VM33's

[Rossco(Iceman Josros)]

Just picked a set of these up and considering putting them on the 1100 Slabby - question is would it be worth it ?

[Ben Slabby]

Yup. They work well on the 1052 once they've been bored.

[Ben Slabby]

Or if you decide to get rid...   

Edited April 3, 2016 by Ben Slabby

[Rossco(Iceman Josros)]

2 hours ago, Ben Slabby said:

Yup. They work well on the 1052 once they've been bored.

Bored???

[vizman]

bored out a wee bit.

[Rossco(Iceman Josros)]

These are VM33 round slide Smoothbores guys not the 750 VM29's

[Ben Slabby]

Ah, ok. Then don't know, sorry.

Do they line up ok? What's the outside diameter at engine side? 

[Rossco(Iceman Josros)]

Line up perfectly with 36mm rubbers and they are a smidge under 34mm on the engine side Ben

[canamant]

They'll go fine I'm sure.  The tune up manual shows 3mm units on the 750 which can feed it at nearly 13000rpm.  An 1100 at 10500 should be no problem.

 

[Wescooley19]

Had a set on my old 1052, with a V&H pipe the old bus flew!! Far better than the tin tops.

 

[Gixer1460]

15 hours ago, canamant said:

They'll go fine I'm sure.  The tune up manual shows 3mm units on the 750 which can feed it at nearly 13000rpm.  An 1100 at 10500 should be no problem.

 

750's had 29mm VM's as std - 0.75L @ 13,000 = 9750L / minute requirement.

1100 - 1.1L @ 10,500 = 11550L / minute requirement.

So an 1100 with std 29mm VM's would be desperately breathless!

[canamant]

Agreed - if they were 29s.  VM33 smoothbores will flow better then the 34cvs fitted to the 1052 originally.

[kokolis]

The lochart slabby had vm 33 smoothbores iirc

[Rossco(Iceman Josros)]

Thanks for the replays gents 

[Rossco(Iceman Josros)]

On 5 April 2016 at 1:58 PM, Gixer1460 said:

750's had 29mm VM's as std - 0.75L @ 13,000 = 9750L / minute requirement.

1100 - 1.1L @ 10,500 = 11550L / minute requirement.

So an 1100 with std 29mm VM's would be desperately breathless!

so how's does this calculation work ? Can you show me the math please

[kokolis]

Displacement x rpm obviusly

[canamant]

I didn't like to say, but a 750 at 13000rpm doesn't induct 9750 litres a minute. It only inducts half that because it only has 2 inductions per revolution.  Similarly the 1100 only inducts 5775 litres at 10500 rpm.  What matters is the air speed through the venturi which is mean piston speed x piston area divided by carb area.   A 750 at 13k is 316 feet per second. A slabbty 1100 at 10500 is 358 feet per second.  On 34mm carbs an 100 would have a speed of 338 fps..  As the VM33 is a smoothbore slide carb it will flow better than the 34mmCV so I'd say the 1052 will run very well on them. 

 

[Gixer1460]

DOH ! Yes brain fart time - Displacement halved true! I though we were talking VM29's not 33mm smoothbores? That was my point - whilst the 29's were fine on a 750 their airflow potential would be lacking on an 1100 unless they were bored out to 'say' 33mm where they would probably work better than a 34 or maybe a 36mm CV? Any slide carb will have a better airflow rating when compared to a comparable CV carb just because there is no butterfly & shaft blocking nearly 10% of the bore!

[canamant]

AND we agree.  I love a happy ending :-)

 

For carb sizing I'd always choose one that was fractionally too small rather than too big,  The higher gas flow speed makes sorting the midrange easier as the fuel atomises much better.

 

 

Edited April 10, 2016 by canamant

[Rossco(Iceman Josros)]

I love the plus points Ant