bigsinky

95 Jap import sti. the turbo kicks in at around 3500 - 4000 and then all hell breaks loose, but how can i get more response at lower revs ie. 1500 - 3500. would a dump valve help? i have ordered a K+N 57i induction kit. will this also help the lower end rev range.

TIA

Big Sinky

Turbo_Steve

I have not tried this yet, but by all accounts fitting a downpipe will have the biggest effect on this.

TonyBurns

iTrader: (3)

A dump valve can only do its job when the turbo is working, ie 3k upwards, you can suffer NO lag whilst your not in this as the turbo ISNT working
Turbo lag is a term for the gap when changing gears in the turbo's powerband and there is a slight pause whilst the turbo catches up.... just think of it as you inhailing some air then exhailing (your turbo dumping the gases) and inhailing again.
The time between you exhailing and inhailing is the same as the turbo catching up again, there is a slight pause (no matter how fast you try exhailing and inhailing ) and this is turbo lag (on a turbo that is )

Tony

dowser

Decat the downpipe and convert your turbo to front entry (if it's got the 90 degree elbow on the input?) will see the biggest reduction in spool point.

Richard

Stuart Knight

iTrader: (2)

Porting the exhaust headers and changing the up pipe will help as well

Jay m A

iTrader: (2)

Turbo lag can happen if you don't change gears, try putting your foot down at 2k rpm in 3rd - not much happens till 3.5k rpm. To increase your spool up time (ie reduce the lag) with a bolt on goodie (rather than ECU changes) I'd personally reduce the restrictions in the intake and exhaust and fit a Dawes device to reduce wastegate creep.

You already have a dump valve, the standard recirc is more than adequate for the levels of boost the OE ECU will let you have, to fit a VTA will only increase sound effects and borewash IMO. To help getting back on boost after a gear change its argueably best to run with no dump valve at all, however its more stressful on the components if you do this.

IMO

Justin

TonyBurns

iTrader: (3)

Justin,
what your describing isnt turbo lag
Just think of how many cars you have put your foot down in at 2k rpm and nothing has happened (or very slowly) and these cars are N/A not turbo charged.
Turbo lag is exactly how i described it, like exhailing then inhailing, the small pause in between is the lag (the time it takes the turbo catch its breath ), everything else is the engine, not the turbo (as the turbo wont be on boost until further up the rev range (ie programmed in to the ecu ).
Adding a decat downpipe will increase spool up due to less back pressure, mine starts to come in as early as 13-1500rpm due to being fully decat but below this my turbo isnt working.

Tony

Forester_GP

Get a DP & remap, that should improove thinks by about 500-1000 further down(recommended). Or if you really want the extra down low response then, get a smaller turbo like my Forester's one where boosts appears from 1300 rpm although, you're going to loose alot further up.

Regards,

George

Turbo_Steve

So...step by by step guide for lowering spool-up point:

1) Buy a bell mouth downpipe (Hayward and Scott are good)
2) Improve boost control (either a Dawes device, or ECU mod. suggest www.scoobyECU.co.uk for an ideal soloution)
3) Remove 90 degree turbo inlet. (This is quite extreme! A fair amount of work)
4) Replace turbo with smaller TD04. (I would only do this if you are really really desperate!!!!)

1 & 2 are the easiest: they are simple bolt ons that will give you a dramatic difference in the driveability of your car.

Edcase

Just playing devils advocate, if the turbo is spooling up at 1500-2000rpm rather than 3000rpm surely that will have a fair negative impact on fuel economy. I know thats not the point, but I'm interested to know.

TonyBurns

iTrader: (3)

Ed,
havnt noticed any difference really

Tony

nom

Also to note - if the air flow is changed to allow the turbo to spool up earlier (turbo with smaller exhaust section, smaller diameter up-pipe), it will impact the high rpm stuff. Air shifting quickly low down (for early spooling) will then cause a 'bung' higher up. You lose your top end.
DP definately the way to go, and a bellmouth at that

Turbo_Steve

Not really, Ed, cos you adapt to the car: the turbo spooling up sooner means more power (and more importantly torque) lower down in the rev range, which means you learn not to push the pedal down so hard, so the throttle doesn't open so much so you get about the same amount of air into the engine which means you need the same amount of fuel.

Roughly.

Er....if that makes sense.

Jay m A

iTrader: (2)

Tony, I hear what you're saying, I'm just not going to listen

I don't know what the industry definition of 'lag' wrt turbos is, but as far as I'm concerned if the turbo ain't on boost (be it through the gears or @ 2k rpm) then the time it takes to get on boost is how much lag its got so the quicker the spool up time the less 'laggy' it is IMO and in the context of the original post on this thread

Justin

dosenöffner

Fit an anti lag kit.

The flames are great. The turbo life ain't.

Turbo_Steve

Uh oh! It's all getting a bit technical again.......

Turbo_Steve

Oh yes! That should JUST fit in the back of a legacy estate.....and leave JUST enough room for the 6 injections manifolds (one per cylinder pair) and 6 SR50 Turbos that would get lovingly grafted onto it. And just enough room under the bonnet for two big nitrous cylinders, A LARGE radiator and a HUGE radiator for the charge cooler.

You just know it makes sense. Would we worry about lag then? NO!

dowser

Where did you get picture's of Pat's engine?

Richard

TonyBurns

iTrader: (3)

Justin,
I take it you mean that every engine that doesnt pull from 1k rpm is "laggy" then as thats what your insinuating
Turbo lag itself has nothing what so ever to do with getting the turbo on boost from low revs, its more promenant in bigger turbo cars like the old cosworths than the newer cars (which still suffer BTW).
Now if you drive your car in 4th at 20mph you will acutally have problems pulling away due to the higher gearing and the way the ecu is programmed, if you suffer this then my suggestion is that you need to down it a gear or two to get the best out of the engine

Tony

Steve3drALS

dosenöffner

ehmmm, NO.

antilag works nothin like that at all...

I REALLY cant be arsed to explain what i have so many times before, so il go find summat ive typed in the past n paste it here.

BTW i actually HAVE anti-lag and have for nearly 3yrs now.

But yea, ALS is overkill for what this blokes askin, FULL exhaust and free as poss induction route will solve his problem.

Cheerrs, Steve

[Edited by Steve3drALS - 12/14/2002 5:25:22 PM]