Will This Work

[Guest craig030774]

having had an accident at work leaving me at home not being able to use 1 hand i have come up with an idea that i have done a bit of research on but want to put it to you guys

 

pinto running bike carbs

 

instead of re- spacing the carbs or making funny bends in exhaust pipes and faffing around with points for vaccuum etc

 

to have a flange with 4 staight round stubs to a 50mmx25mmx2mm box section (sealed at the ends of course) then 4 more straight stubs to the carbs in the right place so no need for re-spacing, thus having common spot for attachment for servo, dizzy and crankcase breather.

 

had a word with a motorcycle engineer who told me that some jap bikes used to have a hole right through the head so all 4 carbs where in effect suppling a plenum . the carbs used to self balance, but dealers had a tube that they inserted to seperate the carbs so they could balance individually

 

hope i explained rightly and would appreciate any feedback

 

this would allow very easy fitment of bike carbs with only a bit of welding of the plenum to fit.

[richyb66]

In theory it can't not work but I'd wonder how well the induction mixture will flow, given that the plenum between the carbs and the head will have numerous dead air pockets which will cause a lot of turbulence in the mixture and could cause fuel droplets to condense out onto the walls of the manifold and affect the fuel / air mixture.

 

My personal view would be while it would probably work to a certain extent, you wouldn't be using the bike carbs to their fullest potential.

[Guest craig030774]

yes but looking on modern inlet manifolds they all share the same chamber the weber on pinto just dollops it at the top and the cylinders take what they want.

 

that is my thinking

 

probally wrong though

[richyb66]

yes but looking on modern inlet manifolds they all share the same chamber the weber on pinto just dollops it at the top and the cylinders take what they want.

 

That's correct but if you look inside most manifolds you can trace a path around the walls of the manifold to the inlet port without encountering any sharp corners or dead ends. The square section plenum would need to have it's ends capped off and the path to the inlet ports would encounter numerous sharp edges and changes of direction all of which would create turbulence in the mixture and disturb the airflow. Granted the engine will basically suck in the mixture from anywhere in the manifold but for maximum power, the object of the exercise has to be getting the air to flow as smoothly as possible.

[Snapperpaul]

One problem amongst many would be pooling of the fuel where turbulance spins the fuel into dead areas and it just spins like water in a river, then when you close throttle the fuel would drop out and pool, this could then be reintorduced when the throttle is opened and over fuel the engine.

Rough running and poor emissions.

 

Plenum chambers tend to be used to even out the induction pulses (of air) but a whole different set of problems arise when you suspend a liquid in a gas.

[Grim]

Slightly simplified but: imagine only one cylinder at a time is sucking in air.

If you imagine 1 cylinder sucking through one carb venturi, as per normally mounted bike carbs, or twin weber40/45s etc, the gas velocity is quite high, good for efficiency. Now imagine you've quadrupled the area of the venturi, efficiency plummets. So, to compensate, you'll need to reduce the size, or number of chokes, probably both.

So you could have two chokes for example, opening in tandem, with a manifold made up to connect the choke to the cylinder head. More efficient due to higher average gas speeds, but a slight loss in power due to the manifold. This is commonly called the weber DGAS carb, which explains why it's probably not worth trying to invent something already invented.

 

In other words, the reason why bike carbs are more powerful is because you have one venturi per cylinder (and very little pipe work between), albeit at the expense of them being more complex to overcome the disadvantages that brings, such as balancing.

 

If i had a penny for every time i've invented something already invented, i'd have at least enough money for a cheap bottle of pop.

[Longboarder]

If you are gonna try and do this then you will end up with low gas velocity through the carbs, Turbulent flow through the manifold, gas reversing flow direction all over the place as each valve opens and closes and poor result. When you draw it up it just looks all wrong. You don't need to respace the carbs. Angling the runners direct to them will have virtually no effect.

 

Nigel