Ed Curtis

All the cam specs are important.

Application dictates which lobe design to use.

Cylinder head characteristics dictate which lobe design to use.

RPM dictates which lobe design to use.

Rocker ratio dictates which lobe design to use.

More thought should go into a design than grabbing some "XER" lobes and calling it a custom camshaft...

As for the rocker ratio varying, do a search on Danny Jesel's thoughts on shaft systems and their design. He was the first to see the merits and explained the reasoning.

Ed

DAPSUPRSLO

iTrader: (14)

In general the second camshaft would given most lsx heads have the peak of their flow in the mid lift numbers. You would take a guess that given 10 more degrees of duration at .200" the second cam has more duration at .300", .400", .500" all the way to peak lift. The second lobe would also have a better idle.

Like EDC said though, there is a tone of variables which may make a difference.

For instance, the first lobes in a cam with a narrow lsa will give you more overlap based on its large advertised duration, unless ofcourse the .050" duration is quite a bit less.

You really need all of the cam lobe dimmensions to get it 100% or closer to.

DAPSUPRSLO

iTrader: (14)

RPM and Rocker Arm ratios would effect how aggressive you can go on your lobe before you start throwing lifters off the lobes and causing other catastrophic failures. It is common practice for a less agressive lobe to be used in applications where 8000 rpm may be seen. Unless you are running 800 pound open pressure springs that you don't mind changing every month or even every race (other things may limit the spring pressure too such as lifter digging into the lobe which I wouldn't think would be a big problem with roller lifters until you are talking about super agressive lobes).

You don't want to go too soft though or you will sacrifice some power through the curve for the added high rpm stability. I guess you just have to define your requirements and go from there.

No wander people get paid to choose cams for people, this stuff will give you a headache.

jrp

iTrader: (16)

i said "heres what im looking for, heres what i have to work with, heres the money. now give me a cam."

turbotacoma

iTrader: (1)

I agree with JRP!!! After you get all your figures together....gearing/weight/head choice and flow numbers/application...intended use/and the rest of the bolt ons...exhaust/pulley/intake/etc. and stick too it....give the man this info...pay him for his time to crunch the numbers and bingo......you got the best cam for the combo you have!!! Then get it tuned.....enjoy your ride!!! End of Story!

Ben R

There's a lot to be learned from this.

Some people are too stupid to realize they know nothing about everything. Some things are better left to the professionals.

LSonederfull

Is this lobe chart still hydraulic roller? With those lifts they look like solid roller before lash is subtracted.

jrp

iTrader: (16)

they are hydraulic.

Sport Side

iTrader: (6)

Does Comp offer the widest majority of hydraulic roller camshafts for the LS1? I'm curious to know how Crane and say Cam motion stack up against Comp...

Ben R

You should call and ask.

2k2blkss

I just got done skimming this post and I may have missed the answer to my question and if so I apologize. Anyway, here goes...

Everyone is talking about durations at .006 and .050 and finding the lobe design from those numbers. I understand that, but what if the cam specs are at .004 and .050 not at .006 and .050, how would I find out how aggressive the lobes are with these specs compared to the later?

I also have another question, this one is about overlap. Is it more accurate to figure the overlap at .050 or at .006 (or in this case .004) if trying to figure the idle quality of the cam? Or does it matter (overlap is overlap)?

Thanks

jrp

iTrader: (16)

.004/.006 are both considered advertised duration, the same principle applies.

i always use .004/.006 when i can to figure out overlap myself, my own cam i 84* @ .004 and 15.8 @ .050.

LIL SS

iTrader: (9)

Ok.. I am brining this thread back from the dead. Here is what I want to know.

When does a lobe become to agressive for it's Valvetrain?

Let's take my set up for instance (Because I am trying to figure what cam to run)..

348
T91 turbo
M6
AFR 225 heads with hollow intake valve, comp 921's with titanium retainers
Comp R lifters

I think that should give enough info on my set up. Hopefully by the end of this thread you'll see where I am going with this.


Lets take the smallest comp XE-R lobe:

.006 - 269
.050 - 220
.200 - 143

.342 lift (1.7 rocker .581 lift)

Pretty aggresive right?


Well what about TR's intake lobe on the Old Man Cam.

.006 - ?
.050 - 214
.200 - ?

.353 lift (1.7 rocker 600 lift)


With out knowing the amount of duration at each lift point it's hard to guess this but I am assuming the TR lobe is more aggressive. Why? 6* less duration at .050 and .011 more cam lift (.019 with the 1.7 rocker). Seems like it would have a much faster ramp at .200. It is very possible for them to cross over though and the TR lobe could have more of a "peaky" lobe.


