1991 SE turbo, thinking about removing the cat ?

[Axel-F]

Dear all,

This has probably already been discussed, sorry for that, but I read several different thinks on this topic and can't figure what to do ...

I own a CAT 1992 SE turbo, (for Italian market, it seem), assuming that the non CAT SE turbo has 10 bph and a few more torque, I had planned to remove the CAT, and get the power (and sound) increase ...

That said, I read on the LEC Wiki, that CAT M100 and in general all types of M100, were optimized to work the better with fitted exhaust, CAT or non CAT, and that removing standard exhaust didn't always improve power, and sometime did reduce it ...
And I am not even sure that SE CAT exhaust is the same as S2 CAT exhaust, so I don't know if S2 CAT threads apply ...

So my question is, if I replace my standard CAT exhaust with a stand non CAT exhaust, what else will I have to do to get the expected power increase ?? (replace ECU because of CAT sensor ?, settle timing ??, ...)

And by the way, is there easyer or best way to go ?
- just replace pre CAT, and keep main CAT ? (or the opposite)
- go strait for an other exhaust (piper, ...)

Any advice / comments are welcome !!
Regards,

[Alan_C]

It all depends on your countrie's annual car test policy, what we call the MOT in the UK. If you have to pass a carbon monoxide test with the cat fitted, then your car probably won't pass with it removed, that said, cars in the UK have been known to pass with just the pre-cat fitted. Exhaust fitting wise, an SE non-cat exhaust will fit your car, there are cat equipped exhausts too, I think your exhaust is the same as a S2. Power increase wise, running an exhaust system with no cats will give the biggest power increase (but may then fail the car's annual test). Just replacing your standard cat exhaust with a standard SE non-cat exhaust should in theory give a power increase, but I'd fit a stainless system anyway, which would give a power increase over the standard SE exhaust.

Doing any of the above may also give rise to turbo boost creep, this essentially means the turbo boost becomes uncontrollable by the engine ECU eventually causing the ECU to limit fuel to protect the engine. This is cured by enlarging the wastegate hole in the turbo (turbo has to be removed to modify it). Loads of topics on this subject and a WIKI on how to do it.

[Axel-F]

Thanks for your reply !

It all depends on your countrie's annual car test policy, ...

As only non CAT SE were delivered in France in 1992, I assume removing my CAT won't be an issue for the MOT,
but I will check that point before anyway !!

Just replacing your standard cat exhaust with a standard SE non-cat exhaust should in theory give a power increase, but I'd fit a stainless system anyway, which would give a power increase over the standard SE exhaust.

Ok, so you confirm the FAQ comment is not so straight ...
"Question: Can you improve the performance by fitting an after-market exhaust? (see also Upgrade Comparisons )
Answer: Probably not. The standard exhaust system although not as “fruity” sounding as some owners would like seems fairly well optimised. However, stainless steel ‘standard’ replacements are reported to improve the sound quality...."

Doing any of the above may also give rise to turbo boost creep, ...

Well, it may solve my poor boost, only reach 0,4 ... no ?

And there is no ECU modification required ? is think there is a CAT sensor that need to be removed, could it disturb the ECU ?? (I think I have seen some thread on that topic)

[Alan_C]

The sensor is located in the exhaust elbow bolted to the turbo, you'll see it sticking up through the heat shield on the turbo. It's actually a lambda sensor and detects the presence of CO, this enables the ECU to change the fuel/air mix keeping the engine running at the optimum program. This remains in place and the ECU does not need to be altered or changed in any way. Unless you also want to fit a Mountain tuning chip for increased turbo boost. The cats are in the system beyond the sensor so as far as the ECU is concerned, the cats make no difference. If your regulations allow, removing both cats will give the greatest power increase by allowing the exhaust gasses to pass more freely. I believe only the cars destined for Japan had an additional sensor, this was a cat temperature sensor, I've never seen one.

The Elan SE has a section of the exhaust squashed to restrict it, so replacing it with an aftermarket system with a bigger bore allows a much less restrictive path for exhaust flow, so increasing power. I'm unsure if your SE cat exhaust has this squashed area, if it does, you'll see it up near the front just behind the flange from the pown pipe. As these aftermarket systems tend to have a more free-flowing silencer, they also tend to be noiser, though the Piper is available with 2 silencers and so is the quietest.

[rip]

cars in the UK have been known to pass with just the pre-cat fitted.

I believe that is only earlier S2's which are subject to the older, more relaxed emissions regs. but all S2s were designed for the newer, stricter limit which only applied to the later ones. Definitely worth checking though.

"Question: Can you improve the performance by fitting an after-market exhaust? (see also Upgrade Comparisons )
Answer: Probably not. The standard exhaust system although not as “fruity” sounding as some owners would like seems fairly well optimised. However, stainless steel ‘standard’ replacements are reported to improve the sound quality...."

