Figured i’d start my first thread by explaining what i’m gonna do. I have a 1984 Polo SP (9000 cars made) and just finished completely rebuilding the engine, gearbox, suspension and rear axle. It is equipped with a 75hp GK engine (i’ve heard it’s quite rare) and the Bosch Dignition ECU (which i figure is even rarer). Had trouble with this one as my stock unit was fried, but a new one came in clutch to make it start. 

 

The thing is i’m currently building a new engine featuring bike carbs, schrick camshaft, ported heads, balanced bottom end and more. I plan on reaching 7500rpm with this setup. I don’t want to get rid of the original ECU, so i need a way to modify values in it. I’ve heard people working on Digifant and Motronic ECUs for 3F and PY engines, but never on the Dignition. I saw one guy in Germany who did it but he never wrote anything about it. 

 

If anyone has ever done this or even heard about it, i’d be glad to hear from you guys. 

 

Thanks!

Axel

Sounds cool but I know nothing about this so whilst this is a positive message it is also useless to you, good luck!

I replaced the oscillator crystal in my GK's Dignition with a higher frequency one that I calculated would let it reach 7200rpm.

 

However, the reduced vacuum of four DHLA40 Dellorto's despite a one-way snubber valve, a vacuum gauge, balance plumbing between the cylinders (even with 26mm chokes) meant that the ignition curve was never right as the Bosch map relies on temperature, manifold pressure sensor and RPM inputs.

 

(Big carbs have less vacuum but flow more air. I assume that also holds for bike slide carbs. You can't disable the Dignition vacuum operation as it's not programmable like Digifant... )

 

So I switched to Aldon Amethyst and spent a very long time iterating to get the curve better, then leaning the mixture, then advancing some more altering the curve, changing the emulsion tubes to finally get good smooth powerful performance with 31mm chokes, on the original GK camshaft (but bigger inlet valves).

 

Edited 16 March, 20242 yr by dvderlm

If the bike carbs have a throttle position sensor you could use that with Amethyst or any other ignition controller that works with a Hall sender for RPM input. 

 

Or fit a missing tooth wheel to the crank pulley, but space is tight down there.

 

I'm using the turbo capable Manifold Pressure Sensor based Amethyst, but have not boosted yet (need PY pistons, decompression plate,a turbo or supercharger etc). If I was to do it again I would probably pick an ECU with more RPM and load buckets.

 

Maybe even injection capable model and use the ignition side only, as could transfer it to the next project.

Other good thing about modern aftermarket ignition is it can help adjust for lower RON with E10 fuel.

 

I can cope with 95 ron using 5% Ethanol which has good knock protection. GK wants 98 RON or higher. I use Momentum 99 when I can.

 

And they have soft-cut at max RPM. The Dignition at 6800rpm would hard cut (or 7150rpm on my modified unit) which just sends the tacho needle bouncing around and loses power instantly. All you can do is wait for the revs to descend. With the Amethyst I can feel the drop in power (and sometimes hear the pops of unburnt fuel in exhaust over the engine clatter and induction) then shift up a gear. 

 

3 hours ago, dvderlm said:

I replaced the oscillator crystal in my GK's Dignition with a higher frequency one that I calculated would let it reach 7200rpm.

 

However, the reduced vacuum of four DHLA40 Dellorto's despite a one-way snubber valve, a vacuum gauge, balance plumbing between the cylinders (even with 26mm chokes) meant that the ignition curve was never right as the Bosch map relies on temperature, manifold pressure sensor and RPM inputs.

 

(Big carbs have less vacuum but flow more air. I assume that also holds for bike slide carbs. You can't disable the Dignition vacuum operation as it's not programmable like Digifant... )

 

So I switched to Aldon Amethyst and spent a very long time iterating to get the curve better, then leaning the mixture, then advancing some more altering the curve, changing the emulsion tubes to finally get good smooth powerful performance with 31mm chokes, on the original GK camshaft (but bigger inlet valves).

