[200q20v] intercooler (or: IA3+ & K24 turbo limits)

Bernie Benz b.m.benz at prodigy.net
Tue Dec 4 07:23:40 EST 2001

Thanks for the info Gene,

Apparently this forced induction system is self limiting, and therefore
designed (?) fail safe.  6 seconds of overboost will deplete the heat sink
capabilities of the IC, and because the IC has nil steady state cooling
capability, the ECU will therefore bypass the turbo because of charge over

As I've said before, Audi is designing cars for short burst performance,
relying primarily on the transient, heat sinking capabilities of the forced
induction system, rather than on the steady state capabilities of a good
intercooler design.  "A quick pop is all you get!"


> From: Gene Caldwell <gene.ghc at verizon.net>
> Date: Tue, 04 Dec 2001 02:10:36 -0500
> To: Brian Link <brianl at starsys.com>, 200q20V mailing list
> <200q20v at audifans.com>
> Subject: Re: [200q20v] intercooler  (or: IA3+ & K24 turbo limits)
> Brian Link wrote:
>> Thanks Bernie,
>> Or...
>> Has anyone done some datalogging and read either the inlet air temp sensor
>> or the mass air sensor.  I'm just trying to run some numbers on 1.  how
>> hard im pushing the k-24, and 2. what are the other turbo options.  Scott J
>> made a comment on the S-car list that there is 100% failure rate on the
>> k-24 above 2.4PR (Is this True?).  I calculate that I'm at 2.6-2.7PR up
>> here in Colorado, sea level folks with chips are at 2.4PR.  Could anyone
>> that has had a k-24 fail chime in of the how's and whys of the failure?
>> Thanks in advance
>> Brian Link
> Disclaimer: If I get any of this wrong I hope Ned will correct me.
> I believe some comments from Ned Ritchie while I was getting a 3+ ECU
> mod done for my 3B motor might be relevant.  Hopefully my memory serves
> me correctly.  The context of the discussion was whether or not the IA3+
> ECU mod would put my K24 turbo in danger.
> Ned told me that the stock K24 turbo rated upper limit is 265hp
> (continuous duty, I think).  That's just another way of stating how
> much air the turbine is designed to move.
> His 3+ software will spin the turbo beyond its designed max speed to
> achieve higher boost levels for short periods of time..much like the
> 'overboost' mode in UrS4/S6 motors.  The only real drawback to this is
> that if your turbo impeller is near or beyond the limit for being in
> balance, or the shaft is not really true; the shaft will begin flexing
> at elevated speeds (read: beyond spec rpm) with a potential for impeller
> to contact the housing (ouch!).  Ned says we are OK (according to KKK)
> as long as we limit the period of 'overspin' to about 6 seconds.
> He went on to say this wouldn't be an issue except that the K24 has
> a small diameter shaft.  Almost any other turbo you might consider as
> a replacment for the K24 will have a larger shaft diameter.
> -Gene
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