SU never had an application on the TR6. The Over Run Valve on the Throttle
is just something that migrated to the TR6 from people who didn't replace
the Throttle Discs
when retrofitting to the superior SU Carbs. Easy fix there, replace the
Throttle Disc for the
plain type everyone's using in most any size SU. The improved Flow in a
it's By Pass circuit is of little benefit when it's only active on the Over
Run. SU's are still considered
a Performance Upgrade to replace Stromberg's. Strromberg's can be made to
live with, but
they have more issues.
From: "Navarrette, Vance" <email@example.com>
Sent: Tuesday, June 01, 2010 10:48 AM
Subject: [6pack] Poor flow in TR6 heads
> I would not make too much of the TR6 head supposedly poor flow.
> The earlier high compression heads had less than optimum flow, but the
> low compression heads got all the goodies - deshrouded exhaust valve,
> port design, better cooling, improved intake manifold, etc. Of course,
> was all done to make up for the reduced compression ratio to meet federal
> Take a look at Vizard's book "Tuning Standard Triumphs over 1300cc". You
> see that the later heads had little that could be done to improve flow,
> although the poor tolerances in the casting somewhat belied this. One
> clean up the poor castings and get some flow improvements. But note that
> TR6 heads came from the factory already gasket matched. While the flow
> benefits of gasket matching are overstated, it does show that the factory
> knew what they were doing. Also the combustion chambers have healthy
> something that was not appreciated by Detroit for another 20 years.
> Likewise for the Zeniths. They are emissions carbs, but the details are
> there. The bypass valves for example, are implemented in such a way that
> is not reduced through the carb. Compare the SU solution for deceleration
> bypass, and the flow through the carb is dramatically reduced since SU
> to mount the valve directly on the butterfly. Simple yes, but it sure
> air flow through the carb. The SU solution is so bad most users simply
> to remove it rather than deal with the performance penalty.
> If I was going to criticize the Zenith, it would be for the rubber
> diaphragms. Unfortunately SU had a patent on the piston solution, so
> was forced to find a method that did not infringe. The result is that we
> to live with the limited life of rubber, and its attendant vulnerability
> pinholes and tears.