Mr Bian

I have a full SS system and am now getting an induction kit (thanks to all those who helpled with my previous post).

I read on a previous post somewhere that a dump valve will help me get the required flames. If this is so, can I;

a) Get a non psssssstttttttting one?

and

b) Can someone give me a technical explanation as to why the dump valve would make the flames?

Cheers

Blackscooby

b) Because the ECU knows of the air that you've "dumped" which doesn't reach the engine. Therefore it runs rich briefly.....

Mr Bian

Thanks Blackscooby.

More questions though - I suppose that means that the dump valve is tricking the ECU, is that harmful at all, or really should you get your ECU re-mapped to take into account the Dump Valve, Induction, Full Exhaust?

SimonM

Mr Bain,

The amount of air entering your engine is measured by your Mass Air Flow meter. The JECS ECU uses the signal it receives from the MAF and adjusts the fueling to create the correct air/fuel ratio.

All Imprezas have a recirculating dump valve fitted as standard. When the throttle is closed the recirc valve releases the pressurised air back into the intake system. With vent to atmosphere dump valves, the kind that go Psssshttt, the air is not released into the intake system, but into the atmosphere. This means that the reading taken from the MAF sensor is now incorrect, and hence the JECS ECU will be allowing too much fuel into the engine, resulting in a rich mixture. An over rich mixture will mean that some of the fuel will be unburnt, that is until it reaches the hot exhaust, on which it ignites, resulting in pops and bangs, and occasionally flames.

It is worth pointing out though, that an over-rich mixture will reduce performance, and over a long period of time may result in bore wash.

Another thing that can happen, is that when you lift off the throttle (and vent the air) the ECU may see from the lambda sensor readings that the mixture is rich, and lean it out. Then when you come back on the throttle you will be running lean, which is not good.

Remapping of the ECU will allow you to take full advantage of the increased breathing provided by your modifications. Unfortunatley the JECS ECU is not re-mappable, so you will need to replace it, with something like a Possum Link. The Link ECU does not use the MAF meter, so if you do fit an atmos dump valve with the Link, then you will not experiance the problems detailed above. To get flames, however, you will have to have the Link mapped to run a very rich mixture, which will reduce performance, and therefore defeat the whole object of tuning your car.

Hope that helps

SimonM



[This message has been edited by SimonM (edited 02 February 2001).]

MorayMackenzie

You could get a link or motec ecu replacement mapped to run rich at high revs in at low load... then you could get flames on demand and not harm the overall efficiency of the engine map in the process.

dowser

ppsssssttt - you *can* hear the OE recirculating dump valve if you remove the resonator!

And the wastegate.......hear it, that is. Not remove it....although that would probably work too

Richard

[This message has been edited by dowser (edited 05 February 2001).]