Straight Pipe on Stock Twins/Whifbitz Hybrids ?

[2JZMKIV]

Hello everyone,

 

I currently own a 1996 jdm bpu mkiv, the exhaust system it has is not stock but some sort of bpu exhaust system. I want to get rid of catalytic converters question is will it over boost ?

 

I am going to buy Whifbitz hybrid turbos which can be pushed up to 1.4 bar as it says on the description would that change anything ? (whatever the answer is still going to buy them because my turbos are old and i believe they are good replacement )

 

Coming out from exhaust manifold there is the first catalytic converter then pipe follows the 2. one middle muffler/converter ( i really do not know if the middle one is a muffler or converter) and there it connects to hks silent type (type-s) muffler

 

So my plan is to delete the first catalytic converter and the middle one and keep the hks muffler replace the middle one and first one with pipes will it work will my car over boost also i have hks evc 4 boost controller which has a max safe boost setting where it limits the boost (apparently)

 

please help any information is strongly appreciated thanks in advance.

[tony tt]

If the cats are still there it ain't bpu mate.

 

What mileage is on the car? I went for decats and raised boost on my car at 120,000miles and they were still good at 165k! It may save you some money buying hybrids. The ceramic j specs will see 1.2bar max but to be fair 1.4 will just generate more heat and you will see the same rough power figures on ceramics.

If you decat it then it might over boost yes. A restrictor ring between the 1st and 2nd decat is required.

Have you thought about larger fuel pump, colder grade plugs and a fuel cud defender? On your initial post bpu is highlighted in blue. If you click on it then it tells you all you need to know about what you need.

 

Do you have a boost guage?

[tony tt]

See here.

 

Fundamentals of BPU

 

Jspec:

To raise boost beyond the stock level the restrictive catalytic converters are removed, thus allowing the turbos to spin faster and produce more boost pressure.

 

There is a down side to this. With both cats removed the turbos will in fact over speed far past their safe limit and reach over 1.6bar (23.2psi). This is due to the small size of the jspec wastegate which cannot cope with the increase in exhaust gasses.

At these pressures the ceramic blades in the turbo can become detached from the shaft and therefore cause catastrophic failure of the turbo.

 

In order to add some restriction back in to the exhaust a restrictor ring is added to the exhaust system. A restrictor ring is simply a metal plate that fits normally between either between the 1st and 2nd decat pipes, or the 2nd decat and cat-back. The centre of the restrictor is drilled out to a smaller diameter than the exhaust itself (normally around 2inches). A properly sized restrictor should bring the maximum boost pressure down to 1.2 bar or less.

 

UK/Euro/US (Export) spec:

To raise boost beyond the stock level the restrictive catalytic converters are removed, thus allowing the turbos to spin faster and produce more boost pressure. Different to the jspec, the export spec has a larger wastegate which can handle the increase in exhaust gasses.

Therefore boost pressure will be maintained at only slightly above stock levels, typically 0.85bar (12.3psi). In order to raise this further it is necessary to install a Boost controller to change the way in which the wastegate opens.

A restrictor ring is not required on the export spec

 

Note: On both models it’s possible to raise the boost with simply adding a Boost controller or Bleed valve; however this is not recommended since the huge resistance of the cats is still in place. This will result in significant extra heat being generated in the manifold and could cause serious engine damage due to raised exhaust gas temperatures.

 

 

Parts required:

 

Obviously all that’s needed to raise the boost pressure is a double decat & restrictor ring (Jspec) or double decat & boost controller (export spec). However, it will not work without further modifications. The following will be required in both models:

 

1) Aftermarket cat-back exhaust

The stock cat back (the pipe after the 2nd decat pipe) is extremely restrictive. In order to allow a good free flowing system this needs to be replaced with an aftermarket system. There are a huge amount of systems available, but any good quality aftermarket system will be suitable for a BPU level of modification.

 

2) Fuel cut defender

The stock ecu will initiate fuel cut when boost pressure reaches 1 bar for a 3 second period. In order to stop this, a device is needed in order to trick the ecu into thinking the boost pressure is lower.

(See quick link for further details)

 

3) Updated fuel pump

The stock fuel pump in the jspecs is not considered suitable for BPU level power, the one in the export spec is higher specification and will be suitable. However as many of these cars are approaching 13 years old it should be standard practice to replace the fuel pump.

The Walbro pump is commonly used, however the standard pump that comes with the export spec is a better specification and has quieter operation (though considerably more costly).

 

4) Colder grade spark plug

With an increase in boost, a ‘colder’ grade plug is required with a closer gap. There are two basic options:

- Iridium IK22 plugs

- NGK BCPR7ES

The iridium’s will last longer (most people get >10k miles) but typically cost £60 a set

The NGK’s need replacing around 3k miles, but cost £14 a set

 

 

Recommended, but non-essential parts:

 

That’s it for the required parts, though there are two items which are highly recommended to ensure you can monitor the health of your engine:

 

1) Boost gauge

A simple electronic or mechanical boost gauge can be mounted in the dash to view the boost pressure. An electronic boost gauge is recommend as most will come with a peak hold or even playback function, thus allowing easier monitoring of maximum pressures

 

2) AFR gauge

Also known as Air/Fuel ratio. This has a wideband O2 sensor mounted in the 2nd decat which measures the air/fuel mixture of the exhaust gases. This is very important to monitor, otherwise you won't know if the air/fuel ratio runs lean under high boost (and therefore result in piston meltdown). Though it won’t allow adjustment, it will warn you that something is not right if it does go lean.

