turbo boost ranges

[cjones]

I have a brand new T25 with an ND boost upgrade, a K&N and a Mongoose exhaust on a '92 s13 and have had it rr'd at 186bhp (flywheel), which seems a little low, however, the guy at the garage said he can't count the number of times he's had people saying the measured figures seemed low. Apparently it's quite normal. My mate has had his '90 S13 with just a K&N and an ND boost upgrade (both of us are running approx 13psi) and his figures came out as low as 153bhp on the same rr rig.

Now the question is, why the hell does mine seem slower? Simple straight line tests have his pulling and beginning to boost at about 2500rpm whereas mine only seems to start at about 3500. The difference is that his feels like it's pulling much harder. There's more of a kick in the back. Mine will easily pull right up to 7000 no problems, his will start to fade just b4 6000.

Despite the 30 bhp advantage and the fact that I have had a full engine recon about 8,000 miles ago (and his shells are going), mine seems slower, although my power range seems to be shifted up the rev range.

The only 2 other things different are that my wheels are bigger (215/40/17) and his are standard - in fact visibly smaller - so this could account for a slight difference in gearing but I wouldn't have thought that it'd be that much. Also, his turbo is a Jap import replacement (any difference?).

Any ideas why the boost would kick in so much earlier? When does the boost kick in on a stock sx? Could the timing still be a bit out? I've had it set while being rr'd but there does still seem to be something holding it back a little

Thanks,
Carl

[Mike_S13]

Just cos you have a higher peak power output, doesnt mean your car will be faster. If its a standard t25, it should Kick at 3000rpm and pull all the way to redline, sounds like you have a fuelling/timing problem?

------------------
Red '93 S13
A Few mods

[Paul_S13]

I've just had a different chip fitted and now the timing needs changing, my turbo (hybrid T25) used to hit full boost @ 3200rpm but now it gets to full boost @ 4000rpm. At least I hope its the timing

[andyf]

I have a T3 which is now broken, but when it worked it would rev to the redline without a problem!!! I really think it's a good one.

[Mike]

circumference of 215/40/17 is within a couple of % of standard. From what I've heard, I suggest you get a chip. Try Jez.

[AshT_200]

Originally posted by Mike:
circumference of 215/40/17 is within a couple of % of standard. From what I've heard, I suggest you get a chip. Try Jez.

215/40/17 is actually smaller than standard by a touch.

[hames_jet]

My T25 would pull from roughly 2500 where it would start to spool up to around 6300rpms but now my T28 will spool from about 3500 and pull to the red line and more.
I think it depends on the timing, mixture, type of mods, engine wear and condition etc.

[bren]

You may bothe be running 13psi but if hes got a larger compressor housing and wheel then although the boost pressure is the same the volume of air being shifted with be significantly greater hence his extra power.

If I ran a T4 on my Cossy at 22psi then Id run it lean and kill the car where as itll happy consume and fuel for the air shifted by my current T34 hybrid.

Ignore the rolling road results, they are generally borrocks, especially flywheels figures, and its pointless to compare cars unless then are run one immediately after then other on the same rollers operated by the same mechanic.

One point though, are you sure your mates figure wasnt @ wheels? That would explain all.

------------------
Bren

http://upload.turbosport.co.uk/gallery2/7365838885307.jpg

[Jezz_S13]

Originally posted by bren:
You may bothe be running 13psi but if hes got a larger compressor housing and wheel then although the boost pressure is the same the volume of air being shifted with be significantly greater hence his extra power.



I may be wrong but i think that's crap, the turbo is still shifting the same volume of air, just at lower revs (turbine revs not engine) and hence is capable of shifting a higher volume of air.
That's why pissy litte T25's run out of steam at 15psi over 6000rpm, they just cannot spin fast enough for the little compressor to deliver the amount of air required to maintain the boost.
A bigger turbo obviously shifts more air per rev because of the much bigger compressor, and hence can deliver enough air to maintain the boost upto redline. Only then you have to put up with lag then because there is not enough exhaust gas at lower engine revs to get the compressor spinning fast enough to probuce max boost.

It's the CSA of all the pipework/trottle bodies/ports/IC etc that makes the difference to the volume of air required surely. And even then it comes down to the volume of air that the engine is demanding that governs how much air is needed.

The best you can do is use the biggest/least restrictive pipework/IC/ports/cams etc to allow the maximum amount of air get into the cylinders as quickly and easily as possible.

Jezz.

[bren]

A large compressor housing and wheel will shift a greater volume of air for a give boost pressure. If you dont agree then fine, Im not getting into a debate about it.

