kleetuz

iTrader: (2)

With the RB full exhaust system and a cold air intake my car will hit around 6psi by 3200 or so and the creep to about 10psi once I get up to the 4300 rpm range, this is in third gear, In second it might hit 10 psi by 5300 or so. I built a manual boost controller to put on my car once I get my boost gauge installed. ( I got the psi readings borrowing my friends boost gauge...) I would like to set it at 10 psi.

Will I experience creep past 10 psi using the boost controller? If so does anyone know how high it creeps up from experience? 12psi?

Don't worry I have a fuel cut defender .

gsracer

it is impossible to use a boost controller to lower your boost. I'm going to assume this is a s4 car. Def. port the wastegate if you haven't done so. Switchiing to a s5 turbo/mannifold would be even better.

Piranha

A boost controller won't limit your boost, and be careful, if you boost too much past fuel cut (8.6 psi) you will lean out, unless you have fuel mods, and blow your engine.

Ryde _Or_Die

If you are hitting 10# in 3rd I'd imagine you get 11 or 12 in 4th. Get a boost gauge, port the wastegate and/or get some fuel mods.

FC Drifter

yeah, boost controlers only turn boost up, not down. an electronic boost controler is better at holding a preset boost setteing than a manual one, but neither can lower boost. port your wastegate, that should help lower the boost creep. then if your boost is lower after the porting, you can turn it up to 10psi.

Scott 89t2

don't floor it in 4th or 5th!! you will hit 12+ easy. not safe. even 10 is pushing it. get a bigger fuel pump right away.

kleetuz

iTrader: (2)

I am somewhat confused. Are you guys saying that I should have blown my engine by now? I have had the RB full exhaust and cold air intake for a long *** time now and almost topped out my car in fifth gear, 151mph. I haven't blown my engine yet or felt anything close to something being wrong, no detonation or hesitations.

Are you saying I will hit 12psi in 4th or 5th gear without the boost controller or with the boost controller?

And I don't want to turn the boost down I want to raise the boost so that it will hit 9-10 psi in second gear, it alreay maxes out after creeping up in high 3rd gear at no mor than 10 psi.

So using just the boost controller I will not be able to avoid having the boost creep up by an extra 4 psi in third gear+?

Also I thought that the stock fuel system was plenty good to around 12 psi? It has to be stoich or richer to 10psi at the very least....

Scott 89t2

why would it be richer at 10psi? the FCD fools the ecu into thinking it's still at 8psi. so when you are at 12psi. the ecu is putting out enough fuel for 8psi


the boost controler will not lower boost, if you are creeping to 10 now. you will hit 10 after too. but yes you can set it to 10 so you hit it faster. that's the point of it.

NZConvertible

The pressure sensor doesn’t control fuelling, it controls ignition timing. As boost increases, the timing is retarded to prevent detonation. An FCD-equipped ECU will stop retarding the ignition beyond 8.6psi even though boost is increasing. The end result is the same (detonation followed by death), but it’s not the FCD that causes lean conditions. That’s from going past the limitations of the stock ECU’s fuel maps and exceeding the capabilities of the stock fuel pump.

kleetuz

iTrader: (2)

This is what I was getting at in the first place . It will hit 10psi faster, but would that make it creep up higher than 10psi in thrid gear if thats what the creep makes it max out at to begin with, without the controller?

Also, I don't mean that the air/fuel ratio is richer at 10psi than at 8psi (it would definitely be leaner with 10 than 8 if 8psi worth of fuel is being supplied) , just that the fuel that is supplied to run at 8psi is at the very least still stoichiometrically correct to prevent detonation when running at 10psi (or my engine would have blown apart by now for sure) and it could possibly be richer than what is stoichiometrically required to prevent detonation. Which is why when I had asked around before I heard that you can handle 12psi with the stock fuel system, but perhaps that is only for a few seconds until boom!


One more then: What are the max limitations of the stock ecu fuel maps and fuel pump?

Evil Aviator

OK, first of all, you need to understand that you are at 5,000' feet of altitude, and you can run more boost (gauge pressure) than the people on this forum who live at sea level. Generally, this value is about 2.5 psig, but it will vary with atmospheric conditions.

