Sexy bell mouths, place your bets...

I'll be playing with different exhausts on the Dyno soon, but the first run will be with no other changes except fitting the super sexy bell mouths shown below in place of the K&N filters and adapters as supplied by CNW.

Place your bets now as to what the BHP increase will be...

Those just got to run as good as they look.

Our setup is very similar - I have those petcocks and put a red mark in the off position to remind me.
Other than that, not so much. :mrgreen:

Stones and sand accidentally getting in the tight, slippery, reciprocating components doesn't sound at all sexy to me.....

concours said:

Stones and sand accidentally getting in the tight, slippery, reciprocating components doesn't sound at all sexy to me.....

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Don't panic. I have a double entry Ramair foam 'sock' to go over them.

But having said that, I ran a T160 and a Vincent on the road for many years on open carbs with no issues, as well as numerous race bikes. So I don't think the risk is as great as it seems (depending on where one lives and what the bike is use for of course).

Eddie

You need a filter mesh over them bad boys they could suck in man spheres at high RPM

You should know better than to ask a simple question and expect a straight answer.

Anyhow, I would think and hope for maybe 5% increase?

Frankie17 said:

Eddie ..... they could suck in man spheres at high RPM

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You guys are funny, I love this forum and I bet they'll give ya....um..... 2 extra hp.

A proper rolled lip flaired bellmouth should flow 25%+ more air than a straight tube with sharp edges and even more w/o a motorcycle size air filter ahead of it. Norman White sells stubby bells with claim of between 1-2 hp. Others designs calim at least 10% more torque from mid range up - which implied a 60 hp Norton my make 6 more hp or torque. Here's a teaser quote in Norton power range to keep ya experimenting till ya can feel it...

The final dyno graph shows a comparison of what can be achieved with the with the Breathe cover and DNA filter installed. The traces are from an OEM factory bike with just the AI removed, and then two traces again from the same 790 bike with a TTP Breathe intake cover, high performance air filter, TTP Ignition Advance, Mega reverse cone silencers with the airbox baffle installed and the second, without the airbox baffle installed. As you can see from the dyno chart, the OEM 790 gave 54.43bhp and 40.86ftlb and when it was modified as listed above with the airbox baffle removed it gave 70.91bhp and 53.06ftlb which is an increase in bhp and torque of around 30% each. Even more impressive is the torque increase in the mid range. This is the area of the rev range you use the most in every day riding, for example when overtaking or when accelerating out of a bend. If you look on the dyno graph you can see at 4,500rpm there is a big difference between the OEM bike and the modified bike. The dyno figures show that at 4,500rpm the OEM factory bike is producing 35.8ftlb of torque and the modified bike is producing 53.05ftlb of torque, this is a massive increase of over 48% right where you need it. We think this is an excellent £$£$ per bhp improvement.

When velocity stacks became the mutts nuts for Amal concentrics, the claim was 5bhp so I'll go for 3bhp because they are not velocity stacks but a good old fashioned bell mouth. the rolled edge was the issue I recall. If you put a sock over them, the airflow will be spoiled for want of another word. My Bantam with a bell mouth ran, with a gauze over the bell mouth it was sick

Read a story years ago about some guys racing a Commando at Daytona. They were running open carbs and it wouldn't pull through he midrange. They called Leo Goff, who said it was likely the typical "Norton midrange flat spot" and advised they bolt up some velocity stacks to add some length to the intake tracts. After checking with every shop in the area, nobody had velocity stacks for Amals, so they improvised and snipped the bottoms and tops off a couple of beer cans. Got out on the banking and as if by magic, the midrange returned and the engine would pull to redline. Now you may think it's all b.s. but I've tried it and it works. Beer cans don't provide much filtration, though.

gripper said:

When velocity stacks became the mutts nuts for Amal concentrics, the claim was 5bhp so I'll go for 3bhp because they are not velocity stacks but a good old fashioned bell mouth. the rolled edge was the issue I recall. If you put a sock over them, the airflow will be spoiled for want of another word. My Bantam with a bell mouth ran, with a gauze over the bell mouth it was sick

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I'll check the impact of the socks on the Dyno, but I'll be surprised if its much, when I tested similar socks on 38mm carbs on a 900cc Weslake, there was no measurable difference.
Gauzes are a different matter. I don't fully understand it, but they have a big and bad effect on the incoming air flow and are generally worse than any sock or K&N type filter for flow. Also, they aren't filters either, (just sieves) so 'worst of both worlds' really!

Nigel, I posted some flow results on here last year using a RH10 head from my race motor , brand new 32mm Premiers on standard length manifolds..
I used different length bell mouths, the short ones that come with the carbs, the long ones with mesh, the long ones without mesh.
The end result being I now run the long bellmouths without the mesh as this was the best gain. Yes there was a difference!!!
I trimmed the outer diameter of where the mesh would normally be trapped so the bellmouths dont foul on each other using the standard manifolds.

3 to 4 more potenial HP
Regards Mike.
PS Scored those Mk 2 Amals out of Belgium, thanks to you!

"Not very long , but I wanted to get the air compensation holes for the float bowls out of the incoming airstream ."

Why?

concours said:

"Not very long , but I wanted to get the air compensation holes for the float bowls out of the incoming airstream ."

Why?

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Not sure, but factory stacks used to be made like Ludwig's only with a base added that slipped over the outer throat openings. Must be a reason.

http://amalcarb.co.uk/velocity-stack-mk ... eries.html

Hi ludwig.
Your induction tubes make wonderful sense as the air flow to/through the venturi will not be disrupted by the step at the lip of the carby.
How have you connected the tubes? and what rationale for the overall length guided you? please.
My tubes extend and curve into the hamcan style air cleaner so I retain full filtration without restriction.
Ta.

I've never used an air filter on my race bike. At one race meeting I rode it through the pits, stopped and when I tried to start it again, it only started with difficulty and let out a scream - revved it's tits off. A stone had popped through the half inch gap under the seat, and got under one of the slides. I have now closed that gap with a piece of rubber. Stones can also come through from the back wheel by riding the chain, and a piece of chain roller is not good for the motor internals (mainly on two strokes).

Seems if one does enough of something all kinds of highly unlikely things can and do occur. Boats and aircraft and short term race engines do better w/o filteration. What a bunch of pigs alluding to smooth intakes as sexy objects...

concours said:

"Not very long , but I wanted to get the air compensation holes for the float bowls out of the incoming airstream ."

Why?

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Two reasons as I understand it:
1. The inherent step, with holes in it, is an impediment to smooth air flow
2. The increased intake charge speed is NOT what the pilot circuits want
The ones on my FCRs are Keihin designed and also miss out the pilot circuits so the stacks match smoothly with the choke.
It was Jack Shemans who first created 'nozzles' like this (similar to Ludwigs) for the MK1 concentrics on the BSA/Triumph triples, which hence became known as 'Shemozzles' (often incorrectly referred to as 'smoothbores').

concours said:

Stones and sand accidentally getting in the tight, slippery, reciprocating components doesn't sound at all sexy to me.....

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Make filtration a priority and finish the season with an engine in much better condition than the winner's.

Bellmouths look great and will certainly add some juice. But for the street, filtration is a must for me. Without it, grit will get into the cylinders and lead to scored cylinder walls and valve seats. Just not worth omitting filters.