My mates running a large turbo at 18-20psi on the same spec engine as mine. Hes getting a hell of a lot more power than me.

As I say Im not going to get into a argument 'cause I cannot be @rsed but Im right!

------------------
Bren

http://upload.turbosport.co.uk/gallery2/7365838885307.jpg

[Jezz_S13]

Originally posted by bren:


A large compressor housing and wheel will shift a greater volume of air for a give boost pressure.

As I say Im not going to get into a argument 'cause I cannot be @rsed but Im right!



Firstly, utter bo11ocks,
If air temp (IE density) is contant then volume and pressure are directly proportional. You cant have more volume for the same pressure. Impossible.
http://dbhs.wvusd.k12.ca.us/GasLaw/Gas-Boyle.html

Secondly, must be true then. http://300zx.co.uk/200sx/ubb/tongue.gif

Jezz.

[SteveCarter200]

I think Bren is right. To make this simple, two water hoses, same pressure, one is 1" diameter, the other is 2" diameter, which one is going to fill a bucket quicker? Obviously the 2" pipe because it can pass a greater volume of water at a given rate/pressure.

Surely this simplified example will apply to turbo sizing?

As for when the turbo starts to spin up, I believe inertia is a major factor. If there is the came driving force (exhaust gases) it will take the turbo longer to spin up to its operating speed.

[bren]

I think Im right as well http://300zx.co.uk/200sx/ubb/wink.gif http://300zx.co.uk/200sx/ubb/biggrin.gif

------------------
Bren

http://upload.turbosport.co.uk/gallery2/7365838885307.jpg

[Jezz_S13]

Yeah i agree with you entirely Steve, the bigger turbo will shift more air, no question.

However governing factor is the restriction of pipework and everything else after the turbo, as the CSA of all of this stuff is constant it is irrelevant that the turbo can shift higher volume.
The pipework restriction causes pressure build up in all the piping from turbo to cylinder to actutor pressure then it opens the wastegate.

The result is just that the bigger turbo doesn't have to work as hard to maintain the pressure.

This is why we use big IC pipework, free flowing IC's, get our heads ported, bigger duration cams etc to make it as easy as possible for the most air to get into the cylinders.

I'm certain that if I put my T25 back on and run it at a boost such that it doesn't drop off at any point before redline say about 7-8 psi and RR it, then put the T28 back on at exactly the same boost and all other conditions exactly the same the peak BHP will be the same.
Throughout the 0 - 3.5K rev range it will vary as the two turbo's spin up differently due to there size and turbine dynamics, and possibly one turbo may heat the air less (probably the bigger one) than the other which would have an effect due to the charge temp being different. Also the bigger turbo will be slightly less restrictive with respect to the exiting exhaust gasses.

Can anyone convince me otherwise, without giving me a slap that is.

Jezz.

[SteveCarter200]

SLAP!! http://300zx.co.uk/200sx/ubb/biggrin.gif

I see what you are saying Jezz but that is presuming that the pipework is in fact a limiting factor at the pressures/volumes that we are talking about, which may not be the case. Unless you have actually flow tested the pipework/IC etc they could be adequate for much higher boosts than we are using.

So basically we have come to the conclusion that yes, a bigger turbo will flow more air but only if the pipework,IC, head etc allows it to.

[Jez]

Take a look at some flow maps for different turbos. You will see that different turbos have different areas of efficiency.

By changing the compressor housing you are changing the efficiency of the turbo for a given flow and pressure.

So where Jezz_S13 says:

I'm certain that if I put my T25 back on and run it at a boost such that it doesn't drop off at any point before redline say about 7-8 psi and RR it, then put the T28 back on at exactly the same boost and all other conditions exactly the same the peak BHP will be the same.

He is in fact wrong because one turbo will be more efficient at shifting the air at this fixed pressure and flow. As one turbo is more efficent that the other there will be a different exhaust back pressure and so one turbo will give more bhp than the other at the same boost pressure and rpm (of the engine)

Another fact is that turbine speed is related to directly to boost pressure and not flow.

If you wanna read more about this get a book - I have "Turbochargers" by Hugh MacInnes - quite good but fairly dated and American

Click the link for some flow maps. The oblong lines with a % are the efficiency lines. http://www.turbofast.com.au/FlowT3.html

Cheers
Jez

------------------
Red S13
264bhp @ 14psi
Horsham Developments (http://bagpuss.swan.ac.uk/horsham-developments) - S13 ECU performance upgrades


[This message has been edited by Jez (edited 06-01-2002).]

[Jezz_S13]

Right.

