Pushing the limits of an I5...

[Jörgen Karlsson]

Hi,

I have managed to get some information about the weak spots on the 10v
engines. Before one can reach the power levels where these things break the
CIS will have to be very heavily modified or changed for an EFI setup.
Proper fueling is of course needed to keep the engine in one piece, the cis
is not known for it's ability to supply a safe mixture to a tuned engine.

Since the MC wasn't used until 87? here in sweden most of this information
is about the solid lifter engines. The MC and the 20v came at more or less
the same time over here, that made the MC less interesting. Most should
apply to the mc.

The head bolts are the first thing that should be replaced, the stock bolts
tend to strech at very high boost pressures. The sign is blown head gaskets.
Using a HIGH grade M12 bolt with the same thread pitch solves this. The
tourque specs i have had for these are something like 120-150N! I would try
that on a junk engine before I dared to do it myself, it is more then twice
the stock torque. The rating that was mentioned was SIS12.9, that is the
highest standard rating available here. A standard bolt has a 8.8 rating,
common audi fasteners are something like 5.8. I guess that an ARP head bolt
is a good choice. Just stay away from strech bolts. I was also recommended
to deck the block and head to make sure that the surfaces are flat.

The same source mentioned that the stock pistons are fragile too, at least
compared to the 20v pistons. I don't know about the MC pistons, the MC
piston looks very strong. The low rings are a good thing for a turbo engine,
I guess that broken ring lands is not the failure mode of the piston.

Rods can also be improved on.

Jörgen