Randell Jesup responed to the following message:
TriumphBee@aol.com writes:
> A while back on this list I read a letter talking about a TR6 manifold
> that would allow 3 SU carbs to be mounted on a TR6. I presently have 2 SU
> carbs mounted straight on the old Stromberg manifold. It offers more
> tunability, simplicity, and performance but I would really opt for the 3 carb
> set up if I can track down this unique manifold. Please help. I do not want
> to put a tri-carb set-up of the Italian manufacturer on my '6'.
Note: while triple SU's look cool, you'll almost certainly get more
HP and torque by using two larger SU's (not to mention easier tuning).
The reason is that in a triple-carb setup, the carbs each see two
intake pulses close together, and then a much longer gap. Think about the
firing order. This causes the air column in the manifold and carb to
decelerate much more during the gap. This is more of a problem at slower
flow rates (lower RPMs). In the dual-carb configuration, the three pulses
are equally spaced, providing much more consistent airflow and mixture
regulation. Triple-carbs do have the advantage of not favoring cylinders 2
and 5 (straight runs), but intake design can minimize this.
Note that the A-series 4-cylinder engine has a similar problem
when run with dual SU's. They try to minimize it with a balance tube, but
it's quite hard to do well. Many high-HP A-series engines using single
large SU's because of this.
This information is based on David Vizard's How to Tune the A-Series
Engine, a top-notch book on engine tuning with much information that's
applicable to almost any engine of even roughly similar design. He's
a strong believer in measuring all supposed effects instead of taking them
on faith.
- --
Randell Jesup, Scala US R&D, Ex-Commodore-Amiga Engineer class of '94
Randell.Jesup@scala.com
#include <std/disclaimer>
Exon food: <offensive words no longer censored - thank you ACLU, EFF, etc>
The triple SU/Stromberg manifold is made by Richard Good, RR5 Box 5341,
Mohnton, PA 19540 Ph: 610-777-4457. He makes an assortment of Triumph
performance part including roller rockers and anti-sway bars. I have never
spoke with nor bought anything from him so your on your own. The Vizard
book "How to Tune the A-Series Engine" is and excellent book with a lot of
information on SU carb modifications some of which could pretain to the
strombergs too. This book has been out of print for awhile but I have just
recieved the latest APT (800-278-3278) catalogue and they list a new
edition.
Pat Starr
El Dorado, Calif.
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