C8 Corvette

[roon]

The frame is steel instead of aluminium, the body plastic instead of carbon, etc etc.

The chassis is aluminum. The bodypanels are FRP like most modern automobiles bumpers. The rear crash structure is CF.

Looks like an aluminium spaceframe with cast engine and suspension mountings. Similar to what Ferrari are doing.

The rear castings look quite large, not sure if they are uniquely so. I've read Tesla are looking in to getting very large die casting machines to simplify assembly.

[NL_Fer]

The numbers do enough talking.

Yes a 4.0l twin turbo, 32 valve, 4x DOHC, Double Vanos will match the LT 6.2L in power and torque. But any weight saved by smaller displacement, is lost in added weight for 3 extra camshafts, timing chains & tensioners, 3 extra valve timing systems, bigger heads, turbochargers & intercoolers.

I am really impressed by the performance they pull from those “dynosaur” pushrods.

[pierrre]

cant think of cheaper mid rear v8 two seater sports car although i still think they could have created a new model from this rather than use the corvette name

[strad]

Anything can win the GT class with the right balance of performance.

Really?

[bill shoe]

The numbers do enough talking.

Yes a 4.0l twin turbo, 32 valve, 4x DOHC, Double Vanos will match the LT 6.2L in power and torque. But any weight saved by smaller displacement, is lost in added weight for 3 extra camshafts, timing chains & tensioners, 3 extra valve timing systems, bigger heads, turbochargers & intercoolers.

I am really impressed by the performance they pull from those “dynosaur” pushrods.

more info along these lines... Here's presentation by GM Powertrain about the similar LT1 engine, circa ~ 2013. In particular go to slides 15-17: they show lighter weight, smaller size, and better efficiency than the equivalent state-of-the-art BMW twin-turbo V8.

If you were designing a sports car without prejudice for technological method, you would clearly prefer the GM pushrod V8 over BMW's latest/greatest.

http://www.c6registry.com/pdf/LT1%20pre ... 4OC12a.pdf

[Just_a_fan]

The performance isn't because of it being a pushrod though, is it? It's because they worked extremely hard on the combustion process and chamber design etc. That could be equally applied to an OHC engine as an OHV engine.

It will be interesting to see how the engine does once it's forced to comply with EU emissions legislation. Has it been homologated for EU sale yet?

Also interesting is that the BMW engine they compare to is actually the original version of that engine back in 2008 - so 11 years old now. It's been developed by BMW since then, of course, and now produces about the same power / torque as the new LT1. The BMW engine was also developed for the sports market such as the M5 where it puts out 590bhp and 550lbft.

[Cold Fussion]

Anything can win the GT class with the right balance of performance.

Really?

The ASO can alter your BOP between qualifying and the race at Le Mans. Even a Bentley GT3 won a Blancpain series championship. GT racing is an entertainment series not a technical excellence series.

[roon]

The performance isn't because of it being a pushrod though, is it?

It depends on what is being measured. If engine power:weight or power:volume, or engine CoG, then yes.

Engine volume and weight will affect the vehicle package, but in road car there are many variables which could permit to compensate or worsen such metrics.

[NL_Fer]

Current offerings from BMW and Mercedes are both 3.0 inline-6 Twin (scroll) turbocharged engines.

Looks like the Germans also see some downsides on DOHC V6 & V8 engines.

[Just_a_fan]

The performance isn't because of it being a pushrod though, is it?

It depends on what is being measured. If engine power:weight or power:volume, or engine CoG, then yes.

As pointed out, the BMW engine was a first iteration from 2008. The same engine today makes way more power and thus power:weight, power:volume are both much better. CoG is not represented by a shaded box. So, no.

[Jolle]

The main reasons manufacturers choose DOHC 4v over pushrod:
- efficiency: a the valve springs need to be a lot heavier on a pushrod because of the extra weight of the rods and the bigger valves
- 4 valves breath better at higher rpm, pushrod is restricted to 2 valves
- air flow is better because there is no rod in the way
- because valves and rods weight higher rpm is possible with a DOHC
- influence of thermal expansion is greater in pushrods then (D)OHC because of the expanding rods
- because of the lighter valves and the absence of rods more agressieve cam profiles are possible.

The hight compared to a pushrod is minimal, because the valves are smaller and you still need a rocker shaft where normally one of the camshafts sits.

[Maritimer]

The main reasons manufacturers choose DOHC 4v over pushrod:
- efficiency: a the valve springs need to be a lot heavier on a pushrod because of the extra weight of the rods and the bigger valves
- 4 valves breath better at higher rpm, pushrod is restricted to 2 valves
- air flow is better because there is no rod in the way
- because valves and rods weight higher rpm is possible with a DOHC
- influence of thermal expansion is greater in pushrods then (D)OHC because of the expanding rods
- because of the lighter valves and the absence of rods more agressieve cam profiles are possible.

The hight compared to a pushrod is minimal, because the valves are smaller and you still need a rocker shaft where normally one of the camshafts sits.

GM make a three valve pushrod engine, rev advantages only come into effect far beyond the range of normal road use engines. The reason OHC so prevalent is because most of the manufacturers invested in machine tooling decades ago so it's simply cheaper for them to stick with it at this point. Whatever rod you think is in the way isnt, pushrods are internal and never interact with the intake air. Higher revs and independent lift/timing control for both sets of valves are the only advantage. Pushrod engines are just as efficient within a normal rev range as DOHC, you can get 30mpg in a Corvette driving like a normal person easy.

[roon]

The performance isn't because of it being a pushrod though, is it?

It depends on what is being measured. If engine power:weight or power:volume, or engine CoG, then yes.

As pointed out, the BMW engine was a first iteration from 2008. The same engine today makes way more power and thus power:weight, power:volume are both much better. CoG is not represented by a shaded box. So, no.

? No one claimed a shaded box represents mass center. If refering to the pdf slide, that box represented exterior dimensions. That presentation compared 2008(?) engines. This thread is comparing 2019 engines. Engines across the board will have exprienced development.

N63 is making 444 - 523 hp these days. The LT2 is making 490-495. Both have improved power density, so the premise is still apt. Exterior engine dimensions wont be greatly different, displacement hasn't changed much if at all.

S63 makes near 600hp but is found in $100k vehicles. The corvette engine in that bracket should make substantially more.

[Just_a_fan]

The reason OHC so prevalent is because most of the manufacturers invested in machine tooling decades ago so it's simply cheaper for them to stick with it at this point.

Likewise with OHV, of course.

[Jolle]

The reason OHC so prevalent is because most of the manufacturers invested in machine tooling decades ago so it's simply cheaper for them to stick with it at this point.

Likewise with OHV, of course.

Yes, you could say everybody upgrades their production lines except Chevrolet... And every new production line and new engine design is DOHC. One conclusion would be that everybody is stupid nog going for a pushrod line or design or that, because of the existing production line, the LS and LT engines are nice and cheap.