Hey i was just noticing something odd while using a Stage 3 Map from Perrin. Sometimes in 5th gear doing wot at low rpms i get a weird like cut out for a split second. And one night i dropped to 4th gear and floored it, it happened again, feels like the engine just stops for a second,sits at a rpm, then i got a backfire(only happened in 4th gear, 5th gear no backfire), then goes back to pulling again, all happens in less then a second, very quick. At first i thought it was just from peak torque kicking in so hard at low rpms and getting slight wheel spin or peak boost spiking to high and getting overboost. But im not sure Anyone else having this? But doesnt make any sense as when im pumping through the gears from 1st to 5th in wot its flawless none of that stuff happens at all.

4th gear only happened once, since i didnt test it again.
5th gear happened twice, then didnt try it again.

Only in immediate wot does it do it. If i push halfway to build up boost then go to wot it doesnt do it. Also had dynos done, and none of this showed up or happened.

Think maybe im spiking to high and engine cuts out to protect from overboost or what im clueless.

 

Mine used to do the same thing but after I got it tuned it stopped. If you are boosting 27psi I dont think you cant push enough fuel and its cutting out trying to compensate. You asking for more boost and your stock injectors are limited. Im not posative but tahts is just my assumption.

 

Could it be turbo lag? The turbo is fully ready if you just driving along in a high gear then you floor it and it takes a little bit. Which would also cause the backfire...just guessing.

 

Oh no def not turbo lag. Its feels like if you floored a car and was at max boost, then just let go of the gas then pushed it back in to a point where your body leans forward and then back again. I was testing it at 5th gear started at 3k 60mph pushed to floor immediatly boost starts rising then at around 3500 peaking boost starts to feel like it struggles a little, then once 4k hits and does it at 4k everytime, that happens then backfire then back to pulling again. Only happens in 5th gear possibly i shouldnt be WOT at 3k in 5th gear with peaking 27psi im guessing. Since gears that dont fly through rpms quick enough will overboost. But only happened in 4th gear once when i was crusing in 5th at 60 dropped to 4th gear and floored it, it also did it. Im just clueless, rpms dont drop or raise , boost doesnt drop. I logged in today so when i get home ill be able to take a look at what its doing and see what Perrin says about it. Also since its a 93oct map even though perrin says itll be fine on 92oct, and ive been using it on 92oct. Ill have to go put some 93oct tmr and see if it creates it again. Maybe i got bad gas or something.

 

sounds like compressor surge to me...try not flooring it at low rpms especially at 27psi your putting your engine in ALOT of load...stay in boost then WOT

 

Does it seem to create like a jolt in the car, like someone tapped the break then hit the gas again, like what some people would use to do to their friends to mess with them lol, but its not as harsh as that its so quick when it happens, like a tiny thump noise, backfire, then your off again? Never had a compression surge so no clue what it feels like. All i know when moderatly push the gas to the floor, im fine. When i immediatly just hit the gas to the floor as 3k in 5th gear it happens at 4k. 4th gear im not sure cause i instantly dropped from 5th to 4th then hit it to the floor. Im so confuzzled I did notice my LICP is starting to slightly slip out of the coupler. Prob from this scenario happening.

 

it never happened in my car but i know what it feels like it happens in my friends 480whp evo...it feels like you hit a wall quick but then the power comes back. its hard toexplain as well as pinpoint your problem..so wait your only at 300whp i think it can be compressor surge and maybe overboost or fuel cut from overboost like other people said...go on youtube and type in all of those and see which one it seems like

 

Well nothing searching google cant do. Found it immediatley.

OK,
I've been answering a lot of question lately about DPs without cats, fuel cut, boost creep, etc. so I thought I'd put a stickey in place. The following is a simplistic explanation. Feel free to respond and correct any errors I've introduced, or provide further clarification. This is to be an instructional stickey, so more information is always better.

Although some EMS claim they can take care of boost creep, in reality, they are adjusting the actuation speed of the wastegate, which actually does provide some protection against boost creep, but this is a "tuning" type fix, and can't fully protect against the "physical" restriction of the wastegate size.

To the explanation (greatly simplified):

Exhaust flow powers the turbine side of the turbo, spooling up the impeller and compressing your intake air to your manifold.

