[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[12 Svo] How to adjust Throttle Body

Carl Morris wrote:
> Wait!  Now maybe I'm not straight on something, but you're saying that
> if you run well without the knock sensor, then that means your timing
> is always too late (retarded)?  But if you get faster without the KS,
> then that means the computer was already pulling out timing.  If the
> computer pulls out timing when you're still too retarded, then I
> have to conclude you'd be better of without the KS.  Am I reading
> your message wrong?

Good question. From a design point, if you're gonna not use the KS then
you MUST stay away from the detonation side. If you do run a KS, again
from a design point, then you can "bounce off" the detonation limit and
stay right on the hairy edge - without breaking anything. There is still
some power to be made with a detonating engine - look at anything
running a nitrogen-based fuel like NOS or nitromethane - both serious
octane degreders. But how long do they last? [Answer to rhetorical
question:] Some do, some don't.
> For the record, I gained 2 mph and 0.3 sec when I disconnected mine,
> with no hint of detonation at that boost level.  I AM running the
> early 85 manifold and computer...

Again, a litle detonation isn't necessarily bad - but whose yardstick
are you gonna use to say what a "little" is? In some engines if you can
hear it, you're walking home but the 2.3L EFI Turbo is more like a truck
engine so it stays together a little longer. Don't try this with the
Porsche 930.

The early manifold design (and associated EEC strategy) allowed for
engine-generated noises very poorly. THe later stuff is much "smarter".
On a stock engine you can gain at least 1/2 second in the quarter by
LEANING the fuel supply at WOT cause it's WAY too rich for max power on
petrol. Same for all years - the EEC commands a 10:1 air/fuel ratio and
this is too fat. If you coule find an easy way to lower it to say 13:1
then you;d gain about 25HP.

Later EEC strategy narowed the window where it will listen for
detonation - I wrote an article on that already if you want to search
the SVOOA back issues. Anyway detonation can only occur between 5 and 20
degrees ATDC so there's no reason to listen during the remaining 700
degrees of rotation for that cylnder. In a 4-cylinder engine, that comes
to 680 degrees of "don;t care" rotation. The 84/85 strategies
(recognized by the early manifold design) weren't selective enough and
the "hammer" test would retard timing easily.

Downside? Higher exhaust temperatures and more detonation cause these
cast iron heads don't dump heat fast enough.

Now, from a testing viewpoint, did you reconnect the KS and notice the
same documentable decrease in performance? 

My $0.03. My therapist is helping me to get it down to $0.02 <grin>.