Turbo Lag When Changing Gears

[Cubes]

A mate of mine with an RB30DET GT35r runs some sheepdog atmo bov.

He was experiencing a strange bog when shifting between second and third. It only appeared since he wound boost up a touch and began making ~270rwkw.

He blocked the bov off and it disappeared. What was happening is on the quick hard change between second and third the bov was letting go of the air in the system, the ecu thought it was still in the system dumps a heap of fuel bogs the car down and blows a flame out the exhaust.

Blocked the bov off and no longer. His options are fit a recirc bov or put up with the light throttle driveability issues when running no bov.

[bubba]

Hmmm.. flames are cool! does sound like my problem is due to the atmo venting bov. Will let yas know how it goes with the standard recirc bov. I don't think this is the same problem that the thread starter is having though, he has the standard bov yes?

[Al]

By installing a BOV you will significantly reduce turbo spool up time. You will notice a substantial improvement in response from your turbo between gearshifts. Boost will come on earlier giving an increase in torque at lower RPM.

Sounds contradictory to some of the advice you have been given above.

In the old days Turbo Lag was a real big problem with F1 cars. Drivers had to use the accelerator befor the apex of a corner just to ensure they were on boost as they exited. The introduction of the BOV was considered the answer to these problems and alowed manufacturers to add turbos to mass produced cars.

WTF?

Am................................................... no

Not sure where you getting your info from

[Gazee]

WTF?

Am................................................... no

Not sure where you getting your info from

maybe you should explain the exactly what happens to the bloke instead of taking the piss (even tho it is a lil funny)??

[Munkyb0y]

since i turned my boost up to 10 psi, i'm seeing more lag. i'm not too worried, prob my boost controller (turbotech) not letting all the pressure out of the line, therefore the wastegate doesnt fully close, and so it takes longer to build up the boost again. only noticeable when hitting full boost, otherwise there's no real lag. only prob is i hit full boost by 3k

so all this talk about bovs. do they have any affect on lag?

lets say its a plumb back bov. would setting a softer spring (ie. pressure recircs always) be more beneficial in combating lag, as opposed to tight spring (bov only opens briefly on gear changes).

what's the theory here?

[Cubes]

The std bovs have a little bleed hole to 'bleed' a little pressure off to improve bov response time. This improves driveability.

Block the hole off and the turbo spools quicker, the same as when you block the bov off completely.

Watch your boost level as when I blocked the hole off boost raised by ~1psi.

Run an aftermarket atmo bov - While the turbo is spooling the aftermarket bov's don't 'leak' so the turbo spools at the same rate as when you run the std bov with its bleed hole blocked off or the bov blocked off completely.

BUT as I mentioned earlier the no bov option really does improve boost response when selecting that next gear or when feathering the throttle then jumping back on it.

[R32Abuser]

It would obviosuly be alot less efficent wit hthe petroleum though wouldnt it as its not seeing as much of this air that is usually being pumped through the engine hence running a bit richer...or so i think?

correct me if im wrong

[Al]

maybe you should explain the exactly what happens to the bloke instead of taking the piss (even tho it is a lil funny)??

Lighten up buddy

I have not used any derogatory names/phrases. But I was thoroughly amused while reading his post. His terminology is more advanced than a newbie’s, but the theory, in the phrases I highlighted, are totally incorrect.

[mad082]

running no bov is only good if you are changing quickly. if you are boosting up a fair bit but don't change quickly you will find a bit more lag than a stock bov as the air has had time to slow the compressor down.

on my old 180 i went for the stock bov to a gfb basic bov, and it made a huge difference on gearchanges. there was a lot less lag on changes. skylines runa much better bov standard.

if you block off the recirulation hole in the stock bov, and your bov isn't that healthy, you may find your boost bleeds off a bit more at high rpm. mine would bleed off about 1 psi more with the hole blocked. i put this down to the spring tension not being enough, and the vacuum created in the plumback pipe was sucking the bov open.

[Munkyb0y]

man you guys talk in circles

gfb plumbed-back bov. (no atmo)

tighten spring? or loosen spring? or go half way, as it is now?

[mad082]

you want tight to stop it stalling at idle, and loose at high rpm to release the air quicker. so you need to have someone sit under the bonnet with a spanner while you drive around.

