Boost cut after modified exhaust

[BiggestRon22]

So as it say I’ve modified my exhaust to be a complete straight pipe no mufflers or cats (it is very loud but I kinda like it that way) and every so often when I push on the gas a bit harder sometimes around 4500rpm all the power I was feeling mostly goes away. I’ll have to do some more testing to see if it does it every time but just hoping to see if anyone might know what’s causing my “boost cut” 

only mods I’ve done is my exhaust and then blocked off my bov for the nice stu stu’s

 

also planned to modify my intake slightly this weekend and hope that is doesn’t make the “cut” worse 

Edited January 21, 2022 by BiggestRon22

[Duncan]

Mentioning what car this is could help a little, and since you suspect it is boost cut an indication of what boost it is at when it starts dying would help.

Having said that, yes it is almost certainly "boost cut", particularly if it is reasonably smooth rather than a misfire which you can normally hear, and the only practical way to deal with it is an aftermarket ECU

[BiggestRon22]

On 1/21/2022 at 11:58 AM, Duncan said:

Mentioning what car this is could help a little, and since you suspect it is boost cut an indication of what boost it is at when it starts dying would help.

Having said that, yes it is almost certainly "boost cut", particularly if it is reasonably smooth rather than a misfire which you can normally hear, and the only practical way to deal with it is an aftermarket ECU

Hey Duncan thanks for the reply! 
my car is a 2000 rs4s, sadly my wagon wasn’t optioned with the gauges so I can’t tell what the actually boost level is but planning to get a gauge in a few weeks and yes it is a smooth cut rather than a misfire, I’ll be driving with normal power then it feels like it’s been cut in half once I put my foot down, the only audible difference I can hear is the car sounds “mean” and when the cut happens all the “meaness” goes away if you know what I mean. i will do my best to get a clip of the sound while I’m doing home for work tonight.
 

Also for the aftermarket ecu would you recommend getting one now? The car is 100% stock except for my exhaust and the 5$ intake mod I’m about to do tonight, do plan on FMIC, pod filter, boost controller and turbo dump pipe once I have money but didn’t think you d have to do much with ecu till I started messing with the fuel and turbo stuff.

 

sorry for the long reply, just tryna learn as much as I can  

[Duncan]

Yep, so the stageas are particularly sensitive to extra airflow, it's not exactly a boost cut as such but the factory ECU has a very narrow band of what it expects and once you go outside that it starts running very rich and retards the timing to protect the motor from what it thinks is some sort of issue. Shame because Stageas can do with a bit of extra go.

You do have options like an HKS Fuel Cut Defender (that is where i started with mine), but realistically if you are going to modify a stagea you need to change the ECU early in the piece because it is very sensitive and you will probably go backwards from everything you listed above without one.

I'd suggest saving for a Link or Haltech before you change anything else. Even now you are probably making less power, not more, than factory.

[BiggestRon22]

On 1/21/2022 at 2:00 PM, Duncan said:

Yep, so the stageas are particularly sensitive to extra airflow, it's not exactly a boost cut as such but the factory ECU has a very narrow band of what it expects and once you go outside that it starts running very rich and retards the timing to protect the motor from what it thinks is some sort of issue. Shame because Stageas can do with a bit of extra go.

You do have options like an HKS Fuel Cut Defender (that is where i started with mine), but realistically if you are going to modify a stagea you need to change the ECU early in the piece because it is very sensitive and you will probably go backwards from everything you listed above without one.

I'd suggest saving for a Link or Haltech before you change anything else. Even now you are probably making less power, not more, than factory.

Okay cool, Thank you for that! 
 

I’ll see if I can find a haltech ecu because I like them a little bit more  also might go with the fuel cut defencer as a temporary “fix” to my problems, most likely won’t be doing the FMIC for a while but will definitely be getting the dump pipe and boost controller. 
 

from your experience how was the fuel cut defencer? Other than getting rid of the cut was there anything else that was a notable difference? Asking because I do plan to do all my big upgrades roughly around the same time and wondering if I should suffer with the cut until then or bite the bullet, get the ecu and get it tuned a few times.

 

also rather than the HKS fuel cut defencer or an AM ecu, do you think the Apexi safc neo would be a good thing to try out? I’ve heard that it doesn’t fix the cut and I’ve heard it does sometime too.  Definitely looking at every option because as I said kinda tight on money and will have to wait to get anything somewhat expensive.

 

had a little thought too, since the cut has been happening since I did up my exhaust do you think putting on maybe one boxy kinda style mufflers would be able to help it too? 

Edited January 21, 2022 by BiggestRon22

[GTSBoy]

On 1/22/2022 at 6:20 AM, BiggestRon22 said:

had a little thought too, since the cut has been happening since I did up my exhaust do you think putting on maybe one boxy kinda style mufflers would be able to help it too? 

Well, yes, because I can't imagine living with a stupidly loud unmuffled exhaust for long anyway. But if you want it stupidly loud and unmuffled, then you could just fit a 2" orifice plate into one of the flanges to cause some restriction, or choe the turbo inlet down, or something, to reduce flow. Then when you fix the management problem, you retain the stupidly loud unmuffled exhaust.

I go on about the stupidly loud unmuffled exhaust a bit, because......hearing damage. I have it. Wanna know how I got it?

[Duncan]

So the FCD is cheapest way to address your immediate problem (other than putting the original exhaust back on) but it has a narrow range that it can help with. You should still probably run in on the dyno after install to be certain everything is OK so that is another couple of hundred. I picked up about 20kw back in the day when I put the FCD on with 3psi extra boost (10 instead of 7psi)

An SAFC is a much more flexible choice than a FCD and it is probably able to deal with all the changes you listed. Again, you really need to set it up on a dyno to be sure everything is safe and it will take a little longer because there is more the set up.