So what about a lobe that looked like this:

.006 - 260
.050 - 220
.200 - 160

.353 lift (.600 with the 1.7 rocker)



My proposed lobe is:
9* smaller at .006
Same at .050
17* larger at .200
Has .019 more lift than the XE-R

Seems like it would fill and relieve the cyl much better than the 220 XE-R. I would think a lobe like this would be better in a Turbo setup. Let's use J-Rod cam calculator..

My 220/220 .600 114 lsa proposal

-----.006 - .050 - .200
IVO -(16)---(-4)--(-34)
IVC -(64)---(44)--(14)
EVO -(64)--(44)--(14)
EVC -(16)---(-4)--(-34)
ECL -(114) -(114)-(114)


Very little overlap from .006 to .050. only 16* at .006 and -4* at .050.
Uses the full range of flow on the AFR 225 Casting.



Would this be too agressive in a car that sees 2500-5k miles a year. If I had to change valve springs once a year, no biggy.


TIA for your input..

Adrenaline_Z

"With out knowing the amount of duration at each lift point it's hard to guess this but I am assuming the TR lobe is more aggressive.

Why? 6* less duration at .050 and .011 more cam lift (.019 with the 1.7 rocker). Seems like it would have a much faster ramp at .200. It is very possible for them to cross over though and the TR lobe could have more of a "peaky" lobe."

The change in duration from 0.004" to 0.050" is probably the most important
aspect of lobe design.

Trying to get a lifter to follow an aggressive profile is a huge objective, but it's
even more of a task to change the motion of a lifter from the lobe baseline
to begin climbing the ramp.

A smaller delta between adv. and 0.050" indicates a faster and more aggressive ramp obviously.

At low RPM, the spring doesn't deflect as much and can therefore withstand
the punishment. The clearances before coil bind don't come into play.

At higher RPM as the acceleration of the lifter and valve increases, so does
the effective mass. This is where deflection can cause the coils to touch.

As the rate of change increases, the spring requires more force to stop the load (lifter, rod, rocker and valve). Once the lifter reaches the peak of the
lobe, the mass still wants to continue rising even though the lobe is ready to
lower the lifter.

While peak RPM points increase, the coil bind clearances must also increase
keeping the open pressure in mind.

IE:

THe same valve train components using spring "X" at 7000 RPM, may require
a spring with 0.020" more bind clearance at 7500 RPM (at the same open pressure).

The baseline clearance before bind (by rule) is 0.040"

Add 0.020" clearance for every 500 RPM peak increase if the reciprocating mass does
not change.

That's the "rule of thumb" I was taught when building the valve train.

LIL SS

iTrader: (9)

So how does this apply to me??

I don't mind trying to figure it out myself but I know there are a lot of things I don't know yet


Lets start here:

Comp 921's
Seat Load: 135 @ 1.770
Open Load: 400 @ 1.220
Coil Bind: 1.040
Rate (lbs./in.): 408

This is where I am going to need help

Right off the bat we need to take .600 out of the coil bind because of the lift the cam and rocker ratio. This leaves us .44"

What else do I need to figure out.

Adrenaline_Z

1.770 install height?

That's an odd number. Did you cross reference that seat pressure on a chart, or is that
what the LS1 stock install height is?

The Comp chart I see has only 1.7, 1.75 and 1.8 install heights.

In any case, the open height is going to be 1.17" at 0.600" valve lift.

That leaves you with lots of room before bind IF THE INSTALL HEIGHT IS CORRECT.

Get back to me on that question above. Then we can estimate the clearances.

LIL SS

iTrader: (9)

I took the 1.770 from the comp website.. I don't have the heads just yet as I am waiting for them to come in.

Adrenaline_Z

http://www.powerandperformancenews.c...&Store_Code=CC

That's what I found.

Now confirm that the install height of an LS1 is 1.770", or do you need offset
retainers/locks to achieve this?

LIL SS

iTrader: (9)

Looking at a few different posts including this one https://ls1tech.com/forums/showthrea...install+height the MFG calls out a 1.8 install height but 1.78 seems to be what they were set up with stock.

From what I understand the 921 is a stock replacement spring (Well Dual and handle a lot more lift ect).

Adrenaline_Z

In the end, you'll have to measure the install height to be 100% sure.

It seems these springs have been shimmed to get the correct seat pressure @ 1.770", or 1.780".

If you have 1.8" to start with, you can cross reference the spring pressure
at that height. Make sure the open pressure and seat pressure is adequate
for the valve lift and RPM.

Since you have more than enough clearance, you can use shims to set each
spring to match seat pressure across the entire valve train. Use that to your
advantage to balance all of the springs. In most cases, you'll see 0.005" to 0.010"
variance on a stock head.

I can't seem to find a chart for that spring on Comp's site. You may have to
call the tech line to receive a breakdown for that spring. We can figure out
the rest of your questions from that chart.