Super vs Turbocharging the car

[carbonBLUE]

Originally Posted by brillo

It would seem to me that the FR-S / BRZ could really benefit from a small efficient low boost s/c that wouldn't require an intercooler. I bet you could create a sub $4k kit that doesn't add much weight, gets you like 50whp/50ftlb on 5-6lb of boost.

What do folks think of a non intercooled low boost s/c? What type would you go with?

i would say you can tune 80-90 whp out of 5-6 psi, my celica can tune 130whp off of 8psi and i cant change valve timing on my exhaust valves, dont have direct injection, .2L smaller
a conservative tune would be on the factory sc/turbo option would yield 50-70 whp to make it reliable, the new wrx is supposed to have 275hp out of its 2.0L

[uspspro]

It's amazing that people are still talking about power band like it's the same thing as responsiveness.

Sure a small or VGT turbo might make full boost by 2000 rpm or whatever, on a dyno pull starting at 1500. That's where the power band starts, cool.

However, transient response is "what do I get right when I step on the throttle?" How long does it take to get the engine's full output (at a given rpm)? On an NA it's almost instantaneous, same with a SC. With a turbo, no matter how low of an RPM it can make boost, it's still needs to spool after you crack the throttle and adds to the transient response.

For example a Rotrex setup will make less low-to-mid range torque than a properly sized turbo setup, but the Rotrex will still have a sharper response to throttle inputs in the real world.

[OrbitalEllipses]

You guys are shooting low. Turbo? Super? Only one? Cmon guys, the answer is twin-charging.

[brufleth]

Originally Posted by old greg

Yes.

They use pivoting stator vanes in the turbine housing to vary both the cross-sectional area of the housing and the effective radius of the turbine wheel. The problem is that these vanes are fairly fragile and not particularly suited to the high EGTs of a gasoline engine. They are very common on diesel engines though.

The intro to that article is confusing effectiveness at different RPM to lag. I think some other people here are doing that too. It is one thing to simply adjust based on RPM but that isn't going to change the need to spin up the turbo. A better but much more complex solution is to use multiple inputs (RPM, throttle rate, load, and of course ambients) to set and change the variable geometry.

The article does mention that they're starting to use electric servos which makes it easier to design a more non linear VG schedule and kicker. It also sounds like that sort of performance enhancer isn't worthwhile for what these things are used on. They aren't worried about slight improvements in low to high power transient times.

[DarkSunrise]

Originally Posted by Turbowned

What's your current car? The most responsive turbo car I've been in are the 2010+ A4's. Peak torque is 258lb/ft and it comes on at 1500rpm. Pretty crazy!

I don't have the energy to spew a bunch of technical data right now (if I even had any), but the seat-of-my-pants dyno tells me I want a supercharger over a turbo. With the exception of the aforementioned A4, every turbo car I've driven has lagged at the low end, which would ruin the personality of a car like this one. The linear power curve of the roots blower (can't speak from experience on a centifugal) can't be beaten. This past week I've rode in 3 Subarus - '04 STi stage 2, '11 WRX stock, and '02 WRX with hybrid 2.5block/2.0heads, VF39 turbo w/ RA gearset, and they all had laaaaaag. Compare that to my S4 which you could put a ruler on the power and torque curve; it comes on and stays on until redline which is just phenomenal. It probably helps that the engine is a 3.0L vs. a 2.5 in the Subies, though.

Anyway, I'll gladly give up peak power for responsiveness in this car, and I think most people would agree. I don't think I want more than 300bhp anyway, which I think an intercooled Rotrex and supporting mods would accomodate.

2011 GTI. Even with a relatively high CR and a small turbo, it still feels less responsive than a NA engine.

Also, you're absolutely right about the Subaru EJ257, it's gutless below 2500 rpm. I'm glad Subaru didn't just drop that engine into a BRZ as some were hoping.

[brufleth]

Originally Posted by uspspro

It's amazing that people are still talking about power band like it's the same thing as responsiveness.

Sure a small or VGT turbo might make full boost by 2000 rpm or whatever, on a dyno pull starting at 1500. That's where the power band starts, cool.

However, transient response is "what do I get right when I step on the throttle?" How long does it take to get the engine's full output (at a given rpm)? On an NA it's almost instantaneous, same with a SC. With a turbo, no matter how low of an RPM it can make boost, it's still needs to spool after you crack the throttle and adds to the transient response.

For example a Rotrex setup will make less low-to-mid range torque than a properly sized turbo setup, but the Rotrex will still have a sharper response to throttle inputs in the real world.

Bingo. I work with small jet engines that can output over 2500HP. Getting that power quickly is difficult though. Hence my VG turbo comments. You can design a turbo to patch up a point on the power curve steady state but the transient response of the turbo is going to lag behind during fast transients from low power.

I currently drive (and love) a 2007 WRX. Fast throttle changes lead to very obvious turbo lag. It can be obnoxious when you suddenly want power unexpectedly. If you know ahead of time you can usually compensate but you don't always know when a hole is going to open up in traffic or whatever.

[Sasquachulator]

Ive always wondered this.
Couldnt they route the header straight to the back instead of snaking it around the front to the other side before going to the back?
And anyone with any boxer or engine knowledge would be able to identify any drawbacks with such a design?