The boost level will depend on load, not necessarily which gear you are in.

A boost controller simply bypasses the car's preset boost limit on the wastegate. Since the factory limit on your car is 6.56psig, you are obviously getting boost creep. All a boost controller is going to do for you is allow the boost creep to manifest earlier. In order to stop boost creep, you will need a ported or aftermarket wastegate.

You got it.

Um, no. The stock system can barely handle the stock boost (at sea level). That's why Mazda installed a fuel cut fuction to keep people from ruining their engines. Why don't you install an AFR gauge and find out for yourself?

BTW, stoich is about 14.7:1, while best power is about 12:1.

NZConvertible

kleetuz mentioned this the other day, and I don’t think that’s right. I replied... This assumes the boost gauge is calibrated to zero at sea level (if it is, it should sit at ~5inHg vacuum with the engine off). It makes sense that if the air’s thinner, you need to do more work to achieve the same pressure, but once you’re at that pressure, the effects should be the same. If kleetuz drove his car down to sea level, the boost would rise by 2-3psi and he’d be in real trouble...

kleetuz

iTrader: (2)

Okay while on this discussion....

Will solely a bigger fuel pump make the system able to handle 12psi at sea level?

I would think that bigger injectors would be a must as well and most likely an AFC if the ecu doesn't map well that high...?

Scott 89t2

hehe, my fun driving roads are only 10' above sea level

kleetuz

iTrader: (2)

What volume fuel pump will I need? There is the Nippon Denso but I'm never going to go 500hp or anywhere close. I only want to be safe from the creep I get using the RB full exhaust and the cold air intake. there is nothing else I want to do to this car for a good while. What pump will suffice for the 13 psi that I can get from creep?

jspecracer7

STOCK FD PUMP. Because of it's nature it will also increase your fuel pressure. Using this pump and you WILL need to use some type of aftermarket fuel enrichment...s-afc should do the trick.

SaabGuy

www.autoperformanceengineering.com
has walbro in tank fuel pumps at $125 shipped for the 255 lph High Pressure pump.. That also includes the install kit.

Youve got to understand.. I speak for most of these people telling you to do fuel mods. We all love these cars and your mods are enough to greatly shorten they motor's life. Everyone on here is extremely cautious. Jump on the bandwagon.

Its nice telling people that your car runs 12.89 in the 1/4, but its another thing when a turbo rotary outlasts a 5.0 mustang's engine.

SaabGuy

I disagree. After simply installing an aftermarket fuel pump, my car started shooting flames out the exhaust. You will run richer, just not tuned.

NZConvertible

You mean fuel adjustment right?

kleetuz

iTrader: (2)

Hell Yeah shooting flames would be pretty tight.

Oh yeah. I don't doubt you guys about needing the extra fuel, but it just doesn't have quite the same importance at this high of elevation. However I agree that it would be better just to be safe. thanks.

Evil Aviator

Yes and no.

No, 10psi is not in the engine. If you recall, there is something called a MAP sensor which helps certain engine ECU's determine the correct air-fuel ratio. MAP stands for Manifold Absolute Pressure. Absolute pressure = ambient pressure + boost pressure, so 12.2psia + 10psig boost = 22.2psia, while 14.7psia + 10psig boost = 24.7psia. I don't think I need to explain that 22.2psia is less pressure than 24.7psia, despite the fact that both turbos are producing 10psig boost. Assuming the same air temperature, the higher pressure air will always be more dense, which means that it will require more fuel to maintain the same air-fuel ratio.

Yes, the turbo will need to run at a higher pressure ratio to boost 10psig from less dense ambient air. Using the numbers from the previous example, 22.2psia / 12.2psia = 1.82 pressure ratio at 5000ft, while 24.7psia / 14.7psia = 1.68 pressure ratio at sea level.

Please note that these are generalizations, as weather patterns change these actual values, and it is even possible for the air to be thicker at a high-altitude point than it is at a low-altitude point. However, the standard conditions (ISA) at sea level are 59degF and 29.92"Hg, with a "standard" lapse rate of 3.5degF and 1"Hg per 1000ft altitude.