Subject: Re: [Fot] Six cylinder cams--some real facts

From: Larry Young <[email-masked]>
Date: Thu, 12 Nov 2015 16:15:42 -0600

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Are you referring to the thread I started on Spitfire cams? I agree 
completely, there is a lack of factual information. A few years ago, I 
had great intentions of developing 6 cylinder cams with an approach 
similar to the one I took for TR3/4 cams 
(http://tildentechnologies.com).  One of the problems is that in order 
to select a cam, you really need accurate and complete numbers, both 
seat-to-seat and at 0.050.  The problem with seat-to-seat numbers is: 
(1) there usually wrong by at least 10 degrees (usually but not always 
understated) and (2) they don't tell you as much about peak power as the 
numbers at 0.050.  The problem with seat-to-seat numbers has gotten so 
bad it is now called "advertised" duration.  What is that? Quoting 
numbers at 0.050 seems to be an American thing (I think started by 
Harvey Crane).  British cam makers either don't have those numbers are 
they will not release them. I will never buy a cam without 0.050 
numbers.  If we all took that stand, then they would have to provide 
them.  Given that, the only way to proceed is to select cams with known 
characteristics and measure the numbers.  Comparable dyno data would be 
nice, but none of us are likely to get this the way Kas did.  The 
exercise of measuring the cam can often be revealing, e.g. (1) valve 
lash that opens and closes the cam on the high velocity flank causing 
seat wear and valve bounce and (2) lift rates (velocity not 
acceleration) that will cause running off the edge of the lifter.  I 
agree that larger lifters could allow a better design.  Also, the lobes 
could be much larger if you run without cam bearings, which could also 
allow a better design curve as well as a stronger and stiffer camshaft.

I don't agree completely with your logic about a 0.490 lift limit. If 
the cam gives 0.490 valve lift, that will occur for zero degrees of 
duration.  To have the valve open to 0.490 for any appreciable period, 
the peak lift would be much greater than 0.490.  Unless there are 
clearance issues, you would not want a cam that goes up to 0.490 and 
abruptly stops due to inertia considerations and valve train vibrational 
problems (valve float, etc.).

We have debated the issue of flat versus crowned lifters several times.  
I still maintain crowned lifters is the industry standard method.  I 
know that Ford has used it for many years.  A properly crowned lifter 
correctly matched to a tapered lobe was first introduced to compensate 
for the imperfect alignment you mentioned. It will also produce better 
lifter rotation.

Just getting the names of cams that work is not going to be of much 
help. You really need the full set of numbers to see trends in what 
works and what doesn't work. I have an old Cam Doctor set up on an 
ancient DOS PC (one with card slots).  It is a PITA to use, but beats 
measuring by hand.  I once requested people send me some good cam 
examples, but Bob Lang was the only one that sent any. Unfortunately, 
they didn't sound that interesting, so I still have them and haven't yet 
measured them. Sorry Bob, at least I haven't forgotten them.  The only 
cam I've measured is a BP270, which is a good street cam (it's actually 
260 duration). I'd love to have detailed measurements on a 150hp PI cam 
and some of Kas's race cams.  I wouldn't mind getting back to this, but 
I'm more interested in street cams now that I am out of racing.  I could 
easily help with some design work, but don't want to get back into 
producing and selling.  Several years ago, I started a spreadsheet 
similar to the one I did on TR3/4 cams and could post it for download at 
my website if anyone is interested.  It is not really adequate due to 
the lack of complete numbers on many cams.
  - Larry

