RE: Subaru prepping BRZ Turbo?

[bicycleshorts]

Here are the top 5 links from Google for "difference between lag and boost threshold":
http://www.uksaabs.co.uk/UKS/viewtopic.php?f=1&amp...
http://www.clubwrx.net/forums/engine-modifications...
http://answers.yahoo.com/question/index?qid=100604...
http://www.pistonheads.com/gassing/topic.asp?h=2&a...
http://forum.miata.net/vb/showthread.php?t=212277

There is also a link my post above discussing how F1 engines are getting around lag.

Feel free to convince me otherwise, but I'm going to need sources, not just your word.

RX7 said:

perhaps you shouldnt believe all you read and gain your knowledge from experimentation and real world experience, rather than wikipedia!!

I've had a 280bhp+ Turbo Impreza, my Dad has a supercharged MX5 and I have a NA MX5. We're also in the process of building up a NA screamer with ITBs, racier cams and forged pistons. I'm by no means an expert, and I'm still learning, but the difference between threshold and lag is pretty fking basic.

ETA: Agreeing with cmoose, this is the last post you'll see from me about semantics.

You're correct, more choice is better. But in my opinion, a Turbo would ruin the drivability of the car, I would much rather see a bigger NA engine or a supercharger.

Driving my Impreza it was a guessing game as to when the boost would come in, often meant applying throttle before the apex of a corner and waiting for it to spool up. That was fine in that car, because it's a jack of all trades, and covered distance very quickly. In a "light", 2wd sports car, I don't think it's a good idea.

Kambites probably knows better than I do, but I'd imagine that's why they choose a supercharger on the Lotus Exige (and Ariel Atom).

I found something interesting while looking through those links, off to investigate if a second throttle body does affect the noise of a supercharger as my Dad is failing noise tests at track days...

Edited by bicycleshorts on Thursday 25th October 13:34

[kambites]

bicycleshorts said:

Kambites probably knows better than I do, but I'd imagine that's why they choose a supercharger on the Lotus Exige (and Ariel Atom).

In the case of the Exige, I suspect it was just what was easiest to do from what Toyota offered them (that engine was supercharged in the Corolla). Lotus don't have much of a development budget for power-trains.

[bicycleshorts]

kambites said:

bicycleshorts said:

Kambites probably knows better than I do, but I'd imagine that's why they choose a supercharger on the Lotus Exige (and Ariel Atom).

In the case of the Exige, I suspect it was just what was easiest to do from what Toyota offered them (that engine was supercharged in the Corolla). Lotus don't have much of a development budget for power-trains.

Now that is interesting, unfortunately a quick look on the classifieds shows they're still fetching quite a bit.

[kambites]

bicycleshorts said:

Now that is interesting, unfortunately a quick look on the classifieds shows they're still fetching quite a bit.

Quite rare too. I didn't know they existed until someone I know bought one.

[ScoobieWRX]

My guess is to reach those 280 ponies they'll use something tried and tested like a TD04 or a VF35 but they are not twin scroll nor ball bearing.

I'd like to see them use something in between maybe like a VF30 but twin scroll and ball bearing so they not only spool up quickly but from fairly low down. That will minimise the lag and should kick in shortly after 2000rpm, make a bar of boost by 2500rpm and keep boosting till near the redline. So long as it makes 16-17psi peak and holds on to near enough a bar by the redline you'll get your 280 ponies and acceleration should be smooth, strong and linear to the redline.

Subaru know exactly what they are doing with turbo chargers and hopefully will come up with a nicely rounded/performing package.

Someone said earlier how about a 2.5. IMHO N/A aspirated would have been a better choice but they have to get the car through stringent euro emissions regs hence why i think they went 2.0Ltr although i'm sure a 2.5 turbo would meet those regs no problem. Now that would be awesome!!

[RX7]

bicycleshorts said:

You're correct, more choice is better. But in my opinion, a Turbo would ruin the drivability of the car, I would much rather see a bigger NA engine or a supercharger.

