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Discussion Starter #1
Hello all S85 owners,

Can this engine rev to 10,000RPM

bore: 95mm
stroke: 75.2mm

very "over-square" design: at 1.26 bore vs. stroke

Is it accessories? Alternator, P.S. pump, etc.?

Transmission?

Electronics?

This bore/stroke design is for HIGH RPM.

Love 8,250, but can we get more?


Mr. P
 

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My guess would be the heads would be a point of weakness. If you can convert it to solid lifters, stiffer springs, etc - it could probably rev a fair bit higher (though I don't know about 10k).

Let's also keep in mind that these engines chuck rods stock.
 

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BMW designed this engine specifically to be a high RPM high power engine. There are basically 2 "things" preventing the engine from spinning faster and generating more power. It is not an easy mod.

1)Software
The PCM/DME has hundreds if not thousands of tables. MAny of these tables are actually 3 dimensional surface plots. The control strategy certainly is capable of running this engine at these higher RPM, however the tables likely range from 0 RPM to something just north of 8200 (let's call that MAX_RPM). After that MAX_RPM value, there is no more corresponding data on any of the tables, so the computer has no way of knowing how to further control the engine. Critical tables like desired air load, desired torque, volumetric efficiency, all have RPM as one of the axis. There is no "tuner" that can just extend the data tables. The array may be fixed due to memory allocation. You'd have to run a separate standalone PCM like a Motec or Pectel to really control the engine beyond the 8200 RPM figure.

2)Hardware
The mass of the rotating assembly must be reduced substantially. Increasing the RPM's fundamentally changes all of the stresses on the engine. Higher RPMs means higher accelerations/decelerations of the piston and connecting rods, that will change the fatigue life of the connecting rods in particular, you'd have to go with something that has much less mass and higher strength like titanium connecting rods, pins, con rod bolts, etc. Then you can reduce the counterweights on the crank too. Likely ditch the dual mass flywheel and move to a carbon button clutch also because you probably don't care much about NVH anymore. Maybe go with hollowed out camshafts to further reduce the inertial load on the engine. Yes stronger springs are a must. Stronger chain drive and tensioner to handle the increased centrifugal force of the chain spinning around. The fuel pump needs to be upgraded to handle the increased mass flow rate required to fuel the engine. Basically you have to redesign the whole engine back to the P84 which the S85 is somewhat derived from.
 

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Other than risk of main and rod bearing damage, #1 main issue would be the hydraulic valve actuation. Camshafts are already hollow......and 'fuel pump'....really? Might want to do a couple searches before such a long-winded reply...

Going to/much past 9k would most likely include a total rebuild for any type of long duration reliability(ie. other than bouncing off a rev limiter drag racing or in lower gears). Obviously to make power up there new higher duration cams, vanos tuning/elimination(and optionally new intake manifold) would be needed.
 

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The OP asked a theoretical question and I was providing a real engineering answer about whether the engine could support at 25% higher redline. Sorry you have to read so much.

I'd assume the OP would want to shift the entire power and torque curve and have the max power near max RPM, so peak power would be well beyond ~7700. This would be essentially be a 25% shift of the average RPM the engine would see in operation. This will cause far higher stresses and severely reduced lifespan. The linear and centrifugal forces are at play within the engine are not merely 25% higher.

If you want to maintain proper air/fuel ratio, you need to ensure that the fueling keeps up with increased airflow. The engine is really just an air pump, let's say the intake tract is capable of flowing a 25% increase mass of air to support 10k RPM, you increase the mass flow rate of the fuel by that same amount. I'm not even taking in to consideration increased fueling needs for max power at 12:1 AFR vs 14.1 for stoich. The stock fuel pump has a specific duty cycle, it is not 100%. In fact, I believe several people have swapped in AEM fuel pumps due to the engine running lean at WOT. This would support my statement that it is a required modification. I don't know what the stock Bosch fuel pump is rated for in terms of mass flow rate and at what duty cycle, however, I don't believe it will adequately fuel the engine with an additional 25% demand, if it could it means the Bosch over engineered the pump.

Help me understand what should I be searching for? I just searched for "fuel pump mass flow", "fuel pump flow rate", "fuel pump mass flow rate", "fuel pump gpm".

Why is it "obvious" that VANOS needs to be eliminated for higher RPM? Is it your belief that there is no need to advance or retard timing beyond 8k RPM.

The BMW intake tract (meaning from inlet to cylinder head) is absolutely brilliant and one of the best things about this engine design and vehicle packaging. The curvature profile of the CNC porting of the cylinder head all the way up to the intake runner in the plenum is simply unmatched in any other production engine. I'd like to see flow bench data that supports the belief that the intake system cannot support increased airflow.

My understanding was the S85 camshafts were cast, most production cams are cast. I assumed that they were not hollow casted or the centers machined out. That's fantastic that they are hollow. I'm happy to know that I was wrong. I'll take a closer look at my cams this afternoon.
 

