johnglenntwo

The valve train has done what?
And maybe:

http://gmauthority.com/blog/2014/02/corvette-racings-competition-complains-about-its-pushrod-engine-design/

lt4obsesses

The idea of the push rod going away is something that was just rattling in my head. With the ever tightening regulations, this platform for the Cadillac engine, turbo charged smaller displacement and DOHC would make sense.

However, before going off the deep end, one thing to keep in mind is that this particular engine is designed to go in what I would consider a commuter/daily driven car. So of course, MPG and emissions are a major factor in it's packaging and marketing. The Corvette may not have such a priority.

But if they were to go strictly DOHC with the small block, going mid engine with the Corvette is necessity, as the DOHC engine would be too tall for the FE Corvette.

JoesC5

Are you aware that the C4(46.7") is not as tall as the C7(48.8"), and it had a DOHC engine(ZR-1) under the hood?

Trackaholic

Usually the engine is packaged under the hood, not inside the passenger compartment.

Not sure the overall height is a factor.

The C4 did not need to contend with the same pedestrian safety regulations either, which might require greater buffer between the engine and underside of the hood.

In any case, a DOHC engine is usually taller than a pushrod design, so if the hood clearance has minimal headroom on the pushrod, it would seem like the DOHC version would require a taller hood.

Seems like a factor, but likely not the only one and maybe not even a significant one. But I was thinking the same thing and mentioned it the thread about the Cadillac engine, as one reason why I felt that engine would not make it into a front engine vette.

-T

MitchAlsup

There are two points, here::

1) The height of the hood and the height of the ME bonnet are not correlated--
Thus the height limitations of the FE car are completely different than the height limitations of the ME car--as shown in the spy photos where the glass over the engine bay gives the ME design at least 7 more inches of acceptable engine height.

2) The DCT has 2 clutches, both shorter than the single dick clutch of the C7, thus the engine can be mounted even lower than the C7 engine.

sunsalem

It is amazing the pushrod was allowed to remain in GM's line-up.
I suspect it is for financial reasons.
Other than Dodge, every other major manufacturer has dumped it AFAIK.
In a certain respect, it makes sense GM and Dodge are still holding on to them: both have had significant problems in the last 12 years or so.

Shaka

Shaka

NY09C6

Really it is not. It was far cheaper to build 6.2 and 7.2 liter engines. CAFE is what is forcing the TT 4.2 engine. All European brands have had to deal with crushing fuel regulations for many years and the reason they all went to higher revving smaller displacement engines first. Kill the regulations and everyone will go back to the larger pushrods engines and car prices will drop.

lt4obsesses

I agree. The beauty of the pushrod engine is that it allows for a greater power density. It is the larger displacement that allows for a much greater amount of torque starting at much lower rpm levels and maintaining that torque throughout the rpm range. True, it's more difficult to get these to spin to 8K, but then, it's also not necessary to spin them that high.

I'm not so sure that the smaller displacement TT engines are really that much more efficient either, except for the one place that the big inch engines are at their worst...stop and go traffic with longer intervals at idle. Going down the open road at 75, it seems the smaller engine would have to "work" harder while the big ol' 6.2 is lumbering along with very little effort to do so. At least this is my perception with my 6.2 LS3, even in a 3,850lb Camaro.

MitchAlsup

While I agree with the point you are trying to make, I disagree that you explained it correctly::

Lets take a car going down the road at 75 MPH (as above), The tire friction and air resistance cause the engine to have to produce a certain amount of power (which is equal to the power consumed into friction and air). Thus the big displacement engine and the little displacement engine still produce as much work (as the other).

So give a little TT engine that produces 450 HP and 500 lb-ft of TQ and compare it to a big pushrod engine that produces 450 HP and 500 lb-ft of TQ, both engines are operating at exactly the same HP/TQ in their RPM/Throttle regime.

What I think you meant so say, is that the little engine is operating at a higher RPM and thus has more friction--and this depends entirely on the RPM point where the turbos start to spool up, the transmission ratios,.....

So, if 75 MPH corresponds to 1600 RPMs in the big pushrod engine, and the little TT engine is operating at a similar 1600 RPMs with the turbos partially spooled up, it is likely that the engines are similarly efficient.

