Update: False. S55 engine has oversquare bore/stroke and shares "nothing" with N55!

[mkoesel]

Thanks for posting NISFAN. I'm sure very valid points are being made from both sides.

Here's a little brain teaser to pass the time:

What ~4.5L engine (naturally aspirated) on the market today makes the most torque? Pickup truck perhaps? (Hint: that was an anti-hint)

The answer is more of a non-point than a point. Obviously, there are many variables at play. But how much more torque, really, could the above engine make by shrinking the bore and increasing the stroke. Can we somehow calculate, that?

[NISFAN]

Originally Posted by mkoesel

Thanks for posting NISFAN. I'm sure very valid points are being made from both sides.

Here's a little brain teaser to pass the time:

What ~4.5L engine (naturally aspirated) on the market today makes the most torque? Pickup truck perhaps? (Hint: that was an anti-hint)

The answer is more of a non-point than a point. Obviously, there are many variables at play. But how much more torque, really, could the above engine make by shrinking the bore and increasing the stroke. Can we somehow calculate, that?

Going by your question, I'll have a guess....a 458 Italia?

Regarding more torque, the important thing to me, it is becoming clear that BMW didn't go the easy option of 'fettling' an N55 which is what so many people were against. We had a ton of threads saying BMW 'cheaped out' with the S55 (before knowing the true engine facts), and that it was no S65 replacement.

I stand up and applaud the M engineers for taking the S55 to the heights it has. To me the spec revelation tells me that this is going to be the best M engine ever.

[mkoesel]

Originally Posted by NISFAN

Going by your question, I'll have a guess....a 458 Italia?

Did I make it too easy?

So how bout the other question in my post? Can we increase torque to even higher peak by adjusting the bore dimensions?

By the way, I think the point about looking at the entire torque curve vs. just the peak value is a very good one.

Regarding more torque, the important thing to me, it is becoming clear that BMW didn't go the easy option of 'fettling' an N55 which is what so many people were against.

Agree, and I would say that this holds true even if they had used (or did use) the same bore and stroke of the N55 with the same sized block. Clearly every part if the engine has been improved, just as we have seen with their past efforts.

[NISFAN]

Originally Posted by mkoesel

So how bout the other question in my post? Can we increase torque to even higher peak by adjusting the bore dimensions?

Not an easy comparison, but consider the F30 Alpina B3 produces 443lb.ft with the long stroke N55

[Boss330]

Originally Posted by NISFAN

Not an easy comparison, but consider the F30 Alpina B3 produces 443lb.ft with the long stroke N55

The Alpina B3 is a very interesting comparison in this regard.

It has a N55 with long stroke/small bore and is equipped with two turbochargers and delivers 410hp and a maximum torque of 600Nm.

The S55 has a short stroke/large bore twin turbo engine that delivers 430hp and "substantially more" than 500Nm (but likely not above 550Nm).

N55 B3: 410HP/600Nm
S55 M3: 430HP/500Nm (550Nm)



N55 B3: 410hp (301kW) between 5500 and 6250rpm
N55 B3: 550Nm between 2200 and 5200rpm (600Nm max at 3000rpm)

S55 M3: 430HP between 5700-7200rpm
S55 M3: 500+Nm between 1800-5700rpm


These two engines I suspect will feel quite different in their power delivery and willingness to rev. The S55 should be more agile, perhaps especially when not "on boost", due to it's short stroke that means less rotating mass and hence less inertia. That aids response when not on boost and makes it easier (I would imagine) to get a engine that responds better and looses some of the lagginess of the N55. Especially considering larger valves possible with larger bore, which means better flow. Better flow means more air and fuel. Which again leads to more exhaust volume and better spool up of turbo's, and less lag...

Also interesting, and in line with what I believe is generally true of oversquare vs undersquare engines, is that the N55 Alpina B3 produces substantially more torque but less HP than the S55 that has more HP but less torque.

