How much does 1psi usually change your a/f?

[jakez]

Sorry but I couldn't find any info on this in Google or zilvia.

Based on a mostly stock sr20det 7psi and afr's at 11.6 at redline, if I were to turn the boost up 1psi how much leaner would the a/f ratio go up?

One more little question so I don't have to make another thread - is it relatively safe to run the sr20det a bit lean (12.2 @ 7500rpm) if you never rev past 6000rpm?

Thanks for any help!

[army240]

It all depend on the tune, injector setup, maf...

If you are at 7 Psi on a stock setup (Stock ECU, 370cc, t25 s13 Blacktop) and you crank it 1 psi... the ECU will adjust itself and inject more fuel...

After some more PSI, the ECU will either not be able to calculate the airflow(MAF Maxed out(15 psi on S13)), or the injector will be maxed out and won't be able to inject more fuel.

Anyway, I say that after every major mods, you get a new tune. This is the only way you won't blow your engine and then cry.

Frank

[jakez]

Originally Posted by army240

It all depend on the tune, injector setup, maf...

If you are at 7 Psi on a stock setup (Stock ECU, 370cc, t25 s13 Blacktop) and you crank it 1 psi... the ECU will adjust itself and inject more fuel...

After some more PSI, the ECU will either not be able to calculate the airflow(MAF Maxed out(15 psi on S13)), or the injector will be maxed out and won't be able to inject more fuel.

Anyway, I say that after every major mods, you get a new tune. This is the only way you won't blow your engine and then cry.

Frank

Wait so if I'm cranking the boost up the ECU is going to supply more fuel by itself??? My friend told me that only cars with a MAP do that and that my MAF powered sr simply reads the air flow but doesn't adjust anything.. and he wonders why I trust people on a forum more than him lol.

This is an s13 redtop btw if that matters.

[army240]

lol, yeah, this is the beauty of electronic injection, it can adjust itself (till a certain point)!

To be technical(as I like to be lol), the MAF actually only read the airlow, and send this information to the ECU... and with other sensor(TPS, CTS, CAS, Knock sensor, O2 sensor, etc...) the ECU will adjust the injection pulse and ignition timing to be optimal.

This is out how an ECU works, 3 phase. Input, Process, and Output.

Anyway, I hope it help you understand a little bit... if you need more info, feel free to ask!

Frank

[jakez]

Thank you Frank that gave me a HUGE peace of mind!

I'm only trying to up the boost to about 9-10psi and I thought it was simply going to lean the engine out on the same amount of fuel, but if the ECU adjusts then I should see the same a/f ratios after I turn it up a few psi?

[army240]

yeah exactly, you should see the same A/F ratio.

What is the rest of your setup?

[jakez]

Originally Posted by army240

yeah exactly, you should see the same A/F ratio.

What is the rest of your setup?

I bought this s13 with a redtop already in it and as far as I know it's all stock with a fmic, intake and (3"?) megan exhaust. Oh and bk7re(?) plugs gapped to like .038 but I'm going to lessen the gap a bit to .035 before I up the boost.

I have my uego wideband sensor installed too far down the exhaust (on the test pipe) but still seeing 11.7-12.0 at redline so I'm trying to up the boost a tad and still keep it in that range, when I relocate the sensor to the downpipe I should see that I'm plenty safe on the a/f's.

[jakez]

Wow, so I got around to installing the profec today, slowly turned up to 10psi and then 12psi just to see, surprisingly the air fuel ratio is much better now on the higher boost! I'm seeing 11.8 around 6000rpm now on both 10 and 12psi. And that's with the wideband sensor over 3ft away from the turbo, I should be pig rich at redline.

I was planning on only going to 10psi on the stock t25 but I think I will make it 12psi hi boost (the feeling between 10 and 12 is a night and day compared to 7 and 10!) for racing or special runs 10psi for daily driving and if it happens to kill the turbo eventually then so be it I'll goto a t28. Only thing I'm worried about at 12psi is if I'm maxing anything else out besides the turbo? I think I'm still on a stock fuel pump but I need to check, hoping it's a walbro lol.

[mattsil80wis]

on a t25 go to 14psi....i ran mine like that for a year and never had any problems...i would put low boost at 7psi and than high at 14psi...i had my t25 spike at 16 and hold at 14psi

once you hit amore than 14psi you will max out the injectors/maf

i would just make sure a walbro is in the tank also...takes 5 mins to check so its worth it

[sean350z]

First off, the stock ecu does not 'adjust itself' in the sense that you can boost to 20psi and it'll compensate to a desired AFR by adding more fuel.