Driving my Impreza it was a guessing game as to when the boost would come in, often meant applying throttle before the apex of a corner and waiting for it to spool up. That was fine in that car, because it's a jack of all trades, and covered distance very quickly. In a "light", 2wd sports car, I don't think it's a good idea.

With regard to drivability are you speaking from experience, i.e have you driven the n/a and this offering, or just making an assumption?

How can it be a guessing game as to when the boost comes on, it will on boost at the same revs every time! N/a is def for you if thats how you drive

And your right, no point discussing semantics, but with your ref to anti lag, how do you think that works? Its nothing to do with boost threshold, it so keeps the turbo spinning so there is no "lag", the clue is in the title

[kambites]

RX7 said:

How can it be a guessing game as to when the boost comes on, it will on boost at the same revs every time! N/a is def for you if thats how you drive

I think he's talking about turbo-lag not the boost threshold - nothing whatsoever to do with the revs; just down to air box volume and turbine inertia. If anything our Octavia's lag becomes more pronounced as the revs rise, not less.

Traditional anti-lag works by injecting fuel into the exhaust up-stream of the turbo when you come off the throttle so the exhaust gas volume doesn't decrease. Again, nothing to do with rpm, as such.

Edited by kambites on Thursday 25th October 17:10

[bicycleshorts]

RX7 said:

With regard to drivability are you speaking from experience, i.e have you driven the n/a and this offering, or just making an assumption?

Yes, I've driven the NA GT86. No, I've not driven this as it doesn't exist.

RX7 said:

How can it be a guessing game as to when the boost comes on, it will on boost at the same revs every time! N/a is def for you if thats how you drive

Here's how a turbo works:
- You press the accelerator pedal.
- Exhaust gases build for X time.
- The turbo comes on boost.

That amount of X time is what I would call 'lag', feel free to call it whatever you want. That time (which is subject to revs, exhaust temperatures, blah blah blah) is what I don't want in my sports car. I then have to second guess when the boost will arrive after I put my foot down, meaning I have to adapt my line, braking and can't feather the throttle as well.

This is what people mean when they talk about throttle response. If you don't mind it, great! I do, as do others here.

RX7 said:

And your right, no point discussing semantics, but with your ref to anti lag, how do you think that works? Its nothing to do with boost threshold, it so keeps the turbo spinning so there is no "lag", the clue is in the title

Correct. The ones I've looked into keep exhaust pressure up by firing fuel into the exhaust, keeping turbo spinning so that when you put your foot down, there is no lag and the throttle response is much quicker. Nothing to do with boost threshold, everything to do with lag and throttle response.

Again, you seem to be struggling with these two separate concepts:
- One is the RPM at which boost comes in.
- The other is the time difference between throttle input and the turbo spooling.

I don't give a st what the minimum RPM for boost is, as long as it's something sensible.

Edited by bicycleshorts on Thursday 25th October 17:37

[Niffty951]

I'm sure you guys would prefer to just argue than to make any particular point but for clarity on the above post. The turbo is always spinning while the engine is running. Below a certain rpm the engine will not spin the turbo fast enough to produce positive pressure. This rpm will be lower in higher gears than lower gears and could be described as the boost threshold.

For most common cars this will be 2000rpm or less so not significant in normal driving. The lag is the reaction time of the system between throttle and response. It's usually very low, tenths of a second in modern cars but in some circumstances, can still be annoying as you lose the ability to instantly modulate the throttle mid bend (such as in a slide) but I would argue that in practice it's perfectly easy to keep the turbo spinning.

I personaly think the lack of ability to break traction on demand in an underpowered car presents far more of a limitation.

[kambites]

anonymous said:

[redacted]

That feeling of surge you get with turbocharged engines is the turbo-lag and I hate it in a sporty car. I want all of the power that I ask for when I press the throttle, not half a second later.

On the other hand, I have no wish whatsoever to be able to break traction under power.

