overboost?

[sailorbob]

If the S4S ecu sees MAP exceeding 2.06 bar for 3.175 seconds then fuel is cut.

 

As the MAP sensor cannot measure pressures above 2.07 bar I would be wary of any chip that claims to run higher pressures as the ecu will not be able to calculate the air mass correctly.

[Qavion]

As for boost levels, I don't know about the S4s, but the SE is 0.85 bar nominal and 1.00 bar during overboost.

 

 

Not 0.65?

 

(EDIT: you had me doubting what I'd written, Vince, but I see you've corrected it in the next message)

Edited February 7, 2015 by Qavion

[troutrou]

Sorry my mistake ! I did read the manual a bit too quickly... yes 0.65 nominal, 0.85 is for throttle angles above 75% (if engine is close to warmed up, 75°C minimum), 1.00 bar is for wide open throttle, pedal to the floor.

Edited February 7, 2015 by Vince

[troutrou]

If the S4S ecu sees MAP exceeding 2.06 bar for 3.175 seconds then fuel is cut.

 

As the MAP sensor cannot measure pressures above 2.07 bar I would be wary of any chip that claims to run higher pressures as the ecu will not be able to calculate the air mass correctly.

 

 

Hmmm... that needs some investigation then...

Edited February 7, 2015 by Vince

[Bibs]

We did that 8-9 years ago Vince and discovered most of Marcus's product claims were incorrect.

[troutrou]

Oh, ok !   didn't know that. It's quite a serious affair though, I don't see hum claiming modifying the boost limit if it's not actually technically possible, I don't understand what's going on here...

 

My next best assumption, then, is that the wastegate solenoid actually has some headroom (duty cycle not quite reaching 100% at 1.00 bar of boost), hence it is possible to increase boost beyond 1.00 bar. The MAP capping at 1 bar (of boost, 2 bar total), just means that the ECU then only relies on throttle angle... which is 100% anyway (since this is mandatory for allowing overboost) 

That means that the ECU lacks the help of the MAP above 1 bar, but since this is overboost region, and is only meant to be used for a few second, maybe it's not a vital information under that particular circumstance.

 

I will ask Marcus for some detail...

 

At any rate it's easy to figure it out : just put the car on a dyno, record the max torque (should improve), and hook a pressure gauge to the MAP pipe with a T connector. There is no way to hide the truth this way...

Plus, an ECU log would show if the wastegate solenoid duty cycle is upped or not, which invariably would result in increased boost. The revised fuel MAP would obviously provide the necessary extra fuel to go with it.

Edited February 7, 2015 by Vince

[sailorbob]

The throttle being fully open is not a requirement for overboost; see post 13 in this thread.

 

When the MAP exceeds the maximum pressure the MAP sensor can detect the ecu does not change its method of calculating air mass from speed density to Alpha-N. This is is why running MAP beyond the limitation of the sensor should be avoided.

[troutrou]

The throttle being fully open is not a requirement for overboost; see post 13 in this thread.

 

Wow that's scary... I mean, the Lotus workshop manual clearly states that WOT is mandatory. If one can't even trust the manuals...  :-/

[sailorbob]

I think you may be thinking of the part of the manual that is about the ecu controlling boost above the wastegate setting rather than overboost.

 

It's also worth noting that generally when using engine management systems referring to wide open throttle means throttle values starting before its fully open (typically 75%).

Edited February 7, 2015 by sailorbob

[troutrou]

I was looking at the ECU manual, section EMH.2 page 20, attached below...

 

 

[sailorbob]

That sentence is in there because the boost control is an open loop system and the ecu doesn't have enough control to handle transient boost conditions. It is not referring to the overboost mode which, AFAIK, is not documented in the workshop manuals.

Edited February 8, 2015 by sailorbob

[troutrou]

Well, I am officially lost... time to go to bed for me I think....

[sailorbob]

It is probably easiest to think of the boost pressure being controlled in four ways:

 

Mechanical boost control - the boost pressure is controlled solely by the wastegate actuator.

 

ECU boost control - when conditions are right the ecu uses the boost control solenoid to bleed air away from the wastegate actuator and thereby increase the boost pressure.

 

Overboost - the ecu adds additional dutycycle to the boost control solenoid opening time when using ecu boost control

 

Excessive boost - the ecu cuts fuel to reduce the boost pressure

[Chillidoggy]

Looking at the manual, I read it that wastegate mechanical "boost" is 0.61 bar?