(We don't know boost pressure of the B3, and the S55 has a function where maximum boost is only applied under high temperatures/altitude etc. So hard to get a realistic comparison on boost levels anyway. But state of tune seems quite close, so the B3 N55 and S55 should still make a valid point re long vs short stroke).

Certainly going to be interesting to read comparisons of these two engines


-

[mkoesel]

Originally Posted by NISFAN

Not an easy comparison, but consider the F30 Alpina B3 produces 443lb.ft with the long stroke N55

Oh, sure, but I am just wondering how much torque we could get from a naturally aspirated 4.5L V8 with a longer stroke. I guess I am wondering if we can calculate that, or is this discussion becoming religion instead of science now?

Regarding, the S55, probably it could never be pushed to 443 ft-lb, right?

[Boss330]

Originally Posted by mkoesel

Oh, sure, but I am just wondering how much torque we could get from a naturally aspirated 4.5L V8 with a longer stroke. I guess I am wondering if we can calculate that, or is this discussion becoming religion instead of science now?

Regarding, the S55, probably it could never be pushed to 443 ft-lb, right?

Of course it could be "pushed" to 443lb ft. But the Alpina B3 makes 600Nm with "only" a 410hp tune. Indicating it makes torque easier and more torque at a similar, or lower state of tune, than the S55.

If you are looking for a engine that could be compared with the 458 engine I suspect it won't be easy to find anything comparable with a long stroke... It revs to 9000rpm. With a long stroke engine the piston speeds would be astronomical...

A long stroke 4.5l V8 would have to be dramatically different as regards to rev range, cam timing. Parametres that make it very hard to establish whether the difference in torque is down to stroke difference or rpm/state of tune...

Possibly a example of this would be a Ducati 848 engine vs a HD 883:

Ducati 848:
Bore x Stroke: 94 mm × 61.2 mm
134 hp (100 kW) @ 10,000 rpm
96.0 Nm @ 8,250 rpm

HD 883:
Bore x Stroke: 76.2 mm x 96.8 mm
53 hp (38.6 kW) @ 6000 rpm
67 Nm @ 4100 rpm

As can be seen here, both engines have comparable volume (848cc vs 883cc), however since the Ducati can rev far higher than the HD it's also possible to make more power and torque. Same issue will be if we should compare a standard 4.5l with the 458.

We cannot compare a 60hp/liter engine with a 158hp/liter engine...

The Honda CBX and Kawasaki Z1300 both featured straigh six engines, one oversquare and the other undersquare.

Kawasaki Z1300 Undersquare:
Bore x Stroke: 62 x 71 mm
120 hp @ 8000 rpm
116 Nm @ 6500 rpm

Honda CBX Oversquare:
Bore x Stroke: 64.5 x 53.4 mm
105 hp @ 9000 rpm
71Nm @ 6500 rpm

Adjusted for volume (1300cc vs 1000cc) the Kawasaki would be at:
92 hp @ 8000rpm
89 Nm @ 6500rpm

At 1000cc the undersquare engine in this example has 13hp less than the oversquare but make 18Nm more than the oversquare engine... Which again falls in line with the N55 B3 vs S55 M3 etc.

There might be other examples that proves the above or makes my point rendered null and void

[mkoesel]

Originally Posted by Boss330

If you are looking for a engine that could be compared with the 458 engine I suspect it won't be easy to find anything comparable with a long stroke... It revs to 9000rpm. With a long stroke engine the piston speeds would be astronomical...

And? The original hypothesis was that for a given displacement a longer stroke yields more torque. No one said anything about an RPM limitation on that claim. If the long stroke ultimately limits the engine in ways that keep it from being physically capable of making as much torque as an engine with the shorter stroke then we simply conclude the original hypothesis is invalid and move on.

Edit: Retracted one statement because I thought it over and felt it was a low blow.

[solstice]

Can we dream of a limited edition M3 with a NA GT3 like version of this over square engine at 9000 rpm dumping all the weight of turbo plumbing as an added bonus? If so I want to know now, I'll pay $100k for it if they do.

