Installing GTI pistons?

[jdbubb@ix.netcom.com (Dan Bubb)]

----- Original Message -----
From: Robbie Cotner <robw_z@yahoo.com>
To: <scirocco-l@scirocco.org>
Sent: Saturday, April 06, 2002 2:11 PM
Subject: Installing GTI pistons?


> Now that I am about ready to put my '84 JH engine back
> together, as a last minute performance upgrade I'm
> thinking about installing GTI pistons.  While I have
> worked on engines quite a bit, I still don't know the
> advantages/disadvantages of doing this.  Better power?
>  Better MPG??  Decreased engine life??

GTI pistons (ie. GOLF GTI) are 10:1 CR and will give you slightly more
power. If they are Rabbit GTI pistons then they are the same as you
currently have. I would suspect little to no change in MPG. No change in
engine life. Knock sensor ignition my be a nice addition if you were to use
these pistons, but is NOT manditory if you use decent gas.

> Would my
> engine still be freewheeling(or whatever they call it
> when your valves don't bend if the timing belt
> breaks).

The term is "interference", and no it wouldn't change.

> Also, these pistons would be used, is that
> OK?

Depends on the condition of the pistons and the condition of your bores.

> Finally, are these pistons the only reason the
> GTI 1.8l was rated at 110hp and the normal 1.8l only
> 90hp?  Are they both JH engines?  I assume exhaust may
> have had a little to do with the power differential
> also-

The 85 and later GTI 1.8L 8V engine was either an HT or RD rated at 100 or
102 HP. These engines had hydraulic heads which in itself didn't change
power, but the hydro cam had greater duration and lift than the solid lifter
JH cam. Also, they had a much better exhaust manifold (anything was better
than the toilet bowl manifold!), so the pistons with the higher CR would
only account for a couple HP.
Changing to an earlier dual outlet manifold, TT downpipe and exhaust and
using a G grind cam will bump power to 115 HP with no other changes to your
engine, so if the pistons are a pain ie. you have to bore the block, then
I'd forgo them and do the exhaust and cam.
Dan

>Thanks in advance,
> Rob
>
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