[Munkyb0y]

cool.

but it doesnt stall at idle, ever. so loose is better for quick response, less lag?

as if its gonna make that much difference anyway

[4door_Sleeper]

4door_sleeper,

Unfortunately that's incorrect.

A bov is there for nothing more or less than emissions and driveability.

The reason for turbo failures in the old days was poor turbo design, lack of water cooling and journal bearing.

Most definitely nothing to do with a bov.

It really is only there for emissions and to improve driveability (smoothness when off/on the throttle).

I stand by my previous comments. The paragraphs I inserted about BOV's above came directly from the Turbosmart website.

CUBES, A BOV will only effect emmissions in a MAF system if it is vented to atmosphere (or infront of the MAF sensor). The BOV itsself has no efect on emissions (ie remove it or block it off and emissions won't change as all air in the system has been accounted for). Atmo BOV's effect skylines because they use a MAF and the car over compensates for the vented air and dumps in extra fuel which is detrimental for power.

Its function is to provent compressor surge and hence allow the turbo to spool up quicker (reducing lag) and to improve the life of the turbo.

You can search the net yourselves or use any of the links below to check this out. Have a look at the following web pages

http://www.automotivearticles.com/123/Turb...ted_Parts.shtml

BLOW-OFF VALVE:

“This is both the insurance policy of the turbo system, and it’s protector. Two things are governed by the blow-off valve; maximum boost levels and pressure spikes in the intake tract. While the first job is primarily handled by the wastegate, in the event of a big enough overboost, the blow-off valve will vent excess pressures to help maintain safe levels of boost. Basically, the blow-off valve is a springloaded poppet valve contraption that will bleed off and excess pressure that builds up in the intake system. This can occur due to either boost creep or a sudden closing of the throttle body when boosting (such as during full throttle, high RPM shifts), but either way it’s the blow-off valve’s job to prevent pressure spikes in the intake tract. This serves two functions: one, to prevent serious engine damaging overboosts, and two, to prevent airflow from reversing direction into the turbocharger itself. The second one is it’s principle job, to keep the intake tract from building up large pressures during sudden lift throttle situations (such as shifting). When the engine is at full boost and full song, the turbo is spinning madly to supply air to the intake system. The momentum of air and turbocharger are not easily stopped on a dime, so when the throttle body is suddenly slam shut, things tend to get interesting in the intake system. There is an immediate pressure spike between the turbo and throttle body, putting great stress on the compressor wheel which is still trying to pump air into a closed system. To keep the turbo’s RPM up and the pressures in the intake tract down, the blow-off valve vents this excess pressure for maximum performance and reliability.”

http://www.rotorsportsracing.com/performan...g/turbo_acc.htm

http://www.prostreetonline.com/store/turbos/blow_off_valves/

and from http://en.wikipedia.org/wiki/Compressor_map

“During a slam-acceleration from, say, a mid-throttle setting, the compressor working line will move rapidly towards surge and then slowly approach the steady state operating point, further up the map. The reverse effect occurs during a slam-deceleration. These effects are caused by the sluggish response of the spool (i.e. inertia effects) to rapid changes in engine fuel flow. Compressor surge is a particular problem during slam-accelerations and can be overcome by suitable adjustments to the fuelling schedule and/or use of blow-off (bleeding air off the compressor, for handling purposes).

In the particular example shown, a slam-accel from ground idle would cause an HP compressor surge. Opening the blow-off would help, but some changes to the variable stator schedule might also be required.

Because an HP compressor 'sees' the choked flow capacity of the HP turbine, the compressor working line is hardly affected by flight conditions. The slope of the working line approximates to a constant corrected outlet flow.”

And from http://jsalmi.com/bov/index.html

“As was stated above, DVs and BOVs are in essence the same. It's simply the nomenclature which is different. They both perform the same function, which is to protect the compressor from 'bad things' when the throttle plate snaps shut during the creation of boost pressure.

The charge in the IC plumbing can travel well in excess of 100 mph, and when the throttle plate closes the charge has nowhere to go. A shockwave can bounce off of the throttle plate and travel back through the IC plumbing to the compressor, and if the impact is great enough can stall the compressor, or perhaps even spin it backwards. Which is 'a bad thing' as far as the health of your turbocharger goes. The wheels are spinning anywhere between 100k and 200k RPM. From 100k to 0 rpm in an instant? No thanks.

