Camshaft Duration Numbers: Discussion

[SS4REAL]

Got a question on Duration.. Specifically on Hyraulic Rollers.
I am comparing cams for my rebuild on my Supercharged 422 sb chevy.
Yes. I am using a very "small" cam
My concerns as comparing cams is the difference in degrees between
duration @ .050 and Advertised duration.
I have always relied on the .050 figure to choose and compare cams.
I have found a few choices that will work for me that have the same ish .050 figures
but the Advertised number vary alot.
EX: Crane has about 60-62* diff between duration #
Comps are about the lowest variation at 50-52*
and Oregon Cams are about in the middle at 54-56*
The cams that I am looking at are in the 214-224 range at 500-550 lift (1.5 ratio).

WHAT IS THE EFFECT on power, vacuum, idle, power range, etc if the
cams are exact but have different advertised figures??

Is it how fast the lifter is accellerated to full lift???
I know my Comp XFI cam that I have now is really noisey - like a sewing machine.
Comp says this is normal for their XFI series due to the speed of lobe lift.
My old cam was Oregon cam with about same duration, but less lift and more degree diff.
between .050 and advertised: it was quieter, a little tamer at idle and pulled almost 20 lbs vacuum.
My XFI will still idle way down, etc. but my vacuum is down 2 to 2.5 lbs across the board.
I really have not "felt" any diff. in power and not any diff. at dragstrip either. Please
chime in if you know something I don't !! :-\

[GibTG]

Re: Camshaft Duration Numbers: Discussion

Since we are comparing hydraulic cams it does make things a little easier - try comparing "seat" duration valves for camshafts with different sized lash ramps, it's no easy task.

Comp and Crane use different values to measure the advertised duration of their cams, it all lies in who says at what point does a hydraulic lifter transmits motion to the valve. Comp says it's .006" up the ramp and Crane says its .004" up the ramp, but this difference is slight, probably only a few degrees...

Even though its old hat by now Harvey Crane coined the term "hydraulic intensity" to represent the speed of a hydraulic ramp early on in its valve motion. Hydraulic "intensity" is the difference between the @.050" duration figure and the advertised or seat-to-seat duration figure. It's logical to believe that this difference would be approximately 44° in the case of a Comp cam since .050" - .006" = .044" --> which would mean that the engine sees about a degree of duration per thousandth of tappet rise. Now, with a Crane cam you assume the difference to be 46° ideally but this is rarely the case - whereas Comp has some fast ramps even with street hydraulic profiles Crane's stuff seems to a be a little farther behind technology-wise, or at least their cheap shelf stuff seems a little "behind."

Since Crane's intensity values usually are somewhat poor (such as greater than 50) its a pretty safe assumption to say that they're probably a little slower than Comp's per the duration involved straight from the seat. A fast profile along the entire lift curve will theoretically show large gains in power since the valve can still see the same total opening area while helping to retain low-end and midrange by not having to extending the valve events to get the same cylinder fill (another one of those all other factors equal cases, a.k.a. benchracing).

BUT, we as the consumer will never know the entire story. The intensity values are just one aspect and will never be foolproof. They don't tell what is going on with the ramp rates after .050" lift where there is obviously more importance because it's the vast majority of the lift curve. This is why companies like Comp are now starting to quote duration @.100" and .200" tappet rise on their lobe profiles since I assume they're confident that they are getting the same or more area under the curve than the competition. I believe that these duration numbers are even more valid since they are farther away from issues from hydraulic lifter leakdown or solid lash ramp lengths, but it may difficult to get these unusual duration figures from other cam companies.

Vacuum will be more dependent on amount of overlap in degrees rather than the rate the valves are opening during the overlap period really. You could argue that a faster opening ramp will expose the induction tract to open atmosphere quicker but I think that this is negligible in almost all cases, we'll assume that you're either open to outside air or you're not. The shear amount of overlap will be the deciding factor on how much vacuum your engine makes at idle.

[CDMBill]

Re: Camshaft Duration Numbers: Discussion

I think the question that is being asked here is if you can predict engine behavior based on readily available, and comprable information from different camshaft companies. Unfortunatly the answer seems to be no. If as was posted previously, two companies have different measures of advertised duration and there are no published figues for both indicating lift at .1,.2 .3 etc. you have no sense of the ramp rate of the cam. Using the Comp Master lobe catalog as an example you have .2 numbers as well as subjective descriptions of the different lobe profiles. If Crane doesn't use the same numbers measured the same way then you're stuck with .50, lobe lift etc..

