A few motor questions (UPDATE TO OP, mod plz sticky)

[Famine]

Which, of course, it does. Since a like-for-like OHV valvetrain will weigh about 15% more than an OHC one.

 

[High-Test]

Famine and his all knowing secret 46.7 Yottabyte Superdupercomputer known as his Brain will give me a thousand reasons why, But What's wrong with Pushrods?

 

[Taurine]

A valvetrain in a pushrod engine has more moving power-taxing parts then a OHC engine does.

I don't really see the harm in chipping (or going piggy-back) your ECU, of course bearing in mind that the chip alters the standard timings cycles and whatnot, as long as the chip doesn't change anything too drastic there should be no problem.

Programmable ECU's are where you need to know what you're doing.

 

[Powripper]

Then there's the Venom 400 reprogramming for the Neon, which costs about $400 and is basically a sticker they put on the outside of your engine controller. After people figured that out, they brought out the Venom 500 which cost $400 and made your engine run worse.

Not to say all 'chips' are bad - I run a Mopar Performance ECU in my Neon that was ~$300 and made a serious dent in my accleration times - but they are no magic bullet, particularly when programmed by people who don't know what they're doing.

I got a chip for my S80 T6, and I couldnt be happier! it boosted my hp from like 260 to about 310 I think, took more than second of my 0-60...now I only have to deal with traction issues....

 

[TheCracker]

.... But What's wrong with Pushrods?

Its a bit like asking 'whats wrong with hexaganal wheels' - sure they work, but they aren't as efficient as round ones.

 

[daggoth]

OK. this is my first one but i have forgotten the other ones, i will post them when i remember.

When your in a traffic jam and there is space to move forward, sometimes when i move forvard my car starts jerking BUT not the 'about to stall jerk'.

You probably need a new clutch disk (not sure that is the correct term, I'm not English so...)

There are two disks that link the engine to the transmission of the car. One at the end of the engine, another at the beginning of the transmission.
The disk located at the end of the engine is where you get the RPM reading. (again I don't know the name in English for this disk)

When you release the clutch and have a gear selected the two disks are pressed against each other and the car begins to move! That is why you need to rev up a little when releasing the clutch, you feed a little more strength in the engine so that it can move the car. If you don't rev the engine, the transmission gives to much resistance to the engine and it stops.

Naturally these disks have a limited life, specially the clutch disk, what is happening when you realease the clutch is a slide-grab situation between the two disks and the car starts to jerk! When the clutch is fully released and the car is in motion the pressure is so great that even with a worn-out disk the car won't jerk.

So, when you release the clutch this happens:
slide-slide-slide-slide-grab-slide-slide-slide-grab-grab-slide-slide-grab-grab-grab-slide-grab-grab-grab-grab-grab-grab

Each time it grabs you feel a little jerk.

I hope that wasn't to much confusing (and sorry for any typos or mistakes)

You should consult a mechanic! He'll tell you right away if it is indeed a worn out clutch disk!

 

[Emohawk]

Sure, the Saleen S7 and the Chevrolet Corvette have done pretty impressive things with pushrods, but I just have to think, 'why?'

Here's something: I've repeatedly heard that pushrod engines are more torque biased, why's that?

 

[Famine]

They can't do much else other THAN torque. Get to 6000rpm and the valves start floating.

WHY the Corvette needs a 5.7 litre pushrod V8 to get 400hp when the same can be acheived with equal - if not better - reliability and efficiency from a 3.6 litre DOHC V8 is beyond me. Yes, you WANT that V8 sound and a DOHC V8 has a different sound compared to a pushrod one (comparison - TVR Griffith. Ferrari 430) but other than that there isn't a single sound mechanical reason for a large capacity pushrod next to a smaller capacity DOHC.

Incidentally, I'm led to believe that the Australian V8s - which are sourced from American Ford and Chevrolet V8s - are converted to DOHC from pushrod for precisely this reason.

 

[///M-Spec]

The valvetrain layout has little to do with fuel efficiency.

...and here he comes.


M

 

[Ghost C]

Its a bit like asking 'whats wrong with hexaganal wheels' - sure they work, but they aren't as efficient as round ones.