The BOVs open when presented with some specific measure of vacuum. Vacuum is produced immediately in the intake manifold when the throttle plate shuts, so as soon as the BOV "sees" whatever level of vacuum is required, (say 10 inches of mercury, for example) it opens and some of the compressed charge is vented out of the IC plumbing and back into the intake stream - between the MAF and the compressor. This venting is what protects the turbocharger.”

[Cubes]

Mad082, I've actually found the complete opposite with the skylines. Never had a 180 so wouldn't know.

Slow normal driving gear changes and there is 100% less lag. It feels n/a with no split second deadness then snap on boost, boost is just there it just accelerates as soon as you select that next gear.

High rpm full throttle slapping gear changes, I didn't notice any difference between no bov and the recirc bov but I don't really drive in that manner so I really can't comment.

Block yours off and take it for a drive and you will see exactly what I'm talking about.

With the 180 maybe you are right. With the skylines, no bov (or a tight atmo bov) its always more responsive and boost builds quicker. BUT they tend to have issues with low rpm & low boost driveability.

And as for the vacuum created in the plumback sucking the bov open.. If thats the case you seriously need to look at your pod/box setup as there must be a massive restriction there, or replace your bov as its stuffed.

[Cubes]

4doorsleeper, I'll dig up a link that states otherwise.

When running No-bov mine and others that I've seen blow flames out the exhaust and occasionally stall.

Run a recirc and its fine.

The turbo's in ALL instances have spooled up quicker. From my poxy turbo to a gt35r .82. But thats in practice.

But yep.. I'll dig up that link that supports my findings.

[4door_Sleeper]

And as for the vacuum created in the plumback sucking the bov open.. If thats the case you seriously need to look at your pod/box setup as there must be a massive restriction there, or replace your bov as its stuffed.

This would depend on where the BOV gets its vacuum from (usually after the throttle body - engine is still running at high RPM and trying to suck in more air than is available- hence the vacuum regardless of how free flowing your intake system is). The BOV is designed to open whenever it sees a big enough discrepency between both sides. The cure is a stronger spring or take the vacuum from a slightly different place (will only make a small difference).

[Adriano]

I am under the impression that running no bov when you release the throttle, the turbo backspin/chatter causes the air to go back and forth through the afm causing richness, also manufacturers fitted bov's to increase turbo life, prevent backspin noise and deal with the above problem.

[Cubes]

Ok a link to support my thoughts.

First up Steve's Post that makes reference to an Autospeed article where a discussion is held with Nispro's Simon Gishus.

http://www.skylinesaustralia.com/forums/in...655&st=160#

And the full link here - http://autospeed.drive.com.au/cms/A_1457/article.html

Steve has a 180, no bov for drift = much better throttle response.

I really do tend to place a little more faith in Simon Gishus rather than some general websites and especially wiki that is open to any one to have their input.

[Cubes]

This would depend on where the BOV gets its vacuum from (usually after the throttle body - engine is still running at high RPM and trying to suck in more air than is available- hence the vacuum regardless of how free flowing your intake system is). The BOV is designed to open whenever it sees a big enough discrepency between both sides. The cure is a stronger spring or take the vacuum from a slightly different place (will only make a small difference).

Mad082 is suggesting the bov is being sucked open through its recirc piping that taps in to the turbo to afm pipe. So nothing to do with where the bov gets its vacuum when on boost.

The bov receives its vac/boost feed via the throttle body. Its impossible what mad082 is suggesting unless his bov's spring is unbelievably light.

All thats holding the bov shut when making boost is the springs pressure as the pressure on both sides is essentially 'equal'.

As I said prior for the bov to lift off its seat you would want some serious vac in the recirc piping. If you have a considerable amount of vac in the recirc piping then you have issues, especially when mad082's is a fairly stock r33.

[Cubes]

I am under the impression that running no bov when you release the throttle, the turbo backspin/chatter causes the air to go back and forth through the afm causing richness, also manufacturers fitted bov's to increase turbo life, prevent backspin noise and deal with the above problem.

The turbo never back spins, its impossible.

Have a read of the interview with Simon from Nispro on autospeed (link above).

Driving with no bov really does support what Simon states. It just feels so much more responsive.