To all my Turbo-Buick brothers: I'm seeking some turbo knowledge as I admittedly have none. My everyday car - a 2003 MazdaSpeed Protege (yes it's an import - sorry!) has a factory Calloway turbocharged 2.0 liter, 4 cylinder engine. I was considering changing my internal blow off valve to an external blow off, for no other reason than to hear the noise when I shift. Yeah, I'm strange like that sometimes... I have been told that I can not do this because my car has the MAF, and the external blow off would create a hesitation between shifts and off the line. I understand the workings of the MAF and the purpose/concept of the blow off, but as far as creating hesitations etc. I have no way to know if this is correct advice. Anyone have a take on this? Thanks, Matt
Matt, I think if you go over to www.turbobuick.com you will probably have a better chance and getting some good responses.
What you have heard is correct. Switching to an external blow-off can cause the problems you describe. Here's why (Sorry if this explains bits of the process that you already know): Air comes into the MAF and gets counted so the engine will know how much fuel to add to the intake stream. That air gets sucked through the turbo, compressed, and sent through the intake tract towards the throttle body at high velocity to get let into the engine. When you shift, the throttle plate closes momentarily, so you end up with a fast moving wave of high pressure air with nowhere to go. In stock Grand Nationals, and other cars without a blow-off valve, this wave is just left to even out on its own. So, it makes its way back to the turbo and actually blows itself backwards into the turbo, slowing it down and stressing the heck out of the bearings and shaft. (This can easily break small turbos!) What the blowoff does is detect when such a wave of high pressure air is coming, and divert the air to save the turbo from all of that extra stress. So, back to your question, where is the best place to divert the air? Well, you can vent it to the atmosphere, or you can divert it back into the intake stream ahead of the turbo. As you know, venting it to the atmosphere sounds cool, but it doesn't really make good sense from a performance standpoint. Like I said, the MAF counted the air before it came through the turbo to know how much fuel to add. So, if you just vent that air away after it has been counted, the engine won't know it and the ECU will still add fuel like all of the air is there. So, it dumps a bunch of gas into the intake stream to use a bunch of air that isn't really there, and the car bogs down from running SO rich. Net result is that the car bogs down between every shift from the extra gas, the turbo doesn't spool up nearly as fast between shifts, and your smooth running motor starts to run like a dog everytime you let off the gas under boost. Your emissions will also go through the roof each time you shift because of all of that unburned gas, so if you live in a state where they do cruising and accelleration emissions testing, venting your blowoff could make your car fail. Unless you are a fuel-tuning prodigy you would be better off getting a speaker that sounds like a dumping blow-off valve in a MAF-equipped car. On a car with a speed density system instead of a MAF, venting to the atmosphere isn't nearly as much of an issue. - Freed
Thanks for your info Freed. I never really understood the logistics behind it, but everything you say makes sense. I guess I'll just have to save that 100 bucks and put it in the Buick where I suppose it rightfully belongs! :TU:
I had a turbo chrysler for a little while it had an atmosphere vented blow off on it... it went a little rich between shifts but it was also a speed density system. I switched an 04 vw 1.8t over to an atmosphere valve th other day it seems to run ok and its mass air car... you can try it by pulling your stock recirc valve out of the air inlet tube plugging the hole and seeing how it runs blowing off to the atmosphere if it gives you trouble or sets an ses light you can always put it back... it just sounds cooler popping off so you can hear it hth
My take is that you have too much free time on your hands. Why don't you do something constructive instead of wasting your time on stuff like this. Build that 455 thats sitting in your garage.
So why not have it re-routed to right behind the MAF? While there would be a delay before the amount of air measured would be returned to the system, it would still get there which might fix or lessen the rich condition. There are multiple MAF cars with turbos and have BOVs.
