S50 Blown Headgasket

[King Mufasa]

^^^ Damn good power!! where are you located? I sure could use a tuner.

[328ijunkie]

To keep things fair, I will answer and inform unbiased.

Duty cycle in general is defined as the ratio of on time vs off time during a period of time. In this case for injection, this would be the amount of time the injector is driven low vs RPM.

As the RPM increases, the number of cycles increases regardless of injector pulse width.

At 1000rpm, it takes the engine 60ms (0.060s) to turn once. So consider a full cycle x2 = 120ms.

At 10000rpm, it takes the engine 6ms (0.006) to turn once. So consider a full cycle x2 = 12ms.

If I just use 10ms of injection time in both situations,
the duty cycle at 1000rpm is 8.3%,
the duty cycle at 10000rpm is 83%

Hope that puts into perspective the dynamic change of an engine through the RPM range!

For fun, just picture at high RPM, and high duty, how long the injector is spraying at a closed intake valve waiting for it to be opened :) Consider the intake valve is only open for a 1/4 of the cycle (it's actually less) - at 10k rpm - that's 3ms!

The injector offset factor has not been mentioned. This is the lag time of the injector, also called deadtime. Injector duty doesn't factor lag time, but because of lag time, anything over 85-90% duty should be considered the injector actually never closes between cycles because of this. Average high impedance injector deadtime at 14v is probably somewhere around 0.800ms for example. A number of factors effect this like battery voltage, fuel pressure, fuel pressure differential (boosted cars), and more.

Running very high duty cycles is bad because :

The injector overheats (it is on all the time)

Control of the injector is not accurate. Most injector flow rates cap out at a certain duty cycle - it is basically open all the time

If the injector timing not adjustable, the mixture per cycle to be uncontrollable . Typically the mixture actually becomes uncontrollably rich, just before it becomes uncontrollably lean. (I can write 2 more pages on this)

Oh ya, and I almost forgot to mention you are at the maximum flow of the fuel system. This means if you have any need to compensate for temps/altitude/etc - it won't work.

Installing a larger injector allows much more accurate control of the injector combating all of the above issues.

So, you guys probably wonder why they just don't install a huge injector in every car?

This is because in order to improve control resolution of the fuel injection system, the OE will ALWAYS choose the smallest injector possible for the application.

For idling and cruising, the more range the ECU has to open the injector up, the more control it has regarding flow.

1ms of variance is much more sensitive on a huge injector vs a small injector. You are still dealing with a mechanical part the has to be powered up, pintle has to move, etc. Factor in the lag time of the injector and this becomes very important!

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The best option is running the "smallest" injector possible with proper margin at high rpms.

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This is similar to the OE concept, and why for performance upgrades they normally offer upgrades in small increments (19-21-24-28-32-etc)

The other reason they upgrade in small increments is because with the factory ECU it is sometimes difficult to remap the fuel system regarding a large flow change of an injector.

That's where you get those cars that run like shit at idle with a medium size injector typically. It is the control system that is the issue in that case, not necessarily the injector.

To throw in a curve ball, if your control system is good (proper ECU system, no negative effects), there are some tricks with running an oversized fuel injector for the application. Not being limited on injector timing due to high duty cycles allows the calibrator more options to experiment with. I have done a few cars prepped for E85 where on 93 octane (E10) the duty cycle was less than 50% at redline, but the cars picked up power with some tricks. This was also comparing to previous fuel systems running at 85+% duty though.

Basically exactly what i said sans i didnt mention dead time to keep it simple
Only things i disagree with is modern injectors dont really overheat. And mind being held open 100% less than they do opening and closing...

And as i said, over ~85% isnt ideal (not even considering dead time) because youre firing at the back of closed intake valves...

328ijunkie,

You should be able to calculate actual injector duty easily if you have your PW logged. It is simple math. If you are already at 85-90% duty, you will find you will eventually be tapped if you keep doing stuff to make more power. In your log, you can also see the injection time drop off on the top end since the VE of the engine is dropping off. That is helping the situation, and typical with M50 series engine.

Can you explain what you mean by these engines not liking sub 12 mixtures? Typically on normally aspirated engines, that could be true, but not necessarily the case always. For example, a richer mixture can control knock at high RPM, which is an issue for these engines around 6000rpm.

