JD_AMG

Point is displacement doesn't dictate gas mileage, and DOHC V engines are over sized/over weight compared to their pushrod counterpart.


Man, you and that reading comprehension again...
His post is referring to a C6 Z06, rated at 26mpg highway but achieving a real world 29-30mpg...in a 505hp 7L V8!

Thanks for proving my point.
Guys with C5 Z06s and C6s are saying 28-30mpg
Guys with C6 Z06s are saying 26-30mpg
Guys with C7 Z06s are saying 22-26mpg (with 650hp, find another 650hp that will top that without an electric assist)

All of which are over EPA ratings.

Warp Factor

No, the Ferrari engine does not deliver 100 more horsepower on the same amount of fuel used. EPA type fuel economy ratings are based on commuter-type driving cycles, and do not involve any evaluation of fuel consumption under full power.

BEAR-AvHistory

And people drive at WOT how often & how long? There is still a 100BHP difference in the 179CI DOHC & the 350CI cam in block. To get to the Ferrari's 250BHP you need to step up a 454 Corvette with maybe 8 to10MPG. Hey what is an extra 275CI when you need a little bit more power.

BTW you have no way of knowing the 350's fuel usage at WOT so EPA is the best you have. Based on how bad the 350 sucked in the EPA test is very safe to believe it also sucked big time at WOT. A 165BHP at WOT,

GM has done well with electronics on the SB but its time is running out. It has to be hard & frustrating to be one of the two smartest people in the room watvhing all the auto manufactures & racing associations are going the wrong way to DOHC-T. If they only knew what you know.

Off the dealers floor the Corvette/Camaro 6.2Lhas 455/460 BHP while the 5.0L Bullitt 480BHP, the 5.2 GT350 526BHP & GM's own Cadillac's 4.2T 550BHP.

Tom73

What are the highest output NA engines?

Guess I am somewhat old school but to me turbos and superchargers are power enhancers that over stress the engine. May as well just use NOX. I would just as soon stick with NA engines.

RapidC84B

That is a horribly inaccurate view of forced induction.

Warp Factor

Bear. you were the one who suggested that fuel economy numbers in EPA-type tests were somehow related to fuel consumption at peak horsepower, not me.
Wrong. Brake horsepower-specific fuel consumption numbers are widely available on Chevy smallblocks, from the plethora of dyno tests.
LOL, wrong again, The most expensive, most reliable, longest-lasting, and highest horsepower internal combustion engines in the world use in-block camshafts.
And the LT5 Chevy pushrod engine puts out 755 horsepower, way more than any of the engines you chose to list
And don't forget the Dodge Demon pushrod engine, which puts out around 840 horsepower.

I will readily acknowledge that the overhead cam Ford engine in your Cobra replica was a cool project, for its day, and so was the Big Block Chevy in your street rod. Time marches on. Gotta stay on top of things if you want to be current. Not that old-school and retro stuff isn't cool.

z06801

From Doug Fehan
Surprisingly, the overhead valve design provides such an advantage, that Corvette Racing's competitors have tried to get it penalized in the past.
"I sit on several FIA engine councils and it always comes up from our competitors. Whether it's Porsche, Ferrari, or Aston Martin, they're always complaining about what they perceive of as the advantages the two-valve engine has [over] their [designs], and want the two-valve engine penalized, said Fehan. "To that I say, 'go back to the road car--if the two-valve engine is that much better for racing you ought to put it in your car.' To which they have no answer."

BEAR-AvHistory

Agree time marches on & the cam in block is on life support. When the cam in block in the Corvette dies with the C8 just the Camaro will be left, at least for a short time.

The 755BHP out of 6.2L is getting up there but we don't know what the 5.2L in the GT-500 will be yet other than its over 700BHP. Be just like them to go to 760BHP.

Yeah 808/840BHP supercharged is very impressive for 6.1L old pushrod technology.. 800BHP naturally aspirated 6.5L is quite a bit more impressive then requiring boost. Mark Gearhart's SEMA FFR truck did 1200BHP on the 5.0 Coyote with twin Turbos. Not as impressive as the 580BHP naturally aspirated 5.2 version but nice anyway.

Put enough boost in & you can dial up any power the engine material can hold. There were 1.6L Turbos making 750BHP+.

Competitors bitching about handicapping in the age of level playing field racing, who would have thought.

Its clearly obvious that you know more then any of the top automotive engineers in the world. Expect someone from GM will be reading this thread & offer you a job as head of power plant development. Think of all the money you can save them by just doing the same old, same old over & over again. You can even drag your buddy along to carry you bag & tell you that you are right.

Warp Factor

LOL, you already tried that lame strategy back in post #823, and it was already answered. Do you just have a poor memory, or is going in circles all you know how to do?

JD_AMG

With an old high strung Ferrari engine? Not very long at all. But don't worry there is a fix for that...


Yea the Dino has been LS1 swapped too...

I guess you forgot about the 640hp CTS-V, and the 755hp ZR1...

