Keeping the exhaust valve closed longer allows a touch more force on the
piston crown during the tail end of power stroke. Keeping the valve closed too
long will hamper the removal of exhaust gas as RPM increases and as charge
increases.

How critical is EVO when designing a camshaft? I have a feeling it's more a
product of where EVC falls as the positive pressure in the cylinder would have
an easier time moving spent gasses out.

Along with MadBill's post, are we limited to the best valve events because of
mechanical considerations? I wonder how much later EVO could take place
if we didn't need to gently open the valve.

This seems to be the desired pattern for race motors. So the trend we're building
is IVC is closely related to low end torque; IVO and EVC are brother and sister
which must be figured carefully to tune a certain upper HP peak...and EVO
would like to be opened as close to BBDC as possible, but is taking a back seat
to EVC for the most part.


With F1/Indy using a pneumatic valve, would it be safe to assume LSA (and
other valve timing) is changing throughout the RPM spectrum?

How else could a motor be efficient from idle to +20K RPM?

 

59*?! You must mean the ramp duration... (Adv Duration - Duratio at .050). A smaller number means a faster ramp rate. Picture the curve between the top and bottom of the lobe. The smaller the number, the more straight up the curve, so faster ramp rate. 59* is a relatively fast ramp rate. 50's is fast, and most ramp durations are around 60-something or higher.

These are the numbers I'm really looking forward to from your cam test. Crane Cams does such a good job on their site, because they have everything you'd find on the cam card. I know you weren't going to test similar cams, but it would really be useful to see dynos from similar cams with different ramp durations. For example a couple of 230 duration cams or 224 duration cams that have radically differnt lobe shapes / ramp durations. Most of us have headers, etc., so we aren't going to see big differences in playing with split, right? Also, most of us are probably looking for cams with lift ranges around .570-.610 (how much of factor are the .650-lift valvetrain parts: dual springs, Comp-R's, etc. on power for the same .600 lift cam???). So that leaves LSA (or really overlap) and ramp duration to differentiate the cams, and of course duration at .050. Assuming again that a lot of us fall into two groups: over/under 230*, for example 224 vs 230 (or in the case of the F13, 230/232), how should we best compare two spec-similar cams, like the F13 and somebody else's 230 cam? By LSA or overlap (not many choices really), or by ramp rate and lift?

Whoa, did I ask that in a way that makes sense???

I subscribe to the idea that LSA is a final choice once everything else is selected, and is a pretty minor variable (considering most off the shelf cams are either 112 or 114, with a few 110s and a 106 or two...).

 

No, it wouldn't be safe.

F1 engines use pneumatic springs and metal cam lobes, not pneumatic valve actuation, (at least not that they will admit for on-track engines).

Indy (IRL) engines use metal springs, AFAIK. They only spin 10,300 or so and are sorta production based engines..

Any DOHC engine with variable phasing on the individual cams can vary LSA of course. Even just varying the exhaust cam on the GM inline 4,5,6 cyls varies LSA as much as 25 cam degrees (LSA being about the only thing quoted in cam degrees).

F1 engines can do neat things like have one bank of cylinders lead the throttle opening by a programmable amount over the other bank to shape the torque curve. Rarely do F1 engines pull at WOT (Wide Open Throttle) below about 10-11000. Cut the r's about in half for a Cup engine and that would be say 4500-9000, about where the Cup engines work at Martinsville. That's without any variable phasing or variable advance.

 

Good topic.....

The EVO and EVC events are both areas to play with. You realize if we start changing just one of them both our ECL, LSA and exhaust durations will change. If you close the exhaust valve at the same time and then open it later then you lower the ECL the LSA and the duration of the exhaust lobe. EVO can be tricky though because too early will kill your TQ and too late will kill the HP.

This all works into the second part of what you said. Mechanical considerations.... Are you talking about P to V clearance (since more overlap causes this to be a issue) or are you talking about the actual physics of running a valvetrain not just the physical aspects of moving the events around?

