Bi-Turbo V6

[dwightlooi]

There has been much talk about a GM Turbo Six. Here’s how I feel it should be built:-

V6 DI Twin-Turbo

• 3.2 liters engine built using as many off-the-shelf components as possible
  
• Engine block from 3.0 DI V6 (LF1)
  
• Crank and rods from 3.6 DI V6 (LLT)
  
• High efficiency turbochargers optimized for flow.
  
• Moderate Boost, High Compression
  
• Air-to-water intercooler to avoid bulky air hoses, intercoolers and minimize pressurized volume
  

Specifications:-

Valvetrain: Chain driven DOHC 4-valves/cyl w/intake & exhaust VVT

Fuel Injection: Homogeneous Charge Direct Gasoline Injection

Bore x Stroke: 89 x 85.6 mm (LF1 Bore x LLT Stroke)

Capacity: 3195 cc

Turbo(s): 2 x Garrett GT2052

Intercooler: Air-to-water

Compression: 10.7:1

Boost: ~13.2 psi (@ Sea Level ~70 deg C)

Power: 430 hp @ 6300 rpm

Torque: 360 lb-ft @ 2200~6200 rpm

Rev Limit: 6500 rpm

Transmission(s): Hydramatic 6L80 6-speed Automatic or Tremec TR6060 6-speed Manual

[ZL-1]

I kick-started the vote; I think it's a great idea.

Edited October 31, 2010 by ZL-1

[Z-06]

Dwight, one thing I would like your opinion is on, is most of the forced induced systems you propose have numerical value of peak torque less than the peak value of the power. Is there any reason for that?

In this case, would it possible to increase the peak torque to match or go beyond the peak value horsepower?

[loki]

In this case, would it possible to increase the peak torque to match or go beyond the peak value horsepower?

Z, it's the HP formula that will make the HP more than torque above ~5200.

hence why diesels with redlines under 5K (all of them?) will have higher torque numbers than hp.

[SAmadei]

Z, it's the HP formula that will make the HP more than torque above ~5200.

First thing I check on any graph... that Torque = HP at 5252.

[Z-06]

Z, it's the HP formula that will make the HP more than torque above ~5200.

hence why diesels with redlines under 5K (all of them?) will have higher torque numbers than hp.

I understand that.

Take MB's new 4.4 Turbo V8, it produces 429 hp at 5000 rpm, and 516 lb-ft of torque between 2000 to 4000 rpm.

As dwight has mentioned before, higher you try to obtain the peak for torque the less flat the plateau becomes. I was just wondering how much less the plateau would be if we peak both torque and hp at same numbers. Would we see a significant loss in the flatness of the current peak curve (2,000 to 6,000 peak)?

[dwightlooi]

I understand that.

Take MB's new 4.4 Turbo V8, it produces 429 hp at 5000 rpm, and 516 lb-ft of torque between 2000 to 4000 rpm.

As dwight has mentioned before, higher you try to obtain the peak for torque the less flat the plateau becomes. I was just wondering how much less the plateau would be if we peak both torque and hp at same numbers. Would we see a significant loss in the flatness of the current peak curve (2,000 to 6,000 peak)?

Well... there are three issues here:-

(1) Driving Experience: If we increase the peak torque to 430 lb-ft -- which we can easily do -- a few things happen. The first is that the power peak won't be 6300 rpm. Rather, it'll probably arrive sooner at about 5300 rpm. This is actually a good thing. The second thing is that the torque plateau of 430 lb-ft probably won't be reached at 2200 rpm, but rather around 2800 rpm or so and will end at about 5200 rpm. So you end up with more torque, but a narrower plateau 2400 rpm wide instead of one that is 4000 rpm. This is both good and bad. It is good because you are making more torque and the car will be faster. It is bad because it takes more boost to get more torque and boost takes more time to build to the higher level. This means that there is more of a "rubberband" effect when the driver floors the gas making the engine feel less linear and making the caar more difficult to control mid-corner when throttle is applied. With a lower boost design we are getting greater linearity and a driving characteristic more akinned to a large displacement NA engine, at the expense of some straight line acceleration performance. With a higher boost, higher torque design the engine will feel like a more traditional turbocharged engine, but the car will be slightly faster.

