Sincere question. With my very limited knowledge of engine design I don't understand the virtues of building a new pushrod engine for the 2027 SR's. Why would GM stay with pushrods instead of building something like the Ford Coyote engine or a tamed down version of the Z06 engine?

 

Economy of scale. It is much more affordable to have a shared powertrain with other products where assembly is similiar with obvious changes for performance vs Truck/SUV applications/

Beyond any other pro's or con's regarding TQ delivery, RPM redline, Sound, Displacement, FPC vs Cross Plane, etc its all cost IMO.

 

In addition to being substantially cheaper to produce, the OHV architecture is also much more compact, which helps with packaging in various applications.

 

This. The only way to hit the pricepoint GM wanted for the C8 Stingray was to use the OHV engine. It's still an incredible engine, with lots of benefits from packaging (size/weight/etc), performance, economy. And on top of that, many traditional Corvette buyers like the characteristics of the OHV V8. Having said that, it would not surprise me if GM doesn't at least consider using a detuned LT6 in the C9 as the base engine since they've already spent the money to develop it. Doing a 600HP, 7500RPM DOHC variation of the LT6 in the C9 Stingray would completely stomp on all the competition.

 

COST.... That's all!

 

Got TORQUE?
The 6.2 and new 6.7 pushrod engines have it in abundance, moves the car out quickly and still gets decent fuel economy.
Z06 5.5 engine is only usable as a street engine because of its high speed horsepower, torque trails well behind the 6.2/6.7 pushrod engine, and a version detuned for Stingray use would make even less torque, plus it isn't as fuel efficient.
The 5.5 DOHC engine is also substantially more expensive to produce than the pushrod engine.
And, the pushrod engine will be used in trucks and SUV's.

 

5.5L DOHC LT6 doesn’t have AFM, so it will have worse emissions than 6.7L OHV running on half it’s cylinders. LT6 makes 1.38 ftlbs/ci with 12.5:1 SCR, Dark Horse 5.0L makes 1.36 ftlbs/ci with 12:1 SCR and the new LS6 makes 1.27 ftlbs/ci with 13:1 SCR so it’s overall torque output is purely because of it’s larger size although it is easier to have better volumetric efficiency with a smaller engine.

 

center of gravity on a dohc engine is higher than a ohv. Also as mentioned a dohc is a spinner engaine making power at hi rpm which means you have to flog it to get the power and torque. OHV has more power and torque lower in the rpm band so more fun on the street. On the track where you are higher on the rpm band the dohc come into it band

 

To the best of my knowledge the engine parameters which effect torque at low rpm are not generally related to how the valves are opened. An exception to that is likely variable valve timing but I don’t know which configuration can best take advantage.

 

The advantage of going DOHC is so you can use four valves per cylinder which increases breathing at higher RPMs.

The small block Chevy is an engineering marvel of refinement. Compact and lightweight for its displacement and power with a low center of gravity. While DOHC is sexier it is also more complex and takes higher RPMs to get the power.

 

That is the part I haven’t come to grips with, I don’t know of a reason why dohc would have any inherent power disadvantage at any rpm.

 

It wouldn't with the same displacement and not being tuned to take advantage of the four valves per cylinder and capability of higher RPMs (valve mass is one of the limiting factors of turning higher RPMs). But the advantage of going of going DOHC is so you can get equivalent power with smaller displacement so you need to run at higher RPMs to get that power.

 

If you look at the torque and hp curves of the Coyote NA DOHC V8 used in Ford's half ton trucks, you'll see it makes a fairly broad/flat torque curve - which you would expect with the variable cam phasing tuned for such.

Ford does use OHV engines in its heavier duty trucks - 3/4 ton and 1 ton trucks.

 

My 2017 Ford F150 was 3.5 liter DOHC with VVT and the thing was a torque monster.That is sort of why I have wondered about some of the torque comments related to dohc. The 3.5 is a turbocharged engine which possibly makes the cheese more binding regarding comparisons.

 

It is the cost which is more than just the sticker price. I believe the LS6 is a steppingstone towards the LT6 and the C9 will have a variation of the LT5. Hopefully a 5.7L cross plane with 595hp, a lower power range and maybe broader.









.

