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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:fot-bounces@autox.team.net] On Behalf Of Enquiries =
Road & Track
Sent: Thursday, 12 November 2015 6:36 PM
To: fot@autox.team.net
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
A recent 2500 engine for a mostly track car............
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> </o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497=
D'><o:p> </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:fot-bounces@autox.team.net] <b>On Behalf Of </b>Enquiries Road =
& Track<br><b>Sent:</b> Thursday, 12 November 2015 6:36 =
PM<br><b>To:</b> fot@autox.team.net<br><b>Subject:</b> Re: [Fot] Six =
cylinder cams--some real facts<o:p></o:p></span></p><p =
class=3DMsoNormal><o:p> </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> </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> </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. <o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p> </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> </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, 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. <o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p> </o:p></p></div><div><p =
class=3DMsoNormal>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.<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p> </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> </o:p></p></div><div><p =
class=3DMsoNormal>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. <o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p> </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" 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. <o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p> </o:p></p></div><div><p =
class=3DMsoNormal>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<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p> </o:p></p></div><div><p =
class=3DMsoNormal>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.<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p> </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. <o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p> </o:p></p></div><div><p =
class=3DMsoNormal>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.<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p> </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. <o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p> </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> </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@25%22@0.550";>150cfm@25"@0.550</a>" =
lift)<o:p></o:p></p></div><div><p class=3DMsoNormal>cam 308 intake valve =
duration, 250@ 050". max lift on intake =
0.495" <o:p></o:p></p></div><div><p class=3DMsoNormal>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<o:p></o:p></p></div><div><p =
class=3DMsoNormal><o:p> </o:p></p></div><div><p =
class=3DMsoNormal><o:p> </o:p></p></div><div><p =
class=3DMsoNormal>Terry<o:p></o:p></p></div></div></div></body></html>
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