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A great deal of the credit for the efficiency of the A type engine must be attributed to the cylinder-head design, which had been evolved by Harry Weslake. Most of the cylinder heads of that period were of simple 'bathtub' design, but Weslake's philosophy was to 'look after the gas'. His cylinder heads incorporated a heart shaped combustion chamber which directed the incoming gas towards the plug. A high gas velocity was maintained into the chamber by running the wall of the chamber very close to the back of the inlet valve. This also created considerable swirl, which seemed to stratify the charge and give a richer mixture near the plug leading to more efficient burning and improved fuel consumption. Using the twin carb setup HS2, HS4, DCOE enhances this short distance added by the balance tube to equalize the pressure between the two carburetors. This is why you see an easier performance transition off the idle circuit. The DCOE carburetor transitions with the aid of accelerator pumps in which the balance tube is not used.

As far as the heat issue, that is a blessing and a curse with the intake and exhaust being on one side. The good points are it keeps the fuel away from any igninition source in case their may be any fuel dripping, also the charging system, starter motor are away from the heat aiding in their efficiency. However heat in it self helps in that it creates an inlet manifold hot spot that added in fuel vaporization that endowed the engine to warm up more quickly. The curse is regulation of this heat, SU or DCOE or DGV inductions. These issues can be corrected with heat insulated shielding keeping temperatures from reaching to high causing vapor lock.
 
Hap, I used the word custom...which it is....not
highly modified...that's another's words.
My understanding is my carbs/intake are stock...just tweeked
by a master's hands. That is what I meant by custom.
:bow:

In any case the ol girl is a real honker wif dem bad boys hangin' off the motor.
:devilgrin:
 
nomad said:
I do however disagree with the engine only seeing the flow from one bore of the twin setup. Both carbs open and are linked albeit thru a torturous manifold.
Kurt.
Click to expand...

Kurt,

You might convince yourself by covering/blocking one carb and see if the engine will still run. It won't, I'll die instantly. The balance tube does nothing to supply both intakes, but rather serves to absorb pulses/shock waves between cylinder pulses. Blocking the balance tube will not keep the engine from running and may even run better.
 
If you block one carb won't that just flood the engine and kill it? If you decouple the two carbs (to set the mixture) and close one carb fully it runs fine on the other carb.
BillM
 
Carburetors will absolutely run without a balance tubes regardless of the number of cylinders it is evident that high performance induction systems are more readily adaptable to engines employing one port to each cylinder. Siamese ports obviously rule out any possibility of individual port ramming; they introduce the likelihood of one cylinder robbing its neighbor and in consequence make for imperfect distribution of flow.

An induction system comprising one port and carburetor choke per cylinder is capable of giving perfect distribution, and lends itself to the use of ram pipes which can be tuned to give optimum power at any given engine speed. Whilst it may be possible to raise the overall b.m.e.p. with such a system, it will be found that different lengths of pipe, whilst raising the power locally, may lead to a slight fall off in power at other speeds. You see this set up in the Triumph Bonneville motorcycle which are not utilizing a balance tube.
 
Well obviously a lot of different opinions on the subject. I'm no expert by any means but where ever the british used a multiple SU setup they always used a balance tube between the carbs. I would think that you would get piston flutter if you tryed to run just 2 cylinders off of each carb but the Harley guys loved these carbs for years. For maximum power the DCOE was the winner before fuel injection. Don't know the answer so I will leave as is!

Kurt.
 
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