2014 C7 Chevrolet Corvette

[WingsofWar]

Rotary Equivalent to aggressive cams lolz

[ame="http://www.youtube.com/watch?v=p8JvfJFBcLw"]Turbo Peripheral Port Start-up and Idle - YouTube[/ame]

[muffinman]

Originally Posted by serialk11r

Yup.

For the people who are willing to swap cams, er, *the cam* and want more power, then the bigger motor is a godsend, but I feel like the motor shouldn't come from the factory with loads of power "locked away" like that.

Thanks for the video btw I'm jealous, oil temp sensor!

Corvette motors have probably had the most different cams made for them than any other motors in history. A bunch of new owners are going to throw a cam in there, a loud exhaust, and get the cylinder deactivation tuned out so the stock mpg rating is just for the epa and gas guzzler taxes

[ZDan]

Originally Posted by serialk11r

@ZDan, I know hp/L isn't important per se, but the issue is that no, 6000rpm peak does not mean it is breathing well. A power peak is just a power peak, but specific torque tells you where it's breathing well.

Peak power rpm tells you where it is breathing the MOST air. This will ALWAYS be at lower volumetric efficiency and lower specific torque than at peak torque rpm. But guess what? Power is more important. I'm a LOT more interested in power produced and engine weight than "specific torque".

Knowing hp/L at some rpm lets you compare specific torque, as I did to my 1ZZ turd pile. The fact is, 450hp at 6000rpm on a modern 6.2L engine means it is NOT breathing well at 6000rpm.

Of course it is. See comments above. At peak power rpm, *any* engine is taking in air as quickly as it possibly can. And for *any* engine, it will be breathing less per rpm than at peak torque.

LT1 = 450hp @ 6000 => 394 lb-ft @ 6000rpm
specific torque at peak power = 394/6.2 = 64 lb-ft/liter

1ZZ "turd pile" = 140hp @ 6400 => 115 lb-ft @ 6400rpm
specific torque at peak power = 115/1.8 = 64 lb-ft/liter

LT1 is breathing as well at 6000 as the 1ZZ is at 6400.

Of course it does breathe better than the 1ZZ at peak torque rpm:
LT1 => 450 lb-ft/6.2 liters = 73 lb-ft/liter
1ZZ => 122 lb-ft/1.8 liters = 68 lb-ft/liter

But anyway, it's all a means to an end. For me, I care about two things: how much power does it make, and how much does it weigh. The LT1 makes good power out of a relatively small and lightweight package. Sweeet...

Knowing that the specific torque on this LT1 motor is very good until like 4000 or whatever only adds to the evidence.

???
The 6.2 LS3 isn't even at peak torque until 4600rpm. That's 200rpm higher than the 1ZZ's torque peak!

For the sake of argument, lets say the LT1 is making its peak torque of 450 lb-ft at 4000rpm. Why would that be a *bad* thing?

*ANY* engine is doing its best at PEAK POWER. Which is at 6000rpm on the new LT1. Guaranteed it will still be breathing well enough at its 6500rpm redline. I would bet that redline rpm will be optimal for every shift.

Any performance metric alone is pretty useless (except maybe peak power),

Power is THE metric. Of course the shape of the power curve is hugely important, but yeah, PEAK POWER cuts through the b.s. and gives you a decent approximation of how a car of a given weight will perform.

it's how it fits into the whole picture that matters, and the picture is very clear in this case.

It's very clear to me, but I honestly think you've confused yourself with random ponderings (without bothering to do the math, apparently!) on specific torque and hp/liter.

You say power to weight is important, and I completely agree. What I'm saying is, they put the wrong cams in there for power/weight ratio, because that motor has just stupid high torque.

Obviously, the thing will make a ton more power with a bigger cam. But they had other priorities than outright making the most power.

These changes are all small, 10% lower displacement means 10% less torque, maybe 5% better fuel economy,

*Not necessarily*. For one thing, to make the same 450hp, the 5.6 liter would have to be tweaked more for higher-rpm power, so might not be at optimal BSFC for cruise. For another, it would be geared shorter. And for another, less time in 4-cylinder mode.

maybe 5% off the total engine mass,

Probably optimistic. I feel pretty OK about my 12 lb. estimate above. Or less than half of 1% of vehicle mass.

when I'm talking cams I am talking like "stage 1" intake cam only. I just think this makes more sense for a passenger car, while keeping with the big displacement, high power/weight ratio tradition. There is absolutely no reason those motors can't be putting out 80hp/L with that rev limit and stroke.

Indeed, the mildly-cammed 6.0 in my RX-7 is making about 86hp/L.

But again, hp/L is not the be-all/end-all. GM developed this engine to meet their power target while providing better driveability with the 6.2. Going to a 5.5 at the same power level would almost certainly make the car less real-world enjoyable for most people who will buy it, and tweaked to give the same peak power output and shorter-geared to provide the same acceleration in gears it would probably get no better fuel mileage.

