The difference is greater. The gas has to go to the turbine, then the air back up to the engine. Roughly about 25 feet in all. Turbos close to the engine just cut out 12 feet of that spagetti.

I see the real problem as heat loss on the way back to the turbine. Lose heat and you are losing energy. You want to hold as much heat in as possible on the way to the turbine. As far as pressure drop you will still have some, but not as much as an undersized intercooler.

For this to work at an optimum, you would want to design the tubing to hold the gas velocity at just under 400 ft/sec.

Lets say you have a 5L running around 12 psi. You are talking about 500-550 hp and roughly 700 cfm.

A 2.5" diam pipe would give you 350 ft/sec. A 2.25" diam pipe would give you 420 ft/sec.

At 350 ft/sec it takes the gas .03 seconds to travel 12' to the turbo so thats pretty quick, but that is at 6000 rpm and it still has to get the turbine moving.

Really what you want is boost down low around the 2500 rpm mark on the street, so if you kept the exhaust feed around 2.25-2.5 with all very smooth bend, wrap the feed pipe, used a hybred ball bearing turbo with one step smaller turbine and one step larger compresser wheel, clip the tubine wheel, I think it would spool just fine. I still think it would work better where the cat should go. You could actually run small twins there.

 

That requires complicated plumbing and controls to prevent one system from backfeeding into the other. Like Tony said, he could feed his twin screw with a rear turbo but simply running the turbo's outlet to his twin screw's inlet. The twinscrew will draw a heavy vacuum helping to spool up the turbo. The turbo will force more air into the twin screw at mid range and high rpms to create a lot more power more efficiently, possibly with a cooler air charge.

 

Weldon makes one that should as well however I know of several people who have tried it out and they did not have near the luck.

There should be a catch tank on the turbo, most turbo manufactures will warn against not having one due to possible increase in bearing damage.

These rear mount setups work "ok" for a lot of other cars. While not a perfect way to set things up they do still make decent power.

-- Aaron Rouse

 

What's the reason for bringing the intake up on the driver's side where you've got the steering shaftin the way? I was going to bring mine up on the passenger side.

 

I was thinking the same thing.

 

I don't think this would yield good results otherwise everyone would do it. The heat generated from the first turbine is too high.... you essentially diminish your returns due to excessive heat build-up. As you may know, heat is the biggest drawback of all boost applications. The only reason you should do that is if you're aiming for multiple thousand horsepower. Twin Turbos in sequence are used in industrial applications. It may be possible to do with an ultra small Turbo, which would mostly be more for novelty than efficient energy transfer

 

"That requires complicated plumbing and controls to prevent one system from backfeeding into the other. Like Tony said, he could feed his twin screw with a rear turbo but simply running the turbo's outlet to his twin screw's inlet. The twinscrew will draw a heavy vacuum helping to spool up the turbo.

Actually all you'd need was a simple clutch mechanism to disengage the SC at a proscribed RPM level, at which point all boost would be generated by the turbo.(Thus freeing the engine from the very significant parasitic loss caused by the SC at higher RPMs, which can be as high as 20% of total engine output!).

"The turbo will force more air into the twin screw at mid range and high rpms to create a lot more power more efficiently, possibly with a cooler air charge."

In reality compressing the air charge through both would dramatically increase the air intake charge temperature, so the higher the boost level the more you'd be affected by the laws of diminishing returns. This is why it is greatly preferable to switch to a larger turbo(or SC) unit as airflow requirements increase instead of simply cranking up the boost level.

 

BTW..i said that jokingly!!
Some of you guys are nuts

 

Tony, there's nothing nuts about a dual SC/Turbo setup, it's been done many times, and as far back as the 1940s!

It works, it is just very complex and extremely expensive.

VW is getting ready to introduce a dual Turbo-SC engine as a matter of fact:



"VW’s supercharged turbo engine

Posted Aug 23, 2005, 8:30 PM ET by Randall Halcomb
Related entries: Gadgets, Trends

Call it a double-whammy, but VW calls it a SuperTurbo. Actually it is ‘SuperTurbo Compounding’ by Eaton, the likely supplier of the system. Essentially, you have a turbocharged engine that is also fitted with a supercharger. The complexities of handling this type of forced induction have limited its automotive application. The supercharger provides instantaneous power. Once the turbo is providing boost, the supercharger’s clutch is disengaged and it is closed off from the induction system, allowing the turbo to take over completely. The result is a power plant that has none of the usual performance compromises found in typical forced-induction scenarios. The numbers are quite impressive. VW will initially offer the system in its European line up. The first engine will be a 1.4-liter four cylinder that will produce 140 hp and 184 lb-ft of torque, with a performance version producing 170 hp and 199 lb-ft. That is crazy power out of such a small displacement engine. Fuel economy is another benefit to this approach. VW plans to offer this power plant up against turbodiesel engines, which could also benefit from this system. VW is also working on 1.6 and 2.0-liter versions of the SuperTurbo, which would produce 195 hp and 240 hp respectively. While all this power sounds great, we wonder how reliable the entire system will be. VW four-cylinders are normally very robust. We worry about the electro-mechanical reliability of the system. What happens when the supercharger’s clutch fails to disengage or engage? Obviously there are a lot of interdependencies involved. We’re hoping that Eaton and VW have developed enough ‘interlocks’ to prevent one failure from jeopardizing the entire system."

http://www.autoblog.com/entry/1234000180055673

New VW engine packs a One-Two Punch; 2006 Golf gets SuperTurbo system
Posted Date: 8/23/05

Volkswagen will reach into the past for a combined supercharger-turbocharger system to boost power and fuel economy in its small gasoline engines.

