Potentially Stupid Question - Overhead Cam Engines
Discussion
doogz said:
I might.
Because you’re talking about 2 completely different cars.
My 270bhp Impreza returned better average economy than my 1.6 little hatchback. Mostly due to the gearing. It’s hardly fair to blame an engine when one’s being asked to spin at 2.5k rpm, the other at twice that, to maintain the same speed. The Impreza was also significantly heavier, with the additional transmission losses, etc.
You seem interested in power against economy as a stat. It's an interesting figure, but it's also a bit useless in some respects as if you wanted to go do some rallying/grass autotesting, stuff like that, the Camaro might have the better power/economy ratio, but it would get mugged.
This thread is about engines, I'm sure you read the op. But maybe a revisit is in order Because you’re talking about 2 completely different cars.
My 270bhp Impreza returned better average economy than my 1.6 little hatchback. Mostly due to the gearing. It’s hardly fair to blame an engine when one’s being asked to spin at 2.5k rpm, the other at twice that, to maintain the same speed. The Impreza was also significantly heavier, with the additional transmission losses, etc.
You seem interested in power against economy as a stat. It's an interesting figure, but it's also a bit useless in some respects as if you wanted to go do some rallying/grass autotesting, stuff like that, the Camaro might have the better power/economy ratio, but it would get mugged.
It has nothing to do with autotesting or anything like that. Although your analogy would suggest anything heavier than the Impreza would loose out regardless.
My point is. The Camaro is heavier with similar drivetrain losses, makes a LOT more power and uses the same fuel. The comparison being OHV vs DOHC.
I thought the point I was making was clear. For example, if you removed the Impreza engine and replaced it with the OHV V8 you'd now have manual and AWD + a 50% power hike and probably better mpg by a noticeable amount.
Basically more of everything with no real negative points.
--- yes I know the LS is longer than the boxer 4 and that it wouldn't be a direct swap. But that also isn't my point.
--- and yes I know you could tune the Impreza engine for more power, but this is also true of the LS.
Without particularly wanting to get involved in an angry fight I do have to ask those that believe these pushrod V8 engines are the be all and end all of engine development why they think that every single manufacturer has developed other engine technology.
In your view is every single manufacturer (including those that still make pushrod V8 engines) wasting their time with DOHC, VVT, turbochargers, and so on just so they can employ thousands of engineers for decades?
In your view is every single manufacturer (including those that still make pushrod V8 engines) wasting their time with DOHC, VVT, turbochargers, and so on just so they can employ thousands of engineers for decades?
300bhp/ton said:
But is there also a displacement limit?
And lets face it, race cars and race engines really have little to no relevance to production cars & engines used on public roads as means of transportation.
I don't think anyone would deny that slapping some DOHC heads on a 7.0 litre LS engine wouldn't produce a shed load more power and a broader powerband.
But the reality is how many 7.0 litre DOHC engines are there as non race production units?
So it has nothing to do with "keeping the pushrod dinosours competetive". You are just looking at one narrow variable and not considering the bigger picture.
They have a 5l displacement.And lets face it, race cars and race engines really have little to no relevance to production cars & engines used on public roads as means of transportation.
I don't think anyone would deny that slapping some DOHC heads on a 7.0 litre LS engine wouldn't produce a shed load more power and a broader powerband.
But the reality is how many 7.0 litre DOHC engines are there as non race production units?
So it has nothing to do with "keeping the pushrod dinosours competetive". You are just looking at one narrow variable and not considering the bigger picture.
The fact is that the European / Japanese manufacturers are being handicapped to avoid them running off into the distance.
Don't think I am anti pushrod v8s - they definitely have advantages in packaging and engine size, and sound nice, but calling a race series "supercars" and then limiting the engines to a measly 7,500 rpm is a bit s
t really.Personally I would rather limit them to production engine blocks / heads / internals, and drop the rev limit. It would be much more interesting to see say 5.5l quad cam vs 7.2l pushrod v8s.
doogz said:
I’m not sure where you managed to draw the conclusion you did about anything heavier losing out regardless. That would suggest weight is the single factor that is used to determine performance? That’s silly.
As you say, if you replaced the Impreza engine with a V8, it’d be sticking out the front, we’re comparing apples with oranges here. The cars were designed for quite different purposes. A large part of the economy advantage your V8 has will be in the gearing. An Impreza with that V8 fitted would be useless. It'd be even more nose heavy than it already is, if you wanted to keep 4WD, or you'd lose the 4WD, which is the whole point in the car.
It's not more of everything with no negatives. If there really were no negatives, we'd all be using them.
