[tech] similarities b/w 7a & 3b

[JShadzi at aol.com]

<< Ok, so after owning my CQ for 2 months I've decided that it thoroughly needs
positive manifold pressure. >>

Good, you are on the right track  =)

<<I'd like to stick with 20 valves, which makes it an expensive proposition. >>

Yes and no

<<But my brain has been cranking the gears, and I'd like to bounce a couple of thoughts off of those that might know. 

Does the 7A and 3B have the same bore? (i.e. could I use 3b pistons in my 7a
motor to get the correct CR. this assumes the heads are identical)>>

The heads are identical regarding fittament and bore/stroke stuff, the bores are different, however, 81mm vs. 82.5mm.  The only way to lower compression is to use a different piston, and nothing Audi that I know of will "bolt in", some VW pistons that Alex. VG just got would though, they have 82.5mm bore and 8.5:1 comp.

<<How similar is the 7A brains to the 3B. I'm hoping that the wiring is the same
and that the box will plug into the old harness. Odds are they're different, but
I'd like to know. >>

Completely different, unfortunately your 20v has a wierd Hitachi system, the 3B uses Bosch Motronic.  The Hitachi system is very hard to tune also, and since they use odd shaped injectors, it is not really possible to get anything bigger either.  Here is where a programmable EFI system like the one I am using would be useful.  Running much more than a few lbs. boost with your current fuel systems will be very difficult however.

<<My simple thoughts are that I'll pop off the head, swap in some new pistons and
put the head back on. Then attach all the external engine pieces needed for a
turbo and convert over to 3b ECU, and I'm good to go. >>

Sorry, see above, not that easy.

Let me know how you come with it,

Javad
www.80tq.com