JD_AMG

Im not 100% sure, but I know it is involves driving around 50mph, and once up to 60 I think.
Yeah... I figured the vettes 6th gear was bigger.

Honestly, I think I can speak for most when I say this but I really dont care what configuration GM uses AS LONG AS its even in weight and size to the LSx engines, provides same/better torque curve, and doesnt cost any more. If GM can pull that off with an OHC engine, more power to them.

slt200mph

iTrader: (42)

NO Speed channel..NO need to watch ..it will be the same old song..Vettes kicking DOHC 4VPC Euro cars assses...If you want to talk about restrictions and penalities..the vettes have weight limit and they have to "breath" through two 38MM holes..they could just about double their HP if thay were not restricted...when the C5's raced in the series you mentioned they had just got back into racing..after that first year with the R&D work and the knoweledge they gained it was all over for the competition..I think thay have only retired due to engine failure once in the last 4 years..your DOHC motors do not make any low or mid range torque compared to what a 2 valve OHV engine makes..no matter what you say that fact remains...and just an FYI for ya..the last time that the Vettes ran the Rolex 24 hours at Daytona they won..they do not compete in that series anymore..they concentrate on the 24 hours of Le Mans and the ALMS ..you are really on the wrong forum if you want to bash the LS serires engine..no body wants to hear the HP per liter crap on here..that is what all the ricers preach after they have been beaten by an LS1...


PS Just an FYI for ya..the 2006 Z06 gets 26 miles per gallon on the highway..there is not another supercar on the planet that comes close to doing that..the badge on the fender says 505 HP..but in reality they are producing about 525 HP...the LS7 like all of its brother LS series engines makes plenty of low and mid range torque..they are loafing along in 6th gear with RPM's in the mid teens getting great fuel economy...another advantage the the 2 valve OHV has..

H8 LUZN

Everyone always equates HP to fuel economy.. which in essence is completely wrong. The only reason they are related is because of the inefficiences accepted as a trade off for maximum power. Those tradeoffs are the focus of Millions of $$ of R&D.. that is what brought you many improvements in the automotive world so far..

The main factors in fuel economy are:

1. Vehicle mass (takes more energy to accelerate a heavy vehicle at the same rate F=ma)
2. Aerodynamic drag (frontal area x Cd @ a given velocity.. drag is not linear to speed)
3. Rolling resistance (tires, bearings, etc..)
4. Drivetrain efficiencies (Transmission, halfshafts, differential, torqueconverter, etc)
5. Engine friction/pumping losses
6. Engine accessories (alternator, AC, PS.. )
7. Combustion efficiency (i.e. how well the combustion reaction takes place at high vaccum conditions/low cylinder filling)
8. Many others.. HOWEVER MAX BHP IS NOT ONE OF THEM!!

You ever wonder why the same V8 gets different fuel economy in pickups as it does in cars??? You can rule out any engine and accesory loss differeneces..

Once Gasoline direct injection and fully variable valve timing (not V-tec) are common place, we will see great increases in fuel economy. Mainly in the area of combustion effciency, increases in swirl and proper fuel charge distribution. But again, a lean burn will be greatly beneficial in terms of fuel economy.. not so much in terms of emmisions control.

BTW... the max cylinder temperature occurs when the maximum amount of fuel is burned per cycle (no excess unburned fuel). Reducing the fuel per cycle will recduce the maximum amount of heat input and thus decrease temperatures.

SSbaby

One word. Refinement.

OHVs have more advantages than disadvantages compared to DOHC.

Advantages
More compact - more easily fit into confined spaces.
Less weight - more power per kg of engine mass and lower center of gravity due to lighter heads.
More fuel efficient - less friction and big capacity ... with appropriate gearing almost always uses less fuel.
Cheaper to make as there are less items of the more costly components - like cams, valves, springs, dual cam phasers


Disadvantages
NVH.
Top end power - albeit with torque holes.

OHVs sometimes don't look good on paper but they have it all over DOHC in real world terms. My idea of real world is a measure of cost and power/kg AND fuel economy.

No good comparing a BMW M5 engine, and gloating about its more impressive hp/liter compared to say an LS7, especially if the LS7 is way cheaper to make. I'm sure GM would make an even better LS7 if they decided to spend as much money as BMW does on its V10 engines. Yet, they're both 500bhp powerplants. In pure performance terms, you wouldn't choose the M5 over LS7, would you?

