2nd turbo - how do we know......

Here is a dead wasy question,

1st turbo - know its working - how? - can hear its whine when it

spools up.

2nd turbo - how do i know its working? i'm not sure its going 100%

as i dont seem to get some massive acceleration or a "push back"

into the seat feeling.

Examples of my suspicious :

1) dual carriageway, think the auto is in 3rd, floor it to the bottom

without o/d on, does the auto change down? NO! does it accelerate

quickly, yes - but no sudden "jump" of speed,

2) o/taking using D-->2 shifting, as i drop it, revs climb to 5/6000,

again no massive jump, floor the pedal, quick - but doesnt seem

like a turbo!

it could be because i have not been in/driven any other supra's that

i'm mistaking it.

is there anyway of telling its working?, i do not have any gadets, boost

gauges etc. yet!

cheers for helping out mr thicko here !

When my boost is behaving itself, I have taken people out and they say that it is a thrill ride.  But I often think that I don't get that feeling, as you say, "push back in the seat".  I think this is because you are driving the car.

When given control of my car to friends they often scare the cr*p out of me.

Have you tried being a passenger in your own car yet ?

One more thing, I understand that the first turbo was purely designed to eliminate lag.  Its the second turbo that will give you the killer speed.

You might want to get a boost gauge installed, for peace of mind.  If you get poor results you can look into the problem that you actually know exists.

(Edited by Lee Hockley at 9:55 am on Feb. 7, 2002)

Your second turbo cuts in at 3,500 to 4,000rpm.  Accelerate in a gear above 3rd from 2,000rpm to 6,000rpm and if you don't notice the sudden large increase in power at 4k, you are either a) dead or b) the second turbo isn't working as it should.

The behaviour described sounds like either both turbos are running in parallel rather than sequentially (which would give you a lot of lag, so it's probably not that), or the IACV isn't opening when it should.  Or it's an NA Supra

If you aren't noticing a power increase, I would say the Inlet Air Control Valve isn't opening.  This means you're basically running a small single turbo system giving 0.7bar boost tops.

-Ian

Strongly suggest you invest in a boost gauge.

Why the MKIV doesn't have even a basic gauge is beyond me, the MKIII did and so do the later facelift MKIV's.

the key word here is auto....You have to push the pedal hard and quickly to the floor to get kick down, otherwise the electronics wont do the kick down and the boost rises but you dont get the massive kick from the second turbo. I have been caught a few times and have had to ease off the accelerator and then floor it again to get the kick down that I want.

The easiest way to check for the 2nd turbo is to be in 2nd and accelerate from about 20mph, it will accelerate quickly and then when you get to 4000rpm the car should surge a bit, or surge quite a lot of the cats have been removed.

Fitting a boost gauge is also pretty essential.

JB

remember that the STOCK MkIV has a very smooth transistion between single turbo 1 and dual turbos 1 and 2 running together.

If you look at a torque curve you see it's pretty much a straight line so there is no sudden lurch.

With a slightly modded Supra (no CATs or boost controller) you will now see the torque curve have a break in gradient and increase more rapidly when the 2nd turbo kicks in.

I think it's normal. The stock Supra is built so you cannot tell when you're on one or both turbos. That's what makes it such a nice smooth ride.

If you get a DROP in power then yes the 2nd turbo may be not working.

Check the tiny 4mm diameter pipe which goes to the exhaust bypass VSV to the right of the exhaust downpipe (you'll notice a flap valve and actuator arm, follow this along and you'll find a VSV with a single 4mm diameter pipe attached. Check this hasn't come off, or actually take it off and then you'll really see what it feels like when you loose turbo 2!

Pete

Thanks for all the info guys,

I'm not driving the Supra at the moment , but when its next due for

a service I'll get a boost guage fitted to it then and then test the

readings from that. (unless its really easy for a complete tool like

me to fit ? i'll probably want one were the clock is - 52mm i think! )

I've heard that stock boost should be 0.8 - is that correct?

will the boost guage slowly climb when turbo 1 comes in and then

increase a lot when 2 kicks in, or is it  a smooth climb as you push the loud pedal ?

From my understanding of documents I have used to determine how to set up my BC, the word is the stock boost setting should be set to 0.65.

If you are right that is is 0.8, then this could be the reason why my winged angel of death is behaving like a teletubbie !

(Edited by Lee Hockley at 11:02 am on Feb. 7, 2002)

stock boost is about 0.7kg/cm2 on turbo 1 and 0.75->0.8kg/cm2 with both.

With a modded car the boost on turbo one increases slightly but the biggest change is when both come on line.

Also...

>will the boost guage slowly climb when turbo 1 comes in and then

>increase a lot when 2 kicks in, or is it  a smooth climb as you push >the loud pedal ?

Did you read my previous post on the subject?

