please explain, before i misunderstand.


edit: i'm assuming you are referring too, as measured at full lift.

 

Zig, you're getting your threads confused again. You did not ask a question about "lift at half". The question itself is an oxymoron. Lift at half of what?

 

ah yes, i did. i just anted spin to know where i was coming from with my lift at half question.

 

You keep saying "my lift at half question", but I don't see that question anywhere in this thread.

Also, and I repeat, "lift at half" has no meaning whatsoever.

 

That said I've still seen a poorly hardened Comp Cam fail and I know you can't predict product failures. But a higher spring rate (outside of the "normal" 110-135 seat range) will cause a marginal heat treat to die sooner than later. You're also discussing a very specific spring pressure now and thats good. I see you know that but others may not. They just need to remember that you don't just pop some shims in there and call it good. You've got to know what pressure you're running on the seat and peak lift. Its good to talk specifics.

 

you're right i didn't ask about lift at half in this thread, but ttrotary did bring it up.

i thought you were following along, we've been going back and forth between this thread and the cam thread. you, spin, i, and ttrotary have participated in both threads. since it appears i was having a difficult time expressing my question in the cam thread i used ttrotay's comment in this thread to show what i was talking about, since the four of us have been participating in both threads.

ok, it might not have any meaning to you but to me it has meaning.

the numbers in this example are not real, soley used for illustrative purposes:

let's say a set of heads have a max. flow of 500 cfm.
when the valves are closed, you get zero flow.
when the valves are fully open, you may get close to 500.
when the valves are half open, you may get close to 200.

by knowing your half lift flow numbers you will able to figure out how close you are to fully utliizing the flow ability of the heads.

a crude way to find out how close you are is to take your half flow numbers and multiply it by 2 (one for each half). 200x2=400.

400 is a little less than 500.

knowing this and knowing what the heads are supposed to flow will allow you to decide if you want a 'fatter' cam or rockers. (more lift).

the cam controls how far and how fast the valves are opened.

knowing how much lift you will get at half, of the cam's, duration will give you an idea of the type of flow you will be working with. imo, the flow as measured from half duration (cam) to full lift (cam), is where you find out how much power you might be able to make.

 

You are correct, it has no meaning to me whatsoever, or to anyone else who is trying to make an informed decision about a cam, or about heads.

NOBODY measures head flow at "half lift". I repeat, NOBODY! The lift can vary from cam to cam, so the "half lift" would also vary. What you want is constant, repeatable flow measurements that are applicable to any cam, not variable measurements that are only specific to one cam.

As was previously posted in this thread, heads are rated by flow at lift points in standard increments, as follows:

.100" 74 57 .100"
.200" 152 106 .200"
.300" 219 150 .300"
.400" 266 190 .400"
.500" 301 204 .500"
.550" 312 208 .550"
.600" 320 211 .600"
.650" 323 214 .650

ALL flow ratings for heads are rated in this manner. NOBODY publishes flow numbers at "half lift", and nobody that I know gives a hoot about what the flow is at half of the lift for their particular cam.

You also seem to have a hard time distinguishing between lift and duration, as witnessed by the following quote:

"knowing how much lift you will get at half, of the cam's, duration will give you an idea of the type of flow you will be working with. imo, the flow as measured from half duration (cam) to full lift (cam), is where you find out how much power you might be able to make.

 

that seems to imply that you don't care how well a cam works with a particular head.

you are correct. i haven't seen anybody publish flow at half lift numbers. that would dictate a specfic valve size, cam, lifters, rockers, etc.

can you explain your statement of:
"heads are rated by flow at lift points in standard increments, as follows:

.100" 74 57 .100"
.200" 152 106 .200"
.300" 219 150 .300"
.400" 266 190 .400"
.500" 301 204 .500"
.550" 312 208 .550"
.600" 320 211 .600"
.650" 323 214 .650

ALL flow ratings for heads are rated in this manner."

wouldn't this tell me if the lift i get from my cam does not reach .500 i will not get 301 204 cfm of flow.

i'm referring to how 'fat' the cam lobe is. cam lobes are more or less egg shaped. a common size base, a ramp, then a peak. the base determines the zero lift point, the width determines the progression or speed of the lift, the length of the ramp determines the duration of the lift/no lift, the peak determines the max. lift. the width of the lobe at half duration determines the half lift.

if my lift at half duration is .500 and i know the heads flow 301/204 at .500 lift, i know the rest of my intake and exhaust system will need to support at least that amount of flow.

valves spend the least amount of time in their full open (max. lift) state. valves spend twice as much time at half lift, well let me explain that. the valves spend more time in the half open state then they do in the full open state.

if i'm able to determine my half open state and the flow rquired for that state and i'm able to provide sufficient flow to support that state while maintaining sufficient flow for the full open state i will come pretty close to fully optimizing my heads and cam combination.

but, yes, i'll agree, this is pretty much just my opinion.

