So why isn't the R56S 1.6L engine a high RPM 'screamer'?
 

I would have expected the low rotating mass of the R56[S]'s engine to have a much higher redline.

One theoretical formula to calculate HP is PLANK/33,000
Where
P = Mean effective pressure in pounds per square inch (This is the average pressure on the piston during the power stroke minus the average pressure during the other three strokes.) ...i.e. the resistance in 'sucking' in the air into the intake, into the cylinder, resistance to creating the compression ratio in the cylinder, resistance to pushing the out exhaust of the cylinder, and out of the exhaust...
L = Length of stroke in feet
A= Area of piston head in square inches
N = Working strokes per minute
K = Number of cylinders in the engine
33,000 = The equivalent in foot-pounds of one horsepower per minute

Of all those, P and N are really the only things that can easily (or not so easily) be changed in an engine to produce more HP, w/o re-engineering.

I've read through many many threads from early 2007 on discussing the new DI engine. However I didn't read anything as to why the redline of this relatively small and 'light-ish' rotating mass engine, is such a relatively low value.

So why not a 7K or 7.5K redline?

One thought that comes to mind is P itself. From the restrictions of the stock airbox, and back-pressure from the turbo and exhaust, the resistance to achieving the 10.5:1 compression ratio, might be a factor, and governor of max RPM... too? After all, you need to be able to flow more air as the RPM goes up. So if intake and exhaust can't easily flow more than what is needed @ 6.5K of the present engine, that might explain it; or part of it.

...informed replies appreciated.

I'm going to forward your question to an automotive engineer buddy of mine. We'll see if he wants to take this on.

On Garrett's website, they use the formula:

http://www.turbobygarrett.com/turbob...3/formula3.jpg

To calculate airflow as part of sizing a turbo.

Where:
· Wa = Airflowactual (lb/min)
· HP = Horsepower Target (flywheel)
· http://www.turbobygarrett.com/turbob...3/formula4.jpg = Air/Fuel Ratio
· http://www.turbobygarrett.com/turbob...3/formula5.jpg = Brake Specific Fuel Consumption ( http://www.turbobygarrett.com/turbob...3/formula6.jpg ) ÷ 60 (to convert from hours to minutes)

To answer your question however, it's because it simply doesn't need to be. It's torque curve is stratospheric for a 1.6L and it's basically flat from 1500 RPM to 5000 RPM. By the time the turbo runs out of breath at 6500 RPM, you're better off shifting to the next gear to keep maximum torque at the wheels. Having an engine run at lower RPM and making tons of torque means it will last much longer than an engine that makes the same torque at a higher RPM, simply because high RPM puts massive mechanical strain on components.

I am not sure your totally point, but rotating inertia is not the only factor in redline limits. 1.6L 2.0 2.4L can all rev past 8500 rpm daily. S2000 have a 9k redline (AP1) and are 2.0L

Major factors are the ratio of stroke to bore, if the stroke longer then the bore is wide the engine is under square, or it can be over square. A larger bore then stoke for the same displacement will allow for lower loads on the piston and connection rods since the deceleration forces are lower. (less distance of time). This will produce less low end torque but more top end capabiliies in a motor of the same displacement.

The other is valve train and the ability for the valves not to float off the followers, at 10:1 compression there is interference in the piston crown and if there is valve float the piston could come in contact with the delayed retraction of the valve. So havening the proper valve springs, guides and CAM duration is key to have a high Rpm system.

and like Ryephile mentioned,

The main reason is in R56 is the turbine efficiency tubo, the turbo already can not provide sufficent boost pressure after 6000rpm, making a higher redline will not produce more power. So why rev it past the power band? better to shift for power. The R56 motor (insert engine code here) rev's to current redline with out issues.

So I have a question related to this.

Is driving on a daily basis in the 4500 rpm range (during acceleration) bad for longevity of the engine life, or are these engines really meant for this and will last just the same as long as taken care of and fluids all checked?

Stressing an engine more is obviously going to wear it out sooner. If you're going to drive your car hard, you need to accept the fact that it's going to put more stress on the engine components, and wear them out faster. No amount of fluid changes is going to eliminate wear.

