Su needles advice with Kent cam?

[tony g]

Hi is there a good starting point for my sprint using a KCDMS1 cam? I havent looked at what needles are in there at the moment, and it drove ok up to the mot station (going steady as its all fresh)
I need to get a lambda boss welded into the downpipe to run my Innovate LM 1 for fine tuning but could do with a starting point.
Car is a 1978 if that makes a difference.

Cheers

Tony

[Jon Tilson]

Start with what you have and compare it with the minty lamb su needle charts.

The old method was to pick the revs at the various needle stations and then try a burst of acceleration at each point.
If it pulls then all is good...if it doesn't then pull the choke a tad to drop the jet. If it pulls then you need it richer etc....

I reckon your sensor would be very helpful.

Jonners

[tony g]

Thanks Jon, I must admit I get a bit lost on minty lamb, Im not very good at lists. I suppose plotting whats happening at the same rpm points may point me in the right direction, Ill give it a test on the weekend (tax tomorrow)

Tony

[Jon Tilson]

Its a pretty common misconception that you can "tune" any SU.

All you can do is make it work properly and adjust the idle mixture....

To tune one to your car means a rolling road session, exhaust gas analyser and range of needles.

What BL chose to fit was always their best guess or compromise and the latter ones were all pretty gutless top end
especially in my experience. Few late ones pull 110 in top without being modified in some way.

Jonners

[tony g]

Do they go lean at the top end or rich?

Tony

[Jon Tilson]

Lean....

All late BL cars using SU's were lean for emissions purposes. Cynically done long after road tests published performance figures
on early cars. Most owners never noticed because of the 70 limit.

Spit 1500's and dolly 1500's were worst. ADN's are far too weak for a spit 1500. Of course few owners take them over 80...and high revs on a 1500 engine are to be discouraged anyway to avoid valve seat recession and shot bearings.

They did get caught when autocar tested a dolly 1850 on a P reg...lamented the sub 100 mph top speed but still said "long may it continue". The early stromberg cars would easily do 100 plus. My early examples did 105.

Before I did the cam on our V reg Sprint I maxed it out at 107...it might have done more with a longer straight or less wind.
Post cam change, vernier pulley and a rolling road session it still pulled at 125, but that was a long time ago now and out of respect
for the old lady and the current road environment I keep below 90...:-=)
I cant remember the needle now but if I get time I'll whip them out and tell you. The mpg did go down a lot though. I probably struggle to get 30 now not that I use it much. It used to do mid 30's pre cam change.

Jonners

[tony g]

ok thanks. Be nice to have it a bit rich at the top end but leaner on cruise like 70 with O/d. I would think there could be a happy medium needle out there. If I can get some lambda readings it may help to decide on needles. Dont go whipping your carb tops off Jon thanks though.

Tony

[trackerjack]

According to Terry Hurrel (SAH) standard needles are "UE" and for richer profiles next "UM" and richer still "UV".
The old tuners of old would lightly file a flat where they wanted it richer usinf a needle file.

E lad tis a black art

[tony g]

My current needles are BDQ . on the mintylamb site what does the column on the left represent? ie 2.6 down to 1.0 ?

Tony

[tony g]

Its ok I can now see mm there graph blindness- its a terrible thing lol

Tony