 

3) EGT gauge (optional to AFR gauge)

Also known as Exhaust Gas Temperature. This has a temperature probe fitted into one of the exhaust runners (as close to the cylinder as possible). It performs basically the same function as the AFR gauge by monitoring the condition of the exhaust gases. High temps (sensor mounted post turbo 950degrees is dodgy, >1000degrees is a very bad thing!) will likely result in engine damage due to lean mixture. However there are some cons when comparing this to the afr gauge:

 

- It is much slower to react

- Failure of the temp probe (i.e disintegration) will result in the particles entering the turbos potentially causing failure

- The exhaust runner requires drilling and tapping which can result in swarf entering the manifold before the turbo. This could result in damage to the turbo blades.

 

A safer place to tap the probe is in the exhaust or downpipe after the turbo. It will stop the risk of swarf ending up in the turbo and turbo damage in the event of probe failure. There is a downside - Installing it post-turbo introduces such a big and variable heatsink into the equation it's pretty much useless. People take anything from 100 to 250degC off the aforementioned maximum, meaning that your gauge could read 800degC and mean anything from imminent meltdown to running nicely. No-one has put an EGT sensor before and after the turbo and datalogged the variance so it's 100% guesswork, and that's the last thing you want on the ragged edge.

4) Intercooler

A replacement or aftermarket intercooler isn't required, however you need to ensure your current intercooler is in good condition and allows smooth airflow though the core. Many of the stock IC's on older cars are now in very poor condition and suffer from corroded fins, if yours is like this it should be replaced prior to going bpu.

[Nic]

The hybrid turbos may be able to run at 1.4bar, but the limiting factor will be the fueling. The stock fueling is close to the limit when running stock turbos at 1.2bar, so with the larger hybrid turbos you will need to run slightly less boost pressure.

 

If you remove both cats then you'll need to fit a restrictor ring, you could limit the boost to say 0.8bar and then raise the pressure with the boost controller, ideally I'd put the car on a dyno to check what the safe boost limit is.

[2JZMKIV]

I am truly sorry for not giving enough details let me be more specific here,

 

reason i called my car bpu was because it pushes 1 bar and it came with sard analayse ecu ( like mines ecu) carbonetic (ats & across) twin plate clutch hks induction system hks evc4 boost controller pretty much basic performance upgrades but for some reason they kept the exhaust system stock i got aem infinity 8 with plug and play harness 5 bar map sensor and wideband its all installed and waiting for the rest now i will be getting aem 320lph fuel pump sard 800cc injectors ngk sparks and hybrid turbos with whifbitz intercooler so i doubt i will be having problems with cooling the air or not flowing enough fuel so the only problem here is the exhausts i will have to ask again after all these would it still be a problem to remove catalytic converters ? do i still need to fit a restrictor ring ? car has around 60k miles 100102km exactly and turbos are operating in true twin mode i cannot remember any more details feel free to ask and thanks for the information!

Edited May 11, 2015 by 2JZMKIV (see edit history)

[Nic]

will have to ask again after all these would it still be a problem to remove catalytic converters ? do i still need to fit a restrictor ring ?

 

If they are j-spec hybrid turbos yes you will still need a restrictor ring, the wastegate on the j-spec turbos is just too small to control the boost levels once the cats are removed. The wastegate is sometimes machined bigger on hybrid turbos but there is very little material on the j-spec turbo exhaust housing and it's a weak point that often cracks.

 

The stock sequential system is quite restrictive, running above 1.2bar with the stock turbos (even with an aftermarket IC) sees a big increase in intake temps, whoever is mapping AEM will be able to see how much boost you can safely run. 800cc injectors are very big for your setup, 540cc injectors would be ample and be easier for the ECU to control.

[masterfett]

i have whifbitz hybrids on mine, double decat and nur spec R, with a RR and a blitz dual spec boost controller. Yes i would say it will certainly overboost, despite the turbo's maybe managing to run 1.4 bar, i personally would never take mine above 1.2 bar the .2 increase doesn't seem worth it to me. go single if you want to upgrade, if not in my opinion stick at bpu and enjoy

[2JZMKIV]

i have whifbitz hybrids on mine, double decat and nur spec R, with a RR and a blitz dual spec boost controller. Yes i would say it will certainly overboost, despite the turbo's maybe managing to run 1.4 bar, i personally would never take mine above 1.2 bar the .2 increase doesn't seem worth it to me. go single if you want to upgrade, if not in my opinion stick at bpu and enjoy

 

i would go single if i could but for that i need at least £8k which i do not have right now. I will go with whifbitz hybrids and eventually will get a single turbo kit. i needed that information so thanks a lot, do you have any idea where i can get a restrictor ring or is it a simple thing that can be made ?i do not drive my supra much did around 500 kilometres in 8 months so ofcourse there wont be much gain but i would run my car in 1.4 bar since i am not worried about turbo life.

[tony tt]

Paul Whiffin sells the RR. Id go for a 1bar RR then raise boost with the EBC to what you want.