As we all know our N75 valves do limit the performance of our cars, many of you are thinking of purchasing aftermarket N75 valves. I had lots of time spent of buggering my N75 valves as it seems that a perfectly(!) working N75 valve was messing up my power delivery big time, finally my problem got sorted by replacing it to another one.
While examining and learning the operation of the N75 valve, i came to the conclusion that it is possible to do a slight modification on -- let's be more precise, before the N75 valve so it will practically behave as a "race N75" valve, causing the turbo to spool up more quickly and hold boost more firmer/further.
What is the N75 valve?
The N75 valve is connected between the turbo's wastegate and the turbo's high pressure output. When the turbo spools up, the boost it produces will open its own wastegate, preventing it from making any more boost (as a kind of protection). This threshold value is set somewhere at 0.3 bar, so when our turbos produce 0.3 bar it will be adequate to open its own wastegate and stop producing any more boost.
Here comes the N75 valve. When ECU wants more pressure than this 0.3 bar, it wents (bleeds) some boost from the turbos wastegate using the N75 valve, so the turbo will produce the required amounts of boost. When the N75 is bad (not wenting boost from the wastegate) or set up wrongly (wents just a few air), the boost level will be a lot lower than requested.
Here comes the trick.
Since the wastegate is air operated by the N75, we may slow down the operation (opening/closing) of the wastegate (which will result in faster boost build up and slower boost release) by just simply restricting the air going into the N75. Before you would ask; "should we do that?! won't it hurt the engine?!", the N75 ALREADY has got a restriction in it, we just gotta do some fine tuning. As you also can see on your own engines, the piping going to/from the N75 has got around 6-8mm inside diameter, BUT the actual diameter is not bigger than 2 mm where air can enter into the stock N75. Since you cant do anything inside the N75 (and also to keep it stock) a restrictor should be put anywhere into the piping between the N75 and high pressure part from the turbo (it's the metal pipe going to the IC on 20VTs, from where N75 gets the boost to operate the wastegate).
What is a restrictor?
Anything which wont let through air at larger diameter than lets say 1mm-1.5mm (stock restriction is ~2mm). A 3-4cm long aluminum rod (~6mm diameter) with a 1mm hole drilled thru its middle would do the trick.
I have not tried this myself yet, but theoretically it will work. Do not misunderstand, I am not encouraging anybody to try this, as an unskilled individual may actually damage his engine by introducing metal filing into the combustion chambers (from the restrictor), but it is a very low budget modification which would cause noticable increase in driveablilty and power. As a side effect, it also may eliminate surging.
What do you think about that?
While examining and learning the operation of the N75 valve, i came to the conclusion that it is possible to do a slight modification on -- let's be more precise, before the N75 valve so it will practically behave as a "race N75" valve, causing the turbo to spool up more quickly and hold boost more firmer/further.
What is the N75 valve?
The N75 valve is connected between the turbo's wastegate and the turbo's high pressure output. When the turbo spools up, the boost it produces will open its own wastegate, preventing it from making any more boost (as a kind of protection). This threshold value is set somewhere at 0.3 bar, so when our turbos produce 0.3 bar it will be adequate to open its own wastegate and stop producing any more boost.
Here comes the N75 valve. When ECU wants more pressure than this 0.3 bar, it wents (bleeds) some boost from the turbos wastegate using the N75 valve, so the turbo will produce the required amounts of boost. When the N75 is bad (not wenting boost from the wastegate) or set up wrongly (wents just a few air), the boost level will be a lot lower than requested.
Here comes the trick.
Since the wastegate is air operated by the N75, we may slow down the operation (opening/closing) of the wastegate (which will result in faster boost build up and slower boost release) by just simply restricting the air going into the N75. Before you would ask; "should we do that?! won't it hurt the engine?!", the N75 ALREADY has got a restriction in it, we just gotta do some fine tuning. As you also can see on your own engines, the piping going to/from the N75 has got around 6-8mm inside diameter, BUT the actual diameter is not bigger than 2 mm where air can enter into the stock N75. Since you cant do anything inside the N75 (and also to keep it stock) a restrictor should be put anywhere into the piping between the N75 and high pressure part from the turbo (it's the metal pipe going to the IC on 20VTs, from where N75 gets the boost to operate the wastegate).
What is a restrictor?
Anything which wont let through air at larger diameter than lets say 1mm-1.5mm (stock restriction is ~2mm). A 3-4cm long aluminum rod (~6mm diameter) with a 1mm hole drilled thru its middle would do the trick.
I have not tried this myself yet, but theoretically it will work. Do not misunderstand, I am not encouraging anybody to try this, as an unskilled individual may actually damage his engine by introducing metal filing into the combustion chambers (from the restrictor), but it is a very low budget modification which would cause noticable increase in driveablilty and power. As a side effect, it also may eliminate surging.
What do you think about that?
. Will try to construct a 1mm restrictor as i'll get some sparetime.
any one got any more mods i can try?
