Classic cars forum & vehicle restoration.

[Kleftiwallah]

Can anyone out there point me in the direction to the answer to this quandary:-

Does increasing the distance between the carb' and the cylinder (extending the manifold length) have any detrimantal effect to starting, performance and economy?

I'm thinking about converting from a single carb' to twin carbs'.

Cheers and thanks in advance. Tony.
_________________
It may work in practice, but not necessarily in theory!

[V8 Nutter]

I don't know how it would work on your car, but in the early 60's Chrysler offered "Sonoramic Ram Induction". Two manifolds were offered the long ram, gave increased power for overtaking at highway speeds (quote from their advert) From memory the manifold runners were about 40 inches long, this placed the left hand carb out beyond the right hand cylinder head, and the right hand carb out past the left hand cylinder head. This was obviously on a big V8. The short ram version of the same idea brought the carbs inboard and the maximum torque moved up the range. It worked well at the time but they dropped it after a few years

[47Jag]

Tony,

A little light reading for you here:-

https://ijmter.com/papers/volume-2/issue-10/a-review-on-design-development-and-optimization-of-air-intake-manifold.pdf

If you look at some of the BMW and Mercedes engines when they started using fuel injection you can see where the designers tried for an optimal length inlet tract (30 cms. from memory) and the manifold starts low down the sides of the engines and sweeps up over the top.

In your case the improvement in breathing IE more fuel/air into the cylinders is really what you are after.

Art

[47Jag]

Tony,

A little light reading for you here:-

https://ijmter.com/papers/volume-2/issue-10/a-review-on-design-development-and-optimization-of-air-intake-manifold.pdf

If you look at some of the BMW and Mercedes engines when they started using fuel injection you can see where the designers tried for an optimal length inlet tract (30 cams from memory) and the manifold starts low down the sides of the engines and sweeps up over the top.

Art

[jp928]

In summary, depending on some other factors, a longER inlet tract will increase torque in the lower rev range, compared to a shortER inlet tract. It may reduce torque and power in the upper rev ranges. Think of the inlet tract as a tuned pipe - resonance at a certain revs will improve gas flow - short tracts, higher revs, long tracts, at lower revs.
jp 26 Rover 9

[alastairq]

Longer manifold runner can increase gas speeds.
In much the same manner as smaller diameter chokes.

On a 1300cc Skoda [Rapid 136] engine, I had made a long-runner inlet manifold to take bike carbs...for trialling...good low down torque...quite responsive [better than a weber!].....without the risk of flooding if I became over-enthusiastic with the gas peddle.

Those who did similar for rallying, got much shorter inlet runners, for better BHP higher up the rev range.

[Kleftiwallah]

Many thanks for all those informative replies.

Cheers, Tony
_________________
It may work in practice, but not necessarily in theory!