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+--- Thread: Race inlet manifold (/showthread.php?tid=5528)
Race inlet manifold - shane - 15-01-2021
Is there a general consensus of opinion on the best inlet manifold for an Austin Seven race engine? and where can I purchase the said article?
Or does anyone have one for sale?
RE: Race inlet manifold - Terrytuned - 15-01-2021
Shane an alloy log type manifold is more effective than it looks I use the 30degree down draught SU manifold inverted as it seems to work better as a semi up draught. Originally it was fitted with an HS2 SU but as the engine was developed it was bored out to take an H4 SU it's a standard JB manifold with ports matched and polished. Terry.
RE: Race inlet manifold - Renaud - 15-01-2021
I'd say the best would be a de-siamesed! (I'm already out...)
RE: Race inlet manifold - Paul N-M - 15-01-2021
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
RE: Race inlet manifold - Renaud - 15-01-2021
Thanks Paul. Very interesting.
RE: Race inlet manifold - tomcotez - 16-01-2021
Is that a breather off the banjo on top of the float chamber? I have seen the same arrangement the other way up on updraft solexes and wondered what the purpose was?
RE: Race inlet manifold - Terrytuned - 16-01-2021
All early SU's (round top bolt float chambers) were pipe vented the HS type with the 3 top fixing screws are vented just under the feed pipe. Terry.
RE: Race inlet manifold - shane - 16-01-2021
Thank you for all the input. I am a complete novice with side valve engines .