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Ashyukun
Ashyukun GRM+ Memberand New Reader
10/15/12 10:58 a.m.

The 350 that came with my $2013 Challenge car allegedly had an improved cam in it. While the block is shot, most everything else on it has been decent (crappy heads aside)- but I can not find any information about the cam. There's precious little in the way of markings on it, and all that netted me in searching on it was apparently the casting it was ground on.

While doubtless getting a new cam would be ideal, if this one is actually well matched for the other top-end changes I'm making I'd certainly not complain about not having to spend the money from my budget on another one. Is there a reasonable way to figure out the relevant information on the cam with just the cam itself?

N Sperlo
N Sperlo PowerDork
10/15/12 11:08 a.m.

If you knew anyone who could measure it, you'd be set. Without any information we're useless. Your guess is as good as ours. I'll keep an eye out for any information regarding measuring a cam, although I can't imagine it would be easy. Someone around here probably knows.

Ranger50
Ranger50 UltraDork
10/15/12 11:12 a.m.

Find a shop with a CamDoctor. Then you will know way too much about a/the cam.

N Sperlo
N Sperlo PowerDork
10/15/12 11:22 a.m.

procedure for measuring cam lobes.

Hopefully this gives you an idea of what the task will be (considering this may not exactly be your goal) without specific information.

Zomby Woof
Zomby Woof UberDork
10/15/12 11:41 a.m.

Measure the base circle diameter and subtract that number from the overall lobe height. You might be able to find a cam with matching lift numbers. I know when I was building small block chevys, there were a only few companies making most of the cams, and it wasn't out of the ordinary for the no-name types to have no meaningful numbers stamped on them.

914Driver
914Driver MegaDork
10/15/12 12:26 p.m.
N Sperlo wrote: procedure for measuring cam lobes. Hopefully this gives you an idea of what the task will be (considering this may not exactly be your goal) without specific information.

That gives you lift, any thoughts on how to measure duration?

I found this on Comp Cam's site, I don't understand it.

http://static.speedwaymotors.com/images/charts/282-122062.jpg

fritzsch
fritzsch Reader
10/15/12 12:40 p.m.

If the engine is removed and head is attached to the engine you can measure valve lift as a function of crank angle with a dial gauge. You will be able to get pretty much all the valve/cam behavior

Ranger50
Ranger50 UltraDork
10/15/12 12:43 p.m.

Exhaust duration on that cam, based on that card would look like this to me....

Exhaust valve opens 64 degrees before bottom dead center and closes 16 degrees after top dead center. You have 180 degrees between bottom and top centers.... 180+64+16=260 degrees of total duration.

To measure duration, you need one piston/rod/crank in block with the cam/solid checking lifter installed, a piston stop, dial indicator, and a degree wheel.

xflowgolf
xflowgolf Reader
10/18/12 2:00 p.m.

I'm in the same boat with a set of 16V VW cams that I acquired with a head. They are not factory and I'd like to run them, but there are no markings on them so I'd like to figure out what they are via measurement.

Zomby Woof
Zomby Woof UberDork
10/18/12 2:10 p.m.
Ranger50 wrote: To measure duration, you need one piston/rod/crank in block with the cam/solid checking lifter installed, a piston stop, dial indicator, and a degree wheel.

No you don't. The pistons have nothing to do with duration. If the crank is in the block, and the cam is connected to it, a regular lifter will suffice. The best way to do it, although nobody does, is at the valve. The numbers WILL be different than doing it the standard way.

GameboyRMH
GameboyRMH GRM+ Memberand PowerDork
10/18/12 2:45 p.m.

Figuring out specs doesn't seem terribly difficult. Measure how much the side opposite a peak sticks out from the shaft, that's your base. Peak - base = lift. Then measure how many degrees opposite the peak are only at the base height. 360 - Base height span in degrees = duration. Amirite?

iceracer
iceracer UltraDork
10/18/12 4:56 p.m.

