Re: 1.8T reliability at 200 hp - HELP!

[Orin Eman <orin@WOLFENET.com>]

Firstly, go get a copy of Corky Bell's book, Maximum Boost for
a _baseline_ understanding.

> THE CASE AGAINST CHIPPING:
> 1.  Audi carefully engineered the 1.8T to run at 150hp, and anything
> higher will cause excessive stress on the engine internals and reduce
> engine life. 

vs

> 1.  The reason the 1.8T is tuned at 150 hp is marketing.  How would Audi
> sell the 2.8 if the 1.8T could outperform it (or the TT roadster for
> that matter)?  They have positioned the 1.8T as a step below the 2.8 and
> so it is tuned down to a less threatening hp level.

This engine is essentially 4/5 of the 5 cylinder.  Boosted to 200hp, the
equivalent 5 cylinder output would be 250hp.  Not a big deal for
the 5 cylinder engine.

In some circumstances, running extra boost at lower RPMs is kinder
to the engine than higher RPMs.  The highest stress in the rods
is tensile, as the piston crosses the TDC position, not compressive
as you might think.  Higher pressure in the cylinder whether it is
exhaust back pressure due to the turbo or intake boost pressure
tends to reduce this stress!

150 is _far_ too round a number to be engineering based.  Marketing
is a far better explaination.

> 2.  The turbo/ engine design was carefully thought out by Audi, and 7
> lbs is where the turbo should be running (150 hp).  Getting 12 or 14 lbs
> boost pressure from the turbo (200 hp or more) is too much for this
> engine if you want it to last more than 75,000 miles or so, or certainly
> too much for the poor little turbo.  

vs

> 2.  The turbo's manufacturer says the turbo unit can withstand more than
> 14 lbs. boost pressure, and can run troublefree at 14 lbs. max., so quit
> worrying.

Insufficient data here.  Maybe the turbo can run happily at 14 psi boost,
but can it flow enough cfm for the engine?

> 3.  If you're going to raise the boost pressure, you should change other
> things such as the air inflow (filter), exhaust, perhaps intercooler,
> etc.  It's not safe to just up the up the boost pressure. 

vs

> 3.  The TT roadster has a 1.8T that gets 215 hp, and it is not
> dramatically different in design.  Audi would not have a totally
> separate re-tooled engine line just for the TT's 1.8T, since it is very
> limited production.  Perhaps the intercooler has been upgraded, and
> maybe pistons, but the engine is basically the same.

The 1.8T's exhaust is reported to be _very_ restrictive.  It is a good
idea to change it as well.  As for the intercooler, guess we will
have to get out the thermocouples.

_IF_ the chip maintains decent engine management eg. monitoring
the intake air temperature and reducing boost if the temp gets
too high and keep the igintion timing in line,
then I don't see much of a safety issue.

> 4.  200 hp from a 1.8T is a very high hp/ liter ratio, getting into the
> very highest range of production cars, including high-end sports cars
> such as the Porsche 911 turbo S.  There must be a reason that few auto
> builders sell production cars with this kind of power/ liter ratio (and
> that reason is reliability).

vs

> 5.  Audi itself has considered (or already has done so in some
> countries) allowing dealers to sell chips as dealer upgrades, under full
> Audi warranty.  Does this sound like they think extra ponies will hurt
> the engine?

Points more towards marketing.

> 5.  Contrary to popular belief, the TT roadster's 1.8T engine is NOT the
> same as the A4's, so the fact that the TT gets 215 hp is apples and
> oranges.  Audi didn't just de-tune the engine management system and
> reduce turbo boost in the TT's engine for the A4.  The compression ratio
> is different, so the engine internals are slightly different.  This
> indicates that Audi feels the 1.8T needed to be strengthened for the TT
> roadster to withstand 215 hp.

Insufficient data.  And the above is a non-sequitur.  Changing the 
compression ratio doesn't necessarily make anything stronger,
it just makes detonation less likely.

> 6.  The REAL factors in engine life are maintenance and how you drive.
> These factors dwarf any affect extra boost pressure might have.

True.  Especially where and how my A4 gets driven.

> 7.  A stock 150 hp engine may be flogged much more to get it to perform
> well, while a chipped engine performs better at lower rpms and isn't
> punched all the time to get the car moving quickly.

Depends on the transmission.

> 8.  If the stock 150 hp engine can go at WOT on the Autobahn for a
> couple hours straight (the common use in Germany that it was designed to
> handle), isn't that less stressful than a 200 hp version driven under
> real world conditions -  mostly in the 2-4000 rpm range with only
> occasional hard driving?

Agreed.

> 9.   Audi has a long history of turbo engines, with many people fooling
> with the turbo boost.  They designed the A4 1.8T as an enthusiast's car
> with the full knowledge that it could and would be chipped up, so they
> designed it to last under higher boost levels.

Audi and indeed the VW 4 cylinder engines have _always_ been
very strong.  When did you last hear of a 5 cylinder needing
rebuilding short of hydro-locking it or running out of oil?
It is more this than designing it for higher boost levels
I would think.

> 10.  Hey, live a little!  Stop worrying.  200 hp in this car is such a
> rush, it totally transforms the car!  Who cares what happens "down the
> road"?   (I had to throw that argument in).

Lease it.

Finally, I'd say disregard all of the above comments if you have the
Auto transmission.  The reliability of this unit is unknown,
even with stock boost levels and may in fact contribute to the
150 hp limit, though one rumour was that it was the same unit
as was used on the V6s.  Can anyone verify this?


Orin.