C8 Corvette

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NL_Fer
NL_Fer
81
Joined: Sun Jun 15, 2014 8:48 am

Re: C8 Corvette

Post

heretolearn wrote:
Fri Oct 25, 2019 4:08 am
Long time lurker, first time poster. I enjoy reading these forums because I am far from being an engineer (so please go easy on me). I'd like to contribute an update and follow it with a couple questions. According to multiple articles, including the one here:
https://www.hagerty.com/articles-videos ... -plane-v-8
the racecar, which must be based on at least 300 produced street cars, will have a DOHC flatplane crank V8 of 5.5L capacity. Thus, unless there is some loophole or waiver, at least some of the new cars will have a similar powertrain. Exhaust scavenging has been commonly mentioned as a reason for the switch away from a pushrod unit. This brings me to my questions.

The benefits of the pushrod seem to be many ( 1) weight 2) low COG 3) low/midrange torque 4) efficiency 5) cost 6) durability). Why would GM move away from a technology in their race car and some of their street cars if it seems to have so many benefits? Is it a combination of the importance of exhaust scavenging combined with the 5.5L displacement limit? If so, then why couldn't GM seek a waiver to run more than 5.5L of displacement in the race car as other manufacturers have done?

My other question is far more open ended. If one were to create a modern "unlimited" series a-la Can Am, would pushrods be the motor of choice due to packaging and the fact that for every additional bit of displacement one adds to an OHC engine, the additional weight and COG would be negate the additional horsepower created via better breathing? For the moderators, I would be happy to take this topic to a different forum if it is required. Thank you in advance!
Because it is a racing car. Most of the time the engine will be reving 6000-8000 rpm. At those revolutions, an engine can really benefit of the better breathing a 4 valve-per-cilinder OHC can provide. This engine is capped at 500 bhp. But won’t be suprised if it is 500bhp @ 6000-7400 rpm. A smaller displacement also has benefits from lighter pistons/rods/crankshaft. From pure performance point of view, (D)OHC is the better.

But for big street engine, pushrod can still push forward, after so many years.

Jolle
Jolle
209
Joined: Wed Jan 29, 2014 9:58 pm
Location: Dordrecht

Re: C8 Corvette

Post

NL_Fer wrote:
Thu May 28, 2020 11:10 pm
heretolearn wrote:
Fri Oct 25, 2019 4:08 am
Long time lurker, first time poster. I enjoy reading these forums because I am far from being an engineer (so please go easy on me). I'd like to contribute an update and follow it with a couple questions. According to multiple articles, including the one here:
https://www.hagerty.com/articles-videos ... -plane-v-8
the racecar, which must be based on at least 300 produced street cars, will have a DOHC flatplane crank V8 of 5.5L capacity. Thus, unless there is some loophole or waiver, at least some of the new cars will have a similar powertrain. Exhaust scavenging has been commonly mentioned as a reason for the switch away from a pushrod unit. This brings me to my questions.

The benefits of the pushrod seem to be many ( 1) weight 2) low COG 3) low/midrange torque 4) efficiency 5) cost 6) durability). Why would GM move away from a technology in their race car and some of their street cars if it seems to have so many benefits? Is it a combination of the importance of exhaust scavenging combined with the 5.5L displacement limit? If so, then why couldn't GM seek a waiver to run more than 5.5L of displacement in the race car as other manufacturers have done?

My other question is far more open ended. If one were to create a modern "unlimited" series a-la Can Am, would pushrods be the motor of choice due to packaging and the fact that for every additional bit of displacement one adds to an OHC engine, the additional weight and COG would be negate the additional horsepower created via better breathing? For the moderators, I would be happy to take this topic to a different forum if it is required. Thank you in advance!
Because it is a racing car. Most of the time the engine will be reving 6000-8000 rpm. At those revolutions, an engine can really benefit of the better breathing a 4 valve-per-cilinder OHC can provide. This engine is capped at 500 bhp. But won’t be suprised if it is 500bhp @ 6000-7400 rpm. A smaller displacement also has benefits from lighter pistons/rods/crankshaft. From pure performance point of view, (D)OHC is the better.

But for big street engine, pushrod can still push forward, after so many years.
Plus, a no limit engine would not only go for DOHC but also a big turbo.

As for NA OHC vs (D)OHC, the price you pay in extra weight and a higher COG is more then compensated in revs that are essential to power.

That’s why every bespoke racing engine since almost forever that hasn’t got rules that it said it must have OHC, is DOHC.
Best testament to that might be the new C8, that in it’s race version goes for DOHC while it could run its OHC (like the Vipers do)

Sevach
Sevach
887
Joined: Thu Jun 07, 2012 4:00 pm

Re: C8 Corvette

Post

Cold Fussion wrote:
Thu May 28, 2020 2:35 pm
Is this required to homologate the C8.R?
The C8.R already raced in the 2020 Daytona 24h, so at least as far as IMSA is concerned it's already legal.
Don't know if ACO or the FIA would've blocked it.

To me it seems like they simply decided to put their most modern engine in the "sporty version" of the car.