Pete

Two things:

1) A few months after I bought my MK4 TT (completely stock) I believed I'd lost power to Turbo #2. After getting it checked out by a member on the list we concluded it was purely psychological as I'd got used to the cars performance.

2) If you have lost power, then check all pipes! They may NOT have come off, but could be loose. I actually lost power to turbo #2 a few months back (you will know when you have... Slooooww) but it was a result of a few pipes becoming loose, each losing a bit of pressure eventually making turbo #2 stop working.

When the problem was fixed I no longer needed my bleeder to boost to 1.3 bar :-)

Peter

MKTT 1993 J-SPec (Caltless Hiper, HKS BOV, H2Oi)

Doh 1: I forgot that the car in question was an auto, so my gear recommendation was nonsense.

Doh 2: I have never driven a stock MkIV so I assumed that all of them go mental at 4000rpm, rather than there being a smooth unnoticeable transition.

If you are going to disconnect any VSVs to see if the second turbo is working or not, I suggest doing both the IACV and the EGCV, as doing only one will either cause the turbo to spin backwards again the exhaust gas flow or build up pressure against a sealed valve - both resulting in unneccesary strain on the turbo...

-Ian

My old Supra blew a pipe off soon after de catting it. This stopped the second turbo working at all.

It happened the other day to the new owner BOLTS, probably thrashing it to bits :biggrin:

The pipe in question is approx 6mm diameter on the drivers side at the back of the engine at the top , you will see a number of small pipes here. Check for a pipe off

If its just stock, with stock exhaust, air filter etc, you can hear the second turbo coming in, its makes quite a different noise to the first turbo.

You would definitely feel the power difference at about 4000rpm (UK cars anyway, Jap spec don't know how much earlier??), and it all goes a bit ballistic at around 5000rpm.

As far as I know, my car is pretty much standard except the exhaust. It too, is an auto.

I can definatly feel the 2nd turbo coming in at roughly 4000rpm but cannot really hear it. The exhaust starts to get noticebly louder at this point.

If you select 2nd gear and accelerate reasonably quick, (not flooring it), and carry it right through the revs steadily, you/I notice the 2nd turbo easily.

I agree with JB completely. If you ease the throttle down it wont kick down and doesn't surge as such either.

Does anybody feel surges from turbo 1 ?  Wheel spin, or anything like that ?

I ask because when I test drove a stock one a number of months ago, I seem to remember that I did.  But my one boosts to about 0 in gears 1 and 2, but unable to get a higher rate or wheel spin.

Lee,  when you say it boost to 0, do you mean 1.0 bar.  On mine at tickover I get about -15lbs, turbo 1 very quickly jumps to 8-10lbs and when turbo 2 comes in at 4000RPM it quickly climbs to 12-14lbs.

You should be able to induce wheelspin in 1 and 2 quite easily.

By 0, I mean 0 bar, half way on my gauge.

I can floor it in gears 1 and 2, and only get that amount of pressure on my gauge.  Is this because my gauge is only reflecting turbo 2 ?  Because when I get into gear 3 and upwards I get slow boost sometimes and too quick others (overboosting).

Me thinks your boost gauge is plumbed in badly!!!

I get .7/8 bar on t1 and 1.3max on t's 1&2 according to my boost gauge. The boost pressure is measured from your intake manifold I believe so it should show you the boost levels right through the rev range.

Possibly you have a kink in the hose that supplies the boost gauge which only opens out once more than say .6 bar is flowing through it?

Thanks.

I'll reconfigure my BC first this weekend, incase it is a symptom of that.  Then check the lines, as you say.

What is a safe psi to run at my stock turbos ?  And whats the FC limit ?

Lee

With all due resoect I think you should go back and read all the information that has been provided to you in the post you have just raised in this technical section. The answers to these questions and many more are within.

I make you right, I have been given a lot of help regarding this matter, all of it very much appreciated.

I looked back on the post that you say the FC cuts in at 15psi.  My problem is that if I get a FCD at the weekend, what level can I set it at  so not to blow the old girl up.

I'll just work it out .. cheers.

(Edited by Lee Hockley at 2:02 pm on Feb. 8, 2002)

(Edited by Lee Hockley at 2:03 pm on Feb. 8, 2002)

Quote: from Lee Hockley on 2:01 pm on Feb. 8, 2002[br]I make you right, I have been given a lot of help regarding this matter, all of it very much appreciated.

 

I looked back on the post that you say the FC cuts in at 15psi.  My problem is that if I get a FCD at the weekend, what level can I set it at  so not to blow the old girl up.

 

I'll just work it out .. cheers.

 

 

Read Pete Betts post, 18 psi is a reasonable boost level, however your car may not hit this level with the cats fitted.

(Edited by GavinL at 2:08 pm on Feb. 8, 2002)