Couple car questions

[lunchie]

1. I just read that the mclaren p1 runs 2.4bar of boost standard, isnt that like 37-38psi? How is that possible over the long term, I mean that sounds like HEAPS and I am guessing they expect the engine to last a while too? Just curious as even in the early 2000\'s sti\'s and evo\'s and euro hot hatches only ran 15-20psi didn\'t they?

Just seems like a lot of boost and I am curious what factors allow that level of boost pressure to be used safely and why such high levels are used in a road car.

2nd question.

Was reading about the revolution sti that makes 510hp with a fully built engine,sequential gear box and roll cage and stripped interior etc etc and yet only managed a 7:53 around the ring.

Now I know that is not slow really but a stock gtr or 911 turbo does it in the 7:20-7:30 time with very similar power but a whole lot more weight (probably 300-400kg.

Why is that? I mean its not like they had a bad driver in the car or anything either.

Just curious if there is some inherent deficiency about the actual sti platform that makes it unable to significantly improve its times as it seems like the STI was rebuilt/tuned with a much more track focused approach than a stock GTR or 911 would have from the factory?

[Kiwi_Fozze]

early 2000s sti / evo did run high teens boost, my sti is running 22psi atm.

the mclaren may be running really low compression ratio, and much higher octaine / water injection to keep the detonation point high.

the quoted pressures, are they bar absolute, or relative sea pressure? because if it\'s absolute, then knock 1 bar off as that\'s atmospheric pressure, which sits you at about 20psi.

[Stodart]

Subarus have a basic mechanical drivetrain where as evos, 911s and gtrs drive trains are more complex with sensors / computers monitoring / controlling the drive to where is needed and in the case of the Gtr changes in the supension as well ie firming / softening the damper setting in milliseconds. Power isn\'t everything for fast lap times is the whole package ie platform, brakes, suspension steering, tyres, computer aids etc . ie the Stock Gtr is quite heavy 1800kg but its fast because of electronic/computer aids in the 4wd system / suspension. and an amazing platform/chassis that has the ability to take a lot more power.

In this top gear video this is an example of a prototype prodrive subaru? in the UK with an e centre diff with with it on and of. in the lap times it was 5 second faster with the electronic trickery on.

[Marky]

Googled out of curiosity, McLaren mp4 thing runs 1.2 bar boosty boosty

[lunchie]

 Marky said:

Googled out of curiosity, McLaren mp4 thing runs 1.2 bar boosty boosty

yes it does, this is not the mp4 this is the P1 as stated

[BC5RA]

Its worth pointing out; for the Revolution STI to develop its 508bhp 500lb ft requires 1.9bar (27psi)

[lachlan]

some tractor pull engines run 3 compound turbos for 120 psi gauge pressure .

a wrx is made for rally / rally x / a fang up the twisties

the gtr was designed purely to beat the porka around the ring

its like comparing a go kart to a mx bike . could have idenitcle power to weight figures but they cant race each other

[BC5RA]

The revolution STI also wasn\'t developing the full quoted power for the record run, I remember reading somewhere. Around 400hp I think.

[Koom]

The P1\'s engine is a boosted version of the MP4-12C which ran at 17.3psi according to Road and Track. And then google tells me that the P1 gets more power using 3psi more than the 12C. So ~20psi makes sense.

2.4 Bar in a 3.8L engine should be making stupid horsepowers, not just quite alot

As for the STI having an inherent deficiency, yeah :: Nice one. Considering how well the same basic layout worked for a decade or so in WRC. Also look at Targa results. There\'s always the odd EVO or STI amongst the 911\'s and GTR\'s at the front. I wonder how much of the Nurburgering times come down to tyres?

Track conditions change. Its not like alot of those guys spend all year trying to set a good lap time. Reading recently about the time they set in the Holden ute, it came down to one last run at the end of the day. I\'d hazard a guess that alot of the other times coming from the ring are done in similar conditions, and there would be a few manufacturer\'s/companies at the top of the times charts that have had the luxury of lots of time spent there.

Just look at the list of cars around the 7:55 mark, it\'s not bad company to be in.

[BC5RA]

Considering the 911 layout is viewed as a dynamic stuff up, then I can\'t see the STI being inherently deficient.

It all comes down to time and testing invested.

[Munkvy]

Haven\'t watched the video as am at work, but how much lap traffic is there? And what tyres/weather conditions? As a few have mentioned, without a closed track and ideal conditions there is plenty of opportunity to have things go poorly.

Also, what is the car geared to? The more expensive cars are pretty well geared to hit 300km/hr. I imagine the Subaru may well not be? Plus 500hp doesn\'t necessarily make it a fast 500hp, depends on what the torque is like and the driveability out of corners...?

