Partial throttle boost and/or partial throttle full boost

[EJ8 944]

I've searched on this forum, and haven't seen anything to discuss the matter. But I've been reading around about this, there seems to be alot of varying information about this, some claim it is bad, stating that it causes lean conditions, others have claimed it being fine because the stock ECU can boost at low rpms.

Does anyone know for sure? Assuming a car (SR or the something of the likes), is running a near stock configuation, with increased boost (via MBC or EBC), is seeing boost in the lower rpm ranges, lets say under 4000 RPM, bad or fine? Please only comment if you have experience with this, whether it be from driving around with a wideband, or seeing this happen during dyno tuning, I'd like to keep all the heresay out.

[Kingtal0n]

Im having trouble with what you are asking. You seem to be implying that during a part throttle situation a turbocharged engine would experience a lean condition?

My answer to this is simply that it will have as much fuel as it is tuned to have for those instances. If a tuner takes a vehicle, one such as with a MAP based stand alone ecu, and he fully tunes the engine for Wide Open Throttle using a wideband, and "forgets" to tune the rest of the map- essentially, when that vehicle hits those load points, yes it could run lean and damage the engine... since the tuner never actually tuned those spots.

The factory does no such thing. If the configuration is all OEM, Then the engine is tuned in every load point acceptable for the factory configuration. It will not run lean unless there is an actual parts failure, or misconfiguration;

an example of a parts failure would be a stuck fuel pressure regulator that only allows for 20psi when it should be much higher.
an example of a misconfiguration would be a vaccum leak after the maf but before the turbocharger- such a leak would allow unmetered air to enter the engine, and the air fuel ratio will be affected (lean).

[Kingtal0n]

Assuming a car (SR or the something of the likes), is running a near stock configuation, with increased boost (via MBC or EBC), is seeing boost in the lower rpm ranges, lets say under 4000 RPM, bad or fine? Please only comment if you have experience with this, whether it be from driving around with a wideband, or seeing this happen during dyno tuning, I'd like to keep all the heresay out.

Something you said reminds me of one specific instance and the revelation thereafter. Perhaps this situation will further answer your question;

The Redtop SR20DET Engine comes with appropriate injectors for a T-25 turbocharger to run 10psi. At least, it should, right?

I've installed at least fifty redtop engines. In my experience, they all run a little bit different. Even the air fuel ratios vary from engine to engine;
That said, yes, its possible, and I have seen it happen, you install one such redtop sr20det engine and run it anywhere from 7-12psi and sometimes you get one that runs a bit leaner than it should. Usually, you can change the maf, to another IDENTICAL maf, and it will fix the problem- in my experience, most of the variation of air fuel ratio from engine to engine is the fault of the MAF sensor, and since these sensors are often overlooked (because the engine "runs right" and "drives right" the maf must be OK) the problem with the air/fuel during some situations might be missed. Especially since a sr20 engine will run great at 14:1 during 10psi of boost, all the while eating away at the pistons, and most of these owners do not own widebands.

There are plenty of people running SOHC KA maf sensors on their redtops; These sensors may have upwards of 200k miles, and I believe this attributes to this variation. S14 and S15 engines do not seem to have these issues with varying air fuel ratio after installation, in my experience. I recommend that all redtops with OEM components should be kept at 7psi to preserve the life of the T-25; if more power is desired, then a different turbocharger should be installed, along with the appropriate injectors/ecu/etc...

[EJ8 944]

Im having trouble with what you are asking. You seem to be implying that during a part throttle situation a turbocharged engine would experience a lean condition?


Essentially I'm asking if a stock ECU, can handle increased boost brought on from a boost controller, especially at partial throttle, and high boost levels. Example would be flooring in top gear to pass someone on a freeway, or climbing up a hill in a higher gear.

A completely stock engine would respond normally, but if you introduce a boost control, and bring on more boost, at a much earlier RPM, can the stock ECU even manage what is happening?

I guess the simplest way to ask it is, can a stock ECU handle above stock levels of boost, at low RPMs? Or does it only have fuel/timing maps to handle the linear boost levels of a stock motor.

[RedTopKA-T]

I have a sohc ka-t and I've been boosted on stock ecu stock injectors and stock maf for about 3 months now,(trying to get a good tune going) but I do have to say the car runs great and does handle the boost below 4000rpm,for instance when I punch the gas my wideband says 10.9-11.5 untill I hit about 4000rpms and then it starts to lean out hard. But under 4k rpms it can take 12psi safely on stock ecu,injectors and maf according to my wideband.

[Frank_Jaeger]

I guess the simplest way to ask it is, can a stock ECU handle above stock levels of boost, at low RPMs? Or does it only have fuel/timing maps to handle the linear boost levels of a stock motor.
Before the turbo spools, sure.

After that you need a tune. Get a tune if you up the boost. Or I'll slap your shit :trogdor:.

[Kingtal0n]

Essentially I'm asking if a stock ECU, can handle increased boost brought on from a boost controller, especially at partial throttle, and high boost levels. Example would be flooring in top gear to pass someone on a freeway, or climbing up a hill in a higher gear.

A completely stock engine would respond normally, but if you introduce a boost control, and bring on more boost, at a much earlier RPM, can the stock ECU even manage what is happening?

I guess the simplest way to ask it is, can a stock ECU handle above stock levels of boost, at low RPMs? Or does it only have fuel/timing maps to handle the linear boost levels of a stock motor.

