VWs Supercharged Turbocharged Golf

[SHO-Z]

I saw this the other day in a mag. Using both a supercharger at low RPMS and a turbo at high RPMS. It looks like VW is coming out with this set up.

 

http://www.jalopnik.com/cars/news/more-on-vws-european-golf-super-turbo-122260.php

 

Now someone needs to do a Z this way!

[titanium]

Just when you thought VW's couldnt get more expensive to fix! ;D

[nienberg.11]

I'm just waiting for Tony D to see this and go off about how his 1980's toyota had the same system, and its not new, etc etc.

[Guest HBZ81]

people have been doing that with the MINI S for since it came out. Also some older rally cars used to do that, but then they started going out of control and killing people. It's a good plan if done correctly, but there is a thin line between effective and insane with twin charging like that. It's real easy to go useless or blowing everything up

 

A bit more info on compound charging or "twin charging"

--------------------------------------------------------------------

Sport Compact Car, June 2005

Techno Babble Colum, Page 26

 

Really Bad Ideas by Dave Coleman

 

At the eye of the swirling vortex of mass hysteria that is the internet, there is a bottomless bucket of bad ideas. If the collective synaptic activity that has been wasted debating impossible hybrids and discussing new engines to subject to the merciless boost of the Jurassic T3/T4 turbo was focused on good deeds, we would have a cure for Ebola, an antidote for turbo lag and Jeff Gordon would be driving a rally car. Instead, we have ideas like this:

 

I've recently been contemplating a supercharger/turbo combo where the supercharger would send pre-compressed air through the turbocharger, which would effectively recompress the air. This would be a very nice setup, as you would have zero turbo lag, as much boost as you could possibly imagine, the low-end power turbochargers lack and the high-end power superchargers lack.

 

You would think that if you took, say, 6 psi of supercharged air and sent it through a 6-psi turbo charger, you would compress it to 36psi of boost pressure. This is where my question comes in. I know air is highly compressible, but would that actually be the case?

If you have time between doing burnouts and taking coffee breaks, dig up an answer for me if you can. Keep up the good work.

 

James Palmgren

Joliet, ILL.

 

 

There are, of course, lots of things wrong with this plan. First of all, I'm the powerslide guy, not the burnout guy. Second, the 6x6=36 theory of compound compressors is all jacked up. But before humbling you with simple arithmetic, let's first burst a few myths:

 

Turbos don't lack low-end power, oversized turbos do. The tiny KKK K3 turbo on the Volkswagon/Audi 1.8 is a perfect counterpoint. It provides tons of low-end torque, but is hopelessly wheezy at high rpm. Likewise, not all superchargers work well at low rpm. Centrifugal superchargers only work at high rpm, doing their wheezing at the small end of the tach. Even a Roots blower or a twin-screw compressor can be flaccid down low if sized wrong or driven at the wrong speed. No matter what kind of turbo or supercharger you use, getting a wide powerband is more a result of matching the turbo or supercharger to the engine than anything else.

 

That said, two at the same time can work, but not the way you might think. First, you must think in abolute pressure, not boost. Six psi of boost is really 6 psi over ambient. Ambient is usually 14.7psi, but let's call it 15 psi because we're lazy. Second, you have to look at the pressure ratio across each compressor rather than the simple increase in boost.

 

In the 6-psi example above, the supercharger takes in air at 5psi and spits it out at 21psi, (15 psi ambient plus 6 psi boost) so the pressure ratio is 21/15, or 1.4:1. Now, if you feed that 21 psi (absolute) into a turbo running the same 1.4:1 pressure ratio, you'll get 29.4 psi out the other end (21 psi x 1.4). Subtract ambient (15psi) and you see that you've got 14.4 psi of boost, not the 36 psi you were hoping for.

 

Since you could easily make 14.4 psi of boost with either a supercharger or a turbo alone, there's little point using both at this level. Run each compressor a little harder, say 2:1 pressure ratio (15psi or 1 bar of boost in the real world) and things get more serious. Air comes out the first compressor at 30psi (absolute) and out the second compressor at 60psi. Subtract 15psi of ambient, and that's 45psi of boost. Now, any turbo capable of this kind of boost would be very laggy indeed, so using a supercharger and a turbo in series might make sense. Neither compressor woulkd be working abnormally hard at 2:1 pressure ratio.

 

But this is where stupidity comes back in. What are you going to do with 45psi of boost? You need forged titanium everything and 600-octane gas to even attempt to handle that kind of boost. Then you're going to break your transmission, axles and every other part of the drivetrain. Make all that stuff strong enough and you'll go so fast you'll crash, but since you spent so much money on two compressors, a built motor and a beefed up drive train, you won't have any money left for doctor's bills and you'll die a sad, tragic death,

If you don't believe me, go study some Group B rally history (you can start on page 80). The 1985 Delta S4 used a positive displacement supercharger, a turbo, and two intercoolers to make more than 470hp from 1.8liters. And guess what? Group B cars went so fast they started killing people and had to be outlawed. So sad.

