D-Jet engine mods (was Re: Typical)

[jadney@vwtype3.org (Melissa & Jim)]

>From: Greg Merritt <gregm@engin.umich.edu>

>>Another piece of VW wisdom that is a load of B.S. when applied to the
>>later Type IIIs, is the belief in semi-hemi cutting your cylinder heads
>>and shimming out your cylinders to lower your compression ratio to 6.9:1.
>>On a D-Jetronic motor, the end result of this exercise is lousy mileage
>>and loss of power (not to mention hesitation and backfiring).  You should
>>always be running at least a 7.7:1 compression ratio and a fuel pressure
>>of 28psi.  *Never* mess with the heads of a Type III with fuel
>>injection--this means that semi-hemi cutting, porting, running bigger
>>valves, and running hotter cams or ratio rockers are all Verboten.  As the
>>D-Jetronic needs to see a certain manifold pressure to run correctly,
>>fooling with the rate of airflow or the compression can have anywhere from
>>annoying to disasterous results.  So keep it stock!

I would be the last person in the world not to take Gene Berg seriously, but 
I have some trouble with this.  In one of Bergs later price lists, he said 
not to use the semi-hemi on FI type IIIs because they already have a knock 
sensor.  Well, there is no knock sensor on any type III.  Perhaps he was 
thinking about the cyl head temp sensor, but this would not have the same 
effect.

Fortuanately, or unfortunately, depending on your point of view, this 
warning came too late for me to agonize over it.  I had already semi-hemi 
three sets of my heads and built two of them into engines which had been on 
the road for a couple of years.  These two cars are still on the road and 
running fine after more than 5 years.

All of my rebuilds have been stock P/Cs, cam, and valves, but completely 
ported per the Bill Fisher book; I later got hold of Bergs porting 
instruction in which he revises some of his earlier work in the book--I 
haven't put any of these changes to the test yet.  In addition I add a Berg 
counterweighted crank and have them balance everything.

Here's what I have found:  I can't see any big difference between the before 
and after.  I certainly feel more comfortable revving the engine much 
higher, and I THINK there is an increase in power due to the porting, but 
this is subjective and subject to dispute.  I note no change in gas mileage, 
and I monitor and log EVERY(!) tankful. There is no hesitation except that 
which was there before with the stock engine. My own current daily driver 
was a lemon that I purchased because the PO couldn't afford to keep paying 
me to try to fix it every weekend. I'm afraid that I have managed to find 
one insidious problem per year in the 5-7 years that I have owned it.  I was 
worried last fall that the semi-hemi problem was coming to haunt me, but it 
turned out to be the pressure sensor (leaking bellows!)  The car just keeps 
working a bit better year after year, but I have not had any problems 
related to the mechanical parts of the engine itself.

This is not to say that it works up to Berg's standards.  It is quite 
possible that Gene would not like any type III D-Jetronix.  Gene's standards 
were very high, but I haven't see any signs in his published materials that 
he spent much time working with type III D-Jetronix.  It's also possible 
that he did, but his test car had one of those problems that can go 
unrecognized/undiagnosed for years, overshadowing all his testing.  Face it, 
our cars have a reputation for being troublesome.

For the record, I've been driving type IIIs exclusively since 1968 and doing 
all my own repairs since about 1970.  My wife has been driving exclusively 
type IIIs since we were married in 1974 until this winter when she finally 
succomed to the
siren song of winter heat and got something new, water cooled, american 
made, and warm.  Of course I did all the repairs on her type IIIs, too.  On 
top of the family's daily drivers we also have several stored for occasional 
use.  All my type IIIs have been squarebacks.  In the meantime I have made a 
bit of a sideline business of repairing type IIIs for other owners, of which 
there are very few any more.

Jim
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       Melissa Kepner                                    Jim Adney
       jadney@vwtype3.org              jadney@vwtype3.org
                             Laura Kepner-Adney
                             Madison, Wisconsin
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