Compound turbocharging: Tell me how it works?

[boomerkk]

Was idly browsing and saw this:

http://www.boostlogic.com/xcart/product.php?produc...

I know the Mkiv supra used sequential turbocharging, which from my simple understanding is when 1 turbo spins first and the other spins a bit later.

Usually twin turbo cars have turbos that spin together.

Can someone explain to me how compound turbos work?

What about the Veyron, how does the 4 turbos work? Are they all the same size and spin together?

[Pannywagon]

My car has two sequential very low-inertia turbos.

First one kicks in from 1200rpm (seriously!) giving full torque by 1500 rpm and the second one kicks in at 2000rpm when going for an overtake etc.

This means that most of the time you can drive around below 2000rpm using hardly any fuel and yet you still have all the power and torque you could want.

Peugeot 607...it is a good car really!

[Wadeski]

The 3rd gen RX-7 used a smiliar sequential system, as does the Subaru Legacy of the mid 90s. Its a way to have the benefits of a big, laggy turbo and a small turbo that spins up fast but runs out of puff at high revs.

[boomerkk]

Thanks!

But this compound system looks like a different kettle of fish?

[Trommel]

Compound turbocharging is not at all the same thing as sequential turbocharging.

In compound turbocharging, one turbo blows into the intake of another turbo.

[boomerkk]

Trommel said:

Compound turbocharging is not at all the same thing as sequential turbocharging.

In compound turbocharging, one turbo blows into the intake of another turbo.

Thanks! That helps a bit. What are the benefits and drawbacks?

[Strike_J]

So its like two turbochargers in series? Would this reduce initial turbo lag for the big turbo to spool?

[eldar]

boomerkk said:

Trommel said:

Compound turbocharging is not at all the same thing as sequential turbocharging.

In compound turbocharging, one turbo blows into the intake of another turbo.

Thanks! That helps a bit. What are the benefits and drawbacks?

Mostly used in diesels.... gets the inlet boost pressure to 100psi+ Handy for tractor pulling, but not a lot of use on a road car (I believe).

Drawback is lots of lag.

[Trommel]

Benefits - big power, little lag.

Disadvantages - plumbing, very high boost levels.

Much more popular with diesel engines (look at pulling tractors and the old Paris-Dakar trucks), but there are petrol cars with them (Boost Logic do a 2JZ kit, I've seen a picture of a compound-turbocharged UK Cosworth)

[Fort Jefferson]

Trommel said:

Compound turbocharging is not at all the same thing as sequential turbocharging.

In compound turbocharging, one turbo blows into the intake of another turbo.

What do sequential turbos do then?

[300bhp/ton]

boomerkk said:

Was idly browsing and saw this:

http://www.boostlogic.com/xcart/product.php?produc...

I know the Mkiv supra used sequential turbocharging, which from my simple understanding is when 1 turbo spins first and the other spins a bit later.

Usually twin turbo cars have turbos that spin together.

Can someone explain to me how compound turbos work?

What about the Veyron, how does the 4 turbos work? Are they all the same size and spin together?

Compond boost is basically what it says on the tin. You compress intake air already compressed.

With turbo systems it allows you to run two or more turbos to give you a broader powerband.

There are other options, you can run a supercharger with turbo's.

In this instance the blower makes boost all the time giving good drivability, but allows you to run massive turbo's for higher end gain. Noramally turbo's of this size would be too big for the engine, but because you are feeeding them pressurised intake air it doesn't matter.

There's agood article on compaound boost where a Mustang Cobra with a DOHC supercharged engine was taken and equipped with a couple of turbo's along with the blower. The results where quite mind boggling, over 1100rwhp!!

[Trommel]

Fort Jefferson said:

What do sequential turbos do then?

With various pipes, solenoids and valves, the exhaust gas is first routed through one turbo (to minimise lag/boost threshold) and at a set boost level/rpm/whatever is also transferred to the other turbo (i.e. MkIV Supra) or the second, bigger turbo takes over (i.e. FD3 RX7).

[boomerkk]

Thanks. Seems like the best thing since sliced bread.

The supra boys stateside have got their knickers in a spin about it

http://www.supraforums.com/forum/showthread.php?t=...

Impressive results tho:

Torque (ftlbs)
compound....Normal setup
310..............195 (3000rpm)
400..............225 (3500rpm)
520..............275 (4000rpm)
550..............400 (4500rpm)
560..............550 (5000rpm)


Horsepower
compound....Normal setup
170..............120 (3000rpm)
260..............150 (3500rpm)
390..............210 (4000rpm)
480..............340 (4500rpm)
540..............530 (5000rpm)

[GravelBen]

Trommel said:

Fort Jefferson said:

What do sequential turbos do then?

With various pipes, solenoids and valves, the exhaust gas is first routed through one turbo (to minimise lag/boost threshold) and at a set boost level/rpm/whatever is also transferred to the other turbo (i.e. MkIV Supra) or the second, bigger turbo takes over (i.e. FD3 RX7).

Not sure about the Supra/RX7 but the TT Legacies operate in parallel at high revs - it isn't a case of changing from primary to secondary turbo but primary to [primary + secondary]. (ETA: just re-read your post and I take it the Supra is similar, misread it the first time)

Mine makes decent boost from around 1800rpm, with over 80% of peak torque available from 2000 to 6500 - peak torque is at 5000, peak power at 6500.

Edited by GravelBen on Saturday 4th April 05:52

[Mr POD]

boomerkk said:

What are the drawbacks?

Difficult fluid flow dynamics calculations ? Phd's required to fully optimise ?

[boomerkk]

Gazboy, u mentioned some people use a gt28 to replace the stock set-up but still run sequentially (one of the special characteristics of the Supra I reckon)...

Is this the cutting edge:
https://www.speedforsale.com/supraparts/speed-sale...

Looks very well developed, and value for money too.

[SleeperCell]

Just to confuse things further, there are also turbo-compound engines used on some trucks and old aero engines that use the turbocharger to feed a bit of power direct to the gearbox.
http://en.wikipedia.org/wiki/Turbo-compound_engine

[boomerkk]

Gazboy said:

I was interested in the Speed4Sale set up when I heard someone was experimenting with the set up with GT2510s (similar size) and emailed TDI to quote an estimate for them, the fuel hardware and engine management to run it but they never returned my email, as it was unproven I didn't chase them and last year started thinking about running Disco Potatoes in parallel with custom fabricated 3>1 x2 manifolds & 2>1 boost pipes into a SMIC but ended up selling the car before starting this project. Three guys in the states are going through with it though.

Why Gt25s? Do you expect the 28s to be too laggy?