I have always had a problem with my stock turbos holding a set boost all the way to 7k. Its a stock S5 turbo, on a stock motor. basically stock everything else.

Im boosting 11psi, but then drops off to 6psi after 5k rpm. Wich is a problem for two reasons. One, my ECU is "pre-tuned" by pan speed (The ECU came with the motor from JDM land). Im 99% sure the fuel curve had been richened up. Im also running water/meth wich comes on at 7psi. Two injectors, one is a 180cc, and the other is a 250cc. Wich while boost is holding at 11psi, it works BEAUTIFUL! But between the chipped ECU, and 430cc of water/meth...its just to much and breaks up bad at around 5500 rpm, because of the boost drop off.

The solution for me is not going to be any type of tuning, or going with less water meth. (yes, both would work just fine) Im just basically asking, if anyone did something for there turbo to hold a consistant boost all the way to 7k or further... what did you do? Oh, and yes the wastegate is ported.

**This is not a thread about any of my other upgrades, unless it has something to do with holding boost. Please keep all other chatter out. If you want to make a comment off topic, PM me and i will respond there. Thank you.

 

Cold side too small maybe?

Because i'm impulsive and like shiny things i'd just buy an ebc to ensure it's controlling the wastegate to keep boost at the psi i expect it to be.....

 

mine doesn't hold boost to red line, but I suspect it's my cheap $20 boost controller, but I really don't know either?. I know it sucks.

 

Boost creep never lets me down
The game I play is called feather the throttle to keep it below 10 psi

 

I have a Turbonetics controller. Either way, boost controllers have nothing to do with it not holding boost, unless theres a leak in the line or controller. this has more to do with exhaust flow over revving the tiny stock turbo.

Feathering the throttle is a no go for me in drag racing...

 

My car runs off the wastegate and still doesn't hold boost to redline. It peaks at about 6 in the midrange and drops to ~3 after 6,000 rpm or so. I've learned to live with it, as far as I know its common on cars with low restriction intake and exhaust setups.

 

you can achieve it with a decent electronic boost controller.

 

Compressor wheel is too inefficient to continually make boost to redline, and the turbine eventually becomes enough of a restriction to add to the drop. C'mon guys, I thought everyone knew the stock turbo wouldn't make full boost to redline. An EBC isn't going to help you overcome the design of the turbo. With my wastegate completely shut, I'm able to hold about 9-10 psi at 6000 RPM. By redline, it will have dropped a little more to around 8 psi depending on the gear I'm in. This is with a 3" TID, 2.5"DP and open exhaust. The exact same setup with the stock TID was only able to make about 5 psi to redline. An open intake and exhaust are critical to making it flow as much as possible. Restriction does nothing but make the problem worse. It's the same reason you need to port your wastegate if you replace the stock exhaust system.

If you're already using an open intake/exhaust setup, the only solution short of changing your aux. injection psi, or reducing the injector size, would be to use a hybrid turbo. Upgrading to a more efficient compressor wheel & clipping/replacing the turbine wheel allows a hell of a lot more flow at high RPMs.

 

something is wrong with this picture, at 4000 ft I can hold 12 on a 90psi comp block.

 

Pics of the car at 4000 ft?

 

Copy pasted from BNR's website.


"Upgraded wastegate actuators are the best way to keep the boost level from falling off up in the top RPM. There are a few things that can contribute to this issue. The issue is backpressure between the turbine wheel and engine causing the pressure to push against the wastegate valve assembly. This opens the wastegate premature and causes you to lose boost pressure. The more you port the wastegate port, the worse the problem will be. The solution is a higher spring tension wastegate actuator upgrade. This is a quick and cheap way to generate a noticible power and torque gain in mid range RPM while holding boost up in the top of the RPM band. There are a few actuators to choose from and it depends on what boost level you are trying to run. From there we will help you decide which actuator is best for your application."

This seems like the answer were looking for. So where to get a new/different acuator or different springs?

 

http://i40.tinypic.com/2q36xdv.jpg

 

Or a good electronic boost controller, it would help keep that gate closed as it wouldn't see any Psi to open till the programed psi

I dont have a problem with holding 10 psi to redline but then again im running a high comp keg

 

having an electronic boost controller does not stop excessive exhaust pressure from opening the gate prematurely by shear force.

boost controllers are NOT the answer.

I have found a few nice wastegates that would go nice with our stock turbo. Garrett seem to be the best choice from the looks. and they come in various set psi. at around 120 shipped, i feel its a good investment.

 

what about cutting the stock wastegate metal rod, threading it and putting a turnbuckle on it to increase tension on the door

I'm not sure then how my wastegate on my s4 turbo is holding 10 psi....

 

That is one way to do it. A friend of mine has always just bent his to fix the problem. But those are not really exact or the "correct" way. And although i have done some cheap fixes in the past, im more meticulous these days. I'll be going with a garrett internal wastegate.

and my guess about your motor holding 10 psi is this. You have the lower comp. 8.5 rotors. And S4 turbos also have larger, less restrictive rear housing. making the exhaust pressure much less and thus letting you hold boost without causing problems.

having the 9.0 rotors and smaller rear housing create more restriction causing a backpressure build up making the wastage door open prematurely. causing the the boost drop off.

This is all in theory of course...

 

i have a stock turbo with an electric bost controller.

Boost is setup at ~12 psi and drops down to 10-9 by 5-6krpm.

Power is awesome below 6k and after 5 peaks out. Kind of lame because i'm used to my old n/a rotary pulling harder and harder until redlne, instead of pulling harder and harder until ~5krpm and then tapering off.

Its lame, but that's the most you can do with a stock turbo. Either get a BNR drop in or upgrade.

 

I have a 6 port turbo with 9.7-1 compression....

I just happened to get a s4 turbo for free so i used it

 

Sounds like a plan, keep us posted on your results

 

My old RX-7 was an S5 turbo motor with a mild port into a stock S5 turbo. 2.5" downpipe to a 2.5" straightpipe, 2.5" straight TID. And yes it held boost to redline with no problem. Creep was more of a problem for me. Is it possible your wastegate actuator spring is damaged?

 

you need an electrical wastegate a mechanical one will open as the pressure increases untill it is fully open

 

 

^^^ hahahahahahhahaha

 

Electrical wastegate?

So are those the new ones that use a stepper motor instead of using a diaphragm?





















































LolZ

 

lol...

yeah... so i didnt order the magic electrical wastegate. but i did order a garrett internal gate set for 11psi. I'll update with news if this is the answer or not.