[fildigger]

I have had many cars of a sporting nature over my 30 years of driving, the one and only car i have ever written off (and the only accident i have ever had..to date!) was in a 2WD Ford Sierra Sapphire Cosworth....and i have no doubt in my mind that the reason i spun the car 180 degrees and broad sided into a very solid curb was because the Turbo came on boost at such an alarming rate, the poor Ford chassis and rear wheel drive completely lost all sense of direction and catapulted me into almost near oblivion

I swore that day i would never own another Sapphire Cosworth...and i haven't


ps. i have had many turbo'd cars since but they have all been All wheel drive!

[Herman Toothrot]

All this turbo na talk, it is pointless. People like different things and how you drive and how its setup makes a huge difference.

I've never driven a car with really good throttle response - but that's because I'm comparing to bikes. Try the throttle response on a litre sports bike and you will understand, instant. Its why there are so many videos on you tube of people flying off the back or high siding as its taken them by suprise.

Turbos if pooling and wanting sudden power you won't get it in the wrong gear. On the road it can be quite hard to keep constantly on boost, you'll be going to fast :-). Track is a totally different kettle of fish and how the boost control is setup, size of turbo, size of intercooler, blow off valves etc can make all the difference. Weight of flywheel can have a more pronounced effect on the throttle response in that suituation.

[s m]

fildigger said:

I have had many cars of a sporting nature over my 30 years of driving, the one and only car i have ever written off (and the only accident i have ever had..to date!) was in a 2WD Ford Sierra Sapphire Cosworth....and i have no doubt in my mind that the reason i spun the car 180 degrees and broad sided into a very solid curb was because the Turbo came on boost at such an alarming rate, the poor Ford chassis and rear wheel drive completely lost all sense of direction and catapulted me into almost near oblivion

I swore that day i would never own another Sapphire Cosworth...and i haven't


ps. i have had many turbo'd cars since but they have all been All wheel drive!

Welcome to the world of the WIDOWMAKER .....


http://www.pistonheads.com/gassing/topic.asp?h=0&a...

It always intrigued me they banned the E21 323i from sale in Sweden as it was too extreme for the road!

Plus the 205gti enjoyed quite a reputation for fast rotation in some quarters

[s m]

Herman Toothrot said:

All this turbo na talk, it is pointless. People like different things and how you drive and how its setup makes a huge difference.

I've never driven a car with really good throttle response - but that's because I'm comparing to bikes. Try the throttle response on a litre sports bike and you will understand, instant. Its why there are so many videos on you tube of people flying off the back or high siding as its taken them by suprise.
.

Wasn't it RobM77 who couldn't get on with the DBW throttle on his 330i ( too much delay ).... but liked the 320d?
I didn't mind my old E46 330i response - heavy flywheel compared to some other cars I've had.... But you get used to it

[kambites]

Herman Toothrot said:

I've never driven a car with really good throttle response - but that's because I'm comparing to bikes. Try the throttle response on a litre sports bike and you will understand, instant. Its why there are so many videos on you tube of people flying off the back or high siding as its taken them by suprise.

I don't understand this - a good car should also be instant. In my experience, fuel injection causes a bit of a delay (no idea why) but a decent carbed car engine with a cable throttle should give better throttle response than a modern EFI bike. I've felt the throttle response on a modern 600cc triumph triple and that certainly didn't seem anything special.

Edited by kambites on Friday 26th October 09:15

[fozluvscars]

In my experience, having a turbo is great for scaring passengers when it kicks in, but not so good for being able to 'make' that gap when overtaking without dropping down a cog. (Although that scares them too)

[JdmRacer]

anything fast said:

ABOUT FOOKIN TIME!

Why not have three models?

The N/A entry level

A turbo with say 250 odd bhp

And a Nutter twin turbo with 400 BHP and wide arches.. a ferrari baiting and porsche ttting monster, such a car would make the whole range more desireable and should be good value for the performance on offer..

Go on... it can be done, why not even badge the twin turbo as a Toyota and stick a little Supra badge on the back?

+1