boost creep
 

I put a racing beat exhaust on my 88 t2 with the na mufflers i had laying around. At the same time i swapped to a stock turbo i had laying around since the other one smoked a little. I ported the wastegate almost to the flapper and boost wants to get to 12 psi if i go any more than part throttle. All i have not stock on the car is a fcd all stock intake. does this seem to be a bit extreem for a exhaust they sell as a direct replacement. Is my actuator bad. it sucks babying around in my car i cant even pull out in traffic without possibly hitting 10+ psi. Is this normal with the exhaust or do the na mufflers flow more than the turbo ones causing this. Any input would be great

The exhaust by itself will cause the system to run 4-5 psi above stock (how bad must the mazda system have been, seriously?), making a FCD almost necessary.

with the fcd how high is safe with stock everything else. should i just keep driving quarter throttle. im in the process of building another engine for it to install this winter but dont wanna detonate a 95 psi compresssion engine regardless

That's normal after an exhaust upgrade. The porting should help keep you from creeping but I am wondering about the wastegate too. It should be opening up around 5psi-6psi. The FCD is doing it's job but 10psi is the most you want to reach with a bone stock car. You need at least a fuel controller to safely hit 12psi.

i think i have a actuator at my moms ill switch next time i go down. i know my wastegate port wasnt extreem but i figured it would be sufficient for a exhaust upgrade made for a stock vehicle

well, the stock one is internal actuator....I assume yours is aftermarket?

maybe my terminology is incorrect but i was referring to swappin the big actuator like thing that has the rod that connects to the wastegate to open it. Its bolted to the side of the cold side housing and has the line that runs to the outlet of the cold side

Don't use an FCD... its tricking the computer by making it think its running lower boost. I recommend an Rtek. It, instead of not having fuel like an FCD, adds fuel above stock levels and retards timing a degree per PSI above 9psi. It also smooths out the staging points. Pretty inexpensive and a safer route for a simple TII w/ a turbo-back exhaust, and ported waste-gate.

Put in a haltech.

$40 FCD + $200 A/F controller
vs
$400 Rtek
vs
$1100 Haltech ECU.

If you're going to rock the stock setup then just stick with FCD and AFC + tune or the Rtek...no point in blowing $1100 on a setup you don't need.

As far as the wastegate, if it's jammed or not opening properly then you should replace the components. Any new info on this issue?

Ive got a full 3" turbo back on my car and I don't have any boost creep. I don't know if my wastegate has been ported or not, but I would assume with a rebuilt motor and the exhaust I would be creeping a lot. Kinda weird I guess.

I agree with Phoenix to a degree.

Rtek imho is the best route to go for higher stock levels but not wanting to get crazy.... yet.

FCD and AF controller doesn't make up for what you can do with an Rtek which requires no wire splicing. Yes it is more expensive, but you get what you pay for.

You left one possibility out.

A screwed up turbo.

That's what I was rocking for a while, check it out if you can.

Full 3 inch turbo back exhaust = boost creep. Anything less means something is either wrong or you have been misinformed.

I have a freshly rebuilt s5 turbo, it has just as many miles as my motor, which is less than 4k right now.

maybe it's ported....unported with 3" exhaust spiked to 15 psi on me....scared teh crap out of me.

Im beginning to think it might be ported as well. Otherwise I should be spiking way more.

From my experience, ported motors spike sooner and then have a lot of trouble holding boost in higher RPM's.

Stock ports with full exhaust is going to creep if your turbo is stock. Keep in mind if you have a FCD and are using the stock boost gauge to read your boost then you will not show any creep at all on that gauge because of what the FCD does.

My car holds .5bar really steadily all the way to about 6k. I don't really red line it too often so I don't know what boost it holds until 8k.

ummm... Rtek does offer a version other than the 2.1 that you can just install yourself or have them install it in your ECU. It's safer than an FCD and an AFC in my opinion and is cheaper than them also. At around $150 shipped to them and back + installation you really can't go wrong with them if your running stock boost w/ a turbo back and a boost controller.

I've been using the 1.5 in my TII for over a year and a half now w/ no problems at all. Previous owner had an FCD in it and that was the first thing to go.

-GReddy fmic kit
-GReddy profec-B (spec 1)
-Racingbeat REVII turbo back
-S5 turbo (ported waste gate) and manifold
-HKS SSQV
-Rtek 1.5
-8 psi

Tho... I have aspirations of going Haltech and 60-1 someday. Rebuild and supporting mods first tho. All in time.

