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R33 Dump Pipe Installed - Now Boost Holding Back

rory_kieran
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rory_kieran Contributor

rory_kieran

Posted
Posted

Hi Everyone,

My friend has a R33 with a 3inch exhaust and runs 12 pound on it. He hollowed out his cat and installed a dump pipe on the weekend. Said it pulls heaps harder but at 4000-5000 it seems to hold and then kicks in again. Anyone think they know why and have any suggestions to avoid this.

He has no electronic boost controller or FMIC either. any help would be appreciated.

R31Nismoid Grand Master

R31Nismoid

Posted
Posted
hollowed out cats create more back pressure than a normal cat..proven

i doubt its the dump pipe.

What drugs are you tripping on?

Proven that hollow is less backpressure... if anything.

12psi stock cooler is just silly behaviour. Its probably 15psi+ before the cooler and i'd say the turbo is going to die very shortly if he keeps that up

The problem is this, its just Rich & Retard mode. Use the search button. Common problem on a boosted skyline with a stock ECU

Denver Grand Master

Denver

Posted
Posted
how does that worK ??

because the air instead of passing straight through, swirls around in the now empty cat, causing turbulance and slowing the air flow through it..

better to get a cat replacement pipe made up, or smashing a piece of pipe the right dia through the old hollowed out cat, so its basically a pieve of pipe inside and not a hollow chamber..

Sydneykid Grand Master

Sydneykid

Posted
Posted
Hi Everyone,

My friend has a R33 with a 3inch exhaust and runs 12 pound on it. He hollowed out his cat and installed a dump pipe on the weekend. Said it pulls heaps harder but at 4000-5000 it seems to hold and then kicks in again. Anyone think they know why and have any suggestions to avoid this.

He has no electronic boost controller or FMIC either. any help would be appreciated.

ECU rich and retard mapping due to excessive airflow as sensed by the AFM.

:glare: cheers :laugh:

PS, write 50 times.........

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

There is no such thing as boost cut

mad082 Grand Master

mad082

Posted
Posted

.

ECU rich and retard mapping due to excessive airflow as sensed by the AFM.

when it kicks in it certainly feels like a boost cut, cause it dies completely then kicks back in.

is it a sudden stop start, or a flat spot where acceleration slows for a bit. if it is a sudden cut out then it is 'boost cut'. if it is just a slow spot then it could be the cams changing over. there is a thread on it somewhere on here, and how you can change when it does it slightly with an aftermarket ecu.

Sydneykid Grand Master

Sydneykid

Posted
Posted
.

when it kicks in it certainly feels like a boost cut, cause it dies completely then kicks back in.

is it a sudden stop start, or a flat spot where acceleration slows for a bit. if it is a sudden cut out then it is 'boost cut'. if it is just a slow spot then it could be the cams changing over. there is a thread on it somewhere on here, and how you can change when it does it slightly with an aftermarket ecu.

Boost cut = 2 words “boost” and “cut”

Boost = The R33GTST ECU has no idea what boost the engine is receiving, it doesn’t do anything about boost, it doesn’t care.

Cut = reduce to zero

Reduce what to zero?

Fuel, nope the ECU doesn’t do that

Ignition, nope the ECU doesn’t do that either.

What you are describing is excessive airflow as sensed by the AFM. When the ECU sees excessive airflow for the rpm and throttle opening it moves to Rich and Retarded mapping. This is done to protect the engine from what the ECU thinks are faulty sensor reading. Either the TPS or the rpm sensor or the AFM (or all three) are reading incorrectly based on the ECU’s programming.

Note the words used “When the ECU sees excessive airflow for the rpm and throttle opening its moves to rich and retarded mapping.” That is why you get a drop in power (R&R mapping) just after the boost has peaked. This goes on for a few hundred RPM, then the sensor readings (the TPS, rpm sensor and AFM) start to line up again. So the ECU returns to more normal (non R&R) mapping.

This is even more proof that there is no such thing as “boost cut”, otherwise it would stay “cut” for as long as the boost was high. But it doesn’t.

Repeat after me;

There is no such thing as boost cut………….

:D cheers :wub:

mad082 Grand Master

mad082

Posted
Posted (edited)

i call it boost cut cause its easier than saying rich and retard mode.

slightly off subject, does the stock ecu have a map sensor? there is a box in the back corner of the engine bay on the drivers side with a vacuum hose hooked up, and wires coming out the other end. what is it for?

