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Corvette, v8 or tt v6?


regfootball

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Just read the new Car and Driver where they had instrumented testing of the CTS V Sport and new Corvette Stingray.

Keep in mind that the CTS is several hundred pounds more than the Corvette. Yet the instrumented test times are not all that far apart.

I bet if the CTS V Sport had the same weight as the Corvette, it's possible it may end up with better times.

I really would like to see the new twin turbo in the Corvette. Vette traditionalists will scream bloody murder, that no v6 should ever be in the Vette.

I beg to differ. If I were well to do enough to be in the market for the Vette, I would probably lean to the tt v6.

This is not to suggest that the v8 is not a truly excellent motor and such. There is no disputing that the v8 is a tour deforce in many ways and a superb engine in the car.

I will not be surprised to the see the tt v6 perhaps made as the base engine in the Corvette in the near future.

I'd actually be interested to see the turbo four in the car too, but that's a whole nother topic.

Thoughts on whether or how the tt v6 would do in the new Vette?

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Yup agree with everyone here that the TT V6 would be a great starter motor, then go to a natural V8 and have a TT V8 for the high end. Course I would miss the wine of that supercharger. :P

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  • 4 weeks later...

Just read the new Car and Driver where they had instrumented testing of the CTS V Sport and new Corvette Stingray.

Keep in mind that the CTS is several hundred pounds more than the Corvette. Yet the instrumented test times are not all that far apart.

I bet if the CTS V Sport had the same weight as the Corvette, it's possible it may end up with better times.

I really would like to see the new twin turbo in the Corvette. Vette traditionalists will scream bloody murder, that no v6 should ever be in the Vette.

I beg to differ. If I were well to do enough to be in the market for the Vette, I would probably lean to the tt v6.

This is not to suggest that the v8 is not a truly excellent motor and such. There is no disputing that the v8 is a tour deforce in many ways and a superb engine in the car.

I will not be surprised to the see the tt v6 perhaps made as the base engine in the Corvette in the near future.

I'd actually be interested to see the turbo four in the car too, but that's a whole nother topic.

Thoughts on whether or how the tt v6 would do in the new Vette?

It is not a matter of purism or tradition. It really comes down to the fact that the TT V6 has no weight, size or performance advantage, while being less cost effective and exhibits some degree of turbo lag. Fuel economy is about the same. One can also make the argument that had the CTS VSport been given a LT1 pushrod V8, it'll be faster, similarly balanced, less complex under the hood, similarly fuel efficient and could be made for $2000~3000 less.

In terms of desirability, there will be those who prefer a large displacement eight and those who like a turbo boosted six. The difference though is that with the TTV6 Cadillac will be fighting over the same turbo loving crowd with BMW and Mercedes. With the exit of the Germans from the big V8 arena Caddy could have gotten a monopoly on those customers.

Powerful RWD cars are in large part traction limited -- especially in 0-60 times for which 2/3rds of the time is spent in 1st gear. In this regard, a heavier car has a mitigating factor. Weight puts additional pressure on the rear wheels which increase traction. A half a second advantage is actually huge. As you get to the low 4 or high 3 sec range, it takes a phenomenal amount of power to lower the times by 1/2 a sec. So when you have the same power to weight ratio, a heavier car tends to be slightly faster just because it tends to have better traction all else being constant.

Edited by dwightlooi
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I would like to see both engines offered in the Corvette.

But dwight, what about how the 3.6TT makes so much torque down low (and with very low lag in the CTS) while the big V8 actually has to spool up higher before the real torque is made? Doesn't have an effect on 0-60?

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I would like to see both engines offered in the Corvette.

But dwight, what about how the 3.6TT makes so much torque down low (and with very low lag in the CTS) while the big V8 actually has to spool up higher before the real torque is made? Doesn't have an effect on 0-60?

Well, that's factually just not true... In fact, at every point on the torque curve, the LT1 V8 makes more torque.

  • The 3.6TT (LF3) makes 430 lb-ft @ 3,500 rpm with about 90% of that (387 lb-ft) available by 2,500 rpm. At 1,500 rpm it makes 335 lb-ft.
  • The 6.2 (LT1) makes 465 lb-ft @ 4,600 rpm with about 88% of that (409 lb-ft available by 2,500 rpm. At 1,500 rpm it makes 350 lb-ft.

