Dual carb set ups - ?

[eight-six]

Guys,

Currently running a dual carb set up on my AE86 and need a bit of help with understanding how it works.
I haven’t played with carbs before and as a result I am not informed on how you run a carb set up on an EFI engine – so bear with me.

The car was converted to dual carbs in Japan so I don’t know exactly how it’s been done. I want to clean the engine bay up and if possible dispose of the wiring loom – or what ever part of it that isn’t needed.

The engine loom was still in place just taped up. I have found that a few wires have been cut (probably the injector feeds)

I am unsure if the ECU is still of any use? The TPS unit isn’t connected to anything, so I can’t see how the ECU would be controlling the timing? So is it safe to assume the timing is locked out and fixed?

If I pull the ECU fuse in the engine bay and the car still runs then is it safe to assume that the ECU is not need?

If people could share their views, or their set up its might shed some light on the matter. Sadly I don’t have much time to work on the car at the moment so don’t have time to investigate properly myself, so any pointers would help me along the way.

Cheers

James

[alimonos]

What about your distributor ? Is it the OEM one or it has been replaced ?
I believe that if you have the OEM one it can't work without the ECU in order to have a non-vacuum advance timing ...

[NoHachi]

Don't know exactly which sensors the std.ecu uses for timing, but maybe there is some RPM based limp home map present in the ecu..probably brought back to normal specs through the base timing.

Without a decent dizzy with vacuum advance or iginition computer you are probably leaving 20hp unused..wouldn't be amazed if the car produced less power then stock.

Lots of complicated and less complicated iginition computers on the market. I would suggest choosing one and having it tuned..should be around 300-500 pounds if you have it tuned by someone else on a rolling road.

[eight-six]

Quote:What about your distributor ? Is it the OEM one or it has been replaced ?

OEM by the looks of it mate.

Quote:I believe that if you have the OEM one it can't work without the ECU in order to have a non-vacuum advance timing ...

I thought, but I might be wrong that the timing could be fixed at something like 35 degrees even with the stock dizzy? Again I don’t know enough about this to be sure.

Quote:Don't know exactly which sensors the std.ecu uses for timing, but maybe there is some RPM based limp home map present in the ecu..probably brought back to normal specs through the base timing.

The engine check light is currently on, so you could be right with that judgment.

Quote:Without a decent dizzy with vacuum advance or iginition computer you are probably leaving 20hp unused..wouldn't be amazed if the car produced less power then stock.

Thing is mate, the car is rapid so it can’t be down on power. On track recently the car happily kept up with a 307bhp Cosworth powered 4wd Peugeot 205 on the straights, so the AE86 definitely has some legs on it.

Quote:Lots of complicated and less complicated iginition computers on the market. I would suggest choosing one and having it tuned..should be around 300-500 pounds if you have it tuned by someone else on a rolling road.

Thing is for the time being its working fine and I am happy with the performance so don’t really want to get a new ignition system if the existing one is working properly, just want to remove what isn’t needed. When I rebuild the engine for high compression then I will probably look at an aftermarket ignition system. I presume by ignition systems you are referring to things like the MSD 6AL?

Cheers

James

[NoHachi]

Jup...and unless the japanese have a custom eprom in that stock ecu the MSD will make your ae86s legs even longer.

Strange that you could keep up with the 205 with 1/3 the horsepower..sounds like it isn't a good measure of performance..maybe compare it to an ordinary car on the highway sometime? 50 - 70 mph roll on

[alimonos]

put some pics of your engine-bay in here !!! :wink:

[eight-six]

Quote:Jup...and unless the japanese have a custom eprom in that stock ecu the MSD will make your ae86s legs even longer.[quote]

Pretty sure its just the stock ECU. I know the tuning garage that owned the car before me, so I would ask them specifically but my Japanese speaking friend has dropped of the face of the earth so I am stuck – is there anyone on here that can speak Japanese?

Am I right in thinking that with a ignition control unit like the MSD 6AL I could bin the ECU and the MSD would control the timing (advance / retard for maximum performance). Cant really find a huge amount about these sorts of set ups?

If I removed the ECU would other things like the dash etc stop working? I don’t know what dependency other basic functions have on the ECU (like lights, fuel pump etc?) I am assuming most of these items are standalone?

[quote]Strange that you could keep up with the 205 with 1/3 the horsepower sounds like it isn't a good measure of performance..maybe compare it to an ordinary car on the highway sometime? 50 - 70 mph roll on

Here are a few straight line road comparisons going from a dig:

Roughly 50mph rolling start, kept with a S14 200sx until about 90mph – had a brief chat with this guy as we went our separate ways at the traffic lights, he said the car was circa 280bhp. He was surprised at how well the AE86 went.

Another rolling start from around 30mph against a ST185 GT4 – Pretty much even pegging all the way until the speedo stopped reading. No idea what the tune was of the car. Stock healthy ST185 GT4 is circa 220bhp, however the 3SGTE is easily boosted so it could have been more.

Quote:put some pics of your engine-bay in here !!!

Here is a link.

http://files.aeu86.org/forum/files/thumb...engine.jpg

If you look at the picture you can see the loom all taped up on the top of the left cam cover – at the far end you can see the TPS unit just hanging there.

Cheers

James

[firehawk]

eight-six Wrote:Am I right in thinking that with a ignition control unit like the MSD 6AL I could bin the ECU and the MSD would control the timing (advance / retard for maximum performance). Cant really find a huge amount about these sorts of set ups?

The MSD 6AL is just a CDI (capacitor discharge ignitition) add-on and still needs an external trigger signal from some other system which controls the ignition advance. So it alone would still not allow the ECU to be removed.

At least here in Finland, rallycars with carbs frequently use a modified vacuum advance 4K/5K distributor for ignition. I believe S.K. on this forum has done this - he might be able to tell how it's done. These distributors can also be used for triggering the MSD 6AL.

I'm also going to be using carbs on my car and am currently working on building a stand-alone ignition computer using a PIC16F84A microcontroller. The first version will use only RPM as a parameter for looking up the advance angle from a table, so it won't be an optimal solution - more like a centrifugal advance mechanism with a twist. But it will allow the ECU to be removed and uses the OEM distributor, igniter and coil. I'll probably extend it to use 2D tables later on and add a TPS for the other parameter (at which point I'll also need to change to a microcontroller with an A/D converter).

[eight-six]

Quote:The MSD 6AL is just a CDI (capacitor discharge ignitition) add-on and still needs an external trigger signal from some other system which controls the ignition advance. So it alone would still not allow the ECU to be removed.

Sorry being a total putz ignore what I was asking about the MSD 6AL – Typical Monday!

Is it safe to assume that seeing as the TPS is disconnected the timing has been locked out?

Cheers

James

[NoHachi]

MAP/TPS/RPM...those are the 3 main indicators of engine load...you probably only have an rpm signal left aka locked out tuning.
Realistically..whatever gazillion horsepower cars you are beating, you are probably doing it with no more then 110 hp at the crank. Welcome to the world of individual throttles and instant respons ;-)