Roller vs. Flat Tappet

Ok, some things were said to me this weekend that makes me wonder on this subject.

Its been said on here many times that the Flat Tappet style cams are better for preformanc than a roller style cam.

From my sketchy memory:

The cummins B series has near perfect valve train geometry coupled with the 1.5" tappets. Giving the cam grinder the ability to make a much steeper ramp on the lobes.

Click to expand...

Paraphrased from Greg Houge.

From what I remember on gassers was a roller can get far more agressive tha a flat tappet with the added bennifit of actually reducing friction (free power).
Of course the tappets in most gas engines are tiny compared to ours.


So, wich is better and why?

At what point does one become better than the other (if so)

Is the gain even worth the money?

Discuss:

the roller lifter does offer less friction than that of the flat tappets but the accelerations of our tappets compared to that if the gassers is way different due to the size of the tappets and cam profiles. i know some people have gone to a roller rocker to help reduce friction but i have not heard of anyone running a roller cam in a diesel yet.

I've never heard of anyone running a roller lifter except in the sense of a cam follower on big rigs. Wish I could get a 5.9 with cam followers.

SKYNYRD said:

the roller lifter does offer less friction than that of the flat tappets but the accelerations of our tappets compared to that if the gassers is way different due to the size of the tappets and cam profiles. i know some people have gone to a roller rocker to help reduce friction but i have not heard of anyone running a roller cam in a diesel yet.

Click to expand...

I guess when you live a sheltered life out east you don't hear of the roller cam engines. There are numerous of them out. I actually think there are more roller cam engines out than roller rockers.

I cant give a list of the trucks or tractors but, I do know roller cams are very popular with the pullers.

Ive actually found a tapper cover for a roller tappet 5.9 online, I have no idea where though.

From looking a the tappet holes on a B series Im very curious how the rollers are made.

Wonder about the cam profiles on a roller.

zstroken said:

I guess when you live a sheltered life out east you don't hear of the roller cam engines. There are numerous of them out. I actually think there are more roller cam engines out than roller rockers.

Click to expand...

X2 Dmax has roller lifters stock.

With a roller you can get the valve open quicker then hold it open longer....witch means more air. Scheid has been using roller cams for years!

:umno:

brushpuller said:

With a roller you can get the valve open quicker then hold it open longer....witch means more air. Scheid has been using roller cams for years!

Click to expand...

Draw the picture, the ramp rate of the cam can be steeper on a roller, but if you look at the contacting surface you can see that if you don't get into side loading the flat tappet can have a rapid rate also.

gotta12v said:

:umno:

Click to expand...

elaborate....

zstroken said:

I guess when you live a sheltered life out east you don't hear of the roller cam engines. There are numerous of them out. I actually think there are more roller cam engines out than roller rockers.

Click to expand...

yeah out on the eastern side of the US they tend not to play much with diesel. but its starting to grow.

gotta12v said:

:umno:

Click to expand...

:doh:

I would like the brushpuller to explain how going roller has anything to do with the grind of the cam which is what would be the factor on how long the valve stays open. (Duration)

That is like saying shell's diesel adds 50 more HP than sunoco's.....

Brandon

Now you can say you have seen one......

Nice pictures, can you tell us who made the cam? I see there was some grinding needed to clearance the pushrods. I understand some manufactures are changing cam lobe locations to fix the pushrod geometry in these motors.

I think KTAcummins makes roller camshafts and the stuff to go along with it. I don't think there would be a benifet until you were in mod-class territory...

97' CTD said:

:doh:

I would like the brushpuller to explain how going roller has anything to do with the grind of the cam which is what would be the factor on how long the valve stays open. (Duration)

That is like saying shell's diesel adds 50 more HP than sunoco's.....

Brandon

Click to expand...

A roller can take steeper ramps, so the valve is open farther, faster.

index

These Guys will do it. Along with a billet block or head.

Zack, Don, Fletcher, Greg.....we are waiting...... op:

Ok this is all dependent on the perimeters . If you have a 1.5 diameter mushroomed flat tappet , with a 54.5 mm cam core , and limited to the stock rocker ratios , IE what 99.9 % of all of the guys ordering a cam have , then A roller tappet dose not produce any when near as quick of a valve acceleration , as a 1.5 mushroom flat tappet. The actuation of the flat tappet is much quicker then a roller tappet in this case , its just the laws of physics If you have a roller wheel that was 8 feet in diameter then you can get the same acceleration rate as a 1.5 mushroom tappet on a 54.5 mm cam.

Now if you are willing to engineer maximum effort engine , which I do almost every day , then you have to first start with needed valve lift . Those numbers are dependent on head port design , valve job , and intended use of the engine.
The lift numbers are only one factors , the meat of the air flow happens under the curve , meaning from .200 tappet lift to 90% of maximum lift
So here is where you start , look at the 90% number , in a 24 valve Cummins its around .500 , but with a lot of the new porting programs it needs to be around .600 lift .
Wow , with only a 1.34 to 1 rocker , your sunk with a roller tappet,


UNLESS


You correlate the maximum acceleration rate , the rocker ratio , and base circle of the cam. and design a cam profile


So at .380 lobe lift you going to need a 1.60 rocker , that will get you lift and acceleration rate . So the next step is to take the ratio even farther , and go to a 1.85 to 1 rocker and reduce lobe lift to .320 , this makes the base circle bigger by .120 the bigger base cyrcle will allow a steeper ramp , and still control the lifter ,

And yes , I do billet steel 8620 roller cams for diesel, I recommen a Jesse style slotted lifter , and lifter bore sleeve.

I have been doing cams for a long time and there is a lot more to it , so for the 99.9% if your money is just burning a hole in your pocket , spend it on a cylinder head, if you still want a roller cam , then call, I do it all the time , but its not for the meek of wallet

can someone inform me on when the roller cam/tappets is a benefit? i no in gas engines a soild lifter motor will spin up alot faster than a roller motor and i thought that a much higher spring pressure is alowwed with a soild lifter motor which we all no keeps the valves in place... i might be totally wrong but thats just what i thought from my dads experince with building race motors..