I am actually the one who tuned berlow94s Vipec, and while I am not looking at his calibration, I imagine the mixture target matches the ignition advance appropriated for making maximum power safely. He uses his car for road racing, and we actually looked at his detailed ECU logs (that the Vipec has on board) after his dyno sessions to totally validate mixture, knock, and more.
Regarding the power levels he is at, upgrading to the larger injector allowed for much more accurate control of the fuel mixture, especially at high RPM.

berlow94,

There are lots of cars that can idle with 1000+cc injectors at 14.7:1 depending on the control system, the ECUs ability to compensate for flow, etc. I hope reading the above puts that into more perspective for you as well!

I posted above the IDC (again sans dead time, which is much less than .8ms on factory injectors)

As far as the mixtures go, of all the 24vs ive tuned they love 12-13AFRs at WOT, below 11.5 you get rich misfires/detonation so it hurts you not helps you.... S54s are different as are other BMW engines, i was speaking mainly about the M5X.

Also if you look at my dyno thread 50+% of the cars i tune are track only as well. I make sure they are tuned to not explode :P.

I'm making around 290 to the wheels on a dynojet.


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Would love to see that dyno sheet and full specs... 290whp is a crapton out of a 24v.

[M3PO]

The guy that I bought this kit from was making 280 WHP with stock S52 bottom end.

[2mAn]

I would probably buy another head that will be rebuilt, or is already rebuilt. A quick way to avoid installing a warped head.

I guess this is one downside to redlining everywhere ;)

[npavlo]

Basically exactly what i said sans i didnt mention dead time to keep it simple
Only things i disagree with is modern injectors dont really overheat. And mind being held open 100% less than they do opening and closing...

And as i said, over ~85% isnt ideal (not even considering dead time) because youre firing at the back of closed intake valves...



I posted above the IDC (again sans dead time, which is much less than .8ms on factory injectors)

As far as the mixtures go, of all the 24vs ive tuned they love 12-13AFRs at WOT, below 11.5 you get rich misfires/detonation so it hurts you not helps you.... S54s are different as are other BMW engines, i was speaking mainly about the M5X.

Also if you look at my dyno thread 50+% of the cars i tune are track only as well. I make sure they are tuned to not explode :P.



Would love to see that dyno sheet and full specs... 290whp is a crapton out of a 24v.

Wait,
You are saying that you that an M50 will rich misfire below 11.5?

Never had that issue... Maybe that's a factory ECU thing.

And you are saying that the engine detonates at rich mixtures?

That's very uncommon too, since detonation is usually controlled by running a richer mixture as a general rule of thumb.

You mention you tune for the track, but all your dyno thread shows is WOT performance tuning. It is all in STD correction too that exaggerates the numbers.

Have you ever tried a good standalone system for these? Here is a plot of a STOCK S52 with a 3" exhaust using the same EMS system Andrew has. SAE correction too. These are done so everything is addressed. WOT, part throttle, deceleration, transients, proper lockouts, etc. Internal ECU logging, wideband closed loop, individual knock, CAN output, and tons of motorsport functions. That car was on 24# injectors, and maxed out essentially.

[M3PO]

I would probably buy another head that will be rebuilt, or is already rebuilt. A quick way to avoid installing a warped head.

I guess this is one downside to redlining everywhere ;)

It's weird though, I don't understand what could possibly have caused it! Yeah, I drive it hard but my cooling system works great!

My buddy loaned me his CLK63 Black Series for as long as I need it so there's no rush now.

[2mAn]

It's weird though, I don't understand what could possibly have caused it! Yeah, I drive it hard but my cooling system works great!

My buddy loaned me his CLK63 Black Series for as long as I need it so there's no rush now.

wow, I need a buddy like that. I love that AMG V8 I am daily driving a C350 now and am itching to make it noisier but want to keep it civil and get stupid with the E30. Its never enough, and I keep changing my mind.

You can take your time, but dont get too sidetracked. Get this thing back on the road!!!

[328ijunkie]

Wait,
You are saying that you that an M50 will rich misfire below 11.5?

Never had that issue... Maybe that's a factory ECU thing.

And you are saying that the engine detonates at rich mixtures?

That's very uncommon too, since detonation is usually controlled by running a richer mixture as a general rule of thumb.

You mention you tune for the track, but all your dyno thread shows is WOT performance tuning. It is all in STD correction too that exaggerates the numbers.

