Who says stock Yank motors don't make power...
Discussion
I don't remember anyone saying stock Yank motors don't make power, I think everyone is aware of how good an engine it is, but your argument as has been pointed out is flawed, the video clearly shows it isn't being tested under the same conditions that they would do for production so why even bring it up? You seem to be arguing that they are almost as good as DOHC....
Its all a bit willy waving isn't it? Going back and fourth, Merc and Audi vs Chevy, they all make pretty good engines, but go about it in different ways.
and 85BHP per litre? Ferrari and others were doing 100 BHP per litre 50 years ago, all their NA V8's since the 355 have been over 100BHP per litre so I am not sure it is really ground breaking is it?
Simpler and cheaper to produce, true enough, but I don't always think simple is best and having seen the recent Corvette "how its made" on discovery (good show by the way) it is clear that a lot of cost savings are due to the production run output, but I wouldn't say they were simple in construction.
So put your chaps away ...err chaps.
Its all a bit willy waving isn't it? Going back and fourth, Merc and Audi vs Chevy, they all make pretty good engines, but go about it in different ways.
and 85BHP per litre? Ferrari and others were doing 100 BHP per litre 50 years ago, all their NA V8's since the 355 have been over 100BHP per litre so I am not sure it is really ground breaking is it?
Simpler and cheaper to produce, true enough, but I don't always think simple is best and having seen the recent Corvette "how its made" on discovery (good show by the way) it is clear that a lot of cost savings are due to the production run output, but I wouldn't say they were simple in construction.
So put your chaps away ...err chaps.
Willy Nilly said:
Not been through the whole thread, but could someone explain the pros and cons of over head cams (double or single) over push rods engines? Thanks. Start a new thread if you like.
In simple terms:The amount of power an engine can produce is directly proportional to the amount of air that is flowing through that engine.
The combustion process isn't continuous in a reciprocating internal combustion engine, but has cycles (the usual "suck - squeeze - bang - blow" or "intake - compression - expansion (power stroke) - exhaust". That means that the air necessary to fill the cylinder has to be ingested in a finite period of time, and that air starts and stops in a stationary condition.
Hence, the fastest and higher you can get the inlet and exhaust valves open, the longer they are open for. Unfortunately, the timescales are quite short (in mechanical terms) and so the forces required to push the valve open, and then shut it are very large indeed.
With a direct acting cam, the force provided is applied directly to the top of the valve stem (via lifter buckets or finger followers) meaning you can use very aggressive cam profiles (ie really belt the valve open and shut quickly)
With Push rods, the rod becomes a spring, and it also adds mass to the system that must be accelerated / deccelerated. Unfortunately, typical length push rods can end up with a fundamental frequency in or very close to the operating speed range of a typical engine, which can lead to uncontrolled valve/lifter motion etc Adding stiffness to avoid bending adds mass, meaning your lobe/follower interface needs to be bigger, adding yet more mass and more parasitic drag etc
The other issue with pushrods is that 4valve heads are tricky to do, not impossible, but difficult, and so total valve area will be limited in comparison to a 4v OHC architecture
Edited by anonymous-user on Monday 27th April 20:26
Max_Torque said:
Exactly, those standards being "production" standard, ie, as you buy it off the shelf from the manufacturer. The 6,2 AMG makes 518 bhp as std, in worldwide Emissions/homologation format. So which N/A LS engine makes that power as std?
A production ls7 is rated at 505 hp iirc with a 7000 rpm redline. That's pretty close albeit it a fraction bigger in capacity.Edited by Boosted LS1 on Monday 27th April 20:53
Most likely irrelevant but my modernish vag has vvt and a turbo making its 1.8 litres more like 2.5 when the old turbo equals x1.4 capacity is taken into account. Giving it a headline figure of 59.5bhp/litre and the same in torque. Meaning the coarse, thirsty ecotec lump that powered my astra trumps the vag tech with a bhp/litre figure of 63.8. So uh yeah, that proves something. (I own a boring car mostly)
Max_Torque said:
skyrover said:
Lets not forget 2 valve engines produce more torque at low RPM's
I would suggest you forget exactly that^^^, because it's boll*cks!Owned 10v and 20v volvo 850's
The 10V's pulled much harder from low RPM and were much more pleasant to drive around town than the 20V's, despite having a 30hp disadvantage.
Mattygooner said:
and 85BHP per litre? Ferrari and others were doing 100 BHP per litre 50 years ago, all their NA V8's since the 355 have been over 100BHP per litre so I am not sure it is really ground breaking is it?
The bore diameter is relevant methinks. ferrari etc had higher bhp per litre because they used small cylinder bore diameters and prob 4 valve heads along with higher revs. The fuel will take less time to burn if the flame front hasn't got so far to travel if that makes sense. A large bore 2 valve engine makes less bhp per litre because of it's design.DonkeyApple said:
skyrover said:
I disagree...
Owned 10v and 20v volvo 850's
The 10V's pulled much harder from low RPM and were much more pleasant to drive around town than the 20V's, despite having a 30hp disadvantage.
Different cams?Owned 10v and 20v volvo 850's
The 10V's pulled much harder from low RPM and were much more pleasant to drive around town than the 20V's, despite having a 30hp disadvantage.
much preferred driving the 10V's even though they ran out of puff if you revved them hard.
skyrover said:
DonkeyApple said:
skyrover said:
I disagree...