You may want to trace the torque curves below and see for yourself.

(source: GM Powertrain: http://www.gmpowertrain.com/VehicleEngines/PowertrainProducts.aspx)

7ybq.jpg8zyw.jpg

Beyond the torque curve, one has to also understand that any turbocharged engine has some degree of lag. In otherwords, even if the torque curve says that it makes 387 lb-ft @ 2,500 rpm, when you floor the gas pedal at 2,500 rpm it actually takes some time before the torque actually rises to 387 lb-ft. That's because it takes the idling turbo some time to spool up to speed, then it takes some additional time to pressurize the intake pipe, intercooler and plenum to maximum boost. This can be about two seconds in really laggy engines, down to about half a second in reaaly responsive ones. But it is always there.

Many people don't know this, but naturally aspirated engines also have induction lag. With the throttle partially closed, everything ahead of the throttle is at roughly atmospheric pressure, but everything downstream of that throttle is in partial vaccuum caused by the engine sucking against an intake obstruction (the throttle plate). When you open the throttle, it takes a small amount of time for the intake plenum and tracks to normalize to atmospheric pressure. This is why engines like the M3's 4.0 V8 use individual butterflies very close to the intake ports. Because doing so minimize the volume in vaccuum and the time to normalize the pressure volume. This makes the engine more responsive that normal.

The big difference here, and the reason turbocharged engines always have more lag, is that turbocharged engines have to wait for the turbo to spin up. This delay is not present in NA engines. Also, turbo engines have to go from vaccuum to twice to three times atmospheric pressure. NA engines only need to go to atmospheric pressure. This is frequently compounded by the fact that the volume to be pressurized is almost always larger on turbocharged powerplants because of the additional ductwork needed to go to and from the Intercooler, and the intercooler itself. We commonly refer to this additional burden of lag "turbo lag".

Edited by dwightlooi
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I think it would be good to offer as an option.

All the individual preferences aside... offering the LF3 on the Corvette creates a dilemma.

Basically, you have a less powerful engine that costs GM more to build. How do you price it? If you price it less than the V8, it doesn't really make economic sense since you are creating a product that costs more but sells for less. If you price it more than the V8, why would anyone pay more than the V8 car to buy the TTV6 when it makes less power, doesn't weigh any less and doesn't really have better fuel economy?

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what if you simply like the feel and sound of an overhead cam turbo vs. a v8?

Well, what if you simply like the sound of a 5 cylinder Audi engine or a short stroke 4 cylinder with a 12,000 rpm redline? Sure, there's that sort of subjectivity, but it isn't based on technical merit. Besides, how many people are there who simply like the sound a TTV6 in a vette who is also able and willing to pay more for less performance?

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I think the V8 will be here a while due to cost not being too high and the history of the Vette. The 3.6TT doesn't give enough fuel economy gain. If anything, I could see them doing a 300 hp turbo 4-cylinder because of CAFE and if they want a low base price Corvette to get sales. And it isn't so far fetched, there is going to be a 4-cylinder Mustang, there is a 4-cylinder 5-series, CTS and Impala, and about 5-10 years ago you wouldn't have thought any of those cars would have a 4-banger.

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make the turbo a special edition geared more towards rally racing like the Z-28

The Corvette is the wrong platform for Rallying... not enough ground clearance, not enough suspension travel from the leaf springs and RWD. You want something with more ground clearance and AWD. A stripped Sonic or ATS perhaps with AWD. You also need it to be no more than 1599cc or 1999cc turbocharged mainly because of WRC and Super 2000 class rules.

Edited by dwightlooi
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I think the V8 will be here a while due to cost not being too high and the history of the Vette. The 3.6TT doesn't give enough fuel economy gain. If anything, I could see them doing a 300 hp turbo 4-cylinder because of CAFE and if they want a low base price Corvette to get sales. And it isn't so far fetched, there is going to be a 4-cylinder Mustang, there is a 4-cylinder 5-series, CTS and Impala, and about 5-10 years ago you wouldn't have thought any of those cars would have a 4-banger.

