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Running lean
Posted: Mon Jun 01, 2009 12:18 pm
by Draco
I have been wondering....can a car that starts running lean cause a slight increase of boost because of the velocity the gass is pushed out of the combustion chamber?
if not, why would boost increase without setting it, it might be actuator related, but if boost pushes the wastegate open because of a bad actuator spring boost will then decrease....not increase....am I right?
Posted: Mon Jun 01, 2009 12:24 pm
by rat
it will lag from the wastegate opening early before the full boost setting
Posted: Mon Jun 01, 2009 12:45 pm
by Gary57
Running lean wont increase boost, running rich with very little timing will increase the spool up of the turbo and make the boost come in a few 100 rpm sooner.
If you are leaning the car out in load the boost can very well increase due to the increased efficency of the motor.
I have been wondering....can a car that starts running lean cause a slight increase of boost because of the velocity the gass is pushed out of the combustion chamber?
Becuase its leaner that doesnt mean the gasses flow faster...
Posted: Mon Jun 01, 2009 1:17 pm
by Charlvdw
Running lean wont increase boost, running rich with very little timing will increase the spool up of the turbo and make the boost come in a few 100 rpm sooner.
What would be rich and what are little timing?
Posted: Mon Jun 01, 2009 1:25 pm
by Gary57
timing would depend on the load and rpm, rich would be down in the low 10s.
Posted: Mon Jun 01, 2009 1:46 pm
by Charlvdw
Gary57 wrote:timing would depend on the load and rpm, rich would be down in the low 10s.
So you dont adjust the timing on idle then, you just slow the advance rate down?
Posted: Mon Jun 01, 2009 2:00 pm
by Gary57
I cant explain this kinda thing on here it takes time, rather just get your dyno tuned properly and dont fiddle you will break things. It would need to be richer than 10s anyway...
Posted: Mon Jun 01, 2009 2:04 pm
by Pinkfluffybunnys
Hay Draco… Rising EGT's could add extra energy to the exhaust gasses decreasing spool-up time but I think we are talking engine killing glowing manifold lean here.
As Gary said a lot of guys dial out timing in the boost transition area’s and add fuel to get the mixture burning slower to lower lag by a few 100RPM but its normally drag cars as the tune makes the car lazy in those area’s of the map because of the decrease timing and plug fouling AFR’s..
Have you changed anything on the Z could there be a loose pipe? How are you controlling boost?
Posted: Mon Jun 01, 2009 2:12 pm
by Gary57
Rising EGT's could add extra energy to the exhaust gasses decreasing spool-up time
How can a increase in exhaust energy lower the spool up time??
Spot on about the drag cars thing. I have done 2 cars which needed this, it also helps getting off the line...
Posted: Mon Jun 01, 2009 2:23 pm
by Pinkfluffybunnys
How can a increase in exhaust energy lower the spool up time??
? Did I use the wrong word? Pressure difference with higher EGT Exhaust Temps that’s why you wrap or ceramic coat manifolds. Higher temp gas want to expand by having higher EGTs there is more energy in the exhaust gasses making the pressure difference across the turbo more resulting in a lower spool up time maybe not much a few RPM.
When running rich with retarded timing you relying in the slower burning fuel to exit into the exhaust manifold and continue to expand creating the same pressure difference.
The more the difference to quicker the spool , it has it down sides but that’s no needed here
Posted: Mon Jun 01, 2009 2:50 pm
by Gary57
No quite sure where this pressure difference is but and increase in entropy is an increase the energy transfered to the turbine wheel. This increased energy transfer will cause the turbine wheel to generate more power. Basically an increase in exhaust gas will cause the turbine hweel to spool faster.
If you are talking about the pressure difference aross the turbine wheel then the difference the increased EGT will make is neglegible.
We add fuel and retard timing to put more energy into the exhaust. The mixture is still burning and therefore is transfering its energy into heat and work done on the turbine, instead of transfering it into work done by moving a piston down.
Posted: Mon Jun 01, 2009 3:18 pm
by Draco
Pinkfluffybunnys wrote:Hay Draco… Rising EGT's could add extra energy to the exhaust gasses decreasing spool-up time but I think we are talking engine killing glowing manifold lean here.
As Gary said a lot of guys dial out timing in the boost transition area’s and add fuel to get the mixture burning slower to lower lag by a few 100RPM but its normally drag cars as the tune makes the car lazy in those area’s of the map because of the decrease timing and plug fouling AFR’s..
Have you changed anything on the Z could there be a loose pipe? How are you controlling boost?
At the moment the boost is controlled by the actuator....which I suspect because even before I got it tuned I was unable to either increase or decrease the boost by normal means("tapping" air from line to actuator).
Before the tune it barely boosted 0.9 bar because of overfueling, after the tune it went up to a bar. As in the post about the Z I had fuel pressure problems, put in the pump and it was sorted, car stopped pinging, but did not tune yet. A week ago I put in fuel to take it for a drive and directly after I put in fuel it started pinging and boosted to 1.3 bar, checked fuel pressure but it was where I set it, I could see nothing funny.
After the fuel pump install I took it for a drive plenty times and had no problems and as I said, directly when I put in fuel that day I noticed the change, car aslo felt lazier than normal.
I have no doubt that I got bad fuel from the garage, but why would the car suddenly boost 1.3 bar?
Posted: Mon Jun 01, 2009 3:18 pm
by Pinkfluffybunnys
but and increase in entropy is an increase the energy transfered to the turbine wheel. This increased energy transfer will cause the turbine wheel to generate more power. Basically an increase in exhaust gas will cause the turbine hweel to spool faster.
If you are talking about the pressure difference aross the turbine wheel then the difference the increased EGT will make is neglegible.
We add fuel and retard timing to put more energy into the exhaust. The mixture is still burning and therefore is transfering its energy into heat and work done on the turbine, instead of transfering it into work done by moving a piston down.
Basically what I just said, now with added Vitamin B and C and Engineering lingo.
Posted: Mon Jun 01, 2009 3:22 pm
by Pinkfluffybunnys
At the moment the boost is controlled by the actuator....which I suspect because even before I got it tuned I was unable to either increase or decrease the boost by normal means("tapping" air from line to actuator).
Before the tune it barely boosted 0.9 bar because of overfueling, after the tune it went up to a bar. As in the post about the Z I had fuel pressure problems, put in the pump and it was sorted, car stopped pinging, but did not tune yet. A week ago I put in fuel to take it for a drive and directly after I put in fuel it started pinging and boosted to 1.3 bar, checked fuel pressure but it was where I set it, I could see nothing funny.
After the fuel pump install I took it for a drive plenty times and had no problems and as I said, directly when I put in fuel that day I noticed the change, car aslo felt lazier than normal.
I have no doubt that I got bad fuel from the garage, but why would the car suddenly boost 1.3 bar?
Have you check all the vacume lines already?
Posted: Mon Jun 01, 2009 3:27 pm
by Gary57
Basically what I just said, now with added Vitamin B and C and Engineering lingo.
Hehe, that is pretty good I like
.
Draco an increase of 0.3bar means something else has changed not tuning. Check vacuum hoses, actuator, WG not seizing up,etc.