Now take the TTs away, and the little engine is operating at 1.6× the RPMs and the pushrod engine will always be more efficient (and probably easier to meet emissions.) Here, there is no argument.

lt4obsesses

RPM is a large part of what I meant by "work".
Of course there are many factors that will be specific to the car, drag, gearing, etc. But given real world circumstances on the road, such as gradual inclines, changing speeds etc. The larger displacement engine may be able to handle those a little more smoothly. For example I was driving on the highway today in some traffic, which was flowing at about 75 mph. I was in 6th gear, and as traffic slowed and regained speed, and as I hit inclines, I never had to downshift and only needed a slight throttle adjustment to get back to 75 from 65. Would the smaller TT engine be able to do that? Perhaps

I am curious to see what the final fuel efficiency ratings will be on the CT6 with this engine.

JoesC5

True. My 7L Z06 can cruise at 70 MPH and get over 30 MPG on the highway all day long.

The smaller displacement C6 ZR1 can't get that good a gas mileage on the highway, and both have the same aero drag, tire rolling resistance, and the same .50:1 gearing in 6th gear.

The lower CR on the supercharged ZR1 with it's 6.2L engine is not as efficient as the higher CR on my NA engine, when both are cruising down the highway with the throttle just open enough to maintain 70 MPH(the ZR1 won't be in boost mode).

johnglenntwo

For a man who sweats the details you aren't on it here, at least!

The EPA prefers boiling fuel vs burning it.
Turbos just do that less not having all the SC's paristic losses!

MitchAlsup

I have a picture of my GLS 450 getting 28.6 mpg over 7+ hours and 475 miles.

Now, everybody understand the GLS has far worse aero, at least 2× the frontal area, weights about 60% more; but it does have one of those little TT engines this thread has become about....

If anyone cares, the trip started in Oklahoma City and ended in St. Louis. The picture was taken about 2 miles before I turned of the interstate and onto city streets.

JoesC5

I also have a picture of my 7.0L Z06 averaging 33.0 MPG for 450 mile trip from Springfield, MO to Natchez, MS. That was not 100% steady Interstate driving. Two and four lane highways in the mountains in southern Missouri and northern Arkansas, driving through small towns, getting caught at traffic lights, etc, about 50 miles of Interstate driving at 70+ MPH, and then a couple hundred miles of two lane driving through small towns with traffic lights in southern Arkansas and then Louisiana to Natchez, MS.



I also have a picture of my 7.0L Z06 averaging 35.0 MPG for approximately 30 miles while driving at 74 MPH(70 speed limit) on I-29 traveling north in Iowa. The 2016 C7 Z51 A8, in eco, that was behind me was also getting the same gas mileage(35 MPG) at the same time on the same interstate highway at the same speed.

When we crossed into South Dakota, I bumped the speed up to 84 MPH(80 speed limit) and my gas mileage dropped to 33 MPG until we hit Sioux Falls for the night.

I do suspect that we probably had small tail wind from the south, but the fact remains that my big ole LS7 was getting the same gas mileage as the smaller displacement LT1 was getting.

EDIT: I don't have the photos any longer as they are being held for ransom by Photosbucket. I do have some photos averaging 31.2 MPG while cruising across northern AZ at 70 MPH on some twisty two lane highways. That gas mileage average was for the first ~1,500 miles of that trip.








On that particular trip, I averaged 29.2 MPG for the entire 2,600 mile road trip that included high speed Interstate driving(85+) slow speed cruising while visiting eight national parks in Colorado and Utah, really mountainous driving in Colorado, etc. Definitely not 2,600 miles of steady cruising at 65 MPH on a Interstate highway.

Mcrider

GM better look long and hard at what has happened to Harley Davidson the past few years as their products became more and more expensive. There aren't enough people out there to support $150k+ vettes for very long. They would never begin to recoup their tooling/manufacturing costs IMO.

johnglenntwo

Everything's relative!

MitchAlsup

Withe the demise of Viper and the expected demise of Audi R8,
the $120-$150 K price bracket is a perilous place to operate.

Viper had the necessary number of customers when it was in the $70-$90 K bracket for its low build rate production plan.

I don't know if R8 was anything other than an attempt at getting Lamborghini Gallardo into the $130K range.

Big Lebowski

Welcome to the club...and by “club” I mean all four of you.

Neither are the rest of us...