K24 vs RS2 Spool-up. RS2 Results is now turbo comparison...

[auditude at cox.net]

On 5 Aug 2002 at 19:25, Robert Myers wrote:
>
> At 06:42 PM 8/5/02, auditude at cox.net wrote:
> >
> >I thought a Schrapnelknobben was different than a simple bleed, in that it
> >applied regulated boost pressure to the upper WG chamber.
> >
> >Is a Schrapnelknobben (the original Timmerman mod) a bleed, or an upper WG
> >mod, or either?
>
> You are exactly correct.  The schrapnelknob consists of an inexpensive
> surplus gas pressure regulator which admits a specific (but adjustable)
> maximum pressure into the top of the wastegate.  The pressure is derived by
> tapping into the pressurized intake system.  This acts as if the wastegate
> spring is stiffer actually than it is.  Use of the schrapnelknob by itself
> in the older systems for which it was used will lead to the dreaded
> overboost cutout.  Paul Timmerman also devised a resistor network
> arrangement which essentially told the ECU a lie.  The lie was that the
> pressure is lower than it actually is.  This allowed greatly increased
> boost levels (such as 18 psig vs. 4 or 5 psig) and significantly increased
> performance as a result.  It also could lead to overly lean mixtures at
> elevated boost levels which could result in overly high combustion
> temperatures and burnt valves and pistons.
>
> BTW, the lie prevented the in-dash boost gauge from indicating true boost
> pressure since the pressure transducer output was electrically clamped at a
> lower than actual value and the gauge displayed this artificial value
> rather than the true one.
>
> Essentially, the schrapnelknob plus the resistor network provided the
> boost/performance gains of a modern chip mod but did so on the cheap and
> without some of the fuel mixture safeguards which are more desirable.
>
> I used Paul's schrapnelknob along with an alternative zener/resistor mod on
> two '89 200 tq's for over 60K miles each.  I saw no indication of damage
> from lean mixtures.  YMMV.  BTW, it was a FUN ride.  :-)  AFAIK, one of
> these cars is still being run by another list member.  I have no idea of
> the current mileage or if these mods are still in effect.

Thanks Robert,

That's what I thought I'd remembered.  So Gary's post could've been (not "trying" to pick at nits, I
promise!):

> Nobody does a pure electronic solution that I know of (i.e., chip and
> transducer, which probably isn't feasible anyway), so I'll either do
> the resistor fakey + big spring and/or schrapnel knob (resistor changes the
> resistance the computer sees, making it think the boost is lower than
> it is), bleeder (device that reduces the air pressure the WG/computer
> sees), or a combo of all three.

Actually, can a bleeder reduce the pressure the ECU sees?  I guess it could.  Would you then need two
bleeders, one for the WG and one for the ECU?  Curious about that now.  I mean, a lower WG chamber
bleed isn't going to bleed off enough pressure so that the ECU will see the lesser pressure.

Damn that looks like another nit, sorry.  Just making sure I understand.  Well, if decisions are being and
all...

I think the shrapnelknob mod is easier on the WG diaphragm than a big spring, since pressure is
equalized.

Ken