees of crank rotation. And to further
complicate things, the piston's position (and speed) at that given crank degree (instance).

It gets pretty intense in a hurry. Engine analyzer programs help put some of it in perspective but at
the end of the day (week/month/year), trial and error on a dyno will sort the rest of it out if you're
willing to spend the time.

For 97% of the people, taking what they give you and running it is good enough.

[MCE]

A small percentage of engine builders are smarter than the engineers the cam companies employ.
Or very few are willing to spend the 100s of hours required to second guess them. Unless you're
competing in some (big money) class racing, it's just not worth it in most cases.

PS: Spending 100 hours (for example) to gain a couple HP is not worth it to most people. To me it is,
but my time (like everyone else) is limited. You don't generally get paid for that time either. (So there's
that too)

I don't do this for the money, but there's still only so much time in a day.

[dave brode]

MCE wrote;

"But that still doesn't tell you enough to make any kind of real comparison. You could run Three cams with
identical .053 durations and lifts and get Three completely different sets of results."

Exactly, and that's my whole point! And w/o the data, we can't know w/o buying first.

Btw, I wasn't second guessing anyone. I just wish to know what I'm buying.

Thanks for your input.

Dave
p.s. - Understood on .050" vs .053", I was just curious as to why that tappet rise was chosen
 

[MCE]

.050/.053 was chosen because what happens below .050" means nothing. It eliminates skewing the duration
numbers for advertising purposes, which helps you compare apples to apples. Ask a couple cam manufacturers what they
recommend. Or ask someone that's built successful combos like the one you're building.

Why was .050 specifically chosen? It's likely that they got a group of engine builders, engineers and whoever else to agree
on a number. Zero obviously isn't a good choice because then, you really wouldn't know what you were getting. They had
to decide on a number that was far enough off of zero but not too far from zero.

Intake close, Overlap, and lobe separation are things to consider when choosing a cam. But the tech departments at the
cam companies are a much better resource than going it alone, especially if you're not well versed in this type of thing.

[Nocvo]

Aside from not making it too easy for someone to copy your cam design translating the entire cam data onto paper would be more real-estate than the surface of the box and how many people would truly understand it all anyway?
Was looking at two cams yesterday, 32H and 590PS, just in lobe profile alone the difference is huge, open and close barely touches on the differences possible.

[MCE]

exactly.

[dave brode]

When someone "steals" a lobe design, they sure don't need the published numbers to do it. 

[MCE]

You generate them on a machine like Audie Cam Pro. You can also load those the files into Dynomation
if you wanted to.
(you still need is a lobe centerline number, That's the only spec you really NEED)

[dave brode]

Of course. Easy to steal.

Back to seat vs .053". the difference in .006" and .053" duration on two lobes with the same .053" duration could well differ by 6 or 8 degrees. The .200" number would be an indicator too. I'd like to have that info. Maybe I'm just used to car cam spec. .006", .050", .200". Maybe I'm the only guy that thinks it's not asking too much.

Would it make me able to choose more wisely? Maybe not, but I'd just like to be able to gaze at the numbers and say golly gee. LOL.

Fwiw, for anyone that's not seen one and cares to, here is a typical lobe listing giving rated duration [.006" hyd, .020" solid], .050", .200". Why should we be happy with less? http://www.compcams.com/Technical/Catalogs/CamLobeMasterCatalog.pdf

I didn't mean to ruffle anyone's feathers.
Sincerely,
Dave