Run better on Bellmouths

Paul Marx said:
They do run better on bellmouths and also run better with the 2/1 rather than the 2/2. That's the way they were designed and tested.
No doubt, they can be set up with filters but is it worth it? Unless you're under 30 and doing many 1000s of miles a year, the bores usefull life is probably superior to yours.

Paul
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I totally agree about the engine, Paul. The slides and carbs get eaten alive much more quicker though.
Lee
 
but mainly to change inlet length
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I experimented with various length of fabricated pipe around the Inlets with various sized Main jets to no avail. It just seems any type of coned entrance baffs the VBH 30's above 5000rpm with these Slater 2 into 1 pipes. I believe the 30's where designed to use the 2" Velocity Cones specifically with the original DMG Dual Silencers. The 30A's seem to be Hi-Velocity Carbs but just too small for any restriction around the Inlets including the original 2" Velocity Cones with a more free flowing exhaust system.

I change Oil, dissemble and clean the open 30A's 1/2 way through the season. The sliders don't appear to have much wear and the engine cylinders are still original bore and in good condition considering I did lean her out once and melted the pistons a few years back.

As I say if a flush mounted rectangle Air Box on the Carb Inlets with a Flat Filter does not work I believe I require larger carbs in order to use Air Filters or an Open Bellmouth Cone for that matter.

One thing I gotta say is that the original 2" 71 & 72 SF Open Velocity Cone looks very much like your #4 example which shows a -5.5% in flow. That probably accounts for my failures. I see that an Elliptical shaped around the bellmouth works much better - Humm!. Certainly giving me something to think about. I wonder if a short Cone with a pronounced elliptical entrance would work inside a Large K&N type Breather?

In the mean time the mill runs great with them Little Open 30A's. Other then the  Oil change and Carb maintenance 1/2 way through the season, it's also rather messy, as the Open Carbs create a Fuel Stand Off that puts brown varnish over the Starter area.  

The Bark of open Carbs on my Twin sounds something like the prop wash from a J3 Cub
300px-PiperJ-3Cub02.jpg

;o)

 
Tippie said:
Paul Marx said:
They do run better on bellmouths and also run better with the 2/1 rather than the 2/2. That's the way they were designed and tested.
No doubt, they can be set up with filters but is it worth it? Unless you're under 30 and doing many 1000s of miles a year, the bores usefull life is probably superior to yours.

Paul
Click to expand...
I totally agree about the engine, Paul. The slides and carbs get eaten alive much more quicker though.
Lee
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Good point. I found that my SFC had been going down hill over the last few years. I started imagining a worn cam and all sorts of bothersome things till I found that the slides were flapping about in the carbs. New slides, needles and needle jets and the thing ticks over for the first time since 1997!

Ciao
Paul
 
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Phil - I like that modification - You got any specs or designs so I can build something like it.

I'm thinking I could use my Drill Press as a Lathe and mold Mild Steel Exhaust Piping to an Elliptical Shaped Bellmouth while spinning it,  heat it with a torch then with a file true it up while spinning it in the Lathe like a Potters turn table ;o).
 
Hi Ron - Here's a shot that shows the set up for inlet extensions - the shot on the triple  shows a method similar to what you  describe - I pressed the aluminium tubes over a cone to get the required shape - regards - Phil
 

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The SFC, along with early Ducati 900SS series bikes, came with those plastic bellmouths with wire screen covers over the opening. That was stock, so if you follow the argument that the factory "knew what they were doing" then these should be optimal. Of course, the counter argument would be that these bikes were not intended for street use, but rather for being a track tool, and street use is a much grittier environment....well, the counter-counter argument would be you I would not be so sure, you should see some of the tracks I've been on.....and the counter-counter-counter argument would be that may be so, but race bikes were intended to be stripped after each race/two or three races so dirt ingestion not as much an issue.....etc...just sayin'.......


My seat of the pants dyno says stacks make the bike run stronger. Did not test on a Dyno, but my point is not to wring that last .0001% HP out of the engine, just want it to run strong, and the looks and nice induction sound are a bonus.

Was really asking why they run better (or not), and I posited that it my have something to do with cams having more lift/duration and a therefore a requirement for more air.....and perhaps the trumpets were better suited to providing this....I am not an expert on air flow dynamics, just some dude with an SFC doing so experimenting......

Now, getting to the real meat of the discussion, I think the lady either appears somewhat in distress; or is having some sort of out of body experience, or perhaps was caught in the throws of a mid coital epiphany....now, this last one may have something to do with her velocity stack smoothing out the intake allowing for more flow or not, and perhaps someone can enlighten us on that subject......
 
Spub said:
The SFC, along with early Ducati 900SS series bikes, came with those plastic bellmouths with wire screen covers over the opening. That was stock, so if you follow the argument that the factory "knew what they were doing" then these should be optimal. Of course, the counter argument would be that these bikes were not intended for street use, but rather for being a track tool, and street use is a much grittier environment....well, the counter-counter argument would be you I would not be so sure, you should see some of the tracks I've been on.....and the counter-counter-counter argument would be that may be so, but race bikes were intended to be stripped after each race/two or three races so dirt ingestion not as much an issue.....etc...just sayin'.......


My seat of the pants dyno says stacks make the bike run stronger. Did not test on a Dyno, but my point is not to wring that last .0001% HP out of the engine, just want it to run strong, and the looks and nice induction sound are a bonus.

Was really asking why they run better (or not), and I posited that it my have something to do with cams having more lift/duration and a therefore a requirement for more air.....and perhaps the trumpets were better suited to providing this....I am not an expert on air flow dynamics, just some dude with an SFC doing so experimenting......

Now, getting to the real meat of the discussion, I think the lady either appears somewhat in distress; or is having some sort of out of body experience, or perhaps was caught in the throws of a mid coital epiphany....now, this last one may have something to do with her velocity stack smoothing out the intake allowing for more flow or not, and perhaps someone can enlighten us on that subject......
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There never was a wire mesh on the SFC.
The bikes with Dell'ortos are civilised, the ones with Amals only work wide open.
I've used my SFC as a road and track bike for near 20 years and I can assure you that it's never needed stripping since I rebuilt it after buying. That's why they won endurance races.

Just ride yours.

Ciao
Paul
 
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