[Fot] FW: TR6 Cannon Intake Manifold

Wed Sep 16 07:06:05 MDT 2015

There is no magic springs, the pressure needed is based on the weight of your components,  your max Rpm plus a safety margin,  and the most important thing is the velocity or aggressive nature of the cam lobe. All of which there is no formula that I know of.I have a 9500 rpm engine that had 60lbs seat pressure. Good luck.

Sent from my Verizon Wireless 4G LTE smartphone-------- Original message --------From: John Styduhar <johnstydo at gmail.com> Date: 9/16/2015  7:20 AM  (GMT-06:00) To: MadMarx <tr4racing at googlemail.com> Cc: Triumph 'Friends of Triumph <fot at autox.team.net> Subject: Re: [Fot] FW: TR6 Cannon Intake Manifold 
Iskenderian racing valve spring kit for the TR-2-3-4 shows a seat pressure of 100 lbs. 
On Wed, Sep 16, 2015 at 6:38 AM, MadMarx <tr4racing at googlemail.com> wrote:
Marcel, I use 55 kg seat pressure. CheersChris Von: Fot [mailto:fot-bounces at autox.team.net] Im Auftrag von Marcel Van Mulders
Gesendet: Mittwoch, 16. September 2015 12:22
An: 'Michael Porter'
Cc: fot at autox.team.net
Betreff: Re: [Fot] FW: TR6 Cannon Intake Manifold  Thanks Keith and Michael. About valve springs and seat pressure : it's a question aboutkeeping the valve train parts together but also to avoid that the valves bounce off the seats after (the first) landing. I suppose this valve bounce is not so clearly reflected in the power  dropping at high revs, . On youtube are very interesting high speed cam video's on valve bounce, spring surge...Van: Michael Porter [mailto:mdporter at dfn.com] 
Verzonden: woensdag 16 september 2015 10:57
Aan: Van Mulders Marcel
Onderwerp: Re: [Fot] FW: TR6 Cannon Intake ManifoldOn 9/16/2015 2:18 AM, Van Mulders Marcel wrote:Thanks to the Fot members for their reactions : most are warnings that triple 45 Webers may be too big on a TR6 engine. But it is a race engine (2720cc) and the owner has already bought 3 good secondhand 45 Webers with identical progression holes : 36mm main venturi's seem  to be a reasonable starting point in this case? If necessary, he can go down to 34mm in 45 Webers. I've seen TR6 racecars with 45 Webers and I wonder if the Cannon manifold, with 40mm diameter bores on the carburetor side, can be reamed to 45mm? Another question : the valve seat pressure on my TR4A racecar is 35 kgs/77 lbs. I've also a cylinderhead with only 25 kgs/55lbs seat pressure. The springs on both cylinderheads are 5.25kg/mm (290lbs/").Do you think 25kgs seat pressure is enough? 
On fitting 45s to the 40DCOE manifold, yes, I think there's enough meat to match the manifold to the carburetor exit.  It would mean increasing the radius by 2.5mm (~ 0.100"), but I wouldn't do it until 45mm soft mounts can be obtained--if only 40mm are available, then it's a waste of time and money.  I would recommend that the shop doing the machining find a suitable diameter end mill with a 10-15 deg. taper, just to minimize the finish work required and to make a smooth transition to the smaller manifold bore.

I don't actually understand the complaints about 45DCOEs being too big for a moderately-sized six-cylinder.  For all-around use on the street, 40s would be more than enough, but on the track, 45s are fine.  In fact, I recall 45s with 38mm main venturis being used commonly, but mostly on engines tuned to 7200 rpm or so.  The advantage of Webers is that they have lots of spares to tune to carburetor to the application, although the expense of having such spares on hand for tuning is rarely part of the equation.

As for valve seat pressures, they're not as important as having just enough spring pressure to keep the follower tracking the cam profile.  For normally-aspirated engines, anyway (seat pressures become more of an issue with supercharged engines, when too much boost can push a valve off its seat if the static spring pressure is too low).  The lower the combined weight of the valve train, the lower the spring pressure required.  The steeper the ramps on the cam, the greater the spring pressure required to overcome the acceleration of the valve train parts.  So, it's kind of a balancing act, and one that can usually only be handled on the dyno, while looking for power drops at high rpm due to valve float.

Cheers.

--   Michael PorterRoswell, NM  Never let anyone drive you crazy when you know it's within walking distance....
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