Lavender

If that was true...we'd all be driving Honda S2000s...

64drvr

nothing utilitarian. Just the sweet music of high rpm like the glorious noise of a 991 gt3 vs a nongt car or the c6z06 redline.

JoesC5

Check out the Mercedes AMG GTR with 577 HP out of 4.0L with DOHC and twin turbo's. 144 HP/L. With 6.2L that would be 893 HP, while meeting all the emissions and the smooth drivability of a Mercedes and with a warranty.

JoesC5

The stock LS7 had no problems with it's 101.6mm stroke with a 7,000 RPM redline and a 7,100 RPM fuel shutoff. Many have upped the RPM to 7,400 RPM with no problems with excessive piston speeds.

The new Mercury Marine DOHC 32 valve 7L uses the LS7 block with it's 101.6mm stroke and has 775 HP with a 7,500 RPM redline. Normally aspirated at that.

sunsalem

Can we be sure of that?
How about gas mileage?

JoesC5

Can't say with 100% certainty. I was just pointing out what Mercedes has accomplished with their 4.0L engine(that meets emissions and had respectable gas mileage). Mercedes is meeting the emissions and fuel economy with it's 144HP/L. So maybe GM can do it with 6.2L at 144HP/L.

If GM were to retain the 6.2L displacement but tune for,say, 750 HP, I doubt there would be any problems with meeting emissions and fuel economy goals. My point was that based on what Mercedes has done, they could possibly reach as high as 893 HP.

GM could also drop to 5.0L and see 720 HP based on what Mercedes has done with their 4.0L engine.

JoesC5

Thanks for the correction, Just additional proof that a 101.6mm stoke can rev pretty high without excessive engine destroying piston speeds.

And that's with unleaded 91 octane fuel, not the unleaded 93 octane(that a lot of people don't have access to)that GM requires for the 650 HP LT4(to obtain maximum rated horsepower).

sunsalem

GM vs. MB in turbo tech is a little unfair.
Currently, MB's F1 engine is a 1.5L (no typo) V6 turbo/hybrid that exceeds 1,000hp.
Certainly some of that technology has creeped into their street cars.

To be honest, I don't know where GM is with their turbo tech.
Because of the upcoming CAFE regs, no doubt they are going at it full force...albeit, behind closed doors.
I'm sure they, like almost everyone else, will have to go all in or the internal combustion engine is toast.
Tesla has demonstrated an all-electric car can handle the vast majority of the normal driving people do AND can work in the marketplace too.

CPhelps

Point taken but I was thinking more along the lines of the Vodoo 8250 or higher redline. I recall reading that the LS7 was piston speed limited (for GM's internal reliability standards, not saying people can't rev higher, as you've shown).

Does the Mercury SB4 use OEM GM pistons or something higher end. I'm not saying GM couldn't figure out how to make it work, just that what they production certify is often more conservative than what people do to their aftermarket LS7s or what Mercury Marine would do with higher end components.

JoesC5

I doubt that the Mercury Marine engine uses the stock LS7 cast pistons as the different valve angles(and from both sides of the combustion chamber) most likely demands different valve reliefs in the piston top. With 775 HP and a 8000 RPM redline, I suspect they are using forged pistons(nothing special about forged pistons as even GM uses them on their LS9 and LT4).

JoesC5

I think GM started with turbos on the diesel electric railway locomotives(EMD) in 1958 and a roots supercharger in 1938, and Roots superchargers in their GMC trucks in 1940(that's where all the 1950's and later drag racers got their superchargers, off used old GMC trucks).

Then they had turbo cars in the early 1960's with the Corvair and superchargers later on, on the 3.8 V6 Pontiacs.

Not to long ago, GM designed and tooled a 4.5L 72 degree V8 with a CGI block diesel engine for their middle size trucks, that was DOHC with reverse flow heads so that the twin turbos are between the heads(like what MB is doing with the AMG GTR 4.0L V8 TT). GM has not used the engine in a production vehicle. The GM TT 4.5L V8 was designed to fit in the same size box that the LS series gas engine fits in. Wouldn't take much engineering to design a DOHC head(and pistons) like MB has done, for running on gasoline, and even enlarging the bore and increasing the stroke to get more than 4.5L displacement, to then use that engine in a Corvette.

They sure have had plenty of time to figure things out.

Even my MB has a supercharger(and it's not a race car but a four door sedan) and I've never gone into reduced power mode or limp home mode because of overheating. My coolant temps never exceed 90*C, but then my supercharger(Roots) has an air to air heat exchanger to cool the air temps coming out of the supercharger.

four0nefive

Yeah but you dont run your supercharged Mercedes sedan on a road course in 90+ degree weather...

JoesC5

And you don't drive your supercharged Mercedes sedan or your supercharged Z06 on a road course in 90+ degree weather; not even your mother's car(which is probably a Honda Minivan).

johnglenntwo

Turbo cooling and American V8 TQ RPM's - Why! The Mercury gets it done, again. Perfect HP over TQ dominance for road tracking.
Maybe introducing the 10 - speed in a Real transaxle for the C8 mid config. too.


!!! And it Validates/Extends the C4 version! They like to do that over there.
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dmaxx3500

guys keep looking at merc marine,,they are already building the DOHC ls chevy engines,theve had running cars/trucks at SEMA for 2-3 years

why would they be building these if GM didn't want to use them?

four0nefive

My point was that driving a car on the street is much different than flogging it on the track for 20 minutes. No one has overheated their Z06 driving on the street, just like your Merc, but hey whatever helps you feel better.

johnglenntwo

With most everyone going TURBO these days GM would be blazing new trails, Again! The key is how efficient they can get a Mercury kind of thing to run?

sunsalem

FWIW, I'm all in favor of a DOHC.
My experience with Fords and my Cadillac XLR has given me positive reinforcement on the concept and design.


The pushrods are kind of embarrassing in such a great chassis as the Z.

JoesC5

My memory is fading, but I seem to recall people posting that their Z06's were going into limp home mode when they are doing rolls on the street.

Do you believe that I never go over 20% throttle in my supercharged Mercedes or that I never run the twisties through the Ozark mountains in my Mercedes(pushing it pretty hard playing around)?

If you do, then you are sorely mistaken.

I didn't get a supercharged Mercedes sedan because I was planning to drive like a soccer mom(or her 16 year old son) in her Honda Minivan.

I purchased my Mercedes supercharged sedan long before Dodge came out with their supercharged Charger Hellcat. Today, the Hellcat would be a great 4 door sedan for high performance street duties that I would seriously consider as a replacement for my Mercedes. A friend has one, and is extremely happy with it. I sure don't hear of overheating when the Hellcat owners are pushing their cars to the limits(either on the street or on the track).

As for overheating in supercharged Corvettes, several of my friends have them(700 bhp C6 GS with a Maggie, cam, long tubes), and a Callaway C6 GS with 606 bhp, and a C6 GS with a 599 bhp E-Force, and a C6 ZR1 with 638 bhp. They don't have overheating problems.

Other brands have gotten it right, but not Chevrolet with their C7 Z06. That's why GM made some changes in the 2017 Z06 to address some of those overheating problems. We still don't know how effective those changes are.

I feel pretty damn good driving my three Corvettes(one being a C6 Z06 that doesn't overheat) or my supercharged Mercedes sedan(that doesn't overheat). How do you feel driving your mom's minivan(that doesn't overheat)?

johnglenntwo

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http://blog.caranddriver.com/the-2018-chevrolet-corvette-zr1-may-debut-this-month-after-all/

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