Please Help Me Decipher My Cam Specs Sheet

-

MobileCustoms

Well-Known Member
Joined
Oct 21, 2013
Messages
1,696
Reaction score
1,820
Location
Inver Grove Heights, MN
This is the only spec sheet I got for the Erson hydraulic roller cam in my stroker build. Just would like to know which numbers are the most important ones when I am being asked for my cam specs. I am ready to have a torque converter built but feeling a little dumb when I look at this sheet. LOL
Thanks to anyone who can dumb it down a bit for me!

Cam Specs.jpg
 
Duration 279°/285° at .050" valve lift.

(The top table relates to the Exhaust lobe specs, the bottom table are the intake specs.)
 
Since I use these for a living here at Crower that is 249/254 duration at 0.050" on a 110LSA lobe lift of 0.365"/0.364" then just multiply that by the rocker ratio to get valve lift. Now that is the obvious stuff but here is the not so obvious info. Look at the left hand side that shows the "Open,nose close ACC" "Acc = Acceleration" that is the second derivative and this info looks not so good. This cam will be prone to noisy lifters and valve float. Notice the open Acc is slower than the closing? well this means that spring set up will be imperative if not critical when going over the nose at anything over 5,000rpm to keep the lifter from slamming down on the cam. I personally would have used different masters than these. This is just my two cents. Ask if you have questions.
 
isn´t it 254/249 @.050"?

Michael
It's....

249/255 duration @ .050" (Intake is normally listed before exhaust.)
307/314 advertised duration
LSA: 110 (as noted)
Tappet lift: .365"
Valve lift with 1.5 rockers: .547" (as noted)
ICL: 110 (or so it is listed...)

ICL is 'as ground' and installed dot-to-dot, if everything is machined right. (But you can install it at a different ICL to move the torque curve around....Does PTC ask for an ICL input?)

Nice to have all of that data IMHO... but, agreed, few people would ever use it.
 
Since I use these for a living here at Crower that is 249/254 duration at 0.050" on a 110LSA lobe lift of 0.365"/0.364" then just multiply that by the rocker ratio to get valve lift. Now that is the obvious stuff but here is the not so obvious info. Look at the left hand side that shows the "Open,nose close ACC" "Acc = Acceleration" that is the second derivative and this info looks not so good. This cam will be prone to noisy lifters and valve float. Notice the open Acc is slower than the closing? well this means that spring set up will be imperative if not critical when going over the nose at anything over 5,000rpm to keep the lifter from slamming down on the cam. I personally would have used different masters than these. This is just my two cents. Ask if you have questions.
I saw those numbers and was very intrigued.... But, if you don't mind my asking, isn't the absolute value of the 'over the nose' acceleration the most important one in determining the spring requirements and keeping the lifter on the lobe? Once the acceleration has gone + again on the closing ramp, then the lifter is already in contact with the lobe...

Do you happen to know the units of acceleration used on this card? Just not clear to me....
 
Since I use these for a living here at Crower that is 249/254 duration at 0.050" on a 110LSA lobe lift of 0.365"/0.364" then just multiply that by the rocker ratio to get valve lift. Now that is the obvious stuff but here is the not so obvious info. Look at the left hand side that shows the "Open,nose close ACC" "Acc = Acceleration" that is the second derivative and this info looks not so good. This cam will be prone to noisy lifters and valve float. Notice the open Acc is slower than the closing? well this means that spring set up will be imperative if not critical when going over the nose at anything over 5,000rpm to keep the lifter from slamming down on the cam. I personally would have used different masters than these. This is just my two cents. Ask if you have questions.

Interesting... Well, here's the dyno sheet off the last pull. It didn't want to go much over 5800 rpm
Edit to add info: I have solid lifters. with 1.5 ratio comp roller rockers

Dyno Pull # 10.jpg
 
I saw those numbers and was very intrigued.... But, if you don't mind my asking, isn't the absolute value of the 'over the nose' acceleration the most important one in determining the spring requirements and keeping the lifter on the lobe? Once the acceleration has gone + again on the closing ramp, then the lifter is already in contact with the lobe...

Do you happen to know the units of acceleration used on this card? Just not clear to me....[/QUO

If the ramp is to steep without enough spring pressure to keep contact with ramp at a high rpm, they will free fall. Also Hydraulic lifters are much heavier that solid lifters so these numbers are much more critical. Here is a pic of a gen III hemi cam that had the same problem. I had to angle the pic so you can see.

cam-dent.jpg


If the ramp is to steep without enough spring pressure to keep contact with ramp at a high rpm, they will free fall. Also Hydraulic lifters are much heavier that solid lifters so these numbers are much more critical. Here is a pic of a gen III hemi cam that had the same problem. I had to angle the pic so you can see.
 
Last edited:
The events are listed in the two columns titled close and open. FRom the .006 events all other relevant specs can be calculated. that thing is huge, and 90* overlap! 90 flipping degrees, I think I ........ mighta maybe ......almost ........hadda accident.
Boy I bet that's gonna be a fun tune.
 
Last edited:
so then... which numbers should I actually use when being asked for my cam specs? Looks like a good shift point is right around 5400 rpm, correct?
 
Chebbys do that all the time right?
The varnish in the dip is the giveaway,lol.

That would be a gen III hemi cam. Not enough spring pressure on a lobe that has way too much Acceleration on the closing ramp. I fix these cam specs everyday. This will happen and does happen alot, when proper care is not taken when picking lobe masters.
 
Looks like a good shift point is right around 5400 rpm, correct?
We don't know the rest of your engine except that it's a stroker (cylinder heads would be most interesting), but a stroker with that much cam
nosing over at only 5400RPM is not a good thing in my book. Unless you are running stock-ish heads. My 2 cents.
 
We don't know the rest of your engine except that it's a stroker (cylinder heads would be most interesting), but a stroker with that much cam
nosing over at only 5400RPM is not a good thing in my book. Unless you are running stock-ish heads. My 2 cents.
Well you are correct, that for now at least, the engine had mildly ported J heads/2.02 valves. So yes, it is very much head-limited. I appreciate the input from everyone.
 
View attachment 1715235961

If the ramp is to steep without enough spring pressure to keep contact with ramp at a high rpm, they will free fall. Also Hydraulic lifters are much heavier that solid lifters so these numbers are much more critical. Here is a pic of a gen III hemi cam that had the same problem. I had to angle the pic so you can see.
Yes, I understood what you are saying. The pix is very good. I am still working through whether it is the peak closing rate, or the peak rate over the nose, that matters.

The closing acceleration rate being + means it is applying force to the valvetrain in the opening direction, correct? (Which is not really 'opening' at that point in time, but is stopping the closing action; i.e. bring the valve train to a stop.)

If you pick a lower peak closing rate, does the over-the-nose rate also typical go lower? (Does not seem likely to me...)
 
Last edited:
so then... which numbers should I actually use when being asked for my cam specs? Looks like a good shift point is right around 5400 rpm, correct?
Forget the acceleration rates for the TC selection; that is a different matter entirely, and is a side discussion to what you want. Use what was summarized in post #12.

As for the best shift point, it depends more on how the torque drops off below the data presented in your dyno sheet. If the RPM's dropped from 5400 to 3200 RPM on a 1-2 shift for a 904, then what is the torque at 3200? Can't tell from the data... IMHO, for drag racing, you would upshift at the point where the after-shift torque is roughly equal to the pre-shift torque... i.e, you evenly 'straddle' the torque peak before and after the shift. (And I can see it varying from there but that's 'in the ballpark'.)
 
-
Back
Top