[urq] Why audi I5 started as 2.1 liters - Audisport HistoricalTrivia

[Martin pajak]

Scott,

I don't see your '83 in your sig line... what happened?

Cheers
Martin Pajak

http://www.quattro.ca

1983 Audi Ur-quattro (305,000 km) for sale : (
1985 Audi Ur-quattro (210,000 km) Euro spec. import mit 3B ;o)
1971 Porsche 911T (45,000 mi) all original



-----Original Message-----
From: urq-bounces at audifans.com [mailto:urq-bounces at audifans.com]On
Behalf Of QSHIPQ at aol.com
Sent: 20-Oct-04 08:26
To: urq at audifans.com
Cc: audi20v at rennlist.org; s-car-list at audifans.com; quattro at audifans.com;
200q20v at audifans.com
Subject: [urq] Why audi I5 started as 2.1 liters - Audisport
HistoricalTrivia


Q-heads:
Been having discussions on Audis use of the I5 and it's origins.
Specifically, why 2.1 Liters.  The answer can be found going back to FIA
Homogolation Rules (x many production cars had to be built to be a
'homogolated' competiton 'production' car) in the early A1 Rally cars.

When Audi introduced Quattro, they wanted to introduce the system and prove
it in racing at the same time.  The theatre of war they chose was WRC rally.
After a full year of behind the scenes lobbying (competition factory efforts
had to endorse the awd allowance, along with FIA), they got the variance to
the rules allowing AWD in WRC competition.

Now comes the engine history.  Turbocharged cars were allowed by FIA, but
they were displacement corrected against the normally aspirated cars.  This
adjustment was known in FIA as 'equivelency'.  The number assigned to
equivelency on Group4>GroupB competition turbo car: 1.4.  This was a key
number to Audi AG in I5 construction and displacement.

Audi chose to compete in the sub 3liter class.  This meant that the maximum
motor equivelency displacement had to be less than 3 liters.  2.1 * 1.4eq =
2.940 Liters corrected.  Sound really close to the max?  Hardly.  By the
time Audi completed FIA Group B (evolution of Group 4 where audi started
competing), they had tweeked bore and stroke right up to 2.133liters.  2.133
* 1.4eq = 2.9862 Liters corrected!

Street cars originally got the 2.1Liter motor (basically the A1 A2 Rally
motors and 016 quattro transmission).  Later production Audi motors got
bore/stroke tweeked a bit to a maximum stock displacement of 2226cc.

There has been much speculation over the years on what would have Audi
chosen for the I5 displacement had the FIA 1.4eq rule not been in effect.
After a lot of calculations on piston speed vs the Audisport cars, I've
proposed over the years that 2.4Liters (overbore + 2.1 liter crank) would
probably be the optimum for a race I5turbo.  That said, the torque and HP
figures we see from 'big block' I5's (2.5 and 2.6L) are pretty impressive in
street cars, but they really aren't conducive to high rpm racing.

The I5 has proven itself in racing and in street car development for almost
25 years now.  A virtually bulletproof motor, the abuse many have put it
thru (not just audisport), sometimes defies logical thinking and accepted
engine limitations.  Gotta like that!

Cheers

Scott Justusson
QSHIPQ Performance Tuning
Chicago IL
'91 v8
'84 RS2URQ Project


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