Super vs Turbocharging the car

[NESW20]

if you size a turbo for spool and low-mid range, you'll be amazed at the response, especially on a high-compression engine that doesn't rely on boost to make torque.

monkey wrench racing makes a 1zz turbo kit utilizing the garret gt28 turbo, and they claim 10psi of boost BEFORE 3000rpms, and roughly 220-240whp.

i am all-for small, responsive turbos just as much as big silly ones, but honestly, lag (or lack of responsiveness) shouldn't be made out to be such a big deal. anyone who's really concerned with lag and responsiveness will learn to size their turbo properly per intended use, and then learn to drive the car appropriately.

years ago i stumbled across a comparison article in a mustang magazine. they tested a turbo, positive displacement s/c, and a centrifugal s/c. the turbo made more torque at a lower rpm than either of the superchargers. as an added bonus it also made more top end power.

[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.

[old greg]

Originally Posted by Dimman

Also are they quieter than the roots?

They're quieter than the old-school three lobe roots blowers, but louder than a TVS. And in the case of Kenne Bell, they're just loud as shit.

[Unamused]

2010+ Legacy GT design^


BRZ design^


This design would minimize spool time. It works well in the LGT. Comparing it to the engine pic of the BRZ it looks like it could possibly fit. Piping might be a different issue though.

[Eurasianman]

For those of you complaining about turbos and lag. See the Cobalt SS turbocharged (LNF). At stock, the car has 260TQ at 2000 RPM, at the crank. One of the main things that I have heard about having a supercharger, is that you get a better linear power band. But as some of you said, with turbos, after a certain point, the power just drops off.

[Draco-REX]

My 03 WRX is stage 2 with an STI up-pipe and an aggressive tune. I get boost pretty much instantly. But it still doesn't have the same response as a N/A car.

I think the BRZ is a car that requires a very responsive engine, and a turbocharger is not going to meet that requirement, no matter how well tuned. Now maybe this "electric turbocharger " that Subaru is supposedly working on will solve that. But I think to get the response needed, it would require the electric motor to be spinning nearly constantly. And I worry the motor might overheat.

[MtnDrvr86]

Originally Posted by Unamused

2010+ Legacy GT design^


BRZ design^


This design would minimize spool time. It works well in the LGT. Comparing it to the engine pic of the BRZ it looks like it could possibly fit. Piping might be a different issue though.

Yes but doesnt the LGT engine sit considerably higher and further frontward compared to BRZ? It would make that setup very confined if not near impossible. Unless the turbo goes toward the front of the engine? even then it still is much lower in the car

[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?

[brufleth]

Have they bothered making VG (variable geometry) turbos yet? Then schedule them to close at low power to keep it spinning and kick it open when there's throttle demand.

That's one method of managing transient power demand on jet engines. It would definitely work but it isn't trivial to build a reliable mechanical system and then to control it properly.

[eikond]

I'd like to know which application has less risk of knock. It would be great to be able bolt on a forced induction kit that does not require me to open up the engine to put in dished pistons, etc.

But, I'm worried that at the stock 12.5:1 compression, either turbo or S/C is going to be very risky.

[DarkSunrise]

Originally Posted by Draco-REX

My 03 WRX is stage 2 with an STI up-pipe and an aggressive tune. I get boost pretty much instantly. But it still doesn't have the same response as a N/A car.

I think the BRZ is a car that requires a very responsive engine, and a turbocharger is not going to meet that requirement, no matter how well tuned.

Couldn't agree more. I have yet to drive a turbo-charged car that offered the level of responsiveness of a N/A car.

Low-rpm boost != responsiveness. My current car has a small, quick-spool turbo and peak torque is available under 2000 rpm. Still nowhere near as responsive as a N/A engine.

[Turbowned]

Originally Posted by DarkSunrise

Couldn't agree more. I have yet to drive a turbo-charged car that offered the level of responsiveness of a N/A car.

Low-rpm boost != responsiveness. My current car has a small, quick-spool turbo and peak torque is available under 2000 rpm. Still nowhere near as responsive as a N/A engine.

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.

[old greg]

Originally Posted by brufleth

Have they bothered making VG (variable geometry) turbos yet? Then schedule them to close at low power to keep it spinning and kick it open when there's throttle demand.

That's one method of managing transient power demand on jet engines. It would definitely work but it isn't trivial to build a reliable mechanical system and then to control it properly.

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.

[Partial Stall]

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?

This is exactly what I was talking about when I created this thread. I know the dynamics of a SC vs a TC when compared in different cars. I'm interested in the best fit (if there is one) for the BRZ/FR-S. I'm thinking a low boost SC would be the safest and most natural bet for this car. I think a simple 30-50whp in this car would totally transform it.

As far as the type, I'm not sure. Would a centrifical s/c be lighter and more compact than a roots s/c? Also a centrifical s/c wouldn't require any kind of cooling.

I'm interested in the civic SI's compression ratio. If I remember correctly its very high. Not sure its it's 12.5, but its a 2.0 L 4 banger with 197 HP. The older one is atleast. I wonder what people's experience with charging that engine is.

EDIT: the 2007 SI's ratio is 11.0. Heh looks like they jacked it up in the BRZ to give it that extra torque.