I have been intrigued by the adverts for roller rockers I have seen. To me it seems like an easy way to add performance without changing the cam. A friend of mine has asked a friend of his (yeah, I know, like my mother's cousin's boy friend's uncle) who is an engineer about them. He said that they are not great because roller bearings like to work in a full 360 and not a back and forth motion.
Given that I will not be putting high mileage on the GT6 are roller rockers something I should consider or avoid like a Chevy Citation?
Thanks,
Tad
Thanks. You nailed it for me... "look cool."
I will put my money elsewhere.
You will see a benefit if you are using extremely high spring rates. The friction created by the rocker sliding across the valve stem and at the fulcrum can be a killer on a very high performance engine. With stock springs, however, I would not bother.
As for increasing the ratio, it all depends on whether the port supports greater flow at the increased lift. At some point the flow thru the cylinder head "stalls" and additional lift doesn't equate to additional flow. It's the same reason that a giant cam doesn't provide much, if any, power gain when coupled to a stock unported head.
I agree with all that, but I should point out that more gross lift means longer duration at partial lift, where the port can use it. In other words, a cam with .500 gross lift will have more duration at .250 than a similar cam with .400 gross lift.
With modern lobe profiles, though, we can get much higher valve velocity -- meaning longer duration at partial lifts -- than with older designs, without having to increase the rocker ratio.
I thought about rollers on my Spitfire racer but then I had two races in one month where I over rev'd the engine (shifter problem). In both cases I broke rocker arms when valves came in contact with the piston. I removed the head both times and checked everything out, no bent valves, no broken springs, no engine parts in the crankcase. It seems to me that the stock rockers acted like a fuseable link, they took the hit and saved the motor from destruction. If I was running a roller rocker set up, I doubt I would have had the same results.
I picked up a few sets of used complete rocker arm assemblies on ebay for ~$20 each and keep them in my at the track spares kit.
my 2 cents
mike