[NISFAN]

Originally Posted by mkoesel

Oh, sure, but I am just wondering how much torque we could get from a naturally aspirated 4.5L V8 with a longer stroke. I guess I am wondering if we can calculate that, or is this discussion becoming religion instead of science now?

Regarding, the S55, probably it could never be pushed to 443 ft-lb, right?

The internal combustion engine is a complex beast. Peak torque value and where it occurs in the rev range is controlled by so many different parameters.

For example there must be hundreds of engine designs out there where the bore stroke, rod ratio dictates peak torque of X is possible at Y revs. However the cams or head design favour a different rev range, which ultimately limit the amount of torque achieved (but may allow increased torque elsewhere in the rev range).

The thing about the 458 engine, is it is highly tuned and fettled, which helps almost every performance characteristic. I would put money on the 458 engine achieving over 100% VE at specific revs, which outside of F1 engines, is remarkable.

Regarding maximum torque achievable for the S55, yes, no question it could reach 443ft.lbs, it would require increased boost pressure, which I would imagine a road tuned car would allow due to a safety margin.

Increasing boost pressure is not as simple as most seem to think. But as long as you keep intake charge temps under control (inter cooler capacity), perhaps go extra rich under boost (sort of fuel excess charge cooling), all to steer clear of detonation, it can be done.

[Boss330]

Originally Posted by mkoesel

And? The original hypothesis was that for a given displacement a longer stroke yields more torque. No one said anything about an RPM limitation on that claim. If the long stroke ultimately limits the engine in ways that keep it from being physically capable of making as much torque as an engine with the shorter stroke then we simply conclude the original hypothesis is invalid and move on.

See my edited post with comparison of two similar engines, one oversquare the other undersquare (Kawasaki vs Honda CBX).

Wasn't the "original hypothesis" about two comparable engines?

If not, the discussion would be meaningless, as we could have said the same about boost pressure as you just did about rpm (undersquare generally tolerates higher boost easier). Just using displacement would make a unusable comparison. CR, RPM, cam timing, ign timing, fuelling, exhaust and intake systems make a HUGE impact. Not just displacement...

You are not seriously suggesting it is fair to compare, say, a 60hp/l engine with a 120hp/l engine? There are many other different factors beside bore/stroke ratio between two such engines

We are talking of a 7500+rpm engine, one which would also be possible with a long stroke (like S54). If you are looking for a 9000rpm NA engine, oversquare is the preferable way to go. BECAUSE of that ability to rev to 9000rpm the engine makes more power and torque than a engine that revs to 6000rpm. But look at the dyno chart and you would see which one would be stronger low down...

I have thought that we discussed apples to apples, ie a engine that could be either over- or undersquare and what advantages either design has.

On the grounds you claimed, I cannot agree that the hypothesis is invalid. The only thing you have established is that a engine that revs to 9000rpm makes more power than a engine that revs to 6000rpm. And that if you want to rev to 9000rpm, you generally want a oversquare engine.

Displacement is just ONE factor. If you really want to know whether over- or undersquare makes more torque, you need to compare two similar engines. Similar as in more than just similar displacement...

[Boss330]

Originally Posted by solstice

Can we dream of a limited edition M3 with a NA GT3 like version of this over square engine at 9000 rpm dumping all the weight of turbo plumbing as an added bonus? If so I want to know now, I'll pay $100k for it if they do.

That would be awesome, and possible with the short stroke S55. If not a BMW version, possibly some of the tuners will go this route

[solstice]

The stroke is almost identical with that of the 991 GT3 so the piston speed at 9000 rpm is proven doable...

[NISFAN]

Originally Posted by solstice

Can we dream of a limited edition M3 with a NA GT3 like version of this over square engine at 9000 rpm dumping all the weight of turbo plumbing as an added bonus? If so I want to know now, I'll pay $100k for it if they do.