The last part about EVO and opening the valves gently is a good point.... might be something you want to ask Overton. He seems to like asymetrical lobes. Just busting on him... anyways. The opening side of the events doesnt have to be gentle at all in a hyd roller. The faster you can open the valve the better for the exhaust side, because you can delay the opening of the exhaust valve even more to hlep produce midrange TQ. When you close the valves you want to do it gently to prevent valve bounce. This is important on the exhaust side due to P to V problems and on the intake side because it really effects the IVC, DCR and the whole TQ curve. When you have the time and money to lighten everything up and play with the valve dynamics on a spintron you can gain power by slamming the intake valve closed, but for most of us it's just going to cause issues.

Bret

 

I have tryed to read all of the postings in cams 1,2,3,and this one and lost track of who said what ( to much to read in one sitting)

but the posting in this thread is drifting off course from what is known about cams .......

first low end power is controlled by the IVO point as you open the valve sooner you will see more low end power

second the EVC point should not dip to far into the intake cycle or you will have to much ex gassses drawn into the cyl at low rpm this causes bad idle and loss of power below 3000 rpm

these two facts are why you gain low end power when you advance a cam 4 degrees

third the EVO point is not that fussy ..... + or - 10 degrees does not change much

forth the IVC point is hard to calulate without some software and info on the motor ...... if you hold it too long you get revertion into the intake at low rpm if you cut it short then the motor falls flat on the high rpm this is where a good cam co can help you find the right one for your rpm use .....

 

Looks like you gotta reread some of this stuff....

IVO is happening as the exhaust valve is closing, opening the valve sooner will create more overlap, which as we have discussed causes issues with the low end TQ, you don't gain more either.

Yes, this can happen, same thing happens when you hold the intake valve open too long during the overlap cycle.

I would disagree. That's why we wrote so much the last week.

Actually this is where you are confusing the IVO and IVC. If the IVC stays open too late then you are going to loose all the air fuel you are trying to compress since the pressure in the cylinder is going to be higher than the pressure in the intake port.

Bret

 

There are those meant to lead forums like this, and there are others who
should just sit back learn, and ask questions (I'll place myself in the latter).

LS1Tech should give titles to those who have experience in certain fields
(IE: In place of tags such as "Teching In", or "Tech Resident").

That's all I'm going to say. I'll be nice.

 

I know I am the NEW guy but that crack is unwarranted

I am not wrong about how cams work and I do understand you are trying to make use of intake pulsation to "supercharge" the the incoming air but that technology is not new and even if you make the 2nd harmonic work it is only going to add 10% pulse strength at peak power while taking away 5% at all other rpm's plus while trying to make a cam for it you are ignoring everything else that has been learned about cams in the last forty years ....

advancing the cam will make more low end power and retarding will make more high end power plus moving the cam like this does not change LCA that is ground into the cam so it does not change overlap ...... having a cam ground with a little more duration on a wider lobe center and then advancing the cam back so that the closeing point of the intake valve is back where it started will add more low end power I know this becouse I have done this very thing peak power stayed the same but low end torque picked up almost 20 ftlbs how far can you go with this I do not know but I have ground the next step up to try when I get time to swap cams

 

No offense, but I do feel that comment was necessary.

You've taken some pretty credible and accurate responses and blown them
way out of proportion with incorrect statements.

This statement is pretty brave:
This statement is incomplete; there are other valve events associated
with creating low end power:
This quote is useless without stating a direction, or target goal. Maybe we
want EVC in certain places to position our average power at a higher RPM.

This one just blows me away. Even if you're talking in seat to seat terms!
Do you have any idea what happens to the valve timing and cam dynamics
by moving EVO +/- 10 degrees?
If I didn't know any better, I'd be confused reading this page of this thread.

 

Yeah, I had to turn up my ** "filter" on some of the posts.

"Who do you trust?"---Joker in Batman

 

Dude ain't so bad he just got confused on intake opening and closing events.

