K-Jet pondering

[penski]

I've been reading the K-Jetronic articles in the last few issues of PPC and something popped into my head:

Seeing as the system uses the volume of air flowing through it to regulate the amount of fuel which is metered to the injectors, would the addition of a positive-displacement supercharger (Eaton or similar) be 'relatively' simple? As the blower does no more than supply a set volume of air per revolution, the fuel side of things should be able to keep up (perhaps swapping injectors for ones from a larger capacity engine?)...

Would it then just be a case of monitoring the spark and possibly advancing it a smidgen?

*n

[carat 3.6]

Yes and no.

The air flow meter is only measuring the flow of air at atmospheric pressure, it cant see positive pressure. So just feeding boost into it wont work. What you can do is set the intake up so the supercharger sucks through the airflow meter, then pumps boost into the inlet manifold. That will be somewhere near to reading air flow correctly.

There will still be some small tweaking involved, and you may need a boost referenced fuel pressure regulator from an audi or volvo.

[penski]

Mar 19, 2015 8:42:20 GMT carat 3.6 said:

Yes and no.

The air flow meter is only measuring the flow of air at atmospheric pressure, it cant see positive pressure. So just feeding boost into it wont work. What you can do is set the intake up so the supercharger sucks through the airflow meter, then pumps boost into the inlet manifold. That will be somewhere near to reading air flow correctly.

There will still be some small tweaking involved, and you may need a boost referenced fuel pressure regulator from an audi or volvo.

It's a positive-displacement blower; it doesn't do 'boost'; it just provides a higher volume of air.

*n

[Deleted]

Cant see that working tbh. If you put it before the metering head its just going to push it down and overfuel .

[carat 3.6]

Mar 19, 2015 20:10:15 GMT penski said:

It's a positive-displacement blower; it doesn't do 'boost'; it just provides a higher volume of air.

*n

Call it what you want, the end result is the same.

Also you'll be wanting to retard the ignition timing, not advance it.

[turbeam]

Providing that the airflow meter/ fuel distributor unit is located upstream of the supercharger this will work perfectly well.
It does need to be on the intake side of the supercharger though.
K-Jetronic and turbocharging or supercharging can be made to work very well together very easily, and prior to the advent of affordable and reliable EFI/ management systems it could provide a relatively simple solution that avoided many of the issues with having to deal carburettors for blow-through use etc

K-Jet systems may largely have gone out of favour now and been largely superseded by electronic systems, but they can still be made to work extremely well with forced induction. On an older engine already equipped with K-Jet there is no reason that it couldn't be retained and tweeted to work perfectly acceptably in conjunction with a supercharger.

[melle]

You might want to have a look at Saab 900 8 valve turbo engines.

[ChasR]

Or the Escort RS Turbo, and Porsche 924 Turbo cars .

AFAIK on an RST the K Jetronic system is the same bar an electro fuel regulator adding in more fuel once the metering head reaches its limits in addition to the ECU dealing with the ignition (in the 924 this was a mechanical process until the later cars).

AFAIK you can fiddle with the metering head to give you more fuel on boost but it is at the expense of overfuelling everywhere in the rev range.

[melle]

Plenty pdf Bosch K-Jet manuals can be found through Google and downloaded for free.

[Smiler]

For anyone who might be interested there is a dumbed down guide on my website, though it's probably below the level of everyone who has commented on this thread.

[melle]

I'm sure nobody will find a clear guide like that to be below their level!

[Smiler]

Ta very much It is the most popular part of the website.

[penski]

Ooooh...

/clicky

*n