Lotus Elan

Add lightness

PostPost by: shaun » Mon Nov 26, 2018 6:15 pm

Trial fitting of carbs and carbon airbox
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PostPost by: pharriso » Mon Nov 26, 2018 10:15 pm

Beautiful! Any plans to manufacture & sell?
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PostPost by: Certified Lotus » Mon Nov 26, 2018 10:26 pm

Carbon Fiber Anything is always of interest. That is one clean engine bay! Do you drive the car?
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PostPost by: Chrispy » Tue Nov 27, 2018 12:51 am

That's a pretty pretty thing! Love it :D
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PostPost by: RichC » Tue Nov 27, 2018 5:12 pm

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
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PostPost by: shaun » Tue Nov 27, 2018 5:46 pm

The bell mouths are equal length , probably not pushed all the way into the carb bodies or a trick of the light
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PostPost by: Andy8421 » Wed Nov 28, 2018 11:18 am

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
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PostPost by: shaun » Wed Nov 28, 2018 3:09 pm

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
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PostPost by: prezoom » Wed Nov 28, 2018 4:37 pm

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.
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PostPost by: The Veg » Thu Nov 29, 2018 6:18 pm

Exactly 60, or at least 60?
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PostPost by: prezoom » Fri Nov 30, 2018 12:44 am

That is a minimum distance. Anything closer to the opening of the air horn starts cutting the engines power.
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PostPost by: el-saturn » Fri Nov 30, 2018 10:42 am

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!!
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