I think you'll agree with me doogz when I say that in the Impreza and Camaro example there, each engine is designed for a different purpose and as such each have strengths in the areas relevant to the intended application.As you say, if you replaced the Impreza engine with a V8, it’d be sticking out the front, we’re comparing apples with oranges here. The cars were designed for quite different purposes. A large part of the economy advantage your V8 has will be in the gearing. An Impreza with that V8 fitted would be useless. It'd be even more nose heavy than it already is, if you wanted to keep 4WD, or you'd lose the 4WD, which is the whole point in the car.
It's not more of everything with no negatives. If there really were no negatives, we'd all be using them.
Neither is exactly better than the other let's say, they each have different strengths relevant to their respective uses.
dme123 said:
Without particularly wanting to get involved in an angry fight I do have to ask those that believe these pushrod V8 engines are the be all and end all of engine development why they think that every single manufacturer has developed other engine technology.
In your view is every single manufacturer (including those that still make pushrod V8 engines) wasting their time with DOHC, VVT, turbochargers, and so on just so they can employ thousands of engineers for decades?
It's so they can meet EU emission targets and be allowed to keep selling cars at a price people can afford to pay. What other reason could there be for putting a 1.0 L Ecoboost engine in a Mondeo?In your view is every single manufacturer (including those that still make pushrod V8 engines) wasting their time with DOHC, VVT, turbochargers, and so on just so they can employ thousands of engineers for decades?
You're involved now. You must fight your corner or be branded a coward.
AW111 said:
They have a 5l displacement.
The fact is that the European / Japanese manufacturers are being handicapped to avoid them running off into the distance.
Don't think I am anti pushrod v8s - they definitely have advantages in packaging and engine size, and sound nice, but calling a race series "supercars" and then limiting the engines to a measly 7,500 rpm is a bit st really.
Personally I would rather limit them to production engine blocks / heads / internals, and drop the rev limit. It would be much more interesting to see say 5.5l quad cam vs 7.2l pushrod v8s.
I certainly agree with your last sentence. And a 5.0 litre displacement limit, well that certainly is bonkers. A stock LS1 wouldn't even qualify...The fact is that the European / Japanese manufacturers are being handicapped to avoid them running off into the distance.
Don't think I am anti pushrod v8s - they definitely have advantages in packaging and engine size, and sound nice, but calling a race series "supercars" and then limiting the engines to a measly 7,500 rpm is a bit s
t really.Personally I would rather limit them to production engine blocks / heads / internals, and drop the rev limit. It would be much more interesting to see say 5.5l quad cam vs 7.2l pushrod v8s.
Pretty much anything that regulates on displacement (emissions, race classes, tax or anything else), just shows a complete lack of understanding IMO.
doogz said:
I’m not sure where you managed to draw the conclusion you did about anything heavier losing out regardless. That would suggest weight is the single factor that is used to determine performance? That’s silly.
As you say, if you replaced the Impreza engine with a V8, it’d be sticking out the front, we’re comparing apples with oranges here. The cars were designed for quite different purposes. A large part of the economy advantage your V8 has will be in the gearing. An Impreza with that V8 fitted would be useless. It'd be even more nose heavy than it already is, if you wanted to keep 4WD, or you'd lose the 4WD, which is the whole point in the car.
It's not more of everything with no negatives. If there really were no negatives, we'd all be using them.
I see you are still obtuse and like missing the point, even when highlighted in bold and gold plated for you. But never mind, you keep living in your made up dream world and the rest of us will carry on and not bat an eyelid.As you say, if you replaced the Impreza engine with a V8, it’d be sticking out the front, we’re comparing apples with oranges here. The cars were designed for quite different purposes. A large part of the economy advantage your V8 has will be in the gearing. An Impreza with that V8 fitted would be useless. It'd be even more nose heavy than it already is, if you wanted to keep 4WD, or you'd lose the 4WD, which is the whole point in the car.
It's not more of everything with no negatives. If there really were no negatives, we'd all be using them.
If you manage to figure out the obvious point I was making, feel free to chime in again though, but currently you are a Virgin Atlanic flight away from getting it.
dme123 said:
Without particularly wanting to get involved in an angry fight I do have to ask those that believe these pushrod V8 engines are the be all and end all of engine development why they think that every single manufacturer has developed other engine technology.
In your view is every single manufacturer (including those that still make pushrod V8 engines) wasting their time with DOHC, VVT, turbochargers, and so on just so they can employ thousands of engineers for decades?
I think that when you look at large displacement engines then there is very little in it. In your view is every single manufacturer (including those that still make pushrod V8 engines) wasting their time with DOHC, VVT, turbochargers, and so on just so they can employ thousands of engineers for decades?
