28 psi (2bar) boost on RS2'd 3b?

[PeterS]

Trying to help out a friend who does not post here...
he is running MTM 3b RS2 code on his 1983 Turbo Quattro Coupe (UrQ)

As he states, he's very concerned about potential spark hop running the distributor.
Any one running this level of boost on a 3B?

Any recommendations on reducing the boost to a "safe" 22psi?
(thinking adjustable V Map instead of Bosch 3 bar Transducer in the ECU

I'll forward the responses.
Thank you

-Peter




From: "Mike Sylvester" <mike@urq20v.com>
Date: May 18, 2010 12:44:26 PM EDT
To: "200q20v list" <200q20v@audifans.com>
Subject: 28psi

I've posted this question on the urq list, but this list would probably
have some additional experience.

I have an RS2'ed 3B in my '83 urquattro

RS2 turbo
RS2 exhaust manifold (extrude honed)
Head is extrude honed.
RS2 exhaust cam
RS2 injectors
RS2 MAF
Pauter rods
Adjustable fuel pressure regulator
New distributor with metal gear and correct small tip rotor
Porsche 951 intercooler

Can you safely run 28psi on a 3B?

I'm sure the hardware is good for it, but I'm concerned about the spark
jumping over to an adjacent cylinder in the distributor cap under high
boost conditions.

Is anyone doing it and keeping the distributor?

Mike

https://www.urq20v.com

[aronmatic2]

are you serious? 2bars with rs2 turbo?

[Jamo]

are you serious? 2bars with rs2 turbo?

Yep been done before with Sal_S2 and SteveH car, gives approx 400 bhp

MRC do a high boost chip set that goes to 1.9bar on the RS2 turbo

Very aggressive setup and fast too!

[PeterS]

Yep been done before with Sal_S2 and SteveH car, gives approx 400 bhp

MRC do a high boost chip set that goes to 1.9bar on the RS2 turbo

Very aggressive setup and fast too!

Mike describes the acceleration as "violent".
28 psi measured on his manual boost gauge.

I haven't had a ride yet in his Urq, I have had a ride in Javad's 80tq, so it will be interesting to compare the seat of the pants feeling of "violent" :-)

Jamo - Sal and SteveH's car - 3b or ABY engines?

Again, the issue here is spark hop with the dizzy, any experience on how to potentially dial down the boost?

[aronmatic2]

Yep been done before with Sal_S2 and SteveH car, gives approx 400 bhp

MRC do a high boost chip set that goes to 1.9bar on the RS2 turbo

Very aggressive setup and fast too!

shame on me.

[Jamo]

Mike describes the acceleration as "violent".
28 psi measured on his manual boost gauge.

I haven't had a ride yet in his Urq, I have had a ride in Javad's 80tq, so it will be interesting to compare the seat of the pants feeling of "violent" :-)

Jamo - Sal and SteveH's car - 3b or ABY engines?

Again, the issue here is spark hop with the dizzy, any experience on how to potentially dial down the boost?

Boost is ecu controlled, if the ecu is requesting this boost then there's little you can do to stop it getting there. You could put in a weaker WG spring I suppose or run of purely mechanical boost.

Sals was ABY

SteveH was 3B, it ended with the rods bending as they were stock

I'm sure S2_Bo is running 1.9bar on his 3b setup with an RS2 turbo

[PeterS]

Mike has carrillo rods so at least they are stronger than stock...

Understand that the boost is controlled by the ECU..
Wondering if switching from the Bosch 3 bar to the adjustable VMAP would essentially dial back the boost.

[porkkis]

You can fool the ambient pressure reading to lower the boost if the functionality has not been disabled in the boost sw. This is also the way factory did this in "trailer mode".
MAP signal adjustment works too of course for limiting, but it may also add some odd part throttle boost behaviour.

I've mapped a 3B with gt71 garrett compressor, 2,2 bar boost between 3500 and 5000 rpm and no spark problems what so ever. This has been running for years now.

[S2central.net]

I've only seen "trailer mode" on the RS2 ECU. I have thought before about using a pot to replace the altitude sensor for some form of manual boost control but never had the time to play with it. Its on the long list of things to explore

I would say if the dissy, rotor arm, coil are in good condition (and correctly aligned) then a 3B should be OK with high boost - especially if uprated rods are fitted. I cannot remember if SteveH 3B suffered a bent rod because of simply huge torque or if sparkhop induced it.

[denniselbows]

i'm sure spark hop results with the combination of high boost and a worn dizzy .if i remember correct the sport quattro,s1 evo 2 and the pikes peak car all ran dizzys and they all had massive power levels

[Jamo]

If your worried about spark hop see this thread by a4kquattro http://www.s2forum.com/forum/showthread.php?t=29457

[20vQC]

well maybe the pauter rods are doing well the job! the weak point of the engine has been solved and now holds a lot of torque and a minor spark hop...in the case he's using the stock 3b one... it's my opinion

[SteveH]

The rods bent in my motor when we got to 2.1 - 2.2Bar! There was no indication of spark hop or missfire.
It was during a mapping session that helped Mik define what was too much for standard rods and the RS2 turbo However it was also a good excuse to rebuild the motor with a set of Carillos

[Rocco]

i was runing in my 3B a software from Hamon Motors for RS2 specs with of course RS2 turbo and YES 2.0bar in 4th and 5th gear ,without any problems and the AFR were between 11´3 / 11´8 with RS2 injectors and 7A FPR in WOT.

and 1´8bar in 3rd gear....

[EspenW]

Worn dizzy gear will be a major culprit when it comes to spark hop. If the gear is still plastic, replace it with a metal one ASAP.

Doubling the boost on an engine will increase the peak cylinder pressure by only 20%, so going from say 1.1 bar to 2.2 bar increases the peak load by only 20%, far less than the loading from even mild pinging/knock. However, turning up the boost increases heat and thus the chance of knock, exhaust reversion, preignition,etc and this can put the engine over its limits.
The average cylinder pressure will increase by more than 20% when doubling the boost, but it is the peak value that determines the load on components.

Timing is a lot harsher, going from say, 10 degrees to 30 degrees will triple the peak cylinder pressure.