Camshaft Ramp rates

Ok i'll bite, I was just reading the lobe post and Nicks post on the ramp rates got me calculating mine, here are my spec


intake exhaust
@.050 180 200
@.020 200 228
@.006 214 240

valve lift .442 .501

lash .008 .008

lobe sep 108

installed @ 100

Comparing the ramp rates of the Helix and mine

Intake

Helix .006 to .020 is 51.6
Helix .020 to .050 is 30

mine .006 to .020 is 14
mine .020 to .050 is 20

Exhaust

Helix .006 to .020 is 83.8
Helix .020 to .050 is 27.3

mine .006 to .020 is 12
mine .020 to .050 is 28

Will my cam live? The ramp rate seems to be faster but will it wear too much?

thanks
 
Hamilton Cams said:
I thought that this was supposed to be about LSA's only. Do we need to start another thread for Helix ramp rates?

Why must you use such slow ramp rates? If you used faster ramps, you could get better bottom end spool with tighter LSA's and better top end as well. Glad to see you have changed your profile up a bit though, the old one was pretty rough.

Zach
Click to expand...

If? LOL Faster ramp rates also eat **** up when you have little room to work with. Some times you have to give a little to get a little and make it live.
 
And that contradicts your statement. A wider lobe will have a slower ramp speed. You have me confused.
 
The lobes width will not affect the ramp rate. No contradiction there. I think you have duration and width confused. If a hill is 2 miles high and has a 45 degree slope, it can have a face that is 2 miles wide or 100 miles wide. You can attack the mountain any where along the 100 miles and it still has a 45 degree incline. Ramp rate is not dependent on lobe width.

If you mean wider duration then yes, slow ramps can be associated with wider duration cams but not wider lobe width. Wider lobes let the oil between the lifter and the cam lobe, have more surface area to distribute the load and stresses of the valvetrain. Today's oils have less zinc which gives them less film strength. Since they have less film strength the wider lobes help reduce the lbs per in. squared and put less stress on the lobe. In this instance you don't have to give a little to make it live. In fact you can get more and it will still live.

Zach
 
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I dont see any information coming forward on any cam but the Helix 2. LOL

We also seem to have a differing definition of what a ramp is. Are we talking the lash ramp or the opening ramp, closing ramp, what?

There has been no groundwork or foundation layed for most to understand. Addition and subtraction first. Differential calc comes later.
 
Looks like you have free time Don. Send me a pm and I'll order some injecters.
 
based soley off the .05 numbers compared to the lift numbers that is not even what I would consider a agressive ramp. the numbers that really need to be compared are .05 to .200 duration and max lift
 
I added more to the other thread. Will it live or not, that's the age old question. Better have some money if you want to push the limits and find out how agreesive and or how high of an rpm something can be pushed before failure. Otherwise best to stay in the realm of what is known. Seems there are much darkness on what is knowns to live and what is known to fail when it comes to diesel valve train. Likely because the amount of people swapping cams in and out of diesel is far less than that of the gas motor crowd. Those that pioneer the realm of failure will not likely share as it cost them alot of money to find that area. It's one of those things where you'd love to know for yourself but can appreciate the time money and effort vendors spend on finding these limits. Long and short call some of our cam gurus, have a discussion, and figure out what works for you. Good luck!
 
We are nowhere near the point of maxing out the acceleration potential of the Cummins cam core.
With a diesel power plant, you must keep the timing events within a given range.

The opening of the exhaust effects blow down and spool. Open the exhaust valve too early and you give up cylinder pressure that potentially could translates in to power. (No Cam in the Street Category is even close to that). With A diesel, you are also opening the exhaust to increased cylinder pressure.

This pressure is a huge stressor on the exhaust valvetrain, necessitating careful consideration with the Exhaust opening Ramp design. The exhaust Lobe opening ramps I use, are very similar to Top Fuel Cam Exhaust lobe profiles I worked with many years back.


Next is the closing of the exhaust valve, and opening of the intake, There are two factors that are major considerations, when designing these events.

First, is that Diesels and for that matter all turbo charged application engines do not like overlap, the time where both valves are open at the same time. Overlap works in normally aspirated engines by helping to purge the cylinders of spent gasses, using new intake charge to push then out the exhaust valve.
This system is very dependent of tuned intake track and tuned headers to be effective. Diesel and other turbocharged applications have drive pressure in the exhaust track, and this almost negates the desired effect


Second is valve clearance, this is critical in maintaining compression ratio , and not having to move the top ring down any farther then necessary. It is also mandatory in street engines, when people do not want to cut the pistons for additional piston to valve clearance.


Now we come to intake closing , it’s a balancing act , keep it open longer and the motor moves air , keep it open too long and you could get reversion in to the intake track. In addition, bleed off dynamic compression. The difference between Dynamic compression and static compression is static is the calculated compression ratio, and dynamic is the actually compression amounting to the air trapped in the cylinder after the intake valve closes.


In reality, due to the poor design, the engine rarely finishes filling and continues to fill even as the piston is traveling up. This concept can become more exaggerated, as engine RPM increases.


Now to the meat of this, a Cummins B series cam is huge 54.5 mm or 2.125, Pro Stock Programs would have killed to have that 25 years ago. The lobe lift is relatively low, less than .400 on race cams and .300 on street cams which gives a very generous base circle. on that note , I have some 60 mm core with roller bearings coming out of hear treat .
these cams are for the 2.6 and 2.8 programs that tommy is now building. this will allow the need .600+ lift on 24 valve and .900 lift on 12 valve we need to work with the newest heads


The Rpm of this engine is very low in the scheme of things
The cam lobe is more than sufficiently wide, considering the load imposed, even the narrow lobes. My lobes are 1.001 wide, which were 30 % bigger then NASCAR flat tappet lobes turning 10,000 rpms with many times the spring pressure even thou my lobes are as wide as anyone’s , this lobe width issue is just a marketing smoke and mirror show. The tappet size and slow speed and spring load , is not a issue .


The acceleration rates are no when near maximum, and faster acceleration rates will allow big lobes with more area under the curve. This allows more airflow without going outside the parameters
 
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mech2161 said:
And that contradicts your statement. A wider lobe will have a slower ramp speed. You have me confused.
Click to expand...

Look at Hamilton's avatar...his cam has a wider lobe...you can't see the duration in that little picture...
 
Comp I know say the wide lobes are a marketing ploy. I would say the same if I used a 12v core. The fact is that Cummins has been making the lobes wider and wider since 1998. They can make the lobes any width and yet they choose to fly in the face of what you are saying and use lobes almost twice the width you are using. I respectfully disagree with you.

Our 181/210.
exh. int.
.006-250 -213
.020-229-201
.050-210-181
.100-180-163
.200-144-128
.300-101-82

zach
 
Are these cam lobes taper ground to rotate the tappet? Forgive me it's been years.
 
I suppose I have more cams circulating around than anyone for the Cummins. We use a .750 wide lobe. We have experienced only a few wear issues. We have used the same lobe width since 2004.

I have seen several worn lobes on cams with wider lobes.
 
.750 at the base circle and .711 on the nose. I guess you need to tell cummins to get the narrow ones back then, they must be crazy using the 1.250 on the current 24 valve engines.
 
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