Interesting, a limited edition turbo less M3/4 that would struggle to keep up with a 335i? Surely an S65 transplant would be more desirable?

[solstice]

You mean like the GT3 struggles to keep up with a 335i...

[Boss330]

Originally Posted by NISFAN

Interesting, a limited edition turbo less M3/4 that would struggle to keep up with a 335i? Surely an S65 transplant would be more desirable?

If it was at the same state of tune as a 458 it would have 383hp, surely would leave a 335i in the dust

But, this is purely a hypothetical engine config... Doubt BMW will go down that route. But if they do, SOLSTICE was the first to suggest it here

[swamp2]

Originally Posted by NISFAN

The thing about the 458 engine, is it is highly tuned and fettled, which helps almost every performance characteristic. I would put money on the 458 engine achieving over 100% VE at specific revs, which outside of F1 engines, is remarkable.

Incorrect.

Although the 458 has a remarkable engine and certainly s VE over 100%, it is not uncommon for a moderate to highly tuned production engine to also do so. I don't have the data handy, but am highly confident the current M3 does. It is a remarkable breather. One fellow posted here about his own lightly customized B MW (Z4 IIRC) intake and airbox mods that got him up to around and I think over 110% VE. He even built his own simple but accurate test system.

[NISFAN]

Originally Posted by solstice

You mean like the GT3 struggles to keep up with a 335i...

No, the GT3 last time I checked is 3.8 or 4.0 litres depending on year model

[Boss330]

Originally Posted by swamp2

Incorrect.

Although the 458 has a remarkable engine and certainly s VE over 100%, it is not uncommon for a moderate to highly tuned production engine to also do so. I don't have the data handy, but am highly confident the current M3 does. It is a remarkable breather. One fellow posted here about his own lightly customized B MW (Z4 IIRC) intake and airbox mods that got him up to around and I think over 110% VE. He even built his own simple but accurate test system.

I believe you are right on VE. But it still is remarkable, both for the S65 and 458

[NISFAN]

Originally Posted by Boss330

If it was at the same state of tune as a 458 it would have 383hp, surely would leave a 335i in the dust

But, this is purely a hypothetical engine config... Doubt BMW will go down that route. But if they do, SOLSTICE was the first to suggest it here

Yes, but as the engine started out in Turbo format, you would have to do a heap of work to get it to 458 output standard. This type of work is not really required to get 400-450hp out of a 3 litre.

Would it be worth it?

Much cheaper to slot in an S65 engine and DSG unit.

[NISFAN]

Originally Posted by swamp2

Incorrect.

Although the 458 has a remarkable engine and certainly s VE over 100%, it is not uncommon for a moderate to highly tuned production engine to also do so. I don't have the data handy, but am highly confident the current M3 does. It is a remarkable breather. One fellow posted here about his own lightly customized B MW (Z4 IIRC) intake and airbox mods that got him up to around and I think over 110% VE. He even built his own simple but accurate test system.

Hmmm, I think I worked out VE of an S65 at around 91% @ 8000rpm, which is very good in today's CAT filled society. Always open to see a more scientific calculation.

[solstice]

Originally Posted by NISFAN

Yes, but as the engine started out in Turbo format, you would have to do a heap of work to get it to 458 output standard. This type of work is not really required to get 400-450hp out of a 3 litre.

Would it be worth it?

Much cheaper to slot in an S65 engine and DSG unit.

Weight. The E90 335i is 220 lbs heavier than the 328i sporting the NA version of the engine. With a similar saving from the F80 we are at 3300 lbs with no other lightening of the car.

The E92 M3 GTS is 300 lbs lighter than a E92 M3. Give this hypothetical NA F80 limited edition the same savings and we are at 3000 lbs ( with driver which close to an E30... ). Then increase bore as far as cylinder walls safely allows it and you will have quite a machine that will have little problems smoking a 335i and the sound of an NA I6 at 9000 rpm will be worth it alone.