Help Reduce Lag

[Kosij]

I have a photo of my old dyno sheet in another thread! That was before the retune with new springs! 289RWKW then 306RWKW

I will find the new dyno chart and upload it also the car is only for street use.

[johno]

My mild tune is fairly snappy off the line, and since fitting standard under bonnet intake, I feel its a bit more lively.

Maybe mind over matter though

[Kroozin]

being in a manual myself I usually just take off in 2nd if Im doing the "its not a race" kinda race against camrys/xt's, etc.. its abit sluggy off the line they may pull 3/4 of a car length but then up and away in no time and ya dont have to do that pesky change up to 2nd.

I find the only prob I have is it sounds like your into it if you take off in 1st with these "its not a race races" when driving a manual.

Theres kinda a limbo between too much or not enough hence the taking off in 2nd keeping lowish revs and a quick change to 3rd..

lol maybe I should just throw in another muffler...mmmmm nah.

[RLF]

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

Quote

Blow off valves what do they really do?

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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, 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

I would say the only reason Ford fitted BOV's to our cars is to eliminate any possible customer complaints about flutter noise. There is plenty of people that would have no idea what the sound is and think that something is wrong with there car.

[Gasman]

A good read every time

[CBXRT]

Combined with hundreds of other opinions such as this (taken straight from online but most read the same)

"Blow off valves ( BOV’s ) are important in helping with the longevity of turbochargers and centrifugal superchargers. These valves open whenever there is enough boost pressure in the intake pipes, and vacuum from the

intake manifold. Essentially, these valves operate every time the throttle is opening enough to create boost pressure, and then backed off to create vacuum. When this valve opens it releases the pressurized air in the intake piping either back to the turbo intake piping or vents it to the atmosphere. The reason this is important is because if that pressurized air is not allowed to escape once the throttle butterfly closes, then the air will apply pressure on the turbo or superchargers compressor wheel putting un-wanted stress on it. While this stress is very small, over time it can cause added wear to the bearings and cause the unit to fail prematurely.

Another great benefit of a BOV, other than adding longevity and reliability to your set-up, is that it can help maintain turbine speeds in-between shifts adding a performance enhancement as well to the vehicle. There are not many modifications one can do to an engine that can give them reliability and POWER, so a BOV should be an essential component on your list if running a turbocharger or centrifugal blower."

Both cant be right?

I have no idea which is correct I might add (I have no bias either way!), but the fact "Simon from Nizspro" suggests that Indy and Rally cars dont break turbos suggests a very biased opinion - do professional Rally and Indy cars do 200,000Ks with minor, cheap and routine manintenance...............DEFINATELY NOT. (and unless he is an Indy mech then how would he know how many they use per season/year/decade etc?)

Edited 17/01/12 08:36 AM by CBXRT

[Krazy Kyle]

^^^ yeah, was thinking the same. race/rally cars arnt worried so much about lasting 100,000km's, can change out parts/use stronger parts, arnt inline to fortk out $6k for a rebuilt if an impellor went into the intake. but in the same token they wouldnt do it if it increced the chances of turbo faliure and loosing points in a championship race... if you are that worried about it I guess u should just leave the whole car stock....