Edited by mad082
R31Nismoid Grand Master

R31Nismoid

Posted
Posted

in the name of correct terminology, and correct information on the forum.

Its Rich and Retard.

There is no point calling it boost cut... if is not boost cut.

That is incorrect. The forums are hear as a source of accurate information to help those that are having problems or need extra help.

Are you an enthusiast? Do you even care about the accuracy of your posts?

mad082 Grand Master

mad082

Posted
Posted (edited)

well everyone calls the skylines with the active diff a 'GTS-T with an active lsd' when they are really called a 'LSTS'. and my source for that is an article in a HPI mag (as well as various websites i found in japanese and translated).

and does it really matter if it gets called boost cut, or rich and retard mode? i doubt that there is someone out there who will read this and think 'i couldn't get rid of my boost cut without changing my ecu, but now that i know its only rich and retard mode i can fix that no worries'.

at the end of the day it is a different name for the same thing. the are plenty of things on this site going by the wrong name.

Edited by mad082
Sydneykid Grand Master

Sydneykid

Posted
Posted (edited)
well everyone calls the skylines with the active diff a 'GTS-T with an active lsd' when they are really called a 'LSTS'. and my source for that is an article in a HPI mag (as well as various websites i found in japanese and translated).

and does it really matter if it gets called boost cut, or rich and retard mode? i doubt that there is someone out there who will read this and think 'i couldn't get rid of my boost cut without changing my ecu, but now that i know its only rich and retard mode i can fix that no worries'.

at the end of the day it is a different name for the same thing. the are plenty of things on this site going by the wrong name.

The problem is when someone is told it is a “boost cut” problem the first thing they think is there is some hard and fast boost limit that they can’t exceed. Then we get silly stuff like;

1. I have been told I can run 1 bar before I will get “boost cut”, is that OK?

2. My mate runs 12 psi and doesn’t get “boost cut” and I run 11 psi and get “boost cut”, why ?

3. Something is wrong with my engine I get “boost cut” at 10 psi ?

4. GTR’s don’t get "boost cut" until 1.1 bar, so why do GTST’s get "boost cut" at 11 psi ?

and 100 more equally wrong questions per week, every week.

The reality is we need to get people on SAU talking about excessive airflow, boost is irrelevant. So if the regular posters don’t use “boost cut” and use the correct terminology then eventually we won’t have to spend time writing explanations as to what it really is and why boost is irelevant

:rofl: cheers :P

Edited by Sydneykid
B-Man Grand Master

B-Man

Posted
Posted
because the air instead of passing straight through, swirls around in the now empty cat, causing turbulance and slowing the air flow through it..

better to get a cat replacement pipe made up, or smashing a piece of pipe the right dia through the old hollowed out cat, so its basically a pieve of pipe inside and not a hollow chamber..

That doesn't answer my question - the post read:

"hollowed out cats create more back pressure than a normal cat..proven"

Which is rubbish.

I can prove you you that with a (brand new catco 3") cat - my skyline made 289rwkw - with a elcheapo compliance cat hollowed out - it made 330rwkw - (only under test conditions on the dyno of course).

rob82 Mentor

rob82

Posted
Posted
The problem is when someone is told it is a “boost cut” problem the first thing they think is there is some hard and fast boost limit that they can’t exceed. Then we get silly stuff like;

1. I have been told I can run 1 bar before I will get “boost cut”, is that OK?

2. My mate runs 12 psi and doesn’t get “boost cut” and I run 11 psi and get “boost cut”, why ?

3. Something is wrong with my engine I get “boost cut” at 10 psi ?

4. GTR’s don’t get "boost cut" until 1.1 bar, so why do GTST’s get "boost cut" at 11 psi ?

and 100 more equally wrong questions per week, every week.

The reality is we need to get people on SAU talking about excessive airflow, boost is irrelevant. So if the regular posters don’t use “boost cut” and use the correct terminology then eventually we won’t have to spend time writing explanations as to what it really is and why boost is irelevant

:D cheers :laugh:

Totally agree as there are ECU's which "boost cut" (subaru, ford,toyota) and there are ECU's which reach a predefined "airflow limit" usually vs rpm (mitsubishi, nissan,GM).

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