Porsche 911 Carrera 3,2 170kW/231PS motorcode 930-20, help needed

[Mac-B]

Hi,

i´m planning on installing a VEMS unit on a stock 89 Porsche 911 Carrera 3,2.
From what I read so far I´m quite confident that it should work, although there are no applictions so far ?
However some questions are left. (as it seems i´m the pioneer for the 911)

Let me start with the facts found so far and my plans for application:
- Motor 3,2litre normally aspirated
- trigger system is 2 VR sensors on flywheel / starter ring gear
- rev sensor is sensing 129teeth per crank rev
- TDC sensor is sensing 1 pin on flywheel (don´t know yet how many degrees before TDC)
- no cam or distributor sensor
- stock NTCII at cylinder head #3
- AFM (flap type) will be removed, will use TPS  instead (exchanging stock idle and WOT switch)
- idle control valve is the "silver cigar" BOSCH thing, not sure if stepper motor or PWM ?
- IGN distribution will remain untouched in first step, stock coil, stock distributor
- stock fuel injector BOSCH 0-280-150-158 low-Z (2-3 Ohms)
- wideband O2-sensor will be used intead of stock narrowband
- no MAP, no airtemp sensor planned
- Firing order for the Carrera is 1-6-2-4-3-5
- wiring should remain mainly stock with stock-DME-connector and only additional wires for wideband, TPS and so on
- planning to use alpha-N only

Now to the open issues:
- What is the preferred SW, i guess VEMStune, but in phat bobs instructions MegaTune i still mentioned ?
- primary trigger: 129 is quite hard to divide, only possible value is 43 ! -> 6 triggers, 120° Will this work ? (AUDI div by n)
- any drawbacks due to the 129 teeth variant, like rev limit or so ?
- secondary trigger is the TDC-mark on flywheel
- do i need to order AUDI-trigger option or should I use VR-option as secondary ?
- what type is the idle control valve ?
- what to do for the low-Z-injectors ? is the 30V flyback ok and do i need the inline resistors (6,8 Ohm) ?

I´m looking forward to get into discussion with you guys.

Best air-cooled grettings,
Marcus

[rob@vems.co.uk]

Bosch IACV should work PWM.
You will need Air temp and you need MAP, even if it is just for barometric correction on AlphaN.

Use VEMS Tune, I'm not in any rush to re-write the User Guide as there is no incentive for me to do so.
43 trigger teeth will be fine, 120deg cylinder spacing is quite normal.

Use in-line resistors.

I don't know anything about Audi trigger - I would have thought that normal triggering would work fine.

[boostd audi]

one reason you have not seen alot of porsche builds is there are not as many people building them and running it on standalone compaired to other car brands.

tdc after the crank is easy to find, you lock ignition and use a strob light, adjust value until tdc is in line.

use vr sensor.. if you have them in there they will work fine.

rob, the user above, wrote phat bobs install.. if you look that install is for vem3.3, now there is 3.6, not that this information is bad or unuseable, but it is from years ago.. it could use an update but like rob said he has no reason to update it. it was also written before vemstune was reliable and useable.. we ALL use vemstune now. the SW has come a long way and continues to get imporvements and new features.. just grab the latest sw download from vems.hu/vemstune, then download newest REALESED firmware being 1.1.95.

if you use the phat bob install sheet as well as the help button in vemstune, you can figure most of the configuration out.. its fairly easy.

[GintsK]

I am not 100% sure about 129 teeth wheel: 0-43-86 (or with camsync 0-43-86-129-172-215) ref tooth table might not work because of high tooth count. Divide by any seems is not usable in this case (it decrease internal tooth count for processor).

also I suggest to use speed-density method as long as you have moderate camshafts. It makes idle air control more easy to calibrate. And it is safer for long term use: MAP sensors are more reliable comparing to TPS. Until TPS isn't Hall type.

boostd audi, 80-90lbs injectors is bit overkill. 260cc is enough for 300hp n/a. OE seems are 230cc - more than enough for stock 230hp.

Gints

[Mac-B]

Hi,

the 129teeth are my biggest sorrow so far. I want to use as much stock parts as possible to be compatible with stock Motronic as well.
From what I see in the VemsTune GUI I would do the following:

129 means 258 for a full eingine cycle, the max value for "Coil-type" + "normal" is 255 !
So i need to use "Auditrigger DivbyN" option and a "Audi trigger divider" of 43.
So number of teeth on wheel becomes 3 (carrying over what I see on the AUDI configs)
First trigger tooth will be 0
Next trigger tooth 1
Angular width of teeth is 120°
trigger patern is 0-5-4-3-2-1 ? (or does it has to be in firing order here?)

Any thoughts on this ?
As it seems I need to use the "Auditrigger" option I guess I also need to order the option for the ECU.

Regarding need of MAP, I always thought this is only neccessary for Turbo applications, I know at least one guy running a KMS on a 911 w/o MAP, can you help me out to understand the advantage ?

Thanks in advance, have a nice Sunday

[GintsK]

My fault - I didn't note before that divide by N designed even for so large dividers. Yes you can try it out. But there is downside: ignition timing lose precision with so rare teeth. Especially in dynamics. But if engine isn't knock limited, it is not a big problem.

[boostd audi]

my mistake i thought i read he was turbo,

[rob@vems.co.uk]

Running MAP means that at the very least the fuel can compensate for air pressure correction due to weather and/or altitude.
Speed Density is a far better fuelling calculation than AlphaN.

[Mac-B]

Hi,

two more issues:
1. the only IGN output will be the single coil connected to pin35 -> so I only adjust 1 IGN output or should I adjust 6 and configure all to fire pin35 ?
2. the Carrera uses 6 injectors, but only 2 pins on stock ECU. the first pin fires injectors 1-3 and the second one 4-6
If i want to leave it like this, how to adjust this in VEMS ? I guess 2 primary injectors and then configure them to the two pins I want to use with the vems-ecu ?

How will VEMS handle this setup then, I don´t see where I can influence the fire order with that setup ?

[Erikk]

1. Yes, 6 outputs and pin35 on every event.
2. Choose two primary injectors and divider 3.

You dont have to care about output order, but i strongly suggest you to do some wiring and running 6 injector channels.

Order the ECU with 8ch LowZ-extension board, then you can run your injectors without resistors. The board is really great!

[rob@vems.co.uk]

Rewire the injectors to fire sequentially, get a Bosch motorsport 3x2 wasted spark coil.
You may as well update to something decent if you're going to the trouble of fitting an engine management system.

[Mac-B]

What if I want to stay with the stock injector setup (3 injectors parallel) what type of resistor would i need ?

[GintsK]

Somewhat to maintain in 1...2A  range in static. Usually 4...6 Ohm 25...50W for each injector.

I am with Erikk and Rob. Go for more up-to date setup. If only you want to keep as much as possible original.

Gints

[Mac-B]

That´s the plan to stay which as much stock as possible in the first step

[rob@vems.co.uk]

Stick to the old ECU then, no point in half doing a job.