Cam Lobe Centers

[58 Plastic Tub]

In my never ending quest for understanding...

Since I was a young man (many years ago), I've understood what is going on with camshaft lift and duration. Lift is easy to understand, as are ramp speeds- and that the longer the duration, the greater the overlap when both valves are open. A long duration cam moves the torque peak up the RPM range at the expense of idle quality and low RPM torque and vice-versa. It was all so easy...

... and then I found out about lobe separation angle, and its effect on pretty much everything.

Most normally aspirated VW cams are ground on 108 deg lobe centers, and the turbo cams are on wider (112 deg or so) centers. According to what I've read- decreasing the lobe centers increases total torque, lowers the torque peak, increases dynamic compression ratio, increases overlap, and narrows the powerband. Increasing it has the opposite effect- total torque is lowered, the peak is raised, the dynamic compression ratio is lowered, valve overlap is decreased, and the powerband is wider.

It's the secret sauce, it seems.

The holy grail, of course, is a cam with a decent idle, good vacuum signal, with a flat torque curve that starts just off idle and doesn't peter out until 5500 RPM, snappy acceleration, and long legs. I'd like to be 25 again too.

Is this best achieved by taking a longer duration cam and grinding it on a narrow lobe center, or by taking a shorter duration cam and grinding it on a wider lobe center.

Nothing is ever said about it, or about advancing the cam relative to TDC. A dozen guys a week ask for cam recommendations, and ther are 15 posts that say, "I like the FK7" or "I like a W120". Nobody talks about getting an FK43 ground on a wider lobe center, and then advancing it 4 deg, or something similar.

Anyhow- everybody talks authoritatively about connecting rod angle and it's effect on moving the powerband up or down- but nobody talks about the lobe centers of the cam, or advancing it, when both seem to have a much greater effect on performance.

Not everybody reading here wants to build a 1776 for $500. There are at least some of us who are willing to do what it takes to build big power- but want to see some actual engineering going into selections of this nature. A W120 really isn't the do-all and end-all answer to every question.

Anyhow- I want to get a handle on what works. Let's call a 2110 the base engine, and a 2332 "normal". Everybody wants big torque early, and doesn't want to fall off until 6K or so. Let's assume that the heads are good, and nobody wants less than .500 of total lift.

Is 300 deg duration cam ground on a 106 deg lobe center better, worse, or the same as a 285 deg duration cam ground on a 110 deg lobe center? How are they different? What is the happy medium?

Inquiring minds, and all that....
_________________
Stan Galat
"Everybody is entitled to their own opinions, but not their own facts."

[RockCrusher]

It's good that you're inquiring and open minded. What you said about what "everyone wants" is why I like the FK-42 with good heads. Now that is a dangerous thing to say since it is a lot like the "I like the W-120" crowd. I don't just like it for everything though. To me it is a bread and butter cam, but even at that it is not so simple.....
Cam choice needs to be based on what the engine REALLY wants and that is about displacement, valve size, port flow and exhaust selection. A very effective exhaust combined with a large intake will require less overlap than an under valved or low port volume head. All other aspects of the cam should be generated by the overlap, not the other way around with overlap being the by-product. Forget about duration....THAT is the byproduct of the right choice.

RC
_________________
[email protected] Please use email for all general inquiries.

I will be happy to speak to anyone who has a serious inquiry (meaning real potential business for RC enterprises) or a parts order. Due to machining noise causing missed calls all calls will be returned promptly.

[modok]

DAM right RC, you got it!

I'm up for it.
We must narrow the parameters more, talk about the seperate events
In order of importance:
IC - intake close (most important)
IO- intake open
EC exhaust close
EO- exhaust open

By adjusting the lobe center and advance we can take two different cams and time them so the IC is the same, but all else is different.

I think we all understand the IC point well enough.

The IO point and the overlap is important too.
Going extra far with the IO point and overlap helps most of the powerband, but it can hurt power at the very top, and funk up down below the powerband.
You know, these guys that complain "it runs funky at 2500 rpm", probably should have used a wider lobe center if they wanted a 'no powerband" kind of engine.
I don't really care how mine runs at full throttle below 3000 rpm. If I'm needing power that low I downshift.
Can't downshift effectively to first, but if I'm going that slow, I slip the clutch instead.