If you're that stuck on hp/L, there are plenty of AP1 S2000's out there. 120hp/L, yay! I love mine. But I also love my vastly inferior hp/L V8 RX-7...

[serialk11r]

@ZDan Nah, I did the math, but turns out I was using a number I had in my head (which wasn't correct), which was 6000rpm, 138hp. My apologies.

There's a reason why specific torque (or mean effective pressure) is the standard pissing contest yardstick for engineers (something like that is how 3MI racing/Homemade_WRX put it), and that's because specific power is largely about how fast you can turn the engine, but specific torque is about how much air you can cram in there and burn efficiently, and not lose out over friction. Specific torque at power peak gives a hint as to how "hot" the cams are. When you have a sophisticated combustion chamber design with direct injection, you would expect a higher specific torque.

In the case of the LT1, the specific torque at the power peak is rather low for a direct injected modern engine. Despite the 1ZZ having the same specific torque, the 1ZZ has a 15 year old design, so the 1ZZ is almost certainly sucking in more air to produce that 64 ft-lb/L. That is to say, LT1 is not breathing as well, because it has a higher efficiency. At 140hp, the 1ZZ is not really breathing well either at its power peak.

I fully understand that when it comes to performance peak power is pretty much the only useful measure. I'm just saying, you can look at the other engine attributes and easily see that they compromised peak power quite a lot. It's still a good engine by any measure, I just think they could've chosen some slightly different cams. I haven't gotten my fingers dirty with actual cam specs, but I suspect that making the intake cam a little bigger would help this engine a lot. Great news for the enthusiast who is willing to switch them though, probably could get 500hp without driveability/smoothness problems, and as you say, in such a compact and lightweight package, that is pretty freaking awesome.

@muffinman of course, but it's not really fair to say "the aftermarket can fix this" because then you could argue that any shitbox with an economy motor could have a cheap cam swap and gain tons of power. That's why the BRZ with its FA20 costs a pretty penny for its 200 horses, and I don't think anyone thinks the car is worse because swapping cams wouldn't have as big of an effect. Also, the only reason to turn off cylinder deactivation is if it's not smooth, but if they haven't gotten the process to be smooth, then we get another shining example of how government bailouts work just great, right?

[ZDan]

Originally Posted by serialk11r

There's a reason why specific torque (or mean effective pressure) is the standard pissing contest yardstick for engineers (something like that is how 3MI racing/Homemade_WRX put it), and that's because specific power is largely about how fast you can turn the engine, but specific torque is about how much air you can cram in there and burn efficiently, and not lose out over friction.

Obviously, minimizing internal friction and pumping losses are a huge priority, but I would bet that the engineers developing these engines fully understand that "specific torque" is not necessarily an absolute indicator of engine "goodness". There are other factors that influence it, other priorities that are competing.

Anyway, had they done a 450hp 5.6 liter rather than going 6.2, it wouldn't necessarily have made more torque/liter.

In the case of the LT1, the specific torque at the power peak is rather low for a direct injected modern engine.

So what? 450hp is 450hp. It freaking WORKS.

It should also be noted that these engines typically respond INCREDIBLY well to minor mods. My LS2/L92 (essentially a 6.0 liter LS3), with a mild cam, makes ~82 lb-ft/liter.

I fully understand that when it comes to performance peak power is pretty much the only useful measure. I'm just saying, you can look at the other engine attributes and easily see that they compromised peak power quite a lot. It's still a good engine by any measure, I just think they could've chosen some slightly different cams.

Hate to nitpick, but this was already pointed out: this engine has ONE camshaft. People generally refer to it as THE cam. Mine does have a slightly different *cam*.

I haven't gotten my fingers dirty with actual cam specs, but I suspect that making the intake cam a little bigger would help this engine a lot.

Different intake and/or exhaust lobe profiles could no doubt increase power tremendously. As already stated, outright maximum power output is one priority for this engine, there are MANY others. Including responsiveness at low revs, emissions, fuel economy, etc. etc. etc.

450hp is a tremendous amount of power.
There are many ways to make 450hp. This way turns out to be a pretty good one as far as weight, size, cost, all-around driveability, emissions, and fuel economy are concerned. Optimizing for these and perhaps dozens of other factors won't necessarily result in stellar "specific output" numbers.

Great news for the enthusiast who is willing to switch them though, probably could get 500hp without driveability/smoothness problems, and as you say, in such a compact and lightweight package, that is pretty freaking awesome.

AGREED!

[muffinman]

Originally Posted by serialk11r

@ZDan
@muffinman of course, but it's not really fair to say "the aftermarket can fix this" because then you could argue that any shitbox with an economy motor could have a cheap cam swap and gain tons of power. That's why the BRZ with its FA20 costs a pretty penny for its 200 horses, and I don't think anyone thinks the car is worse because swapping cams wouldn't have as big of an effect. Also, the only reason to turn off cylinder deactivation is if it's not smooth, but if they haven't gotten the process to be smooth, then we get another shining example of how government bailouts work just great, right?