A really good example is to look at GM's LS3 and Ford's Coyote. These two engines are specifically aimed to compete against each other and both deliver near identical results and are used in near identical situations. The Coyote being DOHC can deliver a comparable set of results to the 6.2L pushrod LS with just 5L of cc. It can deliver matching performance out of less cc but it still isn't any more efficient or powerful.
However, my understanding is that when you look at small capacity engines the same isn't true and the disadvantages of pushrod design are more clear and the advantages of DOHC increase.
As the world has been moving strongly and steadily to smaller cc engines for quite some years it has struck me as logical that the more complex and expensive DOHC solution becomes more favourable and so more common.
I don't think it is coincidence that he petrol pushrods that remain in 2015 are generally large cc but that even GM uses DOHC for its small engines for effeminate types and their life partners.
RobinBanks said:
I think you'll agree with me doogz when I say that in the Impreza and Camaro example there, each engine is designed for a different purpose and as such each have strengths in the areas relevant to the intended application.
Neither is exactly better than the other let's say, they each have different strengths relevant to their respective uses.
Yes they are different cars. They just happen to be two I own, both 'performance' cars and of exactly the same era, so adhering to the same emissions standards and availability of the same technology.Neither is exactly better than the other let's say, they each have different strengths relevant to their respective uses.
The approaches used are almost polar opposites. But one delivers more goods than the other.
For example, there is no reason why you couldn't fit the boxer engine in the Camaro. But all you'd achieve is worse mpg, less power and much reduced performance.
The comparison wasn't about the cars (in fact, forget the actual cars), it was more about the engines.
And the reality is, built two purpose built cars (rwd/fwd/awd who cares it makes no odds), auto/manual whatever. Fit one with a Subaru 2.0T and the other with a LS1 V8. They'll both use similar fuel, but one will make a lot more power than the other.
DonkeyApple said:
I think that when you look at large displacement engines then there is very little in it.
A really good example is to look at GM's LS3 and Ford's Coyote. These two engines are specifically aimed to compete against each other and both deliver near identical results and are used in near identical situations. The Coyote being DOHC can deliver a comparable set of results to the 6.2L pushrod LS with just 5L of cc. It can deliver matching performance out of less cc but it still isn't any more efficient or powerful.
I don't know the Coyote's dimensions or weight, but I'm willing to bet it is physically larger than the LS1 and heavier. Not that this is a major issue when all said and done, but it is part of the reason for OHV V8's - packaging.A really good example is to look at GM's LS3 and Ford's Coyote. These two engines are specifically aimed to compete against each other and both deliver near identical results and are used in near identical situations. The Coyote being DOHC can deliver a comparable set of results to the 6.2L pushrod LS with just 5L of cc. It can deliver matching performance out of less cc but it still isn't any more efficient or powerful.
As for the efficiency, I agree, both are great engines. The Coyote uses multi-vavle technology for a broader powerband, this means it can maintain torque at higher revs and thus make more power per litre and give the same end result. A wider powerband also means you might be able to run shorter gearing to negate the low rpm torque deficit a smaller displacement engine will have.
DonkeyApple said:
However, my understanding is that when you look at small capacity engines the same isn't true and the disadvantages of pushrod design are more clear and the advantages of DOHC increase.
The difference is still there. But don't think of "pushrods" as the main factor. A 2v per cylinder engine will run the same no matter if the cam is OHV or OHC. The combustion chamber doesn't really know any difference.To this extent, look back at 2.0 litre hatches/saloons in the UK market that where 2v per cylinder, most where probably OHC. But they'd make maybe 110bhp in most cases, or the very least in the 105-120bhp sector.
DOHC inline 4's suddenly meant you had 1.8's and even 1.6 litre engines making the same sort of power as the 2v per cylinder 2.0 litres did. The reason? Well it's all down to multi-valve technology and the broader powerbands they can support.
This difference is true for any engine, regardless of number of cylinders, cylinder configuration or even displacement.
The main difference here is packaging. On a Vee engine, you can locate a single cam easily within the block, therefore OHV V8's tend to be narrower, less tall and shorter than OHC ones (even those with 1 cam per bank and still only 2v per cylinder).
On an in-line 4 you need to make the block wider to accommodate the cam, which then negates the benefit of the smaller head assembly.
Basically there is no packaging advantage. And the cost advantage is smaller too.
OHV V8 = 1 cam
DOHC V8 = 4 cams
That's 4x the cost for the cams.
Inline 4, it's 1 cam vs 2 with no other perks.
