Compound Turbocharging

[Brian Hamilton]

Was in Austin last weekend and stopped by a guy I know's shop to see the toys. His name is SW, some of you may know him for having the worlds fastest street car. A Toyota Supra which hit 247mph at the Texas Mile a few weeks ago.

Anyways, I was at the performance shop next door which is called Boost Logic. One of the guys there was talking to another guy I know about a compound turbo setup. I stepped over and started listening in.

Then they guy I knew said, "Have you seen his setup on his 300Z?"

"Nope, what is it now?"

"It's a compound turbo seup. 2 turbo's, one feeding into the other."

"LIKE A DIESEL?!"

"Yeah!"

"Lemme see this..."

Here ya go fellas...

 

[Brian Hamilton]

Explaination on how it all works...

http://www.youtube.com/watch?v=y-Me6yWApzY

 

[Jack]

Interesting video Brian, thanks for the informative post.

 

[Rick S.]

Good info. I wonder what the exhaust manifold looks like?

 

[Rick S.]

ok, sort of understand now after watching the video.

 

[Mark Hamstra]

Pretty much the same thing: Regulated 2-stage (R2S) turbocharging | BorgWarner Turbo & Emissions Systems

 

[Brian Hamilton]

See the cool thing is, you can have both turbo's running at about 12 lbs, and then you have an effective 24 lbs at the intake manifold. Both turbo's are working at peak efficiency, together, at the same time. It's like having 2 super efficient single turbo setups at the same time. It's pretty friggin sweet guys. I'm super impressed. The guy who built the system (guy in the video) is a really cool guy and was really open to talk about the system. I'd love to build one for that crazy 4 rotor I wanna put in the back of an SLC. It'd also be pretty sweet to do on a 4 cylinder on the back of the SLR...

Hhhhmmmm.......

Interresting.

 

[domtoni]

Guys,

As I understand the system, it is like the compound turbo systems being employed on EU diesel engines today. BMW have one, I think Fiat is launching a system or two, and VW had on a 1.4 motor, a turbo / supercharger kit to do just what the chappie talks about (linear power, and no turbo lag).

Sounds like his car is really fast, but how long will his motor stay together?

Dom

 

[JohnC]

Compound turbo's are apparently pretty common in the tractor pulls, and they run some insane boost figures.

For an automotive application both turbo's should be wastegated, or there needs to be other means for controlling the interstage pressure. And both need intercooling. It can get to be a piping and/or control system nightmare pretty quickly.

Some on the Lextreme board have been dabbling with a similar idea, but using a Roots or twinscrew supercharger for low end torque + a big single or a pair of smaller turbos with big A/R's that come on boost higher up for top end HP. One of our Australian members has had this setup on his car already, and said the increase in low end grunt was unbelievable.

It's also a cleaner piping job than compound turbo, especially on a V8, where the Roots or twinscrew supercharger is already sitting in the vee. So the turbo(s) get intercooled in the conventional way, then that intercooled air feeds the supercharger, and at that point you can throw in some methanol/water mix, or a compact W2A intercooler under the supercharger, in the intake manifold to cool that air down.

One of the popular "turbo" magazines put together a setup like this several years ago, and found that once the turbo was on boost, and blowing through the supercharger, it effectively "unloaded" the supercharger, and reduced its parasitic load.

 

[Brian Hamilton]

I have had the idea of compound boosting an engine with a Whipple and large frame turbo for some time, but the problem I kept running into is that people who "knew more about cars than me" would always say I was limited to the boost the blower would produce. I didn't think that made sense as the air can be compressed further than it already is. It's not like 30lbs of boost makes the air change states into a liquid or solid or anything. LOL Anyway, this setup is pretty sweet and yes, it is just like what is used on high power diesels. Only difference is they use ENORMOUS turbo's and produce well over 100 lbs of boost. I've ridden on one of those trucks on the street. Yum yum!! Talk about power!!!

 

[Mark Hamstra]

Only difference is they use ENORMOUS turbo's and produce well over 100 lbs of boost.

And the EGTs are different....