That's a great comparison. Remind me of that one again as a Corvette/GTO/CTS-V spanks your ass in a race. Tell the owners of those cars that you still win because your engine is more "efficient".

See how hard you get laughed at.

They can't do much else other THAN torque. Get to 6000rpm and the valves start floating.

And your point? My car's rev limiter is 5,250rpm and you won't see my complain because I can't rev past that. My car makes 200ft/lbs off idle, I don't need to rev to ungodly high RPM's to be fast.

 

[Famine]

That's a great comparison. Remind me of that one again as a Corvette/GTO/CTS-V spanks your ass in a race. Tell the owners of those cars that you still win because your engine is more "efficient".

What does how much power one car can get out of an engine have to do with anything else? You could get the SAME power out of a SMALLER capacity DOHC, more reliably.

Just because "x" car has "y" pushrod and can go "z" fast doesn't alter this, pretty basic, fact.

And your point? My car's rev limiter is 5,250rpm and you won't see my complain because I can't rev past that. My car makes 200ft/lbs off idle, I don't need to rev to ungodly high RPM's to be fast.

The point being that a DOHC can make the very same torque as you do (even more so, if desired), and rev higher for far more power. Remember that power = torque x (engine rpm)/5252.

 

[TheCracker]

That's a great comparison. Remind me of that one again as a Corvette/GTO/CTS-V spanks your ass in a race. Tell the owners of those cars that you still win because your engine is more "efficient".

See how hard you get laughed at.

I get 210ish bhp from my 1.9ish ltr DOHC four pot engine and often beat 420bhp 289's even on a quick track thanks

 

[Ghost C]

What does how much power one car can get out of an engine have to do with anything else? You could get the SAME power out of a SMALLER capacity DOHC, more reliably.

For twice the price. Just because you can do something doesn't mean you have to, or even should.

Just because "x" car has "y" pushrod and can go "z" fast doesn't alter this, pretty basic, fact.

My point was that pushrod engines are far from a hexagonal wheel.

The point being that a DOHC can make the very same torque as you do (even more so, if desired), and rev higher for far more power. Remember that power = torque x (engine rpm)/5252.

Ah yes. So that's why Cadillac's 4.6 DOHC makes less power than my 4.9 OHV up until around 4k, and only about 40hp more by the end of my rev range? And remember, the 4.6 makes 95hp more than the 4.9 in the application I'm talking about.

Yes, far more power.

I get 210ish bhp from my 1.9ish ltr DOHC four pot engine and often beat 420bhp 289's even on a quick track thanks

In a straight line, they'd hand you your ass all day long, and we both know it.* Discussing road tracks when comparing engine types is moot.


*I don't like drag racing. I'm just making a point.

 

[TheCracker]

No body is disagreing that you can get huge globs of power out of traditional pushrod engines, its just that its age- old technology and that modern dohc engines can do just as well - but more efficiantly.

 

[Famine]

For twice the price.

Mmm. Look at all those expensive Hondas.

Just because you can do something doesn't mean you have to, or even should.

Just because you can't do something doesn't mean you shouldn't try.

Ah yes. So that's why Cadillac's 4.6 DOHC makes less power than my 4.9 OHV up until around 4k, and only about 40hp more by the end of my rev range? And remember, the 4.6 makes 95hp more than the 4.9 in the application I'm talking about.

Yes, far more power.

Oh look! Random application A and random application B disagree with the general principle, so principle is 100% wrong!

Cadillac CHOSE to have an engine with the power they picked. I have no idea of their intentions. I'll just cover the basic principle again for you.

DOHC/SOHC CAN generate more power and more torque, more efficiently and more reliably per unit displacement than OHC. Just because some manufacturers choose not to take advantage of the more power/more torque in specific applications doesn't alter this pretty fundamental principle.

Why do Ford Australia and Holden take OHV engines from their American parent companies and turn them into OHCs?

Why do European and Japanese manufacturers - where reliability, efficiency and package size matter more than outright power - use exclusively OHC engines?

Answer to both: DOHC/SOHC CAN generate more power and more torque, more efficiently and more reliably per unit displacement than OHC.

 

[Ghost C]

Mmm. Look at all those expensive Hondas.