Have you ever tried a good standalone system for these? Here is a plot of a STOCK S52 with a 3" exhaust using the same EMS system Andrew has. SAE correction too. These are done so everything is addressed. WOT, part throttle, deceleration, transients, proper lockouts, etc. Internal ECU logging, wideband closed loop, individual knock, CAN output, and tons of motorsport functions. That car was on 24# injectors, and maxed out essentially.

Any engine can rich misfire/detonate, esp in NA form. You maybe are confusing detonation with pre-ignition. Detonation happens AFTER the spark plug fires....

And i dont have a ton of experience tuning M50s (maybe done 10) but other M/S5X familys are another story.

In regards to my thread showing only WOT Dyno plots, A i dont have an eddy brake dyno and B: how else do you show a non WOT dyno plot? Most of the tunes i do involve 1-1.5hrs on dyno and 2-3 on street to dial in PT.

Setting up a standalone on any engine is alot harder than you make it seem. Cold start enrichment, accel/decel transients, vanos, knock frequencies (which you can guess/learn from seeing it but is no where as finely tuned as a stock DME), etc.

Ive played with Haltec as well as Megasquirt. Only things i like over a stock ECU are wideband AFR targeting (which newer BMW ECUs do anyway), as you mentioned 'motorsports functions', as well as CAN output (on the nicer ones: Motec)

Either way, i understand your point of view but setting up a proper aftermarket standalone without a base tune that someone else has already spent tons of hours on, takes tons of hours....

[npavlo]

Any engine can rich misfire/detonate, esp in NA form. You maybe are confusing detonation with pre-ignition. Detonation happens AFTER the spark plug fires....

And i dont have a ton of experience tuning M50s (maybe done 10) but other M/S5X familys are another story.

In regards to my thread showing only WOT Dyno plots, A i dont have an eddy brake dyno and B: how else do you show a non WOT dyno plot? Most of the tunes i do involve 1-1.5hrs on dyno and 2-3 on street to dial in PT.

Setting up a standalone on any engine is alot harder than you make it seem. Cold start enrichment, accel/decel transients, vanos, knock frequencies (which you can guess/learn from seeing it but is no where as finely tuned as a stock DME), etc.

Ive played with Haltec as well as Megasquirt. Only things i like over a stock ECU are wideband AFR targeting (which newer BMW ECUs do anyway), as you mentioned 'motorsports functions', as well as CAN output (on the nicer ones: Motec)

Either way, i understand your point of view but setting up a proper aftermarket standalone without a base tune that someone else has already spent tons of hours on, takes tons of hours....

Hey man, sorry took so long. I just saw this.

I think we are making similar points. Absolutely it takes a while to get the standalone ECUs setup right, but when it's right... its awesome.

For example, I guarantee you the knock control on a link/haltech/emtron/motec/etc is 10x better than the factory ECU. You don't have to guess on frequencies if you know some details about the engine, plus you can set up windowing, proper lockouts (including transients), adjust gain per cylinder, adjust threshold per cylinder, and count on each cylinder even individually. You can set the retard rate, advance rate, etc. It is pretty comprehensive, and a lot of factory ECU tuning can't even look at those settings. Kinda hard to adjust when the bore size of the engine changes, or the engines sleeved, etc.

You also don't need a Motec for a CAN output anymore! Andrews ECU (that's less than $2gs complete) outputs almost 40 channels over CAN to his motorsport dashboard which he can configure to display whatever he wants, plus alarm functions, etc. It really modernized the old stuff.

M5x I consider 2.5, 2.8, 3.0, 3.2 generation. Sorry I should have clarified.

Ultimately, it all depends what the customer wants and what their budget is. I'd keep an open mind about it regardless!

[328ijunkie]

For example, I guarantee you the knock control on a link/haltech/emtron/motec/etc is 10x better than the factory ECU. You don't have to guess on frequencies if you know some details about the engine, plus you can set up windowing, proper lockouts (including transients), adjust gain per cylinder, adjust threshold per cylinder, and count on each cylinder even individually. You can set the retard rate, advance rate, etc. It is pretty comprehensive, and a lot of factory ECU tuning can't even look at those settings. Kinda hard to adjust when the bore size of the engine changes, or the engines sleeved, etc.

Yes factory ECU isnt as dynamic but it is extensively tested/tuned starting with OBD2 cars. I agree aftermarket ECUs have more capabilities in that regard but as far as accuracy is concerned, nothing can beat the factory flash. I have tuned motec setups and even those have their shortcomings on an unfully documented engine.