The stock ecu is set to flow the injector at a certain duty and advance or retard timing per load that's read off the MAF. It all depends on the map that's in the ECU ok. The load difference of 1psi is very slim and will likely not cause any variation in timing and injection duty in the maps.

The only time the ecu 'adjusts' is when the it senses knock and the knock fuel maps and timing maps get activated and timing is retarded. The ecu is set based on the maps inside until you 'tune' them.

[army240]

Originally Posted by sean350z

The only time the ecu 'adjusts' is when the it senses knock and the knock fuel maps and timing maps get activated and timing is retarded. The ecu is set based on the maps inside until you 'tune' them.

Yeah, it is called correction. There is actually a lot of correction going on in an ECU... Coolant temp, Knock, TPS, TPS Accel, IAT etc... But correct me if I'm lost, but I think there is only 2 Map in an ECU... a fuel map, and a ignition map. An ECU can't store 2 fuel map and switch between them. It will only correct the final fuel trim with all the data from those sensors. Same for the ignition...

If you can have more MAP in an ECU, can you provide an exemple? I would like to read more on the subject!

Thank you!

Frank

[sean350z]

I pretty sure most SR ecu's have two fuel maps and two ignition maps. The second set being the knock maps. If knock is sensed the ecu reads from the knock maps where timing is retarded and fuel duty is greater.

[1slowS13]

really depends

here in nevada, stock blacktop with a s15 t28 on 7 lbs is reading 12-12.5 AFR on WOT, i had to fine tune it with an safc.. but thats given our sub 120 degree weather here, daily..

[army240]

Originally Posted by sean350z

I pretty sure most SR ecu's have two fuel maps and two ignition maps. The second set being the knock maps. If knock is sensed the ecu reads from the knock maps where timing is retarded and fuel duty is greater.

The only thing that bog me with that theory is that Knock is not like "On" or "Off". It's kind of progressive... so that's why it's easier to say it's a correction instead of a different MAP...

Frank

[steve shadows]

Maybe this will make it a bit clearer,

The stock ECU and most all Nissan EFI systems are based on MAF, they use the hot wire to calc air flow and figure out VE based fuel correction from there for the amount of fuel injected in the motor.

You're kind of talking about MAP based tuning when you say AFR or Fuel inputs per PSI. This is what a PFC DJETRO would do or an AEM with an external MAP of Haltech etc.

With a MAF based system the computer is not correcting or deciding fuel input based on pressure, it's doing it based on volume of air coming in the motor for the most part. A better way to try to understand this is for Load X or Volume X coming in the motor the AFR will probably change up and down if the fuel going in the motor in the same example is constant and doesnt change.

Our Nissan turbo motors have rising rate pressure regulators which is why it's possible on a stock or close to stock SR setup to turn up the boost without doing any other mods to the motor and not blow it up. The fuel pressure adds 1 lb of fuel pressure to every lb of boost keeping the AFR more or less within the acceptable range for the stock ECM/ECU, which is actually closer to 12.5:1 AFR if we're talking a JDM Nissan Motor with N62 type or N63 type ecu for example...

cheers

[army240]

Steve, what about the "2 different Fuel MAP" or "2 IGN MAP" in one ECU, used for knock control?

Frank

[Biggamehit]

Very good info.. to add also almost all manufacture tune the ecu to be a little richer for safety. If you put a stock car on a dyno you will see it over and over AFR's around 12.8 13ish...well depending on ambient temps etc.

[jakez]

Well when I was running stock 7psi the afr's I was seeing on my wideband were 11.8-12.0 at redline, as if the engine came with a perfect tune.
After turning the boost up to 10psi-12psi the afr's are now pig rich, 11.8 @6000rpm probably 11.5-11.6 at redline.

So I'm guessing my car is sensing knock and retarding timing and increasing fuel? Isn't knock or changing timing a bad thing?

[sean350z]

Originally Posted by jakez

Well when I was running stock 7psi the afr's I was seeing on my wideband were 11.8-12.0 at redline, as if the engine came with a perfect tune.
After turning the boost up to 10psi-12psi the afr's are now pig rich, 11.8 @6000rpm probably 11.5-11.6 at redline.