Anyhow I was saying that opening the intake sooner may help at every rpm the engine is "on the pipe" and "on the cam", but it may hurt the very top in some cases and it WILL funk the low rpms somewhat depending on the header.
There is no reversion due to intake vaccum with IR carbs. I used to think there was, but I was wrong.

[modok]

Now remember I am talking just changing one thing, leaving the IC point the same.
The "powerband" of the engine will be determined by the header, intake length, intake diameter and head flow, and IC point.

Now the EC point, one thing it can make or break is the top of the powerband if the exhaust flow is marginal up there. If the piston coming up towards the end of the stroke is outpacing the flow, delaying the EC point(and maybe retarding the cam in general) will help the top end by allowing more TIME for the exhaust to keep going after the piston has come up.
But if you have more exhaust flow than you need, extending the EC point should show no gain at all.

how bout that?

[nsracing]

What kind of crock is this, Modok? More overlap ruins the topend? Racing cams have huge overlaps and sloppy at lower RPMs. You have to get the RPM higher to get the volumetric efficiency and get the "seal".

First, the lobe separation is in the design of the cam to compliment the lift and duration and overlap. The cam designers bother w/ the lobe separation, but not us the end-users.

2nd, all the events are important, not just intake closing.

You lift the valve ye high (net lift). How long that particular valve stays open (duration), and the overlap when both intake and exhaust valves are off their seats at the same time in that particular cylinder. Timing of these events are all in the design of the camshaft.

You should not build and engine around a cam. You design the engine and choose the cam last to compliment the components.

Reversion of the intake charge happens when the piston starts to move up on compression stroke w/ intake valve still open, not intake stroke when the piston is on its way down.

Advancing or retarding cam timing has its ill effects. You are better off installing the cam "straight up" according to cam card.

my 2 cents.

[58 Plastic Tub]

It seems as if most questioners on this forum are trying to get 130 hp out of stock heads and an EMPI quiet-pac for $500. I'm not that guy.

I'm a moderately successful small businessman with 3 grown kids and a gear-head streak that runs back to my misspent small block Chevy days. The car is a tube-frame Intermeccanica speedster replica. I don't ever take the car to the strip, but I want V8 type torque, and the ability to drive across several states to an event. In short- I want it all, but I've been willing to pay.

Right now I've got a short rod (5.325") 2332. It's got Chinese nicasil cylinders and Venolia pistons set at .060 deck. The heads are welded port VW castings (for cooling) with 44 x 37.5 valves, and big ports. The combustion chambers & piston tops are coated, and the static compression works out to 10:1. I'm running a 1-3/4" sidewinder and 48 Delloros. The Chinese nicasils were the only compromise, and I've hated myself for it ever since I did it.

Blow-by has been an issue with the steep rod angle and jugs of unknown expansion rate. Total-Seal seconds have gotten it under control, but I think it's just masking a problem. I'm going to put in some genuine LN Engineering 95s with a Porsche ring-pack, and some 5.5 or 5.6 rods. Presently, on a hot day with 93 octane I can't run as much timing as I would like, or run as lean as many posts on this forum would recommend without pre-ignition. I'd like more tuning flexibility.

The builder installed his own custom grind cam, which I'm attempting to get a cam-card for. The engine was built to maximize low end power, made 201 hp on an Orange County dyno (at 5500 RPM) and has a very flat torque curve to about 5000.

I'd like to make a cam selection for a near-2.4 L engine with good heads and good intake and exhaust systems- something that will give me a "no powerband" powerband (thanks Modoc)- power starting off idle and not dropping off until 5500- 6000 RPM. I'm not afraid of a custom lobe center or advancing the cam.

I was running a 2110 with 40 x 37.5s, a 1-58" sidewinder, and dual 40 Dellortos with an FK43 installed straight up before this engine- I really liked that cam.

