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stuart

Mapped Ignition Or Re-curved Dizzy?

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stuart

I am currently in the process of getting together parts for a new engine for my rally car and am trying to decide whether or not to do away with the dizzy and get a Megajolt or to buy a new dizzy and have it re-curved by H&H Ignitions to suit my engine as I've read good things about them.

 

The basic spec of the engine will be a rebuilt and balanced standard bottom end with a slightly worked head, Newman tarmac cam and twin 45 webers.

 

Now a new dizzy and re-curving will be around the £100 mark and should be an improvement over standard but how much extra driveability will I get with a mapped ignition and how much is it likely to set me back including mapping?

 

Cheers

Stu

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unariciflocos

Well you get more flexibility with mapped ignition but at ~£250 for the complete system and maybe a bit more for the mapping it all depends if it's worth it for you.

 

You'll need the MJ unit £130 from Autosportlabs with a hard revlimiter, trigger wheel £20 off ebay, vr sensor, coilpack and edis from a scrapyard £20 maybe less, custom plug leads £50, loom kit £20 ebay.

 

Mapped ignition is more likely to get the most out of your engine and and all the mods. Since it's a rally car every bit counts so my advice is go mappable.

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mattbenselin

Built my entire MJ system for about 150; good old ebay, scrap yard and other spare bits. As for the leads, just use a Peugeot/Citroen coil pack and you can use off the shelf leads for as little as £15.

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petert

If you want driveability then mapped ignition is a must. A dizzy can't compete with dyno mapped ignition for part throttle torque. If you just want bang for your bucks hp, then dizzy. A Cosworth BDA is locked at 30 degrees for example. No advance curve what so ever.

Edited by petert

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Saveit

Regarding recurving the distributor. Just read some interesting things on a Chevy website regarding the vacuum advance system on the 205 gti distributor and then started thinking about how this could be used the other way around. Let me explain; The way the vacuum advance systm works atm is by advancing the timing (think it is about 12 degress, perhaps someone knows?) when idleing because of the vacuum created by the engine with the throttle closed. I read that for motorsport use you could move the vacuum link from the manifold to somewhere on the other side of the throttle body. Then you could turn your distributor about the same 12 degrees forward to maintain the same idle. This would cause the distributor to advance the timing when the throttle opens because of the vacuum link being placed on the "outer" side of the throttle body. Then you would have a distributor system which advances the ignition curve on throttle instead of advancing when idle.

 

How does this sound? Is there something i am missing?

 

Stefan

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Saveit

No one who can tell if this would work or not?

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Sandy

Generally you want more advance at part throttle and the ideal ignition curve for a most tuned engines, is way off what you can achieve with a mechanical dizzy. A Dizzy set up will always be a compromise; mapped ignition is massively more versatile and makes for a much nicer engine to drive as well as a broader power band.

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Saveit

Yeah i know there is a big difference. But what do you feel about what ive written? Does it make sense to move the vacuum link from the manifold to somewhere on the other side of the throttle body in order to use the vacuum advance whenever you are on the throttle instead of idle?

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James_R

It makes sense, but it's stupid and you're missing the point of the vac advance, you want more advance at part throttle. If you want more advance at full throttle you just undo the 11mm nuts and move the dizzy round to give more advance when there's no vacum, then you gain more advance at part throttle.

 

Unless you mean you'd have too much advance low down the revs and want to boost the advance higher up, but then usually you want more advance on a higher cam'd engine and less up top, so you want to reduce the difference in low and high rev advance. (like a 1.6 dizzy for example)

 

 

You're better off using a mappable set up.

 

 

I have one question though, what type of signal feed does the std fuel ecu get from the dizzy/hall effect sensor, would plugging the rev's output from a mappable ign set up mean the fuel still works (something less to map that way)

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wardy18

sorry to thread hi-jack but im going to look into gathering the parts for mapable ignition but dont have a scooby doo where to start!!

 

You'll need the MJ unit £130 from Autosportlabs with a hard revlimiter, trigger wheel £20 off ebay, vr sensor, coilpack and edis from a scrapyard £20 maybe less, custom plug leads £50, loom kit £20 ebay

 

Please expand on the above, ie MJ - I assume this is Megajolt, also what is mean by a "hard" rev limiter!? What would i type in to ebay to find the right Trigger Wheel and VR Sensor and also what is Edis?!

 

Please excuse my dumbness but does this system complete replace the whole Dizzy unit?! if so so you need to make up a blanking plate to stop oil leaking out from the Cam?!

 

Thanx in advance

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pug_ham
Please expand on the above, ie MJ - I assume this is Megajolt, also what is mean by a "hard" rev limiter!? What would i type in to ebay to find the right Trigger Wheel and VR Sensor and also what is Edis?!

 

Please excuse my dumbness but does this system complete replace the whole Dizzy unit?! if so so you need to make up a blanking plate to stop oil leaking out from the Cam?!

I also guess the MJ is megajolt but you'd have to ask who gave that list to be certain.

 

A hard limiter works above a soft limiter, soft cuts the fuel & hard retards the ignition advnace to zero or cuts the spark. Hard limiters are a lot more servere.

 

EDIS; Electronic Distributorless Ignition System (EDIS), one that doesnt require a cam position signal.

http://www.megamanual.com/ms2/EDIS.htm

 

The VR is the same as the CAS, reads off the trigger wheel teeth for the crank position.

