I realize I am ignorant compared to you sir. If you could come to my shop I would show you the difference in complexity of my 03 cobra 4 valve with one of the ls engines I have. BTW the heads on the mustang weigh 56 lbs each and the ls heads are 28 lbs each. I build and race these engines but admit my ignorance before the all knowing internet geniuses.

 

The point remains that an F1 engine looks the way it does because more sensible designs are prohibited by the rules. These rules are necessary for competition purposes but do not apply to street cars. On a street car, the F1 engineering trade-offs are terrible - even if lap times were your only concern (which they aren't).

 

A little research on your part would reveal that DOHC F1 motors were being built in the 60s. My point is very simple, a DOHC motor out preforms a OHV motor when all other factors are equal. The single most important component of an engine in developing HP is...the cylinder head/s. How is the MOST N.A. air flow created in a cylinder head?!...4+ valves per cylinder...PERIOD!!!...Mark

 

Please don't lecture me about racing history. DOHC motors were used in Grand Prix racing way back in 1912.No. It makes more peak power for the same swept volume, but at the expense of weight, center of gravity, complexity, reliability and cost. DOHC is an engineering trade-off, and like all trade-offs, it comes at a cost.

 

Lifters? Hydraulic lifters aren't unique to pushrod motors.

And 4-valve V-motors will have twice as many of them (or shims), plus twice as many valves, valve springs, and four times as many camshafts, cam gears (or pulleys) and a more complex timing chain (or belt) arrangement.

If you can't recognize that a multi-valve DOHC motor is more complicated than a 2-valve pushrod motor, whatever its other advantages, then it's ridiculous to even go on having this conversation.

 

over simplified.

there are obvious advantages that outweigh DOHC in this application.

yeah

 

1. Street tires will only put so much power to the ground. That is a huge equalizer.
2. The type of track plays a big role in what is faster around it. Compare the two around a high speed circuit and the results may vary.

3. I doubt Ferrari owners will care. You're comparing apples and oranges as far as price goes for most buyers.

 

Ferrari owners DO care. I spoke to one a few weeks ago who was talking about buying a C7 because they're way faster than his current Ferraris and he wants something he can track. I doubt he'll be buying an F12. I have no doubt he'll be buying a C7.

Funny thing is that his wife didn't seem to like this talk.

 

That is always the problem with the dohc argument Mark. If we were in a dyno room and were trying to get the most hp per cubic inch from two engines then I agree with you that the 4 valve engine could be made to produce more hp than the 2 valve engine.
Most of the hp advantage in the Ferrari comparison is due to the higher rpm. Not just the 4 valves.
In the real world where packaging, weight, cost, etc are factors it is not so cut and dried.
Getting hung up on hp/liter of displacement is also misleading. GMs method of efficiency with larger displacement engines running a lower rpms almost always lends itself to better fuel mileage and much longer life than the smaller, high rpm engines do. The Ferrari only uses that peak hp for a few seconds each lap where as a corvette uses much more of the available hp (torque). BTW I love the high pitched scream of a formula one engine as much as anyone.

 

She probably doesn't want to fall down the social ladder and be thought of as us commoners riding around in an American car. lol

 

Corvette won't have a DOHC because the economics aren't there. Has nothing to do w the best engine configuration. That's why nobody at GM Powertrain gives a crap about the LT-5. They don't even acknowledge it as being a GM motor because they didn't build it. Typical NIH.
Corvette gains it's Best Bang for the Buck moniker because it can spread the cost of engine and technology development (read PCM hardware/software) across the millions of trucks sold. Ferrari can't, doesn't do that. And just as Porsche has wrung the bejesus out of a flat six hung over rear end of a car, so too Chevrolet has maximized what they get out of OHV. Without doubt, they are the masters of it. Regardless of cost, I highly doubt F1 would select OHV over OHC.

Chuck,

The question of higher rpm hp is due to the design of OHC. That's where they want the hp. And it's available there because you aren't transmitting energy through about a foot of valve train while changing direction at least twice doing it.
Overall, this is really a question of application. No ultimate right or wrong.
But what is it about OHV that GM sees that virtually no other performance car manufacturer does? I submit it's the $$$.

 

GM has experimented with OHC in the past, but why fix what ain't broken?
The SBC has the highest power density of any sports car engine (according to GM).

 

Precisely the mentality that got GM to where it was in 2008.

 

It's was not fixing anything that got them in trouble. The LS is the only thing that kept GM going

 

The fact that a 60k GM sports car is compared to 400k exotics is testament that GM did something right with the c7. Someone commented it is stupid to compare such cars, but I'm happy to see the c7 compared to these cars and win.

Lots of drawn out opinions in this thread, but if you track often as I do you'll know the answer to the ops question right away. Why does a Cayman S with 300 hp have faster lap times than cars with 2x more hp? It's quick light and balanced. 700 hp Lambo will never keep up with newer cayman with pdk and good driver because you can drive 10/10s into the corners. Try that in a Lambo and you'll fly off the track. Same goes with f12 comparison. You have a heavier car with more hp which you would think would equate to faster track times. It doesn't.

