Quote:
Originally posted by PatBuckley
Roller cams - all else being equal, if they only gained 14 -20 HP I doubt they would ever sell another one.
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Pat,
Here is my insight on the roller cam issue. In my first post, I stated to Jamo that I could spec a flat tappet cam that would only lose around 20 horsepower compared to the roller cam that is in HIS motor presently.
I would need to see Jamo's cam card.
The flat tappet I would pick might have more duration and less lift and possibly a different lobe center than the roller in his motor now.
It is true that a solid roller cam, in most applications, can be worth 30 to 50 horsepower over a flat tappet cam if the roller cam is ground to take maximum advantage of the roller lifters. What I mean by this is the radical ramp profiles that can used by a roller that literally slams the valves opened and closed. I have seen roller cam lobes that have over 275 deg duration @ .050" lift
but less than 300 deg duration advertised @.015" lifer rise.
Those lobes allow maximum cylinder filling and produce huge cylinder pressure #s which make big horsepower.
A flat tappet could never do this and live.
At the same time, lobes like that will kill all but the best valve springs ($500 to $600) in no time and even those will die in short order on the street.
The valve seats take a beating as do all the other valve-train related parts.
I love solid roller cams but for these purposes they are not the greatest choice for a street car that has to idle and run at low speeds for extended periods of time.
Roller cams and lifters rely heavily on "splash"
oil feeding. In a racing engine the RPMs are usually run high enough to keep everything plenty lubed.
On the street, when idling or crawling around town, this doesn't happen.
The same thing happens to roller valve springs that rely on lots of
oil to help cool them.
Racers usually have spray bars in the valve covers to direct
oil on the valve springs to keep them cool.
To me, the biggest issue is the "what if" factor.
If the roller lifter breaks a roller wheel bearing, which, unfortunately happens all too often, it can do serious damage to most of the engine components.
Break a valve spring and you can destroy the entire engine.
(just ask some of the Ford roller cam 514 crate motor customers)
This is not to say that flat tappet cams don't break valve springs,
it is just much less likely.
About the worst that can happen with a flat tappet cam is to have the cam go flat.
When this happens, it goes on over a period of time and is hopefully caught during valve adjustment.
The metal contamination is not good but the particles are small enough to usually not cause catastrophic failure, unlike tiny chunks of roller needle bearings that can jam oil pumps.
Then, add in the distributor gear issue that started this post.
One day, some cam company will make a roller cam with a cast gear for a Ford but for now, we just have to envy the Chevy guys.
For the last few years I have been experimenting with the flat Schubeck composite lifters with great success.
I believe this combination is the best of both worlds, the reliability of a flat tappet with cam lobes approaching those of a roller cam.
This combination is what I suggest for those customers that can afford it.
I could talk for days on this subject but for now I'm done.
--HTH,
--Mike
Rick Lake
Linear Mode