GrandSport 2017

So, here's some food for thought when debating the merits of different cylinder head designs because what works best in one application doesn't work best in others.
Lets just talk about poppet valve Otto cycle engines like in the corvette, mustangs, Ferrari's, and Porsche's. No miller-cycle, sleeve valved, barrel valved, rotary valved, etc. etc.

When an engine is a clean sheet design there are several primary parameters that have to be decided on early like power output, torque, weight, size, fitment in the application etc.
These parameters will dictate cylinder configuration, cylinder size, number of cylinders, RPM needed, the airflow of the cylinder head needed, valve actuation type, among many other things like rod stroke ratio, bearing loads, etc etc. it goes on and on.
So now there's the cylinder head, that seems to be the biggest bone of contention here in this thread.
Can we agree that larger valve areas will flow more air for a given cylinder size? (with a balanced V/A port for argument sake)
Can we agree that higher volumetric efficiency makes more HP? (a static trapped volume for arguments sake)
Can we agree that the mass of air at 70 degrees and 30.00"hg anywhere on earth is the same? ( forget humidity and composition for now)

Now lets say we have a 1 liter engine with 4 cylinders. And it's designers wanted it to make 20 hp at 3,600 rpm (think generator) does it need 4 valves per cylinder?

I have to go watch a show now but we will get into this deeper, more later.....

JD_AMG

The ICE is on life support at this point, the pushrod engine will be around for a while though.

755hp is 755hp is 755hp, it doesn't matter if its a 1L engine or a 10L engine, power is power, comparing displacement is ricer math.
Id rather have 755hp out of a smaller, lighter engine with more displacement than 760hp out of a bigger, heavier engine with less displacement.

Again, displacement is irrelevant.
Your little power numbers are cute at best, LSx's have been over 1000hp NA, and 2500hp+ with boost. The BBC has seen 4000hp+ with boost. At the end of the day no body cares about displacement, you run what you bring and don't have to pop the hood.

That get rebuilt more often than actual run time. Again, displacement comparisons are ricer math, you can make a ton of power with boost, the question is how long will the engine hold up.

Why do all those high budget supercars that don't have in house engine development almost always go with an LSx or LTx? They have plenty of budget to buy a Coyote, or other DOHC V8 yet for some reason they pick the LSx pretty much everytime. Could it be that WEIGHT and SIZE are what matters, and displacement is meaningless?

JD_AMG

The question is, is it worth it on a V engine for the added weight, size, complexity and cost of going DOHC over pushrod when the power goal is preset and they are not trying to make the most amount of power possible out of that engine displacement.
If the power goal for the base car is say, 550hp, and if the LT1 can make that while passing emission and passing all other parameters that GM tests for, then why would you go with a heavier, bigger and more expensive DOHC V8 to just make the same amount of power? The car would perform worse due to the added weight and higher center of gravity (and possibly not being able to mount the engine as low as possible and as close to the center of the chassis as possible).

No one is denying that a DOHC head is capable of flowing better and making more power, the question is are the drawbacks worth it in this application?

PCMIII

Just use the LT4 and blow everything away. Reliable, proven and available.

BEAR-AvHistory

CTS-V Chevy engine old news. 755BHP 6.2L supercharged Chevy was mentioned. The the comparable 5.2L Supercharged GT-500 has not been released yet other then a FORD statement that it will be over 700BHP. Would not be surprised if FORD upped the GT-500 with a 760BHP rating just the same way they did with the N/A engines.

You remember the N/A engines rating numbers. Where for $55,900 you can get a 455BHP 6.2L Corvette & for $35,000 you can get a 460BHP 5.0L Mustang GT. Such a deal for only $20,000 more you can get 5 less horsepower.

But look at the up side. With the LT1 you can save 12lbs in weight & 2" on center in width, nothing in height, but gives up 3" in length to the COYOTE which is the key measurement in a mid-engine car.

Maybe the oversized LT1 will not fit the C8 because its too long compared to a 5 liter DOHC T.

Think by about 2021 it will be time to stick a fork in GM cam in block car engines?

Warp Factor

What? Fords latest and and most powerful overhead cam engine will still have less power than the Dodge Demon pushrod engine?

Warp Factor

No, can't agree on that one. There's a whole lot more going on with cylinder filling, air flow, and volumetric efficiency than valve area.

GrandSport 2017

So again were just talking cylinder heads here for this discussion, yes cams and compression are a factor but again the head seems to be the bone of contention here.

