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do you really need a blow off valve...

24K views 19 replies 18 participants last post by  97 Widebody 
#1 ·
just for fun lets discuss these blow off valves..

Now i know we have all seen them both ways, with and with out on supras. I dont really care about other cars but have noticed some diesel trucks dont have them either.

Anyway like the topc say... Do you really need one? and if you do how come the ones without blow off valves havent had problems?
 
#2 ·
I would say the are a neccesary evil if you want to prolong the life of your turbo. The concept behind the blow off valve is that when your intercooler piping is presurized and you close your throttle plate, the pressure will not just stay in the piping, it will end up exiting through your turbine blades, causing a reverse flow (in theory). Now your turbine blades will still be spinning in the normal direction but suddenly you have a 30psi back flow back through the blades, it is going to play havoc on your center section. Now this is in theory and maybe in real life, there is no harm, but I would rather spend 150 on a blow off valve, than 1800 on a turbo.
 
#4 ·
On a diesel truck and also in many European cars; a Diverter Valve can redirect that air with a vacuum line back into the intake or vented to the atmosphere as well. With that said if you car does not need a recirculating system because of it's MAF and ECU I think it's a safe bet to get a BOV only if your car is significantly modified to be looking into those things. So, in that diesel truck when the BOV vents to the atmosphere your ECU reads the MAF values as being out of spec; it will cause the truck to run rich as the ECU is measuring the flow of air that is no longer in the system. If the diesel truck is not making added power then the effect of venting to the atmosphere is useless.
 
#6 ·
That they i understood how they worked as well. We have a friend that has some freaking fast buicks and typhoons. He said its not a big deal and he doesent run them. Granted his are just play toys but he said from the factory GM didnt use on.
 
#8 ·
Yes. The momentum of the airflow when fuel is not being sprayed would be when it could function like a gasoline BOV engine. When you do run into a BOV on these trucks it is used to eliminate surge during heavy towing. Is the elaboration coming from what I said? It is true that most factory turbodiesels will not need it but I was trying to find a good general example.
 
#20 ·
I've been testing stock twins on a Supra I currently have running 20psi with no BOV and so far no problems at all. In fact these OEM turbos seem to be in better shape than many I've seen with a lot more miles. I was about to pull them for a single so I figured I'd see how well they work without.
 
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