On 11/12/2015 1:35 AM, Enquiries Road & Track wrote:
> there seems to be very little factual info in the recent thread and 
> i'm hoping to fix this by starting this new thread and challenge other 
> racers to share some some real info
>
> i previously offered the comment that cams cant be considered in 
> isolation and a race engine is quite different to a street engine, 
> with few practical compromises
>
> it would probably help everyone if interested people listed what 6 
> cylinder cams they have used/are using along with a few other comments 
> and what their thoughts are. of course, every cam grinder/vendor 
> espouses the virtues of their own product, but only on forums like 
> this can we get any real world experiences.
>
> I'll start with some experiences gleaned over 40 years with these 
> engines...
>
> the cam lobes are rarely perfectly aligned with the lifter bores and 
> vice versa. triumph 6 cylinder cam lobes are meant to be perfectly 
> flat and so are the lifters. the rotation of the lifters comes from 
> offsetting the lobes relative to the lifter centre. if you test this 
> during disassembly/ assembly using engineers blue on your lifters, 
>  you will see what is going on and probably be horrified as to how bad 
> some are. experiences with flogged out lifters and/or lobes often 
> point to problems here. i have had occasions to move the cam to 
> correct this (by changing the thrust plate fractionally), but its a 
> trade-off and brings about other issues. some of the the turkish made 
> cam blanks i've seen have poor control over lobe separation and the 
> cam grinder cant correct this.
>
> the factory cam grind  can be identified by the number of rings 
> machined into the front bearing. when we could get factory blanks out 
> the back door, they had no rings on them, but neither did the early 
> 2000 cams. from sometime in mid70's, the cam 'stock" got thicker which 
> is a good thing. early 'thin" cams (Mk1 GT6 etc) cannot be modified 
> very much as the base circle encroaches on the stock . these days, 
> radically welded up cams to fix this shortcoming are rare, so the 
> problem has basically gone away by using new blanks.
>
> the oiling flats machined into the front and rear journals are 
> perilously close to the end plates and some cam makers stuff this up. 
> anyone assembling the engine should check this lest they end up with 
> unexpectedly low oil pressure. a real problem if you have switched to 
> a slightly thinner alloy front plate.
>
> most modified 6 cylinder heads stop flowing at about 0.490" valve lift 
> (on inlet) so there is not much point in a cam/rocker system that 
> opens the valve more then is needed. To choose a real 'race" cam, you 
> really need this head flow info for your engine. without it you are 
> just guessing.
>
> most race spec TR cams seem to rely on long durations, typically 300 
> degrees plus (this is valve motion, not 050" duration which is more 
> like 245 degrees).  if you have a factory/Lucas  PI engine, then cams 
> like this are still quite street drivable with the injection properly 
> set up. The factory TR5/6 PI cam is a struggle on carbies, bordering 
> on horrible, because it produce so little vacuum at idle.
>
> The factory TR5/TR6 PI cam has valve duration of 280 degrees and it is 
> "mild". This cam grind, which is commonly copied, is great on any PI 
> street engine, especially if the compression is raised as far as you 
> can get it with the fuel available to you. On 98RON fuel, i have run 
> these at 12;1 with conventional (but modern) cast pistons. distributor 
> re-curving is a must
>
> The factory 2500PI  cam has valve duration of 260 degrees and works 
> just fine with carbies. we used to fit these to US imported TR6's and 
> raise the compression at same time get another 10-15HP.
>
> it is not possible to grind a modern aggressive long duration, high 
> lift cam, on any original TR cam without an awful lot of welding, 
> which typically bends the cam to a point of useless. it is hard to 
> even find blanks that will do this , but they are out there.
>
> these modern design, aggressive  race cams can't be run with a 
> conventional triumph lifter. the lifter diameter needs to increase 
> about 040" as a minimum to stop what is known as edge riding. The cam 
> acceleration rate (how fast it can lift or close) is mostly governed 
> by lifter diameter. oversized lifters require block modification which 
> is not hard.
>
> For a race cam, the lobe will look like a house brick with some 
> rounded edges. anything that looks like your original cam lobe, 
> probably wont cut it in a race engine.
>
> I have run hundreds of modified 6 cyl engines without cam bearings and 
> with zero issues. having said that, the latest cam grinds will benefit 
> from the added support a block with bearings will give. also, if done 
> properly, this should improve oil pressure by reducing losses from cam 
> journals.
>
> A recent 2500 engine for a mostly track car............
> 98RON fuel, 12:1 comp, long exhaust primaries, highly modified head 
> (intake flows 150cfm@25"@0.550" lift)
> cam 308 intake valve duration, 250@ 050". max  lift on intake 0.495"
> comment. sounds fantastic & pulls like an ox all the way to 6750 
> (imposed) limit. almost too lazy. for a race engine. currently being 
> changed to more aggressive cam
>
>
> Terry
>
>
> _______________________________________________
> [email-masked]
>
> http://www.fot-racing.com
>
> Donate: http://www.team.net/donate.html
> Archive: http://www.team.net/archive