To control boost, you regulate the flow of this exhaust by bypassing exhaust around the turbo once it achieves set pressure. The wastegate is the exhaust bypass around the turbo. As you close the wastegate, this directs more flow through the turbo, increasing boost. As boost rises to set pressure, the wastegate opens to allow exhaust to bypass around the turbo, slowing the turbo down and lowering/maintaining peak boost pressure. In reality, the wastegate is merely a bypass valve though, not a true pressure contol system.

On the stock system, you have backpressure in your exhaust line from the cat, resonator, muffler, and piping sizes. This works to keep the exhaust flow through the turbo to a rate that can be managed in conjunction with the wastegate.

Once you remove these items and free up exhaust flow (reduce backpressure), your turbo now has more exhaust flowing through it at peak throttle than it did before. The wastegate is sized with the stock backpressure in mind. It now can't flow enough exhaust at peak pressure to slow the turbo down, leading to a slow buildup in peak boost pressure, otherwise known as boost creep. This ultimately leads to an overboost condition, usually exhibited by a CEL and fuel cut (your car suddenly lurches and dies or cuts out and back in at full throttle.....a horrible experience believe me!!!!)

The only way around this is to
1. enlarge the wastegate hole (porting the wastegate and some shops call this porting the turbo..so be clear what you are asking/getting)
2. increase the exhaust backpressure (high flow cat or keep the stock catback with a catless DP)
3 or use an external wastegate.

Of the 3, the external WG is probably the best as you can buy one that controls boost in both directions, unlike the internal wastegate the stock turbos come with. Plus the sound it makes is awesome! Of course, this will mean removing the internal wastegate, so this application will usually be found on a larger turbo upgrade. Another good question to ask if considering a larger turbo...does it have an internal wastegate. If you are going external, of course you don't want an internal wastegate.

Thanks for explaining this, I just installed a vf39 with the utec stage 4 map today. The car was being overboosted I guess since it was doing that thing were it shuts down for second in the middle of excelerating, really sucks, feels like your going to break the tranny! I noticed that the utec stage 4 is set at 18 psi, this kinda sounds like alot doesn't it? I turned the boost down a bit and it got a little better so I turned it down some more and seems to be working great. The car hauls ***!
I have a turboxs turbo back exhaust system that has one cat in the middle, turboxs uppipe, stock intercooler on there right now, walbro 255, sti 565 injectors and a bov. Is it safe to just turn down the boost.
Do you know if there is an external wastegate for the vf39? Whats with the helper springs?
Oh yea the car is a 04 wrx.

 

im still not sure because it only happens when your car is under heavy load...your psi is pretty high...only thing is you said you arent getting any CELs if you were overboosting and getting fuel cut im pretty sure you would be getting a CEL

 

Yea the only cel my car is creating and still is up is the p0420 which is inefficienty catalyst system. No cel is being created for overboost or what not. But how they explained whats going on when it happens is EXACTLY what im getting. Which is why im so lol

 

yeah i know i could imagine how clueless you are im buggin out just trying to help haha...i mean other possibilities could be a tune...do u have a wideband if so what are you running at WOT and u also should look into getting a fuel pump

 

Well i remember back when people were fussing about he wastegate mod. I did try it out and notice really no big difference. Maybe i put it back to the wrong setting? If that would cause anything like this. Maybe ill have to check it out and make sure i put it back on the right setting. Its just weird cause ive had a dyno done and they wot in 3rd or 4th gear and it didnt happen. Racing through gears didnt happen. lol Man maybe ill just have to stay away from rolling runs for now and til then figure what it is... tomany things to account for this.

 

yea its really hard to tell..do you have anyone nearby like a tuner? the wastegate thing could be possible but i have no idea what it is i dont do my research much on the X's but just stay away from giving your car heavy load go WOT at higher rpms and it shouldnt happen

 

Yea i have a few people that can look at it. The place i dyno at, theres a worker there that has a evo x thats been tuning it. But for now ive been dealing with Chris at Perrin. Ima be sending him a datalog of it happening i just recorded it today so in about a hour ill be able to send it out to him since the Stage 3 map is made by him. He should know what to do.

 

do u have an aftermarket intake from ur sig no but im just asking cuz i just found something about someone getting fuel cut cuz of an intake