Small CAT on instead of Restrictor ring

During these colder months, I am overboosting sometimes and could do with a restrictor ring to calm things down.

My thought is that because my MOT is only a couple of months away, I will be putting my cat pipe back on (small 2nd Cat) to get it through.

What do you think about getting someone to put it on now for me instead of getting a restrictor ring. Will it bring the boost down a bit because of the built in CAT restriction.

Might save me a bob or too and the hassle of a visit to shropshire.

Sorry for sounding tight

It should limit the boost quite well, if you do try it, let us know!

You don't need to visit Chris for the restrictor ring, it'll fit in an envelope! It's also sub-£20.

-Ian

I suppose if it doesn't work, I've not lost anything coz the MOT needs it anyway.

I assume my local tyre and exhaust place will fit a restrictor ring, if Chris posts one off to me?

I'll do it this weekend and let you know how it goes.

I've just had a restrictor Ring from Chris, dropped me just under 1.2 Bar.......

I've just done this very thing. Anybody want a 2 month old CW second decat pipe? See the For Sale section.

Great minds think alike.

What was your boost before and after ?

I only run the second cat, and have a Blitz DSBC. I can't quite see the point in fitting the decat and then a restrictor.

On a cold day, min 1 bar now 0.7-0.8.

But doesnt the cat removal do a good job of taking heat away from the engine. Although a restrictor will give the same boost results it will keep the pipe breathing instead of storing up heat.

My reason for leaving cat 1 out.

I found the power delivery impractical for everyday use - wheelspin was a pain. Not a lot of point producing the goods if chassis can't put it down on the road.

Generally the reason for cat removal is a cheap boost hike.

Originally posted by ChrisR

But doesnt the cat removal do a good job of taking heat away from the engine. Although a restrictor will give the same boost results it will keep the pipe breathing instead of storing up heat.

IMO saying one way is 'better' than the other is a moot point. Putting a restriction in there, which either way gives the same boost, doesn't really make any odds.

Yes, extra heat will be produced by a cat but it doesn't make any difference. It's all on the exhaust side, and cats are designed to operate when hot. In fact, they like it. Obviously, you can get TOO hot and melt a cat but if anyone manages that on a Supra then I'll be impressed. The exhaust won't melt either, so any heat produced isn't going to be a problem. I guess you could argue that the heat could rise from it and enter the engine bay thereby increasing inlet temps etc. but it's all a bit subjective to say the least.

All IMO.

Regards,

Nathan

TDI PLC

Nathan

I'm Ok with all that. I tried the cats out route and it didn't suit me, and it negated the control the Blitz DSBC gave me. On/off power at 4000rpm caused me a moment or two on wet roads in traffic - like overtaking a truck sideways!

Hi John,

I agree, and most people know my views on removing both cats. One thing CW and I do agree on is that it works for some, and not others.

You can take your pick: both cats out, play with restrictor rings and worry about MOT's or leave the 1st one in and do the rest with a boost controller. For our customers, it's a no-brainer and all go the BC route. We can be confident that the boost is safe and they are happy because they don't have to worry about it. The fact that it costs say five hundred pounds more isn't really an issue, and if it is then they wait until they are financially able. Ultimately most Supras end up with BC's anyway.

The good thing is that the choice is there.

Cheers,

Nathan

TDI PLC

I note you say leave cat 1 in and not cat 2. I've done it the other way round. Should I swap around?

I've done this too. My first cat is removed with a CW pipe and the second one is still there. With a Nur Spec my peak boost is 1.17bar, more usually around the 1.1 level.

Originally posted by John Packham

I note you say leave cat 1 in and not cat 2. I've done it the other way round. Should I swap around?

It doesn't really matter. The 1st cat is more restrictive but if you have done it the other way around and are happy with the boost level then keep it like that.

We only remove the 2nd because HKS have never produced a 1st decat pipe due to the overboost problems. I guess theres nothing stopping you doing it the other way round but thats just the way we have done it for years.

There MAY be a small possibility that some Jap specs could still overboost with just the 2nd cat in; SimonB says that he has hit 1.17bar this way so it's getting pretty near the mark. Something to bear in mind.

Regards,

Nathan

TDI PLC

My 2nd replacement pipe is from HKS and was brought for my JSpec car. Will it fit a UK car or are they different.

Yes, it will fit no problem, but you will need to mount a boss to take the 2nd o2 sensor which is used on the Euro cars.

We normally cut it out of the original cat pipe and weld it into the HKS pipe. However, if you have not got the original pipe then you will need to find a boss from somwhere. I think CW sells them?

HKS do not make a pipe specifically for the Euro cars. I think it's because the USA are so tight on emisisons it's not worth HKS USA pursuing it.

Cheers,

Nathan

TDI PLC

I was just thinking of when I put my original cat pipe back on (and assuming it reduces my boost), I might as well sell the HKS pipe and was wondering if I have the UK market to sell to as well.

A very sensible thread here.......

I never understood the logic of fitting a restrictor ring in a pipe!

I understood why people did it, but as I said it's not 'logical'!

And I won't go into details as many here will get lost.........

At last some sense i run my first cat in and a blitz dsbc. I prefer the fact i can control how much boost/power i have at any given time, most of the time i run on min setting ! I have never seen the point of taking out a restrictor to replace it with a restrictor

And on the rollers my car was putting out the same as fully decatted cars give or take 5/10 bhp! As for exhaust temps yes that might be a issue if your running a race car e.c.t. and you really need that extra 2 or 3 bhp but for on the road

The only plus maybe they sound a bitt louder with both cats out !

