I read too many "what cam?" threads these days so I decided to start a thread in hopes of shedding some light on the nature of cam lobe profiles.. specifically SBC and more specifically the Extreme Energy Series. Basically, take a look and ask a question. And remember when it comes to cams there are no stupid questions.

Comp Cams Lobe Chart

 

I'll see what I can do to help on this one.

Just because the LT1 is a dino compared to the LS1 doesn't mean it can't rock the house!

Bret

 

For reference try to post what page number the chart in question is on.. you will find page numbers in the bottom corner just above every blue divider. The SBC XE chart for example are located on page 243.

 

I don't understand the post. Are you offering to answer questions?

Rich

 

Bret thought it would be a decent subject for an informative thread but looks like nobody is gonna care. Basically the idea was to ask questions about cam profiles and build the thread as the questions come in. Any question really but more aimed at lobe profiles and how to understand the nature of a cam based on the lobe specification.

 

ok, since you're answering questions...
what is better to have-more duration or more lift?
why don't more people use 1.7s in cam applications on the lt1?
does more lift (like provided by 1.7s) make the power "peak" more?
i'll think of some more, just trying to get the ball rolling
thanks for the thread too

 

Well, I guess I will chime in here a bit. You can learn quite a bit from the published lobe specs, but far from everything you really want to know. There is not enough info to adequately describe the shape of the lobe. Using you example of what CC publishes: There are three figures for duration (advertised, 0.050", and 0.200" and three for lift (total lift, lift @ TDC for cam installed at 106 and 110 degrees). These last two are useful in estimating piston-to-valve clearance. The other four parameters are useful in estimating the "velocity" of the cam, how fast the valve opens (determined by the steepness of the ramps). Some addtional figures for duration would more fully describe the lobe shape. Alternatively, the manufacturers could just provide a nice scaled diagram of the lobe. But for whatever reason, they do not.

The velocity of the lobe is important. The steeper the ramp, all else being equal, the more area over time the valve will be open and the more potential hp. But there are limits based on the mechanical properties of the lifter and lobe as well as on the ability of the valve springs to control the high acceleration that results from very steep lobes. Roller lifter can accomodate steepr ramps than flat tappets. The steeper the lobe, the more spring pressure is needed to control the vlave and the lifter. More spring pressure equals more wear and stress on parts and shorter spring life.

The XE lobes are pretty extreme (hence the name?) in terms of velocity. Look at lobes 2194 vs. 3162 (an XE lobe). Both are HR lobes with 230 degrees duration @ 0.050". But 3162 has 292 advertised while 3194 is 281 degrees. 3162 has 128 degrees at 0.200" while 3194 is 157 degress. The total lift is .285" vs. .389". So, even with the same duration at 0.050" the 3194 will have a MUCH larger "area under the (lift) cirve" than the 3162. It will make more hp but be much harder on parts. For comparison, look at a lobe like 5216. It is a high performance hydraulic flat tappet lobe with 230 degrees @ 0.050". It is 280 degrees advertised and only 137 degrees at 0.200".

So, here are the number of degrees each of the three "loses" between 0.050" and 0.200".

3194: 73
3162:102
5216: 93

I find this number a reasonable way to compare lobes in addition to the duration and max lift. The XE HR lobes are about the same as race SR's in terms of my "index". For example, #4151 goes from 252 to 172, a difference of 80 degrees when opening from 0.050" to 0.200". Pretty similar to the #3194 XE HR. The mechanical limits of the roller and lobe are what keeps the difference from getting much smaller. Larger diameter rollers allow steeper lobes.

Rich

 

Those CC EX-R (LS1/6) lobes are also really “extreme”…especially when you account for their rocker arm ratios. I think the real challenge is selecting the proper lobe for the application, and then the correct valvetrain to support it.

 

They also have a big journal 55mm so they can have a more aggressive lobe and it's still controlable.

Bret

 

How can you work out the valve lift at TDC for a 112 or 114 LSA? The charts give tappet lift at tdc for a 106 and 110 but is this of any use?

For example, the hotcam or a 224/230-112.

 

If ya know the lift with 1.5 or any ratio divide the lift by 1.5 and that gives ya the cam lobe lift. Then multiply by whatever rocker ratio ya are going to use.That will give ya the lift you are using.

Lift don't change with LSA.

 

Even though the LSA may or may not change as the lobe centerline(s) change, the lift at a given point in the crank rotation will. With the question being in regards to lift at TDC, as the lobe centerline (peak lift) is moved either way (advanced or retarded) it will alter accordingly, the amount of lift at TDC. The max lift is unaffected however. HTH.

 

Wasn't the question for lift AT TDC?????

 

Yes it was!

I wanted to know how to tell just how much valve lift would occur at TDC for a given LSA, assuming a tighter LSA would give for a higher valve lift at TDC so as to allow easier scavenging and less LSA would be the oppisite.

For example, the Hotcam with its 112 LSA, assuming its timing is neither advanced or retarded, how much would each valve be open at TDC of the exhaust stroke? I am assuming that at TDC both valves would be open by the same amount (when the sum of both valve events at this point of overlap are at the maximum for the given LSA i.e. slap bang in the middle of the two cam lobes), or would this occur before the piston reached the top?

Not to be confused with maximum lift.

 

Both valves are closed on the compression stroke and on the overlap cycle both valves are open a tad at TDC depending on grind.
Again depending on grind there is a point in the overlap that both valves are open and at some point they will be equally open. The E has gone Way past TDC fixing to close and the I is just coming on and a long way from TDC opening.
The cam grinder knows all these pieces of the puzzle and ya need not worry about trying to out figure them,they have been there done that. Unless ya put a degree wheel and indicator on a given cam and measure it it's a lot of figuring and I'm lazy.
Don't know what ya are trying to accomplish with this thought train.