 

 

Thanks ! The carbs i’ll be running are 32mm so i don’t have a clue about the amount of vacuum i’ll get and if it will be enough. My camshaft has a rating of 302° on stock valves, which means totally different tuning from what you’ve done if i’m not mistaken (first time i put this aggressive of a camshaft). I’ll try to do anything to keep the ECU, even though your Amethyst looks way better to tune. I think decompiling the curve and modifying it in a dedicated software could be the go to option for me. Thing is i never touched these types of chips and never reprogrammed an eeprom. I’ll try to see if your settings work in my unit to begin, then adjust if needed. 

302° - cool! That's not Schrick then.

Got any other cam specs?

Valve timing, lift, overlap, lobe separation.

 

 

4 minutes ago, dvderlm said:

302° - cool! That's not Schrick then.

Got any other cam specs?

Valve timing, lift, overlap, lobe separation.

 

 

 

In fact it’s the only thing i know. The french guy i bought it from said it was a 302, which came from an engine he bought in germany with all the paperwork (that’s why i also bought the double valve springs and pistons at the same time). I can assure you its a schrick, maybe an old model and i don’t really have anything more… i didn’t try to measure anything as of right now but ill try to and keep you updated. 

"bearbeitet kolben ventiltaschen" suggests it is a high lift cam

= "modified piston valve pockets"

 

"Um 300" = "around 300".

That and the Schrick and SV2 markings suggests to me it's the 296 Schrick. That'll be awesome.

 

You could measure the base circle and lobe height to see if it is 292 or 296.

 

 

Or maybe reground (smaller base circle, lash caps or steep angled tappets) and nitrided for hardness to achieve a bit more oomph? If anyone would do that. [Guess]

Edited 17 March, 20242 yr by dvderlm

14 minutes ago, dvderlm said:

"bearbeitet kolben ventiltaschen" suggests it is a high lift cam

= "modified piston valve pockets"

 

"Um 300" = "around 300".

That and the Schrick and SV2 markings suggests to me it's the 296 Schrick. That'll be awesome.

 

You could measure the base circle and lobe height to see if it is 292 or 296.

 

 

Or maybe reground (smaller base circle, lash caps or steep angled tappets) and nitrided for hardness to achieve a bit more oomph? If anyone would do that. [Guess]

 

I’ll do just that, for now i need to port the conduits before installing it. I don’t think it has been reground so most surely a 296. I had also measured the valves on an injection model head (AAV) and found both were bigger by 1mm for the same boring. Do you think this could be a good addition to make power ? 

I’ve also seen a guy do the same tune as me (but without any electronic ignition) with a 55hp base and GT cam and got out 95hp at the wheels. I think i’ll be able to put out a great 100-110whp which i’m more than happy with (I think the lift from the Schrick will help greatly). 

95HP at wheels with ~15% transmission loss is ~109HP.

You can get theoretical 120HP max at the crank with 34mm inlet valves

http://www.wallaceracing.com/hp-valve-size.php

 

And the lift of the 296 will indeed help. 

The 32mm chokes are smaller than the inlet valve, so that's your tightest restriction and good for your 7500rpm target. Should be fine. 

 

WL Motorsport are selling a big valved 306° cammed Polo race engine with claimed 128PS = 126bhp. (I'll guess 58Nm at 8500rpm).

 

So yeah 100 to 110 wheel HP sounds doable.

https://www.wlmotorsport.de/teile-fuer-vw-polo-1-und-2-fuer-1-3-l-1-6-l.html

 

The late closing intake valve of the 296 will also keep the Mach index in safe territory.

 

I have 36.2mm inlet valves with the (229° at 0.1mm?) GK cam, which also does not lift exhaust valves as far as it could. 