So what you are saying then Jez is that because the turbo is more efficient at effectively sucking the exhaust gasses out, it in effect _pulls_ a bigger volume of air through when the valves are overlapping open.

So this volume is in addition to the 13psi boost being pushed into the cylinders.

Makes sense now, cos the engine is in reality our main contributor to the air restistance creating the boost pressure, in having a better exhaust backpressure this resistance is reduced, so it's like having a bigger pipe for the water to pass through.

Agreed?

So it's got fvck all to do with having a bigger compressor housing and wheel, it's all to do with efficiency of the HOT side of the turbo.

Right so that's the same principle of a Free Flow exhaust, allows more fresh air into the cylinders as the exhaust is taken away quicker, or is pushed out easier depending how you look at it.

Jezz.

[JackaL]

Could the difference in turbo response and 'kick' be caused by the older car not having a cat, and the newer one having a cat?

[Jez]

Originally posted by Jezz_S13:

So it's got fvck all to do with having a bigger compressor housing and wheel, it's all to do with efficiency of the HOT side of the turbo.


The fact that the compressor is more efficient means that there is less engery removed from the exhaust gasses and therefore its easier for the exhaust gasses to escape from the engine. This means there is less exhaust gas (more air/fuel) in the cylinder for the next power stroke. Also, because the compressor is more efficient the compressed air is cooler and therefore more dense - more power for a given boost pressure, but obviously you're flowing more air mass here.

I was assuming that the turbine wheel and compressor stays the same and we're only changing the compressor wheel and housing.

To get the correct sized compressor and housing you figure out what boost pressure you want and how much air you need to flow and then choose a compressor wheel and housing with its maximum efficiency at that point.

Does that make sense?

[This message has been edited by Jez (edited 06-01-2002).]

[Dave_the_B]

Originally posted by bren:
As I say Im not going to get into a argument 'cause I cannot be @rsed but Im right!





There isn't much in this life I really respect, but utter arrogance is most certainly one thing I do respect


Bren...You are the man http://300zx.co.uk/200sx/ubb/smile.gif http://300zx.co.uk/200sx/ubb/smile.gif


Dave


------------------
Grey S13
T28
Evo 6 IC
261bhp @ 16psi
I'm sure it was more last time.....

[This message has been edited by Dave_the_B (edited 06-01-2002).]

[SteveCarter200]

Originally posted by Jezz_S13:


Right so that's the same principle of a Free Flow exhaust, allows more fresh air into the cylinders as the exhaust is taken away quicker, or is pushed out easier depending how you look at it.

Jezz.

Which in turn allows more air to be forced in to the cylinders, requiring a larger compressor if remaining at the same boost level.

So we are back to where we started.

AAAAAAAGGGGGGGGGGHHHHHHHHHH!!! http://300zx.co.uk/200sx/ubb/biggrin.gif

[Jez]

Originally posted by bren:
A large compressor housing and wheel will shift a greater volume of air for a given boost pressure. If you dont agree then fine, Im not getting into a debate about it.

My mates running a large turbo at 18-20psi on the same spec engine as mine. Hes getting a hell of a lot more power than me.

As I say Im not going to get into a argument 'cause I cannot be @rsed but Im right!



Bren is right - I can't be arsed now either... http://300zx.co.uk/200sx/ubb/biggrin.gif

[Jezz_S13]

Yeah but what if ..... http://300zx.co.uk/200sx/ubb/biggrin.gif

Complicated little fvckers aren't they these here turbos.

At least I understand something, if you want to learn something, start an argument. http://300zx.co.uk/200sx/ubb/smile.gif http://300zx.co.uk/200sx/ubb/biggrin.gif

Jezz.

[sideways tony]

...i need an aspirin and a dark room....how did i end up in this thread?...........

------------------
s13,very white and very loud, thanx to the mongoose and the a'pexi induction.gonna fly if it kills me.

[barryjdart]

For an indepth clarification try www.turbofast.com.au (http://www.turbofast.com.au) and/or www.gnttype.org/techarea/turbo/turboflow (http://www.gnttype.org/techarea/turbo/turboflow[/URL])[/url]
Best of luck in understanding whats here.

[This message has been edited by barryjdart (edited 06-01-2002).]

[This message has been edited by barryjdart (edited 06-01-2002).]

[This message has been edited by barryjdart (edited 06-01-2002).]

[Jez]

Originally posted by sideways tony:
...i need an aspirin and a dark room....how did i end up in this thread?...........



