Carb air scoops?

[Lolat492]

Thanks as ever to you all.

will look at the Porsche kit.
The chokes body dia is 46mm and the trumpets are 60mm tall so that is a very tall filter stack. I imagine the Porsche kit is made for the historic rally set-ups in a 911.

[redturner37]

Originally Posted by Lolat492

Thanks as ever to you all.

will look at the Porsche kit.
The chokes body dia is 46mm and the trumpets are 60mm tall so that is a very tall filter stack. I imagine the Porsche kit is made for the historic rally set-ups in a 911.

Take the trumpets off. Most Webers running modern filters dont need them. Just bolt straight to the stubs as supplied.

[TheEsses]

On the next test day why not try a piece of alloy bit higher than carbs, tie wrapped across the bottom of the roll cage to try and put them in same airflow and see the difference.

Hope the carb problems are sorted, last time I saw you at Shelsley you could still smell petrol vapour at Top S as you crossed the line !

[Lolat492]

The engine lost a lot at that Shelsley meeting and I've rebuilt it again!

All seems ok according to the sniffers on the rollers!

[Lolat492]

Looking at the ITG/Pipercross etc just found K&N (who made the ones i now have) make a tall filter element, 5.5" instead of 3.75".

[judgie]

i would not remove the trumpets. your'll lose torque and you will end up with fuel stand off problems.
on my air cooled 914 engine we picked up nearly 30lb/ft of torque just by fitting 130mm trumpets over the 30mm ones.

[kintryin]

This suggestion of snorkels brings me round to thinking about the air flow when the car is stationary and when moving. The rollers are optimising the engine in a relatively stationary state. The snorkels will considerably change the immediate environment of the carbs.
If the rollers can set the motor up whilst replicating the forced snorkel airflow then all well and good. But, I've never heard of that being done on a set of rollers . And certainly your car has been set up without. Dont forget too much air will possibly create lift too !
Now think about the racing ff2000s they are set up on rollers/dynos without snorkels and are optimised in a stationary airflow environment ..... You will certainly not have a vacuum
in your engine bay !
The only issue that you might consider will be the induction temperature within the engine
compartment when stationary . When it is moving then there should be no issue.

[grahamb]

David Vizard did a lot of work on downdraughts on Minis. May be worth trying to get a copy of his Tuning BL's A-Series mini book, as the theory in there is probably still quite relevant.

[Cameron Winton]

I am sure that the minis with downdrafts had a scoop facing backwards but may have been for them to feed off the high pressure stalled area in front of the windscreen. Any scoop should lead into a plenum as you are trying to increase the mass of the charge at the carb inlet. It is more complex than "scooping up" more air.
A good first step would be good aftermarket filter with the plate at least 1.5 times diameter off the top of the trumpet.

[Lolat492]

Interesting.
Also they conditions on an engine dyno are different again!

To be honest I'll run the car as it has been set-up on the rollers just, no filters and the trumpets recommended by the carb manufacturers (PMO in the USA)

Some of the Porsche sports race cars had simple wire mesh guards over the inlets, all had trumpets. None ran open top but you wouldn't on the Targa Florio or Le Mans.