 

Yes, this is definitely just your opinion, and your opinion only. If it makes sense to you, so be it.

However, there is no such thing as "lift at half duration". That is some sort of unique term that you have coined. Taken literally, it is the same as peak lift. In other words, if the duration is the number of degrees that the valve is open, then at the halfway point of the duration the valve would be all the way open ----- at peak lift.

So, talking about "the width of the lobe at half duration determines the half lift" is nonsense.

If you're interested in ramp rates, and how quickly the cam opens the valves, there is at least one simple way to gauge this using the published specs of the cam. That was is to compare the "advertised" duration (measured at .006") to the duration at .050". The smaller the difference between the two figures, the steeper the ramp. You can see this on the Comp Cams website by comparing two cams with similar profiles. The cam with the "high energy" XE-R lobes will have a smaller difference between the advertised duration and the duration at .050". The greater the difference, the slower the ramp rate.

Here's a link to a whole bunch of tech articles on camshafts and lobe design.

http://www.compcams.com/Community/Articles/

 

I think everyone agrees that an incorrectly manufatured anything will fail and it has nothing to do with what an in spec cam will perform. I've seen failures for everything. You cant make general statements about spring pressure by looking at the excetion to the rule or a manufacturing fault. You set a motor up and if it fails it fails. Cams arent perfect and can fail if the materials used arent perfect. I dont know what bringing up a manufacturing fault has to do with a good cam. I've seen plating come off and I've seen pitted surfaces. That doesnt mean that the same failure you saw would happen over and over with a replacement cam of the exact size and source with higher spring pressure.

Talking specifics is fine. Talking absolutes on mods for cars by quoting the exception to the rule rather than the statistical successes of cams running high spring pressure are dead wrong.

You run the right spring pressure for the application. If you need more than that you use it. In the case we are talking about here, there is valve float on the ETP heads with the springs shipped with the heads and it is verified by a lot of users on the LS1 tech boards. You cant argue about using it or not. The head/springs need to be able to work or talking about cam life is silly. The lobes on an XER cam and the heavy valves used need and work well, with the spring pressures I stated. If one cam failed because of it you dont state that high spring pressures are bad. My cousin has 77k miles on his huge springs with a 232/234 XER with 2.05 valves and heavy open pressure. That is a single example but does or should it carry the same weight as your example of failure?

Running spring pressure is mandatory not an option on the et heads. Cams have and will survive it. The spring pressures the xer lobes used in the LS series motors are nothing compared to huge solid roller cams. They dont fail from the spring pressure so that tells me the cams and what we call heavy spring pressure are nothing to these cams. The hydraulic roller lifters absorp such a huge amount of the strees that I dont see the relevance of your statements here. I have pulled out old school non roller lifers/cams that used heavy pressures and they didnt look all that bad. How can you say anything about wear on a cam that can be removed from a motor at 100k and have no visible wear? Failures from a hydraulic roller cammed car will never be from the cam and spring pressure. It is a manufacturing fault or something else gives up...usually oil consumption. This is a 300k motor design.

You also brought into the equation longevity. No motor that is of max design will last as long as a GM stock motor. Candles that burn twice as bright...

 

You are absolutely right about some tuners wanting to make more money by selling you a head with huge shiny ports that flow great at .600-.6xx lift. I run AFR 205's in my setup because they were designed from the beginning to be a superior head than the LS6 head(the benchmark of LSX heads at the time). I know the LS6 head is a good product & with some skilled work can be made even better, but the new heads on the market like AFR, ETP, etc..., are all designed to be a superior product right out of the box than ported LS6 heads. Personally, I would never spend $1500-$2??? on a port job(prices I have seen advertised on tuner websites). IMHO

Scotty

 

I was referring to tuners that do in house porting for their 6-7k head-cam packages. Some are good but some need to get with the low end TQ times.

 

Well, I guess you don't see that we aren't on different sides of this issue. We're not.

I'll just simply restate...

All spring pressures need to be verified. If you go outside the operating parameters with too much pressure you can and will cause damage. 135 on the seat is not excessive. Anything beyond that is excessive for hydraulic rollers in my opinion.

I'm not gonna get into the cam failures... I've seen it with my own eyes more than once. It just illustrates that proper pushrod length checking and spring pressure verification are a good idea for all. Either one being wrong can cause cam and or lifter damage. It's just a fact and I was simply tossing it out there.

 

but didn't you say it was the same thing.
thanks for the shortcut, i forgot all about it.

Here's a link to a whole bunch of tech articles on camshafts and lobe design.

 

No, I did not. I said it was nonsense. How can "half lift" be the same as the peak lift? At "half duration" the lifter is riding the top of the lobe, so the lobe "width" is effectively zero. If you want to know the "half lift", why not just divide the peak lift by 2?

Enough said on this subject.

 

I have a set of ETP 215s for sale!

http://forums.corvetteforum.com/show....php?t=1533141