Again I'll use a Cadillac example. Look up the price for a set of heads for the 4.9, then get the price for a set of DOHC Northstar heads. Are you convinced yet?

Oh look! Random application A and random application B disagree with the general principle, so principle is 100% wrong!

I never said DOHC or SOHC can't make as much power as OHV. Ever. I said that writing OHV off as being junk because it's old or whatever the reason is this week is stupid.

Cadillac CHOSE to have an engine with the power they picked. I have no idea of their intentions. I'll just cover the basic principle again for you.

Actually, Cadillac went to DOHC because of people like you that jumped on the DOHC bandwagon. A decade after it's last use, the 4.9 OHV V8 is still regarded by Cadillac owners, who have driven both 4.9 OHV and 4.6 DOHC powered cars, as the best engine Cadillac has ever made.

DOHC/SOHC CAN generate more power and more torque, more efficiently and more reliably per unit displacement than OHC. Just because some manufacturers choose not to take advantage of the more power/more torque in specific applications doesn't alter this pretty fundamental principle.

Did you ever see me say this was wrong? No.

Why do Ford Australia and Holden take OHV engines from their American parent companies and turn them into OHCs?

Why do European and Japanese manufacturers - where reliability, efficiency and package size matter more than outright power - use exclusively OHC engines?

Because of people who thumb their noses at OHV because they don't know what they're talking about?

Answer to both: DOHC/SOHC CAN generate more power and more torque, more efficiently and more reliably per unit displacement than OHC.

If you say so.

 

[Famine]

I said that writing OHV off as being junk because it's old or whatever the reason is this week is stupid.

Please tell me where I said that.

Because of people who thumb their noses at OHV because they don't know what they're talking about?

Yes. I'm SURE all the European performance car manufacturers chose to go with ill-informed customer opinion rather than what is better for their cars. I'm similarly SURE that all the European luxury car manufacturers chose to go with ill-informed customer opinion rather than what is better for their cars. I'm further SURE that all of the Japanese and European economy car manufacturers would MUCH rather have pushrod engines but chose to go with the inferior OHC and make fuel economy and horsepower per unit engine size - their desired goals - much harder to acheive.


You're stuck on one example. Cadillac. The rest of the world, meanwhile, has moved on. Mitsubishi get as much power out of a 2-litre DOHC - admittedly turbo - as Chevrolet get out of a 5.7 litre V8 pushrod. Ferrari and Mercedes-Benz get more power and torque out of a 4.3 litre V8 and 6 litre V12 as Dodge manage to get from an 8.3 litre V10 pushrod. Hell, Suzuki get more power from a 0.6 litre OHC than Ford did from a 1.3 litre OHV. If Chevrolet or Dodge moved to DOHC they could send their power figures through the roof - not to mention reduction of weight, increased fuel economy and improved reliability.

But no, it's just "people like me" who decide these things, and not the entire rest of the world's car markets.

DOHC/SOHC CAN generate more power and more torque, more efficiently and more reliably per unit displacement than OHC.

If you say so.

Find an engineer.

 

[Ghost C]

Please tell me where I said that.

Your whole argument is that OHV is junk. Please tell me where you didn't say that.

You're stuck on one example. Cadillac. The rest of the world, meanwhile, has moved on. Mitsubishi get as much power out of a 2-litre DOHC - admittedly turbo - as Chevrolet get out of a 5.7 litre V8 pushrod.

And to make it fair, we stick a turbo on the 5.7, and it makes nearly double the power it did, completely voiding your whole argument. Stick to normal aspiration or forced induction. Don't try to compare one to the other. If you slap a turbo on anything, it will make alot of power. It doesn't matter what the valvetrain is.

Ferrari and Mercedes-Benz get more power and torque out of a 4.3 litre V8 and 6 litre V12 as Dodge manage to get from an 8.3 litre V10 pushrod.

Now let's compare price tags. The Ferrari costs at least double, if not triple, and the Benz costs one and a half times as much, I'm sure.

Hell, Suzuki get more power from a 0.6 litre OHC than Ford did from a 1.3 litre OHV.

