vx211

Had a GIAC chip done a few weeks back but stayed with stock bpv. The stock bpv sounded like it was working (that nice whistel when shifting) BUT installed a TT bpv today and their was a VERY noticable differnce in lag when returning to max boost from a shift. Hope this helps anyone running a chip with stock bpv!

turbosyl 8E

cool... Did you install the TT bpv by yourself???

Peppe1.8T

Where did you buy the TT bpv?

ben gt/cs

<ul><li><a href="http://greedspeed.com">Greedspeed</a></li></ul>

quattro-head

Hi,

I have the '02 1.8T 5-speed. Is that what you chipped? If so, what kind of power are you now getting, and can you explain what the tt bpv thing is and what it does and cost?

thanks,

quattro-head

B_Chicago

When you let off the gas, your throttle plate closes. However, your turbo is still sending air towards your engine. The pressure "bounces" off of your closed throttle plate and back towards the turbine blades in the turbo. With nothing there to stop it, the result is the turbine blades slowing down. This might not be good for the longevity of the turbo, but the main concern is that when you shift and get back on the gas, you have turbo lag as the turbine blades come back up to speed. You deal with this by installing one of two things in the space between the turbo and the throttle - a blow-off valve or a bypass valve. A blow-off valve is nothing more than a valve that is forced open when the pressure buildup reaches a certain level and allows excess air to vent into the atmosphere. A bypass valve works the same way except the air is directed back into the engine air intake system, but before the turbo (so it can be re-used). Both types of valves work well to prevent large pressure drops and wear on the turbo. The advantage of a blow-off valve is that it is louder and sounds much cooler, while the advantage of a bypass valve is that it allows air to be reused, resulting in a quicker spool-up when you get back on the gas.

The TT bypass valve is designed for higher boost, so most likely the difference is two-fold: The amount of pressure required to open the valve is better suited to a high-boost application, and the size of the valve is likely larger to allow for more air to be vented back into the intake stream.

a4elias

Great description -- thanks much!
Also, if I got it right, it looks like BPV is not such a big deal for CVT, since there is no shifting and consequently no sudden boost drops during acceleration. So if A4 CVT is chipped, it may stay with stock BPV (if it has one). Is it true?
TIA

B_Chicago

Well, you don't <i>have</i> to change the BPV when you chip a manual A4, you just get a little better performance with it. So yes, you could stay with the stock valve with your CVT. Because of the lack of true shifts, performance gains with the TT valve are likely to be slim to none for pure acceleration tests, but in real-world driving you may be able to notice a difference. If you have the extra cash laying around go for it, but if you don't then don't worry about it.