Howdy.
I have recent experience with this topic, so I'l sound off a bit.
The correct answer to "How do I get more horses from my TR6?"* is:
Make it breathe better.
* note: this is true for all engines. Pick up a book by Smokey Yanuck or
David Vizard... the key to power is to get more air/fuel through the
engine. Of course, this is easier said than done...
Note: Dave Hogenbush from TRF also told me the same thing.
To make it breathe better, you need to reduce any air restrictions and
you need to limit or eliminate exhaust backpressure.
Some ways to do this are:
1. port matching the manifolds. This has some benefit.
2. enlargening the ports in the head. This is also benficial if done
correctly, but it is not allowed in some forms of competition under
"stock, no internal engine mods" rules.
3. A free-flow exhaust.
4. low restriction air fiters.
5. a cam with increased lift and/or duration.
6. changes to the induction system.
7. increasing compression ratio
8. lightening and balancing engine and driveline components.
If the motor is apart, you can do 1, 2, 5, 7 and 8.
While the motor is still in the car, you can do 3, 4, 6 and possibly 5.
In terms of direct payoff in performance, 6 will not necessarliy increase
power without other mods like 1, 3, and 4.
In other words, your engine is a system, and changing one component may
not necessarily increase your power.
Now, triple Weber DCOE's are a popular bolt-on choice for the Triumph
set. Heck, I just put a set on my car. However to derive maximum benefit
from DCOE's, you really need to do 1 and 3 as a minimum.
As for tunability, once you get them jetted correctly, there is almost no
adjustment except for idle mixture and air-flow balance or
synchronization. So, in that respect your mechanic might not be "right
on-base". The car will not idle rougher with Webers if it is tuned correctly.
Note: the Triumphs e-mail list was very helpful in helping me sort my
Webers out. Thanks to all the folks that gave me feedback!!!
The trick to installing triple DCOE's on a TR6 is that once you get it
all bolted on, then you have to play with the jetting etc. I took my set
off a running car. So far to get it running correctly, I have spent over
$200 on venturis and different jets to get the carb to work smoothly in
all RPM ranges. The books on Webers all tell you that you need to play
around with the jetting etc, so even if you buy new, expect to lay out
some money for at least some new jets. This makes the conversion cost
really ad up.
I would not trust a mechanic to set them up correctly unless they have
direct experience with DCOE's on a TR6. Otherwise, you'll be paying $$$
to have him figure out the right combo of jets etc., and the process is
not completely self evident to many mechanics...
I would (and did) get my hand on one or more of the books about Weber
carbs when delving into this area. I got the Pasini book and the Pat
Braden book (from HP Books). Pasini's book is written in toungues. Once
you get past the anecdotal reference, there is good info in there, but it
is really hard to sort out the good stuff, IMHO. I found the HP Books
book to have very easy to understand reference. There is also a book by
Haynes that many recommend. At the rate I'm going, I will own that one
soon also.
All that being said, you will not fully realize the power benefits of the
Webers until you start to really crank on the engine. By that, I mean
that with the stock ZS175-CD's, you will notice a power drop off in the
4000 RPM range. With the DCOE's on my car, it still keeps pulling very
nicely right up to the red line. This is an advantage to me as I do
compete with the car. You will very likely not see a real big difference
in the lower power bands from the setup. The drawback for Webers on the
street is that you will suffer from increased fuel consumption without
any useable low-end power. Now, if you drive around a 90 MPH like some
folks with this setup (Hi Steve!), then you'll love the Webers.
So, if you want to spend the money, go for it. I'd be suspicious of your
mechanic suggesting Webers before a free-flow exhaust (unless you already
had one), as he is likely to derive mucho $$$ benefit if you "upgrade" to
DCOE's and you don't know what you are getting into. Call me paranoid,
but that's the way I am.
On the other hand, they look really kool!
Have fun with your decision, and send a line to the Triumph list if you
have any questions.
rml
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