And now we're talking about engines not sold in the US, so you've got me at a total loss. I couldn't care less about the engines you have in foreign countries, honestly.

If Chevrolet or Dodge moved to DOHC they could send their power figures through the roof - not to mention reduction of weight, increased fuel economy and improved reliability.

Of course, then there's the problem of making all new heads for current engine blocks. Then there's the problem of fitting them in the car (Which, btw, they won't). That's expensive - Really expensive. Do you think there might be a reason you see more Corvettes and Vipers on the road than Ferraris and V12 Benz's?

And for future reference, a DOHC setup weighs more than an OHV setup. Four cams as opposed to two, more weight. Twice as many valves, valve springs, etc more weight.

 

[retsmah]

Pushrod engines have their advantages and disadvantages. A pushrod engine is more efficient when it comes to space... at the last autoshow Toyota had one of their 4.7l DOHC V8s on display, it's significantly larger than a 5.7l GM motor. In trucks this really isn't a big deal, but in sports cars where underhood space is often limited it is. All of that added weight goes on the top of the engine too, not where you want it for a low center of gravity.

To resond to something said eariler, there is no reason that a pushrod engine can't have four valves per cylinder, or be high revving. My Honda has a pushrod engine, which is also a 4 valve/cylinder design and revs to 10,000rpm. It's actually got a higher redline than the SOHC engines that Honda was building at the time.

A twincam pushrod engine has, as far as I know, never been done. That would require some fancy pushrodding... I'm sure GM could do it, but there's probably not any good reason to.

I think the bottom line is that there are some people than you will never be able to convince that pushrod engines aren't necessarily bad, and there are people on the other side too. The valvetrain, like everything else on a car, is a compromise between several different factors, in some cases a pushrod engine may work better.

 

[///M-Spec]

I think we've had the power/displacement debate before.


M

 

[Firebird]

...and here he comes.

They can't do much else other THAN torque. Get to 6000rpm and the valves start floating.

WHY the Corvette needs a 5.7 litre pushrod V8 to get 400hp when the same can be acheived with equal - if not better - reliability and efficiency from a 3.6 litre DOHC V8 is beyond me. Yes, you WANT that V8 sound and a DOHC V8 has a different sound compared to a pushrod one (comparison - TVR Griffith. Ferrari 430) but other than that there isn't a single sound mechanical reason for a large capacity pushrod next to a smaller capacity DOHC.

Incidentally, I'm led to believe that the Australian V8s - which are sourced from American Ford and Chevrolet V8s - are converted to DOHC from pushrod for precisely this reason.

I love this table :

Power (in horsepower):
Dodge Viper SRT-10: 500
Ferrari F430: 483 (SAE)
Chevrolet Corvette Z06 (2004): 405
Chevrolet Corvette (2005): 400
Ferrari 360 Modena: 400
Ford Mustang SVT Cobra: 390
Jaguar XKR: 390
Maserati Coupe GT: 390
Chevrolet Corvette Coupe (2004): 350
BMW M3 Coupe: 333
Nissan 350Z: 287

hp/L:
Ferrari F430: 112.3
Ferrari 360 Modena: 111.1
BMW M3 Coupe: 104.1
Jaguar XKR: 92.9
Maserati Coupe GT: 92.9
Ford Mustang SVT Cobra: 84.8
Nissan 350Z: 82.0
Chevrolet Corvette Z06 (2004): 71.1
Chevrolet Corvette (2005): 66.7
Chevrolet Corvette Coupe (2004): 61.4
Dodge Viper SRT-10: 60.4

Fuel economy (Transport Canada figures in miles per Imperial gallon; they'll seem inflated to American forum members because Imperial gallons are larger than US gallons. All have 6-speed transmissions. All manual, save for the Jaguar):
Chevrolet Corvette (2004): 23 city/37 highway
Chevrolet Corvette (2005): 21 city/37 highway
Nissan 350Z: 24 city/34 highway
BMW M3 Coupe: 19 city/31 highway
Ford Mustang SVT Cobra: 20 city/29 highway
Jaguar XKR: 19 city/30 highway
Dodge Viper SRT-10: 14 city/26 highway
Maserati Coupe GT: 14 city/22 highway
Ferrari 360 Modena: 13 city/21 highway
Ferrari F430: 11 city/21 highway

