Initial map for VW 1776 aircooled...advice please

[vanorak]

Hi. I've just purchased a secondhand MJlite Jr. and done a basic bench test with 3.2.1 configurator software.
All seems to work fine. No issues with communication, connection etc. I'm planning to install this to a VW 1776 aircooled Bus. (mild road cam, ported head, full flow exhaust, single progressive carb...so nothing too extreme)

The stock engine works at its best with a Vacuum/mechanical advance distributor. I've acquired the advance settings for the stock dizzy, in 100 RPM increments (X degrees@600, y degrees @700 etc.)
As a starting point for my bespoke map, I plan to input these figures into the MJ spreadsheet, see how it runs, and fine tune from there.

Sounds too straightforward to be true...Am i missing something?
Any input or advice would be most welcome, as this is my first foray into engine mapping...


Also, if there are any MJ veterans/gurus in the North West UK, I'd love to hear from you, as I'm sure your experience and expertise will prove invaluable to a newb....

Thanks in advance, Jonathan (Bolton UK)

[leorest]

Your approach seems entirely logical to me.
Hopefully someone with specific aircooled experience will chip in soon.
I'm about to do the same to a near stock 1600 aircooled lump.
One issue I foresee is not being able to hear the onset of pinking due to the noisy nature of the engine/bus. So I have been considering buying a cheap electronic stethoscope to be bolted to the block and feed the headphones up to the cab so I can hear what's going on while driving.
Fancy posting up the data you have on the stock dizzy?
That would be really useful to me!
Best of luck.

[Alex B]

Do you also have list with vacuum advance values? You need to know at least maximum vacuum advance. When you know that you can play around and find out what suits best.

Alex

[vanorak]

Hi...been on the back burner for a while but now finally got my trigger wheel and pulley sorted. The advance values I'll be using are based on the SVDA distributor which used to be sold by Aircooled Net in the states. I believe they took a stock 034 Dizzy of the mexican variety and 'tweaked' it. Out of interest, one aircooled guru (Ratwell) ran up a few dizzies on his machine to see what sort of curves they gave. The SVDA didn't venture very far from the stock mexican 034...better safe than sorry I guess. If you go to Ratwell's site http://www.ratwell.com/technical/FAQ.html
and search 'new distributors' on the left hand list, you'll see some reasonably good info on both mechanical and vacuum advance curves.

Below are the mech and vac figures for the Bosch 034, which is most commonly used as a replacement for Type 1 engines


VW Mexico Vacuum distributor

RPM Crank degrees of mechanical advance

800 0
1000 0
1200 2
1400 4
1600 10
1800 11
2000 12
2200 13
2400 14
2600 15
2800 16
3000 17
3200 18
3400 19
3600 20
3800 22
4000 23


Vacuum advance Inches of Vacuum
1 Degree 3.5 inches
2 Degree 4 inches
3 Degree 5 inches
4 Degree 6 inches
5 Degree 8 inches
6 Degree 9 inches


other figures for other dizzies are available at The OldVolks Home....sorry I can't post links btw.

[vanorak]

So to work up a map, I plan to book the bus onto a rolling road, used a 'locked out' dizzy (ie zero advance at all RPM) and get the operator to note the pre-knock advance figures at various RPMs...he should also be able to measure/record the corresponding load via the vac signal form the manifold at the same time. These figures will provide the map for the MJ....all well and good in theory

The only thing I'll need to figure out is the cranking advance at start up, but this should be a case of trial and error

[Alex B]

The only thing I'll need to figure out is the cranking advance at start up, but this should be a case of trial and error

Not really when you know the static advance that is used. Must be known somewhere in the VW-community. Might even be vsible one the engine block or pulley with a specially marked notch. In order to get a good MJ startpoint you must add the static advance degrees to the mechanical advance.

But why start with a ''locked-out'' dizzy for measurement? And what is locked out, mechanical advance, vacuum or both? And why waste time with that? You know the vacuum advance values, with a conversion program you'll have your values calculated and programmed within an hour. Google on ''From inches to KPa'' or something similar and you will find websites that can calculate the KPa that corresponds with your inches vacuum values. That is a much better way to start imho and then you can use your valuabe dyno time for real fine tuning instead of fumbling around trying to get your basics in order.

Alex