Boost Pressure Dropping

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Retoxified

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Hey guys, I tried searching for this problem but I couldn't find any topics about it. I have noticed that after tuning certain cars (the audi le mans quattro and the 3k GT VR4) the turbos react strangely. The closer I bring the car to redline the less boost pressure I have. Is this because of me or is this a bug? Perhaps this is supposed to happen? If you have had this problem, what did you do to fix it? Thanks in advance!
 
Retoxified
Hey guys, I tried searching for this problem but I couldn't find any topics about it. I have noticed that after tuning certain cars (the audi le mans quattro and the 3k GT VR4) the turbos react strangely. The closer I bring the car to redline the less boost pressure I have. Is this because of me or is this a bug? Perhaps this is supposed to happen? If you have had this problem, what did you do to fix it? Thanks in advance!
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Most cars will hit peak boost and then drop off to a stable pressure,same happens in real life.
 
Holdenhsvgtsr
Most cars will hit peak boost and then drop off to a stable pressure,same happens in real life.
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That or Gran Turismo decided to include Blow Off Valve and not tell anyone :sly:

There's not much you can do in terms of tuning boost in GT. If you wanna stay within that boost range where its highest you could probably throttle back a little to stay inside it.
 
bergauk
That or Gran Turismo decided to include Blow Off Valve and not tell anyone :sly:
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They did with some cars.....boost up the RX7 and take off the throttle at around 6500rpm and you hear a decent "WHOOSH", and the same happens on gearchanges. :sly:
 
mafia_boy
They did with some cars.....boost up the RX7 and take off the throttle at around 6500rpm and you hear a decent "WHOOSH", and the same happens on gear changes. :sly:
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Actually that happens with turbos. The way it is structured makes it sound whoosh when you change gear and when you let off the accelerator. Same happens in real life. All car's with turbos do it. It has nothing to do with blow off valves.
 
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The short answer is: GT4 is not a true to life simulator.

The explanation is:
A factory car dropping boost pressure only happens in cars with turbochargers that are too small. The boost pressure starts to drop when a turbo simply cannot flow any more air, and the pressure starts to drop as engine RPM's increase. This happened to my Nissan 300zx Z31 with a boost controller, but it does not happen to the factory car. Stock boost pressure is 6.8psi. With a boost controller installed on the factory turbocharger, the turbo hits 14psi at 3200rpm and drops off to 10psi by 6000rpm. Removing the exhaust completely gave me 12psi at 6000rpm, and fitting a bigger turbocharger gave me a constant 14psi from 4000rpm till rev limiter. (at a guess, the turbo I fitted would be roughly equivalent to stage 2 in GT4, but real turbos don't have "stages")

Fitting a blow off valve, diverter valve or pop-off valve (all are totally different components) will not make boost drop off at a certain rpm, but they can limit the boost to a certain PSI. My 300zx had a pop-off valve that limits boost pressure to 8psi to avoid engine damage. I had to remove this when installing the boost controller.

I have noticed the boost drop-off in GT4 happens in the Golf V GTi and the Australian Ford Falcon Typhoon 4L i6 Turbo, and I can definitely say boost pressure does not drop off in a real Falcon turbo.


The boost pressure dropping off on standard cars in GT4 is somewhat realistic, but it should not drop to 0, and it should not drop at all on any car fitted with an upgraded turbocharger.

No, I'm not a mechanic. A mechanic wouldn't know most of this stuff anyway.
I used to work in a turbocharger shop.
 
Mitchd03
A factory car dropping boost pressure only happens in cars with turbochargers that are too small.
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Hmm not sure on that its because its too small my friends evo has a GT35R and that peaks at 2.3 bar but then holds 2.0-2.1 bar,doubt its because the turbo is too small its almost the same size as the block.
 
The 3000gt with over 800 hp mean that there’s near 80lb/min of mass flow rate through the engine…..80lb/min is alot,even divide by 2 (40lb/min each turbo) its big for a 3liters engine..you can’t achieve those numbers with small turbo..a too small turbo will run out of the compressor map(efficiency islands)and go in the choke zone,wheel speed increase dramatically,while compressor efficiency plunges.This means high outlet air temperatures(more heat=more pressure and more pressure=more heat)Higher temperature means lower air density=less horsepower…But no pressure drop!!!!!!! I really dont know why it falls to zero:P


Holdenhsvgtsr what you said is called Boost spike ..Take a look at dsmtuners.com (boost spike vs boost creep) for more informations:tup:…..sorry for my english
 

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