Annual greenhouse gas emissions (in tons; from US Department of Energy):
Ferrari 360 Modena: 15.0
Ferrari F430:14.7
Maserati Coupe GT: 14.1
Dodge Viper SRT-10: 12.8
Jaguar XKR: 10.8
BMW M3: 9.9
Ford Mustang SVT Cobra: 9.8
Chevrolet Corvette (2005): 8.9
Chevrolet Corvette Coupe (2004): 8.5
Nissan 350Z: 8.5
Chevrolet Corvette Z06 (2004): 8.5

Environmental Protection Agency emission standard ("----" meaning not high enough for LEV certification):
Ferrari F430: LEV
Chevrolet Corvette (2005): LEV
Ferrari 360 Modena: LEV
Chevrolet Corvette Z06 (2004): LEV
BMW M3 Coupe: LEV
Chevrolet Corvette Coupe (2004): LEV
Dodge Viper SRT-10: LEV
Jaguar XKR: LEV
Maserati Coupe GT: LEV
Nissan 350Z: LEV
Ford Mustang SVT Cobra: ----

Evidently there isn't a single sound mechanical reason for a smaller displacement DOHC next to a large(r) displacement pushrod. The four pushrod engines above were as good or better as the supposed "high-tech" Ferrari engine.

Incidentally, I'm lead to believe you don't quite know what Australian V8s you're talking about (there hasn't been a single Ford or GM engine reworked from OHV to OHC by their respective Australian subsidiaries).

 

[Famine]

Your whole argument is that OHV is junk. Please tell me where you didn't say that.

My whole "argument" is not that at all. Please learn to actually read people's posts before going in with both feet as you so often do.

Let me put it a simpler way for you. Oral sex <- Penetrative sex. Do you think I don't enjoy oral sex?

As you'd know if you'd read ANY of my posts in this particular section of the site, any way you want to build or design a car, from wherever you like in the world is fine by me, as long as the end result is a good car.

And now we're talking about engines not sold in the US, so you've got me at a total loss. I couldn't care less about the engines you have in foreign countries, honestly.

And it's that attitude which has you parked so firmly in the mechanical dark ages.

Of course, then there's the problem of making all new heads for current engine blocks. Then there's the problem of fitting them in the car (Which, btw, they won't). That's expensive - Really expensive. Do you think there might be a reason you see more Corvettes and Vipers on the road than Ferraris and V12 Benz's?

You'd be amazed to learn that, in fact, it's the other way round for me. You see in Europe where these things actually matter, Corvettes and Vipers aren't sold. At all. Much though I'd love to see one.

And for future reference, a DOHC setup weighs more than an OHV setup. Four cams as opposed to two, more weight. Twice as many valves, valve springs, etc more weight.

To mis-quote someone...

Stick to two-valve or four-valve. Don't try to compare one to the other... completely voiding your whole argument.

Which of course it doesn't, but hey - you only see black and white (I prefer DOHC so I MUST hate OHV, right? Right?), so why not?

Stats

So the Nissan 350Z's DOHC has a higher specific output than all but one of those pushrods, a better fuel economy than all but two of those pushrods - with the best city fuel economy - joint best greenhouse gas emissions (not that I give a rat's ass about those) aaaand... what does that mean, precisely?

You can read statistics any way you wish. You're reading that, presumably, to show how great pushrods are. Yet, on a Spearman's Rank of your numbers, the 350Z turns out comfortably top of the pile, ahead of the '04 Corvette in 2nd and the M3 in 3rd. Intriguing, eh? Who'd have thought it? Two OHCs in the top three by the numbers you posted... And the "expensive DOHC" Nissan is US$26,800, some way undercutting the OHV 'Vette at US$44,510 (Source: Manufacturer's US websites).

Edit: And I believe the FPV Typhoon uses a turbocharged version of the Falcon XR6 4.0 DOHC based on Ford's 4.0 OHV.


Pushrod <- SOHC <- DOHC. DOHC can produce more power and more torque per unit displacement more efficiently and more reliably. Consult an engineer.