DonkeyApple said:
As the world has been moving strongly and steadily to smaller cc engines for quite some years it has struck me as logical that the more complex and expensive DOHC solution becomes more favourable and so more common.
It's true, there has been big developments in the UK/EU and USA markets for small engines, although these have long been more common in Japan.But there is also growth in large engines.
Land Rover today use 5.0 V8's, bigger than anything in the companies history.
Jaguar too, if you exclude the V12 of past eras as it was never really the main engine, unlike the V8's are today.
Most supercar makers such as Ferrari and Lambo are all using bigger displacement engines than they did in the 70's, 80's, 90's and even 00's.
Chrysler has a range of 5.7, 6.1, 6.2 and 6.4 V8's, all used in mass production vehicles. And of course the 8.4 litre Viper engine. Probably one of the largest displacement production engines for a car available in the past 40-50 years.
BMW, Mercedes and even Lexus/Toyota are also churning out large displacement V8's still.
And even the likes of Hyundia make their own 5.0 Tau V8 engines. Only we don't get them in the UK...
doogz said:
And this is where your point ends. Yet, there's quite a lot more to it than that. Firstly, you're comparing the lowest powered EJ20 turbo in the range. If you consider a P1, the 2 door 'coupe' (a fairer comparison I'd suggest) you'll see that it's rather a lot faster to 60mph than the Camaro. And rather a lot faster through any sort of corner.
What has 0-60 got to do with OHC vs OHV??? Stick to the point.And lets not forget the P1 needs 100 octane fuel (as did/do the JDM engines of the same era).
The LS1 is also the lowestest powered LS engine in it's range. The LS6 of the same displacement was rated at 405bhp and still
gets the same mpg.
doogz said:
Yes, it's still going to use more fuel, but that's the trade off.
A big trade off when my ENTIRE point was power vs mpg in two cars with potentially similar drivetrain losses.doogz said:
The flat 4 is also more suited to the 4WD layout, really, there's a lot more to engine selection than power/economy, regardless of any other variable or preference. Or as has been said, we'd all be using them.
Nope, you are still missing the OBVIOUS point by a country mile my dear fellow.300bhp/ton said:
V8RX7 said:
300bhp/ton said:
Who frankly gives a flying smeg about bhp/litre.
It's total power output that matters. And 450bhp beats anything 200-250bhp.
Everyone in a race series.It's total power output that matters. And 450bhp beats anything 200-250bhp.
450bhp in a 2ton car loses to 250bhp in a 1ton car.
I like the LS engines - they are small, light and powerful and simple to retro fit into other cars however they are made to do a job in the US and they aren't suitable for Europe, if they were then they would be used. It's a shame the manual gearbox attached is crap.
They certainly aren't as advanced - whether this is good or not depends upon your point of view.
I used my LS2 RX7 as a daily as I did my LS1 Monaro - and I can tell you that getting 14mpg commuting nose to tail following a Supermini getting 50+mpg isn't fun !
Admittedly if I were wealthier it might not matter but £20 a day on the school run isn't on for the vast majority of us.
And-I-was-pointing-out-that-it-doesn't.
Particularly-relevant-as-most-production-cars-with-LS-engines-in-are-heavy.
(spacebar-broken)
V8RX7 said:
You-said-"And 450bhp beats anything 200-250bhp."
And-I-was-pointing-out-that-it-doesn't.
Particularly-relevant-as-most-production-cars-with-LS-engines-in-are-heavy.
(spacebar-broken)
It does when it comes to top speed when drag coefficient, gearing and power are most important. That's when 200-250hp looks decidedly "ooh ducky".And-I-was-pointing-out-that-it-doesn't.
Particularly-relevant-as-most-production-cars-with-LS-engines-in-are-heavy.
(spacebar-broken)
Corvette zo6 weighs 1420kg and that's powered by an LS engine.
Edited by anonymous-user on Monday 3rd August 18:56
Mr2Mike said:
How often is top speed even remotely important?
Because at 100mph a 450hp car will leave a 250hp one for dead and its owner crying like a girl. Pointless on the road maybe but nice knowing you can if you want to. I don't know anyone who goes around challenging people to 0-60 races.wormus said:
Because at 100mph a 450hp car will leave a 250hp one for dead and its owner crying like a girl. Pointless on the road maybe but nice knowing you can if you want to. I don't know anyone who goes around challenging people to 0-60 races.
And, by strange coincidence, I don't know of anyone that goes around challenging people to top speed contests. Leaving a 250bhp car in his dust is more likely to leave the 400bhp car owner crying into his wallet whilst he catches the bus for the next few months.Edited by Mr2Mike on Monday 3rd August 22:54
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