How to make an SU piston lift indicator
Turbo Mini Forums

In my recent quest to polish the perfect needle I realised I needed to be able to see the position of the needle at all points of drive and with a turbo that has a pressurised piston chamber thats not easy.. So I came up with this, Its pretty cheap and works well.




You will need

A spare dashpot piston (I bought a new one for my car and used the old one)

A piece of aluminium wire approx 80mm long (lightweight so as not affect the piston)

Some nylon or alluminium tubing 25mm long to support the wire

Some kind of "ring" as an indicator.. maybe a small plastic bottle top? as long as it fits loosley inside the tubing

Clear plastic tubing about 100mm long, that fits nicely over the top of the daspot piston - I used a 35 ml syringe --maybe try aquarium shops?

This picture:- Print ot so that its 2.55 inches high




At this point its probably best if you can remove your carb or even better get hold of a spare one as its easier to alighn and check everything off the car.

Edited by Turbo Tel on 14th Jul, 2008.

website:- http://www.terryhunt.co.uk

First drill a hole same size as the ally wire in the cap of the dashpot piston that aligns with the top surface of the piston shaft (the bit you put the oil in) make sure its aligned properly. The cap pretty much shows you where to drill as the shaft goes right up iinto it and the plastic is grooved to take the shaft, just drill in the groove.




Next use some epoxy glue to attach the tubing to the cap above the piston. This acts to stabilise the wire. You could drill 1/2 way through to "set" the tubing, use plenty of epoxy to support the tubing and as it sets keep checking that everything is aligned.

Once thats set glue the indicator ring to the end of the wire, drop it in and try things out on the carb. make sure the wire does not drop off of the carb shaft and everything works smoothly.


Then glue the plastic tubing on top the dashpot piston cap and again check all is smooth and not sticking. Finally seal the top of the tubing after ensuring that the wire does not drop out of its hole when the whole thing is inverted.

Edited by Turbo Tel on 14th Jul, 2008.

website:- http://www.terryhunt.co.uk

Next, you can apply the paper position scales to the tubing.




Here you should take a look at how far down from the bridge the jet is sitting, you may want to offset the position of the scales by the same amount i.e when the piston sits on the bridge the jet is probably at station 1-1/2 in reality due to the jet being down a little.

I cut them out and just used clear tape to apply them, make sure you do this with the device screwed in so that the scales face you when you are driving. Also make sure you double check the static reading from your car seat to check for any paralax errors.

Obviously this device requires that you remove the bonnet! but with it you will be able to see where the piston is at any point of drive. I found that a rubber band or tie wrap around the tube at a particular station I was interested in helped me see it

Good luck..

Edited by Turbo Tel on 15th Jul, 2008.

website:- http://www.terryhunt.co.uk

Cooooooool!


Thumbs up for this one!

I would like to make one of these, but one that i could see when i was driving along. Im thinking maybe some kind of potentiometer connection to the rod and a digital read out in the car. Not sure how to execute the mechanical connection to a pot, any thoughts?

done years ago, why does it have to be a pot?
look on the "polishing an su needle" thread for some inspiration

Yes i moved to the darkside

Instagram @jdm_brett

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=159683

also page 19 of my build thread

Edited by Brett on 23rd Nov, 2015.

Yes i moved to the darkside

Instagram @jdm_brett

Yeah a slide type variable resistor

Yes i moved to the darkside

Instagram @jdm_brett