 

Back in 01 the posting on cams was good what you guys have written on page 4 is hard to read at the top of page 5 I do understand you are trying to gain more hp by starting the intake draw sooner using the ex velocity to draw chamber to a vacuum lower then the intake runner …. First off at low rpm you will not get a draw and ex gas will flow back into the intake port and dilute the incoming charge. Second this only works when the ex is very free flowing as in open ……and when it does work it will be at only narrow band of rpm so why worry about it at all? And how will this help make my car faster on the street where the rpm band is mostly 2000 to 5000?

And if you open the intake valve sooner but do not increase overlap you will see more low end power because the highest draw on the intake is at peak piston speed which is about 70 to 75 degrees after tdc so as the center line (which is peak valve lift) of the cam moves closer to this point you get a better draw and therefore more power in the low rpm and mid range it does not help in high rpm because the air does not move fast enough to fill the cyl before you are past the centerline of the cam …. At this point the intake-closing event is going to help make more power due to the velocity of the air column in the intake runner ……. So opening helps low rpm and closing helps high rpm I have run cams from straight up to 10 degrees advanced and more advance helps low end power

If you look at race cams they are at tight lobe centers…… this is not to make use of the fifth cycle but to make power with big durations when the ex has a lot of duration on a wide lobe center you cut the power stroke short…… for the most part you do not want to go more then 70 degrees bbdc on the EVO point but on the other hand with the tight lobe center cam you have a lot of overlap which kills low end power this is why race motors idle at 1500 rpm and run 5000 stall converters ….. Something that I would guess few here want in a cam

If you go to a wide lobe center IE say 122 you will have a late start on the IVO unless it is a big duration and will hold the intake open to long and cause reversion

The factory thought that something like 114 or so was good but made sure the duration was short enough that there was little overlap when we look for more power it would seem to me that if you keep the lobe center at this point and up the duration some then if low rpm is not good enough advance the cam a little to open and close the intake sooner (both of which will help low rpm power) you can get more power with out the drawbacks of a wide or narrow lobe center

Here are some links to information that supports my claims about how cams work

http://www.hotrod.com/techarticles/1...am/index2.html

http://www.hotrod.com/techarticles/1...am/index2.html

On this Isky link look to the right under figure 17

http://www.iskycams.com/pdfcatalog/PAGE184.pdf

http://www.iskycams.com/pdfcatalog/PAGE184.pdf


http://www.actionspeedparts.com/calc2.html

http://www.actionspeedparts.com/calc2.html

http://www.elgincams.com/campaper.html

http://www.elgincams.com/campaper.html

This is from Elgin link above

VALVE TIMING EVENTS - ORDER OF IMPORTANCE
Let us now take the four valve timing events and put them in order of importance. The LEAST important is the exhaust valve opening. It could open anywhere from 50 degrees to 90 degrees BBDC. If it opens late, close to the bottom, you will take advantage of the expansion, or power, stroke and it will be easier to pass a smog test, but you will pay for it with pumping losses by not having enough time to let the cylinder blow-down. You must let the residual gas start out of the exhaust valve early enough so that the piston will not have to work so hard to push it out. Opening the exhaust valve earlier will give the engine a longer blow-down period which will reduce pumping losses. But, if you are only interested in low speed operation, say up to 4000 RPM, you can open the exhaust valve later.
The next least important timing point is the exhaust valve closing. If it closes early, say around 15 degrees ATDC, you will have a short valve overlap period. Less overlap makes it easier to pass the smog test, but it does not help power at the higher engine speeds. Closing the exhaust valve later, in the vicinity of 40 degrees ATDC, will mean a longer valve overlap period and a lot more intake charge dilution that will translate into poor low-speed operation. Some compromise must clearly be made to determine just how much overlap one needs to use. Many factors such as idle quality, low speed throttle response, fuel economy, port size, and combustion chamber design must be considered in making this choice.

http://www.hotrod.com/techarticles/18218/

http://www.hotrod.com/techarticles/18218/

So far the case looks good for tight LCAs, and so it is, but there are tradeoffs. Increased overlap equates to reduced idle quality, vacuum, and harsher running prior to coming up on the cam. Probably the most significant factor to the engine tuner though is a tight LCA’s intolerance of exhaust system backpressure. Remember, during the overlap period both valves are open. If there’s any exhaust backpressure or if the exhaust port velocities are too low it will encourage exhaust reversion. The tighter LCAs are, the more likely problematical exhaust reversion into the intake will occur. Put simply, we can say that a tight LCA cam produces a power curve that is, for want of a better description, more "punchy." At low rpm when off the cam, it runs rougher, and it comes on the cam with more of a "bang." A cam on wide centerlines produces a wider power band. It will idle smoother and produce better vacuum, but the price paid is a reduction in output throughout the working rpm range.

