-----Original Message-----
From: Jones, Daniel C <Daniel.Jones@MW.Boeing.com>
To: Aluminum V8 List (Buick/Rover) <buick-rover-v8@autox.team.net>
Cc: mgb-v8@autox.team.net <mgb-v8@autox.team.net>
Date: Saturday, 26 February 2000 4:28
Subject: RE: Hydraulic roller camshafts
>My '87 Mustang has an OEM hydraulic roller cam with max lift of 0.444".
>It quits making meaningful power around 5000 rpm. It is by no means a
>match for an aggressive flat tappet cam. In fact, it's timing events are
>very similar to the flat tappet grind in my truck. If the OEM roller were
>anything special, you'd see stiffer valve springs. No matter what the
>tappet, the quicker the valves are opened, the stiffer the springs must be.
Agreed - I am not refering to an agressive roller profile that is to be used
for a high RPM application, but a speciality application that is best suited
to a roller cam used in motor that is street driven with a maximum RPM limit
of 5500 (see comments below).
>
>Plus, springs for a hydraulic roller have to be stiffer to begin with to
>offset the extra weight of the roller lifters.
>
>By comparison, the hydraulic flat tappet cam in my '66 Mustang has
>moderate duration (225 degrees duration @ 0.050) and 0.550" lift.
>The springs are substantially stiffer and the lift rate is higher.
>Coincidentally, those specs are very similar to Ford Motorsport's
>X-303 grind, one of the hottest they offer for the 5.0.
>
>The smooth idle you mention is due to wide lobe centers (116 degrees
>for the OEM roller I mentioned above) and short duration which
>together limit the overlap when both intake and exhaust valves are
>open. Narrower lobe centers will make better power at the expense
>of idle quality.
...that's exactly why long duration, flat tappet cams are not a good
choice - especially in street driven vehicles using an auto trans.
>
>When duration and lift go up, flat tappet lobe life goes down. A roller
>cam has a substantial advantage there. Recently, I've been looking into
>cams for the next engine for my Pantera. I'm looking at a cam in the
>neighborhood of 0.600" lift and perhaps 240 degrees duration @ 0.050".
>Because of the lobe life issue, I wanted to go with a roller lifters but
>after discussing the issue with cam grinders, it looks like I'm stuck with
>a flat tappet. The hydraulic rollers won't support my desired max rpm and
>require too much spring for an aggressive profile due to lifter weight.
Valve spring pressure is not influenced by lifter weight - even for roller
cams. The primary function of a valve spring is to keep the valve on its
seat not to keep the lifter in contact with the cam lobe. The reason
hydraulic roller cams aren't used for high RPM applications is because the
inertia created in the valvetrain at high rpm's will limit the stability of
a roller setup.
Putting in heavy valve springs to combat this problem will achieve nothing
except put more stress on all the valve train components. If your objective
is to use a hydraulic roller for high rpm's (>7800), then you're defeating
your purpose. If however, you are using a solid roller and there is a
problem keeping the lifters in contact with the cam lobes, then auxillary
springs should be used at the lifters, NOT by overcompensating and using
heavier valve springs instead.
>Solid rollers are another option. Since they are lighter and don't pump
up,
>
>they can rev higher (or support a higher lift rate) at the same spring
rate.
>
>The racers I've talked to love them but their reliability on the street is
>suspect. Apparently, any clearance in the valve train beats up the needle
>bearings. So I'm back to flat tappets.
>
>>The extra lift would allow time for the cylinder to fill more completely
>>over a longer time period (at max flow) and would certainly not be wasted.
>
>The additional lift will not increase peak flow. That part will be wasted
>on heads that peak below the maximum valve lift. You are correct that the
>area under the curve will increase but, with the off-the-shelf grinds I've
>looked at, the difference hasn't been that great.
>Dan Jones
.............That's probably because most roller grinds offered are not
developed to meet design limitations imposed on existing engine components.
In the case of a standard 215 V8 heads, the ports and valves are too small
to cater for the requirements of a large capacity (5.0L) version of this
motor - as they were never designed for this purpose anyway. The roller cam
in this situation is, in effect, compensating for a poor flow situation. The
purpose of using the roller cam is effectively turning the 215 port flow
into the flow of a 300 port, instead of resorting to a flat tappet cam
profile that would compromise the idle quality in achieving this objective.
This, in turn, allows a more tractable engine in the lower rpm ranges
(1000 - 2000 revs). The sort of cam profile that we are looking at here is
one having a large lobe-separation angle and a high lift - hence using a
roller instead of a flat tappet cam. These stroker motors produce a heap of
low rpm torque and therefore need a cam to "flatten out" the steep torque
curve at lower rpms so that it is spread throughout the useable rev range -
up to 5500 rpms for a street driven application. If you look at the torque
curve for a stock Buick V6 3.8L L36/L67/LG2 motor (yes it uses a roller
cam!) and you'll see what I mean. The high lift roller cam will not improve
the flow at max lift, but it will allow the inlet valve to stay open for a
sufficiently long enough time frame for the cylinder to fill more
completely. Sure you can play around with ECU mapping and inlet manifold
tuning to fine tune the result, but the camshaft will singularly play the
most significant role in the overall shape and position of the engine's peak
torque and power output in this instance.
Paul Rakich
Rover V8 SD1 SE2
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