Yeah I just thought as long as you keep the engine healthy its basically good to drive hard and in the higher rpms

+4

In general, today's crop of OEM engines are more rigorously tested than any of us in the aftermarket have the ability to test. OEM's use several engine dyno cells that are temperature controlled to run the engine at full throttle, at full power, at top RPM for DAYS straight in the worst environment possible [the Amazon, for example], without failing. Of course, when it's in the real world, ancillary components to the engine will typically fail much sooner.

Here's an easy example; the Mazda Miata. The car is so slow that every time you drive the car, you simply must floor it to get out of your own way. Every light, every gear, it's to the floor, to redline. I have a couple friends with over 200k miles on their completely stock Miata engines and they absolutely try the hardest they can to get that engine to fail, but it won't.

Long story short; if you drive the piss out of your MINI, it's going to last at least 150k-200k miles as long as you perform competent maintenance on it. If you drive it easy there's no guarantee it'll last any longer; something is going to fail eventually and it may have little to do with how you drive it.

Continuing what Bhatch said, the MINI's engine isn't designed for Formula1-style RPM running mainly due to the bore, stroke, and rod-ratio [ignoring the likely valvetrain deficiencies]. High-RPM engines like the S2k and F1 engines use a very short stroke and a small rod ratio to keep piston acceleration low, thus being able to spin the engine faster without breaking something.

If you were hell-bent on making the Prince a higher revving engine, the first two things you'd have to do would be improve the rod ratio by having new [longer] rods made along with shorter crown [sic?] pistons, and run a larger turbo so you can effectively use it at higher airflow rates. The downsides here are a massive tearing of your wallet, and significant turbo lag at lower RPM [think Evo VIII]

Cheers,
Ryan

Good is probably a stretch... Running an engine up to higher RPM's every once in a while WILL burn off *some* carbon deposits. This should in theory make the engine run a bit better.

I'd say it's probably bad to NEVER take an engine above 3000-3500 RPM's, but it's worse to spend a lot of time in the upper RPM band.

I'll agree with that.

I normally took my C43's stock 4.3L engine up to redline at every opportunity, and it loved it up there. (I wish I didn't sell that engine) At 65K miles on it, it was pulling very strong still. The 5.4L engine I put in the car has so much torque, I do it far less, but up to 4K and some redlines is still done almost off every stoplight or stopsign if I don't have someone in front of me (p.s. I usually run in 'W' [winter/wet] mode on the tranni selection all the time, to start in 2nd w/all that torque) . But I do so realizing an engine can be looked at as having a rev cycle counter built-in ... The more revs you use to drive each mile, the sooner the top-end, bottom-end and cylinder walls/rings are going to wear. However, consider how long it's staying up in that region? Seconds at a time compared to the hours you're cruising at low RPMs?

However the 560SL I bought of eBay had a 1st owner who put the 90K or so miles on it that I believe never redline'd it or took off at anything above silly-slow levels... ever! I bought the car knowing it would most likely have a leaky head, and would need new timing chain and guides; normal problems for that engine. When I had it done, the heads and piston was CAKED with carbon; about 1/16" thick - 1/8" thick at the edges! I kid you not.

Me, I live by the "Italian tune-up" motto... but I do realize instead of getting 350K - 500k miles (not Km) of life from the engine, I'll probably get 300K - 450K miles of life... eh, good enough for me. Engines can come [ahem] cheap [ok, in the eye of the beholder]; there's always going to be youngsters who crack their cars up or others who unfortunately are hit or cars go up in flames from an electrical problem (was the case for the car I bought my engine from) to keep us supplied with parts. :grin:

All this still however doesn't change wishing the Mini's DI engine had at least a 7K redline to sqeeze out a few percent more power (if the airflow could be kept up so that the torque didn't fall off faster than it already does now up there). And I bet in years to come, we will see that. The venerable AMG 5.4L engine started at 6250 redline, and that went up to 6400, then near 7K for WOT runs in the last years of its run before AMG went to the 6.2L engine. But everyone's answers has helped me greatly in understanding why not ...or not yet at least. You could look at it as the initial few years of this engine's use is going to be a more conservative 'tune' range, than until BMW gets a few years of use under it.

