Straight inlet manifolds

I thought they would aid the gas flow into the head but a learned colleague advised me that the bend in the standard inlet manifolds helps disturb the gas flow which aids firing .
Both seem reasonable arguments to me, anyone here with a view?Â

Cranked inlets are to give room for your knees. The Le Mans has straight inlets and your knees have to take care of themselves. So straight must be the way to go for performance … right?

And on the CX500 they went to all of the trouble of canting the heads so the carbs cloud still be tucked in but with straight manifolds. And ended up with push rods. So it must be true.

When I put the T3 bodywork on my Mk111 I bought the extra cranked in manifolds so I could keep the T3 side panels without cutting them.
I felt an immediate increase in power and discussing this discovered that the biggest benefit was the elongated inlet manifold tract which ideally should be over 12’’.
So straight inlet manifolds don’t work I asked.
They do, negatively was the reply.
I cannot remember who the learned chap was but he was well respected in the club.

[quote=“cyclobutch”]Cranked inlets are to give room for your knees. The Le Mans has straight inlets and your knees have to take care of themselves. So straight must be the way to go for performance … right?

The Le Mans inlets are not straight, there is a slight bend.

Interestingly, modern car intakes have long convoluted intake tracts or even special eddy chambers to add turbulance to the air prior to the fuel being injected into it, apparently this improves efficiency of the burn (by making sure fuel and air are thoroughly mixed) and therefore more power / lower emissions etc. Ford’s ‘VIS’ (Variable Induction System) springs to mind.

I still can’t believe Honda to be wrong on this one.

You are talking about the CX500.

Can someone comment on the new single injector with long manifolds on the new small blocks which have apparently 4bhp more.

Velocity stacks to you too… :laughing:

And the winnah is…

A mate of mine many MANY years ago said that when gas flowing a head you didn’t polish the inlet ports to a shine as the rough surface helped mix the air and fuel but you did polish the exhaust port

I think that lengthening the inlet tract improves pulling power at low revs, on Trials bikes for example, maybe why Ian’s bike felt more powerful. Years ago we believed polishing ports and inlet tracts improved things now apparently an unpolished surface promotes turbulence which is better still, and somewhere, also years ago I read that gas or vapour can speed up as it travels round a curve. It was probably an April 1st edition of Motorcycle Mechanics or Motorcycle Sport mind you, or of course any edition of MCN. :wink:

The respected member I quoted earlier said the same.

Apparently, the ideal surface for the inlet tract would be like the surface of a golf ball and for the exhaust like a mirror, who is going to give it a go?

And it was 40 odd years ago.

More likely just a style thing, just looks like it should be right to the prospective punters. But what do they know

Did cause quite a stir at the time I remember.