So I'm guessing my car is sensing knock and retarding timing and increasing fuel? Isn't knock or changing timing a bad thing?

The stock fuel map is very rich in the high rpm/load values from the factory so it's likely that's what you are seeing with rich afr at higher loads.

Also it's doubtful you are running into the knock maps because the flags (where the ecu listens) for knock are mostly in the low rpm/high load section of the maps.

[negrosx13]

o2 is what tells the ecu,how much fuel and air is going out. ecu takes the info and allows more or less fuel for a better mixture,this goes on no matter what happens(unless unplugged).

Also fatory boost is 11psi!!!!!!!!!!

[army240]

Originally Posted by negrosx13

o2 is what tells the ecu,how much fuel and air is going out. ecu takes the info and allows more or less fuel for a better mixture,this goes on no matter what happens(unless unplugged).

Also fatory boost is 11psi!!!!!!!!!!

First of all... an oxygen sensor sense only... well... oxygen. If there is a lot of oxygen in the exhaust, it's because the mixture was lean. If there is only a small amount of oxygen in the exhaust, it's because the mixture was rich. The factory o2 is a narrowband(working from .1 to .9V), and can't "tell" the exact amount of oxygen in the exhaust. It just tell if you are richier or leaner than it should be.

Also, it only work when the engine is in "Closed loop". The state is reached when the engine is at working temperature, along with other parameter, like when you aren't WOT. When you slam the gas pedal, it won't take care of the o2 feedback, because it has primarely made for fuel economy, which you don't care when you are WOT.

And factory boost is 7psi... I don't know where you read it was 11!

Frank

[s14unimog]

Originally Posted by army240

And factory boost is 7psi... I don't know where you read it was 11!

Incorrect sir... The factory actuator has a spring rate to hold 7psi and the standard Silvia has a boost solenoid (as do most all factory turbo applications) to maintain 10-11psi. This is done so the ECU can limit boost supply if there is an issue (high coolant temperatures, etc.)

Saying an S13 SR20DET's factory boost is 7psi is like saying an Evolution's factory boost is 10psi. They use a boost solenoid to achieve the factory 19psi. An S13SR is a dog at 7psi

[SLiDe_WaYz]

Originally Posted by s14unimog

Incorrect sir... The factory actuator has a spring rate to hold 7psi and the standard Silvia has a boost solenoid (as do most all factory turbo applications) to maintain 10-11psi. This is done so the ECU can limit boost supply if there is an issue (high coolant temperatures, etc.)

Saying an S13 SR20DET's factory boost is 7psi is like saying an Evolution's factory boost is 10psi. They use a boost solenoid to achieve the factory 19psi. An S13SR is a dog at 7psi

This guy is correct. Factory boost is 10-11psi. The actuator is set at 7. So you only reach 7psi. This is why most people who use a stock setup get the HKS actuator which raises boost levels to around 12psi on the actuator.

So technically yes 11psi is factory, and yes 7psi is the wastegate actuator psi.

[army240]

Originally Posted by s14unimog

Incorrect sir... The factory actuator has a spring rate to hold 7psi and the standard Silvia has a boost solenoid (as do most all factory turbo applications) to maintain 10-11psi. This is done so the ECU can limit boost supply if there is an issue (high coolant temperatures, etc.)

Saying an S13 SR20DET's factory boost is 7psi is like saying an Evolution's factory boost is 10psi. They use a boost solenoid to achieve the factory 19psi. An S13SR is a dog at 7psi

Ok thanks for the info! I have never installed that boost solenoid on my swap... lol

But what you say make sense!

Frank

[s14unimog]

Originally Posted by army240

Ok thanks for the info! I have never installed that boost solenoid on my swap.

Not many people do.

[smelly240]

The s13 sr ecu requires a knock sensor failure to enter the knock maps. You cannot enter the knock maps without some sort of sensor failure... even having 2 spun rod bearings we couldnt get one to switch over - even tried a brand new sensor. So pretty much - without destroying or unplugging the knock sensor - YOU ARE NOT ON THE KNOCK MAPS.

Nissans also ignore knock sensor inputs after around 4000rpm - they understand that the units are unreliable at distinguishing between normal engine noise and knock.. Even the best new ecu has difficulty with this.

