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Old 08-22-2016, 03:22 PM   #1
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Possible insight into one of the new C8 engines



Your reaction: WTF, did LT just post a pic of a Cad concept in the C8 section?

Response: Yes I did, and no I'm not nuts ... er ... not certifiable anyway. Last week the above Cad Escala debuted at Pebble Beach. So what? Seems like every other year Cad offers up a stunning design there that is never more than...well in high school we called them PTs. Regardless, here is a quote from Cad's High Mucky Muck, Johan de Nysschen about the Escala:

Quote:
...uses a new 4.2-liter twin-turbo V8 for theoretical power, which is a prototype for new models.
(BTW "theoretical power" is usually show car speak for, "Don't open the hood or you'll see one of our current production engines.")

All of us here know the virtues of the LS/LT type OHV engines. They are light and compact. However, they will always be perceived by Euro snobs (and by extention USA snobs) as low tech and semi obsolete. We KNOW and point out that this "low tech, semi obsolete" engine annually leads Europe's most famous race and VERY frequently wins.

That said, the Cadillac demographic might or might not know the word LeMans. They do, know the words Mercedes, Audi, Jaguar, etc. The sales people for those cars know how to press a customer perceived advantage. Cadillac engines NEED to be OHC - warts and all. An OHC engine avoids trying to re-eduate a high end customer about something he doesn't really want to know about - just that it's perceived to be state of the art.

The Northstar V8 (RIP) was a pretty good effort, but didn't adapt well to power tweaking or MPG improvements. Ford's first gen OHC was the same, but their Coyote is a pretty good engine that "borrowed" a LOT of the block ideas from the GM LS engines. The Ford looks the same as the 10 year older LS1 upside down - crank view - to any layman.

I think the 4.2 L TT that Nysschen described will be a VVT, DI, OHC engine that will enable better MPG and performance than our lighter OHV engines by the time they finish tweaking it.

I'm not saying the LT OHV engines will be dropped...not at first and maybe never. But if the OHC 4.2 (or whatever ultimate displacement for this new engine series) can match the MPG in Chevy trucks that Ford gets in their TT V6 Trucks .... that would be a marketing coup for GM. However, long term, I can't see GM producing 2 V8s unless they share the same block, which is probably too big of a compromise to maximize either design.

....or all of my thoughts above are wrong and Nysschen pushed for a small displacement OHV LT V8 - but that sounds MORE wrong to me.

FWIW
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Old 08-25-2016, 10:41 AM   #2
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I hope they never get rid of the OHV V8s. Ever! They're just such an elegant and compact design. Yes, progress marches on, but a good design is a good design. No need to throw it out. I always crack up whenever I watch a Youtube video of a Miata with an LS engine in it. It should be so wrong, but it just seems so right.

That new Caddy engine sounds very interesting though. I wouldn't be surprised if it ended up in the Corvette. GM is changing from old Corvette traditions alot lately.
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Old 08-25-2016, 01:56 PM   #3
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The V8s are a tough call for GM, IMO. Caddy absolutely must sell a DOHC lineup - 4 / 6 / 8. Both the 4 & 6 perform well but have been criticized for being noisy compared to Europe's best of those engines.

But the SBC in all of its OHV versions has always proven to be extremely versatile for tuning [power / torque / economy], packaging and weight - especially torque in the trucks. However, as CAFE increases rise dramatically (even though the 53 MPG will be pushed out later years) intake / exhaust controls require more fine tuning than two valves can provide.

The most efficient answer is one that is risky given today's technology level: cam-less. For years they have been working on opening and closing valves using individual, computer controlled solenoids to determine lift and duration.

Basics (please forgive the elementary information and feel free to skip this):
The head forms the round top of the round combustion chamber with round valve(s) to enable intake of fuel/air mixture and round valve(s) exhaust spent gases. The more valves there are in the chamber, theoretically, the faster the mixture can get into and the faster the exhaust can leave, the chamber. These days they even know where in the chamber and what shape the mixture is forming in the chamber.


Code:
Please note that I am NOT an engineer so for those of you who are, please chime in if I have misinterpreted or omitted important issues about computer controlled electronic solenoid valve controls
Advantages of solenoid valve control:
1. No cam, means few moving parts; less drag and less metal wear being circulated throughout the engine.
2. All specs being equal, the solenoids would likely be lighter than cam(s). Realize that the challenge is not only the reliability, but also the compactness of these solenoids.
3. Physical valve arrangement would no longer be determined by the placement of a cam and mechanical valve train. Need more control over the mixture in the chamber? ... how about 6 or 8 small valves? Probably inefficient, but you get the point.
4. This is implied above - better capability to control what is going on inside the combustion chamber. Think of this as Infinite Individual Variable Valve Timing.
5. Exhaust sensor results sent to the ECM enable immediate, minute, fine tuning of the lift and duration to assure minimum emissions / maximum economy / maximum performance from the fuel.
6. A 4 valve per cylinder solenoid engine would be significantly narrower and lighter than today's DOHC arrangement. No need for cam cradles and bearings.