So as power requirements go up so does the total volume of air required to go threw the engine right? So lets just stay with N/A engines (14.7 psi available pressure)at 100% VE here and keep this over simplified for now.... if we double the air consumption of the engine we double the hp right?
So once we reach 100% ve we can only increase the total air consumption of the engine in two ways, 1 is to increase cylinder volume, but we are still talking about the 1 liter 4 cylinder engine, or 2 is to fill the cylinder more times in a minute, lets say twice as many times, that means spin the engine at 7200 rpm.
So now you need to feed the engine at 7200 rpm. The 14.7 psi available to fill the cylinders didn't change nor did the mass of the air but the charge velocity did change as did the time available to complete one engine cycle (4 stroke otto cycle) and fill the cylinder to 100% VE
So the bottom line is that the engine only needs the head to flow the required CFM to fill the cylinder to the 100% VE. If you can do it with 2 valves then so be it. But there's more to it as rpm's go up. A lot more. Remember the mass of the air doesn't change but the time available to move the air is cut in half. So you can only as big a valve diameter as the bore allows whether its 2 or 4 or 5 or 6 or more valves. Remember were talking poppet valves here. It so happens that four smaller valves that will fit in a given bore size can have more valve area than two valves. So if you exceed the air flow requirements of two valves you have to go to 4 valves.
We know that GM 2 valve engines are capable of producing a lot of power per CC of cylinder volume but I can tell you that they are near the max for a 2 valve engine with a 4.060" bore. They could shrink the exhaust valve some and enlarge the intake valve some and change the guide spacing, etc. etc. but this is a production engine and they need a safety margin of material between the valves for proper heat transfer. These engines need to go hundreds of thousands of miles. These intake ports flow excellent for there volume and are large. They got away with this for two reasons. 1 variable valve timing and 2 direct injection. Port velocity is much slower at a given RPM with these heads VS the ls6 heads due to port volume. By changing the intake valve timing they can trap more air in the engine when cycle times are low and the cylinder fills "too fast" at larger throttle openings. It allows more control over VE at any given engine speed.
I haven't done the math yet on this LT1 engine but the VE is probably in the 115-120% range at peak torque.

So now we get to the C8 engine.
We know that Chevy will have to offer a higher HP engine as the base engine. Even if its the same engine the HP will be higher because of marketing. So we know they can either rev the engine higher and that would require more air or make the engine larger, but don't count on that. There is room thou for tweaking this engine in many ways to get more HP. One way is higher valve acceleration but the AFM lifters will limit the valve acceleration so any additional valve acceleration will come from the rockers and some slight cam ramp tweaking to get the major and minor intensity numbers down for the ramps. They are not going to want to over spring the valves, that robs power and fuel mileage. And these lifters are already causing them headaches.
They could tweak the ports and valves slightly but that would require a new head. Or add some static compression while reducing the dynamic compression with the cam phaser. Its a balancing act between warranty claims and offering what marketing thinks will help sell more product. Id go out on a limb here and speculate that they could get 20-30 more hp and keep everyone internally happy.

Now if they want to offer an engine that makes more than the .080 hp per cc they will need to move more air thru the engine right? So again they can either increase displacement or rev it higher. I highly doubt they want larger harder to fill cylinders (yes larger cylinders are harder to fill than smaller ones because the mass of the air doesn't change nor does the available 14.7 psi air pressure to fill them) So my money is on smaller cylinders and fill them more times in one minute. This is where the 4 valves per cylinder will come into play. I just dont see how they can offer a N/A engine that will make over 600hp .12hp per cc without using 4 valves.

If I was designing the new optional engine for the C8 it would be 4" bore and 3" stroke 5.9" rod with 83mm intake valves and a port MCSA of 3sq in that flows 400 cfm@28" with a MCSA average velocity of 320fps@28" of water and use 4th order runner length. This would give the engine the ability to rev to 9600 rpm with a .9/.8/1.2mm ring pack. This engine should be capable of 670 N/A hp on 13 to 1 CR. That's pump gas compression for an engine with a high tumble chamber.
If you guys want a Ferrari from Chevy that would be it. It would make over 1000 hp with only 8 psi of boost and 10.5 to 1 CR if you really needed more power.
Now the question is does Chevrolet have the ***** to produce the first 1000 hp American made car. It may trigger the end of the new golden era of hp wars. The political atmosphere is ripe for dissent from the politicians on high hp cars, well some of them with one particular persuasion anyway. You know the new young ones that "don't think anyone should be able to own a car that everyone else cant afford" ones. Do you guys remember the outrage when the 1999 Hayabusa and 2000 zx12r motorcycles came out and the manufacturers were pressured to limit the top speeds to 185mph electronically in 2001?

Our current 1.64 liter 294hp race engines produce .180 hp per cc or 180hp per liter n/a with 87mm bores and 69mm stroke.

If any of you guys are hard core engine guys and want to really dig deep into this stuff I highly recommend the book by Gordon Blair, The Design and Simulation of 4 Stroke engines. Its available on amazon but its fairly pricey unless you are an SAE member then you will get a discount.

GrandSport 2017

Valve window area is the predominate factor in making hp with a cylinder head.

JD_AMG

And just like Furd, Gm hasn't had their hp bump yet with the LT1, they will and it will be above the Coyote.
How well does that Mustang do on a roadcourse compared to the Corvette? Or better yet the Camaro? Whoops, don't want to talk about that one...

Look I know you have a really hard time reading things but this one is pretty simple.
The LSx/LTx is atleast 7" more narrow while being 1" longer at best and about the same height. Length (especially and inch or two) doesn't mean squat in a long, mid engine'd car. If you think it does you better go talk to Lamborghini and Ferrari about sticking those physically massive V12s in their cars.

Nope, its smaller.



Why? They're smaller, lighter, cheaper and make just as much power as comparable DOHC engines.
It took Furd over 20 years to catch up to GM with their DOHC V8, its just now making hardly more power before GM updates the LT1.