Oh and retsmah is right - OHC's main disadvantage is physical size, but that can be overcome. And if that was all sportscar manufacturers were bothered about, they'd all be using the Renesis, which would appear some fair distance to the right on my chart (Oh no Ghost! I said Renesis is better than DOHC piston! I must hate piston engines! )

 

[High-Test]

Let me put it a simpler way for you. Oral sex <- Penetrative sex. Do you think I don't enjoy oral sex?

That's a good point. I actually didn't think you were calling OHV crap, just saying that OHC was more efficient.

But Ghost C has a point. look up a 4-71 Blower on Ebay. Then look up a jackson racing supercharger kit for a Honda Civic/prelude/integra. Tell me how much they were. not surprisingly, You could get a 4-71 blower for an SBC(smallblock chevy) for around 12-19 hundred dollars. That could double the power of your Smallblock.

Now, the jackson racing kit costs around 2500 dollars. and it would probably add 100-175 horsepower.

I think I'll take the 4-71. Parts for OHV engines cost less. and OHV engines are probably easier to get more power out of.

Firebird made a few good points defending the almighty pushrod. look at the emissions, power, and gas mileage of the Corvette's 5.7. 37 highway (the highest) 8.5 tons per year of emissions (the lowest) and 400ish Horsepower.

the Ferrari had the lowest gas mileage, (11/21) and the highest emissions (15 tons per year)

The 5.7 is clearly the most well-rounded engine of the group. you can tout hp/l all you want, but look at Semi trucks, or Gil's Expedition. they might not have the greatest Power to displacement ratios, but they do their job well.


But still, the Cosworth DFV pwns all.

 

[Famine]

Firebird made a few good points defending the almighty pushrod. look at the emissions, power, and gas mileage of the Corvette's 5.7. 37 highway (the highest) 8.5 tons per year of emissions (the lowest) and 400ish Horsepower.

the Ferrari had the lowest gas mileage, (11/21) and the highest emissions (15 tons per year)

Removing specific power output from the list puts the 350Z in second behind the 2004 Vette.

The 5.7 is clearly the most well-rounded engine of the group. you can tout hp/l all you want, but look at Semi trucks, or Gil's Expedition. they might not have the greatest Power to displacement ratios, but they do their job well.

Would they NOT do their job well if they were OHC instead?

 

[Firebird]

So the Nissan 350Z's DOHC has a higher specific output than all but one of those pushrods, a better fuel economy than all but two of those pushrods - with the best city fuel economy - joint best greenhouse gas emissions (not that I give a rat's ass about those) aaaand... what does that mean, precisely?

I don't know what that means, precisely. From what I can tell, you could opt for the Nissan's DOHC engine and have the best city fuel economy and tie for greenhouse gas emissions, or you could opt for GM's "antiquated" V8 which does everything as well or better (save city fuel economy) than the fancy-schmancy DOHC-job, including over 100 more ponies to play with.

Edit: And I believe the FPV F6 Typhoon uses a turbocharged version of the Falcon XR6 4.0 DOHC based on Ford's 4.0 OHV.

So, which cars did this mythical 4.0L OHV V8 appear in? (emphasis on the sixes above )

Pushrod <- SOHC <- DOHC. DOHC can produce more power and more torque per unit displacement more efficiently and more reliably.

I think we've had the power/displacement debate before.

Consult an engineer.

The ones I've talked to agree that specific output is advertising fluff for the most part. I've also consulted myself on the subject. Coincidentally, I agreed with myself. Although I'm still a mechanical engineering student who probably doesn't know as much about mechanical engineering as someone with a B.Sc. and M.Sc. in molecular biology and genetics and human genetics and disease, respectively.

 

[neanderthal]

i like how famines chart compares engines ranging in size from 3.2 to 8 liters.

i also like how he conveniently overlooks the fact that fuel economy is governed by many more things than just power or engine size like gearing! (pop quiz. how many of those cars in his chart have an overdrive sixth gear ratio of 0.5) weight, tire size, coefficient of drag etc etc etc

as someone has already stated; pushrod<OHC<DOHC

OHV engines make good torque though. mostly coz they're limited to two valves per cylinder than because of the pushrods. two valve OHC engines generally make more torque than four valve ones anyway.

