[ku4zs]

Got a buddy of mine that is a car guy (I'm a computer guy and nuclear engineer), that says you should change the blow-off valve and down pipe on turbos to get more horsepower. Anyone know about that or plan on it? He said it would likely void the warranty.

 

[lasstss]

Bov

The blow off doesent add horsepower. What it does is keep you from loosing power between shifts by preventing boost air from backfeeding the T/C impeller, slowing it down. It keeps the T/C spinning at high RPM, hence, maintained power. Much less of an issue with an automatic as you can keep your foot on the floor! Turbo cars love automatics!!:thumbs:

 

[ilber]

hey there.
downpipe is the part of exhaust system. so say changing downpipe and leaving cat back restricted would not make sence. Of course having supporting mods would make sence....more air in, more air out, however being a turbo u don't want to put a simply huge downpipe.... backpressure (to a reasonable degree) is useful, because that what would help to spool up the turbo. Hence I would say running out first day and getting Down pipe would be foolish.
I view BOV as estatic/longitivity. As it mentioned manual tranny has a lot better use for BOV simply because u got to shift and let the skinny pedal up...usually on a turbo car. especially the one that running a bit of boost you would here kinda turkey cal sound... basically when you would be under the boost a rapid lift of the accelerator- you have compressed air, but butterfly plate in TB is shot, so air needs to go somewhere. It will try to force back to the turbo but all it would do is slow the turbine, extra loads on the bearings (like 90k rpm or something like that is the trbine speed). this "surge" can be limited by Blow off. basically a valve in the air plumming that controlled by the intake manifold pressure....result u get a load wooosh, whisle or some other noise of the compressed escaping air. there are bypass valves, which basically will route the surge to the intake of the turbine vs to the atmosphere so no loud woosh...
hope this helps
ilber<-former rocket engineer, now just industrial one

 

[TOY4TWO]

just don't vent the blow off valve to the atmosphere, it will mess up the ECU's air metering, it won't know you let that air escape and your engine will run richer so you could LOSE power.

I also don't think any of the blow off valves on the market will fit on the Redline, because the stock valve is built into the turbo housing.

 

[CrackerJackToy]

This may be true, but can easily be fixed with a chipped ECU or some sort of standalone.

First of all, turbo's hate back pressure. 3" downpipe all the way down through a 3" exhaust will free up some horsepower. Yet, the statment is true, with a smaller downpipe, you WILL be able to spool faster, but its not going to be a HUGE difference. I rather have the extra power & since I hear 2007 models are the start of OBD3, there is going to be some serious restrictions. I really want to hold out for the Redline if insurance isn't going to kill me, but I was hoping to do 3" downpipe (perhaps 2.5" if there is a complication with a 3") & a full 3" back. Intake, better front mount i/c, all hard piping, bov, manual boost controller & then get it tuned. I was hoping for 300 WHP knowing that GM usually under-rates the horsepower of there newer cars. (Ex. The Cobalt they gave 205 I think?.. A guy i know just dynoed his bone stock at 220 to the wheels.) Anywho...

 

[Nimisys]

a lot of misconceptions here

first off all forced induction vehicles for the last 20 years have had a blow-off/bypass system. it is neccessary to increase compressor life. what happens when you are in boost and slam the throttle plate closed is that you get a backwards pressure spike that slams back against the compressor blades. this is called compressor surge. now the approach most automotive companies employ is the bypass/hooter valve. what this does is when the throttle is closed, or now when less boost is needed they open a valve allowing the compressed charged air to recirculate back into the turbo' s suction pipe / intake duct. this prevents compressor surge, but also allows the compressor to remain spooled. when the throttle is reopened, or more boost pressure is needed, the bypass valve is closed and charge air continues into the throttle body like normal. a blow-off valve for some stupid reason is favored by the tuner crowd, mainly for the noise they make, as it indicates to other cars you have forced induction. the down side is that it wastes the charged air already built up. instead of re-circulating it, they vent it to the atmosphere.

second i believe i read somewhere on gm's tech info that the redline will already come equipped with a 3" exhast, however because it has a close coupled cat, there is no downpipe per se. the cat functions as the downpipe, directly mating to the turbo's exhast output. considering who did the forced induction work (saab) and given their past experince (twenty plus years) and the current implementations on the market from them, the exhast from the factory should be very good indeed.

finally the OBDIII spec has not been finished yet, but MY2007 will require a CAN bus for all Generic Mode OBDII implementations by all manufactors, which could be considered OBD 2.5 but has been refered to, incorrectly, as OBDIII. the main sticking point for OBDIII is that they want a complete telematics system implementation required for all vehicles that would report to federal officials of any emiisions related or reducing effiency failures, who would then send you a smog like notice requireing you to have it fixed.

 

[Mattr762]

hey there.
however being a turbo u don't want to put a simply huge downpipe.... backpressure (to a reasonable degree) is useful, because that what would help to spool up the turbo.

