Camshaft Duration Question

[nathan s]

Hi, here is my problem.

I need to find out what the duration on our camshaft is for intake calculations. I have a spreadsheet of the cam profile, but I have no idea how to get the duration out of it.


If you need to see it to give advice, let me know.

[nathan s]

Hi, here is my problem.

I need to find out what the duration on our camshaft is for intake calculations. I have a spreadsheet of the cam profile, but I have no idea how to get the duration out of it.


If you need to see it to give advice, let me know.

[BeaverGuy]

Most cam durations are listed somewhere. For example, the duration for the cams in our 2000 ZX6R are in the repair manual for that bike. Another idea is to look at an aftermarket cam companies listing as they occasionally list the specs of stock cams as a comparison.

If you have an custom ground cam I wouldn't be able to help unless I was to look at the data and I wouldn't neccesarily be able to tell you as I'm not familiar with it. But I wouldn't mind seeing the data. http://fsae.com/groupee_common/emoticons/icon_wink.gif

[nathan s]

Beaver Guy-

I have looked on the internet and can't even find a repair manual for the bike. I sent you some data in an email. Thanks for the help.

[woollymoof]

Try measuring at 1mm lift or 50thou. It's a common way to determine duration. If the largest angle in your data is 360degrees, double the duration figure you get and that will give you duration in crank degrees.

[BeaverGuy]

From the data it looks like the intake duration at 0.040" of lift is 260 degrees and the total duration is about 340 degrees.

The exhaust duration at 0.040" of lift is 290 degrees and the total duration is also 340 degrees.

The yellow marked angles in the spreadsheet appear to indicate the opening and closing locations of the valves.

BTW what motor is this as the lift and duration values are larger than any of the specs I have for CBR 600 motors.

[nathan s]

Hmmm. Ok, that sounds good. How did you figure that out? Yeah, I made the yellow marks so I could remember where the openings were.

Sorry, I can't say anything about the engine because some of our sponsors don't want to be named at this time (aka, it is top secret http://fsae.com/groupee_common/emoticons/icon_biggrin.gif). Don't worry, all will be revealed at Detroit. Just don't laugh too hard.

[BeaverGuy]

Adding the absolute values of the opening and closing locations gives the total duration. Adding the values for where the valve is open at 0.040" of lift gives what is generally the advertised duration.

On another note, were you the guy that stopped by OSU here in Corvallis? I think the guy and his girlfriend were from UAH. It was an Alabama school at any rate.

[John Bucknell]

One caution to all you using cam duration data - all that really matters is valve motion. Obvious I know.

If you have the complete cylinder head, measuring valve events isn't really that hard.

This is the process every engine builder uses:
If still on the engine, make a degree wheel to fit somewhere on either end of the crank (marked with TDC of the cylinder being measured) and fixture up a dial indicator that can reach in beside a cam cap and measure either the spring keeper or the tappet (for non-hydraulic lash compensation, otherwise you'll need some patience to wait for the lash adjusters to bleed down which changes timing somewhat. You'll need solid lifters for accurate measurement in pushrod engines). A long extension is usually necessary on the indicator, and keeping it parallel to the valve stem is relatively important. Make sure your timing chain tensioner isn't loose and in all the below steps rotate the engine in the running direction to avoid errors from the timing drive lost motion. Bar the crank over until the valve is at maximum lift (your indicator will be at maximum extension here, make sure you aren't measuring air by letting the indicator hit its stop), and zero the indicator. Bar the crank over until you have 0.020" movement on the indicator (or 0.040" if your total lift is huge, ie more than 10mm) and read your crank position. Proceed with nearly two full crank rotations until you read 0.020" before your zero on the indicator. Take another crank position reading, and average to get centerline. For duration you should now be able to rotate around until you get ~0.040" from maximum lift (zero indicator at the other end of travel) - record crank position as the indicator sweeps past either side of maximum. This will not only give you opportunity to measure actual opening and closing points (forgetting the thermal impact of a growing cylinder head and even more growing exhaust valve, cause it is really small), thus overlap and duration.

Should the head be off the engine - you'll have to remove the valve springs and replace with extremely light springs so the cam doesn't snap around as you try to rotate it. These light springs can just be light gauge wire wrapped around your finger. Unfortunately, you lose the angular position portion of the exercise.

Sorry if the above was too basic - just trying to spread hard-won knowledge.

[BeaverGuy]

I actually plan on going through the "head on engine" procedure when we get our engine back together. It was supposed to be tomorow but we'll have to wait until the middle of nest week. http://fsae.com/groupee_common/emoticons/icon_frown.gif I did the off engine procedure directly measuring the valves last year to get data to have custom pistons made but we decided against it.

[nathan s]

Hey, thanks. It makes pretty good sense now (clear like mud http://fsae.com/groupee_common/emoticons/icon_smile.gif)

No, that wasn't me at OSU, it was most likely Devin Johnson, our assistant team leader.

Thanks John, I hadn't thought about that yet.

[Devin Johnson]

Beaver Guy,

Ya, that was me that stopped by in Corvy. My girlfriend I were visiting my parents. Most of my friends from high school are OSU students, and I keep telling them to join FSAE, but so far they are all being losers http://fsae.com/groupee_common/emoticons/icon_smile.gif.