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Cam design

M

matt5112

New member
Topic for pro's only so I hear.


Playing with an engine dyno sim.

Assuming stock 3.8 rotating, using abbott racing heads stock and stage three flow numbers and an M90 as the power adder

Things I've observed:

It seems lift doesnt matter much as long as you have enough to reach the max flow of your heads.

500 thou or slightly over is all you seem to need for optimum power up to 6000 rpm.

duration is good up until around 220, then gains quickly turn into losses down low.

Ramp rate has a huge affect on power. Higher the ramp rate, the more power overall the motor would apparently produce.

Overlap, seems to be bad. 0 overlap results in best power. LSA 111.

ess overlap, say -15 you see a loss in the top end, yet no gains down low.

LSA of 114.3 or so.

10* of overlap sacrifices power under 3000 for power from 6000-7000. LSA of 108.5

Next week, I attempt to find out why this is, or how I've made mistakes here.
 


Where did you get this program? I'd like to mess around with it.
On a side note, I wish I knew as much about cams as I know now when I was cam shopping. I would have never got the XP... definitely custom grind with more aggressive lobes.
 
SWEET!!! i was looking for one of these programs a while back. considering the plans i have with my build a custom cam was always in the back of my mind. i didnt have the option of cams for my DOHC as it would have been too expensive to do 4 cams for one engine... i did go as far as designing a replacement upper intake manifold with new runner and plenum design that would have really opened up the power on it...
 


I liked the look this cam timing: .050" valve timing:

IVO: 0, IVC: 42, EVO: 42, EVC: 0.

111 intake centreline, 111 LSA, 222/222 duration, .512/.512 lift.


For the same bottom end, yet more top end, try:

-2, 41, 51, 3.

111.5, 112.8, 219/234, .512/.512.

Best part is, low lift.


What it seems is: all of vendors give us info that might make it easier to compare, but they really dont.

To be 100% accurate you'd need valve timings at 0.006 and 0.050, intake centreline and lift.

Duration and LSA can be calculated from the above.


Edit: FUUUUUUUUUU this new software SUCKS for editing your posts.
 
EDITED: ^^Don't know.

NIC has a LSA of 112...

And a duration of 220/230...lift of .507" across the board.

So, "Matt's Cam" has lightly more lift and a little less duration...and has a tighter powerband from the closer lobe separation.

Give me something along the lines of an XP's lift with stupid LSA like 108*...chop the rollmaster in half @ 650 rpm's.
 
going from .512 to .580 on the intake resulted in 1 more peak ft lb.

Either this program is broken, i'm using it wrong, or lift past 500 thou doesnt matter.

Found an XPZ cam card, now I see why they don't advertise it.
 


Had another potential cam, but it seems the original 222/222 111 lsa with either the same or higher ramp rate would still be better.

It involved a little overlap.
 
this is why you piss us off, scott. you say things with zero background information. explain your damn self every so often.
 


Bio248 said:
this is why you piss us off, scott. you say things with zero background information. explain your damn self every so often.
Click to expand...

Meh, its not that there is much to explain by it. The heads are just overall restrictive, valve seat and port size is too small to justify more "length" in the valve opening. Also the valve angle is very shallow which does not promote flow at high lift like a steeper valve angle would.

When force inducted you also run into issues of the intake not needing alot of lift to achieve the same results... Less valve lift and minimal ramp rate is going to give you better real world results by increasing your valvetrain accuracy on sub 150# springs.

ZZP has been there and done the lift thing, its not worth it for power, so now they only sell cams with 550-580 total lift on stock rockers. I was out there in grand rapids when they put 3 different cams in the impala, and it was clear that lift only hurt things, while installation angle actually produced more WHP swings than any other thing we could do in the cam profile (for reasons unrelated to valvetrain I may add, but that is a different thread all together).

So, there is your blanket response, any questions?
 
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