Turbo fundamentals.

[Otto M Bartsch <obartsch@juno.com>]

	Well, I got my 4ksq this last weekend and I am eager to begin the
process of making it into a rally car. One of the things I want to do is
to put a turbo on it, and to that end I have located a MC engine in a
wrecking yard. I can get it with all the manifolds, turbo, ECU box(es?),
and fuel distributor for around $250. So that is going to be my source.
But, having only really dealt with NA cars in the past, I have some turbo
questions.
	1.	I was initially thinking about just putting the head and manifolds
from the MC in (plus the wiring, but not the short block). However,
someone mentioned that this might not be such a great idea because then I
would have 8.5:1 compression instead of the MC's 7.8:1. Here is what I
don't understand (and pardon my very simplified example, I am no physics
man): why do you get more power from running say 20 psi boost with a
7.8:1 CR than running 15psi in an 8.5:1 CR? I mean, assume I set up the
compariosn so that the difference in CR was made up by higher boost.
Wouldn't that equal the same power? Or is it the case that more boost is
always better, therefore it is better to start with a lower CR and run
max pressure?
	2.	How good are our rods? Do I need to think about getting aftermarket
ones to run anything above say 15 psi? Any recommendations? Any known
crank weaknesses? Also, are VW pistons compatible? They have a lot of
forged turbo options on the VW platform.
	3.	What about supplemental fueling for the higher boost levels? Is it
necessary to install a secondary injector setup, or can I put in
injectors with more flow and bump up the fuel pressure?
	4.	How much boost loss do you factor in for an intercooler? I know
different displacement intercoolers equal different losses, ditto for
different routing paths. But how do I figure out what is going on loss
wise so that I can make up for it by cranking up the boost?
	5.	When I get the turbo rebuilt, should I just upgrade to the next
higher size? What benefits could I expect in doing a larger turbo, along
with what drawbacks?
	6.	Assuming I set this thing up well, with a ported head and appropriate
cam, exhaust, and intake, what kind of max power are we talking about
here? There is a poster up in the local dealership for some top speed run
by a 5kcsqt with a larger Garrett turbo that says it gets like 650hp!

	Thanks for the education.

		otto
___________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com/getjuno.html
or call Juno at (800) 654-JUNO [654-5866]