Disadvantages of solenoid valve control:
1. Today's valve train - springs, rockers, rods, cams - are very reliable and under normal conditions and maintenance, wear slowly and usually(but not always) alert the driver of problems before a cascade failure that destroys the engine. Failure of one solenoid leaving the valve in the down position would likely destroy the engine.
2. Availability, reliability, and the capacity of electric power for the solenoids is obviously critical. In the event of a failure in the electric power system (Battery? Alternator!!?), there must be enough reserve power to enable the engine to shut down normally (valves completing their close cycles).
3. Again - Not an engineer. I can't think of another disadvantage.

Will we see this high tech on the C8?

IMO, it would be shocking to see solenoid valve controls first appear on a V8. If I controlled one of the BIG car companies when the tech was ready, I'd apply it to a 3 cyl Hybrid first. Less to replace if there are problems and most likely to be able to "limp" into a dealer when the lights and buzzers go off because of a failure. Also a deeper reserve of electrical power is available.

IMO, either this technology will come to production soon, or the gasoline engine will be legislated into extinction....in fact, this might happen anyways, eventually. Faster if Clinton is elected. Just a fact, not a political statement.
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Old 08-26-2016, 10:29 AM   #4
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Alot of food-for-thought there LT. That tech sounds very promising.
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Old 08-26-2016, 12:55 PM   #5
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GM will be moving with the times with this motor...maybe not for the Corvette...but moving on none the less.

My BMW 750Li has a 4.4 twin turbo V8 pushing 445 HP and 480 lb/ft of torque paired with an 8 speed tranny. The motor runs smooth and quiet with excellent fuel economy and more than enough power to push that 4700 lb car in the fast lane. On my trips back and forth to Ohio I average 80 MPH and get 26.5 MPG. The motor is great.....GM needs to start borrowing the technology.
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Ain't THAT the mofo truth
Old 08-26-2016, 06:27 PM   #6
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OOPS - look again brain fart

Ponch hit it on the head. The DOHC with TT is MUCH heavier than an LS/LT OHV, but with matching tech, vehicle weight and trans, the DOHC could probably get 10% better MPG.

BTW, we know that GM had a prototype 4 valve OHV engine they worked on before the release of the C6, but we haven't heard anything about it since. Guessing they couldn't make it work or production cost would be more than OHC heads. As I recall it used two cams stacked in the V of the Block, each with unique rods. Imagine trying to incorporate VVT into THAT set up.

I'm rooting for the solenoid valve train!
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Old 08-26-2016, 08:11 PM   #7
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Quote:
Originally Posted by Longtimer View Post
Ponch hit it on the head. !
I was just coming out of a nap
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Old 08-28-2016, 01:34 PM   #8
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Quote:
Originally Posted by Poncherello View Post
GM will be moving with the times with this motor...maybe not for the Corvette...but moving on none the less.
I don't see GM producing two V8s in this market that is looking at an ultimate 53 MPG CAFE (and no doubt more later). Just does not make economies of production sense to me. However, there could be an overlap period of a year or two when both are offered...to ween us off the OHV.

Although it is certainly possible to design a blank block to accomodate a DOHC head or a cam in block OHV I don't see production / demand that would justify the inefficiencies of producing both.
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Old 09-06-2016, 01:43 AM   #9
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This has been talked up to death on other forums, LT1 engine beats European twin turbo V-8 engines when it comes to fuel economy.

The sole reason why European car makers are switching to turbocharging comes down to the European fuel economy testing loop. The increased fuel economy is coming from down sizing of the engine, Mercedes use to run for example in some applications a 6.2L V-8 engine and that has been down sized to. They down sized to 4.0L in order to get better fuel economy, they bolted on two turbochargers in order to get the power back.

People believing that this move was made because it was a superior direction to go into is pure marketing. Sure there are big benefits to turbocharging as you can boost power/torque easily.

The big fuel economy boost that could come for the Corvette would be if they dropped the engines displacement (lets say bring back the 4.8L). Bolt on two turbochargers, fuel economy goes up as long as you stay out of the boost.... this is nothing new. That is why some years ago when one of the major publications test drove an LPE C5 with 600BHP they got 30MPG on the highway out of the vehicle. Add VVT, direct injection, and a 10 speed to the equation and you might have a 305MPG 600BHP car.
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