pkincy

One of the recent car mags had an excellent article on Turbocharging. Basically saying that the hypercar mfgs hated it but it was the only way they could meet emissions requirements at the power levels they wanted to produce. The stated reason for Supercharging was that turbo lag became a greater problem with bigger Turbo's so the larger engines (Ford and Chevrolet come to mind) use SCing instead. Apparently so far it is a physics problem.

corvettecop

"After General Motors applied a trademark for LT5 in 2013 with the Patent and Trademark Office, it all comes clear now - the fifth-gen LT5 small-block V8 won’t use a supercharger as the 2015 Corvette Z06’s LT4, but a twin-turbo setup. This statement is backed up by Cadillac CEO and prez Johan de Nysschen.

Speaking to Jalopnik, Nysschen told that the 2016 Cadillac CT6 “includes a very wide mix of engines, starting with a 2-liter turbo, up to, eventually, a high-performance advanced V8 turbo.”

http://www.autoevolution.com/news/20...lt5-92587.html

lawdogg149

agree but I really think the LT5 will be in the mid engine car. Looking at the spacing now no way they could put twin turbos in the area they are working with on the current C7. Indeed they will go twins.

DDSLT5

Theres only one LT5 and it is in my avatar.

lawdogg149

That engine was a flop. LOL.

DDSLT5

Totally! Still annoys me that GM is recycling the exact same moniker - damn fools.

SBC_and_a_stick

A race engine has very few things to do. Meet the race regulations, last for the duration of the race/fraction of season, and maximize power. That is much simpler than a road engine's requirements, which needs to meet NVH, throttle response, EPA, safety, and other requirements.

Turbos are commonplace in high end streets cars because they make power, increase MPG, and lower emissions. Since the LT4 meets emission targets and makes 650hp, why on earth would you desire the throttle response of turbos and a larger frontal area on the car to fit it? It will ruin the drag coefficient, reduce viewable area, induce lag, and increase the weight up front. All for what, 20 hp? I don't think cooling challenges will be lessened in the least bit.

Many of the engine manufacturers choose turbos because they simply don't know how to build a proper head for NA. There are only a few companies that have a top of the line head design, Honda, Yamaha, Ferrari, and Porsche. What car companies resisted turbocharging the most? Honda, Ferrari, and Porsche (GT3). Sure BMW used to love NA, but that's when they were almost as good at head design as everyone else. Once they figured out valvetronic cannot work with high rev designs they started turbocharging everything under the sun.

Steve Snake Driver

More because of the Viper-esqe pricing model than anything else in my opinion.

Had a twin turbo C6 (APS). Cold sweats everytime I saw a speed bump because I only had about 2.5 inches of clearance (oil return line from turbo) because turbo's were located in most efficient location right off the exhaust ports. Much easier packaging on the C7Z06 system. Charge cooling lines are much easier to route than a large pressurized air line to an external charge cooler, and of course line from charge cooler to intake manifold. Ford and Fiat Chrysler ( ) seem to agree since all use essentially the same system configuration on their front engine big (relatively speaking) displacement engines. If you use a nice big turbo charge cooler infront of the radiator, you reduce unobstructed air flow to the engine coolant radiator. And of course, the turbo's are a heat source if located for most efficiency.

kverges

Ferrari's 288 GTO and F40 are contrary examples, as is the Porsche 930 that dates back to 1976 or so and the landmark 959. The 911 Turbo is THE uber Porsche street car and has been for decades, now. The GT3 is the track-oriented special that is slower in a straight line but sounds great and is lighter. Honda just doesn't make performance cars other than the NSX, that died about 10 years ago or so and the new one has twin turbos. Yamaha consults on limited numbers of street engines as far as I know. And I don't understand how a turbo power adder is any worse than S/C in terms of frontal area? Both need a charge cooler in the airflow (either directly or the heat exchanger if it is water-to-air). I agree cooling issues for forced induction are a real challenge, but really high RPM also puts a lot of heat in oil, too

I think there is more to it than cylinder head design and today since CO2 is an "emission," it is critical to have small displacement for low emissions at cruise. All the hi-po cars need 600+ hp and NO ONE is going to get that out of under 5 liters reliably. Even Ferrari has given up with the upcoming 488.

SBC_and_a_stick

The F40 story is simple. Like many early Ferrari's, the street car is simply giving the owner the race car experience. Turbos were widely adopted in racing during the F40 era, and so the F40 was turbo. Ferrari never claimed the F40 formula was right for the road, they simply sold the race car for road use.

The really fast Porsche's at HPDE's are GT3, sure the better drivers likely select the GT3 over the turbo but nonetheless. To the better drivers, the GT3 is the better car. We are talking about overall street car performance. The vote is in.

Honda also makes the S2000, with an even better head design than the NSX. But don't just look at their two sports cars, look at how long Honda has been producing NA engines for Civics, Accords, and the like. Honda was the F1 turbo era champion, yet for a street car they never found it to be a good formula. Case in point. The know how Honda has in engine head design, means that they can design an NA head that is both efficient and powerful.

Turbos, when used appropriately to reduce lag, are installed in the vee of the engine. This results in a huge increase in engine height. When installed in the vee, they act as a heat source much like the TVS supercharger, except they need a much taller engine bay and ultimately they still have more lag. Anyway, taller engine = increased frontal area.

ChucksZ06

That is a fact. Reliability for 100k miles is not something easily attained with high hp engines, especially with the emission constraints oem's have to deal with.

fdxpilot

Hey, they're on their third iteration of LT1. '70, '93, and '14.

kverges

The Porsche/Ferrari comparison confuses me. For the track, the F40 is the race car experience yet so is the NA GT3. So it seems either way works. And the 911 Turbo is by almost all measures the better street car. STREET.

