Amal GP Carbs

You’re bang on there kommando. It was on 4 valve per cyl NRE motors that I saw as you describe. On 2 valve Triumph twins the smoothbores worked well.

I have a pair of 33mm CRs on my 920 & it runs very well on them. Before fitting them I used a pair of 32mm MK1s with Schnozles & it ran just as well. I have run this bike on the dyno with the Keihins but not with the Amals, although my backside dyno thinks there is very little in it if anything. If I were to do this again I would fit a pair of Premiers with one of Dons gantries.
I was out today making a few changes to the CRs fitted to my 930 O.I.F. Trident, & finally seem to be getting somewhere. Making changes on Keihins is a costly business. The great thing about Amals is parts are considerably cheaper.

Martyn.

kommando said:

On 4 valve engines they lose low down torque in comparison to 2 valve engines due to lack of turbulence in the incoming charge, it can be gained by making one of the 2 inlet valves a different size which induces turbulence.

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David Vizard published some of his work on this under the name of PolyQuad.
http://www.motortecmagazine.net/the-future-of-4-valve-engines/

If you test your inlet tract on a flow bench, what does that really tell you ? Because you get better flow figures, you might assume that the system would work better on the motor when in normal use. I suggest that is not necessarily the case. How would you ever express any correlation between the tests and what happens in practice ? If the pulses in the inlet tract become sonic, different rules apply to the flow patterns.

Matchless said:

I have a pair of 33mm CRs on my 920 & it runs very well on them. Before fitting them I used a pair of 32mm MK1s with Schnozles & it ran just as well. I have run this bike on the dyno with the Keihins but not with the Amals, although my backside dyno thinks there is very little in it if anything. If I were to do this again I would fit a pair of Premiers with one of Dons gantries.
I was out today making a few changes to the CRs fitted to my 930 O.I.F. Trident, & finally seem to be getting somewhere. Making changes on Keihins is a costly business. The great thing about Amals is parts are considerably cheaper.

Martyn.

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Just because you have access to a physicist's black box, it does not mean it will tell you everything. Seat of the pants is good, but often an improvement in torque can only be detected by increasing the overall gear ratio. How good are most dynos at measuring torque - who has studied the correlations between what the inertia dynos say and what happens in practice ?

Setting up your bike on a dyno has great advantages over spending time at track days or practice race days.
They get a good result ,(hopefully) the out put graph whether power or torque together with the AF ratio will give you a data baseline to work with and saves time trying the seat of the pants method.
It doesnt matter what the P & T numbers are, as long as their peaks correspond to the rev range you would like to race with. Luckily my race motor has a really good torque curve where I need it most and makes power all the way to the rev limiter.
If you can get the AF ratio and timing right, the power and torque graphs at their peak based on fuel and timing, you can then change your sprockets at the track on race days to suit the track conditions.
Just another tool to help if you regularly race.
If your bike sits around for long periods and isn't raced regularly , you are always wondering what the f%$$#@ was the last setting used at this track!
Make sense to me to use every tool available to gain any advantage..
Regards Mike

The thread is about AMAL GP Carbs, not dyno's