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    Are you referring to the thread I started on Spitfire cams? I agree
    completely, there is a lack of factual information. A few years ago,
    I had great intentions of developing 6 cylinder cams with an
    approach similar to the one I took for TR3/4 cams
    (<a class="moz-txt-link-freetext" href="http://tildentechnologies.com">http://tildentechnologies.com</a>).  One of the problems is that in
    order to select a cam, you really need accurate and complete
    numbers, both seat-to-seat and at 0.050.  The problem with
    seat-to-seat numbers is: (1) there usually wrong by at least 10
    degrees (usually but not always understated) and (2) they don't tell
    you as much about peak power as the numbers at 0.050.  The problem
    with seat-to-seat numbers has gotten so bad it is now called
    "advertised" duration.  What is that? Quoting numbers at 0.050 seems
    to be an American thing (I think started by Harvey Crane).  British
    cam makers either don't have those numbers are they will not release
    them. I will never buy a cam without 0.050 numbers.  If we all took
    that stand, then they would have to provide them.  Given that, the
    only way to proceed is to select cams with known characteristics and
    measure the numbers.  Comparable dyno data would be nice, but none
    of us are likely to get this the way Kas did.  The exercise of
    measuring the cam can often be revealing, e.g. (1) valve lash that
    opens and closes the cam on the high velocity flank causing seat
    wear and valve bounce and (2) lift rates (velocity not acceleration)
    that will cause running off the edge of the lifter.  I agree that
    larger lifters could allow a better design.  Also, the lobes could
    be much larger if you run without cam bearings, which could also
    allow a better design curve as well as a stronger and stiffer
    camshaft.<br>
    <br>
    I don't agree completely with your logic about a 0.490 lift limit. 
    If the cam gives 0.490 valve lift, that will occur for zero degrees
    of duration.  To have the valve open to 0.490 for any appreciable
    period, the peak lift would be much greater than 0.490.  Unless
    there are clearance issues, you would not want a cam that goes up to
    0.490 and abruptly stops due to inertia considerations and valve
    train vibrational problems (valve float, etc.). <br>
    <br>
    We have debated the issue of flat versus crowned lifters several
    times.  I still maintain crowned lifters is the industry standard
    method.  I know that Ford has used it for many years.  A properly
    crowned lifter correctly matched to a tapered lobe was first
    introduced to compensate for the imperfect alignment you mentioned. 
    It will also produce better lifter rotation.<br>
    <br>
    Just getting the names of cams that work is not going to be of much
    help. You really need the full set of numbers to see trends in what
    works and what doesn't work. I have an old Cam Doctor set up on an
    ancient DOS PC (one with card slots).  It is a PITA to use, but
    beats measuring by hand.  I once requested people send me some good
    cam examples, but Bob Lang was the only one that sent any. 
    Unfortunately, they didn't sound that interesting, so I still have
    them and haven't yet measured them. Sorry Bob, at least I haven't
    forgotten them.  The only cam I've measured is a BP270, which is a
    good street cam (it's actually 260 duration). I'd love to have
    detailed measurements on a 150hp PI cam and some of Kas's race
    cams.  I wouldn't mind getting back to this, but I'm more interested
    in street cams now that I am out of racing.  I could easily help
    with some design work, but don't want to get back into producing and
    selling.  Several years ago, I started a spreadsheet similar to the
    one I did on TR3/4 cams and could post it for download at my website
    if anyone is interested.  It is not really adequate due to the lack
    of complete numbers on many cams. <br>
     - Larry<br>
    <br>
    <div class="moz-cite-prefix">On 11/12/2015 1:35 AM, Enquiries Road
      &amp; Track wrote:<br>
    </div>
    <blockquote
cite="mid:[email-masked]"
      type="cite">
      <div dir="ltr">there seems to be very little factual info in the
        recent thread and i'm hoping to fix this by starting this new
        thread and challenge other racers to share some some real info
        <div><br>
        </div>
        <div>i previously offered the comment that cams cant be
          considered in isolation and a race engine is quite different
          to a street engine, with few practical compromises</div>
        <div><br>
        </div>
        <div>it would probably help everyone if interested people listed
          what 6 cylinder cams they have used/are using along with a few
          other comments and what their thoughts are. of course, every
          cam grinder/vendor espouses the virtues of their own product,
          but only on forums like this can we get any real world
          experiences. </div>
        <div><br>
        </div>
        <div>I'll start with some experiences gleaned over 40 years with
          these engines...</div>
        <div><br>
        </div>
        <div>the cam lobes are rarely perfectly aligned with the lifter
          bores and vice versa. triumph 6 cylinder cam lobes are meant
          to be perfectly flat and so are the lifters. the rotation of
          the lifters comes from offsetting the lobes relative to the
