RPM Switch - How?

M

MADXF

Active member
Hi guys, been a while since I've ben here. (previously knwon as AussieXflow).

Anyway I'm looking at throwing an EF/L 6cyl into my XF on straight lpg (to do away with the computer).
What I need to knwo is how I would get a vacuum switch to operate at a certain RPM, to switch the dual length manifold butterflies.
I have seen people mention these type of switches before but I have no idea where I would buy one, or how I could make one.

Thanks for any help.
Paul.
 
I don't think you could rely on a vacuum switch to kick in at a preset engine speed as the level of manifold vacuum is dependant more on load demand recquirements.

You would need to build ( have built) the equivalent to a shift light only set for lower RPM's. basically a tacho circuit with a self resetting trip circuit to pull in a solenoid valve which would allow the vacuum motor to open and close the manifold flap thingy.

Either that or use a non butterfly fanimold.
 
Do what Ferryman says :D

I've been thinking along the same lines myself for the same means. I've been under the impression that most shiftlights are end-user adjustable?
But in anycase, it wouldnt be too hard to pull one to pieces, and fabricate an electronic relay that'd actuate the variable intake runners, without frying the circuitry..!
 
Ferryman":147yi57c said:
I don't think you could rely on a vacuum switch to kick in at a preset engine speed as the level of manifold vacuum is dependant more on load demand recquirements.

You would need to build ( have built) the equivalent to a shift light only set for lower RPM's. basically a tacho circuit with a self resetting trip circuit to pull in a solenoid valve which would allow the vacuum motor to open and close the manifold flap thingy.

Either that or use a non butterfly fanimold.
Click to expand...

What I meant is what you ended up recommending...what I meant by 'vacuum switch' is a electronic switch to control the flow of vacuum.

Can you get shift lights separate from a tacho? and any idea on the cost?

Thanks.
Paul.
 
yes you can get shiftlights seperate but its proberly worth buying another aftermarket tacho with a shift lite would be cheaper anyways
 
What about modifying the LPG cutoff circuitry that shuts of the flow of gas when there is no RPM signal.

It works by alternating pulses from the coil to keep the switch closed, but would there be a way to make it require a certain number of pulses?

Paul.
 
I still think the shift light would be the easiest. Some (IIRC) have a separate switched out for a limiter - why not use this aspect to control the vacuum switch? The LPG thing is just a relay of sorts; it doesn't count pulses per unit of time.

Adam.
 
Well for a start I would prefer not to spend $100 just to hack it up to make it do what I want it to, and I dont want a monster (wank) tach.

I know the LPG circuit doesnt count revs, but I thought maybe there would be a way to make it trigger at a certain level of pulses rather than just any pulses.

How exactly does a shift light work anyway? ie: How does it determine when to power the output?
 
I had a browse on the Web for DIY kits, and didn't find any aux switched ones. Mate, I'm 110% with you on the wanky tach deal. You could always put it in the glovebox or somewhere else - doesn't even need to be inside the cab. In the engine bay would be good for tune-ups. :wink:

I don't know if the shift lights work on aggregate pulses/time, or by correlating to your preset actual value. I would expect the former, or threshold approach.

You could maybe work on the "threshold" basis paralleled off the tach feed to the gas relay. Ie; adjust the relay with a trim pot until it came on and stayed on at the desired RPM. "Softening" the response would be the challenge - you don't want it on and off like a bride's nightie.

A cheapo shift light could be sacrificed (under bonnet, again) so that the incandescent lamp socket switched the solenoid.

I guess a lot of it comes down to nous and willingness to spend time vs money.

Adam.

p.s. You don't have to write funny stuff in your sig. Unless it's about being eaten by ducks.
 
HAHA @ ducks

I'm have all the time in the world to use/waste/learn and not a lot of money, so unfortunately I have to use my brain, as much as it protests to this, we have had many successful adventures.

I will open up the LPG cutoff and see how it works and see what I can do from there. I'm tipping I will probably have to buy either a shift light or the kit from jaycar.

Thanks for your help.
 
aussie7mains":yvwjhqgl said:
What will control your ignition advance, XFs dont have dual tract runners, thats Ed on.
What are you planning to do?
A7M
Click to expand...

Sorry I missed this post earlier.

I'm thinking one of two things, either using an XE dizzy with vac adv removed, or the jaycar kit and an XF EFI dizzy.

Or if I somehow find a lot of money, i'll go for an MSD or similar.

The plan is to put an EF/L motor into my car running straight LPG.

Paul.
 
Well I opened up the LPG cutoff circuit and all it requires to keep the relay closed is an alternation of +12V and GND signals to it from the coil.

Dont think there would be any way to make it only come on at a desired RPM.
 
What about a transistor switched relay with the feed paralleled off that circuit; just use a pot to control the resistance - this should regulate when the transistor opens the relay. As I mentioned, softening the abruptness of the switching in and out, will be the fun part. You could try various cap values to get this aspect working.
 
The abruptness shouldnt be too bad as it is only an electronic switch controlling the vacuum flow, so the butterflies will open by vacuum once the switch has closed.

I dont understand what you mean by paralleled off the other circuit
 
I simply meant as opposed to wiring it in series. One in from the ignition (I guess this is from the coil), and the positive feed. But I would be aiming to keep the current drawn small, so not to upset the ignition system or LPG relay. That's why I pondered using a tranny to switch the relay.

Hey, I'm a carpenter! I should be saying just gum it open with Liquid Nails, not talking electronics. :roll: If it wasn't raining, you wouldn't have me confusing you.
 
Jaycar sell a three stage shift light kit. It has 3 outputs adjustable by turning a pot. It costs $35 and you have to build it yourself.

The third light is linked to an output which then can go into the optional ignition cut circuit also available as a kit from Jaycar. This will cut about 50% of the ignition firing to limit revs.

You might be able to still use the rev limiter and 2 stages of the lights. Just set the first stage up running your valve. There is no order. Each of the lights can be set independantly of each other. The last light has to be the one which triggers the rev limiter though.

By the time you by the case and some bits and pieces it will be $45 and the ignition curctit will be extra again.

You can use one of the outputs to trigger a relay which in turn could operate a VSV (vacuum solenoid valve) that will allow the butterflies to change position. Now that I think about it the kits probably has enough power to switch the VSV without having to use a relay. A vsv wouldn't require much more power than a relay anyway I suspect.

The kit will work of a Hall sensor, reluctor, coil etc input so is quite versatile. If you are using single coil dizzy it is easy. if not then you will have to retain your crank angle sensor (which you would be for ignition anyway if it is mutli coil)

I have built one of these for my car and they work well.

Try this link for a bit of info from their site:

http://www1.jaycar.com.au/productVi...xxx&pageNumber=&priceMin=&priceMax=&SUBCATID=
 
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