I've typically run all of my cars between 3k and 5k in daily driving and have NEVER had one problem. This accounts for 200k miles on a 944t, 115k miles on an e36 M3, 30 years on a 914-4, and 40k miles on an e46 M3. I wouldnt think any differently running an R56 normally at 3-5k daily without any loss of engine life (and of course with red line shifts ocassionally).

As expected, my buddy responded with as little tech jargon as possible, since he knows me.


"Rick,

Max rpm is based as much on stroke as anything else in the motor. The guy is mixing apples and oranges in his analysis. As always in an engineering situation there are a series of compromises. Hope what follows clears this up.


The main thing that limits an engines rpm is the velocity of the piston in the cylinder. This is based on the stroke. For example a motor with a 3 inch stroke the piston travels 6 inches every revolution, 3 up 3 down. A motor with a 4 inch stroke will travel 8 inches in the same revolution. So at a given rpm the longer stroke engine’s pistons are traveling 25% faster. Stroke is controlled by the throw distance on the crank shaft, so a longer stroke means a larger throw. The longer throw the longer the lever to the center of the crank, and the longer the lever the more Torque.


Along with this is the concept of Horsepower, made up by Mr. Watt with his steam engines. He had to convince a farmer that his steam engine would be better than the horses the farmer was using. So he came up with a relationship between his engine and a horse. Mr. Watt’s formula is horsepower = torque X RPM / 5252. Where 5252 is the relationship between revolutions, and pi to make the units work out, think of it like a fudge factor.

Now to talk about engine speed in terms of RPM. The higher the rpm the shorter in time the intake stroke and the exhaust stroke, because the pistons are flying faster. To accelerate the column of air in the intake track in less time means that you have to open the intake valve earlier. To make sure you get all the exhaust gas out you need to leave the exhaust valve open longer. What happens is at very high rpm like over 7000 you have both valves open at the same time. This is called valve overlap. The up side of valve overlay is that the engine can really spin. The down side is that you loose idle quality and the pollutants in the form of unburned hydrocarbons go up dramatically.


Also there are the designers of the mini. Who wanted to create certain driving experiences, namely one that give the car good umph off the line and good sounds from the engine compartment. The get off the line requires Torque. The good sounds come from an engine turning relatively low rpm on the freeway. Now to get to 60 quickly you want horsepower, hence the desire for high rpm’s which allow lower gearing, so there is a trade. Then again the BMW engineers had to deal with pollution regulations in the design.


What BMW has done is make a motor with a longer stroke which does several things for the design. 1) it increases torque across the speed range of the engine. 2) it decreases pollutants, due to little if any valve overlap. 3) it allows higher gearing in the car to keep rpm down at freeway speeds while still allowing good top gear acceleration. 4) it improves gas mileage by not pumping the hydrocarbons through the exhaust pipe. 5) it improves engine life by making life on the piston rings much easier.

Hope this helps.

John


PS, Race car drivers have a saying “There is no replacement for displacement.” Which means torque is what you want."

unless we're talking centrifugal supercharger --there is no need for forced induction motors to make power at high rpms.

engines with a fixed displacement and natural aspiration have nowhere to go for power except through gearing and rpms....so i guess the question should be more aimed at the standard 1.6L engine. but even there, because it is valvetronic, it's also handicapped to not be efficient at high rpm operation.

