88 Rx7 Turbo II BNR stage 3 Overboosting
 

My car is over boosting. I had it set on 15 and just recently noticed when pulling hard in 4th gear at 4200 rps it boosted to 18 psi and ignition was cutting. I have lowered this so it is now cutting around 15 psi. From all the reading people say port the wastegate. Well at spring pressure NOW it should never hit that. What am i missing here? Here is what I have done to troubleshoot the issue.

1. I move the wastegate with the connecting rod. I used my hands then I used an air compressor I had to set to about 10 lbs or so. And it worked like it should I think and moved.
2. I connected the hose from turbo outlet to wastegate so it runs at spring pressure.
3. I pulled exhaust and opened the wastegate area to take a peak and verify it was working inside.

How cold is ambient temp?

Colder temps make it a lot easier to overboost, even with a ported waste gate.

:iwstupid:

It was 40-50 degrees out today. I do have ECU cutting ignition when it over boosts. I guess I will try porting it like this thread says.I have an S5 turbo on the car.

http://fc3spro.com/TECH/HOWTO/KWG/kwg.html

So I have have tried to port the waste gate as best I can. I will post results as soon as I can. It is supposed to rain and snow flurry tomorrow though. I hope I was able to make a difference.

Well I wired the wastegate wide open and still overboosting. This is actually after I ported it a bit.Has anyone actually had success with porting? I have went a ported it a bit more now. Just sucks to have to port it and put it on and see how it does. I am thinking of contacting a local turbo shop to see if they provide any services. I will put it on again and see if my latest porting made any difference.

how much fuel are you throwing at it?

The BNR upgraded turbo specifies they already port the wastegate as part of the hybrid conversion service. If you're still having problems with overboost there's a few options I know of to help combat it.

You can port the internal wastegate beyond the current diameter of the flapper block and weld on a larger one to retain it as an internal wastegate. Aaron has a write up for the S4 on doing this and S5 shouldn't be that much different.
https://cimg2.ibsrv.net/gimg/www.rx7...8e8a3fafd9.jpgS4 IWG enlarging
https://www.aaroncake.net/rx-7/s4wastegate.htm

You can also convert the turbo from an internal wastegate to external one by plumbing into the manifold but that would be the more expensive option.
https://cimg3.ibsrv.net/gimg/www.rx7...6cf93efeb4.jpgStock manifold external wastegate


A second option for external wastegate conversion is extreme port the internals wastegate ports and mount the external gate source on the turbo itself.
https://cimg4.ibsrv.net/gimg/www.rx7...58e311b548.jpg
https://cimg9.ibsrv.net/gimg/www.rx7...dfeb923c7d.jpg
https://cimg5.ibsrv.net/gimg/www.rx7...90644e1ead.jpg

These engines were originally meant to run around 6-8 psi depending on series, the BNR turbo supports up to 17+ and I'm guessing you're on a more free flowing exhaust and intake system so even porting will be a minor compensation.

Great post Mlammert! I did see aaron cakes write up as well. I ported it and this time I didn't overboost. However I am using the stock flapper still. I didn't port the runners any as well. My port is outside the flapper door a bit in a spot or to also. I will make some more runs and log it to see what boost levels I am hitting now. The guage still showed 12 psi about. The logs will tell me exactly where I am though.At least it is not to hard to pull off to do the work.

I wonder what would happen if you made it one big hole instead of the 2 holes? Would it hurt anything? I also could take it to get someone to weld a bigger flapper door on it also.

I still am over boosting it seems. I logged it but, have not looked at it yet. I want it much better so I guess I will look at increasing size some possibly and a bigger flap. Stay tuned.

I know your pain. I have a large street ported engine, HKS intake and 3 inch turbo back exhaust on a stock S5 turbo. Thing overboosts on anything over half throttle going up to 12 psi almost instantly on full throttle. I've tried taking the turbo off and porting following the example Here FC3S Pro v2.0:&nbsp How-To - 1989-1991 Kouki FC3S Turbo Wastegate Porting

Found a small leak on the vacuum line to the wastegate when I was checking everything. Put it back on and I really didn't notice any improvement in boost control. I think the fact that the flapper door can't open all the way because of the lever hitting the turbo on the outside and flapper hitting the backplate on the inside really limits bypass flow so I'm going full bore and following the example that BlueTII did and porting the runners on the turbo and attaching a external to it.
https://cimg0.ibsrv.net/gimg/www.rx7...54e5299f5f.pngCurrent Progress

I wanted to get a BNR stage 3 like you have but was also considering the stage 2. How do you like the response of the stage 3?

Yeah the door doesn't open very much on these wastegates. I ported so the 2 holes are almost touching on mine and also past the flapper door in some areas. I am still debating on pulling it back off right now. It does seem a lot better. I may run it some today and see how it goes. I don't think I would go external unless I chose a different turbo and get away from the hybrid. maybe get one of the SXE models later on down the road. If I pull it I am thinking of making it one big hole instead of the 2 holes. I was wondering if this would cause any issues or not though. I have been using a dremel. I went and looked for other tools and wasn't sure what I needed to be honest and lowes probably doesn't have anything good for grinding in this tight space.

I like the way the car boost. I don't really have a lot of experience in boosted cars though. It seems like it is never enough power to be honest. I wish I would have just went bigger at the start to be honest.

So after a few hard pulls it seemed to do well. I don't think it was hitting boost cut. It might be ported just enough. Today it is like 48 degrees out. I think I am gonna let it go for now unless I notice it more at a later time. It is still boosting well and pulling hard. I didn't run it up in 4th gear and see though. Mainly just 2nd gear pulls and a 3rd to redline held pretty good.

You could add an exhaust restriction, perhaps a high quality high flow cat (eg https://vibrantperformance.com/catal...124da069314628 )

You are going to be working around some restrictions with your hybrid. Can you enjoy it at the current boost level or slightly less? That or go full aftermarket single turbo and all the extra plumbing that entails.

Yep I thought I read you could restrict the exhaust as well. Also thought of going aftermarket turbo setup as well. If the funds were there I would go that route. I wish I would have just went went that way instead of the hybrid. The problem was I couldn't control the boost level so no that was no fun. The car was hitting the 18 psi limit I had at first until my ecu cut the ignition. So when I was getting on it it was stuttering between boost and ignition cut and I would have to let off the throttle. Then I lowered that to 15psi to be safer until I get it boost figured out. The cat could be an option. I wonder how long they last though on these cars. My car is behaving pretty good though now. Will it hold on a really cold day? Probably not, but it is a lot closer now that I ported the waste-gate pretty aggressively.

Just put a high flow cat in there and be done with it. Save the stress of wondering whether you're going to fuel cut today or not. Save the hassle of the smell attracting attention.