But, through 20 years of doing this and watching other people doing this...I can say 99% once you have done all your current plans, you will put on a bigger turbo, need bigger injectors and a new (or deleted) air flow meter and at that point you need an ECU.

I have a Link on my Stagea and Haltech on the GTR, the Link does everything a street car needs and is cheaper (actually for that matter a PowerFC is way cheaper than either and does everything most people need) - but if you are going this route what really matters is what your tuner prefers because their time to tune something they are not familiar with will cost way more than any difference in purchase price

[BiggestRon22]

On 1/21/2022 at 9:09 PM, GTSBoy said:

Well, yes, because I can't imagine living with a stupidly loud unmuffled exhaust for long anyway. But if you want it stupidly loud and unmuffled, then you could just fit a 2" orifice plate into one of the flanges to cause some restriction, or choe the turbo inlet down, or something, to reduce flow. Then when you fix the management problem, you retain the stupidly loud unmuffled exhaust.

I go on about the stupidly loud unmuffled exhaust a bit, because......hearing damage. I have it. Wanna know how I got it?

Yeah sadly I’m one of the guys that like it loud, but I will definitely be considering putting at least one muffler in there to make it sound a little smoother and less raspy up top. 
 

Guessing it was the loud exhaust that did the damage, I definitely understand where you’re coming from so I do my best to have all the noise be coming completely out the back and not anywhere near me, I had a ls400 and had it dumping from the headers because I didn’t think it was loud enough at first, very quickly realized that was dumb and had to drive home with ear plugs because I have a 30 minute commute back.

On 1/21/2022 at 10:02 PM, Duncan said:

So the FCD is cheapest way to address your immediate problem (other than putting the original exhaust back on) but it has a narrow range that it can help with. You should still probably run in on the dyno after install to be certain everything is OK so that is another couple of hundred. I picked up about 20kw back in the day when I put the FCD on with 3psi extra boost (10 instead of 7psi)

An SAFC is a much more flexible choice than a FCD and it is probably able to deal with all the changes you listed. Again, you really need to set it up on a dyno to be sure everything is safe and it will take a little longer because there is more the set up.

But, through 20 years of doing this and watching other people doing this...I can say 99% once you have done all your current plans, you will put on a bigger turbo, need bigger injectors and a new (or deleted) air flow meter and at that point you need an ECU.

I have a Link on my Stagea and Haltech on the GTR, the Link does everything a street car needs and is cheaper (actually for that matter a PowerFC is way cheaper than either and does everything most people need) - but if you are going this route what really matters is what your tuner prefers because their time to tune something they are not familiar with will cost way more than any difference in purchase price

I plan is to run around 450hp so I’ll definitely look into the link ecu and PowerPC, currently trying to find out what my local tuner prefers but they’re moving so can’t get much info.

Definitely do plan on the bigger turbo once I have a fuel pump, injectors, r35 coils and arp head studs, I’m mostly looking at the hypergear turbos because I’ve heard pretty good things about them and will either start with an external waste gate high flow stock turbo rated for 400-500 or just get an aftermarket turbo from them both would be similar rating and would have all the added goodies to them. I will be a bunch of other upgrades before I do my turbo because I’d rather over build than not and have things blow, don’t plan on doing a whole rebuild until I want to go past the 450 mark 

also thank you both for the insight  this has been very helpful for me as I’m 19 and still have a lot to learn! 

[QLDR31]

For the brains trust:

So if the exhaust had mufflers and the bov was hooked up would he still have the same issues? I thought if you were adding a cat back or turbo back aftermarket back exhaust things would run alright with a bit more power. I still have the boost restrictor maybe that would help things?

I drove an old R31 skyline for a lot of years with a drony 3" exhaust. Adding an extra muffler was the best thing I ever did. But i'm old.

Invest in ear muffs and save up for defects  

[joshuaho96]

Don't decat street cars, end of story.

[BiggestRon22]

On 1/22/2022 at 6:19 PM, QLDR31 said:

For the brains trust:

So if the exhaust had mufflers and the bov was hooked up would he still have the same issues? I thought if you were adding a cat back or turbo back aftermarket back exhaust things would run alright with a bit more power. I still have the boost restrictor maybe that would help things?

I drove an old R31 skyline for a lot of years with a drony 3" exhaust. Adding an extra muffler was the best thing I ever did. But i'm old.

Invest in ear muffs and save up for defects  

Yeah I’m thinking if the mufflers were still in and bov doing what it’s supposed to it would be fine, but I also thought just freeing up the exhaust wouldn’t be enough to cause the cut. Definitely thinking of putting the bov back on to see what happens but I did notice with my butt dyno the car felt a lot faster but then the cuts started happening too.

love the r31s man, sure it didn’t sound too bad with the mufflers but I know what you mean lol adding a muffler or two just makes the sounds that little bit better.

had to buy a pack of earplugs when I had my Lexus, started to notice my ears ringing after I drove it a few times.

have been quite lucky with Cops in my decatted cars somehow don’t know how cause one of em use to set off car alarms!

On 1/22/2022 at 7:41 PM, joshuaho96 said:

Don't decat street cars, end of story.

Yeah I think for my next car I’ll just get highflow cats instead of test pipes, just like the cheapness of the test pipes cause some highflow cats can get really expensive.