I want to get an rtek 1.8 but I've been hearing that you shouldn't run an rtek on a street ported motor, so I'm not sure. Really though, I think with a wideband, afc neo and 850cc injectors I should be able to run it.

I have the REVTII exhaust and a ported wastegate, to at least 35mm, and it STILL creeps a little. I run about 12psi and the other day in 4th gear I saw about 16psi so I let up a bit. Granted, I use a cheap ass manual boost controller and I'm looking for an EBC setup, that may help a little.


I use the rTek 2.1 on my S4 streetport and it runs pretty well. I have 550cc primaries and 720cc secondaries.

I have stock ports, HUGE wastegate port, RB DP, RB silencer and an Apexi N1 EVO catback. Cone filter, and FCD and I have never hit higher than 10psi.

I was getting spikes to almost 12psi with a shitty dual catback and stock BOV, once I put in the Apexi Twin Chamber, and the Apexi catback, all spikes and lag went away.

I swear, every FC is a little bitchier than another.

I put a series 5 engine and turbo into my series 4 turbo and used the s4 wiring harness and ECU. I have the racingbeat REVTII w/ FCD. i ran great fro about 2 days boosting at 11-12 psi. I took it on a trip to northern VA from southern SC and about 5 hrs. into the trip it started boosting at about 15 psi.. being 250 miles from my destination i had to keep going and sure enough it spiked to 15 psi on last time a the front rotor blew :( . pretty sure my waste gate or ABV wasn't opening at all... but i haven't had time to look at it yet...all in know is Okpa on rotor #1. ....amazingly enough it made it to VA on one rotor:)

Boost,
My S5 has a ported motor, and this is exactly what I'm seeing. 2nd gear hits 11psi and then slowly drops to 5psi by around 8k rpms.

The statement I keep reading is that the turbo can't keep up - this makes no sense to me as the wastegate would completely close if boost pressure dropped below the target.

First gear is different for me, I see only 8psi of boost, which also drops to 5psi. Anyone have an idea whats going on here?
Best,
John

wastegate is not closing properly? What's the mileage on the car/turbo? could be grimy? Have you tried taking it apart?

In my case at least, and I'm sure a lot of other guys use these, too, it's the manual boost controller that's part to blame. Unless electronically monitored I don't think there's a real smooth way for a boost controller to hit peak boost and simply keep it there unless it's set at or only slightly above the stock boost level. A bleeder valve simply isn't the best solution, but since it's very cheap we do it anyway. At 4000 RPM and 12psi there's a lot less air moving than at 7000 RPM at 12psi, that little bleeder valve can only release so much air so fast. What does this mean? It means the wastegate actuator ends up seeing more pressure as the RPM rises while boost is up, which will unfortunately bleed boost through the wastegate.

Another factor is the turbo itself. For one, the stock turbo is built for holding stock boost levels on a stock motor. It can perform better than that, but we can't expect too much from it. It can only be pushed so fast before it just becomes a heating fan and stops helping you make more power. What I've read is that the stock turbo is pretty useless past 12psi and many people have blown stock turbo's or apex seals by boosting higher on the stock turbo. You may help the situation a little with a FMIC, but not by a lot. The stock turbo simply can't push a ton of air at high RPM. You might look into BNR turbo's if you're looking for a cheaper turbo upgrade. I've heard a lot of people are happy with that route.

I have all my intake and exhaust ports mildly modified. The funny thing is that even if my boost peaks around 5000 RPM I can tell I'm making more power at 6000 RPM at ~3psi below peak boost than at 5000 RPM at peak boost. I'm aching to get a good electronic boost controller to see how much improvement I can make over the stupid MBC. I'll probably start roasting tires at the top of second gear...

Gimme a sec and I'll explain in depth. A lot of people see this and don't understand it.

Ender, you are on the money like usual, but there is one thing that needs to be explained better.

It all starts with separating the turbocharger and the engine in your mind. It will make this a hell of a lot easier. Also, I am going to make up a lot of numbers here to make this simple, so please don't flame for the false data.

A stock port turbo motor ingests less air than a ported motor, everyone knows that. So on to my fake math.

If you could measure the amount of CFM a stock 13B ingests as the revs increase, you will see a rise in CFM as it approaches its VE (volumetric efficiency) peak, which should also be it's torque peak (usually, but this is different from motor to motor.) If you measure the CFM of a ported 13B as the revs increase, down low they will be close to the same, but as the revs increase, the CFM goes up MUCH more rapidly. Basically, a streetport flows an ever increasing amount of CFM as revs increase.

