overboost?

[jimblob]

I know the s4 has this feature but is it on other esprits too?

[Bibs]

All fuel injected 4 cylinder Esprits.

[jimblob]

even the GT3?

[Bibs]

Even the GT3. You can check if it's working with a Freescan log. 

[jimblob]

ok cheers mate I'll do one when I get the chance

[Chillidoggy]

What's overboost?

[Bibs]

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

 

[troutrou]

The S300 from memory has no overboost, the turbo blows full speed all the time !

Edited July 14, 2014 by Vince

[jimblob]

interesting I wanna know what the GT3 and s4s overboost to because I have 1 bar already

[Chillidoggy]

I just may hide this one from the missus.

[sailorbob]

The information on the espritfactfile website is incorrect about how the overboost works. The maximum boost allowed is not increased, what happens is the wastegate dutycycle is increased (by just under 44% in the SE code).

[Chillidoggy]

So does that mean the waste gate doesn't open until 44% more pressure has been achieved?

[sailorbob]

The wastegate dutycycle is the percentage of time that the boost control solenoid port vent is open for.

In overboost mode the ecu adds 44% to the calculated wastegate dutycycle for the current rpm and throttle position. So if the wastegate dutycycle is normally 0% (i.e. low rpm and throttle position) it becomes 44% in overboost mode. If the wastegate dutycycle is normally 50% (i.e. high rpm and 2/3 throttle position) it becomes 94% in overboost mode. Wastegate dutycycle obviously cannot exceed 100% (where the boost control solenoid port vent is open full time).

Edited July 15, 2014 by sailorbob

[Chillidoggy]

So is the duty cycle, and therefore presumably the owner's driving style, "learned" by the ECU?

[sailorbob]

The wastegate dutycycle is defined by a table of rpm vs throttle position. There is some adaptive learning applied (above 94.1% throttle and 2810 rpm in the stock SE code) to the dutycycle to adjust the boost so that it meets the required maximum boost setting.

[sailorbob]

The S4S overboost additional wastegate dutycycle is only 2.35%. Probably reduced as the S4S start to run wastegate dutycycle at 25% throttle position (stock SE is 75%)..

[jimblob]

Thanks for clarifying how the overboost works Derek, I guess the GT3 would work the same as the s4s.

[sailorbob]

The GT3 overboost additional wastegate dutycycle is the same as the SE and S4.

[jimblob]

So just to see if I understand this correct your saying that the over boost function just adds boost where there normally would be none and for longer through the rev range?

[sailorbob]

Hmm, not really, I suppose using the term overboost is a bit misleading. The overboost mode increases the amount of air bled away from the wastegate capsule thereby creating the possibility of increased boost. It will generally increase boost but not always as the turbocharger may not be able to pump enough air under certain conditions regardless of the amount of air being bled off.

[troutrou]

I think a simpler way to put it is to say that the waste gate included in the turbo, mechanically/physically sets the "normal"/sustainable boost level of the engine, whatever it is for a particular engine (0,65b for an SE ?).

 

 

Then on top of that basic mechanical setting, in order to get some extra ponies under hard acceleration at slow to medium speeds, the ECU uses a trick to cheat the wastegate.  That trick is the wastegate solenoid. The ECU uses the solenoid to divert some of the boost away from the wastegate. The wastegate setting obviously doesn't change, but it now sees only a fraction of the actual boost happening in the inlet (said amount being accuretely controlled by the ECU, by means of the duty-cycle applied to the solenoid).

 

The ECU has therefore, technically, potentielly, the ability to completely disconnect the wastegate (by diverting 100% of the air), thus actually rendering the wastegate inoperative. There is then nothing keeping the turbo from blowing the engine (rather than blowing into...), other than the turbo's  technical specification, by its construction/design limitations.

 

Obviously the ECU won't allow that to happen, it's aim is only to add a little bit more boost under some circumstances, it has no particular interest in destroying the engine

 

 

Well not sure that was any clearer in the end.. .but well I tried !

Edited July 19, 2014 by Vince

[Escape]

Thet's a very clear explanation, it's how I understand the system to work, but I couldn't put in in writing like that.

It also explains why it's relatively easy to increase boost by changing the chip, because the duty cycle is increased.

 

Filip

[bullit]

wat ? ... i replaced mine  with a  gt28  ball bearing turbo, and used an classic boost regulator

(hand regulated)  price 30 dollar. working outstanding no problems at all , full power always

some pictures  of this project  in the treat of

http://www.lotusforum.be/viewtopic.php?f=16&t=5873

vr gr  sietse // holland

Edited August 13, 2014 by bullit

[Chillidoggy]

Where does the air that the boost solenoid bleeds off go to? Atmosphere? Inlet manifold? And what does the S4s overboost to?

[troutrou]

Yes the wastegate solenoïd vents to the atmosphere, as you can easily see by just looking at it in the relay box, it's screaming at you ;-)

 

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. So the S4s has to be a little over 1 bar then, maybe 1.1.    PUK rate their 310 bhp S4s chip as 1.1 bar, and red race chip at 1.25, so I guess a stock S4s chip hast to be somewhere between the 1.0 and 1.1...

Edited February 7, 2015 by Vince