 

[Brian Hamilton]

And the EGTs are different....

LOL

Yeah just a little... hehehe

 

[JohnC]

the problem I kept running into is that people who "knew more about cars than me" would always say I was limited to the boost the blower would produce. I didn't think that made sense as the air can be compressed further than it already is. It's not like 30lbs of boost makes the air change states into a liquid or solid or anything. LOL

There are always naysayers and keyboard racers in any crowd.

That's nonsense about the boost being limited to the blower boost; if that were true, then there would be no multistage compressors.

Roots and twinscrews are PD type devices, so whatever pressure you give them at their suction, they're going to pack it a little harder and shove it out the other end. Now it's true if you have a monster turbo, and a small Roots, you can restrict the flow, but you'll see that happening when the interstage pressure starts climbing.

The trick with compound boosting is the same as sizing multistage gas compressors, it's all about making sure the two devices play well with each other, and one doesn't hog the show. It's about sizing them correctly, and controlling the interstage pressure.

 

[Brian Hamilton]

I was trying to convince some of the guys at the shop I worked for that we needed to do that to a 2003 Cobra. Swap out the POS Eaton with a 2.3L Whipple (largest one made then) and put a 75mm turbo on there as well. I didn't see the problem with it, but apparently everyone else did. LOL Oh well, I'm always thinking out of the box and I guess they thought this was another of Brian's crazy ideas.

Just like the one I had in 9th grade (1993) where you take a muffler with a single 3" in and dual 2" out and put a butterfly in one of the outlets to create backpressure for more low end torque and have it open for more flow up in the upper RPM range. "That's crazy!" "What's the point of that?"

Ferrari has it in every single one of their new cars starting with the 550 Maranello. Oh yeah, I was a pissed off puppy when I noticed that. The only thing I couldn't figure out back then, was how to regulate the rate of opening that butterfly. Well, that and the cash needed to make a prototype and patent the idea.

Another of my stories I guess....

 

[Mark Hamstra]

LOL

Yeah just a little... hehehe

That's actually a pretty significant issue. If you think about this compounding more abstractly, the goal is really to have two compressors working on the intake air -- one that works well when the engine is fairly lightly loaded, the other working well under higher engine loads. There are different ways to turn those compressors and make them do useful work.

If both compressors are powered by exhaust gas flow, then you've got the compound turbo setup that this thread opened with. However, routing and proportionally distributing the exhaust gas to the two turbos is tricky -- and doing so reliably with high EGTs even more so. That is why compound turbo systems like Borg Warner's R2S are far more common on diesels.

If you run one of the compressors off the crankshaft, then you've got the supercharger+turbocharger compounding solution. That avoids the problem with reliably routing and distributing high-temperature exhaust gases, but it also has its own drawbacks -- principally with getting the supercharger out of the way in high-load operating conditions and not being able to easily put the supercharger compressor in the preferred position upstream of the big turbo's compressor.

If you want to look at something interesting, have a peek at Borg Warner's eBooster. In that approach Borg Warner drives the low-load compressor with an electric motor -- think of it pretty much the same as the turbo compounding solution, except that the first, small turbo is an electrically-powered blower, not exhaust gas powered. That approach has some real advantages in terms of exhaust gas routing, flexibility in booster placement, avoidance of parasitic loads (the eBooster is completely turned off and bypassed during high-load engine operation), etc. Pretty cool stuff, but very limited availability and very few implementations on the road right now.

 

[Price Walton]

I'm sure the Ferrari F1 cars of the early 80's had a compound super/turbo setup, which gave them a significant driveability advantage over the Renault/BMW engines of the day.

If anybody can find a reference - Paolo?

 

[Ron Earp]

Quite different from another term that shares the same words:

turbo compounding

 

[Brian Hamilton]

Quite different from another term that shares the same words:

turbo compounding

WOOOOOW!!!

That's cool right there!

 

[Price Walton]

Ron,

Thanks, I'll get me coat......

 

[JohnC]

Twincharging is another popular term for it, although as Wiki point out, it's still somewhat of a misnomer.