Just glad I could hinder... http://300zx.co.uk/200sx/ubb/biggrin.gif

[Jezz_S13]

I think this is an ace thread, I apologise to cjones for hijacking it, and to Bren ofr being arrogant back but I reckon we've all (apart from Jez) learnt something here. http://300zx.co.uk/200sx/ubb/smile.gif

Jez, while on the turbo-ey topic.
This anti-lag mechanism, would the use of a vent to air DV create a similar effect?
As the air is dumped on a gear change the injector dump a load of fuel in don't they. Is there any remote chance that this could actually be beneficial an act like the anti-lag system you use?

Jezz.

[Jez]

Originally posted by Jezz_S13:
Jez, while on the turbo-ey topic.
This anti-lag mechanism, would the use of a vent to air DV create a similar effect?
As the air is dumped on a gear change the injector dump a load of fuel in don't they. Is there any remote chance that this could actually be beneficial an act like the anti-lag system you use?

Jezz.

Not quite sure what you mean here.

A little fuel will be injected when a atmos DV dumps but as soon as the ECU "sees" the throttle is shut (via the throttle angle sensor/switch) it cuts fuel anyway (until idle rpm is reached)

[Jezz_S13]

Originally posted by Jez:
Not quite sure what you mean here.

A little fuel will be injected when a atmos DV dumps but as soon as the ECU "sees" the throttle is shut (via the throttle angle sensor/switch) it cuts fuel anyway (until idle rpm is reached)

Ah right so the Anti-Lag thing basically doesn't cut the fuel when the throttle is shut?

So in your opinion would you say the fuel injected when an atmos DV dumps is a positive or a negative thing?

Jezz.

[SteveCarter200]

I would think it will give some good flamage when you go back on the throttle. Which is nice http://300zx.co.uk/200sx/ubb/biggrin.gif

[SteveCarter200]

As I understand it, Anti-Lag works by having a small bypass throttle, so that when the main throttle is closed on lift off, there is still some air/fuel entering the engine therefore producing exhaust gas, so keeping the turbo spinning. Obviously all controlled by electrickery.

[Jez]

Originally posted by Jezz_S13:
Ah right so the Anti-Lag thing basically doesn't cut the fuel when the throttle is shut?

So in your opinion would you say the fuel injected when an atmos DV dumps is a positive or a negative thing?

Jezz.



Which anti-lag thing? My attempt at one? What I did was to make a chip that chucks loads of fuel in at high rpm / low loads. Didn't really work as anti-lag - makes a nice noise though http://300zx.co.uk/200sx/ubb/smile.gif

With the S13 any DV is better than none - stops the turbo surging. BTW if you look on compressor maps for turbos there is a surge limit line. If you go into the surge area everything gets a bit unstable. The cha-cha-cha (often incorrectly attributed to the wastegate) noise that you can hear on cars without a DV (during lift off) is the turbo going into the surge area (i.e. very low air flow and high pressure)

I use a re-circ DV mainly cos I didn't want to noise from an atmos DV and also people have probs when running atmos DV at high revs low load. The vacuum in the manifold sucks open the DV, it leaks and air is entering the engine that hasn't been measured by the AFM.

------------------
Red S13
264bhp @ 14psi
Horsham Developments (http://bagpuss.swan.ac.uk/horsham-developments) - S13 ECU performance upgrades

[This message has been edited by Jez (edited 07-01-2002).]

[Jez]

oops

[This message has been edited by Jez (edited 07-01-2002).]

[Jez]

Originally posted by SteveCarter100:
As I understand it, Anti-Lag works by having a small bypass throttle, so that when the main throttle is closed on lift off, there is still some air/fuel entering the engine therefore producing exhaust gas, so keeping the turbo spinning. Obviously all controlled by electrickery.

That'd do it http://300zx.co.uk/200sx/ubb/smile.gif - just have to retard the ignition loads too cos otherwise the engine will still produce power as if the throttle was part open.

This is how my "anti-lag" chip was supposed to work - on a light throttle dump fuel and retard the ignition loads. Should do nice flames too, but I got a bit concerned about knackering my engine/turbo and have just settled on a popping/bang map which sounds really cool.

[This message has been edited by Jez (edited 07-01-2002).]

[Jezz_S13]

Originally posted by Jez:
Which anti-lag thing? My attempt at one? What I did was to make a chip that chucks loads of fuel in at high rpm / low loads. Didn't really work as anti-lag - makes a nice noise though http://300zx.co.uk/200sx/ubb/smile.gif



Yeah that's what I meant, your attempt.

Might order me that book later on today, I need to understand this better.

Jezz.