Lost My License

iTrader: (1)

Not Sure at all what everyone is whining about but heres a fun fact that some people would enjoy. DOHC was invented in 1909...If anyone happens to go to Indianapolis Motor Speedway pay 3 dollars to visit the museum in the middle of the track and you can see one of the very first cars with DOHC from 1909.

slt200mph

iTrader: (42)

Thank you for the informative post..I was not saying that HP and fuel ecoonomy were nessassarily related..just that the LS series engine and particularly the LS7 does get great fuel economy compared to other super cars engines...and when the Active Fuel Managment (DOD) is incorporated into the high performance LS engines the fuel economy that is good as it is will get much better..these "old tech" push rod motors are not going anywhere..they are just getting better with refinment..GM chose which way they were going in their engine delvelopment and they are proceding with their plan..

300bhp/ton

you still seem to miss the point, you just CAN'T compare the Corvette to a heavy weight saloon and claim well that proves the engine is more economical.

If you chucked the LS7 into the BMW with the same gearing would it still be more economical???

300bhp/ton

So you're saying they would be producing somewhere around 1200-1400bhp n/a


You still seem to be confusing a small displacement and short stroke engine with a long stroke large displacement engine. It is THAT fact that makes the low end grunt, NOT the OHV valve train.

Bash - where

I OWN one are you blind????

As for ricers, eh? don't have them in the UK so WTF would I care what they say.

300bhp/ton

Then why are there so few of them, come on no ones been able to answer this. If your statement is TRUE, then why is OHC dominate across the world.

I'm not siding either way as I just like cars/engines and things that go fast. I'm trying to be an unbiased intermiediary (sp?)


That's a nice list, but where's the proof? What do you mean by less friction?? You ca have big capacity DOHC, it's just rare that anyone bothers becuase they don't need to be.

And did no one read the quotes about curtain area?? On equal terms a DOHC has a bigger operation rpm range. They can and DO match OHV for low end grunt, but they will then be able to exceed OHV in the high revs. This is PROVEN fact and physics not hear say or make believe. Any true engineer will be able to tell you this.

But how do you know this???

The LS7 is HAND built and derived from a very expensive race program.

I'm not saying it is or isn't cheaper, but you have no more idea than I. And are just guessing or makeing an assumption under false pretenses.

Again where is all this money, what numbers. Remember GM is a much BIGGER company than BMW is.

No because you compared an M5 (which is a CAR) against an LS7 (which is an ENGINE).

They are not directly comparable.

M5 or Z06, well of course the Vette is the "performance" choice because it's a 2 seat sports/supercar the BMW is not, it's a saloon car. So once again that comparison proves nothing because the decision is being made on factors outside OHV and DOHC configuration.

Bimmer Tech

iTrader: (1)

Yeah, well so is the BMW V10. The assembled heads of the BMW engine are more expensive than the entire LS7 crate engine. I looked up the prices a few weeks ago. If you need any specific info on the V10, please let me know.

SSbaby

I just said it, refinement. When used in 4 cyl applications, DOHC would be the better option as packaging isn't as critical. Most of the engines produced are 4 cylinders, and small engines need to rev to make their power. A DOHC would provide better power/torque characteristics in a 4 cyl engine given the relatively lower weight of the vehicle compared to largish cars.

Bigger engines, particularly V types are a different matter.

Well, I thought more cams, valves and springs would have been obvious to you. More moving parts means more friction. Hence the reason they use more fuel.

If you want proof, maybe you should consider the price of fuel in Europe compared to that in the USA and then look at the types of vehicles Europeans drive compared to Americans. If fuel was cheap in Europe, I dare say you will see a lot more SUVs and big capacity V8s.... and possibly OHVs, too. Since most of the world drives 4 cylinders, OHCs are a better alternative, IMO, as there isn't the same weight penalty (one head vs two) and packaging limitation on a 4-cyl engine as there is on a V8.

Compare the LS1 to Fords DOHC V8, for example... the LS1 makes at least as much power and weighs considerably less. The advantage offered by the LS1 powerplant is obvious on a bhp/kg basis.

300bhp/ton

Cool yeah, I'm just interested from a car enthusiasts point of view.

300bhp/ton

I can see that with respect to straight 4 eninges. But again if OHV is so great why not go with V4 engines?

Also what about all the DOHC V6's and V8's that are produced the world over.


I guess, but no push rods and again due to curtain area milder cams are used so softer valve springs can be used which has less impact on the drivetrain.

