Triumphrat

happyray · 05-05-2008

Hi,
last saturday at the local swapmeet I met a fella who`s got quite a good reputation when it comes to ole Twins.
Anyways, I lamented him my torque-woes with my 1973 T140 Tiger.

He asked why I would`nt fit a second carb (Amal 930 MK1) with a separate intake-manifold ?

Actually I thought about it before (fitting a 2nd carb with separate manifolds)
but I shyed away cause I once heard that the total lenght should be some 18in !).

Apparantly he did this a few times already with reasonable results.
He went on that this is the cheapniks way to improve the torque. It`s by far not the same as with installing another exhaust-cam but remember: "...gotta change the left crankshaftbearing...gotta check the housing wether the cam will fit at all....is your cylinderbase strong enough...maybe need other tappets ...a pro may need some 20hrs to do this job of putting another cam in (I mentoined a Megacycle 510-65)" ....

Question:
Anybody here who put a 2nd carb on in a such a way that each carb has got its own intake-manifold ?

ray

GrandPaulZ · 05-05-2008

The length doesn't HAVE to be 18".

However, if you want to quantify your results, you'll need some dyno time which is probably the biggest stressor on an older bike that you'll ever encounter. Of course you also need access to some nifty materials and equipment for custom intake fabrication.

You might try hunting down some existing manifolds for the job; I'd think that there are some out there to be found...

Dropping the tranny sprocket one tooth can have amazing results for a lot less money and effort.

panda · 05-05-2008

If I 'Really' wanted more torque, I would install a set of 6T (T for touring) cams and tappet followers.) On teh unit 500's at least they will still run out to well over peak power revs without problems but the low down power is much improved.

Woody1911a1 · 05-05-2008

stolen from MAP tech papers .

TUNED INTAKE LENGTH - It is possible to improve volumetric
efficiency by harnessing the natural kinetic energy and the
resonant pulses that occur during the intake cycle. When the
intake valve closes, a pressure pulse bounces back out the intake
tract, and then in again toward the valve. By making the intake
tract the proper length, the returning pulse can be timed to arrive
at top dead center of the next intake cycle, forcing extra air in and
keeping exhaust gases out of the intake port. In order to utilize
this pulse, the intake tract, from the carburetor bell mouth to the
inlet valve, must be the correct length. See fig.#2 (Appendix A).
There are actually several pulses that can be used corresponding
to the 2nd, 3rd and 4th time the pulse is reflected. These pulses
are called harmonics. The 2nd harmonic being the strongest.
There is a simple formula for calculating the length using the
second harmonic.
Tuned Length (in inches) is 132,000 divided by RPM
For instance, if our usable peak RPM was 7000: 132,000 divided
by 7000 - 18.8 inches. This is a very long tract and difficult to
accommodate on a motorcycle. The use of the 3rd harmonic will
result in a slightly shorter tract:
97,000 divided by 7000 = 13.8 inches.
Still a rather long distance. What real benefits can we derive from
intake tuning? The real joker in this whole thing is that although
we may derive some peak power from increasing the ram effect,
it will only work during a relatively narrow RPM band (a little
over 1000 RPM usually). It also has the effect of reducing engine
power outside of the narrow RPM band. Is it worth it? For an allout
road racer it may be. For a modified street bike we will
probably lose more than we gain. A close look at the latest factory
road racers would indicate that this theory has been all but
abandoned and carburetors are now being placed as close to the
head as possible with relatively short inlet bells. Perhaps the mid
range losses were found to be greater than the top end gain.

happyray · 05-06-2008

Hi there,

thanks for your replies !!
The 18in is my assumption (distance: valveseat-intakemanifold-carb-airtrumpet/cleaner ).
Actually at the swapmeet I found some "curved adaptors for the intake manifold".
~4inches long.
Those adapters fixed at the head will make it possible to lead the carb + trumpet around the central tube of my oif. One left, one right.

@GPZ
A Dyno is the best anyone can do but it ain`t cheap and none is available here

@Panda
I still have the imperial bearing on the transmission-side of the crank. I need to change that I believe.
I don`t know wether the increased lift of the new cam will fit into the case !

@Woody
Yea this sounds familar.
Wether the enlonged intake is just good enough for small band of maybe a 1000rpm I don`t know. The guy I talked to apparantly fitted a few T140`s with this setup already and he "claims" that every owner was pleased by the outcome. It isn`t a WOW-effect more an AHA.

Some modern bikes do have variable intake-length equipped with servo-motors (geez...).
Don`t nail me on this one but I believe some Ninja-Kwak bikes using it.

Don`t you get me wrong:
Personally I look at it doubtfully. Thought that someone tried it already...

Thanks
ray

panda · 05-06-2008

Quote:

Originally Posted by happyray

Hi there,

@Panda
I still have the imperial bearing on the transmission-side of the crank. I need to change that I believe.
I don`t know wether the increased lift of the new cam will fit into the case !

Thanks
ray

Bearing does not matter if fitting a thunderbird cam set, if it is still good leave it alone, if not replace it. That has nothing to do with fittinga cam and is entirely a separate issue. The Tbird cams are not high lift, and have silencing ramps. makes for a very quiet and tractable motor. You always have power available at any revs.