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Lag Between Gears..

R32 TT
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R32 TT Mentor

R32 TT

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Hey guys,

I have just got the car back on the road. Had standard turbos before, and now have Garrett ball bearings that are about the equiv of N1's. Additionally I have Mines dump pipes on there - where before I just had the stock items.

One thing that hasn't changed, which I had hoped would - is that there is noticeable lag between changing gears, even when changing up around 7000rpm.

I have HKS SSQ bovs which were already on the car when I got it.

Is this normal?

I would have thought that once a pair of ball bearing turbos had the RPM up, that they would have reasonable inertia to keep going? Or is it because when the bov's fire, I have to 'refill' the Intercooler? The Intercooler is an Apexi Hybrid and is a bit bigger than standard (not sure 'how much' bigger)

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R31Nismoid Grand Master

R31Nismoid

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what do you deem as lag though???

there will be a small period where it needs to build again, but it depends how long you take to change gears etc.

Thats the main bit.

Faster you change the less time there is inbetween etc

Ive heard some people change so fast i can hardly hear the BOV give more than a little noise rather than a full dump before they are back onto the throttle. :P

i'd say its more driver being nicer to the car than anything.

If i snapped a gear fast i could hardly hear mine go and it would rocket off. But then i could also take a second to change a gear and it would have to build again

grim32 Community Regular

grim32

Posted
Posted

my old turbosmart dual stage had a problem with it, on low boost it would keep the wastegate open for a long time after gear changes and took at least 2 seconds for it to close and make boost again. on the high setting if was fine and made boost straight away, just something for you to think about.

R32 TT Mentor

R32 TT

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Cheers for all those answers guys,

tighten your BOV a little, and see if that fixes it. Then maybe a little more if it doesn't.

I'll have to look at the HKS Bov's to see if they have some sort of adjustment and then have a play to see what results I get.

what do you deem as lag though???

I guess its true, my question is a little bit like "how long is a piece of string". Everyone has different ideas about what is and what is not 'acceptable' lag. I can do ultra fast gear changes though, and yes this alleviates it a bit, but on the track, to be 'nice' I probably do something like a half-second to maybe 1 second gear change? Not super fast... And it falls back to about 5000rpm and then seems to start building boost again. Since my turbos are still small (GT-SS size) I would have thought that will still have them on song...? I am wondering if it is filling the intercooler again.. perhaps I have TOO much BOV? Could that be the case?

oooo... All installed? How's it going?

Hey there Lucien, Yup! I'll have to PM you all the details! :( Hows the Thesis coming along?

well bigger turbos push more air and so dont make full boost until higher revs....so maybe when you change down the revs are too low to make full boost now

Yeah I agree, but since they are "already spun up" and I am just changing gears, wouldn't they more or less keep going? I mean, these things are ball-bearing and going at 150000rpm.. how come they slow down in a half second gear change?

How does someone figure out if you have too much BOV (emptying the Intercooler), or not enough BOV (stalling the turbo) ?

my old turbosmart dual stage had a problem with it....

Hmm... I think I really need to suss out these HKS SSQ's on the car first and see if there is a problem first..

Cheers guys, if I find the 'issue' I'll post it up for sure.

R32 TT Mentor

R32 TT

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probably aftermarket turbo's you went to are more laggy - due to heavier exhaust wheel (compared with stock ceramic wheel which is also smaller)

Yup, and I agree that they may take a little longer to spool up first try, but then the opposite is true too once they are spinning. Since they are a little heavier they have inertia and so should take just as long to spin down as they did to spin up shouldn't they? And given that nothing is 'applying the brakes' to them they shouldn't fall off that quickly I wouldn't have thought..?

There has to be something wrong somewhere. Maybe I need a smaller intercooler.

Duncan Grand Master

Duncan

Posted
Posted

Well theres 2 things that might feel like lag up

1/ how long it takes to go from 0 revs to full revs when it has enough air flow. This would be like when you mash the throttle at high revs

2/ what rpm it makes full boost at.

I suspect what you are noticing is 2 not 1. 1 is generally a very short space of time, while 2 depends on what the revs are, where you start, and how fast revs rise.

I hope my rambling made sense

R32 TT Mentor

R32 TT

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Well theres 2 things that might feel like lag up

1/ how long it takes to go from 0 revs to full revs when it has enough air flow.  This would be like when you mash the throttle at high revs

Hmm. Well I had it flat out at 7500rpm (so the turbo is fully spooled making maximum boost) and I change gear and mash it again. The tacho falls back around 5000rpm.. and then it 'winds up' again.. I would yhave thought at those rpms and air-flow it should be straight on boost again?

2/ what rpm it makes full boost at.

I suspect what you are noticing is 2 not 1.  1 is generally a very short space of time, while 2 depends on what the revs are, where you start, and how fast revs rise.

Ok, this I am not sure. The boost gauge and boost controller got taken out when I fitted Motec, so don't know exactly what RPM full boost arrives, but I would think well before the 5000rpm that I am falling back to when changing gears yeah?

I'll be refitting the gauge and checking out the Motec logging to see. But don't have that data yet...

I hope my rambling made sense

yup! :(

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