Price is a b*tch trust me I know

But we still have big engines over here, all of the premium manufactures offer V8's and/or V12's. Plus turbo chraged V6's and the like

I agree, the Ford modular range is not the pinnicle of OHC technology, but as already stated it often appears that many American's take the Ford unit for being the best DOHC can offer

Having said that, the aluminium block 5.4 DOHC is actually a very good engine and up against a stock displacement LS1 I bet it can hold it's own very well.

slt200mph

iTrader: (42)

Hay English dude...We do not drive saloons we drink in them.. ...I never said anything about large sedans...the A Ms and the Ferraris that have been getting their *** kicked regularly for the last 5 years by the Corvette are sports cars..quit changing the subject..if you would like to compare the same size power plants..look at the LT5 compared to the LS series engine family...the weight and external demintions are very different not to mention the amount of moving parts and cost to produce..and they favor the LS engine family..

300bhp/ton

Yeah but the LSx engines didn't exist when the LT5 was developed.

If you want to do a comparison then it would have to be the cast iron Lt1. How much work does it take to get a stock displacement LT1 to produce 405bhp and still remain streetable and emissions legal and could it be done running thru a stock exhaust and manifolds as the LT5 did.

And then how would it compare mpg wise?

SSbaby

It's probably to do with the fact that the differences to external dimensions isn't that great between OHV and OHC for 4 cylinders... If you popped the hood there's usually lots of space around the engine... although most of it is taken up by the transmission (transverse layout).

I'm not contradicting myself as I can see a bigger capacity OHV 4 cylinder doing equally as good a job as a DOHC... although the output (on paper) might not reflect this. The DOHC 4 cylinders produce slightly more top end power... there's not much disputing that. Therefore, you'd have to say that marketing would also have to be a valid reason why most 4 bangers are DOHCs.

Similar story for V6s... there aren't the same packaging constraints around V6s as there are for V8s as the V6 is a compact design, no matter if its DOHC or OHV.

However, the scenario is different for V8s, they are a physically bigger engine in all respects and an OHV V8, especially the LSx series of GM engines show what a great package it is in every respect. Remember, the LS7 weighs around 100lb less than BMW's tour de force V10 (est. 243kg), that counts for something.

Another factor is that OHVs better lend themselves to cheap mods than DOHCs. GM has long looked after the aftermarket. Customers want cheap upgrade paths and LSx engines certainly provide that. Err, what cheap upgrade path do you get with Bimmer, Merc, Ferrari, Jaguar etc engines?

We can keep arguing about this until we're blue in the face but if you forget the marketing spin for a moment (DOHC does sound more high tech than 'pushrod') you'll realise there isn't one single answer to your question. It's different strokes for different folks.

At least GM can't be accused of ignorance when it comes to DOHC V8s... the LT5 in the ZR1 made them have a rethink. Thanks to GM, cheap power still exists today.

slt200mph

iTrader: (42)

You are hopless..go to your saloon and knock back a few drinks ... ..why only go back to the LT1 or LT4...how about we just go back to the Ford flat head V8..

RussStang

Those numbers are kind of high, but I would suspect in the area of 1100hp is not out of the question.



As I stated, I think the only fair parity to be drawn between OHC (especially DOHCs) and the current run of OHV engines is in race engines, where budget restraints virtually do not exist. OHCs generally still make more power, but OHVs close the gap considerably over there street counterparts. I have not been able to find any direct numbers regarding comparison costs between OHC engines and OHV engines (its harder than I thought), but just thinking about how cheap a set of pushrods are (and the lifters aren't that expensive either), and how expensive 3 more cams, 16 more valves, and another timing chain will be in a DOHC applications really makes this a no brainer to me.

RussStang

I have noticed with DOHC v8s in cars sold all over the world that they tend to be lower specific output than the models you refer too. A DOHC v8 in a bread and butter car over here in the States does't tend to have an enoromous lead in specific hp/l over their OHV rivals. None of these DOHC v8/10/12 engines you keep bringing up find their way into normal everyday vehicles; they are all exotic engines in extremely expensive vehicles.

My point is cost governs alot of what is going on here.

SSbaby

GM's technical bochure on the 3-valve OHV head design states that it produces up to 10% more power over comparable 2-valve designs... whereas DOHC 4v heads produce up to 15% more power.

But here's an article on the 3v... http://www.findarticles.com/p/articl...9/ai_108875676