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TR2/3/3A TR3 SU Needles in relation to modified cam?

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karls59tr

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I'm not sure on how to decipher cam lingo and I realize that there are a lot of variables involved however.......Kastner Competiiton manual says:( They are refering to a "D" spec cam here)."You will find that with an optional camshaft fitted,more fuel will need to be be available. So install a pair of RH needles in the S.U. carburetors." I have an M518 camshaft: duration 227degrees@.050"......280"camlift....420"valvelift on 109 degree lobe c/l. Anyone know if replacing the standard SM needles with the RH needles in the SU's would make sense with this particular fast road cam? Other mods were header, TR4A intake manifold, Petronix ignition.
 
RH was the richer needle for H6 carbies on 83mm fast road engines, or SW for 86 or 87mm engines. Same if you've got later HS6 (fixed needle) carbies on the TR4A inlet manifold, These are a starting point, but as every competition engine is different, I've found it best to get a dyno tune.

Then ignition and fuel supply will be accurately matched to release maximum available horsepower.

Viv.
 
Try this site. teglerizer.com More info than you can ever imagine. Have fun.
 
I've got a cam profile (Erson 149) that is similar to yours and the Triumph "D" Type. I have an oxygen sensor in my exhaust so I can monitor the air fuel ratios. The standard SM needles runs too lean at higher power and rpms when adjusted according to the book. I've adjusted the carbs (enrichened by a bunch of flats) and the readings are better up top, but at idle, it's pig rich. The "RH" needle looks to have about a 3% increase at 1500-2000 rpm and gradually increase to about 16% at the redline, or a bit higher. The "SW" needle only shows a moderate gain of about 3% at about 2500-3000 rpm to about 10% at the high end. All of this is based on some graphs of a program downloaded from the internet.

I'm going to get a few different sets of needles to try this spring, and one set will be the "RH", along with a few others that give more on the high end.

There is a program out there that you can download for free that compares all of the SU Needles. That's where I got this info from, based on their graphs. It's kind of a guesstimate, but the program will set you in the right direction. At least, it will compare one needle against another.

It's like others have said, each engine is different, so you'll have to experiment a bit to find out what's best for you.
 
In regard to vivdownunder's comments. Isn't the SW needle the
"lean" needle? So the stock 87 mm piston setup would have necessitated a leaner carb mix or am I missing something?
 
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