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Discussion Starter #7
Hello All!

This hypothetical question is based on the rotating assembly. The stroke is so small at 75.2mm that piston speeds are not that high.

10,000 RPM a dream, but is 9,000 attainable? I "believe" the rotating assembly is good for it with sorted bearings.

The heads, electronics, accessories, and drive live are a bigger question.

Anyway, this thread is "food for thought" because the S85 is SO over-square in design. Its dimensions are much closer to a motorcycle or F1 car than the Audi/Lamborghini v10's when comparing bore to stroke ratios.

Mr. P
 

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Other than risk of main and rod bearing damage, #1 main issue would be the hydraulic valve actuation. Camshafts are already hollow......and 'fuel pump'....really? Might want to do a couple searches before such a long-winded reply...

Going to/much past 9k would most likely include a total rebuild for any type of long duration reliability(ie. other than bouncing off a rev limiter drag racing or in lower gears). Obviously to make power up there new higher duration cams, vanos tuning/elimination(and optionally new intake manifold) would be needed.
Gmtegear’s response is actually very appropiate and holistic from an engineering point of view. You can definitely rebuild the engine with tougher components but that wont be enough for long term reliability. Apart from the software limitations, design changes to reduce inertial loads and forces are the key to long term reliability if the goal is to have a permanent 9k+ rev limit.


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Hello All!

This hypothetical question is based on the rotating assembly. The stroke is so small at 75.2mm that piston speeds are not that high.

10,000 RPM a dream, but is 9,000 attainable? I "believe" the rotating assembly is good for it with sorted bearings.

The heads, electronics, accessories, and drive live are a bigger question.

Anyway, this thread is "food for thought" because the S85 is SO over-square in design. Its dimensions are much closer to a motorcycle or F1 car than the Audi/Lamborghini v10's when comparing bore to stroke ratios.

Mr. P
I agree with you that this engine can take the revs as is but the question is for how long? Even F1 engines have to be rebuilt after every race.


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Discussion Starter #10
Hello CucoM5,

Agreed! And gmtegear is spot on an normal.

This post was an exercise on the rotating assembly. IT it is SO over-square!

Pic below from an Excel sheet I made...not the best resolution but should have value.

Thanks to All again,

Mr. P
 

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Hello CucoM5,

Agreed! And gmtegear is spot on an normal.

This post was an exercise on the rotating assembly. IT it is SO over-square!

Pic below from an Excel sheet I made...not the best resolution but should have value.

Thanks to All again,

Mr. P
Thats really cool...I’d figure we can make 9k easily and reliably with titanium rods/pistons, stronger springs/timing chains, modified crankshaft and software to support it.


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The OP asked a theoretical question and I was providing a real engineering answer about whether the engine could support at 25% higher redline. Sorry you have to read so much.

I'd assume the OP would want to shift the entire power and torque curve and have the max power near max RPM, so peak power would be well beyond ~7700. This would be essentially be a 25% shift of the average RPM the engine would see in operation. This will cause far higher stresses and severely reduced lifespan. The linear and centrifugal forces are at play within the engine are not merely 25% higher.

If you want to maintain proper air/fuel ratio, you need to ensure that the fueling keeps up with increased airflow. The engine is really just an air pump, let's say the intake tract is capable of flowing a 25% increase mass of air to support 10k RPM, you increase the mass flow rate of the fuel by that same amount. I'm not even taking in to consideration increased fueling needs for max power at 12:1 AFR vs 14.1 for stoich. The stock fuel pump has a specific duty cycle, it is not 100%. In fact, I believe several people have swapped in AEM fuel pumps due to the engine running lean at WOT. This would support my statement that it is a required modification. I don't know what the stock Bosch fuel pump is rated for in terms of mass flow rate and at what duty cycle, however, I don't believe it will adequately fuel the engine with an additional 25% demand, if it could it means the Bosch over engineered the pump.

Help me understand what should I be searching for? I just searched for "fuel pump mass flow", "fuel pump flow rate", "fuel pump mass flow rate", "fuel pump gpm".

Why is it "obvious" that VANOS needs to be eliminated for higher RPM? Is it your belief that there is no need to advance or retard timing beyond 8k RPM.

The BMW intake tract (meaning from inlet to cylinder head) is absolutely brilliant and one of the best things about this engine design and vehicle packaging. The curvature profile of the CNC porting of the cylinder head all the way up to the intake runner in the plenum is simply unmatched in any other production engine. I'd like to see flow bench data that supports the belief that the intake system cannot support increased airflow.

My understanding was the S85 camshafts were cast, most production cams are cast. I assumed that they were not hollow casted or the centers machined out. That's fantastic that they are hollow. I'm happy to know that I was wrong. I'll take a closer look at my cams this afternoon.