[sailorbob]

0.65 bar on pages 15 and 19 of the EMH manual.

Edited February 8, 2015 by sailorbob

[troutrou]

Assuming you didn't make a typo, then that's 0.65 not 0.61, but still in the ballpark...

 

And how comes my avatar title reads "LOTU" instead of "LOTUS", hmmm.... Bibs ?!

 

 

Edited February 8, 2015 by Vince

[ramjet]

The word builds as you post. Post more.

[troutrou]

LOL !!! Oh OK, I will keep posting then  !

[bens4s]

Id be interested in markus reply to the questions above. I have the red race chip. Now that the car is running properly.. No cel. I floored it yesterday and was reading 17 psi on my boost gauge. In limp mode, I was at 9 psi. I assume that means my wastegate is proper. I didn't notice any cutout from the ecu. I also didn't stay on it long as I was sideways

[troutrou]

Well Marcus told me that his customers don't complain about his chips (bar the dumb ones who are "clever" enough to fit them the wrong way around in the chip socket... but what can you do for such people...) and that they do get the extra >1bar of boost promised. You seem to confirm this, so thank you for your feedback...

[Vulcan Grey]

17psi is 1.17Bar, not sure which boost gauge you are using or the accuracy of it, but I could see a gauge being inaccurate to ~+/-0.1Bar or +/-1.5psi.

 

The original dash gauge on the Esprit is very inaccurate.  Mine pegs the dash gauge almost all the time, and my engine is stock with Marcus' S4s chip.  Though I live at high altitude  

[bens4s]

I just replaced my boost gauge setup with a digital. All new wiring,hose,and sender. It seems spot on with mechanical boost only. its much easier to read and goes to -+30. Its autometer Not some ebay crap. It cost $200

It was worth it.

I did have to relocate the hose to read vacuum.

Edited February 24, 2015 by bens4s

[Bibs]

On 14/07/2014 at 20:39, Bibs said:

http://www.espritfactfile.com/overboost.html

 

Following a post about overboost on facebook which will disappear and be unable to be searched in about an hour...

Looks like EFF was taken down in 2016 but for prosperity and future owners...

https://web.archive.org/web/20220116190242/http://espritfactfile.com/overboost.html

A Lotus Tech showed me a neat trick I had not heard before

If you rev the engine to over 5000 RPM momentarily, but the vehicle speed is zero (i.e. the car is in neutral and/or the clutch is in), then for the next 15 seconds or so,  the ECM will essentially skip over the lines of code that tell it to open the wastegate at its regular setting. This means that on an SE or S4, which normally allows about 0.84bar, you  will be allowed to go to a full 1.0bar. The S4s already goes to 1.0bar,  as does the gauge, so I don't know how far beyond that it will allow you  to go. Let's just say the needle was pegged!

Lotus manuals state that on the SE and S4 max boost is 0.65bar. At coolant temperatures between 75 and 115 degrees Celsius, and at throttle angles greater than 75%, the boost control solenoid valve is activated which allows up to 0.84 bar of boost. Under wide open throttle (100% - WOT) conditions, a short duration of additional boost up to 1.0bar *may* occur.

If boost in excess of 1.01bar is detected for more than 3 seconds, the fuel pump and ignition are shut off as a protective measure. This overboost trick will allow you to get 1.0bar for about 15 seconds, thus skipping the 0.65 and 0.84bar limits temporarily.

On the S4s, 1.0bar is normal max boost and doing the trick gives even higher boost although I have yet to find the specs as to what is the overboost maximum.

Also, note that the maximum boost readings of the boost gauge in the instrument panel will tend to rise with increasing altitude and decreasing atmospheric pressure. Actual boost is controlled by values determined by the MAP sensor which is independent of these variations. What this means is that you can't always believe the readings you get on the gauge as they can be higher that the actual boost.

I was told that the reason overboosting is done is so that Lotus can get lesser 0-60mph times for the Esprit's specs. By allowing overboost under these conditions only, they can get max performance for short bursts, while making sure that owners don't regularly blow their engines.

This would also help explain why magazines get such different 0-60  times. Maybe some magazine's test drivers know this trick and others don't. Add to this, driver skill, weather and track conditions,  heat-soaking of the chargecooler, etc. and you can see how the numbers might vary.

By the way, I feel compelled to put a big disclaimer on this: If you blow your engine trying this out, don't come crying to me!