          lifter centre. if you test this during disassembly/ assembly
          using engineers blue on your lifters,  you will see what is
          going on and probably be horrified as to how bad some are.
          experiences with flogged out lifters and/or lobes often point
          to problems here. i have had occasions to move the cam to
          correct this (by changing the thrust plate fractionally), but
          its a trade-off and brings about other issues. some of the the
          turkish made cam blanks i've seen have poor control over lobe
          separation and the cam grinder cant correct this. <br>
        </div>
        <div><br>
        </div>
        <div>the factory cam grind  can be identified by the number of
          rings machined into the front bearing. when we could get
          factory blanks out the back door, they had no rings on them,
          but neither did the early 2000 cams. from sometime in mid70's,
          the cam 'stock" got thicker which is a good thing. early
          'thin" cams (Mk1 GT6 etc) cannot be modified very much as the
          base circle encroaches on the stock . these days, radically
          welded up cams to fix this shortcoming are rare, so the
          problem has basically gone away by using new blanks.</div>
        <div><br>
        </div>
        <div>the oiling flats machined into the front and rear journals
          are perilously close to the end plates and some cam makers
          stuff this up. anyone assembling the engine should check this
          lest they end up with unexpectedly low oil pressure. a real
          problem if you have switched to a slightly thinner alloy front
          plate.</div>
        <div><br>
        </div>
        <div>most modified 6 cylinder heads stop flowing at about 0.490"
          valve lift (on inlet) so there is not much point in a
          cam/rocker system that opens the valve more then is needed. To
          choose a real 'race" cam, you really need this head flow info
          for your engine. without it you are just guessing. </div>
        <div><br>
        </div>
        <div>most race spec TR cams seem to rely on long durations,
          typically 300 degrees plus (this is valve motion, not 050"
          duration which is more like 245 degrees).  if you have a
          factory/Lucas  PI engine, then cams like this are still quite
          street drivable with the injection properly set up. The
          factory TR5/6 PI cam is a struggle on carbies, bordering on
          horrible, because it produce so little vacuum at idle. </div>
        <div><br>
        </div>
        <div>The factory TR5/TR6 PI cam has valve duration of 280
          degrees and it is "mild". This cam grind, which is commonly
          copied, is great on any PI street engine, especially if the
          compression is raised as far as you can get it with the fuel
          available to you. On 98RON fuel, i have run these at 12;1 with
          conventional (but modern) cast pistons. distributor re-curving
          is a must</div>
        <div><br>
        </div>
        <div>The factory 2500PI  cam has valve duration of 260 degrees
          and works just fine with carbies. we used to fit these to US
          imported TR6's and raise the compression at same time get
          another 10-15HP.<br>
        </div>
        <div><br>
        </div>
        <div>it is not possible to grind a modern aggressive long
          duration, high lift cam, on any original TR cam without an
          awful lot of welding, which typically bends the cam to a point
          of useless. it is hard to even find blanks that will do this ,
          but they are out there. </div>
        <div><br>
        </div>
        <div>these modern design, aggressive  race cams can't be run
          with a conventional triumph lifter. the lifter diameter needs
          to increase about 040" as a minimum to stop what is known as
          edge riding. The cam acceleration rate (how fast it can lift
          or close) is mostly governed by lifter diameter. oversized
          lifters require block modification which is not hard.</div>
        <div><br>
        </div>
        <div>For a race cam, the lobe will look like a house brick with
          some rounded edges. anything that looks like your original cam
          lobe, probably wont cut it in a race engine. </div>
        <div><br>
        </div>
        <div>I have run hundreds of modified 6 cyl engines without cam
          bearings and with zero issues. having said that, the latest
          cam grinds will benefit from the added support a block with
          bearings will give. also, if done properly, this should
          improve oil pressure by reducing losses from cam journals.</div>
        <div><br>
        </div>
        <div>A recent 2500 engine for a mostly track car............</div>
        <div>98RON fuel, 12:1 comp, long exhaust primaries, highly
          modified head (intake flows 150cfm@25"@0.550" lift)</div>
        <div>cam 308 intake valve duration, 250@ 050". max  lift on
          intake 0.495" </div>
        <div>comment. sounds fantastic &amp; pulls like an ox all the
          way to 6750 (imposed) limit. almost too lazy. for a race
          engine. currently being changed to more aggressive cam</div>
        <div><br>
        </div>
        <div><br>
        </div>
        <div>Terry</div>
      </div>
      <br>
      <fieldset class="mimeAttachmentHeader"></fieldset>
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---

