Single point injection and megasquirt
Turbo Mini Forums

I’m building a 998 and adding the turbo unit from a metro. I will be using a Saab throttle body which has a single injector. I’d also like to run electronic ignition instead of a dizzy.

I believe Megasquirt can do a good job at controlling all this but not sure what setup i require. There are a lot of variations and additions. Anyone got any advice or done anything similar?

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Megasquirt can do what you want but you need to consider the fuelling and ignition seperately.

Using a single throttle body and appropriately sized injector is often refered to as "wet manifold" as well as SPI - you can actually use more than one injector but the fact they are in the same place at the throttle body still makes it SPI or wet manifold. Megasquirt will deal with two injectors at the throttle body just as well as one.

You will simply have created an electronic carburettor.. The most basic Megasquirt and basic code will deal with this with no problems.

Have a search around the forum, quite a few have done this.

(there is a much more advanced option for fuelling but it's not relevant to your build with throttle body injection)

But when you get to the ignition you need to think a bit further, as there are various options.

The basic design is to run a coil/dizzy, including an ignitor chip to run the single coil.

To remove the dizzy, there are three options.

1 - Ford coilpack (or equivilant) but with a Ford EDIS module. The sparks are generated by EDIS, Megasquirt just tells it when to.... just the same as Megajolt.

2 - A modified Megasquirt with two ignitor chips inside to drive the coilpack direct. No need for an EDIS module, everyting is controlled by Megasquirt. However, apart from the internal mods, you need to run the "Extra" code.

3 - Further internal mods to drive individual COPs or CNPs. I wouldn't suggest this until you have tried a coilpack !!!

Have a good search around the EFI parts of the forum, quite a few are doing "wet manifold" and the choice of ignition setup is then down to you.

Some people use Megasquirt just for ignition, rather than Megajolt, becuause of the added functuonality and the fact you can throw the EDIS module away.

EDIT - apart from the electronics, you might find the standard Metro Turbo T3 setup a bit too "large" for a 998.

Edited by Rod S on 6th Aug, 2009.

Schrödinger's cat - so which one am I ???

Thanks for the reply, very helpful.

I'm on a budget (student at the moment) for the EDIS option i'd try and get one from a local scrappy, is the cost of option 2 similar or much more?

I plan on seeing if i can build the Megasquirt from scratch (sourcing all the components myself and making a "spider" type circuit) with the idea that it will work out cheaper. Has anyone got a list of UK part no.s or done this before?

As for the T3 setup, yeah i've read that it may a little too large but can't seem to find low priced T2's. Will it be a huge problem? Would it just be a longer spin up time?

Cheers

1275 N/A Sprite, 998 T2 Turbo Mayfair
1275 EFi Turbo

Option 2 requires two "ignitor" chips (and 330 ohm resistors) instead of the EDIS module. They are VB921s on the MS parts list but people tend to use the Fairchild or Bosch equivilant as the VB921s are no longer made so hard to source. I use the Fairchilds and they can be sourced at about £4 each in the UK. However, it is a "specialist" chip so you won't find it at Maplins.....

Building your own from scratch is a bit political because of people copying the original design but modifying it slightly, adding the code, then selling it as a new product. You would need to buy the genuine MS1 CPU (or MS2 daughterboard) anyway because of embedded code so I won't comment specifically on that level of DIY but a sensible option is to buy the "partial" kit which is just the main PCB, the CPU (or daughterboard) and MAP sensor then source all the remaining components yourself. I did start to make a list of RS or Farnell equivilants but it's complicated because of component sizes, pin spacings etc. Digikey now have a UK website so you can just enter the MS list straight in but they actually supply from the USA so you get stung for tax, import duty etc. anyway. You can also replace a lot of the standard MS build with add-on boards, Jean (jbelanger on this forum) sells them http://www.jbperf.com/ for example for the injector and ignition driver circuitry.

T3 - I don't know, only what I have also read..... I'm building a 1360 so it's not an issue. I expect it would not spool until much higher RPM (rather than taking longer, which is different). It all depends on how much exhaust gas your engine will provide at low RPM.

Schrödinger's cat - so which one am I ???

I have sourced the components myself from Farnell, but components change so much my lisy will be out of date. You will just have to do it from scratch looking at the parts list. I have to say that the kits are so cheap anyway that you won't save much and the extra hassle and reliability issues are not worth it in my mind.

From experience the T3 on a 998 is not a good combination. Keep looking for a T2, one will turn up.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

I don't know how it is in the UK but from here in Canada, the cost of sourcing all the components and getting a partial kit is actually more than just getting a complete kit from one of the 2 major MS sellers (DIYAutotune and Glen's garage). And getting the case and machining it is a pain since it's not readily available from the major electronics vendors.

And while making your own board is acceptable for your personal use, you won't get any support on the forum. And that may cost you much more than the cost of the "official" board since it could make the difference between a successful installation and a pile of electronics left in some drawer.

So just make sure you take everything into consideration before making your final decision on how you go about this.

Jean

http://www.jbperf.com/

The issue with components is the minimum order quantity. If you make just one board you will end up with lots of components left over, adding cost.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.