Tech Article: GM 4.2L, DOHC, 32 Motor

[John]

This is an incredibly interesting, technical article on the 4.2 L, 32V, DOHC, "Hot Vee" Motor going into the CT6 V SPort. It is being built within BGA, specifically inside the Powertrain Build Center.

We learned today, in a separate thread on "Cosworth," that the heads for this motor are being made by the renowned Cosworth Engineering. Also in that article is a note that a complete new manufacturing plant was being built by Cosworth just outside of Detroit, and that a major announcement is coming soon on additional manufacturing of components, perhaps even whole motors, for amajor OEM. Is this facility the location of the ME's 2021+ high performance motors being built. That we will now soon. In the interim, for GM performance motor tech junkies, this article is your brad and butter.

First our earlier thread about Cosworth's new Plant (again with thanks to member Fasttoys who found this article).

https://www.midenginecorvetteforum.c...cale-me-motors


The following technical article about the motor is 14 pages (pictures) long. The last seven of them are in post # 2.


Now to one of the most interesting, highly technical articles as to GM’s newest V8 motor’s features:

[John]

The is the last half of the technical article on the latest GM V8 engine.

[dcbingaman]

Very nice article. So, if we just scale this baby up to 5.5L, we can expect 550*[5.5/4.2] = 720 HP. With a little freer packaging, 800 HP seems quite possible. Very exciting. My guess is the OHV small block may have met its match, but probably not until MY2021-2022.

[John]

I can not wait to experience the 5.5L ME’s motor, whatever its final specifics are. My personal guess is that the 2020 OHV, LT1+ (whatever GM chooses to call it), will be a 5.5L motor, echoing the C7.R’s and the Cadillac Prototype race cars. And, none of us forget the IHS Markit Engine Forecast which predicted a 5.5L motor for the Y2/ME chassis (as well as a 4.2L version) — though both were listed in the Forecast as being only 32V, DOHC motors in those two sizes.

https://www.midenginecorvetteforum.c...-consideration

[JB]

Call me crazy but after reading this engine description i believe the corvette c8 version will be slightly smaller in stroke and have a flat plane crank..

it goes against all logic im sure but thats my best guess..

i fully exoect to be proven wrong and thats ok. For some reason thats the engine i see in the upcoming higher end corvette models.

should be quite the laugh when the higher performance models reveal with a larger displacement engine with a cross plane crank And twin turbos

[Boomer]

Very informative and impressive. The CT6Vsport would be on my buy list when I trade my XTSvsport EXCEPT it comes equipped with summer only wheels/tires. Because the tires and wheels are specifically designed for the CT6Vsport and GM warns only that approved wheel/tire combination can be used, AS tires cannot be substituted like we can with our Corvette. For that kinda full use vehicle I cannot live with the restrictions of summer only tires. Summer only tires are fine for the Corvette cause I only use it in summer only tire conditions i.e. above 40F, no snow, etc.

Cadillac will also offer a 500 HP CT6 that is equipped with all season tires. That car is on my buy list for 2020 or 2021. Cadillac has put out this info:

"Also debuting is an all-new Cadillac 4.2-liter twin-turbo DOHC V8, the first of its kind for GM’s top-level luxury brand. In 550-horsepower trim, this clean-sheet engine will power the CT6 V-Sport; a lesser, 500-horsepower version will find its way to non-V-Sport models."

That tells me the same engine described in this thread albeit with 50HP less will be available in a CT6. That CT6 will be designed/equipped with AS tires allowing it to be driven year around in all wx conditions. Looking forward to that.

[AbqVic]

Very informative article John,

What's amazing to me is how much engineering value we are getting with current and future cars. I have been a hot rod enthusiast all my life, though I never have built one. I'm happy about that now, because I know that no one off car could ever be as problem free and integrated as a new production car, no matter how much was spent on it.

Vic

[dcbingaman]

Call me crazy but after reading this engine description i believe the corvette c8 version will be slightly smaller in stroke and have a flat plane crank..

it goes against all logic im sure but thats my best guess..

i fully exoect to be proven wrong and thats ok. For some reason thats the engine i see in the upcoming higher end corvette models.

should be quite the laugh when the higher performance models reveal with a larger displacement engine with a cross plane crank And twin turbos

Maybe, but flat plane cranks work best in SMALL engines. The harmonics get out of control if you go over 4.0L requiring fairly sophisticated engine mounts to prevent excessive chassis vibrations. The Ford 5.0L Coyote flat plane crank reportedly shakes the hell out of the dashboard at certain RPMs.

I think a balanced crank makes more sense for a big engine with very few performance sacrifices. The CFD-based tailoring of the head, valve port and turbo geometries are much more important than the crank geometry in a 2018 engine design.

[John]

With the vibration issues for the flat plane on the Mustang GT 350 that some customers are reporting, I too am not believing that the Corvette ME will have anything else but a balanced crank.

[Fasttoys]

Maybe, but flat plane cranks work best in SMALL engines. The harmonics get out of control if you go over 4.0L requiring fairly sophisticated engine mounts to prevent excessive chassis vibrations. The Ford 5.0L Coyote flat plane crank reportedly shakes the hell out of the dashboard at certain RPMs.

I think a balanced crank makes more sense for a big engine with very few performance sacrifices. The CFD-based tailoring of the head, valve port and turbo geometries are much more important than the crank geometry in a 2018 engine design.

How does Ferrari build FPC without vibration issues? Small displacement and customers with endless bank accounts so they can spend more on R&D

[Quinten]

That’s purely a luxury engine. It’s more like a Rolls-Royce V12 than a Mercedes-AMG Biturbo V8. Corvettes won’t get engines with such a big low end(compared to the top end) on the torque curve. We’ll see higher revving V8s with larger turbos that spool quicker, possibly with dual-injection. They’ll make much more power than the Cadillac 4.2, with minimal to decent decent torque gains.

[dcbingaman]

Ferrari uses very large, silicone fluid-filled engine mounts that damp the engine vibrations. The largest V-8 with a flat crank they ever made was the 4.5L in the 458 Italia. Reportedly if / when the engine mount boots crack and lose fluid, the engine can shake the car pretty noticeably. It has happened to older Ferraris, (355's, 430's, etc.). The mounts can readily be replaced, however.

[JB]

Cadillacs engine has a long stroke design. For the chevrolet to increase displacement bore would have to be increased. Does the engine have the cylinder wall delth to accomodate a larger bore and still be capable of higher boost levels?

thats why im thinking a slightly smaller displacement kind of makes more sense.

should be interesting when details on the corvette tt dohc motor.

would gm just have a new block to work with for corvette?

get ready to pay much more for this dohc tt engine

[ltomn]

This is a fascinating read! I am not savvy enough to glean all the details from the paper but the prospect of a version of this to be included in the C8 is quite invigorating.

[John]

I too do not understand a bunch within that article, but did learn some good things. I keep hearing from different sources that the 2020’s only motor offered will not be an LT1, but an advanced, smaller displacement engine, yet still a traditional GM V8 OHV motor. Nothing wrong with getting better performance out of a smaller, more efficient motor; if nothing else, a smaller displacement motor will weigh less.

And who amount us would not celebrate the C8 weighing less than the C7.