The new and better way to monitor knock is all done through monitoring the coil activity after the spark... pretty much it has a oscope that watches fluctuations after the cylinder fires. No more crappy piezoelectric microphone BS.

you can disable the stock o2 sensor and the car will make the same power - at WOT o2 feedback is disabled... Army is correct on this - however fuel economy is not the reason for this sensor - emissions is. MOST cars are set up LEANER than stoich without o2 feedback - so technically the o2 sensor feedback will fatten the car up and use more fuel.

11psi - this has been covered for years...

Stock S13's get extremely rich up top - like 9.9-10.2 when they're stock @ 11-12psi. they're good up until about 5000rpm and then the AFRs will just hit the floor. also - they come with remarkably conservative timing maps.

[army240]

Originally Posted by smelly240

The s13 sr ecu requires a knock sensor failure to enter the knock maps. You cannot enter the knock maps without some sort of sensor failure... even having 2 spun rod bearings we couldnt get one to switch over - even tried a brand new sensor. So pretty much - without destroying or unplugging the knock sensor - YOU ARE NOT ON THE KNOCK MAPS.

So there is really knock maps for ign and fuel on stock ECU? I am kinda stumped hearing that... I tought it was like the EMS and PFC who just correct the fuel trim and retard the ignition until no more knock is heard by the sensor.

Thanks for the info!

Frank

[s14unimog]

yup, two separate separate maps for both fuel and timing. If you have a CEL for a faulty knock sensor it will stay tracing the knock map. I've copied my tuning adjustments to both maps for this reason.

Oh, and another thing you mentioned earlier a plug gap of 0.035". You'll find yourself closing that down to 0.025-0.028" once you get at/over 14psi. Hopefully you won't be doing this on that stock turbo though.

[jakez]

Originally Posted by s14unimog

yup, two separate separate maps for both fuel and timing. If you have a CEL for a faulty knock sensor it will stay tracing the knock map. I've copied my tuning adjustments to both maps for this reason.

Oh, and another thing you mentioned earlier a plug gap of 0.035". You'll find yourself closing that down to 0.025-0.028" once you get at/over 14psi. Hopefully you won't be doing this on that stock turbo though.

I gapped them from .038 to about .04 (because I read that you should gap as wide as possible without misfiring) before installing the boost controller and the car ran fine, the same as .038.

While installing the boost controller I put them down to like .035 and the car was stuttering/sputtering sometimes off the line or when driving with light throttle (afrs rich). Regapped them again to like .037 - .038 now on 12psi and it fixed the stuttering problem. Although the problem never had anything to do with the amount of boost I was running because it only happened near idle rpms.

[Def]

Originally Posted by smelly240

The s13 sr ecu requires a knock sensor failure to enter the knock maps. You cannot enter the knock maps without some sort of sensor failure... even having 2 spun rod bearings we couldnt get one to switch over - even tried a brand new sensor. So pretty much - without destroying or unplugging the knock sensor - YOU ARE NOT ON THE KNOCK MAPS.

Nissans also ignore knock sensor inputs after around 4000rpm - they understand that the units are unreliable at distinguishing between normal engine noise and knock.. Even the best new ecu has difficulty with this.

The new and better way to monitor knock is all done through monitoring the coil activity after the spark... pretty much it has a oscope that watches fluctuations after the cylinder fires. No more crappy piezoelectric microphone BS.

you can disable the stock o2 sensor and the car will make the same power - at WOT o2 feedback is disabled... Army is correct on this - however fuel economy is not the reason for this sensor - emissions is. MOST cars are set up LEANER than stoich without o2 feedback - so technically the o2 sensor feedback will fatten the car up and use more fuel.

11psi - this has been covered for years...

Stock S13's get extremely rich up top - like 9.9-10.2 when they're stock @ 11-12psi. they're good up until about 5000rpm and then the AFRs will just hit the floor. also - they come with remarkably conservative timing maps.

The stock S13 SR timing map is stupid conservative in the midrange, then gets super aggressive at higher RPM. This is even more of a problem if you put something like a T28 that can flow more air than the T25.


Run the T25 at 14 psi - they last for quite a while like that, but the boost drops off towards redline and the car feels like it's got kinda lame top end as a result. If you swap to a T28 or bigger, don't run over 11 psi on stock injectors/MAF - it maxes the MAF out and it WILL run lean with more boost.