Cam profile design 10

[EngJW]

Hello,

Just discovered this forum. I have been searching for a forum on camshaft design. That is, actual design like ramps, profiles, materials, machining, and so on, as opposed to "what cam should I use?" I found a gear forum but no cam forum. Anyone know of one, or is this forum the appropriate place?

Thanks,
John Woodward

 

[ShaunT]

It is a rush to go cruising with customers in their cars. When a customer has an aspirated motor at only 8:1 compression, and no power adders, it makes my day when the car runs so good that everyone thinks it is a really big motor with a solid roller cam and tons of compression. Actually, the most recent case from this last Saturday Night is a very successful combination that utilizes a fast ramp flat tappet cam that has a short seat duration, and a middle of the road LSA of 110 with a 104 intake C/L.
Why? Because it only has 8.17:1 compression. The motor runs hard to 6500. I see low compression (especially carbeurated) motors with some huge seat duration cams with stupidly wide LSA's way too often. They are usually in heavy cars with automatic trannys too. People always ask me what is their best choice for LSA. I like narrow LSA's even when compression is not an issue.
The narrower LSA's aid low comp motors. I feel that most of the choices made by consumers are due to ignorance. Many cams are so lazy in reguards to high lift area, that they only RPM because of their wide LSA. I see this in Pro Stockers daily. I also change their opinions and make them smile daily. But, Pro Stockers are the Extreme and they don't get my recommendation of 106 or even 110LSA cams. I usually preach 114 to them when everyone else is 118.

Economy and emissions aside, and since they flatten and broaden torque curves, low compression motors only need wide LSA's when they have really small cams that are also having to RPM. In Drag cars, the 106 LSA's are hardly ever slower than 112 LSA's especially in heavy cars with automatic tranny's. In dirt track cars, sometimes a 108 will be faster than a 106 simply because the track is slick, or the driver is having trouble controlling it and putting it to the track and he is getting out ran on the top end. Incidently, I recomend 108's to dirt trackers regularly. Many of them are my own loyal customers with 106LSA's who call me reporting a problem such as hard to hook up and also running out of steam a little early. A 108LSA fixes them and usually they win the race. My advice to the big cam wide LSA heavy car with small motor and low compression scenario's is: Either narrow the LSA 4+degrees or remove about 15+degrees of seat duration from the motor, and open the valve faster if you don't want a motor to be a slow reving lazy dog (especially one with low compression) with your wide LSA cam.
Bersides, It will be alot funner to drive and have more hit at idle, which is something most ask for.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

 

[ShaunT]

I will comment on something I have advised about in the past. When looking at Hydraulic Cam specs, make sure you look at advertised duration. If they are showing it at .006, it is a lie. In other words, the cam will open the valve at approx .0045. This will add SEVERAL degrees of duration to the opening of the valve depending on oil thickness/temp, but it will not add any duration at .050 or any where else. Here is an example of a cam that I LOVE to pick on: Marketed as a 292 Magnum H10 (what a Dog)
It is advertised at .006 with a .050 of 244. However, it is over 300 duration at .0045, hence it is quite a bit bigger in the motor than it is on paper. Even though this is a STUPID mass produced junck camshaft, I will say that if all that was changed was the offering of this cam ground on a 106 LSA, it would be a major improvement in overall performance. I love to sell guys a cam to replace this one. It is awsome to watch their car run a full second or sometimes quicker in the 1/4 mile with the new cam that is many times 20+ degress less advertised duration and still runs over 7000RPM with power. For anyone who has this cam, have you noticed that at WOT the motor seems on the brink of exploding into it's power band, but it never does. It feels like it wants to really bad. It gives me that sensation all the way through the RPM's. It is a let down. Incidentaly, I have never seen anyone buy a cam like that unless they are still very wet behind the ears and wouldn't know what real power feels like. They think they do, but are clueless.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

 

[EngJW]

Hi Shaun,

Do you mean that both cams are 244 @ .050, while one cam is 300 @ .0045 and the other 280 @ .0045? It sounds like a difference in ramps.

John Woodward

 

[ShaunT]

Sorry for the delay. The difference is in the ramps. One is advertised at .020 while the other is advertised at .006. Incidently, one is a Hydraulic, and the other is a Solid. They are the same at .050, but the solid is much smaller at the lash point and much bigger up at .200 and over the nose. You can put these two cams side by side and see a visual difference. One is a pointed nose "Hatchet" cam, and the other one has a nice fat rounded nose.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

 

[ShaunT]