I've got 1.4 rockers and sleeved lifter bores. Static compression ratio will follow the cam selection (the JEs with LN's package are custom, so they can be dished to set CR). I'll be running a .040 deck no matter what.

I'm open to (soliciting, actually) suggestions, but they need to make sense.

Let the pontificating begin.
_________________
Stan Galat
"Everybody is entitled to their own opinions, but not their own facts."

[slalombuggy]

Why such short rods? On an 84 stroke crank even a 5.5 rod is a comprimise as a 5.7 will get you near the ideal rod ratio.

My next "street" motor is a 2332. 44x38 wedgeports, 48idf Webers 1 3/4 merged header, Pauter 1.4 rockers and an Fk-87 probably run at -2* from straight up to get the power band down a bit.

brad

[58 Plastic Tub]

Short rods bring the powerband down, although it's tough on wrist-pins, rod bolts, and cylinder seal (all things accounted for in the build). Long rods are better for high RPM operation, which holds less appeal than you would think on a street engine. I want big power just off idle- 7000 RPM shift points, while exciting, are of little value for my application.

Either extreme is, well, extreme.

I've gone to one extreme- I'll not be going to the other. 5.5- 5.6 rod (a 1.66- 1.69 rod ratio) seems about right for an 84 mm stroke (target for something "all around" would be about 1.65).

It doesn't matter as much as the cam, and cam selection is what this thread is about.
_________________
Stan Galat
"Everybody is entitled to their own opinions, but not their own facts."

[RockCrusher]

[slalombuggy]

You could also consider a split cam with different intake and exhaust durations and lifts. I've seen them on here from SLR and Webcam. But RC is right about talking to a cam grinder and telling them what you want and need as the best idea. You'll get 1000 answers here and not really get to the goals that YOU want.

I wasn't suggesting going to a 5.7 rod, but at least a 5.5. My motor with 5.5 rods is only .180 wider a side and a good compromise for durability and power band. You'll be more than able to compensate for the longer rod length with a cam.

brad

[nsracing]

Cam designers and cam grinders are very different people. The latter will probably not have a degree in Engineering. But I am sure he or she can set that grinding machine to whatever angles your heart desires.

Well if there is a cam designer in this house, let him speak. This will be the proper person to give advice.

Seems to me the original poster has grasp of how a combustion engine works. But if you want lower-end torque, why use extremely large ports in the heads? Airspeed is key.

Also, the engine is making power and no slouch. I will do smaller changes so you can gauge the effect. Change rods if like and see. Or Try a pair of smaller port heads and see. Then of course, a change in cam itself.

There are endless articles on making HP everywhere in the RPM range. There will be no guesses here. These are actual not theoretical.

Is it a stump-puller that you require?

[modok]

NS- I meant early IO can show no increace in the top end, dispite the fact you have "more overlap" got to be careful how I word thing huh? hehe

Big power off idle? whoa there 58 Tub, I mean YOU have to be careful how you word things too. With the big cc big stroke short rod setup you have I see that as an attempt to bring the powerband down, have a torquey engine that is on the cam soon, but you'll never get it "off idle" unless you idle at 2500 rpm. i mean it may SEEM like the powerband goes down that low, but really you have the wrong kind of engine and car to be wanting TRUE off idle power.

Wider LC will make it so it runs better "off the cam", more tractable at lower rpms and but also does not kick as hard when it kicks in. Perhaps a bit less overlap and other changes will give you what you want.
I do not know a lot about engines of this size, but Ken Tabor has reported that even with 84 stroke monsters it takes an fk-65 or fk-41 to allow the engine to pull a full load off idle.

I mean for real this guy has a 4-cylinder sports car with italian racing carbs and he wants "big off idle power" ?? scuse me?

How about "smooth driveable power at low rpm", would you take that?
It being a sportscar, seems like agood idea to build an engine with a sportscar type of powerband.

[nsracing]

Modok, when you say early Intake Opening.... are you talking about wider lobe separation?? ...or larger duration to achieve the early intake opening???

