Ancient History, and Djet and cams

RD Rick rickydik at ix.netcom.com
Tue Sep 3 05:42:27 GMT 1996


I wrote: 
>> The Djet and Ljet EFI in the aircooled opposed VW and Porsche 914 
>> engines sprays directly at the intake valve from three inches away.
>> With the Djet, the fuel is squirted in at the beginning of the 
intake >> stroke two of the cyls, and at the beginning of the power 
stroke on the >> other two cyls, so its operation is compromised.  

Correcting myself here:  fuel squirts at beginning of intake stroke on 
two cyl, and beginning of exhaust stroke on the other two.  
Note: injector duration at Op Temp, WOT, 6,000 rpm, is 8.3 ms, while 
the valve is open only 5 ms.

Bryantt piped up from down under:
>What I want to know, is what happens when you have radical
>cam timing? This nice puddle of fuel on the inlet valve
>gets blown back up the inlet duct when the valve opens?
>Makes nice flames, if you don't run an air cleaner :-) 
>But this surely can't make for repeatable fuel volume supplied
>to the cylinder?
>comments?

My '73 914 just happens to have a high lift cam with a lot of overlap.  
It won't idle decent below about 2000 rpm.  To pass a smog check, I set 
the lifters out to .030", and then it idles fine.  Clatters like hell.  
I've never had backfires with it.

An additional problem is the low vacuum, about 12", below 2000 with 
that engine.  The Djet responds to low vacuum by squirting more fuel, 
which makes it richer until it dies.  I have found a fix for the ECU to 
alter the fuel curve, but haven't tried it in the car yet.

RD



More information about the Diy_efi mailing list