Once you add in variables usch as displacement, induction, exhuast, weight of the car the answers to SS4Real's questions become just opinion based on experience with other combinations. So, SS 4Real, You have a baseline, you appearantly made a change from the Oregon Cam to the Comp XFI and got less drivability and no improvement at the track. We don't have any information about ambient temps, other changes to the car etc.. Assuming everthing is the same and it almost never is, then you should go back to the Oregon cam and start over. Given you have a blown, large cubic inch SBC you are already well outside of the cam catalog listings. Whomever you choose as a supplier, it will be worth spending some time with their tech support, online and anywhere else you feel you can get good information to make a deviation from your baseline. Be sure of what you want becasue you will be trading off something for something else, vacuum and low RPM response for high end HP as an example. Good luck. Go Big.

[SS4REAL]

Re: Camshaft Duration Numbers: Discussion

Thanks guys for the detailed answers.
Although it looks like there is no "real" obtainable answer here.

Here is another q? I would like to broaden the torque curve out just a little.
I am making so much down low as is. Will going with a wider LS help this out a little
I was thinking of going out to 115* LS on the Oregon cam. Maybe this will help reduce the
low end "hit" I get now that limits traction greatly.
My previous Oregon cam : 214 .517 lift on intake
224 .537 lift exhaust with 1.6 rockers. 114 lobe sep.
Current Comp XFI Grind 214 .565
224 .565 with 1.6 rockers, 113 lobe sep

I cant' say that I gained a lot of hp or tq when going to the "faster" higher lift cam.
On the chasis dyno, I gained about 8 hp, 10 tq. BUT this could be just as easily accoutable
with temp, humidity, etc. My only change to engine when I put in this cam was
a Reduction in Compression ratio from 9.4 to 9.15 and bored another .010 to 4.165 bore.

I did lose 2 lbs vacuum and picked up a noisyer engine.

The Oregon cam I'm leaning toward would be:
215 .498 w. 1.5's .531 w. 1.6's Intake
224 .560 lift 280 adv. duration Exhaust or
224 .553 lift 274 adv . duration or
224 .538 lift 286 adv duration

the exhausts are pretty similar, just a little lest lift, but adv. duration
is different.
I think I'll put this on 115 lobe sep.
The crane numbers are pretty close to these but have
about 4* more adv. duration.

I can use 1.5 or 1.6 on intake to change it's charactaristics a little,
but I'm defin. going to use 1.6 on exhaust side.

Do you guys think the Intake is " ust along for the ride" with the forced ind?

This is on my 94 chevy truck, 4900 lbs, 4l60e, 3.70 9" rear, 1800 stall.
I ask it to pull my 5000 camper as well as knock off low 12 sec 1/4's as on drag week!

Thanks for your time guys!

[Caveman]

Re: Camshaft Duration Numbers: Discussion

Post or PM me with all your engine specs & shift points, & I'll plug a couple of cams into my DynoSim. If you're wanting less of a traction 'hit' torque-wise, that's a tradeoff I presume you're willing to accept--less low-end towing torque.

It'd really help to have your head's flow #'s, carb size or F.Inj cfm rating, blower psi, everything, etc.

Or... you could call Comp, and order it for your PC... fyi, the low end version doesn't have CamManager though...

[nosnerd]

Re: Camshaft Duration Numbers: Discussion

the diff between the adv and the .050 number is the LOBE INTENSITY.the lower the number the better...there are more variables but i am too tired to type
...


later guys



al

[nosnerd]

Re: Camshaft Duration Numbers: Discussion

back...

i just re read posts as i was speedreading last night...

GIB hit the nail right on the head...GREAT INFO and very concise..

224 is 224...the .050 number is the standard of the industry for camshaft numbers...and as he said...200 numbers are where the 'secrets' lay..but at 224 you'll be splitting hairs...if you get into 266+ @.050 then thats a diff story...


keep the XFI...great piece...



al

PS: GIB...nice to see you over from the CC bb....i go under "nitrousnerd67" as i was bounced off in 06...

[min301]

Re: Camshaft Duration Numbers: Discussion

GibTG was his old handle at HRF, and it's really nice to have you here.

Pick his brain, it's useful. ;D