For duration you need a degree wheel and a dial indicator. Measure from the pushrod not the valve .

Ranger50
Ranger50 UltraDork
10/18/12 5:20 p.m.
Zomby Woof wrote: No you don't. The pistons have nothing to do with duration. If the crank is in the block, and the cam is connected to it, a regular lifter will suffice. The best way to do it, although nobody does, is at the valve. The numbers WILL be different than doing it the standard way.

Then how are you determining TDC? Cam/crank sprockets lie fairly regular. Reason for the blocked lifter is to avoid a false reading associated with hydraulics.

Zomby Woof
Zomby Woof UberDork
10/18/12 5:53 p.m.

You don't need TDC to determine duration.

In reply to iceracer:

On a pushrod motor, valve events are measured at the lifter, or pushrod. When you're doing an OHC motor, it's measured at the valve.

Everything should be measured at the valve. Rocker ratio will affect the numbers.

Ranger50
Ranger50 UltraDork
10/18/12 6:16 p.m.
Zomby Woof wrote: You don't need TDC to determine duration. In reply to iceracer: On a pushrod motor, valve events are measured at the lifter, or pushrod. When you're doing an OHC motor, it's measured at the valve. Everything should be measured at the valve. Rocker ratio will affect the numbers.

Uh, ok. I'll make sure you never touch anything I own.

NSS. But unecessary most of the time.

Zomby Woof
Zomby Woof UberDork
10/18/12 8:10 p.m.
Ranger50 wrote: Uh, ok. I'll make sure you never touch anything I own.

Alternatively, you could learn the difference between calculating timing events, and calculating duration.

iceracer
iceracer UltraDork
10/19/12 9:04 a.m.
Zomby Woof wrote: You don't need TDC to determine duration. In reply to iceracer: On a pushrod motor, valve events are measured at the lifter, or pushrod. When you're doing an OHC motor, it's measured at the valve. Everything should be measured at the valve. Rocker ratio will affect the numbers.

Provided the OHC engine does not have rockers.

AngryCorvair
AngryCorvair GRM+ Memberand PowerDork
10/19/12 11:21 a.m.
Zomby Woof wrote:
Ranger50 wrote: Uh, ok. I'll make sure you never touch anything I own.
Alternatively, you could learn the difference between calculating timing events, and calculating duration.

92CelicaHalfTrac
92CelicaHalfTrac MegaDork
10/19/12 11:23 a.m.
AngryCorvair wrote:
Zomby Woof wrote:
Ranger50 wrote: Uh, ok. I'll make sure you never touch anything I own.
Alternatively, you could learn the difference between calculating timing events, and calculating duration.

Zomby Woof
Zomby Woof UberDork
10/19/12 2:49 p.m.

In reply to iceracer:

Regardless, for ohc, it's always measured at the valve. You have no way to do it otherwise.

iceracer
iceracer UltraDork
10/19/12 6:30 p.m.

No, you just measure at the cam.

Zomby Woof
Zomby Woof UberDork
10/19/12 9:25 p.m.

You can't. The (shape and size of the) pad on the rocker has such a significant effect on the actual duration, and even lobe centers, the numbers you would get would be meaningless. I'm not aware of anybody in the industry that degrees an ohc cam at the lobe. It doesn't work.

Curmudgeon
Curmudgeon MegaDork
10/20/12 8:25 a.m.

Every 'cam card' I have ever seen was measured in crankshaft degrees and at a given amount of lobe lift as measured at the lifter. That's because valve event timing in relation to piston position is the most meaningful part of camshaft operation. No, you don't have to have a piston/rod installed to check duration but knowing duration without knowing when things happen is only one part of the puzzle.

Notice on this card they give 'gross valve lift', then further down they give a completely different lift number. That's what the dial indicator is going to say as measured at the lifter.