 

I think something else to note here is that in higher compression motors the earlier opening of the exhaust valve will not hurt things quite as much cuase higher compression motors tend to exert most of their forces on the piston in the upper part of the power stroke not making the lower part, during where the exhaust valve may be opening depending on your cam, nearly as important. I think this works well for these high compression motors cause they tend to be race oriented with a much larger intake valve in proportion to the exhaust valve; therefore, they need to open the exhaust valve much earlier to avoid loosing power do to pumping losses created by stubborn exhaust pressure which may be hard to remove from the cylinder if enough time is not aloud via early exhaust valve opening. As I've stated before I think this is why you see most of these high compression big rpm cams run with wide splits and wide lsa, that is cause they will be opening the exhaust valve much sooner relatively speaking in comparison to a tight lsa shorter split cam.

I think to assume that the EO is not as important is just foolish. It think your combination is the determining factor in which event is the most important. My opinion is that the IC is probably the most important; however, the following three events importance are determined by your combination and needs from the camshaft.

 

Also, would it be wise to say that a long rod motor with longer dwell time at top dead center would want more overlap or more overlap could benefit the longer rod motor? Overlap occurs when the pistos is primarily at top dead center. Now if you have too much of it in a short rod motor and the piston starts to travel down it's bore during the intake stroke couldn't this cause contamination of the intake charge via pulling in exhaust gasses into the combustion chamber. A long rod motor will not start down quite as early so may benefit from a little more overlap. This is more of a question I'm asking then anything.

 

Carlo, you are certainly not proving to be the engine tuner you claim to be,
or have understanding of camshafts - mainly the bold point.

Overlap is a very necessary evil to make power. Read back between
pages 3 and 5, the answer will lay within.

Look at any cam grind, there is overlap. Ask yourself why?

You'll gain my respect if you can throw down as set of numbers for a cam
to work well between 2000-5000 RPM (which is a pretty weak range for
racing applications I might add...)


Seems like you've started with the wrong cam grind since you're dialing in another
ten degrees? 10 degree advance...wow
I guess we can really take advantage of scavenging without overlap then.
Thanks for the info.

I didn't know all race motors idled at 1500 RPM and used 5000 stall torque converters?
Geez, I wonder what the pro-stock, pro-mod, top fuel engines idle at?
I can tell you it's a touch higher (and guess what? No torque converters!)


I'm thinking there's a lot of bench racing going on here. Too bad it had to
come between the pages of a decent thread.

 

I would agree with that. Something more suited for a strip oriented engine,
as opposed to a dialy driver. That recipe is asking for rough idle no doubt.

Good theory. I think this is going to depend on how strong the pressure
waves are exiting the exhaust at certain times in the engine cycle/RPM.

Let's assume that there is a strong negative pulse reflected back at the
exhaust port as the piston begins to drop down ~ -5 PSI.

Even at the point when the inside cylinder pressure reaches - 5.01 PSI, there will
be a period of time and energy needed to reverse the exhaust gasses (inertia).

It's possible that the intake charge will continue to flow down the exahust port
and limit/prevent the exhaust gas from contaminating the mixture.

During the next cylce, we might not be as lucky and end up with a higher exhaust
port pressure (~ -3.0 PSI)

Those are my thoughts anyway.

 

Its cool that you find the elgin stuff good to read. They actually grind all my cams. Have a good friend that works there.

