So a few years ago now the Comp Cams Xtreme lobes were what everyone was after, probably the first of the really fast, aggressive cam lobes out there. Everyone was getting whatever they wanted to run ground with the XE lobes.

Then it started turning out that on a lot of setups, somewhere in the low to mid 6K rpm range they just stopped playing nice. Even with relatively heavy springs and light valvetrains a lot of engines were just falling flat in that range, especially when .050” durations exceeded 230 or so. Some people went to rev kits, some people went to tamer lobes and some went to mechanical rollers.

So my question now is a multi part:
- are there better, possibly even more aggressive or similar profiles that are easier on the rest of the valvetrain?
- Are there better ways of dealing with the whole “area under the curve” issue?
- What lobe profiles do you guys like and why?

The reason that I’m asking is that I’m specifically looking for something with a .050” in the low/mid 23x range but for an application that specifically needs a very short advertised duration (not “it would be nice,” but that it will go a long way in accomplishing what I want to accomplish with the engine combination), and an even somewhat exotic valve train (ei, rev kit…) is probably out of the question for the app.

 

The theory behind a fast ramp cam is sound... it makes all the sense in the world to me... wish I could say it always works like it should.

One thing I'm learning as I go along is just how important every component of the valvetrain is. Changing one thing could throw the system off. I've seen a few race engines that would fall on their face through an rpm range... only to run perfectly fine with another slightly different pushrod. Which leads me to believe that it's a sensitive thing... kinda like mentioning Jenny Craig during an all-you-can-eat buffet on Mother's Day.

So you're definitely going to need a little common sense when trying to get the most of a fast ramp cam... namely alot less valvetrain mass on the other side of the pushrod. I'd be prepared to spend a little more money if that's your goal.

I also have to keep going back to the 1st Engine Masters challenge & Joe Sherman's winner. Not exactly running a max-area camshaft in that little small block but it didn't really seem to matter either. For me... I'm putting fast-ramps right up there with longer connecting rods till I see more proof in the pudding. The DO stress the valvetrain more and they do have the theoretical edge.... just haven't seen the cow eat the corn yet.

In my experience... there are just good grinds and bad grinds. Some just flat out work. One, just so happens to be a CC Extreme grind but it's also a solid roller. The 280XR, which is like 242/248 .570 110ş lsa. That cam rocks with the right valvetrain stuff and it's drivable in a stick-shift 355... very drivable in a stroker.

Your best bet is going to be found in a custom grind. I like Cam Motion and Bullet cams for customs. Isky, Crower, Comp, Crane and Schneider all have "good" grinds but you need to know which ones they are.... or know an engine builder who does.

The straw that breaks the camel's back will fall to the valvetrain though.

Good luck.

-Mindgame

 

My exact point and the reason for the question



I’ve usually taken this to be an issue with harmonic frequencies of the different valvetrain components, that sometimes you’ll just assemble a pile of parts that will not work well through a specific range. There are lobe designs, spring and damper designs… that make this much more unlikely. I’m not sure that I’m worried about that… it seems to be a distinct enough problem that it’s pretty easy to spot if you’re looking for it.



I’m not sure that I’d agree. Sherman’s engine master’s engine doesn’t have any really good reason to use a fast ramp cam, at least in my mind. Since the thing is really just judged in a medium power band and higher there really isn’t an advantage to having a comparatively short advertised duration. AAMOF, in his example there are advantages to running a “slower” lobe ramp. Primarily, it lets him get away with slightly more compression bleeding off cylinder pressure below the tested range while still filling the cylinders in the higher rpm testing range. It’s also easier on the valvetrain and probably takes a little less power to turn both helping him put down the numbers and go more radical but still stay within the rules.

In my case, I’m looking at a totally different issue. First, the engine has to pass emissions (not really my major issue, but it is one), and second, I’m building this setup primarily to experiment with boost and exhaust pressures and I want to severely limit their effect on both sides, where with significant pressures in the ports the low lift timings become more important.



