Roller vs. Flat Tappet

COMP461 said:
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
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Hamilton Cams said:
Stock 12v ratio is 1.69 +/- a little (high oem tolerance) we can take them up to 1.8

The stock 24v is 1.38 int 1.34 exh. +/- i believe. These ratios are actually all over the place depending on which year model the rockers came out of and if they are made in brazil, usa, india,or mexico. Once again we generally try to get another point out of them which takes them to 1.48 and 1.44.
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Greg, what are you doing to get a 1.60 ratio on a 24V?

Or were you refering to a 12V?

If this new 12V head has the a low lift flow curve greater than a 24V, a roller cam and rockers with a 1.8 ratio rockers would seem to be a fanrastixc set up.
 
Iv been down this road with my pro stock gasser back in the mid 90's, we had a no roller cams rule...so i had ford mushroom lifters(ford lifters bodies have bigger bodies then a BBC) with 1.25 dia. mushroom. Went through many cams, when i had the right valve spring PSI (no valve bounce at xRPM) it woud dig the mushroom lifter into the lob and grind the lob off. Biggest PITA iv ever delt with!!! Rule change and wen't roller...WOW gained 100ish HP and way more reliable! I think the aftermarket hasn't caught up with the roller cams for a diesel yet! Give it a few years and it will be as common as a roller for a gasser!

Now i know all you are going to down me for compairing a gasser to a diesel...but a diesel isn't that much different then a fuel injected turbo'd gasser! Its all the same prinsable...piston goes down filles up with fuel and air...piston goes up BANG piston goes back down...makes power.... IMO we need to look more at the injected turbo'd gassers to learn!
 
Seems I remember seeing a gain of 100hp on a dyno going to a roller. Same engine, cams had very similar profiles.

Acording to that article the gain was from loosing the parasitic friction of a tappet style cam.
 
roachie said:
Seems I remember seeing a gain of 100hp on a dyno going to a roller. Same engine, cams had very similar profiles.

Acording to that article the gain was from loosing the parasitic friction of a tappet style cam.
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That is true. Also you have a lot more control over the valve with a roller (more spring psi, with a flat tapet style cam the lifter wants to ramp off the back side of the cam then slams the valve closed at high RPM's and low spring psi.)
 
I kinda figured this would be a good ol' fashion mud slingin cam dabate.

Yall pussin' out on me?
 
Haha, you guys are great! Hopefully this won't turn into a "brand x vs. brand Y" pissing contest. There are benefits with each style of cams. With the flat tappet, when using the 1.3" or 1.5", your low lift or initial acceleration is much greater than with the roller. This allows you to get the valve open much faster initially. With such large tappets, very aggressive ramp rates are possible. There is a ding in the parasitic loss department, but for the most part for simplicity sake and for the daily driver, this is the route you want to go.

Rollers obviously have advantages in freeing up lost frictional horsepower. They also have another benefit. Even though they have slower initial acceleration, they can take advantage of inverse ramps. Inverse ramps allow the duration at .200"+ to be much greater. Flat tappets are, for the most part, only used on fairly straight ramps(except some mushroom flat tappets on Motto Guzzi's and very few others). Rollers, depending on the size, can take advantage of an inverse ramp which will accelerates the valve varying speeds at different parts of the lobe. This combined with less friction, make these cams ideal for high rpm, and allow the engine manufacturer to give the valves plenty of spring pressure without the worry of lobe failure.

Now for some practical information, not fairytale this is better than that land. If the main benefit of rollers is greater duration at higher lift numbers due to greater acceleration rates from inverse ramps. Try calling your cam grinder(which ever brand you use) have them grind a very aggressive flat tappet cam. Next get a set of higher ratio rocker arms. For most people this will give VERY aggressive ramp rates, and should get you what you need. If you are running 6000+ rpms and going for 1.000" lift. the flat tappet is not going to cut it. At this point get your credit card out and call Van Haisley, Scheid, Woodruff or some of the others with roller cam programs. Now dangit, I can't even say program without laughing. Greg, please get a new catchphrase so I can put the word program back into my vocabulary.

zach
 
Bahahahhahah!! Get with the program Zach! :hehe:





(sorry, I just had to say program. ... program.)
 
I can't remember the last time I have laughed that hard.

So I'm never going to give up, Never gunna let you down....... I don't know. I will have to think on that one for a few days. Should I print that on our boxes?
 
Hamilton Cams said:
I can't remember the last time I have laughed that hard.

So I'm never going to give up, Never gunna let you down....... I don't know. I will have to think on that one for a few days. Should I print that on our boxes?
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I'm sure that laugh was good for a discount on a cam right? :)

But I do like the "rickrollercam program" that's perfect!
 
The very simple short answer is:

If your under 5000 rpm dont worry about it.

Correct?
 
Partly. The law of diminishing returns applies here. You can do pretty much anything need with a flat tappet. If you want a little more duration at the higher lift numbers, and you don't mind paying over three times the amount for a cam and related hardware, then yes go with roller. Most people have bottle necks in other places and wouldn't know much difference going with a roller cam.

If you have higher duration at higher lift numbers but your head is not up to flowing at those high lifts, then it would be a waste getting a roller. The same applies to bottlenecks on the exhaust side, too small gates, cast manifolds with the gate after the t3 flange.

If you have a well thought out engine program:hehe:, then yes there are benefits.

Zach
 
SmokinCummins said:
Now you can say you have seen one......
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That cam and motor looks VERY familiar!! I spent the day at Haisleys and found out who else runs that cam. I was very pleased to know that they did. Their turbo set up is about $20,000 more than mine though. By the way, thats a Haisley cam.
 
Cummalong said:
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..
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a solid roller motor can life longer at higher rpms than a solid flat tappet. and make more power..

roller will alow you to run heavier spring pressure.. without risk of side load or flatening a flat tappet cam.

for the most part a flat tappet cant handle much more then 200-250lb of seat pressure... when talking about motors that live are 8,000+ for extended periods of time majority they do not have flat tappets camshafts in there...

this what happen with valve float..
YouTube - Valve Float
YouTube - Short Valve Float Movie

couple things will cause this.. valve train wieght. and RPM.

now this is just falt amasing... elimintating then valvsprings completely!
YouTube - Springless Valvetrain For Push Rod Engines!
YouTube - New Engine Technology/Springless Valves
 
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