Bellmouth for fitting inside air filters.

[Lebro]

So I was bored. Waiting for parts to arrive so I can carry on with my cylinder head refurbish.

I have read that airflow into a carburettor is improved by introducing a bellmouth shape even if it has a very small radius. I have TR4 type paper element air filters, which are sealed, so not possible to simply buy  two suitable bellmouthsfor H6 (HS6 in my case) carbs since you could never get them inside the filters.

So, after quite a bit of thinking, I came up with this:

          

I very conveniently had some aluminium tube 1 3/4" internal dia, & a suitable O/D as well, so I just had to cut & polish the rounded inside profile, then part off.

A line was marked on the inside filter plate to show the OD of the bellmouth, & then 4 holes were drilled inside that line for attachment purposes.

A slot was cut at the bottom of the inner filter plate, & the metal pulled outwards to allow the bellmouth to be inserted into the filter, where ,

once held in the right position the position of the 4 holes were marked on the bellmouth, along with the position of the two cutouts required to line up with the upper two holes on the carb face.

The bellmouths were then drilled, & tapped M3 where the 4 holes were marked, & a round file was used to create the airways required to match up with the upper air holes in the carb.

4.5mm holes were used in the filter plate, so that when the M3 csk screws were tightened up there was very little protrusion of the heads.

After assembly, the metal tab, which had been pulled outwards to allow the bellmouth to go inside the filter, was pushed back down again, & will be flush once re-attached to carb.

I assembled them back onto the carbs using double gaskets to absorb what protrusion was left of the screw heads.

Bob.

 

Edited April 19, 2020 by Lebro

[DavidBee]

Very ingenious. Question — then I'll explain why I'm asking — what make are the air filters? They don't look like the pricey K&Ns. Nice and shiny (but at what cost?). They don't look like Redline filters, which cost a fraction of the price of K&Ns.

The reason I'm asking is that I have come to see, from Forum expert advice, that foam filters, even if fitted with fire retardants, are a hazard, potentially conducive to an engine bay flare up, either because of blowback, misfire, whatever.

So just wondering about effective, paper element durable performance alternatives.

The ATGs, incidentally, include or are fitted around stacks which are very small, but where ram pipes end straoght, on these the edges curl.

Edited April 19, 2020 by DavidBee

[Lebro]

https://rimmerbros.com/Item--i-212278

 

They are these, I spray painted them black.

Bob.

[Hamish]

Very impressed bob. 
 

the things we do with idle hands and the right skills 

[Deggers]

+1. Nicely done, Bob.

[Nigel Triumph]

Clever stuff, I'm impressed too.

Nigel

[BlueTR3A-5EKT]

Made mine out of sanded and varnished MDF, a copy of the old donut K&N used to sell.

Here's how to do it for your H4

Explanation https://mgaguru.com/mgtech/power/pp104.htm

Production Drawing  https://mgaguru.com/mgtech/power/pp104a.htm

Rolling road test  https://mgaguru.com/mgtech/power/pp104b.htm

Cheers

Peter W

PS They are claimed to be worth 5% more hp

Edited April 19, 2020 by BlueTR3A-5EKT

[Z320]

+1

[Motorsport Mickey]

+2

Mick Richards

[ChrisR-4A]

Very neat job Bob, but wont you have to refit the bell mouths to new filters when you replace them every other service?

Chris

[Hamish]

I have considered these instead of trumpets 

https://www.med-engineering.co.uk/ancillaries/stub-stacks/med-stub-stacks

 

[Motorsport Mickey]

They are the same as what Peter W made and I did also out of some plastic (polypengco as I remember) back in 1988

They fit and work well on the SU carbs and will fit within an airbox and still allow ample clearance between the airbox cover and the end of the rampipe.

Mick Richards

[stuart]

That type of full bell mouth work really well and a lot better than smaller radius ones, we need the Prof tosee this as he did some extensive testing of bell-mouth shapes.

Stuart.

[john.r.davies]

Beautifully made, Lebro!

I have an old article by Dave Walker, I think from CCC magazine.    He was testing on the flow bench and after trying some bells as you made, wondered if a full 180 degree bell would be better than the 90, like you made.    So he made some from Plasticene!    And they were no better!    So yours are the creme de la creme!

Edited April 20, 2020 by john.r.davies

[Lebro]

Well, given that I cannot open up my filters, there was not much choice about the maximum size I could go to.

Anyway, it must be better than nothing, & it kept me off the streets for an afternoon !

Bob.

[BlueTR3A-5EKT]

This is the cheapest basic 1 3/4" stub stack I have seen.

https://www.ebay.co.uk/itm/1-3-4-Pair-Stub-Stacks-for-K-N-or-Other-Pancake-Air-Filter-SU-HS6/200962949913?epid=1087623430&hash=item2eca534319%3Ag%3ATjgAAOxyBvZTRVzT&LH_BIN=1

heers

Peter W

[Hamish]

I tried those Peter and they are cheap for a reason. Smaller than

1 3/4 and very rough. 

[DavidBee]

40 minutes ago, Hamish said:

I tried those Peter and they are cheap for a reason. Smaller than

1 3/4 and very rough. 

Which brings me, gentlemen, back to my question: what about Redline performamce air filters?

[Hamish]

Sorry don’t know them. 
 

and I don’t use filters. 

Edited April 20, 2020 by Hamish

[DavidBee]

I can see why there'd be no point using filters, whatever the make, in good, dry, sunny, dust-free, weather, devoid of dirt on the road, on track, but in all weather conditions? I'd be inclined not to let stuff get into the engine in dusty dry or muddy wet weather. Perhaps I'm over cautious, though.

http://www.redlineweber.com/SEMA2002/html/Super_Flow_filters.htm

"Redline Performance are providers of high quality racing and performance car parts and exclusive stockist of many top racing and performance car part brands."

Made in the US, and also well known in Australia, New Zealand.

My real point, Hamish, was to ask imwhether there is no alternative to pricey K&Ns. Perhaps they have a monopoly? I never see anything about other makes here.

Edited April 20, 2020 by DavidBee

[DavidBee]

REPETITA NON IUVANT

Edited April 20, 2020 by DavidBee
Same text twice

[stuart]

16 hours ago, DavidBee said:

I can see why there'd be no point using filters, whatever the make, in good, dry, sunny, dust-free, weather, devoid of dirt on the road, on track, but in all weather conditions? I'd be inclined not to let stuff get into the engine in dusty dry or muddy wet weather. Perhaps I'm over cautious, though.

http://www.redlineweber.com/SEMA2002/html/Super_Flow_filters.htm

"Redline Performance are providers of high quality racing and performance car parts and exclusive stockist of many top racing and performance car part brands."

Made in the US, and also well known in Australia, New Zealand.

My real point, Hamish, was to ask imwhether there is no alternative to pricey K&Ns. Perhaps they have a monopoly? I never see anything about other makes here.

They dont actually seem to do any for side-draught Webers anyway from what I can see.

Stuart.

[spyder dryver]

[Lebro]

Interesting. So my efforts should produce some gain but not as much as the larger dia ones (No. 11 above).  But that sort would have been impossible to fit in my filters. Anyway, 'tis done. maybe re-think if I get some filters which can be taken apart.

Bob.

[john.r.davies]

Most interesting spyder dryver!

That complete 180 degree rims caused MORE resistance to flow than a 'mere' 90 degre rim, AND 360s even more!   Confirms Dave Walkers finding (see my post, eleven above) - Dave is a 'seat of pants' style tuner, not a scientist!

John