You might want to do some more research on turbo's before you spread untrue information. What makes the turbo spool up is on the exhaust inlet side NOT the downpipe (exhaust outlet side). The best exhaust for a turbo car is NO exhaust at all.

 

[snaponbob]

As a Snap-On dealer I have been selling diagnostics tools for 17 years. THERE IS NO OBD lll on the immediate horizon. THERE IS NO OBD 2.5 either. In 2007 ALL vehicles must have CAN (Controlled Area Network) systems. CAN simply is the grouping of all the computers (abs, trans., stability control, body, dashboard, hvac, engine, evap system, etc.) on one network with a main computer controlling all of them. It was part of the OBDll protocal from the beginning. In 2003 it started being used on some highline imports and is federally mandated for 2007. OBDll is so effective it has altered the IM240 requirements in a lot of areas of the country. It is also why we see cars like the Z06 producing 500hp out of an ohv 427, get very good fuel mileage, and go over 195 mph, and a 2 liter Ecotech produce 260 hp. Without the tremendous power of OBDll it would not happen. OBD3 has not even had federal minimum requirements written by the US gov., and until that happens, OBD3 won't happen.

 

[Moparrbust]

I also don't think any of the blow off valves on the market will fit on the Redline, because the stock valve is built into the turbo housing.

Easily fixed. My SRT-4 came with a stock "surge valve" on the turbo and all I did was take it off and bolt on a block off plate. I then installed my hard pipes and Greddy BOV; venting to the atmosphere, with no issues and no temporary running rich problems.

 

[theirishgonzo]

i thought the bov also controoled the max presure the turbo will go to befor it starts and also a better bov closes and poens faster for better and more controlled bost.

i drive a turbo car it runs at 12psi it is a 92 the 93-94 was set at 14 psi and i read the stock plastic pipeing and clamps would be good up to 16 psi
i have seen dinos of the stealth with bov set to 16 psi and new plugs and wires at 400 whp

now some pther options will be for adding a better inter cooler, intake i red that the rl bov is computer controlde

 

[Inwo]

i thought the bov also controoled the max presure the turbo will go to befor it starts and also a better bov closes and poens faster for better and more controlled bost.

i drive a turbo car it runs at 12psi it is a 92 the 93-94 was set at 14 psi and i read the stock plastic pipeing and clamps would be good up to 16 psi
i have seen dinos of the stealth with bov set to 16 psi and new plugs and wires at 400 whp

You're thinking of a Wastegate or maybe even just the wastegate actuator. That is what ultimately controls how much boost you can hold on the car. The wastegate actuator modulates the wastegate to stay closed and keep the exhaust flowing through the turbine and then releases to bypass some of the exhaust gasses when the pressure desired is reached (actually it starts to release much earlier usually but that's another discussion)

What a BOV does is release the excess pressure before it hits the turbo so that you don't get compressor surge. It's necessary in manual transmission cars due to the constant release of the throttle to shift. It's not so much necessary in automatic transmission cars; the Grand National didn't even have one if I recall.

Most stock BOVs are good enough provided they don't leak like the stock 95-99 plastic piece of garbage on the DSMs. When you increase the boost most stock BOVs start to leak beyond a certain point so that's when you want to buy an aftermarket BOV.

 

[articfury]

a lot of misconceptions here

for some stupid reason is favored by the tuner crowd...the down side is that it wastes the charged air already built up. instead of re-circulating it, they vent it to the atmosphere.

Actually, the need to recirculate is because of the air metering system design. If you measure the air after the turbo, or use MAP, then there is no need to recirc the air. When manifold pressure is no longer positive and the bypass valve is opened, the compressed air is forced into the intake tract. There isn't a benefit of pushing compressed air into an unsealed tube. The popularity of vent to atmosphere (VTA) BOV is related to the fact that the Hondas that helped push the import performance market use a MAP sensor and don't need to recirc the air. Additionally, WRC cars vent the BOV and wastegate to the atmosphere. Race cars have always been inspirational to hot rodders and modifiers/tuners. I know I wouldn't mind if my Evo sounded like a WRC car when driven spiritedly

second i believe i read somewhere on gm's tech info that the redline will already come equipped with a 3"...there is no downpipe per se...the exhast from the factory should be very good indeed.

There are couple of points here.

1) Due to the location and integration of the catalytic converter, a street-legal downpipe will be tricky. (I use downpipe in the typical sense of the pipe that comes off the turbo, this one just happens to have a cat integrated into it.) The stock piece does appear to be fairly large in diameter. The question of how restrictive is the stock catalytic will determine the benefit or replacing it. I am not refering to off-road parts, because obviously a downpipe without a cat would be less restrictive.

2) The rest of the exhaust system, while it may have a fairly large diameter, has quite a few points that look to be a bit restrictive, the inlet to the muffler for example. See for yourselves

I bet there is quite a bit to gain from a full turbo back exhaust (TBE).

D

 

[Moparrbust]

I plan on making mine a full 3'' turbo back exhaust with no cat(s) or mufflers. The turbo quiets the exhaust enough for me.