[Jez]

ITs worth getting but as I said before its fairly old and american - you might want to have a look about for a newer book

[Jez]

you could try this one: http://www.amazon.co.uk/exec/obidos/ASIN/0760308373/qid=1010407791/sr=1-2/ref=sr_sp_re/202-3306896-4983029

[AshT_200]

Some rally anti lag systems injected fuel directly into the exhaust manifold. As soon as you came back on throttle, this fuel woiuld ignite in the exhaust manifold and produce a hooge flame out the exhaust.

[Billy]

Damn! Have I missed a technical punch-up?

Everybody is right...ish.

The airflow is determined by the engine, not the turbo. If the engine sees 15psi, it will suck the same volume of air in whether it comes from a T25 or a T3. However, engines don't make power from air volume, but from air mass.

The efficiency of a compressor consists of two main elements. One is the ability to hold pressure, determined by how closely it all fits together, and is one reason turbos don't work well at low revs (an unavoidable aspect of centrifugal compressors), and why superchargers do.
The other is the adiabatic efficiency, which is basically a measure of how much heat is put into the air. This is the reason the bigger compressor makes more power for the same boost level. The pressure is the same but the mass isn't.
So that'll be the combined gas law then. http://300zx.co.uk/200sx/ubb/wink.gif

As far as anti-lag systems go, dumping excessive fuel in won't do anything (other than wash your bores, poison your cat, and waste fuel) unless it is accompanied by air. It will make nice flames as the mixture becomes combustable towards the tailpipe, but what you want is combustion before the turbo.
There are two ways to do this as far as I can see. The first is to inject fuel and air into the exhaust manifold. I believe this is the way the rally boys do it (Baaaaaarp CRACK Baaaaaaaaarrp BANG!). The second is to induce afterburn by retarding the spark or advancing the exhaust valve opening or both. I don't know if anyone uses this method or if I've just made it up, but the principle is the same (and would require a bypass as mentioned by SC, and a bit of re-mapping). The trouble is you're still basically using the combustion chamber, so engine braking may suffer, and prolonged over-run will make the engine feel like it has two flywheels (my Alfa has!) making fast clutchless gearchanges a bit trying.(What am I thinking!)
Personally I wouldn't consider the benefits to be worth the extra stress on the turbo, but then I have to pay for mine, and saving 0.5 seconds/KM is not a high priority!

[Matt_S]

Seeing as this thread seems to have "evolved" into one about anti-lag systems etc...Paul at SE-Nissan has this fitted to his Sunny GTiR. As the thread shows - a management system is required to make these run. Well - he has Motech system on his car as far as I know. It has the facility for the anti-lag built in. He says that it does make for better acceleration etc, but that it is a complete nightmare to try and use on the road, cos when you lift off for a bend say, the car wants to keep going!

My 2p worth

Matt

[Jez]

Just thought I'd say I agree with Billy...

[Nathan_200sx]

Hmmmm me like sound of afterburn http://300zx.co.uk/200sx/ubb/biggrin.gif wait while I dig out that top gun cassette http://300zx.co.uk/200sx/ubb/wink.gif
I want a switch with a lable saying afterburner in the dash to take on pauls "super pursuit mode" button.

------------------
Nathan
Red S13 few bit's n bobs 330ish BHP
Dont get even -- Get odd!!!

[Jezz_S13]

I bought both of them books for a stunning £26 delivered.

Can't wait to read those in bed, my life's about to become a better place. http://300zx.co.uk/200sx/ubb/wink.gif http://300zx.co.uk/200sx/ubb/biggrin.gif http://300zx.co.uk/200sx/ubb/biggrin.gif http://300zx.co.uk/200sx/ubb/biggrin.gif

Jezz.

[AshT_200]

Originally posted by Nathan_200sx:

I want a switch with a lable saying afterburner in the dash to take on pauls "super pursuit mode" button.




Don't you already have Turbo Boost Button http://300zx.co.uk/200sx/ubb/wink.gif

[docwra]

Originally posted by Jezz_S13:
I bought both of them books for a stunning £26 delivered.

Can't wait to read those in bed, my life's about to become a better place. http://300zx.co.uk/200sx/ubb/wink.gif http://300zx.co.uk/200sx/ubb/biggrin.gif http://300zx.co.uk/200sx/ubb/biggrin.gif http://300zx.co.uk/200sx/ubb/biggrin.gif

Jezz.


Im sure you must be able to think of something else to do in bed ..........

[Nathan_200sx]

Originally posted by antmcp:

Don't you already have Turbo Boost Button http://300zx.co.uk/200sx/ubb/wink.gif
Actualy your right I forgot about that http://300zx.co.uk/200sx/ubb/smile.gif



------------------
Nathan
Red S13 few bit's n bobs 330ish BHP
Dont get even -- Get odd!!!