 

This replaces the dizzy & you can either blank the thermostat housing where the dizzy would bolt to get one from a coilpack equipped XU engine Pug or citroen.

 

Graham.

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unariciflocos

MJ - Megajolt

EDIS - same as above, looks like this.

VR sensor is the sensor that reads rpm off the trigger wheel

 

The MJ comes with soft rev-limiting capabilities built-in, this means that it will retard the ignition to 0 when it reaches its threshold. Hard rev-limiting cuts the feed to the coil, it's very good for waking up neighbors.

 

You can find Edis, VR sensor and coilpack on older Ford Escorts, but there's a complete list on hat cars you can find them on the autosportlabs website.

 

Trigger wheels are available on ebay, you'll need a 36-1 wheel that fits the pulley on your crankshaft.

 

This is a complete replacement for the distributor and gives a lot more flexibility in fine tuning the engine. Apart from that you have a few nice features, like running two maps switchable on the fly, shift light and programmable outputs.

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wardy18

Thanx guys great bits of info, ill check out the links and the Autosportlabs site and start gathering it all!!

 

I was going to ask what the trigger wheel was all about but that explains it!!

 

Can i just clarify this whole Soft and Hard limiter issue as between the the 2 descriptions above it seems quite confusing, i currently run a OMEX Clubman Rev Limiter, and i assume this just cuts the coil feed, what else do i need?!

 

So shopping list is:

 

Megajolt Unit

Edis

VT Sensor

Coilpack (can i not use my current coil?!)

Trigger Wheel

Limiter

 

 

So what else from the durrent Ignition set up do you retain, Coil, Ignition Amp, leads etc?!

 

Thanx again

 

Simon

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unariciflocos

Depends what you current setup is... distributor or coilpack?

 

My advice is sell the Omex limiter and get a hard rev limiter with the Megajolt from autosportlabs, it's far more precise.

 

I'll try and explain again the soft and hard limiting thing. The ECU will advance the spark from let's say 10 degrees at idle to 30 degrees at high rpm. If you set the rev limit at 7000, when the rpm reaches 6900 the ECU will retard the spark to 0 degrees to keep the engine from over revving. This method is not very efficient. The hard rev limiter requires additional circuitry and when the engine will reach the limit it will cut the feed to the coil so the engine doesn't have spark. This causes the rpm to drop.

 

Standard Megajolt has soft limiting built in, but you can order another hard rev limiter board that connects via 4 wires to the MJ motherboard. In the MJ the soft and hard revlimiter work together. This is the best i can explain, hope it's a bit clearer.

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M@tt

i've got an EDIS setup going if anyone's interested (coilpack, leads and edis module), bought it a while back for a MS project but now surplus to requirements.

 

drop me a PM if interested

Edited by M@tt

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wardy18

Im currently running a H&H Dizzy

 

Am looking at the Autosportlabs site but am only seeing Megajolt Lite Jr, is that what im looking for?! but then theres 4 options TPS Assembled, Map Sensor Assembled, TPS Kit or Map Sensor Kit, also how do i get the Hard Limiter chip to go with it?

 

Thanx for the help

 

I love installing new age technology to old school machinery

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wardy18

sorry found the hard limiter add on

 

Is it the MJ Lite jr i go for as i havent heard the Lite Jr bit mentioned by you guys

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pugpete1108

sorry for another hijack but i'm using a ford coil pack running wasted spark and ms on my 6 but not using this edis thingy?

 

is it needed with wasted spark? what does the module do exactly?

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James_R

If you're running the 60-2 bosch set up then no you just need a coil, if you run the EDIS set up and 36-1 then you do.

 

The Edis module is an intermediate control bit which gives a pulse to the ecu, and then the ecu modulates the advance to the unit, if nothing is hooked to the EDIS is gives 20deg advance (form memory)

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pugpete1108
If you're running the 60-2 bosch set up then no you just need a coil, if you run the EDIS set up and 36-1 then you do.

 

The Edis module is an intermediate control bit which gives a pulse to the ecu, and then the ecu modulates the advance to the unit, if nothing is hooked to the EDIS is gives 20deg advance (form memory)

 

that would be why i havent used one then as i'm using the stock 60-2 gti6 wheel

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wardy18

what size trigger wheel do i need?

 

im seeing 2.5" up to 8" and also what size pilot centre hole do i need?!

 

does this just bolt onto the end of the crank pulley usuing the crank pulley bolt??

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welshpug

I thought you were going the full management route Wardy?

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wardy18

i was only looking for Ignition management as im on Carbs

 

assumed from what people have said that MegaJolt is a great budget option?!

 

I might have got confused though as this is very new to me, what Full management are you referring to, KMS etc?!?

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James_R

Would be a better idea if you're planning injection later to put the likes of a V3 MSII on using the 60-2 flywheel set up (and fit a lightened Mi flywheel like a TTV item) and use just the ign then later put bodies on and presto for the outlay it's not a bad idea.

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wardy18

how much is this sort of system costing?!

do i still use the EDIS and coilpack etc that i would with the MJ?!

 

dont really wanna change my flywheel as i have a Helix Ally flywheel which cost £300, would i have to change?!

Edited by wardy18

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