OHV engines win on cost, center of gravity, and complexity (lack of.)

 

[standard235]

They call it the internal combustion "Engine"

Not the internal combustion motor.

Sorry to nitpick!

 

[retsmah]

mostly coz they're limited to two valves per cylinder

Again, pushrod motors are not limited to two valves per cylinder.

 

[Firebird]

i like how famines chart compares engines ranging in size from 3.2 to 8 liters.

i also like how he conveniently overlooks the fact that fuel economy is governed by many more things than just power or engine size like gearing! (pop quiz. how many of those cars in his chart have an overdrive sixth gear ratio of 0.5) weight, tire size, coefficient of drag etc etc etc

Famine's chart?! MY chart, beeyotch!


6th gear (#.##:1):

Ferrari F430: 0.85
Maserati Coupe GT: 0.85 (Cambiocorsa)
BMW M3: 0.83
Ferrari 360 Modena: 0.82
Nissan 350Z: 0.79
Jaguar XKR: 0.69
Ford Mustang SVT Cobra: 0.63
Chevrolet Corvette (2005): 0.57
Chevrolet Corvette ZO6 (2004): 0.56
Chevrolet Corvette (2004): 0.50
Dodge Viper SRT-10: 0.50

Every car from the Jaguar down has two overdrive gears, while the 350Z and up have only one.

Weight (lbs):

Jaguar XKR: 3865
Maserati Coupe GT: 3682 (3704 w/ Cambiocorsa)
Ford Mustang SVT Cobra: 3664
BMW M3 (coupe): 3415
Dodge Viper SRT-10: 3410
Nissan 350Z: 3247
Chevrolet Corvette (2004): 3218
Ferrari F430: 3197
Chevrolet Corvette (2005): 3179
Chevrolet Corvette ZO6 (2004): 3118
Ferrari 360 Modena: 3064 (Challenge Stradale is 2579, but fuel economy is the same)

Power to weight ratio (hp/lb):

Ferrari F430: 0.1511
Dodge Viper SRT-10: 0.1466
Chevrolet Corvette ZO6 (2004): 0.1299
Chevrolet Corvette (2005): 0.1258
Ferrari 360 Modena: 0.1305 (Challenge Stradale = 0.1551 )
Chevrolet Corvette (2004): 0.1088
Ford Mustang SVT Cobra: 0.1064
Maserati Coupe GT: 0.1059 (0.1053 w/ Cambiocorsa)
Jaguar XKR: 0.1009
BMW M3 (coupe): 0.0975
Nissan 350Z: 0.0884

Coefficient of drag:

Chevrolet Corvette (2005): 0.28
Chevrolet Corvette ZO6 (2004): 0.29
Nissan 350Z: 0.30
Chevrolet Corvette (2004): 0.31
Ferrari F430: 0.33
Ferrari 360 Modena: 0.33
BMW M3 (coupe): 0.33
Ford Mustang SVT Cobra: 0.33
Maserati Coupe GT: 0.34
Jaguar XKR: 0.35
Dodge Viper SRT-10: 0.40 (still pretty damned impressive for a cabriolet)


The point that you make regarding fuel economy is quite valid (you didn't include variations in drivetrain efficiency as one of your points though, which I find probably the second biggest factor next to gearing). Still, what does that extra-tall gearing in the Tremec T56-equipped cars tell you? You could say it inflates their highway mileage (even though, if I remember correctly, the fuel economy tests have them running in 4th or 5th). I could also say that the Viper and Corvettes make so much torque over the rev range that they don't need shorter gears to keep the power on tap like the Ferrari and BMW do.

 

[Jay]

The Ford 4.0L was a single overhead 2 valves per cylinder design intill the current BA model where the made it a DOHC 4 valve per cyl engine, I am pretty sure the even eariler versions of this engine were push rod designs, I think Ford switched to OHC in 1988.

Also note Ford Australia dicthing the OHV 5.0L in replace for their 5.4 DOHC, problem is my boats Big Block chev engine is smaller that it due to the gigantic size of the heads.

Holden also has recently switched to DOHC now also with thier 3.6L Alloytech V6 engine.