15-01-2021, 04:51 PM
Nice compact well detailed enginered solution Terrytuned. I like it. I also like the breather.
I suppose in answer to Shane's original question it all boils down to how much you are trying to get out of your race engine.
Log manifolds are not the most efficient but allow compact insallations. Y shaped designes with a good plunum chamber will flow better, small dia. higher velocity, larger more potential volume lower velocity. However your carb will be sticking out into the wind. Look at some post war 750 specials as examples.
The 'less efficient' log may not actually restrict the HP anyway as its only going to be 35/40 bhp so as long as it can handle the demand with enough volume then there is little point in a theoretically better design. Terytune has increased his SU to 1.5" presumably because his engine could use the extra volume whith good results (I presume?) over the 1.25" and the log manifold still coped. Possibly with a little fettling of the runners.
The siamesed inlet shape in the block is another major contributor to poor gas speed/flow so again volume may well help in overcoming this.
Look to see what the fast boys are doing and you wont go far wrong.
Of coursr these are just my own thoughts others may have differing views.
Paul N-M
I suppose in answer to Shane's original question it all boils down to how much you are trying to get out of your race engine.
Log manifolds are not the most efficient but allow compact insallations. Y shaped designes with a good plunum chamber will flow better, small dia. higher velocity, larger more potential volume lower velocity. However your carb will be sticking out into the wind. Look at some post war 750 specials as examples.
The 'less efficient' log may not actually restrict the HP anyway as its only going to be 35/40 bhp so as long as it can handle the demand with enough volume then there is little point in a theoretically better design. Terytune has increased his SU to 1.5" presumably because his engine could use the extra volume whith good results (I presume?) over the 1.25" and the log manifold still coped. Possibly with a little fettling of the runners.
The siamesed inlet shape in the block is another major contributor to poor gas speed/flow so again volume may well help in overcoming this.
Look to see what the fast boys are doing and you wont go far wrong.
Of coursr these are just my own thoughts others may have differing views.
Paul N-M