[SpeedR]

The reason a supercharger will be a smarter option than a turbo for the FR-S is boost control and 12.5 to 1 compression.

With super high compression you must have very good control of boost turbos do not give that. Fine control and liner boost path are what small superchargers do very well making them consistent and EZ to tune.

Turbos are better in just about every other way but for this car till they change the engine out SC is the way to go.


For RR and big auto/X I currently run a 67/65 with .58 hot side that spools as fast as the stock twins in TT and makes 750 to the wheels. For the road I run a .98 hot side and it makes just under 850 to the wheels (that’s about 1K to the crank). I am a BIG fan of turbos but they are not for every application!

[Turbowned]

Originally Posted by SpeedR

I am a BIG fan of turbos but they are not for every application!

+1. In case you couldn't tell from looking at my SN

[serialk11r]

Originally Posted by brillo

It would seem to me that the FR-S / BRZ could really benefit from a small efficient low boost s/c that wouldn't require an intercooler. I bet you could create a sub $4k kit that doesn't add much weight, gets you like 50whp/50ftlb on 5-6lb of boost.

What do folks think of a non intercooled low boost s/c? What type would you go with?

Yea this is what I think is the best thing for this car, although I think you still might want some intercooling (alcohol injection?). The SCed Lotus engines for example give 15% boost but still have intercoolers even though the temperature increase is modest.

[Jordo!]

What would be best is a roots blower.

If someone can figure out how to fit one...

Fitting an A2W IC is they way to go. Big HE in the front, mount the IC core wherever and add a nice water pump.

Done.

[NESW20]

Originally Posted by Dimman

It was noticeable even if it was very, very slight on my 1j car and it had two tiny ceramic turbines. Even punching it at 4k. It's the disconnect between throttle open and power. Turbines still take time to spool up and intake-side then takes time to pressurize.

i understand what you're on about, however i disagree with a technical aspect of your complaint. during sporty driving, i can't think of a situation aside from upshifting where one should ever go from closed throttle to 100% open throttle immediately. it is generally preferred to "roll into" the throttle, as opposed to "punching it," per se.

Originally Posted by Turbowned

What's your current car? The most responsive turbo car I've been in are the 2010+ A4's. Peak torque is 258lb/ft and it comes on at 1500rpm. Pretty crazy!

I don't have the energy to spew a bunch of technical data right now (if I even had any), but the seat-of-my-pants dyno tells me I want a supercharger over a turbo. With the exception of the aforementioned A4, every turbo car I've driven has lagged at the low end, which would ruin the personality of a car like this one. The linear power curve of the roots blower (can't speak from experience on a centifugal) can't be beaten. This past week I've rode in 3 Subarus - '04 STi stage 2, '11 WRX stock, and '02 WRX with hybrid 2.5block/2.0heads, VF39 turbo w/ RA gearset, and they all had laaaaaag. Compare that to my S4 which you could put a ruler on the power and torque curve; it comes on and stays on until redline which is just phenomenal. It probably helps that the engine is a 3.0L vs. a 2.5 in the Subies, though.

Anyway, I'll gladly give up peak power for responsiveness in this car, and I think most people would agree. I don't think I want more than 300bhp anyway, which I think an intercooled Rotrex and supporting mods would accomodate.

this again comes down to driving style, in my opinion. in the recent past i ended up autocrossing a 100% bone stock 2011 wrx. it was the first time i had driven the vehicle when i pulled it to the starting line (no exaggeration). my first run was basically a throw-away run, when i learned i needed to open the throttle sooner to overcome the throttle lag coupled with the turbo lag coming from off-throttle to on-throttle. once i overcame this, i ran the 2nd fastest d-stock time of the day. i noticed that once i was on-throttle at all in a "spooled" region of the rev range, the throttle was as responsive as i needed it to be. it was simply a matter of adjusting my driving style to the vehicle i was in at the time.

Originally Posted by DarkSunrise

2011 GTI. Even with a relatively high CR and a small turbo, it still feels less responsive than a NA engine.

Also, you're absolutely right about the Subaru EJ257, it's gutless below 2500 rpm. I'm glad Subaru didn't just drop that engine into a BRZ as some were hoping.

it's true. subarus (and evos, for that matter) are pretty much worthless outside of boost at low rpms. however, who drives them that way? is anyone here really anticipating spending much time cruising around at 2000rpms and expecting instant 200ft.lbs. of torque or something? let's be reasonable here.

[Nobilis]

Hi all, i am a former sc'ed S2000 driver. What i can say is, as this is a 2.0 lt. N/A car like S2000, it will need more torque at low rpms which it misses. A centrifigual sc will be a nice and reliable option but still, you will need more torque at low RPMs as the torque graphic will be linear to RPM.

My choice will be a root type supercharger if anyone produces N/A will never be enough!

[Dimman]

Edit: @ NESW20:

'Punching it' is a bit of an extreme example to put the difference between low rpm torque/boost and transient response into perspective. Some people have no idea about it, having only 'bench-driven' the BMW 335, or whatever. "But it makes peak torque at 1200 rpm!!!" Low rpm torque on a turbo is not the same thing as response.

I know you get it, and thankfully some more recent posters show that they do too. But a lot of people unfamiliar with driving a turbo car don't.