Hey guys ! Coming back to this topic after quite some time (was getting ready for my degree). As i am still struggling to make this car work and frankly have tried anything that came to my mind i thought i’d give it a shot here. Here’s the problem : I am currently still running my stock pierburg 2e3 (which was rebuilt, everything was checked and thoroughly cleaned) but the car still has trouble running good. Idle rpm is good when cold (even though the automatic choke cuts off too soon, still need to address this) and when hot. When driving normally (stable 2000-2500 rpm) and then clutching in, the car start to stall, slowly losing rpm (around 500). I narrowed the problem down to a drown inlet, as everything seems to go after I open the throttle all the way to 6000rpm (also noticed an abnormal amount of fuel in the manifold when shutting the car down and removing the carb. Changed the electric fuel pump i had and put the original one back to check, same issue. As I said, the carb doesn’t seem to have any leaks (fuel level is within specs and the fuel needle seals great too). I think it might be due to a bad venturi tube, but i’m not sure at all.  I’d be glad to hear your opinion about this. 

Sorry a year late.. only now seen this.

Sounds like vacuum leak symptoms. The fuel needs to be sucked into the engine by the pistons descending to cause atomization into fine droplets so it will all burn not just the volatile compound vapours.

This only works because of the atmosphere pushing down on the top of the reservoir of fuel in the carb float chamber and the wells surrounding the emulsion tubes. The effect is enhanced by the Bernouilli effect creating a suction due to faster moving air by the venturi ring shape.

If the carb base mount has a leak the same air pressure is applied on the reservoir and the jet outlet in the Pierburg. No fuel moves.

Any condensed on the walls of the inlet manifold stops being emulsified and pools when you look at it. There's a part channel heater in the 2e3 which electrically warms the idle circuit. Make dure carb has good earth.

Also check the automatic choke coolant pipes.

Warming the choke so it deactivates and heating the inlet manifold is important. The hedgehog heater also assists with vapourisation for cold starts and there's a switch in a pipe to manifold that turns off at 60°c. Check that too.

And the thermoswitch in the intake elbow for the hot/cold air flap has good vacuum from the engine running and the pipes are not split.

Most importantly

Replace the base mount. Do not overtighten.

No worries mate. I think you won’t believe what really happened. As I had already tried everything and made sure EVERY (when I say every, it’s really every thanks to the VW manual that covers it and the Dignition) part of the 2e3, I wondered if the carb wasn’t just dirty as heck, and boy was it full of junk. The first time I dropped my fuel tank, there was still 1992 gas in it. Thing is fuel rots, and when mixed with rust makes a sort of goo that gets stuck everywhere no matter what you do. I deep cleaned it at the time but I think the fuel lines were full of junk too. In the end I replaced everything with new lines and a 42L instead of a 36L tank.

Right now the car has been running for almost a year flawlessly, I’m running bike carbs with the bike airbox connected to the stock one in which I kept a k&n for road use. I’m redesigning the airbox to print one in ABS that’ll fit the firewall a bit better.

Took it to the track, handled it like a champ ! I drive it every morning to work, the manual choke is a pain in the a** to operate but it almost never let me down, and it rips ! Will need to dyno it sometime, i’m thinking 90hp with the GK cam.

Had to replace the head gasket in May of this year tho, it decided to unite cylinders 2 & 3…

Rn the SP is my daily, currently working on my 79 mk1f gls which is great too. When this one will be ready i’ll focus on the brand new engine meant for the SP with the schrick cam mentioned in the earlier posts. A quick pic of the engine bay as it sits compared to when I got it

Very fine passageways in a carb. I've got a huge petrol filter to act as filtration and stop starvation in long corners.

Is that still on the Bosch Dignition?

If you can plumb the inlet manifold temp sender switch back in (maybe branch off the water pipe)

you can get more ignition advance while it warms up.

Indeed still running the Dignition. Seems to run fine, advance wise i thought about getting a 123ignition dizzy as it’s the same as the 16v KR from the mk2 Golf. At first I planned to remap a new chip to solder on the original ECU, but I found out the EEPROM VW used on the Dignition was a very old 40-pin processor, which is far from the standard 28-pin you’d find in a Digifant or Motronic ECU, so extracting the original data might be a challenge. The 123 dizzy might be the best bet, however i’m still wondering about getting a fully standalone ECU to be able to map as accurate as the stock one, which i’ll modify later. The Dignition seems to like the temp of the thermostat housing, the one on the inlet manifold doesn’t communicate i think.

Yes I meant thermostat housing temp sender. Like head of a drawing pin.