Tuning Weber 40dcoe Trumpet or Filter?

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Tuning Weber 40dcoe Trumpet or Filter?

My engine is tuned not sure to what extent, 652 126 with lumpy cam, 123 ignition the guy that fitted prior to me buying it. He fitted a Weber 40 which by the consensus of the forum is too big, but as it's there i might as well leave it on. At the moment it has a k& n type of filter but I noticed a lot of people fit trumpets rather than a filter apart from the obvious danger of sucking in debris are there any benefits of fitting trumpets? if so does length matter?
If driven without either i have noticed the occasional flash & popping exiting from the carb.
 
The occasional 'popping and flashing' back through the carb is probably down to the 'lumpy' cam. Whether you fit a filter, or only a trumpet is sometimes dictated by where you drive the car---if it is a very dusty area, than I would reccomend a filter. If not, than a simple trumpet (preferably with a gauze) will probably suffice. I have only a 'gauzed' trumpet on my FZD and have experienced no problems, but then I do live in North Wales, an area NOT famed for its dusty atmosphere!
 
Thanks for your feedback. Would you know if the length of the trumpets make any difference? Plus If I fit trumpets would the carb need any adjustments, i.e i assume more air is being sucked in .
Many thanks again Barry

Hi Barry, Depending on the set up you have with the size of venturi fitted into your carb you may be able to elicit a slight gain with 'Trumpets' fitted. There are many types and sizes for the weber, but suffice to say that the length, size and angle all have effects on the airflow into the carb. A proper 'Trumpet' will smooth the air into the carb throat and enable a more efficient mixture to the engine. I would think that 'Eurocarb' should be able to give you good advice once you have told them what you set up is. I have had to use original Trumpets on my twin Solex as it's reported that the carb will be difficult to set up without them. I have been using Pipercross filter socks too, they fit onto the carb easily and don't effect the carb in any way. (y)(y)
Ian.
 

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I seem to remember that the consensus ‘back in the day’ was that longer trumpets gave better torque whereas shorter ones gave better BHP. :chin:
 
I ran my old mk3 Austin Healey Sprite, 1098cc, with ram tubes (as they were called) on the twin SU carbs and that was clocked at 100mph on the M4. Also had a full length fastback hardtop that may have helped. I was always worried about not having air filters but I ended up doing 101,000 miles in that car and sold it with 176,000 miles on the clock.
 
You are correct Ian, generally speaking within reason, longer trumpets are fitted to improve torque. There is a formula for optimum inlet length (and one for optimum exhaust length as well), which I have somewhere in my notes---I will try and dig it out.
 
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