I have already replied privately w.r.t. the primary benefit of the high
ratio
roller rockers (higher lift) so I'll leave that alone here.
I do want to comment on the reputed benefits of roller rockers Vs
conventional rockers.
My experience is that with quality guides (sintered bronze) the wear rate
is not perceptibly different. Granted this was on a race motor not a 50,000
mile road motor but I'd still say that if the wear difference was really
significant
I would have seen it after 2 seasons of racing. If we are feeling generous
we'll still give this a tick because in theory it would seem better.
Two problems I have seen are
1) the roller rockers are significantly heavier than conventional rockers.
One brand was nearly double the weight of high left conventional rockers!
The additional weight does stress the valvetrain and will also reduce the
maximum RPM for a given setup (esp valve springs)
2) Unless you have stellite tipped valves, the roller rockers will just wear
a
cylindrical groove in the top of the valve stem. On my road/rally motor with
roller rockers, the depth of this groove after 1 season was a staggering
1.6mm (approx 1/16th")!!! The resultant loss of lift was almost identical
with the amount I gained in going to the higher ratio! The 2nd and bigger
problem with this is that the groove prevents the rolling/sliding action
that
is necessary when the valve opens/closes. What does this do? Yep, you
guessed it - it puts very high side loads on the guides. So much for the
supposed benefits!
The second problem can be overcome by having hardened tips, but if
you don't - watch out.
My vote is for non-roller high ratio rockers.
Mike
-----Original Message-----
From: Andy Ramm <aramm@concentric.net>
To: Barney Gaylord <barneymg@ntsource.com>; mgs <mgs@autox.team.net>
Date: Monday, November 23, 1998 8:56 AM
Subject: Re: Roller rockers...worth the $$$?
>There are a couple of other things to consider about roller rockers.
>The bigger benefit beyond performance is that they impart much less
>stress to the valvetrain overall, making your head and valve guides last
>longer. They are also stiffer, resulting in less deflection when a
>valve is opened and follow the pushrods better, resulting in smoother
>running.
>
>Are they a miracle power source? No. Are they a way to protect a big
>investment in a new head? Yes.
>
>I strongly recdommend you go to Doug Jackson's website and look at his
>methodical and scientific tests on roller rockers before making a
>decision. The address is:
>
>http://www.mgbmga.com/tech/mgb16.htm
>
>He also sells roller rockers and they're a lot cheaper than the Moss
>variety. I'd bet they're higher quality too, knowing Doug. You may
>also want to get Doug on the phone regarding your aluminum head. He did
>a number of flow analyses and lots of testing on these. I don't think
>he liked them very much.
>
>YMMV
>
>Andy
>
>Barney Gaylord wrote:
>>
>> At 07:18 PM 11/22/98 EST, BDurgin1@aol.com wrote:
>> >I've decided to buy an alumininum head (not cross-flow) with the new
valves
>> >etc for my 64 B with a 3 main engine. .... I've been looking at the
roller
>> assemblies .... was wondering if they are indeed worth the BIG $$$? I'm
>> trying to squeeze more HP out of the engine .... by "bolting" on stuff
>> like K&N's, modified head, etc.
>>
>> I wouldn't spend $$$$ just because they're roller rockers, but, most
roller
>> rockers also have a different ratio of arm length and increase the valve
>> lift significantly for better flow without changing the valve timing.
This
>> is one way to get more torque out of it without screwing up the other
>> running characteristics like it may do with a more radical cam.
>>
>> $.02,
>>
>> Barney Gaylord
>> 1958 MGA with an attitude
>
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