Is the power a turbo'd car produces totally dictated by the boost?

Hypothetical scenerio:

Take one standard MY99, add dawes and boost gauge and a fuel cut defender and crank up to 1.3 bar :eek: With the standard exhaust, etc the car would stuggle like hell with this and the turbo would not doubt let go eventually.

Now, take standard MY99 add dawes, boost gauge, fuel cut defender, full scoobysport decat, ITG filter and crank up the boost to the exact same 1.3 bar.

Then RR them and race them? Would the decat car have more power and be faster or would the hightly stressed dawes only car be as quick?

No prizes for guessing which one will go pear-shaped first though :D

Boost = torque, if applied correctly.

I very much doubt the first example will work. The standard exhaust is far too restrictive and will create back pressure which will make the car det like hell.

Well to start with id stick with the standard air filter, it seems more reliable than any of the aftermarket ones.
Performance wise... if you wanted to extensivly modify your car then no matter which exhaust you had on, i would get a remapped or new ecu to compensate.
Theoretically, the fully decat car would be the quicker as there is less resistance but you then have to hope you dont get overboost, in which case the car with the more restrictive car would gain some ground back until you hit about 120mph when your overboosting would go as the boost starts to drop off about then.
Lots of pro's and con's when tuning a car really but id do the brakes first thou ;):D

Tony:D

Problem is/will be heat related - as mentioned, OE exhaust would see EGT's go through the roof.

1.3 bar on the OE turbo and TMIC will see inlet temps do the same - chances are you're getting less power at 1.3 than at 1.2 bar due to the charge temp.....

A key requirement for power is the amount of air you can flow through an engine, and the temperature of that air - boost is, of course, a major factor in this. But there's lots of other considerations, it's not just 'whacking up the boost' :D

Richard

I was aware that the EGT and charge temps would go through the roof very quickly on the near standard car but I was just curious to know if you nailed both cars when they had just warmed up (hence less chance of det) would there be any difference in performance.

The real reason for asking is that since I put my centre cat on boost has started to creep up towards 1.3bar. This is probably not safe with the standard downpipe on so I've been making sure I limit myself to short blasts and sometimes use the right foot to limit boost to 1.2bar. However, when the downpipe is on it'll run 1.3bar(ish) nice and safe and I was wondering if the acceleration I felt this morning at a not quite safe 1.3 bar was as good as it's going to get when running at a nice and safe (and less restricted) 1.3bar. Does that make sense :rolleyes:

No bothers it was holding fine at 1.21 as set that night but as soon as the centre section went on it crept up to 1.25 but will start to go higher and higher when pushed (suggesting the turbo is struggling)

I'll bring her back a half turn to keep everything safe till I get the decat on and we can set it up permanently - well, until you persuade me to get a big turbo ;) :D

That seems to answer the original hypothetical question :)

What's FCD by the way?

Fuel Cut Defender.

Turbo is not struggling just spooling up more enthusiastically so needs to be compensated for by a change to the Dawes.

Set it so that it never goes over 1.25 bar in hard driving - this will mean you get a bit less the rest of the time.

Fitting the centre section really seems to have made a big difference. Obviously the boost has gone (but will be coming back down) up so that makes it a little quicker but it seems to spool up a little quicker, eariler and a with a bit more brutality as well. Actually, the car 'feels' pretty darn fast and it feels like she wants to 'go' all the time :)

I am beginning to think though that even with full-decat and 1.25bar I'll still want more :rolleyes:

The slope has got me hasn't it??!! I'll book myself into slope-a-holics anonymous tonight :D

Power is related to torque, so best stick to torque for comparison, and leave power to the rev heads.

Torque is proportional to the absolute manifold pressure, all other things being equal. But equal they are not.

Torque is generally a function of VE (volumetric efficiency), or airflow in simple terms. By increasing the MAP, you will stuff more air in for sure. But using a turbo to do it might lead to higher temperatures. Since pressure is a function of temperature, you may get nearly all your apparent boost increase by simply heating the air.

SO then you are pushing not much more air in Mass wise, which is what counts. You are also increaseing inlet temperature and cylinder temperatures, leading to pre-ignition and detonation.

Ragging the balls off a small turbo is bad, mainly for the following 3 reasons.

1. To get the boost, you need to spin the turbo fast. SO your compressor wheel will start to do work on the air that doesn't actually compress it, but as with all work, it will heat it.

2. The exhaust side of the turbo will be sized with the turbo as a whole. Small turbos will run smaller ex. housings creating good gas speed for spooling, but more back pressure, reducing VE and increasing heat a little.