C7 is comparable to cayman on the track in terms of balance. It's a little heavier but very capable. That's why I'm selling my FBO 480 whp 335 for the c7.

 

Mostly agree with Chuck. There are three ways to make power:

(0) Forced induction
(1) Displacement
(2) RPM

There are different automakers experimenting with all three and with combinations, but those combinations get expensive fast.

If you go down the high rpm path, which Ferrari did, you need to maximize the valve area to enable airflow in and out of the engine cylinders but you also need to minimize valve weight, to allow the rpm. That's why virtually all high rpm engines use 4 valves/cylinder (instead of just two giant valves).

If you go down the large displacement path, which GM mainly did, it gets hard to run the engines at high rpm because the reciprocating assembly is too heavy and so the forces needed to accelerate the rods+pistons are too high.

The best combination of displacement+rpm is the Mercedes M156 (6.2L) which, in the SLS AMG Black series, turns up to 8000 rpm from the factory. Pure awesomeness. And that engine alone probably costs as much as a 2 yr old C6.

Note that in this context, 6500 rpm is not considered "high rpm".

Pat

 

If you were given both cars would you be able to run a lap time in either car that is even remotely close to the what the pro- drivers ran ??? I don't know why that is even a consideration when buying a car like the Corvette and Ferrari....If you have to choose the vette over the Ferrari based on lap time, it means you can't even afford the Ferrari period. I am a C6 Z06 owner and I am in the process of buying a Ferrari...the two car have nothing to do with each other other than that they are the best car in their respective class and they are sport cars. Th experience of owning a Ferrari is drastically different that a Corvette and I want them both. If yo want just numbers buy a GTR ....one of the Fugliest cars ever made but produce great number with no soul, it's a Xbox with a engine. he Vette is all ***** (American) when you drive it and Ferrari is all heart, two totally different experience like a Harley to a Ducati.

 

so what happens to MPG when you lower the rpm to a highway cruise rpm that is 8000rpms from redline when you do the part in bold?
sorry for the shitty sentence lol

 

Just a short note on this. The 2 vs 3 vs 4 value debate is not totally valid. It is not a question of the number of values, but the total linear cliff area of the value line. A single value can out perform a double valve and a double value can out perform a single valve. It is much more complex than valve count. It involves the value angles and how many angles, and the seat area and the lead-up curves, but also the exhaust performance and it involves the total line of cliff. If yo want to know more, David Vizard has a great 2 hour lesson on how these all perform and relate. It is worth the time if you are really into this. It is a bit old, but the principles are constant. Click on... and have a beer and be ready to listen to an engine wizard. I wish I know half of what he does.

 

You get fantastic MPG, that's what happens. When the LT5 was being developed for the C4 ZR-1, it easily met the EPA requirements to avoid the gas guzzler tax while the low RPM torque monster L98 struggled. In one high level GM meeting, one executive blasted the L98 team asking them how a 400 HP engine could meet the specs and their 250 HP engine couldn't. I own a '93 ZR-1 and can tell you from experience they are torque monsters down low...way down low. I can drive in 6th gear at 25 MPH with the engine turning over ~500 RPM...it not only cruises smoothly, I can actually step into it and it'll accelerate (slowly) without lugging, sputtering, or one single hiccup. I invite you any time to ride along and see for yourself, I've amazed many people who've listened to the old wives tale that DOHC engines have no torque down low and you have to wind them up to get anywhere...once over 45 MPH, I rarely downshift from 6th to keep up with traffic.

I invite you to try the above with any LSx engine, even the LS7...it won't happen. Keep in mind the LT5 is 5.7L displacement...many people have taken the engine to 415, 427, and 442 cu in and made 600+ HP with the stock cams which made a silky smooth 500 RPM idle and even more torque at 500 RPM. BTW, the common rev limit is at least 7500 RPM when doing any mods (even just a tune) because the HP curve is almost a flat line from about 5500-7500 RPM.

The LS7 is at the limit for N/A HP at 505 and it really isn't that reliable at that point...there are many threads in the C6 Z06 forum about blown engines with most of them valve related. The LT5 is as reliable as an anvil, you can beat on it all day and it comes back begging for more. I've been beating on mine for 21 years now with zero issues. To get to the 600 HP level with an LSx engine, a supercharger had to be added which now makes it equal to the LT5 in weight, packaging, and complexity. Add DI and VVT to a 7L LT5 and 650 HP N/A is easily attained in a very quiet running reliable package...and yes, it will also run at 500 RPM in 6th gear and it will get way better MPG than any similar HP LSx.

Keep in mind I love all Corvettes and the LSx engines, I bought a '99 coupe and then a '11 GS for my daughter so I'm not a hater. I will say I absolutely love the LT5, it's just a disappointment to see a lot of hate on this DOHC engine based on misperceptions about all DOHC engines. And just a FYI, the bottom end architecture of the LSx engine came from the LT5...so in a way, they are at least brothers.