And turbos have to be in the V of an engine? Since when? What about boxer engines like Porsche? I can actually only think of one example packaged that way, the AMG V8 turbo.

And for that AMG engine I have read "Boosting induction are a pair of Borg Warner-produced turbochargers mounted atop the engine within the space between the two cylinder banks -- a layout AMG engine boss Christian Enderle says helps make the M178 some 3.5 inches shorter than the M159 engine." See more at: (http://autoweek.com/article/car-news/503-hp-mercedes-amg-gt-engine#sthash.WlQNBYKc.dpu)

Turbos seem to work fine external to the engine in plenty of cars and in any event have to be that way for in line and boxer engines.
Bottom line for me is turbos work just fine street and track and are also much more usable today with synthetic oils and ceramic ball bearings, among other things.

Finally, although I have not recently studied volumetric efficiency charts , it is long been that a centrifigal volute is far more adiabatically efficient than any of the positive displacement systems. I know the positive displacement systems are much better these days. But I suspect that the most efficient turbos surpass positive displacement.
If anything, supercharging is much more rare than turbocharging for FI and I have t think engineers have some reason for that.

SBC_and_a_stick

Porsche is rare in that it can build a proper NA engine and proper turbo. But lets say the turbo is the best choice for street. Is the average 911 turbocharged? Neither the most desirable on the track or the most common on the road is a turbo variant.

Turbos don't have to be in the vee if you don't care about throttle response. The turbos in M cars and several other BMW cars are in the vee. Basically a high end powerplant will have this configuration, together with a clever turbine and exhaust manifold pairing.

The m178 and m159 height comparison is curious. The M159 made between 562 and 622 horsepower. The M178 somewhere around 510. I'm sure if you downsized the M159 architecture to match the power output, or upsize the turbos on the m178 things would look different. The M159 had a huge intake manifold. I bet you could reduce the size of it and still make more power than the turbo engine. In either case, none of this applies to the LT4, which is the subject here, and for sure would gain at least 3 inches in height going with turbos in the vee for 650hp.

kverges

BMWs M5 is a TT V8, but the M3&4 are inline 6s. And the hood line of the M5 sure does not seem any higher than the outgoing V10. And the point of a turbo is that you can use less displacement, ergo less stroke and deck height.

Throttle response can be just fine in a turbo car. My crappy bolt on turbo Miata does fine as does my crappy bolt on turbo Elise. Of course they both suck if you mat the throttle at 2500 rpm. Utterly idiotic to drive them that way, but whatever. Same thing happens in my MP4-12C. But since they all spin to at least 7K rpm (8500 for 2 of them) only a moron expects to have torque at 2500, just like you can't demand the Z06 to do anything beyond 6500 (actually looks like torque drops 75 ft lb or so after 5000 rpm) Use each engine as intended and they all have a decent amount of torque for 3-4000 rpm. Tune them with a good blowoff valve to keep turbines spinning and some spark retardation/enrichment on lift throttle to put some extra heat and energy in the exhaust and turbos stay on boil quite well. Also, modern turbos have much less rotating mass and less friction in the bearings and soon will have electric motors to also keep them turning. Bad throttle response is, IMO, a driver refusing to have mechancal sympathy with the engine to get it to do what it's capable of.

Finally of course more 911s are NA, just like more C7s are. I thought we were discussing the BEST of a model and at that you offered best on the street when I remarked that the 956, 962, 917/30, all late model Audi endurance race cars are turbo. So when you suggested that the needs of a street car that is forced induction are best served by a supercharger I disagreed and still do. Other than Dodge and GM who uses belt-driven superchargers for forced induction?

I've tinkered with belt driven superchargres, both centrifugal and positive displacement but turbos are simply better IMO. And I own and love my V Wagon and even a hotrodded Gen2 Viper with S/C, so it's not like I have not tried all flavors.

MavsAK

It's also worth noting... the C7's LT1 makes what 400 lb feet at 2k rpm...
It's not going to be hurting for throttle response as it's not a Weeny Motor.

kverges

The Chevy Small Block in all of its iterations is a world class engine; it's well packaged, and has great torque but never spins past 7000 rpm in any stock configuration. One of my favorites is the LS7 - in a time when the exotics like Ferrari and Lambo had to pay gas guzzler tax for their exotic high RPM OHS engines, Chevy put together a 505 hp OHV engine that spun 7000 rpm and made 505 hp and had no gas guzzler tax despite 7 liters of displacement. Driven gently, the C6 Z06 got pretty respectable mileage.

I am not sure I'd call the current crop of engines that spin 8500-9000 "Weeny," just a different strategy. Power is torque x RPM so either part of the equation can get the job done.

MavsAK

Sure, but when it comes to boost....having an engine that thumps out that kind of torque at mere 2k rpms...turbo lag really isn't going to be a factor.

That lag people fear so much with turbos is squarely because of tiny displacement engines, which don't produce any meaningful torque below the height of their powerband. Never mind that turbo charging has come a very long way, particularly in performance applications and has a great reduction in lag.

GM could mount the turbos where the mufflers are, and it really wouldn't suffer for it.

SBC_and_a_stick

You can have all the torque in the world, lag is lag.

Turbos as applied to tall DOHC blocks does not transfer to pushrods 1:1. The LT4 will be much taller with turbines in the vee. No way around it.

blipit_

The latest new Porsche to burn to the ground.

This time a 991 Turbo S.