[lunchie]

 Koom said:

The P1\'s engine is a boosted version of the MP4-12C which ran at 17.3psi according to Road and Track. And then google tells me that the P1 gets more power using 3psi more than the 12C. So ~20psi makes sense.

2.4 Bar in a 3.8L engine should be making stupid horsepowers, not just quite alot

As for the STI having an inherent deficiency, yeah :: Nice one. Considering how well the same basic layout worked for a decade or so in WRC. Also look at Targa results. There\'s always the odd EVO or STI amongst the 911\'s and GTR\'s at the front. I wonder how much of the Nurburgering times come down to tyres?

Track conditions change. Its not like alot of those guys spend all year trying to set a good lap time. Reading recently about the time they set in the Holden ute, it came down to one last run at the end of the day. I\'d hazard a guess that alot of the other times coming from the ring are done in similar conditions, and there would be a few manufacturer\'s/companies at the top of the times charts that have had the luxury of lots of time spent there.

Just look at the list of cars around the 7:55 mark, it\'s not bad company to be in.

Yeah seems odd about the boost. Some people are quoting over 2bar, some only 1.5, I dunno maybe different way of measuring it/calculating it

[Marky]

If in doubt go to the sauce

 mclaren website said:

The 3.8-litre twin-turbo V8 petrol engine in the McLaren P1™ is a new version of the M838T unit, called M838TQ. It is fitted with an all new pressure charging system to optimise cooling and durability under the higher loads. The engine block has a unique casting, to incorporate the electric motor and also to provide increased stiffness.

The turbochargers are new and run at 2.4 bar (compared to the 12C which runs at 2.2 bar), while the compressor and turbine housing are bespoke to McLaren. As with the 12C and 12C Spider, the turbos are water-cooled and oil lubricated.

The petrol engine on its own produces 737PS (727 bhp) at 7500rpm, and 720Nm of torque from 4000rpm. Naturally, the engine has dry sump lubrication, as on a Formula 1 car, and a low sited flat plane crankshaft – to lower the centre of gravity.

- See more at: http://media.mclarenautomotive.com/model/7/EN/doc/49/#sthash.iabW9Vj1.dpuf

http://media.mclarenautomotive.com/model/7/EN/doc/49/

They measure in "absolute" terms

1 bar absolute = atmospheric pressure / nothing

2 bar = 14.7 psi "boost"

0.2 bar increase over the mp12c which as has been said runs 1.2bar - the P1 is assisted to make its 900-odd by the 180hp of electric motor

[D-Style]

Well if subaru ever bring out a $800K plus super STi.. who knows what it could do.

A top spec Super-Kart witgh a good driver would be faster round the track than most of these supercars.

[Stodart]

 D-Style said:

Well if subaru ever bring out a $800K plus super STi.. who knows what it could do.

A top spec Super-Kart witgh a good driver would be faster round the track than most of these supercars.

Yeah totally agree why didn\'t Prodrive UK or (even Subaru itself) build something like this with 500hp

[GC8E2DD]

Maybe because a 500HP EJ20 is something the bean counters were not keen to give a new car warranty on ...

Perhaps Prodrive could have, as they are not selling that thing anyway, but then again it seems the point of it was to showcase drivetrain technology rather than big horsepower. In a way making that showcase car push 500HP would kind of dilute the drivetrain technology message.

[Koom]

Also, its a UK car so they are talking 500BHp.

But then, Tommi Makinen did a 7:55 in a closer to stock STI. I think from what I have read on the internet, that he had 320Hp (so at a guess, 400 odd BHp).

[subieboy]

 Koom said:

Also, its a UK car so they are talking 500BHp.

But then, Tommi Makinen did a 7:55 in a closer to stock STI. I think from what I have read on the internet, that he had 320Hp (so at a guess, 400 odd BHp).

Yup

http://www.caranddriver.com/features/2011-subaru-impreza-wrx-sti-sets-nrburgring-lap-record

[Marky]

I do love those BritishHP\'s and their endless optimism

(Yes I know it\'s brake)

[lunchie]

are you guys comparing referring to the difference between power at the flywheel and power at the wheels?

[Marky]

Yes

Brake HP means flywheel HP - that\'s what the manufacturer will quote as well, they know exactly what it is

However 95% of the info you see from UK forums etc will say "I made XXX BHP" as they will "calculate out" the driveline losses by multiplying the wheel hp by say 1.3 for a 30% loss through driveline. It\'s an educated guess as the only true way to measure flywheel power is to whip the motor out, and actually measure it on an engine dyno

For arguments sake the 206kW @ flywheel most jap cars are quoted at can equate to anywhere from 140kW @ wheels to 190ish if you look at cars which might be a bit under-quoted for the @ the fly figure - it then varies depending on the gear tested in, the type of dyno, even the size of the wheels if on a rolling road can vary the power figure