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What is WinSU?

WinSU is a computer program which contains information about SU carburettor needles. The taper of the needle inside an SU carburettor dictates how much fuel is delivered for a certain engine speed and load. It is vitally important that this taper is correct for the engine specification.

WinSU will suggest the best needle and dashpot spring for your engine specification and allows different needle profiles to be graphically compared. It will also estimate power, torque, and many other performance related values.

This software will be useful to owners of cars equipped with SU carburettors (Austin, Triumph, Jaguar, MG, Rover, etc). It contains extensive databases of dimensions for over 700 different needles, for both common and rare needle codes, for HS and HIF carbs of different sizes. You can graphically overlay needle profiles to show the differences in lean/richness at various throttle openings.

Why do I need it?

If you have modified your engine in any way, there is a high chance that the fuel/air mixture will not be correct over the entire rev range. Running your engine with the wrong mixture can lead to serious damage! The carburettor mixture at specific regions of the rev range can be adjusted by changing the profile (taper) of the needle. This cannot be fixed by simply adjusting the mixture screw!

How do I use it?

Using WinSU is very simple. You enter your car's details, and then select the carburettors you are using, your car's type of engine, gearbox, and wheel/tyre size. Then you select the detailed engine specification, choosing things like air filter type, ignition system, camshaft, etc. WinSU will then suggest the most suitable needle for your engine , and give performance estimates such as power, torque, 0-60mph time, etc.


The technical library contains dimension data on over 700 needles. Users can view these dimensions in mm or inches, and plot the profile graphically on a graph. Up to 8 needle profiles can be overlaid on the graph in different colours. If you already know your current needle then you can search for similar needles which are, for example, slightly richer at the top end, or slightly leaner in the mid range.


The project can be saved and easily loaded in again in the future. WinSU contains a full help system, as well as optional settings for metric/imperial units for distance/weight/speed/power.

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