Normally, you can turn the boost up on any Stock SR20 Engine to any level, and if the boost is "too high" it will maf cut. In other words, usually, the ECU will cut out the fuel supply (FUEL CUT) If the airflow capability of the maf sensor is exceeded. So, generally, the maf is the limiting factor for OEM SR20DET engines....

On the other hand, it does not always work like that. Like I already explained, these engines and these maf sensors can be old or misconfigured, they can be dirty or the wiring or electronics can be faulty... and too much boost will result with piston failure. and it happens all the time.
I recommend the same: keep the boost at 7psi to preserve the T-25. If you are running a T-28 keep it around 15psi MAXIMUM to preserve it's life. If you want more power- upgrade everything and get a real standalone/wideband. Well, get a wideband no matter what, they are so cheap these days it doesnt make sense to not have one on a turbocharged engine.

[EJ8 944]

That first part answered it exactly, MAF will cut the fuel as a safety precaution, with the caveat that the MAF is working correctly.

[AdamR]

Essentially I'm asking if a stock ECU, can handle increased boost brought on from a boost controller, especially at partial throttle, and high boost levels. Example would be flooring in top gear to pass someone on a freeway, or climbing up a hill in a higher gear.

A completely stock engine would respond normally, but if you introduce a boost control, and bring on more boost, at a much earlier RPM, can the stock ECU even manage what is happening?

I guess the simplest way to ask it is, can a stock ECU handle above stock levels of boost, at low RPMs? Or does it only have fuel/timing maps to handle the linear boost levels of a stock motor.

It will go into a higher load part of the same RPM row on the timing and fuel map.
It should be safe to do so, but i'm not familiar with the SR stock maps.
Also, on a Subaru the stock tune keeps the engine in closed loop (14.7 AFR) until about 20 different parameters are met. Throttle position, RPM, coolant temp, all kinds of stuff if factored in. I doubt the SR ecu does that, but i don't know.

[steve shadows]

When we finally checked the AFRs on the dyno of some of the cars running stock mafs and upped boost levels on the stock turbos most of them were at least 12.5:1 - 13.0:1 with no other mods. If you're going to go the super ghetto route or just want to get the cheapest possible max out of your stock turbo stock maf motor then I suggest getting a decent adjustable fuel pressure regulator so that you can at least be under boost safely under higher load.

[EJ8 944]

Thanks for responses guys, AdamR, interesting you brought up the Subaru's, alot of threads I read were regaurding them, I didn't know any of what you posted, interesting stuff.

Steve shadows - for the cars you witnessed this on, did they have any fuel mods? pump or anything? Where the cars using electronic or manual boost controllers?

There have been a loot of great responses, this all helps to better understand the workings of the stock SR components, and their limitations.

[Croustibat]

Thanks for responses guys, AdamR, interesting you brought up the Subaru's, alot of threads I read were regaurding them, I didn't know any of what you posted, interesting stuff.

Steve shadows - for the cars you witnessed this on, did they have any fuel mods? pump or anything? Where the cars using electronic or manual boost controllers?

There have been a loot of great responses, this all helps to better understand the workings of the stock SR components, and their limitations.

If you want to know how nissan engine management works, have a look at the definition and patents of nissan talking about 'TP' . This was a major improvement at that time and you can get enough information from that.

Basically, the 'TP' value represents the load of the engine; and the management choses how much fuel and timing to put in a 2D table with load and rpm as scales.

The chosen value is altered by various sensors, but this was the idea (and it works quite well).

Running more boost can lead to an ECU issuen as you will not have optimal timing (which means "small power gain"); but the biggest problem is the fuel system and air measurement system (on which the TP computation is based) cant cope with it. Your injectors and MAFs will be maxed. And the turbocharger will be in a very unefficient zone on its map.

So if you want to get more power, try to see it as a package:

a bigger turbo to get more efficiency and more air flow;
a bigger intercooler to cool the charge;
a bigger MAF to measure that airflow;
bigger fuel injectors to allow for 12:1 AFR tuning at highest load;
a tune to get all these working together.

in that package, only the 2 first parts give more power; the others are mandatory to use that power reliably. You can just make your turbo work harder and do nothing else, but that basically means you overspin the turbo, have mediocre turbo efficiency further increasing IAT, have a completely heat soaked intercooler that will drop 3 to 7 psis , a fueling system that fails to deliver enough fuel, and an ECU that does not pull more timing when going on higher boost ( higher pressure means fuel burns faster, if you still ignite at the same time as before, you are just wasting power and creating heat)

What does that mean ?

Basically it means you will end up running lean and poor timing, resulting in so much heat you are going to crack your turbo or/and manifold, if not your engines head, or melt your pistons.

The choice is yours. Do things properly, or dont do them. Going the messy way just means it will just cost you more in the end, so if you dont have money, stay stock.

[EJ8 944]

Thanks for the response, I think you may have misread what I was going for, I'm not personally looking for any information about modifying my car, I'm just trying to get a better understand of the stock components and their limitations.

[Kingtal0n]

Thanks for the response, I think you may have misread what I was going for, I'm not personally looking for any information about modifying my car, I'm just trying to get a better understand of the stock components and their limitations.

The T-25 on 1989-1998 "S13" sr20det engines is very fragile. The oem pistons/rings in all sr20det/rb25/26 engines are fragile. Limitations you speak of... contrast to these components.