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With my experiences to date, i'm starting to think that we are approaching the flow limit of the turbo, intercooler or both. As i understand the system, turbo pressure, is measured at or near the manifold and is therefore relative to the pressure on the other side of the manifold. Ergo, it takes a much greater flow to achieve 15psi at say 5500rpm than 3000rpm as the engine is expending greater amounts of air. I base these suppositions on my following experiences.
1. when i was first testing my new manual BPC unit i NEVER hit the fuel cut off above 4500 rpm in any gear with the thing completely dialed in. only later did i discover that max boost was down lower and had to dial out 30-50% to prevent the fuel cut at 3000rpm.
2. in 5th gear, i can sustain 25-35% into the red indefinitely (well i haven't gotten above around 3300rpm while watching my boost gauge, for some reason ;) at same speeds in 4th (around 4200) we're looking at 10-15% or so into the red and in 3rd probably barely into red, trickling into yellow as redline approaches.
so it seems like the limitation may be flow rate of the system. If it was the intercooler then:Dean, you should have had somewhat higher WOT high rpm pressures with your manifold tap, as the pressure drop increases as the intercooler flow rate is approached. If it's the turbo, then you shouldn't see very much difference relative to the turbo tap. I don't know how your new tap will work.
However, it is most likely a combination of the intercooler and turbo (makes sense that the Viggen gets upgrades in both departments). Additionally we can’t rule out engine restrictions (cylinder head and valves) which are also different on the viggen.
this is where we need input from ABBOTTized ECU owners (or perhaps Abbott themselves) and anyone else who can contribute...
i'd like to know what types of pressure readings do you Abbottized guys get at the above stated rpm's at WOT (today was 65 degrees) and i was on mostly level terrain. mods are also a factor and i currently have saab sport exhaust, k&n air filter and a modified air box) we'll see how turbo silencer and perhaps transition casting affect things after this weekend.
anyone else with any input please chime in.
chris
'94 900SET 85k
'87 900 turbo -RIP
, Sat, 21 Apr 2001 02:33:04
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