Well, that’s part of the issue… to some extent all of those manufacturer’s sell “custom” grinds. What makes a CM or Bullet custom grind more custom then a Comp custom grind? In both cases you can choose the lobes, timings… (Comp tends to my and most people’s favorite example since there is easily more information out there about their available lobes then any other and they make it probably the least hassle and are most vocal about basically doing whatever you want with the cam grind).

 

On a custom grind it all depends on the grinder that has the profile that will best suit your application. They don't all have the same masters.Comp don't need masters now days.
If getting a cam from Comp ya got to talk to the right people(like Scooter)
If ya talk to Crower the man is Dave etc,etc.
Ya also need to talk to people at these companies that have a bunch of experience in cam design and not a salesman that just goes to the track on Sunday.
These companies build cams for all different kinds of people and engines and racing.If you talk to the people that do this then the spillover is tremendous, if ya pick up on it and the info is from the right people.Then you can get an idea of what the cutting edge is and if ya don't mind experimenting ya might get a hold of something that nobody will have for a long time and be a winner during that time in the smaller ranks.
That's the only way a small timer gets ahead or even, in this game we call racing.

If ya think ya can put a cam spot on out of a catalog, better than the people that do it for a living,more power to ya.

 

This is going to be fun.............

Actually, that contest is the perfect place for a Max Area type lobe.

Lobe aggressiveness is directly related to RPM range of the motor. More RPM you have the tamer the lobes actions have to be to control the valve and make the system happy.

On Sherman's motor he worked very hard trying to make the motor work well over 6000rpm. Between the 155lbs on the seat dual springs and the AFR Hydra Rev kit he had lots of spring pressure there for cam lobes that were very tame. So to say he was loading the valvetrain less to make it easier to turn is silly, that's just not the case.

Could it be said that he was trying to bleed off some compression, or lower the dynamic compression ratio, but he was only around 8.5-8.6:1 DCR in that motor, which on 160° coolant and the Union 76 fuel that detonated less than the Sunoco 94 that we have around here, actually was really easy to do, trust me I know something about it. Hell I have a can of the fuel from the contest in my shop. That combination with a good burning chamber and proper quench only needed a little bit of timing dialed back below 3000rpm to work properly on a even higher DCR.

His cam was a 234/234 108LSA straight up BTW..... With a AFR 215RR head it peaked at over 6500rpm, around 6600rpm. So he could have used a little less cam in that motor, but he wasn't taking custom grind cams, he was just using them off the shelf from Isky.

Aggressive ramps can help you pass emissions by cutting down the overlap area.... Problem is you are already cutting down your RPM range of the motor with the duration specs. Pile on that you need to spend lots of time making sure the valves will not bounce something silly on the seat (like Mindgame said) and it might not be the best idea....

Actually the problem people don't realize is that the Max Area stuff is more aggressive off the seat, but also more thru the mid section of the lobe.

Take for example two Comp Lobes....

230 @ .050", .340 Max Lobe Lift, 290 @ .006", 143 @ .200"
230 @ .050", .340 Max Lobe Lift, 282 @ .006", 151 @ .200"

The 8° that you take off @ .006" you add after .050" to the .200" number (to make this simple), that not only means that it's more aggressive in the .006-.050 and back area, but that it's more aggressive from .050-.200+, that can give you just as much problem with valve control as the aggressive of and on the seat movement. There are a lot of things to look at here IMHO worrying about valve control on a hyd roller is the best way to make them work properly, those hyd lifters are a pain in the *** once they start bouncing on the seat.

As far as your use for boost goes on this (with a turbo I would bet) I don't know what you are doing there but that opens a whole new can of worms in this.... but the lobe designs don't really mean much in that context in terms of power gains.

Yep, worry about the valvetrain mass and you might find something there. Problem is the coin for this is not cheap. You can run the aggressive stuff, even above 6000rpm, but it's not that easy.

Bret

BTW.... This is a good discussion, but the last thing I'm going to do is tell you which lobes I like the best in the catalog. They aren't all in the same series for the most part and most of them have a good use for different applications.