Owned 10v and 20v volvo 850's
The 10V's pulled much harder from low RPM and were much more pleasant to drive around town than the 20V's, despite having a 30hp disadvantage.
Different cams?Owned 10v and 20v volvo 850's
The 10V's pulled much harder from low RPM and were much more pleasant to drive around town than the 20V's, despite having a 30hp disadvantage.
much preferred driving the 10V's even though they ran out of puff if you revved them hard.
In theory SOHC engines are supposed to have higher torque at low rpm than the comparable DOHC because the DOHC loses energy running the additional springs etc (or similar). But the DOHC wins overall as you can run bespoke cams for inlet and exhaust and because you can place the spark in the centre of the chamber giving more efficient burn.
My understanding has always been that the twin can set up just allows you to squeeze far more performance out of the top end than you lose to the SOHC at the bottom end.
But there is also a difference between 2 valves and 4 where the 2 valve equivalent means heavier valves so a loss of power at low RPM in direct comparison.
But these differences are really marginal when looking at big displacement, mass produced cooking engines but become more significant quite quickly as you start tuning/stressing engines or making them smaller.
Edited by DonkeyApple on Monday 27th April 21:47
Camaro said:
skyrover said:
Here is a "modern" DOHC V8 next to a Chevy LS1. The Chevy makes similar power.
That is not an LS on the right, it's not even a Chevy. That is an SBF. 
A bit more information on why 2 valve engines are superior at low RPM.
When you have 2 valves, the intake pressure at low revs is actually higher. Thats why at one time toyota 16v heads came with T-VIS. To shut one of the 2 intake ports per cylinder to increase intake speed at low revs. Higher pressure increases intake speed resulting in more air.
These days, they use a medium port size to reduce this problem.
DonkeyApple said:
Ah, OK.
In theory SOHC engines are supposed to have higher torque than the comparable DOHC because the DOHC loses energy running the additional springs etc (or similar). But the DOHC wins overall as you can run bespoke cams for inlet and exhaust and because you can place the spark in the centre of the chamber giving more efficient burn.
My understanding has always been that the twin can set up just allows you to squeeze far more performance out of the top end than you lose to the SOHC at the bottom end.
But there is also a difference between 2 valves and 4 where the 2 valve equivalent means heavier valves so a loss of power at low RPM in direct comparison.
But these differences are really marginal when looking at big displacement, mass produced cooking engines but become more significant quite quickly as you start tuning/stressing engines or making them smaller.
I think at the end of the day we can look at the Chevy engines as perfectly adequate for the task at hand.In theory SOHC engines are supposed to have higher torque than the comparable DOHC because the DOHC loses energy running the additional springs etc (or similar). But the DOHC wins overall as you can run bespoke cams for inlet and exhaust and because you can place the spark in the centre of the chamber giving more efficient burn.
My understanding has always been that the twin can set up just allows you to squeeze far more performance out of the top end than you lose to the SOHC at the bottom end.
But there is also a difference between 2 valves and 4 where the 2 valve equivalent means heavier valves so a loss of power at low RPM in direct comparison.
But these differences are really marginal when looking at big displacement, mass produced cooking engines but become more significant quite quickly as you start tuning/stressing engines or making them smaller.
Would they get a bit more power going DOHC? yes almost certainly, but they would lose a lot of the advantages of of the small block family such as packaging, low center of gravity, fuel efficiency, simplicity and cost.
wormus said:
swerni said:
Here have my dyne.
Maybe you can tell me if it's any good
That must be one of those AMG 32 valve Corvettes. Maybe you can tell me if it's any good
I think the area under the curve is sufficient.
skyrover said:
I think at the end of the day we can look at the Chevy engines as perfectly adequate for the task at hand.
Would they get a bit more power going DOHC? yes almost certainly, but they would lose a lot of the advantages of of the small block family such as packaging, low center of gravity, fuel efficiency, simplicity and cost.
I think you are right. Would they get a bit more power going DOHC? yes almost certainly, but they would lose a lot of the advantages of of the small block family such as packaging, low center of gravity, fuel efficiency, simplicity and cost.
The easiest commercial comparison to make is between the LS series and the Ford Coyote which was built specifically to compete against each other in the absolutely enormous market of truck vending in the US.
Two solutions to the same problem. Look at the equivalent pick ups and they have near identical performance, near identical economy. Yet as expected, the DOHC Ford can do it with 5 litres versus the LS 6.2, helpin to show that the pushrod engine benefits from larger displacement but this isn't leading to a loss of economy in contrast.
Look to the aftermarket and the GM unit is much cheaper, much easier for the average punter to work on (although if you read any of the LS forums the average modder soils himself at the sight of GM's cam phasing system and their displacement on demand so as someone mentioned earlier the new LS Gen 4+ are not a huge amount more simple than their DOHC competitors today). And the crate LS is much cheaper than the crate Coyote and due to its compact size fits in many more applications.
You couldn't fit a Coyote in a 911.
I'm not a fan of GM or the LS engine. I've always been more of a Ford person and also, frankly as a bit of a snob, the LS always made me turn my nose up. However, over the last four years of researching what engine to fit in one of my Rangies every single route took me back to the LS as the engine that just ticked every box better apart from my snobbish opinion and want to do something different. And as every route brought me back to the same bloody engine I ended up reading up quite a bit about it and learnt that in fact it is a very, very good product indeed.
Edited by DonkeyApple on Monday 27th April 22:02
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