[Fot] Camshaft recommendation

Wed Feb 12 15:57:52 MST 2020

interesting comment re newer cam blanks

i got some 6 cyl ones recently and they are hard as XXXXX. and the cast
iron appearance is unbelievably rough...yes, agree, they have much
bigger cores and base circles.  I suspect they are of turkish origin. it
looks like an original cam had each lobe widened a bit (crudely) and then a
mould was made.

i dont have a cam grinder in my shop, but my local cam man also commented
on the hardness

On Thu, Feb 13, 2020 at 2:15 AM Richard Good <goodparts at verizon.net> wrote:

> Terry,
>
> True.  The original cams do not have very large lobes to work with.
> Re-grinding to a higher lift requires reduction of the base circle radius
> which also reduces all of the radii in the profile.  Any cam profile has a
> minimum recommended base circle radius in order to maintain an acceptable
> radius at all points on the profile.  The smallest radius may actually be
> on either side of the tip but it is easier to visualize if you think of
> having, let's say a healthy .200" radius at the tip when the base circle is
> at .60" radius.  If you grind that profile onto a small core that requires
> grinding the base circle to .40", the radius at the tip will now be zero.
>
> The new chilled iron semi-finished cams with un-finished lobes offer much
> more meat to work with and harder material than the original cams.
>
> Richard
>
> Sent from AOL Mobile Mail
> Get the new AOL app: mail.mobile.aol.com
> ------------------------------
> On Tuesday, February 11, 2020 Enquiries Road & Track <
> enquiries at roadandtrack.net.au> wrote:
> thanks Richard
>
> some folks might like to read this link
> https://www.tildentechnologies.com/Cams/TriumphCams.html
>
>   I disagree with your comment about grinding stock cams. You cannot
> always get the lift desired as in some cases, you would end up grinding
> below the core of shaft. Again, this was a real common problem with early
> 2000 & 2500 cams , which is whey they were often welded on the nose as part
> of the modification process. In later production, the factory used a larger
> diameter core , presumably to aid stiffness, but that gives a bit more
> flexibility when regrinding.
>
> You correctly point out that as you increase the lifter diameter then the
> peak velocity can also change. if you run the maths, a  change of 0.100"
> in lifter diameter (a lot really) gives a 10% increase in acceptable peak
> velocity. Changing the lifter diameter is not for the feint-hearted,
> especially in a 6 cylinder where the lifter bores are angled to the block
> to promote lifter rotation.
>
> It would be good if Geoff Byrne elaborates a bit on his comment
>
> Terry O'Beirne
>
>
>
>
>
>
> Road and Track
> enquiries at roadandtrack.net.au
> ph 0428 815 117
>
>
>
> On Wed, Feb 12, 2020 at 11:23 AM Richard Good via Fot <fot at autox.team.net>
> wrote:
>
> Michael,
>
> People often seem to overlook the main performance benefit of increasing
> the rocker ratio.  That is the increase in valve velocity.  The velocity of
> a flat tappet is limited by it's diameter. If you grind the cam lobe for
> too much velocity the contact patch will move out past the edge of the
> lifter and things will self destruct.  So tappet velocity is limited.
> However, since tappet velocity times rocker ratio equals valve velocity,
> increasing the rocker ratio will increase valve velocity.
>
> First decide what will be the optimum valve lift for your engine then
> divide by rocker ratio to determine the net cam lift needed to achieve that
> valve lift.  Yes, you can grind the cam with a large enough lobe to reach
> desired lift using stock rockers but you are limited in how fast you can
> open the valve.  Now if you grind the cam with less lift then use 1.65:1
> rockers to reach that same desired valve lift you will be moving the valve
> about 13% faster. That means it will be open further in a given period of
> time.  Graph it out and you will see a big difference.  Valve velocity is a
> huge factor in performance.
>
> I can understand why someone who has tried to use high ratio rockers with
> a cam that was already maxing out the valve lift with stock rockers would
> decide that high ratio does not work.  Valve lift was already at max.
> Increasing it further may be a detriment.  If duration was also maxed out
> for reasonable torque then the increase in lift during the overlap period
> caused by the increase in rocker ratio may reduce the low end torque.
> Properly applied with the right cam profile, high ratio rockers enable
> performance that is just not achievable with stock rockers.
>
> Richard Good
> Good Parts Inc
>
> Sent from AOL Mobile Mail
> Get the new AOL app: mail.mobile.aol.com
> ------------------------------
> On Tuesday, February 11, 2020 Michael Zbarsky via Fot <mzbarsky at yahoo.com>
> wrote:
> Thanks everyone! Good stuff. I’m sticking to a redline of just over 6K.
> I’d also like to keep the 1.65 setup rather than invest in a 1.55 so keep
> the intel and suggestions coming. The GP3 is a definite contender.
>
> Mike
>
>
>
> On Monday, February 10, 2020, 4:07 PM, Geoff Byrne <
> gkbyrne at optusnet.com.au> wrote:
>
> Ditch the 1.65 rockers no good for racing
> Geoff Byrne
> TR6 racer down under
>
> Sent from my iPhone
>
> On 11 Feb 2020, at 12:52 am, van.mulders.marcel--- via Fot <
> fot at autox.team.net> wrote:
>
> 
> I also once bought a Goodparts 1.65 rocker roller assembly for a TR6
> engine, but in the end I had to use a 1.55 roller rocker assembly, also
> from Goodparts, because, with the 1.65, it is difficult to find a race
> camshaft with a  lobe lift that is low enough. With lobes of 8mm or higher,
> I could not find valve springs to cope with the high valve lift. I bought a
> G5 camshaft from Schneider, they call it  the 320-F grind (duration is 268°
> at 0.050", timing is 57-83    87-53 , installation figure is then 103° :is
> that the same as the G5 grind?) with 0.340"/8.6mm cam lift and that makes
> for a  valve lift of 12.9mm with the 1.55 rocker arms. With 1.65 rockers ,
> valve lift would be 14.2mm and I could not find valve springs for that
> lift. The valve springs I used are part no 281003-063.20 from Summit
> (Isky), 320lb/inch spring rate. They recommend 0.45"/11.43mm  (1.250" -
> 0.800"from closed to full open position, so it is about 1.4mm more in my
> engine, but there is no problem concerning  coil binding : the installed
> height is a 1mm more than 1.250 , the pressure in closed position is lower
> of course, but still 34kgs (105kgs at full lift) an that seems to be enough
> till 7500 rpm
> Racetorations have a race cam with 7.6mm cam lift, probably that would
> work with 1.65 rocker arms. I still have the 1.65 rocker assembly, it is
> new and it could work with a road cam or any camshaft with a maximum of 8mm
> cam lift.
> Marcel
>
> ------------------------------
> *Van: *"fot" <fot at autox.team.net>
> *Aan: *"fot" <fot at autox.team.net>
> *Verzonden: *Maandag 10 februari 2020 02:34:27
> *Onderwerp: *[Fot] Camshaft recommendation
>
> Hi all, I’m building a TR6 race engine and have a set of 1.65 ratio roller
> rockers from Goodparts. Any recommendations for a suitable camshaft? I will
> be putting in cam bearings.
>
> Thanks, Mike
>
>
>
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