 

I just wanna share with you a problem I'm having with my valvetrain. My conclusion is that the cam lobes are to aggressive.

My set up is a 383 with AFR 190, comp cam pro magnum Roller lifters and roller rockers (1.5). I also have the AFR rev-kit and a Lazer cam.

I used to have valve float at around 6000 rpm with my AFR #8015 springs spec are 1.540 OD 145#@1.820 and 355#@1.250 with steel retainers.

I'am now having valve float at around 5800 rpm with comp cams 987's spec are 1.430 OD 121#@1.800 and 388#@1.200 with titanium retainers.

This is what I think is happening to me. The valve floats and the lifter plunger pumps up and takes up that slack, it will HOLD the valve open as the oil filling the lifter body cannot bleed out of the feed holes fast enough to allow the plunger to go back down to where it won't be holding the valve open anymore. At that point the engine just stay at that rpm as long as I keep it WOT. Used to be 6000-6100 rpm with the AFR spring, I'm now down to 5700-5800 with the 987's from comp cams.

I'm having that problem with 1/4 of a turn preload on the lifters, if I preload them with only 1/16 of a turn I will then be able to rev higher (6700 rpm) BUT, the valvetrain will still be unstable and I basicaly won't make any more power above the rpm it used to stop reving with 1/4 of a turn.

I will be trying a new set of spring soon with more seat pressure than the AFR I use to have and see what happen.

PAT

 

Ya don't have enough seat pressure and right at to much over the nose.
Ya are exactly right as to how the lifters work.
Springs are advertised at pressure before break in.Depending on the spring they will loose 15-25lb on both ends after a few heat cycles.A set of $500-600.00 springs will loose less, Call Crower and see if they can fix ya up with the pressure ya want.
Remembering the losses, I would shoot for 130 on the seat and 350-375 on the nose AFTER break in.Valve weight and any weight on the valve side of the rocker is going to have a big effect on your pressures also,so if ya are running 2.080 they will take more pressure to control than 1.95 or 2.0.

 

My new combo...which is going to be firing up sooner or later, is a somewhat aggressive solid roller with aggressive ramp rates.

My springs are 250 lbs on seat and if I recall correctly, 700 lbs open.

I am hoping this combo can net some very, very low 10's leaving with the t-brake...

 

I ordered a set of springs from the guy at Lazer Cam after telling him what problem I had with my valvetrain.
He told me that one guy in the Engine Master contest ran 7500 rpm with no exotic parts (even used GM roller lifters) with those springs.
The spec are 165#@1.800 and 335#@1.200.

My valves are from AFR, exhaust valve # 7057 (REV CL-1632) 1.600'' and intake valve # 7002 (REV CL-1636)2.020''. 0.050’’ longer than stock valves Stainless 1 piece swirl polish HP valves with chrome stems.

PAT

 

That should give ya 140 on the seat and 310 on the nose minimum and should be good to go.
Those aren't the lightest valves in the world.Have ya got titanum retainer's? They will help.

I keep telling guy's on this board and elseware that GM lifter's will take them past there RPM and HP level and people WANT the brain damage of Comp super dupers and there no adjust ,fly apart,lifters.If ya adjust your stock lifters at 1/8 turn the will act just like a solid(almost) and won't bust the cap or knock the lock ring out.(set running of course)

 

I had steel retainers with my AFR springs but I bought some titanium retainers when I changed to the comp cams springs and they will work with the new springs.

PAT

 

OK sounds good.Let us know how it does.

 

Pat,

You should look at a set of 26918-16 beehives and steel retainers. They will have a lower spring pressure and seated pressure, but they also have a lot less mass, and less mass requires less valvespring pressure to control.

What are the specs on the cam lobes? Total Duration, .050 Duration, .200 Duration and Max Lift?

Bret

 

I almost bought those springs, but I didn't like the fact that they are single springs and if one fail the engine is dead $$$, I've seen that on a couple of LS'X' engine family.

I'm not at home but the specs at .050 are 234/240 max lift is .544/.537 with 1.5 RR.

Thanks

PAT