From: "geoff byrne" <[email-masked]>
Date: Thu, 12 Nov 2015 22:10:15 +1100

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Terry

Thanks for starting the tread. Your flow figures match mine . I have =
tried cams above 300 duration and found the power band too high, nothing =
much below 4500 and too narrow

I have found the problem with the PI motor is getting the AFR correct =
over the power band.

Geoff Byrne

TR6 Racer down under=20

=20

=20

From: Fot [mailto:[email-masked]] On Behalf Of Enquiries =
Road & Track
Sent: Thursday, 12 November 2015 6:36 PM
To: [email-masked]
Subject: Re: [Fot] Six cylinder cams--some real facts

=20

there seems to be very little factual info in the recent thread and i'm =
hoping to fix this by starting this new thread and challenge other =
racers to share some some real info

=20

i previously offered the comment that cams cant be considered in =
isolation and a race engine is quite different to a street engine, with =
few practical compromises

=20

it would probably help everyone if interested people listed what 6 =
cylinder cams they have used/are using along with a few other comments =
and what their thoughts are. of course, every cam grinder/vendor =
espouses the virtues of their own product, but only on forums like this =
can we get any real world experiences.=20

=20

I'll start with some experiences gleaned over 40 years with these =
engines...

=20

the cam lobes are rarely perfectly aligned with the lifter bores and =
vice versa. triumph 6 cylinder cam lobes are meant to be perfectly flat =
and so are the lifters. the rotation of the lifters comes from =
offsetting the lobes relative to the lifter centre. if you test this =
during disassembly/ assembly using engineers blue on your lifters,  you =
will see what is going on and probably be horrified as to how bad some =
are. experiences with flogged out lifters and/or lobes often point to =
problems here. i have had occasions to move the cam to correct this (by =
changing the thrust plate fractionally), but its a trade-off and brings =
about other issues. some of the the turkish made cam blanks i've seen =
have poor control over lobe separation and the cam grinder cant correct =
this.=20

=20

the factory cam grind  can be identified by the number of rings machined =
into the front bearing. when we could get factory blanks out the back =
door, they had no rings on them, but neither did the early 2000 cams. =
from sometime in mid70's, the cam 'stock" got thicker which is a good =
thing. early 'thin" cams (Mk1 GT6 etc) cannot be modified very much as =
the base circle encroaches on the stock . these days, radically welded =
up cams to fix this shortcoming are rare, so the problem has basically =
gone away by using new blanks.

=20

the oiling flats machined into the front and rear journals are =
perilously close to the end plates and some cam makers stuff this up. =
anyone assembling the engine should check this lest they end up with =
unexpectedly low oil pressure. a real problem if you have switched to a =
slightly thinner alloy front plate.

=20

most modified 6 cylinder heads stop flowing at about 0.490" valve lift =
(on inlet) so there is not much point in a cam/rocker system that opens =
the valve more then is needed. To choose a real 'race" cam, you really =
need this head flow info for your engine. without it you are just =
guessing.=20

=20

most race spec TR cams seem to rely on long durations, typically 300 =
degrees plus (this is valve motion, not 050" duration which is more like =
245 degrees).  if you have a factory/Lucas  PI engine, then cams like =
this are still quite street drivable with the injection properly set up. =
The factory TR5/6 PI cam is a struggle on carbies, bordering on =
horrible, because it produce so little vacuum at idle.=20

=20

The factory TR5/TR6 PI cam has valve duration of 280 degrees and it is =
"mild". This cam grind, which is commonly copied, is great on any PI =
street engine, especially if the compression is raised as far as you can =
get it with the fuel available to you. On 98RON fuel, i have run these =
at 12;1 with conventional (but modern) cast pistons. distributor =
re-curving is a must

=20

The factory 2500PI  cam has valve duration of 260 degrees and works just =
fine with carbies. we used to fit these to US imported TR6's and raise =
the compression at same time get another 10-15HP.