 

It doesn’t have a disadvantage as far as power is concerned. An engine is an air pump, the more air in and out the more power you make. It becomes harder to do so at higher rpm’s because there’s less time to do so. The valve’s opening and closing points dictate the power band most. Variable cam timing helps to broaden things, but even then has it’s limits. 4 valves per cylinder allows more air in and out as well as lighter valvetrain to better handle the stress of high rpm. Big cubic inch engine typically isn’t high revving like in a truck, so it sticks with simpler OHV technology. The 5.0 in the F150 still makes 410 ftlbs or only 8 less than the Dark Horse albeit at 4250rpm vs 4900rpm, that’s still a better ftlb/ci of 1.33 than the new LS6 with 1 point less compression and a more comparable redline.

 

Simple answer is then no one would buy a ZO6 ! Plus one more answer. The new pushrod engine is cheaper to build , less complicated and has lots of low end torque which I for one, as another "old fart" prefers!

 

• $
• Weight
• Compact size
• MOST Important: GM announced in 2020 their plan was all models would be available as EVs by 2035! Put over 10 billion in the effort.
  • They moved 1/2 the Corvette Engineers and the Chief Corvette Engineer, (Ed Piatek) in 2020 to work on EVs.
  • Have a full line of EVs for their big money maker the 850,000 Silverado/Sierra's the sell each year.
  • Appears the New Small Block was planned to fill the Truck need to 2035. We're lucky they spent the effort to get a great Vette variant the LS6! The 30,000/yr Corvettes are not significant profit contributor in comparison to Trucks!
  • They have now backed up on what they said in 2020 they would skip because too complex and costly, PHEV. Smart.
  • Pics below were in a 2027 Sierra video discussing the New Small Block, available Diesels and this Option of a PHEV for their I4 Turbo.

These Pics taken from the GM Video. My words from video.


Smart they are putting the electric motor like our BMW in front of the transmission. In our BWM case it's a ZF Supplied Transmission Electric Motor System. I thought we would need both the ~200 hp electric motor and the same ICE we had in our prior non Hybrid X5 SUV to merge into ~70 mph traffic from the stop sign at the end of our rural road into ~70 mph, often heavy traffic on a 4 lane highway! .NOPE. They multiply the already high torque electric motor from 0 mph when starting and it accelerates FASTER to ~50 mph without the ICE that with the 300 hp ICE! In fact the ICE only comes on for longer trips. Wife gets all she needs with 50 mile electric range. Feels great to "fill up" each night for ~20% the cost of gas! We have been on time of use rates with Duke Power since we moved the SC in 1985. At night weekends we pay 1/3 the daytime electric power rate.

BTW, for those who want a modern design, more efficient, 4 valve/cylinder, DOHC engine: it's the Truck 2.7 Liter Turbomax I4! Looks like with the help of battery power it gets 400 hp!

 

The new 409 makes more hp and torque than any other production NA V8.

 

All those added cams/valves/etc result in substantial added mass/bulk/cost. I used to work in an OEM engine plant that produced pushrod inline sixes and fours, as well as a small four cam four valve V6 and a larger two cam four valve V6, all at the same time. Those multi-cam/valve Vs are huge and heavy for their power curves, and were by far the most expensive to produce.

The Ford Coyote is a huge engine, and was heavier, larger and less powerful than the GM LS3 that was the current pushrod state-of-the-art when the Coyote came out. The manufacturers tend to under displace these engines for some reason. In Europe, it makes sense: cars over there are taxed based on their engine's displacement. That's the whole reason that their engines have tended to be tiny, relatively torque-free screamers. If you need to make X amount of hp with a limited displacement, your only recourse is to wring the engine's neck with elevated rpm. So, all the fan boys have come to equate high rpm's as "better", or racier somehow. High rpm means high internal friction...is this really the most efficient way to a usable power curve? American engines have been unencumbered by artificial constraints on displacement, so the development path over here has been to use the smaller, lighter pushrod combination with whatever displacement (which is empty space and weighs exactly nothing) was necessary to achieve the desired power curve. Two different schools of thought...

If your multi-cam, multi-valve 3.5L V6 has "plenty of low end torque", it's because that was achieved artificially with forced induction. Once you introduce forced induction, all bets are off, as an engine's power curve can be anything you want it to be. Pushrod engines can work just as peachy with forced induction too...and they'll always be smaller, lighter and cheaper in the bargain.