Adjustable Vacuum switch needed,

[migmag]

Evening Chaps and Chapesers,

I am currently messing with water meth injection on my latest victim a 01 Polo SDI,

Now normally one would use an adjustable pressure switch to trigger the pump as water meth is mostly fitted to turbo charged engines.

As the SDi is normally aspirated I have no boost only Vacuum,

So I need an adjustable vacuum switch to trigger the pump so as the water meth starts misting on full throttle and full throttle only.

Anyone got any bright or even totally daft ideas??

 

[Lawnmowerboy]

Vacuum advance system out of an old Lucas dizzy and a small microswitch

 

[rtbcomp]

Hyperdermic syringe with a microswitch and spring fitted to the plunger.

 

[711jrp]

Micro-switch on the throttle pedal.....

 

[Wallace]

Item #71V2 just over half way down this page, adjustable.

 

[AndyStobbs]

Micro-switch on the throttle pedal.....

That's what I would do, vacuum isn't going vary with throttle position or load. Got a feeling the acc pedal has a full throttle switch built into it anyway.

 

[rtbcomp]

That's what I would do, vacuum isn't going vary with throttle position or load. Got a feeling the acc pedal has a full throttle switch built into it anyway.

I would have thought that for a given throttle position the vacuum would vary with engine speed, it would rev faster on a light load and generate a higher vacuum than on a heavy load.

Certainly that's what happened on my Landrover with a vacuum gauge fitted.

 

[Robotstar5]

Bottom of the page here other makes available.

 

[AndyStobbs]

Have had a vac gauge on a good few diesels myself and found very little variation from 1500rpm upwards. I have found them to be slightly less at idle, does depend how its driven I guess ie. Alternator or camshaft as the alternator revs are always going to be higher than camshaft.

Missing your jist about it revving faster on a light load, I was reading it as if OP wants the meth at full throttle regardless of revs? That way it would make the most difference.

 

[migmag]

Thanks for the replies fella's some very good points and ideas,

I have decided to steer away from the vacuum switch idea as high air flow and most importantly the engine produces pretty much as much vacuum on idle as it does and revs and overrun.Diesels run a vacuum pump so although the vacuum does vary with rpm its always pretty high regardless of engine speed.

I had thought of the micro switch on the peddle box idea but the way the peddle box is set up the potentiometer for the fly by wire takes up all the space.

I do like the idea of using the rpm signal but how can I set it up to trigger at say 2500 rpm anyone?

 

[Robotstar5]

Could you modify a shift indicator as used on motorcycles, they normally work from the tacho feed and drive an LED or lamp but use the output to drive a relay?.

 

[Pete.]

I never heard of anyone using water/meth injection on a NA engine before. What's the reasoning behind it?

 

[migmag]

Rev light idea could be the one.

I never heard of anyone using water/meth injection on a NA engine before. What's the reasoning behind it?

Same as forced induction really but predominantly its the most effective way of de-coking without dismantling the engine.
http://www.methanol-injection.co.uk/product_info.php?products_id=170



I could also use the EGR signal from the ECU but this would only work on mid rpm not full throttle....

 

[711jrp]

The problem with having it RPM activated at say 2500rpm is it is quite feasible to bump into this RPM at light throttle openings IE high speed cruising on the motorway. Have you done a pin-out of the throttle pot? I wouldn't be surprised to find a feed for WFO..

 

[AndyStobbs]

Egr signal modulates though so that would be useles, and backward as egr is used most at cruise idle and least at wot.
Check a wiring diagram to be sure there isn't already a full throttle switch built into the acc pedal. Sure I saw it on a tdi seat wiring diagram, granted that's with a turbo but it would be a pity to over look.

 

[migmag]

Cheep asrse'd shift light ordered off flee bay see what happens.