=20

it is not possible to grind a modern aggressive long duration, high lift =
cam, on any original TR cam without an awful lot of welding, which =
typically bends the cam to a point of useless. it is hard to even find =
blanks that will do this , but they are out there.=20

=20

these modern design, aggressive  race cams can't be run with a =
conventional triumph lifter. the lifter diameter needs to increase about =
040" as a minimum to stop what is known as edge riding. The cam =
acceleration rate (how fast it can lift or close) is mostly governed by =
lifter diameter. oversized lifters require block modification which is =
not hard.

=20

For a race cam, the lobe will look like a house brick with some rounded =
edges. anything that looks like your original cam lobe, probably wont =
cut it in a race engine.=20

=20

I have run hundreds of modified 6 cyl engines without cam bearings and =
with zero issues. having said that, the latest cam grinds will benefit =
from the added support a block with bearings will give. also, if done =
properly, this should improve oil pressure by reducing losses from cam =
journals.

=20

98RON fuel, 12:1 comp, long exhaust primaries, highly modified head =

cam 308 intake valve duration, 250@ 050". max  lift on intake 0.495"=20

comment. sounds fantastic & pulls like an ox all the way to 6750 =
(imposed) limit. almost too lazy. for a race engine. currently being =
changed to more aggressive cam

=20

=20

Terry

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</o:shapelayout></xml><![endif]--></head><body lang=3DEN-AU link=3Dblue =
vlink=3Dpurple><div class=3DWordSection1><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>Terry<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>Thanks for starting the tread. Your flow figures match mine . I have =
tried cams above 300 duration and found the power band too high, nothing =
much below 4500 and too narrow<o:p></o:p></span></p><p =
class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>I have found the problem with the PI motor is getting the AFR correct =
over the power band.<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>Geoff Byrne<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'>TR6 Racer down under <o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'><o:p>&nbsp;</o:p></span></p><p class=3DMsoNormal><b><span =
lang=3DEN-US =
style=3D'font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span>=
</b><span lang=3DEN-US =
style=3D'font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Fot =
[mailto:[email-masked]] <b>On Behalf Of </b>Enquiries Road =
&amp; Track<br><b>Sent:</b> Thursday, 12 November 2015 6:36 =
PM<br><b>To:</b> [email-masked]<br><b>Subject:</b> Re: [Fot] Six =
cylinder cams--some real facts<o:p></o:p></span></p><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p><div><p class=3DMsoNormal>there =
seems to be very little factual info in the recent thread and i'm hoping =
to fix this by starting this new thread and challenge other racers to =
share some some real info<o:p></o:p></p><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p class=3DMsoNormal>i =
previously offered the comment that cams cant be considered in isolation =
and a race engine is quite different to a street engine, with few =
practical compromises<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal>it would probably help everyone if interested people =
listed what 6 cylinder cams they have used/are using along with a few =
other comments and what their thoughts are. of course, every cam =
grinder/vendor espouses the virtues of their own product, but only on =
forums like this can we get any real world =
experiences.&nbsp;<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal>I'll start with some experiences gleaned over 40 years =
with these engines...<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal>the cam lobes are rarely perfectly aligned with the =
lifter bores and vice versa. triumph 6 cylinder cam lobes are meant to =
be perfectly flat and so are the lifters. the rotation of the lifters =
comes from offsetting the lobes relative to the lifter centre. if you =
test this during disassembly/ assembly using engineers blue on your =
lifters, &nbsp;you will see what is going on and probably be horrified =
as to how bad some are. experiences with flogged out lifters and/or =
lobes often point to problems here. i have had occasions to move the cam =
to correct this (by changing the thrust plate fractionally), but its a =
trade-off and brings about other issues. some of the the turkish made =
cam blanks i've seen have poor control over lobe separation and the cam =
grinder cant correct this.&nbsp;<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal>the factory cam grind &nbsp;can be identified by the =