Here is a tip for those of you who also like to race on dirt. I have several cam profiles that are a little better in rate than the one cam that made us famous, especially in the dirt track arena. It is the 288 296F6 and the 288 296R6. One is a solid flat tappet, and one is a solid roller. Both are on a 106LSA. This cam is very good on tacky dirt tracks as it is very strong off the corner. It has a ton of mid-range. The roller runs hard to 7800 in 350's with 6 inch rods. Especially with Alchohol. I have many clients who swear by this cam, however after I quiz them they tell me that once the track dries before the last race, the car is very hard to put the power to the ground.
Here is my tip: If you need some more RPM and need to soften the shock on the tire when getting back on the throttle out of a turn, try a 108LSA. You will take some of the mid-range "spike" out of the motor, while giving it a little more down low and extending it on top. Once you try this, you will see the motor pull upwards to around 8300RPM before it fades away. If the 106LSA cam is faster around the track after a spark plug wire is disconnected, you need a 108 because the 106 is blowing the tires in the corners.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

 

[ShaunT]

I spoke with a dirt racer the other day who has a short stroke long rod combination. He told me that I can't take a bunch of seat timing out of the motor because he runs a very limited right rear tire and if I put a bunch more torque in the motor, he won't be able to control it. I explained to him that the shorter seat timing cam with the faster ramp speed than his current favorite, can be more controllable because it won't act like a LIGHT SWITCH.
Here is an update: He is now running lap times that are right in the middle of the 410CID territory. Funny thing is that everyone protested him by saying he was running a 410 inch motor in the 360 inch class. Everyone was STUNNED to find that upon a tear down inspection, it was less than 335 inches. HA HA!

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

 

[ShaunT]

I have been receiving a fair number of comments about people being affraid to run Flat Tappet cams because of lobe failure experiences associated with break in Etc.
While my reply here does not relate to cam profile design, it should shed some light on things and calm some fears.
There are few things that can go wrong with a cams ability to deliver a long life. One big problem that is not too common, but will surely kill a lobe is a block with an out of spec lifter bore angle. Ever continously change cams and lifters only to keep killing the same lobe? It's time to have your blocks lifter bores trued. While you are at it, have them bored to a bigger size too.

Here is a simple break in procedure for flat tappet cams that I personally have never had fail me even on 600+Lift Big Block Chevies with 140lb seat pressures. Keep in mind that all of this is in vain if you grind on the starter for an hour before the engine fires. It's also a waste if you are not practicing Hygiene.Assuming things are ready for assembly, step one is to clean all components with Lacquer Thinner and then visually inspect things. Next, Take some A.R.P moly paste( you know the stuff they give you with their Rod Bolts, it's the best.) put it on the bottom of the lifters and all over the cam lobes. Then, pour some 5W20 non synthetic oil in a clean bowl and dip the lifter in upside down to coat the body. Put some oil in the lifter bores too. This assures the best possible chance for the lifter to spin.(this is why you don't use synthetic oil on break in of a new cam). Make sure that end play of the cam is around .010. Put a thrust button on it if you have to.(You will be amazed at how this really cuts chain stretch,especially in Chevy's) Once it's all installed and valves set(I like to set solid lifters .005 tighter then typical .025 spec, this also means an additional .005 tighter for cold lash on Alum Heads), put some of that 5W20 stuff in the oil pan and filter. Now prime the pump untill the oil comes out of the rocker arms. Once you are ready to fire, assuming the fuel system is primed too, it should light off instantly, and run at 1800+RPM's. After a few minutes, drain the oil and put in a fresh filter and fresh oil. Now, go play.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

 

[ShaunT]

Has anyone ever seen a square nose cam? Ever rotated a motor and watched the square nose cam toss the lifter off the back side of the cam's nose while watching the valve action? Slam! Bounce,bounce. Too bad we don't have the sound effects from the cartoon's of the 60's. These are cams with extreemly high negative nose deccelerations. The NHRA stocker classes are flooded with cams like this.

Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)

 

[ShaunT]

????

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

 

It would seem to me that there is little point in that, since a bouncing valve might have a similar leak-effect to a slower closing one? Is that what you're getting at?

 

[ShaunT]

What I am getting at is that when a valve bounces, the piston is at or very near max velocity on the compression stroke. Bouncing the valve creates an instant hichup in the intake port. A valve usually bounces open a couple of times. Closing a valve a little slower and hence later creates a tighter packed cylinder if you are using it to compliment the inertia you have created from the opening side of the cams ability to minimize reversion via our design. When the reversion is kept down, more real time has been allowed to build velocity in the port and fill the cylinder. The more velocity (inertia) we build in the port, the longer the port will continue to fill the cylinder with a charge after BDC. This is why our origional consept of a slow closing was born. Remember: a port that starts flow late will never catch up.

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

 

[EngJW]

Square nose cam-

We have a cam that is flat on the top, with a small radius on each corner blending into the flanks. I don't know why it was done like that. The negative acceleration segment has a sudden change over the nose where it drops to zero and then back to negative. There are also extra jerk spikes because of this. I don't know if this was having any effect on the performance, but I just converted it to a smoother polynomial profile. We don't have enough test time yet to tell if it is better. The problem we are having is pounding out the exhaust valves and seats.

