What Is The Best Option

[richardm6994]

As my rolling road session is fast approaching, I've been thinking about my air filters on my twin 48's (weber).

 

I'm currently using K&N filters on the front of the carbs, but the trumpets I have are too big (OD) to fit inside these filters.

 

My choics are as follows;

 

1) leave the K&N filters as they are and run without trumpets.

 

2) ditch the K&N's....and fit the trumpets with wire gauze over the ends

 

3) ditch the K&N's.....and fit the trumpets with pipercorss sock filters over each trumpet (I have 4 left over from another engine)

 

4) the final thought I've had.........I can machine the tumpets so they fit within the K&N filters. This can be achieved by either turning down the OD of the trumpets....or machining 2 flats on the trumpets (12oclock and 6oclock positions) so that they do not clash with the fliters?

 

What do you think would give the best result?

[Shaft]

Simples.... Option 4

[richardm6994]

I don't really fancy running without filters..because my luck would be that a stone or sommate gets sucked in a buggers up the engine!

[Longboarder]

They are all power robbing options. No trumpets causes terrible turbulence in the carbs. Gauze or socks can rob a load of power. Short but well shaped trumpets will reduce top end BHP and possibly torque but may be good for low mid range power. Shortening the trumpets but still giving them a full 180 degree turn back lip is the least worst option. K&N's have a solid face with air entry round the sides don't they? I doubt they will work well. Can they flow enough? Can you get enough distance between the ends of the trumpet and the face of the filter. (1.5 x Dia)? A pipercross type filter only needs 20mm from trumpet end to gauze.

 

Nigel

[richardm6994]

Cheers Nigel,

 

Good point! the trumpets are 30mm long (full back lip) and the K&N filter are 54mm long and yes they are solid face, which would mean that the end of the trumpet would only be 24mm away from the end of the solid filter face....

 

I guess that rules out option 4 (trumpets in the K&N filters)!

 

So i'm left with K&N on their own.......Trumpets with gauze......or trumpets with socks.....

 

which will rob me of the least amount of power?

[Grim]

option 5) ditch the 48s as they are vastly oversized for the engine and will rob you of all low / mid range power anyway and find a solution that fits.

[richardm6994]

The 48's are choked to 36mm which is the same size as 45's are. They work fine

 

[miikae]

I ended up with Piper trumpets and then obtained a pack of stainless mesh samples,chose the size i thought would be the best and then made domed filters,

I have tried K&N and Piper socks, but i found them too restrictive, the socks i found would posible have been ok if they werent so flexable ie had a metal frame inside to stop the foam from getting sucked towards the trumpets.

 

The DCOE 40s carbs work well and stay intune mixture wise now.

[Snapperpaul]

40's are to small for any 2L exept standard

45,s with 36 to 38 chokes ideal

 

[Longboarder]

Now there's interesting, said with an engineering accent and a bit of teeth sucking. 12.5% difference between best and worst shapes to stick on a carb but only 5.8 gain over the bare carb and you can have 5.2% (i.e.90%of the gain) with a dumpy little pipe as long as it has a good lip.

OK so I thought it would be a little different to that and that is only for one carb mouth in one set of circumstances. Recent work by Dave Walker of Emerald fame is interesting. He is experimenting with variable length trumpets and has been out to 300mm and more with huge variations in BHP and Torque output and positioning up and down the rev range. He still doesn't have the universal answer as each install is unique. There are generally good things to do and generally bad things to avoid but the best for your engine is to trial the options and see.

 

Nigel

[richardm6994]

I think I'm going for trumpets and socks. I had considered gauzes but have read a lot of bad things about them...i.e. disrupting the air flow, better off without them at all etc...

 

I know the ideal solution is to run trumpets on their own, but I just don't feel comfortable doing that.

 

I'll keep a look out as well for the socks being sucked in, however I don't think that's going to be a problem.

[Snapperpaul]

I always thought trumpet length was used to tune the intake runner length I.e. back of valve to trumpet lip.

Therfore you could fit your K&N if you fitted shorter trumpets as you have not got a specific runner length set up so shorter should not make much difference.