The system, dubbed SuperTurbo Compounding by supercharger supplier Eaton, eliminates turbo lag while boosting overall power and fuel economy by 15 to 20 percent. Eaton, the apparent supplier of the supercharger for the engine, says a car fitted with the system will likely be shown at the upcoming Frankfurt show.

Engineers have combined superchargers and turbochargers in the past, most notably in World War II-era aircraft to avoid engine power losses at higher altitudes. Automotive applications have been limited, but include an Abarth-developed system used on the 1985 Lancia Delta S4 rally car.

Today’s computers make the complex induction system seamless in the new application, which uses a mechanical supercharger operating at low engine speeds to increase low-end torque, and a turbocharger engaging at middling revs to provide added muscle up high. Once the turbo reaches sufficient speed to provide boost, a clutch disengages the supercharger and an induction valve closes, bypassing the supercharger.

VW’s plans call for widespread use of the system, starting with a 1.4-liter direct-injection engine that is expected to debut in the 2006 Golf before heading into other VW models.

Two different versions of the 1.4-liter engine are planned. In standard guise the four-valve-per-cylinder unit kicks out 140 hp and 184 lb-ft of torque, with a more performance-oriented variant producing 170 hp and 199 lb-ft. By comparison, VW’s existing 2.0-liter four-cylinder delivers 150 hp and 148 lb-ft.

Also under way at VW are more powerful 1.6-liter and 2.0-liter versions of the supercharged/turbocharged engine with a rumored 195 hp and 240 hp, respectively.

Eaton officials said the system will initially appear on cars in Europe where it is expected to compete with turbodiesel engines. The system also could be fitted to diesels, but its future in the North American market could depend on fuel prices and demands for bigger engines.

“In the U.S., displacement is still king,” said one Eaton exec.
http://www.autoweek.com/news.cms?newsId=103048

 

Tarek, Porsche also has used twin sequential turbos on a street driven car.....".Porsche's 1988 wundercar, the 959.

The all-wheel-drive, twin sequential turbo 959 was conceived to serve as Porsche's entry into the FIA's stillborn Gruppe B rally-racing class. With 450 hp from 2.85 liters, and a top speed of 192 mph, the 959 stood atop the world supercar pyramid for many years after limited production ceased." As noted that was 1988 or 17 years ago !

 

How about a small shot of nitrous to get the heat and pressure up so the turbine would spool rapidly at lower rpms? Cut off the nitrous at around 3500 RPM.
Another thought would be to pump some air (through a check valve) into the exhaust ahead of the turbine. Inject some fuel downstream of the air inlet and light it off with a spark plug. That should heat things up in a hurry and make a nice flame erupt from the exhaust. I could really get into that sort of experiment and it would give the smog air pump a useful purpose.

Louis Ott

 

Um Hello,

Lancia did a SC - Turbo setup many years ago for Group B rally cars. They were competitive, and made some street versions as well. Of course, none were sold in the USA. Google search: ( Lancia Delta Integrale), and you should see something.

This is not new science, as is most of the engine technology. New to some as information, but the science exists for quite a long time.

On another note, the heat in force fed engines comes from compression of the air, the heat transfer from hot parts is minimal due to the resident time of the air being very small, and air is a poor conductor of heat............

Hope that helps..

By The Way, congrats on the Rear Turbo setup...! A for effort..!

 

Louie- "How about a small shot of nitrous to get the heat and pressure up so the turbine would spool rapidly at lower rpms? Cut off the nitrous at around 3500 RPM."

Yep, that would definitely work too.
Turbos work GREAT with nitrous, not only because they spool the unit faster by imparting a positive pressure on the compressor, but also because of the massive cooling effect nitrous has on the air intake charge.

"Another thought would be to pump some air (through a check valve) into the exhaust ahead of the turbine. Inject some fuel downstream of the air inlet and light it off with a spark plug. That should heat things up in a hurry and make a nice flame erupt from the exhaust. I could really get into that sort of experiment and it would give the smog air pump a useful purpose."

LOL....you're describing an AFTERBURNER!!!!!

NIIIIIIIIIIIIIIICE.

 

The rear turbo begs for an anti-lag system. Use a Coanda (ram jet) effect pipe just before (after?) the turbo to keep the gases unidirectional.

 

Jim,

I recall vividly the disappointment in receiving the news of Henry Toivonen's death and the ensuing FIA decision that eliminated the 959, Ford RS200, and the latest revision of Audi Quattro Sport. The 959 swept the Paris Dakar and several Rally Raids in the Arabian deserts, and was promising a spectacular Pro Rally season...

...but I had thought sequential meant in sequence, but not in series, meaning they were plumbed in parallel, but with different specs.... I guess I'm wrong... and thanks for the clarification