Lotus Elan and Lotus Elan Plus 2 Forums

Trial fitting of carbs and carbon airbox

Beautiful! Any plans to manufacture & sell?

Carbon Fiber Anything is always of interest. That is one clean engine bay! Do you drive the car?

That's a pretty pretty thing! Love it

my question would be: What, if any , effect would arise from having different trumpet lengths on cylinders 1&2?

If you're having the shorter trumpets on 3&4 , why not stick to shorter trumpets for 1&2 ?
I thought i read somewhere ( here?) about the effects of trumpet length on air flow characteristics / standing waves etc etc

The bell mouths are equal length , probably not pushed all the way into the carb bodies or a trick of the light

Shaun,

Not wishing to rain on your beautifully made airbox, in racing circles it is generally believed that that taper on the original airbox was too steep, and as a result the rear carburetor intake was too close to the airbox restricting airflow. There are a number of 'deep' airboxes available from the usual racing suppliers.

As mentioned above, air does not 'flow' into the carburetor, but forms a complex set of standing waves. There are some interesting youtube videos of fuel being blown out of the carburetors with throttles wide open and engine on full song. I did find some fancy analysis somewhere about the minimum distance from trumpet mouth to airbox wall (it was some multiple of trumpet diameter), but I can't find it now, and my maths is too old to figure it out myself.

Probably not an issue unless you regularly touch 8000 RPM with a trick cam.

Really nice job on the carbon fibre.

Edit: - I take it you didn't have the 'D' washers fitted when you took the pictures? The trumpet on intake 2 (counting from the front of the engine) is definitely not seated properly and is sticking out further than the others.

Edit again: - Its all been discussed before http://www.lotuselan.net/forums/lotus-carbs-f40/airbox-trumpet-clearance-t18361.html

Thanks for the comments , i didn?t make the airbox it was bought from a user on this site . The car has a fast road engine fitted so hopefully airflow shouldn?t be a problem

Quick and simple. The distance from the end of the air horn should be one and one half of the diameter of the throttle plate. In other words, a 40mm carb should have a distance of 60mm from the end of the horn to the vertical surface of the outer cover. This was discovered in a dyno tuning session on a 40mm DCNF and should apply to a DCOE.

Exactly 60, or at least 60?

That is a minimum distance. Anything closer to the opening of the air horn starts cutting the engines power.

my motor man "allowed" me to use 75mm trumpets with a foam "sock" as cover - after my previous overhaul my engine had/has appr. 150hp (11,0 compression and 11mm lift!) sandy ......and it roars beautifully! 2 inch exhaust system, starts right after the collector/header!!