Thanx... your buddy and others here are all supporting each other to the reasons why it's got the redline it does then. Case closed. :nod:

There's this other racer (perhaps "hot rodder") that's made an impact on me who likes to say "Repeat after me 'It is better to make torque at high rpm than at low rpm, because you can take advantage of *gearing*.' :-)"

Being 1st a member of the MB camp that lives by "no replacement for displacement", it was an epiphany for me a few years back actually to finally understand the 'BMW camp' you might say (and others of course) and appreciate the benefit[s] brought on by 7K - 8K redlines ... so another reason I was asking. (190E Evo not withstanding, which had high RPM screamer engines instead of the standard torquey engines)

...and here I thought a benefit of variable valving was to enable the engine to operate optimally at both high and low rpms. :(

A big reason the R56 MCS "falls off" at higher RPM is because the ECU runs less boost the higher your get in the RPM band. While in "overboost" at low and mid RPM, the car will run at about 16 PSIg, however by the time you get to redline the car it only running at about 7 PSIg, that's just how the ECU is programmed. That said, the turbo is SO small it can't flow a ton more air anyway without having extreme compressor outlet temperatures.

too bad Porsche's 911s with lower redlines but greater displacement kicked the living daylights out of PTG's straight six E46M3s --to the point that PTG switched over to illegal V8 motors.

but sure, i see your point.
:)

Um, yea... lol.

I was gonna say, that's sorta the only reason most Japanese motors even rev past 6500 RPM's.

Try telling an S2000 that VTEC hurts top end performance... :sly:

You don't think torque, weight, and handling had anything to do with that? What does the redline have to do with anything. I'd rather have a redline that lets me pull an extra 2.5 seconds into the corner without shifting over another 400 cc's of displacement (At nearly the same HP). :roll:

It's sort of a completely different price bracket... $95k car vs a 50k dollar car? Riiight...

no, no. you missed my point entirely! i was saying that head to head, factory race team to factory race team, auberlen basically said that the 911s were eating them alive out of the corner because of their torque advantage -despite equal braking power and a better handling car (the PTG M3).

that's all --this notion that power using gearing at higher rpms is not an absolute (point#1).

point #2 --valvetronic is subtly different from VTEC and ask yourself why valvetronic is not on any of the high rpm screamer M cars?

point#3 --back to the forced induction issue. this sort of precludes the original question a priori.

That's not true at all.

The S65B40 in the E90 series M3 has Double VANOS and an 8400+ RPM redline.

The S85B50 in the M5/M6 also has Double VANOS with an 8250+ RPM redline.

Yes there are differences between VTEC and VANOS but they do the same thing. The difference is that VANOS can alter valve timing endlessly (Continuously Variable VT), and VTEC swaps between two sets of cam lobes to change timing (Variable Valve Timing).

Most of the more sophisticated cars out there have SOME sort of valve timing capability.

Variable Valve timing has nothing to do with a car's ability to make power at upper RPM's. Almost every single car out there with Simple VVT makes MOST of it's power at high rpms (Honda, Toyota, Nissan, etc.

I don't understand your first comment...

Forced Induction? I don't recall mentioning anything about forced induction. Both the E46 M3 and 997 Carerra are Naturally Aspirated.

As for torque, having torque to punch through corners is nice, but it's no engineering secret that having 400 additional cc's of displacement is what accomplished that feat.

M motors have variable valve timing and lift --but they do not use valvetronic. savvy? if that is not clear, google works to explain perhaps better than i can evidently?

my other point about the GT3s eating the PTG cars alive was yes, due to increased displacement which is a physical characteristic which is linked to mechanical torque. i.e. you have two scenarios: power by high revs and using gearing at high rpms versus displacement, a more moderate redline with accompanying torque. people who discount the value of torque and displacement in race cars --this is a clear example of two very different approaches to making power. one where the BMW approach failed miserably. street car to street car isn't exactly analogous as per your previously stated reason that the price differential makes people uncomfortable in comparing the 2 cars.

The lack of Valvetronic in M engines has to do with greater efficiencies using individual throttle bodies... It's also mostly a gas milage technology, not a performance one (That's where VANOS comes in). Most of the gas milage gains are lost when stiffer valve springs are installed for the higher RPM redline.

Here's a decent explanation:
"The efficiency of Valvetronic engines drop rapidly at over 6,000 rpm since stronger valve springs are required. The stronger springs create higher friction losses. Don't expect to see Valvetronic in the "M" series engines any time soon."

I though only the R56 non turbo used valvetronic. And the turbo was something else.