RE: turbo fundamentals

[Jay Rabe <j-yr-be@snet.net>]

1.      "then I would have 8.5:1 compression instead of the MC's 7.8:1"
    You have to decide how much boost you want and what kind of gas
you'll be using (race or street) to get what your compression will be.
A lot of turbo cars run 8.5, but the 7.8 allows more boost and after the
.7 compression loss will make more power.  Compression helps with bottom
end but in my opinion isnt worth it.  A friend with a 2.0 16v pickup
recently lowered his compression from 11:1 to 8.5:1 (in prep. for a
turbo).  He can barely notice the difference and 1/4 mile times are
about the same.  BTW the piston makes the 7.8:1 compression, not the
block.  The only reason to use the 5kt block that i can think of is the
oil squirters, and the oil pressure line(off the oil filter neck) and
return line into the block.  There is a formula for boost + compression
ratio to total compression ratio but i dont have it in front of me.

2.    "How good are our rods?"  Intended acceleration has a yellow car
with a sick motor in it.  He bent a rod in it.  I've heard 100hp per rod
is the normal, but the IA car didnt have 500hp.  Stock rods are cast and
therefore weak.  If you want a high power reliable motor get rods too.
I've been recomended pauter rods and im getting them.  As for pistons
I'm having forged JEs made for ~$700.  There are no oversized pistons
available for this motor from anyone i talked to.   VW pistons fitting
wouldn't be likely, i've never seen a dished one out of a vw (required
for 7.8 compression).

3.    Secondary fueling is necessary above 15psi.  I've been told by
injector companies and audi pros. that larger injectors wont flow more
because they are limited by the fuel dist.  There is a fuel dist.
upgrade, but i dont know what car its from.  IA should know.  For every
manifold pound of boost you go up your fuel pressure will effectively
drop one.  Manifold pressure works against fuel pressure.

4.    Intercooler loss is tricky.  Some IC companies claim low boost
loss, but as air cools it also becomes more dense lowering the actual
boost psi, but the cooler the air at a given boost the more O2 it has.
So 15psi at 100deg.F has a lot more O2 than 15psi at 300deg.F.  Just
because the boost pressure is lower because of the IC it doesn't mean
you'd lose power.  E-mail an intercooler company to find out because
each one is different and it is pretty technical.  Dont forget that the
stock 5kt intake manifold is restrictive.  Sprongles car looks like a 4k
one with a 90 deg. piece welded on the back (in european car).

5.    An upgraded turbo is only necessary if you plan on pushing more
power than the stock turbo can provide.  The upgraded one might be more
efficient cfm to psi, but it will probably lag a little more.

6.    Dont count on rediculous figures unless you can get some really
good brew (really good race gas).  Hp depends on a lot of stuff, but i'd
figure above 300hp wouldn't be a problem.

Jay
4kqt