I'm currently buying soem aftermarket products for my car....even though the bypass valves aren't really a power inducing prodcut for my car.... I'm jsut wondering what are the pros and cons for dump valves and the infamious noisy Blor off valves...... I really do like the sound a "psssssshhhh" type BOV...but ive heard alot of red flags on this matter.....

 

wow.. its good to have such well informed people in a forum like this... makes me feel so much more secure once i get my Evo... watever

 

blow off valves don't really add performance. there is nothing wrong with them. but they can make your engine stall because all of the air that is released into the atmosphere was read by the MAS. well..i dunno if evo's have MAS's...maybe a MAP?? whatever...anyway this air that was read is all of a sudden gone and your computer is like WTF? where did the air go. so thats why a bypass valve is better in a sence. but i don't think blow off valves are bad at all.

dump valves as in an external wastegate? like the dump tube...well...having a bigger dump tube and wastegate is necessary for controlling boost with a bigger turbo. i think bigger turbo...bigger wastegate needed? well there are 2 types

1.atmosphereic - exhaust gases just blown right out of the header into the atmosphere bypassing the turbo. i don't think race tracks like these.

2. the other is just blown back into the exhaust after it bypasses the turbo.

of the 2 i don't know which is better. i'm guessing atmosphereic if your going to race because it gets rid of the gasses faster.

 

I can't believe someone who is going to own the car and doesn't know would make a sarcastic comment about EVERYONE ELSE being well informed.

I don't know a lot about turbo systems, but I believe venting atmosphere will allow your turbo to spin down faster meaning you're increasing its spool time. Increased spool time means turbo lag. Someone please correct me if I'm wrong.

http://www.howstuffworks.com/turbo.htm
If nothing else it's a start on how turbo systems work. It's easy to understand and fairly detailed. Follow the links afterwards.

 

yes you are correct hobie. a bypass valve helps keep the turbo spooled up so it helps out turbo lag. its not really that noticable tho from what I have expreienced with a 400hp DSM. i think when they guy made it a blow off instead of a bypass valve it spooled 200 rpm later. something like that.

 

From how I looked at the difference between bypass valves and dump valves was exactly the way you saw it.... BOV=more turbo lag.... Dump Valves=help relieve Turbo lag.. My brothers S4 uses forged valves, and i always wondered why he didn't want BOV... bu ti always came up w/ that conjecture.

 

After WRC4ever and I get the cars upgraded we will be able to tell. We both have very similar set up except he has a Blitz SSDD Blow-Off Valve and I will have the stock by-pass. We will both have datalogging ECUs so then we should be able to detect any performance gains.

My feeling is, get it if you like the noise. I don't think there is any performance difference.

If I find something I will let you all know.

Erik

 

Both atmospheric and recirculating dump/blow-off valves do essentially the same thing. The function of the valve is to reduce the pressure spike that results from the sudden closing of the throttle. This spike not only slows the turbo but creates added stress on the turbine. The difference is that one reintroduces the compressed air to the intake the other wastes it to atmosphere.

With an air flow meter an atmospheric valve may create problems as the volume of air getting to the engine differs from that reported to the ECU by the air flow meter. This can result in over and under fuelling depending on the situation. A recirculating valve returns the measured air to the intake and avoids the potential problems.

On the Evo 7 and I presume the 8 the ECU measures the air by monitoring manifold pressure and temperature to derive volume. Air wasted to atmosphere has no effect on fuelling. Under specific conditions it is possible that air can be drawn in through the dump valve. Though this will not normally be a problem some atmospheric valves are fitted with a filter for very dusty conditions.

A potential benefit with atmospheric valves is that the air heated by the turbo is not reheated as with a recirculating valve.

Some respected authorities suggest that a dump valve is a complete waste of time and offers little or no performance benefit and provides little relief from mechanical stress to the turbo.

 

I have to agree with Braf Overall.

<MHO>
My theory is that by the time the pressure raises far enough to open the valve of either style of blow off valve it has already slowed the turbo. The other assumption is that the stock BOV is inadequate. People claim to feel the difference but I would still like to see a datalogded run before and after.

Testing transient responses like these is very difficult. Either way the performance benefit is offset by the potential trouble with stalling and the like. I am going to spend my upgrade money on other things. WRC4Ever and I should be able to run a datalogged test after we upgrade our cars. We have the same set up enginewise and can switch his HKS SSQ between our cars easily.

<MHO/>

Erik

 

so in my setup.... the BOV would be a very good accessory to the car... the dump valve woudnt improve on anything then riight?

 

Um. Your brother's s4 probably uses a FORGE valve. As in Forge Motorsport. The valves are a diverter/bypass type that reroute the air back into the intake. You wouldnt want a bov on the s4 because well, it wasnt designed for it. The car would run rich and stall.

 

You just negated your own comment. A dump valve and blow off valve are the same thing.

 

so everyone says BOV??

next question to add to this:

What kind of BOV? I notice there are differrent sizes.
How do you choose from the many out there?
Is it just noise?
What would be the best for a T-28 turbo as far as performance?