C8R - SEMA Show

[Eric P.]

Here are a few pictures of the C8R from the SEMA show as we wait for Daytona!

Eric Patty

[Duke W.]

Re: C8R - SEMA Show

...looks amazingly "stock" other than the wider fenders and aero aids... front splitter, rear diffusor, and wing. I just hope it doesn't get saddled with too much weight and too small an air restrictor.

Duke

[Chris H.]

Re: C8R - SEMA Show

The real question is what kind of motor is in it. Rumor has it’s a flat-plane DOHC V8.

[Mark E.]

Re: C8R - SEMA Show

The real question is what kind of motor is in it. Rumor has it’s a flat-plane DOHC V8.

A new engine? I would expect a souped up LT2.

[Chris H.]

Re: C8R - SEMA Show

https://www.motor1.com/news/375287/chevy-corvette-c8r-engine-sound/

[Chris H.]

Re: C8R - SEMA Show

That my friends is no pushrod mill lol

[James G.]

Re: C8R - SEMA Show

The animation I saw of the engine earlier this year definitely had a balance shaft - that and the exhaust note leads me to the conclusion of FLAT PLANE CRANK.

[Steven B.]

Re: C8R - SEMA Show

It is a flat plane in the C8R. It was published earlier and verified by one of the GM staff here in Dallas at the C8 reveal a few weekends ago.

[Roy S.]

Re: C8R - SEMA Show

I personally believe the C8R will be DOHC V8, the LT2 is too large with respect to displacement. I do not know the requirement but believe it is smaller displacement and restricted to possibly 500hp. Some individual involved in these type programs will know.

Secondly I think the flat plane crank has some very significant complications in displacement approaching or over 5.0L

[Duke W.]

Re: C8R - SEMA Show

Secondly I think the flat plane crank has some very significant complications in displacement approaching or over 5.0L

A 90-degree V-8 with a flat crank is basically two inline fours tied to a common crank, 90 degrees out of phase. Each bank generates a second order (twice per crank revolution) vertical shaking force. On a flat crank 90-degree V-8 this nets out as a horizontal shaking force with a peak of SQRT 2 times than the peak vertical shaking force in each bank.

The larger the engine the larger/heavier the reciprocating components and the larger the force.

Most modern four-cylinder engines over two liters have twin counter rotating balance shafts, mounted horizontally, rotating at twice crankshaft speed that balance out this shaking force. This scheme was invented and patented by an Englishman named Lanchester back in the early 20th century. Somehow, I never understood why, Mitsubishi was able to "repatent" them in the seventies. Since GM hates to pay license fees, the Quad 4 turned out to be a rough engine.

On a V-8 the second order horizontal shaking force can be balanced out with twin counter rotating balance shafts, disposed vertically (one above and one below the crank), and, as you can probably imagine, creates a significant "packaging problem" in a addition to the parasitic power loss of the ten extra bearings. I don't know of any flat crank V-8 that has such balance shafts.

These shaking forces are sine waves and I've calculated that the peak accelerations generated by the two-liter DOHC I-4 in my Cosworth Vega is +/- 15g at 233Hz at 7000 revs. This means that everything on the engine must be stiff enough to have a natural frequency well above 233 Hz to avoid resonance, and, indeed, virtually every stamped sheet metal part on my Cosworth Vega engine has broken at least once from 5-8000 miles of race track hot lapping.

The primary advantage of a flat plane crank in a 90-degree V-8 is equal firing intervals of 180 degrees on each bank. At the 2018 National Convention in Las Vegas I managed to pigeon hole Dave Hill long enough to ask him... all others things equal will a flat plane crank V-8 make more power than a conventional cruciform crank V-8. He said yes, but he couldn't quantify it.

The original Ford GT40 achieved equal exhaust pulse phasing on a cruciform crank V-8 with the "bundle of snakes" exhaust system that grouped the inner two cylinders from one bank to the outer two from the opposite side and I recall that GM did this on a '69 Corvette with a ZR-1 all aluminum big block.

Duke

[Steven B.]

Re: C8R - SEMA Show

Right Roy, the rules limit displacement to 5.5 liters, 500/480, HP/Torque.

[Terry M.]

Re: C8R - SEMA Show

The original Ford GT40 achieved equal exhaust pulse phasing on a cruciform crank V-8 with the "bundle of snakes" exhaust system that grouped the inner two cylinders from one bank to the outer two from the opposite side and I recall that GM did this on a '69 Corvette with a ZR-1 all aluminum big block.

Duke

I heard a replica of that 1969 Corvette run and the sound was nothing short of terrifying. That engine was alleged to be 427 or 7 liters. I say alleged because it was hard for me to reconcile the sound with a 427. A most interesting car.

Also the ground clearance of that exhaust system was very limited.

Addition: I should mention that I heard that engine operate at a Michigan Chapter NCRS event.

[Duke W.]

Re: C8R - SEMA Show

Oops... I meant ZL-1 all aluminum big block. I recall the first time I heard a GT-40 without background noise from other cars was in the movie "A man and a Woman" circa late sixties, which had shots of a single GT-40 testing on a track. It sounded almost as good as a Ferrari V-12.

Duke

[Chris H.]

Re: C8R - SEMA Show

Seeing GT40s run at vintage events I always thought they had a strange exhaust note for a pushrod V8. Now I know why. Thanks Duke.