ric

Sorry, but one question:
How could you run the Imprezas engine with such high boost level reliable? I think the UK-Impreza has a small turbo. This requires very high speed for the turbine crankshaft at high boost levels. (-> a lot of heat!)
MRT (from Australia) wrote me (by email) that a remapped ECU with high boost level could be dangerous for the small turbo. They advised me to fit a bigger turbo (the one from STI5). They say that the bigger turbocharger makes a lot more power at 1bar of boost than the small one at 1.3bar? The bigger turbo is about 1000£. You can fit it and the car runs with the standard ECU, no problem. +25-35bhp +25% torque.

Lee

A good point, however proof of pudding is in the eating they say...

All all the incidents where a chipped (whether is be PE / superchip / HKS etc) car has had a problem, turbo failure wasnt mentioned.

However MRT are correct. If you spin the turbo faster than normal it will generate more heat. Jap scoobs have the intercooler offset I believe with a cooling funnel for the turbo.

I guess at the end of the day the £1000 may have a lot to do with it. From your (MRT) figures, spending £1000 on the turbo would have been better spent on a PE remap if power gains are the order of the day.

Andy Tang

iTrader: (3)

You have to sure that's the way you want to go. You will be getting more power, but there is more lag. Bigger turbos, take longer to spin up! At least that's what I've been told!

Andy

Ian Cook

I have jsut had a quick read through some earlier threads regarding the PE Phase 1, and it appears to be running max boost of 18 PSI and 16-17 PSI as standard, this does not sound as high as some people that have been running 20PSI and above, I suspect in the 20 PSI bracket unless you do some serious rework on the car, including the bigger turbos etc, you are going to have a lot more problems.

Lee

Bob Rawle was running some serious boost on his STi 2..on the 14thAug dyno day it was peaking at 22.5psi and holding 18.5psi

I imagine a UK turbo would pop !

Scottie

Don't quite get this...

"They say that the bigger turbocharger makes a lot more power at 1bar of boost than the small one at 1.3bar? The bigger turbo is about 1000£. You can fit it and the car runs with the standard ECU, no problem. +25-35bhp +25% torque."

Surely power and torque (all else being equal)will be a function of boost, not turbo size? If the intake manifold and ports are the same size before & after, less (boost) pressure = less airflow = less power. I always thought the reason for bigger turbos was to run higher boost pressures to go for big power and torque figures.

Sorry, but I don't believe that by simply changing to a bigger turbo with the standard ECU you will get +25-35 bhp and + 25% more torque (especially at lower boost).

If anything, I would expect to see a reduction in power & torque with the bigger turbo running less boost.

At the risk of putting my neck on the line here, methinks this is more ill informed Australian advice.

Re turbo cooling and offset intercoolers, my Scoob (UK MY99) has a slightly offset intercooler and part of the bonnet scoop provides air flow to/heat vent from the turbo.

Scottie

[This message has been edited by Scottie (edited 03-09-1999).]

JohnS

iTrader: (1)

Its not just the boost pressure that matters, but tha volume of air that the turbo can push into the engine that matters.

Small turbos spin up quicker, giving better low end response and reducing lag, but are limited by the volume of air they can flow at higher rpm. When boosting at say 1 bar, they can't flow as much air into the engine as a bigger turbo running the same boost pressure.

Scottie

John,

I agree that in isolation a bigger turbo will flow more air than a small turbo at the same boost pressure. It is, after all just a pump. Its simple physics - to attain the same pressure a larger turbine will have to flow a greater volume of air.

My point (VERY generally) is that a bigger turbo running less boost will flow the same air as a smaller turbo running higher boost (give or take about 100 variables!).

In this application, though, the turbos are not running in isolation and there are several variables. The big issue in an internal combustion engine is density, not volume. The volume of air is constant turbo'd or not and dictated by cylinder volume. Volume flow rate is dictated by (forgetting induction filters, etc) the narrowest diameter of the pipework (hence the use of restrictors in motorsport)through which that air must flow. If you want to pass more air through a given diameter of pipe (which remains constant) you need to increase the pressure to increase the density for a given volume of the gas.(Boyle's Law - I think)

Thats why scoobs go better when its wet and cold - higher air density (or more correctly more oxygen molecules for a given volume)

The same applies in naturally aspitated engines, albeit in reverse as they suck the mixture in thus generating negative pressure. You increase the flow rate to minimise the negative pressure on the induction stroke to get more power.

To get meaningful power & torque improvements from a turbo change alone you also need higher boost(to increase density) and high revs to make the most of the available incease in gas density provided.

If all remains constant, as per the original post (including the ECU)a bigger turbo alone running lower boost will not give those levels of power and torque enhancement.

I could be wrong but I stand by my original argument that to get more power you need higher pressure, not just the ability to flow more air.

Over to you all for the flaming

[This message has been edited by Scottie (edited 03-09-1999).]

DYNT

Turbocharger- IHI VF23 & IHI VF24 & TD04L ..tested all.

I find that IHI VF24 spool up time is faster then IHI VF23.

TD04L .... 500rpm lower spool-up time then IHI VF24 but ....5600rpm peak power.

I'm using IHI VF24 right now...all the way to red line.

Want to know more about Turbocharger developement ........ call 01865 821062 (Owen Developement).

Lee

Scottie..your UK99 must be different to mine which I doubt

The cars I've seen have the intercooler at about 20-30 degrees angle, plus the turbo has a funnel all the way to the bonnet. Not the same as mine.

Perhaps you have a "special"

Scottie

At the risk of being controversial again, is the amount of boost not regulated by wastegate actuation as opposed to turbine speed which would be dictated by exhaust gas pressure?

Thus small and big turbos would (once up to speed) spin at the same speed anyway - just that the bigger one would have the capacity to deliver more boost at that speed?

Just a thought - you tell me

Scottie

Scottie

Lee,

Not a special and will be the same as yours

Looks like you could rig up a bonnet scoop to turbo cooling duct quite easily though as the intercooler sits right of centre as you look from the front.

Scottie

Darren Soothill

The offset intercooler and vent running down to the turbo was a feature of the early cars ie pre 97 models. These cars had a bigger turbo. Post 97 the cars didnt have the direct vent running down to the turbo.

Darren