Anyways, here is my quick thought. LSA is nice to talk about, but not always worth talking about. Valve events are where its at. When you build a motor, you need to sit down with your motor specs. You need to look at things like what are the valve events at 75 degrees. You need to look at how much lift you want to achieve because of your cylinder head at a certain given time. You need to figure out if you have X amount of static compression, then where do you want to close the intake valve to have X amount of effective compression. Or better yet, Its actually better to pick the valve event first, then choose your compression last. This also helps too. Alot of your power band is dictated from when you close the intake door. You can also control how much TQ your motor will put out when you know all this stuff as well.

Some people talk about nitrous like it only needs a wide LSA. Well, I guess that would be true if everyone had the same gears. Has anyone ever tried nitrous on a car that had a tight LSA and on a camshaft that made good cylinder pressure? Its fun. And with the right gears out back, no one can touch you. The car I am currently doing right now has almost 300PSI cranking pressure during a compression test. Stock bottom end, 91 octane, and with only a LS6 intake is doing about 435TQ through an Auto. This car is responsive. And nitrous will go on this car.


the advice that would help others is this. When I first started, I would here about one thing on cams, and I would only try and work with that particular portion of the cam. I thought if I learned about LSA, I would play with that. then I learned about duration, so I played with that. then I learned about valve events.....you get the point. Just be careful. Cam tech is alot to take in. If you ever ask anyone about cams, take a sheet of paper, make a list of what you want out of your car. Send it to someone who can build you something. I do this for people everyday. I sit here with multiple programs, scratch paper, cam cards, ect, trying to help others understand more about what they want. It works. And its a great way to be satisfied with the cam you choose.

Not to bash internet cams, but alot of people choose them because of the HP factor, or the bigger is better theory. Well, I always ask, how much more compression do you plan on putting back in the car with that cam? Or, what gears do you have? They will make power, but only if done right. And the whole idea of +2, +4, well, thats just to help with drivability if you ask me. grind it straight up and go for less duration if you want that. Hope this helps.

FWIW.....I too learn new stuff everyday, and love to hear other views as well. Thanks.


Rick

 

caddycarlo,

Go to the store and pick this up.......

http://www.popularhotrodding.com/eng...rs/toc/em_toc/

Read the article:

Separation of Power
Does Lobe Separatioin Really Matter?

Changing from a 112LSA(13° of overlap @.050") to a 108LSA(21° of overlap @.050") had a peak gain of 24hp and a average TQ increase of 10ft lbs.

That might help you make up your mind.... This is just a recent test of this, David Vizard has done tests like this for YEARS all you had to do is look in the right spots for them. Hell his out of print book was copywrited in 1992.

I do agree that EVO is the least important event.... but that doesn't mean you shouldn't play with it. IVC will always be the most important, with the IVO and EVC being 2nd and 3rd because they deal with the overlap.

Rick,

That was some great thoughts.

Yep.... and what does the lower ICL do to this? It usually improves it.

AdrenalineZ adds a good thought to this.....

The inertia of the air/fuel charge is very important as well, because even though the piston speeds are the highest at 75° ATDC, the air/fuel charge speeds are still increasing 30°-40° after the piston is at max speed. (105°-115° ATDC) The air/fuel speed stays higher than what it was at 75° up to around 140°-150° ATDC and starts to drop of very quickly after that, as the piston is moving up the bore and the valve is closing. The cool thing is the pressure in the port is turning from a vacuum to a postive pressure in a well designed motor as the speed goes down.

Or work them back and fourth until you find the best mix of IVC, Dynamic Compression, Octane and Static Compression for the RPM band of the motor.

Bret

 

True, I do find myself doing alot of that. Although it works good picking compression last sometimes, I find that I need a goal with my compression first so I know what I want. So yeah, your right.

Rick

 

Are we able to discuss the relationship between secondary collector length
and valve timing?

Maybe we can pick an RPM and work from there? See how exhaust length
alters the overlap tuning, etc.?

My first question is:

How isl the secondary length calculated? Do engine tuners look at EVO & EVC, or do they tune exhaust length for overlap (factoring intake runner length as well)?