02GF74
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 posted on 24/11/08 at 11:55 AM |
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rev limiter?
let's say one has a box of electroinckery driving a Ford EDIS and one wanted to implement a rev limiter.
Is there are recommended way of doing this? i.e. does one trun off all sparks to the engine when it hits the specified RPM?
or is there a better way of doing it that stesses the engine less for example cut off every 3 spark thus slowing the engine down less than the
afroementioned method. (soft limiting)
Does not cutting off all sparks at high RPM result in the exhaust and instake systems being filled with unbrunt mixture (oh, engine is fuelled via
carbs) that will explode in specatacular style once engine is firing again? The "soft" spark kill will reduce that.
So what is commonly done?
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BenB
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| posted on 24/11/08 at 12:06 PM |
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I wouldn't turn off all sparks.
Or rather I'd have two rev limits. Somewhat like a soft cut and a hard cut. Soft cut = missing out some sparks, hard cut = stop all sparks.
You can, of course, also cut power to the fuel pump as a simple way of having a rev limit, though I wouldn't want to do that on it's
own.
If you cut out some sparks you'll run rich. If you had a fuel cut on it's own you'll run lean at full throttle and likely under load
 If you cut fuel pump supply at the same time as doing the "soft cut" alternate firing you'ld probably get a nice reduction in
revs without blowing a piston......
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David Jenkins
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| posted on 24/11/08 at 12:11 PM |
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Megajolt has a built-in rev limiter that retards the ignition timing to 0 degrees. This has the effect of robbing the engine of most of its power.
Works quite well.
You can also get an add-on board that interferes with the plug firing - rather like your original question 
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02GF74
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| posted on 24/11/08 at 12:16 PM |
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ooooh, changing the timing, didn't think of that! nice.
So how did the rev limiter in points distributors work? Kill all sparks?
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coozer
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| posted on 24/11/08 at 12:25 PM |
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My old Honda VFR750 had a mint way. It cut the spark to two cylinders and left the other tow running... stopped the revs dead at the red line and sent
a nice huge flame and bang out the exhaust on each cylinder stroke
1972 V8 Jago
1980 Z750
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David Jenkins
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| posted on 24/11/08 at 12:37 PM |
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quote:
Originally posted by 02GF74
ooooh, changing the timing, didn't think of that! nice.
So how did the rev limiter in points distributors work? Kill all sparks?
You used to be able to get a special distributor rotor that would break the HT connection above certain revs... apparently they were evil things that
would make the engine cough and bang!
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Humbug
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| posted on 24/11/08 at 01:47 PM |
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quote:
Originally posted by David Jenkins
Megajolt has a built-in rev limiter that retards the ignition timing to 0 degrees. This has the effect of robbing the engine of most of its power.
Works quite well.
You can also get an add-on board that interferes with the plug firing - rather like your original question
Oi David!
 
Rescued attachment images.jpg
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Canada EH!
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| posted on 24/11/08 at 03:48 PM |
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A Lotus Cortina I once drove had that switch in the rotor, usually killed the ignition just as the rear end stepped out, lots of fun.
Don't kill all the cylinders at once, Ford tried that with Crown Victoria Police vehicles, threw you into the seatbelts, near tore you head
off. The next year they went to soft setting, retarded spark, alternet cylinders.
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rusty nuts
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| posted on 24/11/08 at 07:02 PM |
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quote:
Originally posted by 02GF74
ooooh, changing the timing, didn't think of that! nice.
So how did the rev limiter in points distributors work? Kill all sparks?
Some old Lucas and Bosch distributors used a centrifugal rev limiter that was in effect a rotor arm with a spring loaded contact that shorted the HT
circuit to earth when limit was reached. Or at least that was the theory , don't think they were too reliable??
Really must remember to read all the posts before replying
[Edited on 24/11/08 by rusty nuts]
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goaty
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| posted on 24/11/08 at 07:07 PM |
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Omex make a adjustable limiter you splice in with 3 wires.
Has option for hard and soft cut.
Had one on one of my swift gti's, worked very well about £80
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MikeRJ
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| posted on 24/11/08 at 07:57 PM |
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quote:
Originally posted by rusty nuts
Some old Lucas and Bosch distributors used a centrifugal rev limiter that was in effect a rotor arm with a spring loaded contact that shorted the HT
circuit to earth when limit was reached. Or at least that was the theory , don't think they were too reliable??
The ones I've seen connected the coil output to the opposite cylinder, which (on a 4 cylinder at least) would be on the exhaust stroke. This
will always fire it's plug at a lower voltage than a cylinder on it's compression stroke so it robs the spark from the cylinder the rotor
arm is pointed to.
It's pretty difficult to achieve fancy soft cut methods with the EDIS without quite a few extra components. The standard "retard"
soft limit coupled by a the full on spark cut should be adequate anyway. If you are holding it on the limiter for long periods of time maybe consider
a higher final drive ratio 
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02GF74
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| posted on 25/11/08 at 11:05 AM |
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quote:
Originally posted by goaty
Omex make a adjustable limiter you splice in with 3 wires.
Has option for hard and soft cut.
Had one on one of my swift gti's, worked very well about £80
£ 80 !!???
I had to pinch myself in case I had posted on wealthy arab sheik gold plated diamond encrusted cateringvan forum?!?!?! 
You are having a laugh. I will be making my own megajolt for less than a tenner and may add rev limiter function. Work is still in progress - had a
bit of a sep back yesterday as I realised the timer I will be using for the SAW may have issues with setting a pulse of correct width, oh well, back
to drawing board  but I think I can overcome. (and yes, it is reinventing the wheel but what else is there to do on long dark winter nights?)
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MikeRJ
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| posted on 25/11/08 at 12:07 PM |
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quote:
Originally posted by 02GF74
quote:
Originally posted by goaty
Omex make a adjustable limiter you splice in with 3 wires.
Has option for hard and soft cut.
Had one on one of my swift gti's, worked very well about £80
£ 80 !!???
I had to pinch myself in case I had posted on wealthy arab sheik gold plated diamond encrusted cateringvan forum?!?!?!
You are having a laugh. I will be making my own megajolt for less than a tenner a
If you can make something as well built and packaged as the Omex for a tenner I'll be mightily impressed.
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02GF74
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| posted on 25/11/08 at 06:42 PM |
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quote:
Originally posted by MikeRJ
If you can make something as well built and packaged as the Omex for a tenner I'll be mightily impressed.
Not that impressive since the price I mentioned does not include package - just the board and components, and I may have undereestimated that, butthat
sort of figure though. It doesn't include development, warranty nor any furture support. Plus I won't be selling it to make profit, if I
did, the price would be much more, much much more.
Then why do it? Same reason why people cut up bits of squaretube and weld together rather than buy a chassis.
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