Originally posted by Nathan

Yes, it will fit no problem, but you will need to mount a boss to take the 2nd o2 sensor which is used on the Euro cars.

 

We normally cut it out of the original cat pipe and weld it into the HKS pipe. However, if you have not got the original pipe then you will need to find a boss from somwhere. I think CW sells them?

 

HKS do not make a pipe specifically for the Euro cars. I think it's because the USA are so tight on emisisons it's not worth HKS USA pursuing it.

 

Cheers,

 

Nathan

TDI PLC

Yep, if you don't want to butcher the second cat I can supply a weld in boss for 20 quid, and will weld it in for another 8 quid.

You MUST run this second O2 sensor, weird things can happen if it's left in fresh air, and WILL happen if it's diconnected.

Originally posted by Supra Pilot

A very sensible thread here.......

 

I never understood the logic of fitting a restrictor ring in a pipe!

I understood why people did it, but as I said it's not 'logical'!

And I won't go into details as many here will get lost.........

for most its a question of cost. You can decat a car for £250, restrictor is about £20, minimal insurance cost as its not a mod that gives masses of power (or the insurance companies think it doesnt).

Cheapest boost controller is going to be £250, single cat decat is £150 and then you have to find an insurance company willing to insure you with a boost controller on board (Bell refused somebody recently on here who had an SBC-ID fitted).

JB

I dissagree,

Most here have done a 'de-catt' for more power(the big BPU) and then realize that the boost is running away/or gone too high.

Going too high is not bad but it's the associated high temps to accompany this is not good...

So to combat this, a quick fix is the magic restrictor ring........

This IMO is not really solving the problem as you are going back to square one in lowering the boost!

When the reason in the first place(de catt) was to get MORE BOOST!!!!!!

Seems like 'Pissing into the wind there.....'

The real problem is not being address, 'High Temps'.....

Many many ways to solve this problem.....but someone comes up with a 'quick fix' or cheap fix and says put this ring in,,,,, ok we will sir...

And see's results that the boost is stable and all is well.......but what was achieved in the first place...nothing really was it........

When an exhaust system was designed, do you not think they thought about all this, 'restriction and flow etc', whats the best for the engine performance and turbo function.......

Anyway I won't get into more about tis as I can go on with it and prove it more and more......

At the end of the day, you cannot convince me that a restrictor ring is required......

'It is a cheap fix for a modification that is in complete!'

A restrictor ring is unarguably a crutch, a bigger wastegate and better sized turbos are the real cure, but the big davantage of a ring over re fitting a cat is the ring is tuneable by the owner, with a file, to get the most safe boost pressure, without MORE restriction than necessary and the then need for a boost controller to bring it back up again. That and the fact a ring doesn't generate or hold heat like a cat. The restrictiveness of a stock cat is not user adjustable

OK chaps, we have come full circle and I think it might be wise to clarify this in a way which some might find helpful, ie a pros and cons listing:

FULL DE-CATTING:

Pros:

1. Cheap (relatively).

2. Reduces exhaust heat.

3. Possibility of insurance being cheaper.

Cons:

1. Will render vehicle illegal on emissions, although can be rectified by replacing one or both cats.

2. Boost levels can spike.

3. Boost levels can vary, requiring fitment of additional restrictor ring.

4. Even with ring fitted, it may need 'fine tuning' to each car for correct boost levels, thus incurring additional labour and/or the need for the owner to be involved with getting under the car to remove and replace the ring as many times as is required.

5. Advisable to fit boost gauge to monitor levels due to reasons above. An accurate gauge would start @ £75.

6. Boost level is fixed and cannot be adjusted in-car, thus set limit @ 1.2 bar will require use of at least 97RON fuel at all times.

7. If larger replacement turbos are fitted, pipes will be unnecessarily restrictive.

8. Most vehicles end up with boost controllers fitted anyway, thus negating the saving. Indeed, the overall conversion will be more expensive due to purchasing pipes and/or restrictors that are no longer needed, including the labour needed to fit them in the first instance.

2ND DE-CAT & BOOST CONTROLLER

Pros:

1. Vehicle remains legal, without the need to replace cat/s for MOT.

2. Boost levels are stable throughout the year.

3. Boost curve can be smoother.

4. Is fitted and setup at same time to be 'fit and forget'.

5. Several boost levels can be pre-set and adjusted in-car. For example 0.8 bar/1.0bar/1.2bar is a common configuation. One benefit of selectable boost levels is the ability to run 'regular' fuel on low boost if required in an emergency.

6. The 2nd de-cat pipe will flow enough for 800bhp meaning it is future-proof for further upgrades.

7. Boost controller has built-in boost gauge, thus avoiding the need for an independant gauge to monitor boost levels.

8. Boost controller is able to run to 2.5bar, meaning it is future-proof for further upgrades. It is also universal to all turbo vehicles and can be kept by owner if required for next car.

Cons:

1. Approximately twice as expensive for conversion (£965 Vs £485).

2. More heat produced in exhaust.

3. Possibilty of insurance being more expensive.

With all respect to CW personally I'm unconvinced that the reduced heat provided by full de-cat will produce any benefits whatsoever. Neither am I convinced of insurance being cheaper by using the full de-cat method. This is because most insurance companies I am aware of ask for the bhp gain irresepective of parts used. In which case the quote would be the same. However, I have included the aspect anyway due to JB's comment. So IMO most potential purchasers are simply talking about the initial cost difference.

With the pros and cons listed above it will hopefully make it easier for interested parties to decide which would be best for them.

Best regards,

Nathan.

TDI PLC