3. The exhaust side of the turbo is a turbine. If you look in carefully you will see the gas is run around the outside of the turbine wheel, and out through the middle, and relies on the pressure difference alone to do this. However, at high speed, the turbine, however efficient will start to throw the gas to the outside, similar to the compressor. If run too fast, you end up creating hugh back pressure because the gas just can't get out through the middle.

Inlet temperature and exhaust back pressure are what will ultimately kill you.

Dropping both will reduce cyinder temps, allowing increased ignition advance, which is more power for free, getting the most out of the same quantity of fuel.

And it goes on....

Paul

Pavlo

But isnt there a limit on how far you can 'advance' a certain enginee regardless of the turbo choice...
Once you advance past a certian point the power falls off

Presumably running water injection then will lower intake temps, but if your already at peak advance then its just for safety?

Surely if you have a 2 litre power is boost when you hit a certain point, larger turbo's and higher and higher boost, on uprated internals

The cossies used to run silly boost figures..... then you start with the 2.2 and 2.5, but you ultimately end up raising the boost and the power of your car is governed by the size of the turbo you are running on it..........

Minimum advance for best torque (MBT) - it is debatable whether you can hit this on a Scooby. Some have claimed they have, but on the other hand increasing heatsoak during mapping may lead to lower torque rather than crossing MBT?

Dont fancy a £1k + Dyno session to get this for the extra power!

Could hire out an RR - but then again would suffer from rising temps no doubt.....

Once the car feels slower on the road I'll know for sure its been passed. So far have not hit this limit yet from a driving feel viewpoint....

yes you can go too far with advance, but unlikely at 1.3 bar, unless you are running hugher FMIC and water injection, a la trout.

Worth noting is that the closer you are to MBT, the smaller the gains in torque are, so it's not always worth finding it at all costs.

paul

Pavlo

Yes your right...

I'm hoping to raise the boost, once various tweaks have been done 1.8 bar should be comfortable

I have a fmic and have had erl mappable wi on for some time...... - just waiting for the 'tweaks' before its remapped with the WI.

1.8 Bar :eek: What mods have you got??

john banks
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Posts: 5448
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Registered: 04-11-2000
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posted Monday, December 09, 2002 13:01


John he posts from the future :D

Saxoboy weird thing is that I decatted the centre section today and it seems more sluggish than with the the cat in.

I put a Dawes in on monday and wound it up to 1bar (Not going to go much higher than that!) and it was fast as. Went to have the centre fitted and it seemed slower!

Any ideas?

No idea why that is cause mines is defo faster and better responding. Don't be scared to go more with the dawes (assuming you have non-standar bb here as well). The scooby runs rich as hell so your ok for a healthy 1.1 or even 1.15bar provided you only go near 1.2 on the coldest of days. You shouldn't run lean and shouldn't get detonation as long as you've got optimax/sul. I've seen the logs for my car at near 1.2 bar with just a scoobysport bb and dawes and it was all pretty safe, 1.1 with a partial decat should be completely trouble free.

A lot of tuning IMO is common sense, if the car sounds funny or seems to be grumbling try and figure out what you've done to upset it :D

I take it back what I said.

I have just been out and wound the boost up a bit further and been out for a run in it and I didn't realise that you could wheel spin a Scooby :D

Just over the 1bar but will wind it up even further tomorrow when I have a play.

Contigo the time thing is a Scoobynet bug AFAIK.

Saxo Boy

A few tweaks here and there ;)


[Edited by steve McCulloch - 9/13/2002 10:09:39 AM]

Care to ellaborate? :D

Nah - I could tell you - but then I'd have to kill ya......

We'll see what I get at the Well Lane RR day!

It includes a big turbo Kenny so get buying one ;)

Edited - because I can

[Edited by steve McCulloch - 9/13/2002 3:41:19 PM]

1.25 bar tops please Kenny even with a full decat. When we were logging that night I showed you what happens to ignition timing when you run too much boost. If you want to run more get a bigger turbo. Part throttle is not a panacea either.

The decat car will run more airflow, less exhaust back pressure and less lag, more ignition advance so will be quicker at the same boost pressure.

The other problem with using a FCD to increase boost is that the timing will be inappropriately advanced - hence why your ECU map has the last column sensibly retarded to cope with a sensible amount of extra boost. But the sensible limit is 18 PSI or 1.25 bar.

[Edited by john banks - 9/12/2002 1:05:36 PM]