 

There are a few rare instances where "twin-charging" makes sense. Take the MINI Cooper S featured on page 68. The 45-cubic-inch Roots blower on the Cooper S is already working very hard to feed 11psi into the little 1.6 liter. Since Roots blowers are inefficient at high boost, spinning the supercharger faster to make more boost would be counterproductive, adding a lot more heat for a little more boost.

 

Add a turbo making a modest 6 psiof boost 21psi absolute, again) and things get interesting. At 11psi, the stock supercharger is running a 1.7:1 pressure ratio, so that 21 psi going into the stock supercharger will come out at 35.7psi. Subtract 15 and that's about 212 psi of boost. You could easily make 211 psi of boost with just a turbo, but in the case of the Cooper S, removing the supercharger would be quite difficult, since the water pump is driven off the back of it.

 

Now, if it were me, I would run two air/water intercoolers, one after the turbo and one after the supercharger. The Mini's nose is too small for anything air-to-air and the stock intercooler and knife-slit hood scoop can't shed heat fast enough even for stock boost, let alone a double decade of it. I would also run a bit more boost on the turbo and slow down the supercharger a bit with a bigger pulley, since Eaton's Roots blower do their best work in the 6-to-8psi range.

Of course, if it were me, I'd just sit here pouring fresh ideas into that bottomless bucket instead of driving around in a twin-charged MINI like Hubie Fuh, owner of this month's tinw-charged MINI does, so I'll shut up now.

 

But before I do, let me flew my cranium one last time: In the event that you decide to execute this bad idea on some other car, remember when you're choosing a turbo for a twin-charging setup, you need to plan for the mass flow rate of the engine with the supercharger installed, not the engine itself. Mass flow, in English, is how much air the engine pumps. The mass part is because you want to measure the mass of air (usually in pounds), rather than the volume, since all that compressing changes the volume of the air.

 

Also, turbos will be different depending on if it's before or after the supercharger. In the Cooper S example, packaging dictates putting the turbo before the supercharger. If it were after the supercharger, the turbo's compressor should actually be smaller. Think about it: In either case, the same mass of air is going through the turbo, but if the supercharger compresses it first, that mass of air will take up less volume. The air will be physically smaller, so the compressor should be too. Strange, but true.

 

And yes, about a thousand years ago HKS made a twin-charging kit for first-gen. supercharged MR2. Don't write me to tell me that, everybody already knows.

[AK-Z]

I didn't read any of that in the last post.

 

I remember HKS coming out with there own twin charge system for the supra a while ago.

[Guest HBZ81]

I didn't read any of that in the last post.

 

.

 

I don't blame you, i probably wouldn't have either until I had some time. lol

[Guest Crema240z]

http://www.cardomain.com/ride/565513 If it can be done in an rx it can be done in a Z , i would like to see this happen.

[AK-Z]

The problem is how to pumb it. turbos and blowers are preasure producing units. Meaning that no preasure in one end (example number) 6 psi on the other, now putting something that produces preasure on the intake side at will be theoretically multiplyed by the number the secondary unit will produce

normally with out preasure.

 

 

So with unit 1 preoducing 4 psi into unti 2 "producing" 6 psi will make it the overall psi on the outlet be 24 psi.

 

I've seen a diesel truck boasting 100 psi of boost at a truck pull comp using 2 turbos.

[AK-Z]

[url=http://www.cardomain.com/ride/565513]http://www.cardomain.com/ride/565513[/url'] If it can be done in an rx it can be done in a Z , i would like to see this happen.

For a RX 7 its easier because they already have a sequencial turbo setup a would only have to have the exhaust manifold replaced with w single turbo mainfold, blower mounting, and belt/pulley install, and maybe some plumbing.

[zane9000]

For a RX 7...

Its an RX-4

[Guest Crema240z]

The one on that cardomain site is a 16 valve twin cam not a rotor.

[AK-Z]

Sorry I didn't even look at the link. I re RX and assumed RX7, my mistake.

[Guest Crema240z]

well whaday think of that engine setup? is it cool enough to go in a Z? I think so

[zane9000]

Its pretty nice, but I love my L series engine too much to swap for anything else.

[Boosted1]

Air pressure isnt multiplicative regardless of using a turbo or supercharger or both.

 

"So with unit 1 preoducing 4 psi into unti 2 "producing" 6 psi will make it the overall psi on the outlet be 24 psi."

 

That line of logic is incorrect, if unit 1 produces 4 PSI and unit 2 produces 6 PSI your net boost (over ambient pressure of 14.7 PSI that is) would be 10 PSI, not 24.

 

Multiplication plays no role whatsoever in this matter.

[Dave88SS]

Just when you thought VW's couldnt get more expensive to fix! ;D

 

German engineering in the haus, ya!

[zane9000]

LOL, I love those commercials.

[Some-Guy]

Theres a guy in vancouver area that has a 7 litre diesal making 1600 hp and about 3400 lbs of torque running 150 psi of boost his truck is actualy in petersons 4wheel about a year and a half ago ill see if i can find the mag!

 

It was some wild **** 3 turbos not sure exactly how it worked i just remember the wild numbersi think each turbo was feeding the next if i remember correctly he usualy runs 50 psi to just drive around with and 150 to compete with..