Hank Scorpio
03-22-2003, 11:31 PM
Ok, heres another installment.
On 240 turbo's there is no sort of pressure relief like later volvo turbo's. This is important because when you close the throttle at high boost levels, that pressurized is stopped by the Throttle Body (TB) and has no where to go but out through the turbo, the wrong way. This is extremely hard on the turbo and causes the turbo to spool longer after each shift.
So, theres really two routes to go.
The first is a Compressor Bypass Valve (CBV) which is what most OE turbo systems use. This works by having an open valve that recirculates pressurized air back into the air box under normal cruising. It closes under WOT and then re-opens when you lift of the throttle venting the pressurized air, quietly, back into the air box.
The other style is called a Blow Off Valve (BOV). These are valves that are placed on the piping between the intercooler and TB. It has a piston that stays closed under all conditions except with high vaccuam levels created by getting off the throttle under load. This pulls the piston back and vents the pressurized air to the atmosphere. Its loud, but sounds cool.
Concerns:
Some people have said that BOV's because they don't vent the air back to the airbox that it basicly "loses" that pressurized air, causing a lean condition. This would be a problem if the BOV was open all the time like a CBV however, it is not and has worked flawlessly on my 242ti.
I however, wouldn't use one on an auto, to me it wouldn't be worth the expense to only have it work when you let of the gas once, vs on every shift for an auto. That being said, I know they work just fine on an auto too.
Heres a couple pictures of mine, everyone enjoy!
http://www.pbase.com/image/11088063.jpg
http://www.pbase.com/image/11088102.jpg
On 240 turbo's there is no sort of pressure relief like later volvo turbo's. This is important because when you close the throttle at high boost levels, that pressurized is stopped by the Throttle Body (TB) and has no where to go but out through the turbo, the wrong way. This is extremely hard on the turbo and causes the turbo to spool longer after each shift.
So, theres really two routes to go.
The first is a Compressor Bypass Valve (CBV) which is what most OE turbo systems use. This works by having an open valve that recirculates pressurized air back into the air box under normal cruising. It closes under WOT and then re-opens when you lift of the throttle venting the pressurized air, quietly, back into the air box.
The other style is called a Blow Off Valve (BOV). These are valves that are placed on the piping between the intercooler and TB. It has a piston that stays closed under all conditions except with high vaccuam levels created by getting off the throttle under load. This pulls the piston back and vents the pressurized air to the atmosphere. Its loud, but sounds cool.
Concerns:
Some people have said that BOV's because they don't vent the air back to the airbox that it basicly "loses" that pressurized air, causing a lean condition. This would be a problem if the BOV was open all the time like a CBV however, it is not and has worked flawlessly on my 242ti.
I however, wouldn't use one on an auto, to me it wouldn't be worth the expense to only have it work when you let of the gas once, vs on every shift for an auto. That being said, I know they work just fine on an auto too.
Heres a couple pictures of mine, everyone enjoy!
http://www.pbase.com/image/11088063.jpg
http://www.pbase.com/image/11088102.jpg