Now, if you understand that, on to the turbo.

Our turbo's suck for what we want to do with them. The stats on your turbo are static. For any given PR (pressure ratio) they can only flow so much air. A lot... and I mean A LOT of people think that the power comes just from the boost, and that is what gets a lot... and I mean A LOT of people in trouble with RX7's. The CFM is actually more important to me in regards to the PR than boost is. But on to the WHY your car can't hold boost.

Example 1 : Stock car in third gear from 2k to redline, stock turbo, 3 inch DP and some other bolt on goodies.

At WOT (wide open throttle) the turbo will come online. Full boost is usually realized before 4k rpm. The turbo is spinning merrily and you sustain a solid boost number, we'll say 10 psi for ease of use. On stock ports and stock turbo, the extra exhaust energy from the increase in boost and the freer flowing exhaust utterly defeats the wastegate so the turbo starts spinning faster (boost creep). The motor can't ingest all the air the turbo is feeding so you will see an increase in boost. If left unchecked, the system will literally self feed itself and your boost will go to the choke point of the turbo. Hence, some aftermarket goodies on your car means your car has a tendency to creep unless you port the wastegate A LOT.

Example 2: Nasty streetport in third gear 2k to redline. stock turbo, 3 inch DP and other goodies.

At WOT at 2k, your car is producing a retardedly higher amount of exhaust energy due to the porting, so the turbo will start to spin up MUCH faster than stock. As the turbo comes online headed to the 10 psi peak, your exhaust volume and energy is increasing way more than the stock example above. Therefore the turbo hits 10 psi, your wastegate opens, but the turbo was accelerating so fast there is almost no hope of controlling it without an EBC. So you end up with what is normally a large spike at the midrange in the RPM, which also puts it dangerously close to the torque peak, which is where the engine can get closest to it's detonation threshold, but that is for another post later. Anyways, you spike to 15 psi, then the turbo comes back down to 10. As your revs increase, the engine starts ingesting more air until it reaches equilibrium with the turbo. (I'll take a guess and say it is usually around 5k plus for most of us.) Now something really cool and really bad starts to happen. The motor revs increase and it starts ingesting more air than the turbo can actually put out. The boost level starts to drop and it is sad faces all around. But here is what is actually really bad. Your wastegate cares not for IAT's or CFM's, it only cares about PSI. So when boost drops below threshold, it shuts the wastegate to play catch up. Guess what, your motor is still eating more air than the turbo will ever put out now and the boost still continues to drop. Your exhaust energy is now increasing the impeller speed of the turbo to pretty close to the choke point, which increases IAT's and wear on the turbo itself.

Now, example 3 : same motor as above with a BNR stage 3.

The revs increase, the turbo comes online a little later (takes more time to spin up a larger turbo). Motor starts eating the air and the turbo keeps thumping it out at 10 psi. BUT!!! at 10 psi this turbo flows more air than a stock turbo so your power output is going up drastically. Since the compressor wheel is larger it can flow more air at a higher psi and maintain it throughout the power band.

Conclusion, go get yourself a BNR stage 2 or higher and have fun in your car again. You have no idea what the difference will feel like if you have the fuel for it. Streetport with a BNR stage 3 at 15 psi = you rolling up lots of fools.

I'll try to get some more real data if there are any questions whatsoever.

P.S. Bridgeport and a 42R is what EVERYONE in this forum needs in their life.

That is all.

P.P.S. I missed one question.

The reason your car can't hit your target boost in first gear is because our turbo's suck and the engine load isn't high enough or long enough to get to your target boost in time, so the engine gets to the point where it is eating more air than the turbo can put out before the target is even reached which is why you see only 8, followed by a drop to 5. I bet every gear drops to around 5 by redline (please don't try in fourth or fifth gear, you may hurt yourself, your car, or someone's dog running across the road.)

sweet! so porting does help spool the turbo faster after all. nice info here, I'm doing my first rebuild of a S4 T2 to swap my NA but I still need to acquire an intercooler, turbo, and the turbo mani. I was going to go with an S5 turbo and mani but after reading this, I think I will just get it and send it to BNR (or if they have one available straight from them). also decided to port mildly for the spool up. was reading a lot of cons of porting besides MPG going down so wasn't sure. thanks for all this info, this car should be pulling hard after my restore.