John Woodward

 

[ivymike]

If I read you right, you have a dwell profile, where peak lift is maintained for a time. The acceleration profile will show a ramp, a flank, a negative region, a zero region, a negative region, another flank, and another ramp. Sometimes there are constant velocity portions (zero accn) between the flanks and the decel-to-dwell portions of the profile.

That is sometimes done when the cam designer wants to increase the period without increasing peak lift, and wants to maintain the same flank rates. If the springs could take the additional lift (or whatever other constraints weren't there) it would probably be preferable from a vibratory standpoint to use a more "normal" looking profile, and it will probably improve your seating velocities, but sometimes that's not an option. If you keep the same period and peak lift while removing the dwell portion of the profile, you'll be reducing the area under the lift curve, which may have a detrimental effect on breathing.

I'm not sure what your closing ramp looks like (constant velocity? constant accn?), but sometimes you can bring down the seating velocity a bit by changing from a constant velocity closing ramp to a constant acceleration closing ramp, with little change to the valve timings. Making the profile a bit asymetric, such that the opening flank has a lower peak acceleration than the closing flank, can also help sometimes.

 

[EngJW]

Mr. Hiding-

Thanks for the enlightenment. Those old-timers new a lot of things that are not in the books today. The springs do not have much room left before coil bind at max lift, so maybe they had to limit lift. I probably did reduce the lift area but this is a low bmep, 3000 rpm engine so it may not be noticeable.

The cam uses solid lifters with constant velocity opening and closing ramps. The thing that did not seem right to me is that the exhaust clearance is .014 and yet the ramp height is only .008 inches. The exhaust valve may have been hitting the seat at a high velocity. I kept the same end points but changed the ramp to .014 (same ramp velocity of .0005 in/deg) which of course made it much longer.

This is my first attempt at designing a cam, so whether or not I know what I am doing remains to be seen. I wrote a nice program though!

John Woodward

 

[ivymike]

the only reason why I can imagine using more cold clearance than the ramp heights would be if the clearance shrank as the engine heated up (this does happen on some engines).

 

[ShaunT]

A tighter clearance can reduce bounce. In the case of a square nose cam, I don't think there is much hope for cutting bounce. I've seen some pretty nice low/mid range torque gains by puting a design in a motor without the square nose. We made one a couple years ago that was over ten degrees less seat timing and over ten degrees bigger at 200 than the current favorite. It took so much reversion out of the port compared to the crowd favorite, that the torque was much better everywhere. We are still trying to make it work, since the reversion picked up the airflow past the point of the fuel system's ability to keep up with the motor. Incase you are wondering, these are stockers and rules RULE. Therefore we can't take care of the obvious and still be legal. We try it on the dyno with unregulated motors and the gains over the other cam are very nice. Enough that some racers would kill for. Too bad it won't work with the rules regulated fuel systems/fuel bowls.

Shaun TiedeULTRADYNE/LUNATI Arl,TX(stiede@ev1.net)

 

[EngJW]

It is an air cooled engine with aluminum heads. Valve lash is .008 intake and .014 exhaust. Carved in stone- no one will change it. The intake ramp is .010 high and exhaust ramp is .008 high. Both have the same constant velocity. Of course the exhaust is going to get hit with a much higher velocity by the time the clearance is taken up, and I would think that it would likewise hit the seat at a higher velocity.

I might be interested in trying the accelerated ramp. However, I thought they were only used for hydraulic lifters?

The opinions around here are that it is a temperature problem. However, we are only running part load. Also, valve faces are Stellite, seats are a compatible high temp material, and guides are hardened.

Shimming the springs helped a little but there is not enough room to increase load much before they go solid.

John Woodward

 

[patprimmer]

If the loos tappets are carved in stone, would it be to dirty a trick to grind 0.005 off their feeler gauge, and only tell them after the problem is seen to be solved.

Just hope they don't use the gauge on something else in the meantime.

I ran air cooled VW's many years ago. We set them at 0.004 as they opened up considerably as the engine warmed. This was air cooled, alloy head. The aluminium expands a lot more than the pushrod, but the exhaust valve only expands a little more than the head, and the inlet, not as much as the head.

Regards
pat

 

[ivymike]

I might be interested in trying the accelerated ramp. However, I thought they were only used for hydraulic lifters?

Hmmm... I've never heard any such rule. I thought they were used anywhere that dynamic analysis / testing showed that they reduced seating velocities w/o compromising duration.

 

[PolgainCamshafts]

I have seem rectangular cam lobes on old engines circa 1910. I am Manager of a camshaft manufacturing company. We do little design work but plenty of small batch and prototype manufacturing work for engine developers and the OEM. If you need any manufacturing help just as I do this sort of thing every day. Cheers guys