(2) Fuel Economy: If gasoline has unlimited octane rating and combustion chambers are knock proof under any circumstance, the aforementioned would have been all there is to be said. But they don't. To get to the higher torque peak, we have to run higher boost. 430 lb-ft will require about 18~19 psi instead of 13.2 psi. Consequently, we need to lower the static compression to accommodate the increased boost level. Instead of 10.7:1, we'll need to lower it to about 9.2~9.7:1. This in turn hurt fuel economy and power production at cruise and at light throttle when the engine is off boost.

(3) Accessory Bulk: This is relatively minor, but since we are discussing the consequences in detail, I thought I should mention it. With higher boost comes the need for bigger intercooler assemblies, adding bulk, weight and reducing responsiveness of the engine because the increased volume in the plumbing between the turbo and the intake valves needs more time to get pressurized.

My preference is for a more linear, easier to drive, more fuel economical and more compact power plant. Hence, I prefer the low peak torque, wide plateau setup -- aka the high compression, low boost setup, higher revving. The Nissan GTR's VR38DETT follows a similar philosophy. The BMW 4.4 and M-B 6.0 Bi-turbos are the exact opposite, focusing on delivering as much torque as is practical which enhances performance especially on heavier vehicles. The GM 2.0T (LNF) engines is somewhere in between.

430hp / 360 lb-ft will feel like a 5 Liter DOHC V8. That's not a bad feeling IMHO, especially when the high compression makes it more likely that the 3.2 Bi-Turbo will post a tangible fuel economy advantage over a Pushrod V8.

Edited November 1, 2010 by dwightlooi

[dado]

There has been much talk about a GM Turbo Six. Here’s how I feel it should be built:-

V6 DI Twin-Turbo

• 3.2 liters engine built using as many off-the-shelf components as possible
  
• Engine block from 3.0 DI V6 (LF1)
  
• Crank and rods from 3.6 DI V6 (LLT)
  
• High efficiency turbochargers optimized for flow.
  
• Moderate Boost, High Compression
  
• Air-to-water intercooler to avoid bulky air hoses, intercoolers and minimize pressurized volume
  

Specifications:-

Valvetrain: Chain driven DOHC 4-valves/cyl w/intake & exhaust VVT

Fuel Injection: Homogeneous Charge Direct Gasoline Injection

Bore x Stroke: 89 x 85.6 mm (LF1 Bore x LLT Stroke)

Capacity: 3195 cc

Turbo(s): 2 x Garrett GT2052

Intercooler: Air-to-water

Compression: 10.7:1

Boost: ~13.2 psi (@ Sea Level ~70 deg C)

Power: 430 hp @ 6300 rpm

Torque: 360 lb-ft @ 2200~6200 rpm

Rev Limit: 6500 rpm

Transmission(s): Hydramatic 6L80 6-speed Automatic or Tremec TR6060 6-speed Manual

Would that be mid engine for CTS(beteen 3.6 l v6 and 556 HP v8) ..or maybe top engine for ATS-v. It does sound good. But i would like to see how it would compare against let's say 5.0 l v8 pushrod with turbocharger (so it get flat curve) and around same HP. I think in price small block would win. Dimension..well length will have to go to V6 but height and width ..i think SB also win. What would specific fuel consumption for this two engine be?? Weight of the engines? Price?

[dwightlooi]

Would that be mid engine for CTS(beteen 3.6 l v6 and 556 HP v8) ..or maybe top engine for ATS-v. It does sound good. But i would like to see how it would compare against let's say 5.0 l v8 pushrod with turbocharger (so it get flat curve) and around same HP. I think in price small block would win. Dimension..well length will have to go to V6 but height and width ..i think SB also win. What would specific fuel consumption for this two engine be?? Weight of the engines? Price?

(1) I honestly don't think they even consider turbocharging the Pushrod V8. It kind of defeats the mission of the engine which is to make a lot of power in a simple, cost effective, light weight, compact and fuel efficient package. There is plenty of torque in the big displacement eight -- around 430~440 lb-ft with about 80% available from 1500 rpm or so -- and there really isn't a lot of need to fltten the curve of that one.

(2) If you compare the aforementioned turbocharged 3.2 V6 to a Pushrod V8, I'll give the weight advantage to the V8, but not by much. The 3.6 V6 (LLT) is 172 kg. The 6.2 V8 (LS3) is 183 kg. A 3.2 with smaller bores will be slightly heavier as it is. And, the Turbos, intercooler and plumbing will be more than 11 kg (~24 lbs). If I have to guess, I'll peg he 3.2 V6 Bi-turbo at about 200 kg.