Do you know at what power level the stock fuel pump maxes out at? You think increasing the rpm limit with ANY n/a upgrades will push it beyond its limits?.....even with boost(which obviously will lower its max flow) it handles 700+ hp at the crank. Mentioning the fuel pump was a waste of time. Fuel pump cares(ie knows about) pressure and flow, that's it. A very inefficient boosted system may need more pump at 700hp running high boost. The most powerful N/A s85 I've seen dyno'd was a bit past 700hp at the crank....

1000's of tables, mostly 3d....do you know the size of the flash memory on the dme? And its speed....give you a hint, its not referencing anywhere near 1000's of tables in real time....definitely not for spark advance and fuel injection pulse width calcs...

May want to re-read that. Vanos elimination isn't needed for very high rpm power, but either vanos tuning OR elimination and absolutely higher duration cams...

BMW's brilliant intact tract on the S85 is designed for a specific power band, as every intake tract(helmholtz, tract width etc..). The internal velocity stacks are nice. Doubt it's the best of any production engine though. No doubt its bmws best engine. Pushing past 9000rpm and expecting peak hp up there(otherwise why do it at all) doesn't make sense. Shorter runners will be more efficient, length tuned to the rpm your targeting.

I don't believe they machine the centers out....I believe its casted with the space taken up by another substance...check it out.....

Luckily I'm a fast reader, but its just too much fluff(and exaggerations) for me. We all have opinions though, so keep doing you.
 

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gmtegear,

You know what, my replies haven't been so pleasant. It seems we're both big s85 fans, so I apologize for being less than polite. I let dumb little things bug me, ill admit it.

I'm actually working on a project with a built s85 going in a different chassis(a 'custom' one, non bmw). Currently designing a composite intake manifold for it. Although its boosted, it will also make power much higher in the powerband than a stock s85, when I have more to share ill make sure to post on this forum.

Again sorry bout that.
 

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Do you know at what power level the stock fuel pump maxes out at? You think increasing the rpm limit with ANY n/a upgrades will push it beyond its limits?.....even with boost(which obviously will lower its max flow) it handles 700+ hp at the crank. Mentioning the fuel pump was a waste of time. Fuel pump cares(ie knows about) pressure and flow, that's it. A very inefficient boosted system may need more pump at 700hp running high boost. The most powerful N/A s85 I've seen dyno'd was a bit past 700hp at the crank....
I just maxed out the fuel supply on the stock pumps, I am pushing 757hp but using meth to give me some extra wiggle room.
My setup is a little different as I am on a low compression 10.1.1, 5.1L engine and boosting 8psi.

Now upgrading the fuel pumps and fuel supply and then moving to higher boost, only thing holding me back is the new tune I will require.
 

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Discussion Starter #16
Hello Carbons85,

I'm a newbie here at the M5Board, but I have to give you some RESPECT for posting and accepting that we all get frustrated. I hate conflict. My short experience here has been very NICE!

You want grief....try a MR/S board.....grrr and so many strong opinions without REAL knowledge.

Cheers!
Mr. P
 

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9000rpm is attainable on a stock 5.0. Cams and Ported heads and long tubes will allow 9500 which is the limit of the vanos pump. You don't really want to go past this as you don't want to remove vanos the engine will make no power. There is a 6.0 stroker of mine running 9200rpm essentially no limiter. Has titanium rods, billet lightweight pistons, shrick cams, springs, larger valves, ported heads, supersprint long tubes, 880090 thermostat. The only way to make power this high is with a 305 duration camshaft.
 

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Hello all S85 owners,

Can this engine rev to 10,000RPM

bore: 95mm
stroke: 75.2mm

very "over-square" design: at 1.26 bore vs. stroke

Is it accessories? Alternator, P.S. pump, etc.?

Transmission?

Electronics?

This bore/stroke design is for HIGH RPM.

Love 8,250, but can we get more?


Mr. P
.No absolutely.it's 5 liter and for hardware it can't reach more of 8500 rpm
 

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9000rpm is attainable on a stock 5.0. Cams and Ported heads and long tubes will allow 9500 which is the limit of the vanos pump. You don't really want to go past this as you don't want to remove vanos the engine will make no power. There is a 6.0 stroker of mine running 9200rpm essentially no limiter. Has titanium rods, billet lightweight pistons, shrick cams, springs, larger valves, ported heads, supersprint long tubes, 880090 thermostat. The only way to make power this high is with a 305 duration camshaft.
Thanks for sharing...longer duration cams make sense as they will shift the power range into the higher RPMs...how is the power at the upper limit on the 5.0?, is it usable or does it feel like it plateaus? Just curious.

As for the head porting, I would have expected the heads to be ported to their limits by BMW. How much more room for improving these heads is there when it comes to porting? I’m not questioning you just curious to know more as head porting and camshaft upgrade is something I am familiar with and would like to look into it myself later on.


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