number of rings machined into the front bearing. when we could get =
factory blanks out the back door, they had no rings on them, but neither =
did the early 2000 cams. from sometime in mid70's, the cam 'stock&quot; =
got thicker which is a good thing. early 'thin&quot; cams (Mk1 GT6 etc) =
cannot be modified very much as the base circle encroaches on the stock =
. these days, radically welded up cams to fix this shortcoming are rare, =
so the problem has basically gone away by using new =
blanks.<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal>the oiling flats machined into the front and rear =
journals are perilously close to the end plates and some cam makers =
stuff this up. anyone assembling the engine should check this lest they =
end up with unexpectedly low oil pressure. a real problem if you have =
switched to a slightly thinner alloy front =
plate.<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal>most modified 6 cylinder heads stop flowing at about =
0.490&quot; valve lift (on inlet) so there is not much point in a =
cam/rocker system that opens the valve more then is needed. To choose a =
real 'race&quot; cam, you really need this head flow info for your =
engine. without it you are just =
guessing.&nbsp;<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal>most race spec TR cams seem to rely on long durations, =
typically 300 degrees plus (this is valve motion, not 050&quot; duration =
which is more like 245 degrees). &nbsp;if you have a factory/Lucas =
&nbsp;PI engine, then cams like this are still quite street drivable =
with the injection properly set up. The factory TR5/6 PI cam is a =
struggle on carbies, bordering on horrible, because it produce so little =
vacuum at idle.&nbsp;<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal>The factory TR5/TR6 PI cam has valve duration of 280 =
degrees and it is &quot;mild&quot;. This cam grind, which is commonly =
copied, is great on any PI street engine, especially if the compression =
is raised as far as you can get it with the fuel available to you. On =
98RON fuel, i have run these at 12;1 with conventional (but modern) cast =
pistons. distributor re-curving is a must<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal>The factory 2500PI &nbsp;cam has valve duration of 260 =
degrees and works just fine with carbies. we used to fit these to US =
imported TR6's and raise the compression at same time get another =
10-15HP.<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal>it is not possible to grind a modern aggressive long =
duration, high lift cam, on any original TR cam without an awful lot of =
welding, which typically bends the cam to a point of useless. it is hard =
to even find blanks that will do this , but they are out =
there.&nbsp;<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal>these modern design, aggressive &nbsp;race cams can't =
be run with a conventional triumph lifter. the lifter diameter needs to =
increase about 040&quot; as a minimum to stop what is known as edge =
riding. The cam acceleration rate (how fast it can lift or close) is =
mostly governed by lifter diameter. oversized lifters require block =
modification which is not hard.<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal>For a race cam, the lobe will look like a house brick =
with some rounded edges. anything that looks like your original cam =
lobe, probably wont cut it in a race =
engine.&nbsp;<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p class=3DMsoNormal>I =
have run hundreds of modified 6 cyl engines without cam bearings and =
with zero issues. having said that, the latest cam grinds will benefit =
from the added support a block with bearings will give. also, if done =
properly, this should improve oil pressure by reducing losses from cam =
journals.<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p class=3DMsoNormal>A =
recent 2500 engine for a mostly track =
car............<o:p></o:p></p></div><div><p class=3DMsoNormal>98RON =
fuel, 12:1 comp, long exhaust primaries, highly modified head (intake =
flows <a =
href=3D"mailto:150cfm@[email-masked]">150cfm@25&quot;@0.550</a>&quot; =
lift)<o:p></o:p></p></div><div><p class=3DMsoNormal>cam 308 intake valve =
duration, 250@ 050&quot;. max &nbsp;lift on intake =
0.495&quot;&nbsp;<o:p></o:p></p></div><div><p class=3DMsoNormal>comment. =
sounds fantastic &amp; pulls like an ox all the way to 6750 (imposed) =
limit. almost too lazy. for a race engine. currently being changed to =
more aggressive cam<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal><o:p>&nbsp;</o:p></p></div><div><p =
class=3DMsoNormal>Terry<o:p></o:p></p></div></div></div></body></html>
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