[TR] zenith or su's ?

[Wayne Lee]

HS6's should be fine for improved performance over the ZS's in a GT6.
It's only a 2-Litre and they're an improvement over the ZS's on the 2.5 TR6.
Drivability wise they come on just off idle without the Stromberg's flat 
spot.
If He was doing a lot of other Mods he could go bigger with an SU still, 
like
HS8's off of a Rover 2000 TC or whatever. That would be overkill unless it's
wound up tight.

I know Jim meant he needed Yellow springs not Needles, That sounds strange
it would need a Spring more than twice as strong as the Red one that came in 
the
P1800's that had  more stock HP. I run the Yellow as well in my TR6, No 
power
being thrown away, it's a balancing act against fuel economy. The Pistons 
are fully
opened before max revs.To run Webers
would throw away a lot more wasted Fuel unless it's being driven in Time 
Trials
etc. The whole package is only as good as the weakest link. HS6's are plenty
of Carb for a street driven 2-Litre. HS6's should be good to 135 HP anyway.
Running larger Carbs wouldn't avoid this situation,
there's plenty of them being driven out there not in an optimal state of 
tune. It
would take just as much time to get them right as well. But if You were to, 
at
least You can't over Carburate using SU's like Webers. If You were to run 
DCOE
48's or something without the rest of the package to back it up, there'd be 
bigger problems.
Wayne



--------------------------------------------------
From: "Randall" <tr3driver at ca.rr.com>
Sent: Tuesday, December 01, 2009 1:53 PM
To: <Triumphs at autox.team.net>
Subject: Re: [TR] zenith or su's ?

>> 2. There is a behavioral change between the piston operating
>> in its range and topped out.  Once it is topped out the
>> mixture will get richer as the airflow increases, regardless
>> of how well or poorly it was set before.  If you use
>> full-throttle behavior as a data point you will be mislead by
>> that change.
>
> Seems to me that this is exactly the same thing that happens when using 
> too
> small a fixed venturi carburetor.  Not only does the mixture go rich, but
> the pressure drop across the carb increases, leading to less than maximum
> power.  In general, if you are going to all the trouble of doing a carb 
> swap
> for improved performance, it's probably best to choose a carb large enough
> for your application and thus avoid this situation.
>
> Same thing applies (to a lesser extent) for using heavier springs.  You're
> throwing WOT power away by reducing maximum airflow.
>
> -- Randall