I don't disagree with most of your points. I'll comment on these though:

1) Somehow I doubt they would make a "secretary" Corvette. You don't seem to be that convinced either.

2) Most Mustang fans will point to the old SVO as justification for an I4T today.

3) The 5 Series has offered a 4-cylinder for years. Just not here. :-P

But like you and Dwight both said, there's pretty much no justification for the LF3 in the 'Vette. Performance, economy, and cost point to the LT1.

Now, a smaller-displacement LT1 (LT3?), maybe.......

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I think the V8 will be here a while due to cost not being too high and the history of the Vette. The 3.6TT doesn't give enough fuel economy gain. If anything, I could see them doing a 300 hp turbo 4-cylinder because of CAFE and if they want a low base price Corvette to get sales. And it isn't so far fetched, there is going to be a 4-cylinder Mustang, there is a 4-cylinder 5-series, CTS and Impala, and about 5-10 years ago you wouldn't have thought any of those cars would have a 4-banger.

I don't disagree with most of your points. I'll comment on these though:

1) Somehow I doubt they would make a "secretary" Corvette. You don't seem to be that convinced either.

2) Most Mustang fans will point to the old SVO as justification for an I4T today.

3) The 5 Series has offered a 4-cylinder for years. Just not here. :-P

But like you and Dwight both said, there's pretty much no justification for the LF3 in the 'Vette. Performance, economy, and cost point to the LT1.

Now, a smaller-displacement LT1 (LT3?), maybe.......

A smaller displacement small block was evaluated during the corvette C7's development. It was rejected for three reasons...

  1. It made less power and less torque
  2. It was actually slightly heavier because the cylinder walls were thicker while the external dimensions are about the same
  3. It had worse fuel economy -- because lower torque output limited 4-cylinder AFM operation to a narrower rpm and load range

Smaller displacement 5th GENeration Small Block engines do exist. It mannifests itself as the 5.3 Ecotec3 V8 with 355 hp on a 87 octane diet.

What's next (for sure) for Corvette is a Supercharged version of the LT1. This engine is already done and being certified. Expect at least 600 hp / 600 lb-ft from this engine perhaps as much as 650 / 625. These estimates are based on the 7% output advantage from DI and the apparent air-to-water intercooler size of from the engine photos. There is every reason to believe that this will be the Z07 and CTS-V engine.

c7-chevrolet-corvette-z06-engine_1004427

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  • 2 weeks later...

I don't think they will go away from the V8, but there could be an argument made for a turbo 4. The CLA45 AMG makes similar power to a Corvette of 10-12 years ago, match that to a 7 or 8 speed transmission and vet weight to about 3,000 lbs and it would DBE fast and get pretty good mileage. I don't think they ever do that though, I think other vehicles will be sacrificed for CAFE instead. But CAFE is going from 35 to 54 in 10 years, something has to give, unless they go diesel crazy on their sedans.

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I'd buy a vette v6 turbo

What about a Nissan GT-R?

To put things into perspective... the GT-R is a $90K car. The Corvette starts at $51K. Big difference in price there -- almost double.

The GT-R isn't a faster car because of the engine, it is a faster car because of it's AWD system with three active differentials. The VR38DETT engine itself weighs 276kg making 485~545hp (depending on the year) for 1.75~1.97 bhp/kg. Compared to the LT1 Pushrod V8's 460 bhp @ 211 kg for 2.18 bhp/kg it has inferior power to weight ratio. If you count the intercoolers and pipings it is also bulkier under the hood. Fuel economy isn't that great either at 16/23 mpg compared to the Corvette Stingray's EPA 17/29 mpg rating.

Now, let's say the Corvette gets the LF3 TTV6 making about 420 bhp. The LF3 is not the VR38DETT and it'll never be. It'll be a little slower and a little more expensive for GM to build than the V8 car. With 17/25 mpg on the CTS Vsport expect about 18/27 mpg on the lighter and more aerodynamic Vette -- which isn't exactly better than the V8. Other than trading the V8 soundtrack for the whistle of two turbines what exactly does it offer?

Edited by dwightlooi
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