K24 vs RS2 Spool-up. RS2 Results is now turbo comparison...
auditude at cox.net
auditude at cox.net
Mon Aug 5 18:48:20 EDT 2002
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.
That's what I thought I'd remembered. So Gary's post could've been (not "trying" to pick at nits, I
> 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
I think the shrapnelknob mod is easier on the WG diaphragm than a big spring, since pressure is
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