Lift as measured at the cam can be multiplied by the rocker ratio (if it uses them) to get valve lift (that's the 'gross valve lift' number). The gross lift can be changed by changing the rocker ratio. If it doesn't use rockers (OHC with bucket tappets) then cam lobe lift is also valve lift.

Cams turn at 1/2 crank speed. For that reason, the duration measured directly at the cam (i.e. by putting a degree wheel on the cam) won't tell you the duration at the crank, which is the important part.

If you have a pair of cams to compare, it would be pretty easy to stick a degree wheel on the end of the cam and stick a dial indicator on the lobe to get a 'rough and ready' idea of which has more duration and/or lift, but for real world numbers that mean something it's back to crankshaft degrees.

You can get an idea of the lobe spread too, but again it's back to crankshaft degrees for a meaningful number. That's because if you have a given duration number but the lobe centerlines are close together you have a lot of 'overlap' which means a lumpy idle and not much low RPM HP. Move those same centerlines apart without changing the duration, now you have moved the HP lower down the RPM range. Yeah, I know this is grossly oversimplified but it's a reasonable rule of thumb.

Timing events on an OHC bucket tappet engine are a little odd. The point of contact will move across the tappet face and this does change timing events. The only real way to check this is a dial indicator on the tappet face and then we are back to using a crankshaft degree wheel for a meaningful number.

iceracer
iceracer UltraDork
10/20/12 8:50 a.m.
Zomby Woof wrote: You can't. The (shape and size of the) pad on the rocker has such a significant effect on the actual duration, and even lobe centers, the numbers you would get would be meaningless. I'm not aware of anybody in the industry that degrees an ohc cam at the lobe. It doesn't work.

sort of have to disagree. Are we measuring the cam or the valve action.? Rocker arm ratios have a huge effect on valve action. Particularly lift. Also, when measuring at the valve, you will need to allow for the clearance , to get a true measuremnet. I don't know that word "can't".

Zomby Woof
Zomby Woof UberDork
10/20/12 3:45 p.m.
iceracer wrote: sort of have to disagree. Are we measuring the cam or the valve action.? Rocker arm ratios have a huge effect on valve action. Particularly lift. Also, when measuring at the valve, you will need to allow for the clearance , to get a true measuremnet. I don't know that word "can't".

You may not understand the word can't, but maybe you understand the words industry standard.

In no application (OHV/OHC) do you ever measure or degree at the cam. I know, you disagree with that too, but think about it, in an OHV application, it's measured at the LIFTER, correct? The lifter has a significant effect on the lobe profile as seen by the rest of the valvetrain. In other words, if you measure the lobe without the lifter, then with the lifter, you will see completely different numbers. Remember, we're talking duration. For an OHC application, the bucket style is also measured at the lifter, but it's also the same as the valve. For an OHC rocker application, it's not always easy or possible (think slipper type follower) to measure at the cam side of the rocker, so it is industry standard to measure right off the valve.

The reality is, everything should be measured at the valve, but it is only industry standard to do so for OHC applications. Because, of course half the OHC stuff can only be measured at the valve. Lift is a simple calculation, but duration is not. The rocker pad, and ratio have significant effects on the duration (same as the lifter) that you can't easily calculate. For this reason, it must be measured at the valve. You can measure it any way you want. but the numbers won't mean anything.

I'm not looking for an argument. There was a question about duration, and some misinformation and I'm only trying to explain how it's correctly done. I have degreed thousands of lobes. Because I mostly do specialty stuff, when I develop a cam, or do a custom grind for a customer, all my development is done in an actual cyclinder head for the application being used. For some OHC rocker applications, the effect of the rocker, follower, follower angle, pad shape and size, lobe shape and size, ratio, and their effect on duration, lobe center angle, and (to a lesser degree) lift are huge. To degree it any other way would be nothing less than a complete waste of time, and only produce some meaningless numbers. This is not my opinion, but the industry standard.

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