Just one of those curiosity Q's.

[Boomy]

After seeing a few cars with those trumpets on webbers etc as apposed to filters, is there any advantage to it?

Or is it mostly to do with the sound they produce?

Also, some appear to have no mesh etc covering the ends, just how dodgy is that from a worst case scenario point of view?

[Man On The Clapham Omnibus]

Mine has both trumpets and a pair of K&N filters that fully contain them. I certainly would not run mine unprotected (Oooer! in case it 'caught' something. The trumpets have an effect on airflow speed and resonance, exactly what I'll leave others (who know) to explain.

[Jenko]

there are lots of theories on trumpet length giving more or less tourque / more top end / more low end etc, all to do with plule lengths, I think the shorter the inlet the higher the top end, but this then effects the low end performance....I THINK!!!...Im not sure I would notice however.....I guess if you use longer, you have to cut a hole in the bonnet...also, the induction noise perception will be louder if the filters protude from the the car...Of course, thats not such a bad thing :-)

No filter=very dodgy....if a stone went down a trumpet and into the cylinder, I would hate to see the mess it left...even water can destroy the engine...A BIG no no me thinks...

[Blatman]

As MotCO has said, even if you have filters you still need trumpets. They help smooth the airflow into the venturi's. Not having them causes all sorts of problems that you can drive around, but it ain't any good for the way the engine runs.

As for induction length, I think we're all agreed that a total induction length of 17" from the rear of the valve to the end of the trumpet is about the best you can do in a Westfield (discussed at length in the last two weeks. You know the drill...) and remain practical, but *any* length trumpet is better than no trumpet at all.

And running open bellmouths is very dodgy. I have done it, but I didn't like doing it...

[Boomy]

Righto cheers  

I was under he impression you had either or before this thread and thought the filters were just sort of mesh caps on the end or further down the tubes.

I'm not even sure what trumpets with k+n filters on them look like.

Can you just buy trumpets for example, whip off the larger style k+n filters i currently have in place and bolt the trumpets onto the Webbers in a made to measure type way?

[YouMustBeJoking]

If you undo the K&N filters there is a good chance that you will find that trumpets are already fitted inside of them.

[chazpowerslide]

The ram pipes (trumpets) bolt directly to the face of the carb, the filter base plate goes onto the carbs first and then the ram pipes go on, when the securing bolts are tightened (two per ram pipe) the ram pipes and their washers hold the filter back plate in place.

The 40 and 45 DCOE Webers have the ram pipes held on in different ways depending on the ram pipe design.

You are best off going for the ITG or foam type motorsport  filter which has a single base plate spanning both carbs.

This is because the base plate adds some ridgitiy accross the carbs and helps keep the carb balance more constant.

On your Prelit you will certainly need a bonnet hole to accomodate the ram pipes and filter.

As a rule of thumb you need at least a 35-40mm clearance from the end of the ram pipes and the inside of the filter so the airflow is not restricted.

Wire mesh over the ends of the ram pipes restricts the airflow more than you'd think and does nothing to "filter" the air.

Ok, it'll stop small rocks going in but the grit and muck that will destroy the bores and pit the valves and their seats will still get through.

Chaz.

[hilux]

I quote (courtesy of Jenvey)

The air horn serves three main purposes; 1) To convert the pressure difference between bore and mouth into air velocity with the minimum of energy loss. 2) To act as the interface between the induction system and the atmosphere, i.e. the point at which pressure waves change sign and direction. 3) To complete the system to the required overal length.

For ease of description the air horn may be considered in two parts; the 'flare' and the 'tube'.

The main job of the flare is to spread the low pressure zone over the largest possible area - to reduce local pressure reduction - whilst guiding incoming air into the tube with minimum disruption or induced vortices. The flare should be shaped to encourage air to enter from the sides, but not from the rear, of the mouth. This is achieved by either finishing the mouth with a sharp edge when the arc is a little beyond 90 degrees from the air horn axis or by folding material back, parallel to the axis, when the arc is at, or just below, 90 degrees to the axis.

The main job of the tube is to accelerate the airflow smoothly and progressively. This is best achieved by an exponential shape - i.e. one where the radius of curvature is increasing constantly until the angle of the sides matches the next part of the system, usually the throttle body. At the intake end this should blend smoothly with the flare.

It should be noted that the requirements for fuel injection and carburation do not always coincide and the best horns for one may not suit the other.

[cast iron]

The advantage of K&Ns over foam filters is that when correctly set up the steel plate of the filter acts as a pulse plate and fires an air signal down the trumpet carrying more air and hence more performance - If you dont believe me have a go on your local rolling road with various spacers. The original GT40 for example has such a plate in the engine bay over the trumpets.

IMHO Stick with your K&Ns and have a look inside to see if there are any trumpets fitted.

[Boomy]

Great info all, thanks for that