Large overlaps do not work very well in slow engine speeds. The purpose of the overlap is so you have a running start on each event of a 4-stroke engine in very high engine speeds.

If you want the power to come on "off idle", it is gonna have to be a lawnmower camshaft. You can forget overlap on that cam. The engine will be pulling up a stump and it is just idleing.

[modok]

I'm saying like if you took a given cam on 108 LC, and used 5 degrees more intake duration and went from a 108 to 105 LC, thus moving the intake open point sooner but the other points are the same.
Like my web 110/165 on 105 lc, advanced 5 degrees. vs an engle 110

[SamT]

You won't hear experts talk about changing lobe centers and advancing/retarding cams because that is a trade secret of theirs. It is what makes an engine special. Some grinders will make a suggestion for you. Steve Long Racing has done pretty good for me as far as "custom" cams, All that I have bought from him were his popular grinds with lobe center changes he suggested, and I have felt that they outperformed a off the shelf cam that is very similar. Price is pretty good too, I don't think he charges extra for lobe center changes.

[RockCrusher]

Like I said, MOST cam grinders won't do a special lobe and that's because they use cam masters (old school) but will allow you mix and match any existing lobes they have and any separation angle you want. The ideal cam grinder would own an CNC cam center.....ahhhh if only I were rich.

RC
_________________
[email protected] Please use email for all general inquiries.

I will be happy to speak to anyone who has a serious inquiry (meaning real potential business for RC enterprises) or a parts order. Due to machining noise causing missed calls all calls will be returned promptly.

[mark tucker]

well it also depends on the duration of the cam, just saying a wide or a narrow will kill the low or topend power is ridickulass.. I sugest to the op to contact harvy crane or download his book(s).yes he is still kicking .I have talked with him a few times and he is still sharp as ever.but he dont grind cams any more..when I had engle grind my hyd type 1 roller I has a 110 not a 108, duet to it not being a killer size cam.and yes it is a lot easyer and cheeper to build the best of what you can and then make a cam for it.rather than trying to make a pile of parts fit the cams specs. and hear is a funny thing I bought a book on HOW TO CHOOSE YOUR CAM !!! it list almost everything about camshafts and explains them pretty well for beginers,but when it came to lobe seperation they said it was to hard to explain so they would skip over it !!! this was a very nice book, newely printed,but why would any body do that??? what a effing moron.thats like a chiltons manuel telling you to take your car to the dealer wtf??? morons. plain & simple morons.

[58 Plastic Tub]

[mark tucker]

It would be nice to be able to put togeather a dyno mule with the ability to change cams fast& make small changes and see what happends . like a 260 @ 05, 108 vs a 110 &112. then a 264 &108&110&112&throw in a 105 to see .you could end up with defrent opening or closingon the same size,or the same opening or closing with a biger but changed lobe sep. I reckon I could do the desktopdyno for a day or so.but thereare alot of variables not accounted for but with that said everything but the cam would stay the same.I ran a symulation many years ago on my small mopar,and the #'s for time mph,&weight were within about 6 hp of what the symulation said and that was within 4 hp of what the flow bench data came out to be.it has been years since I have used it,probably cant find the program any more.think I might try this week if I can find it.just for funn. I do know I went from a 108 to a 112 on 3, 572 chevys (42'cigerette boat) and it lost a lot of low rpm torque but gaind a shitload of topend, (about 13 mph),but also had a deferent chamber head,but that chamber should of worked better on both ends.so I tend to think it was mostly cams.and these were kinda small cams for these motors but the motor was only 9.5 cr (due to fuel on the watter) but still over 720 lift &over 800 hp.
and I dont quite understand cam that is good up to 5500.thats just about an off the shelf nobraner cam.unless you are diesel.

[rosevillain]

I found a local cam builder. His feedback and presence on other forums was good, and he offered close to what I thought that I needed. We spoke on the phone, then met in person and discussed just what I wanted to do. He listened, and then designed a cam for my application. I took him a core, and he made me a custom reground cam ($60). I didn't think that I needed a blank.

Of course, it took a month, with poor customer service, and I haven't built the engine yet.