Help Reduce Lag

[Dillz]

I also have one..

[Ralph Wiggum]

I still need two.....

[1600dave]

Going against the grain here. I dont run a BOV, I used too run a 32mm Turbosmart Vee port and notice less lag on gear change with no bov than with with.

Nizpro also don't run BOV's on their kits for our cars either (although they can be added if the customer insists)

Here's an explanation Simon from Nizpro wrote a few years ago on the topic of BOV's (taken from the Nizpro forum):

Blow off valves what do they really do?

--------------------------------------------------------------------------------

Blow off valves what do they really do?

This is fairly simply if you have a good under standing of what goes on with the engine and how most engine management systems work. It still amazes me how many professionals don’t quite understand and want to add them to everything they get their hands on. The bigger and shiner they are the better.

Now there is no hard or fast rule that says you must or must not have one. It greatly depends on your application. There are also a number of reasons how and why you use them. So I’ll start with why they were invented in the first place and give some examples of why they were fitted to some vehicles and not others. These examples and the reasons also back up the truth of what they were designed to do.

Firstly they were never designed to keep turbo charger from blowing up on trailing throttle.

Example 1:

Lets look at the first of the modern mass-produced turbo charged cars that we will all be familiar with' date=' you guess it the VL Late model camira turbo. They were also known for having a very reliable turbocharger and yet not a BOV in sight, even with increased boost that 99% of them had the turbo charger gave great life often in the 200,000 k mark.

So why weren’t they fitted with a BOV? This is simply it was back in 1986-88 and the emission laws were relatively simple. Hey, I hear you say what the EPA got to do with it? Well actually everything.

Lets have a look at what happens when the car is driving down the road changing gears, accelerating and decelerating . Lets also look how the ECU is determining how much fuel is required with all this going on. The ECU is getting two main signals, RPM from the crank angle sensor and the other, airflow from the air flow meter {AFM}. The afm measures the air entering the engine, it dose this by a heated wirer element like your average light bulb, inside a know diameter hole call it 55 mm. Now the ecu heats this wirer up to lets say 700 deg c with a voltage normally between 0 to 5 volts. The air entering the engine goes past the wire and cools it down, so the ecu puts more voltage into it to restore the 700 deg c. It can now determine how much air is passing the sensor by how many volts are required to keep it at the desired temperature.

So now lets look at just one example of what happens when you decelerate. Your driving down the road accelerating with 5 psi of positive pressure in 3rd gear with an open throttle and then change into 4th , as you shut the throttle to push the clutch in and shift gears the incoming air now has no where to go, it banks up against the throttle and the pressure rises, at the same time there is no air going into the engine any more so there is very little exiting the exhaust to drive the turbine wheel of the turbo charger. The turbocharger starts to slow, the air that is banked up at the throttle is pressurized and only has one way to go, back out the front of the turbo. Now isn’t this what destroys the turbo? Wait I’ll get to that. Once the air goes past the turbo it then travel up the pipe to the air cleaner on its way passing the afm and at that time the afm measure the air {AGAIN} remember it’s already measured this air on the way in and the afm is not smart enough to know which way the air is traveling, so it then tells the ecu to add fuel to the air that’s going in the wrong direction. A-HA VERY MIXTURE ON GEAR CHANGE. EPA says get stuffed go away.

So as emission regulation tightened up car manufactures came up with a devise called the recirculation valve, AKA, the blow off valve. As these valves are placed between throttle and the AFM with the turbo in the middle They recirculate the pressurized air that we just spoke about on the gear changes so the afm does not see it. No more black smoke.

Now as the EPA laws got tighter, engines became smaller [GTR, EVO etc'] but more powerful, intercoolers became std and turbocharger compressor wheels got bigger, this problem became worse as there was more air being banked up, which meant more air traveled the wrong way and was measured. So recirculation valves were fitted to all of them. And that's the truth the whole truth and nothing but the truth, and it sort of makes sense don’t you think.

Then came the aftermarket, who really didn’t understand the BOV theory very well, they made really big shinny ones, didn’t quite understand what they were for, thought it was to save the turbo from spinning backwards, they normally got you to plumb them up so all the air just blew out to atmosphere again this was measured air so the ecu added fuel although the engine never saw any of it, and it then ran really rich on gear changes but they did make a dunny flush noise that seems to have attached a cult following.

Funny thing is that Indy cars and world rally cars don’t have them. Maybe the epa isn’t on to them yet. They also don’t blow up turbo’s very often. There goes that theory.

So you asked about the BA XR6T. Guess what it hasn’t got an AFM. It does its calculation via the manifold pressure sensor [map] and its mounted after the throttle so it never sees the pressure rise on gear changes. So why do they have a BOV STD? Makes you wonder, may be the after market guys are not the only ones that haven’t quite got a handle on it. The other reason would be they properly didn’t like the dunny flush sound. That my guess.

By SIMON G

[Ralph Wiggum]

Im currently running a nizpor kit and quoted the same text about 5 years ago in another bov thread.

I want too try running 2 stock bosch bov's as (and im not going too argue the point, as its been argued many times before ) I believe the bypass flow through them under engine vacum helps spool up speed.

[Dillz]

So does that mean if we argue the point we should be able to run atmo bovs?

[Ralph Wiggum]

Knock yourself out. But I aint getting involved. Get your hands on another stock bosch bov and I'l send you a nice atmo Turbosmart bov that your can argue for/against until your blue in the face :newrussian:

[Dillz]

I already have a Kompact, next is a HKS SSQV aka Fairyfart bov.

[Ralph Wiggum]

well then sell the other bloke your stock bov and we can all move on with out lives.....

[MiKa]

My mate took his Bov off his wrx, and between gear changes it seemed to push harder once the next gear was selected, pressurised air still in the piping making the turbo not have to spool as much to get the air going? I dunno, but it certainly had more kick.

[Kosij]

Might just leave it without a BOV!

Anybody have a 4sp running roughly 300RWKW what 0-100 do you run???

I run 5.8