I have no doubt that they'll be reasonably smooth transitions. I think the main reason to do it is to hear 8 cylinders running through a loud exhaust, even when cruising. U know, cause it sounds badass.

[WingsofWar]

you guys are silly...

the new LT1 is doing everything right imo, and manged to be spunkier, lighter, and greener than its predecessor the 7.0L LS7.

I think its just amazing that the LT1 uses VVT with cam phasing, and a high compression but GM claims it doesn't require premium fuel anymore unlike the previous generations.

[Ryephile]

Originally Posted by serialk11r

....There's a reason why specific torque (or mean effective pressure) is the standard pissing contest yardstick for engineers (something like that is how 3MI racing/Homemade_WRX put it), ...

True, BMEP is pretty much the universal ICE comparator, as is removes all whining and excuses from the situation.

The LSx engines' BMEP has never been impressive, but then again they don't really need to. They make massive torque, efficiency be damned. It's the American way.

That said, I'd be happy if they went quasi-Atkinson cycle during the V-4 low-load mode to get >30MPG hwy while also churning out 450HP at WOT. That'd get me amused no matter what the BMEP is.

[wbradley]

Aside from the discussion, looks kinda like the GTR from some angles. Hmmm...I bet that is the car that stole significant customers away from the ZR1

[serialk11r]

Originally Posted by muffinman

I have no doubt that they'll be reasonably smooth transitions. I think the main reason to do it is to hear 8 cylinders running through a loud exhaust, even when cruising. U know, cause it sounds badass.

Hahaha fair enough. If you watch the video however they do say that there are 3 bypass valves in the exhaust system or something, and one is specifically meant to make it sound better in 4 cylinder mode. It could be good, who knows.

If you really like noise though, you should try engine on pulse and gliding on the highway. Hearing the same note from the engine gets a bit old, but hearing it growl as you accelerate never does, and those V8s growl pretty good

[LSxJunkie]

Originally Posted by muffinman

Corvette motors have probably had the most different cams made for them than any other motors in history. A bunch of new owners are going to throw a cam in there, a loud exhaust, and get the cylinder deactivation tuned out so the stock mpg rating is just for the epa and gas guzzler taxes

Yes and no. I want to do one badly. I will be buying a C7 at some point and my goal is to toss a cam in it. However, the major holdup isn't going to be physical parts, it's going to be figuring out the tuning. Supposedly it's a very smart PCM, possibly with onboard wideband, but you're locked out of fuel tables. Unverified rumors state that GM anticipated the aftermarket and set up the PCM with that in mind, but we'll see. Either way, I'm excited as all hell.

[Grishbok]

I liked the looks of the c7 at first, but after about 20 minutes, the novelty of its vents and overly sculpted body panels reminded me of the song, pretty fly for a white guy from the Offspring. Its like its trying too hard...

Technically, its a wonderful advancement, theyve done what they needed to do to make a successor a success and raise the bar a little more.

[serialk11r]

Originally Posted by LSxJunkie

Yes and no. I want to do one badly. I will be buying a C7 at some point and my goal is to toss a cam in it. However, the major holdup isn't going to be physical parts, it's going to be figuring out the tuning. Supposedly it's a very smart PCM, possibly with onboard wideband, but you're locked out of fuel tables. Unverified rumors state that GM anticipated the aftermarket and set up the PCM with that in mind, but we'll see. Either way, I'm excited as all hell.

Piggyback that tampers with O2 sensor readings?

[ZDan]

Originally Posted by Ryephile

True, BMEP is pretty much the universal ICE comparator, as is removes all whining and excuses from the situation.
The LSx engines' BMEP has never been impressive, but then again they don't really need to. They make massive torque, efficiency be damned. It's the American way.

Quite the opposite. They needed to ensure that this car got decent fuel economy. 450hp, upwards of 120mph in the 1/4, and 28mpg (guessing here, sure to be an improvement over the LS3 C6's 26)? Not too shabby.

That said, I'd be happy if they went quasi-Atkinson cycle during the V-4 low-load mode to get >30MPG hwy while also churning out 450HP at WOT. That'd get me amused no matter what the BMEP is.

Optimizing a sports car to be fast *and* efficient clearly doesn't require stellar BMEP, specific torque (same thing), or specific power. Maximizing those is necessary for getting max performance from limited displacement, but if you free up the displacement, other solutions are viable.

Worth noting that larger-displacement at lower rpm will inherently be at something of a compression ratio disadvantage, hence lower BMEP. That doesn't mean the big-inch/low revs solution can't be both powerful and fuel efficient, while also being compact and lightweight.

Big OHV V8s will never set torque/ or power/displacement records, but damned if they don't work BRILLIANTLY