I completely disagree with that answer.
A bigger exhaust will allow the engine to breathe better. Boost creep is caused by too much exhaust for the wastegate to cope with. The fact you are getting boost creep with a bigger exhaust & unmodified wastegate is proof that the volume of exhaust gas has increased. Unlike NA's, valve timing on a turbo is optimised for the turbo to be pushing the charge into the engine against a closed exhaust valve (NAs are designed for the piston to pull it through with a bit of help (valve overlap)from the outgoing exhaust gas to kick things off). That being the case, increased volume = increased power.

I hope that made sense? Does to me

And there is no ECU modification required ? is think there is a CAT sensor that need to be removed, could it disturb the ECU ?? (I think I have seen some thread on that topic)

As Cutlea mentioned, No. A bigger exhaust will not be fooling any of the sensors. The ECU will still understand what is going on & will not have a problem with it.

[Axel-F]

Thanks, that make thing clear for me !

cars in the UK have been known to pass with just the pre-cat fitted.

I believe that is only earlier S2's which are subject to the older, more relaxed emissions regs. but all S2s were designed for the newer, stricter limit which only applied to the later ones. Definitely worth checking though.

I have checked, no CAT required before 1993 if engine > 2l, so it's Ok on that point !!

"Question: Can you improve the performance by fitting an after-market exhaust? (see also Upgrade Comparisons )Answer: Probably not. The standard exhaust system although not as “fruity” sounding as some owners would like seems fairly well optimised. However, stainless steel ‘standard’ replacements are reported to improve the sound quality...."

I completely disagree with that answer.
A bigger exhaust will allow the engine to breathe better. Boost creep is caused by too much exhaust for the wastegate to cope with. The fact you are getting boost creep with a bigger exhaust & unmodified wastegate is proof that the volume of exhaust gas has increased. Unlike NA's, valve timing on a turbo is optimised for the turbo to be pushing the charge into the engine against a closed exhaust valve (NAs are designed for the piston to pull it through with a bit of help (valve overlap)from the outgoing exhaust gas to kick things off). That being the case, increased volume = increased power.
I hope that made sense? Does to me

Yes that make sense, I fully agree with you, that's the reason is put this FAQ on the thread, it seemed strange to me ...

And there is no ECU modification required ? is think there is a CAT sensor that need to be removed, could it disturb the ECU ?? (I think I have seen some thread on that topic)

As Cutlea mentioned, No. A bigger exhaust will not be fooling any of the sensors. The ECU will still understand what is going on & will not have a problem with it.

My point was not only with the bigger exhaust, but with the sensor, and as Cutlea said, the Oxygen sensor is before the starter CAT, so is not impacted by the CAT.
I was wondering about a potential other sensor, the one Cutlea mentioned which is the overheat sensor, located on the starter CAT, but only for Japan (thanks Cutlea, I have checked the documentation and you are wright !)
I will just check I don't have this one, it should be easy to see it on the starter CAT.

So thanks again, that mean I can now focus on the CAT removing, not sure I will go for aftermarket exhaust, I tend for more power but also I want to keep my car as original as possible ...

If I go for a standard non CAT exhaust, do you think I need to replace the complete line, or just the CAT ? (Main CAT replaced by the standard rear silencer,...)

[Alan_C]

Don't forget you can also remove the starter or pre cat located in the big cast iron down pipe, I think it can be taken apart and the cat falls out, or get a PCE (pre cat eliminator) to replace it. As to keeping the car standard, I wouldn't want to refit a Lotus supplied standard mild steel exhaust, it's more expensive and doesn't work as well as a Piper or Peco stainless system, and you've already deviated from standard by removing the cats. If you don't want the car to be any noisier, then opt for the twin silenced Piper system. A stainless exhaust is an asset should you want to sell the car at a later stage.

[steve matthews]

Federal SE -w- PCE from piper (pre cat eliminator).
No main cat, 2 1/4 Peco installed.
Dyno 5-07-10. Produced almost 55 additional hp. over stock set up.
Everest ship corrected over boost for now and produced additional 15 hp.
Steve -w- new lady

[tigerdog]

Wow, Steve! Quite a difference. I wonder how much is due to the precat, how much due to the main cat. My guess is the precat is the major culprit here. Also, quite possible one of yours was clogged to begin with. As for me, I'm keeping my main cat in place, 1) because California requires and 2) because I got behind a de-catted car the other day and about gagged on the exhaust fumes. "Do unto others..." and all that. YMMV

[steve matthews]

Environmentally speaking yes I agree.
Sound volume also increases and can be detrimental to the ride.
I understand that a sport cat reduces HP by only about 6 to 10 HP.
Is this correct and would it also help with the decibels?
Sorry if I am off topic, or am stealing this thread.
Steve

[Axel-F]

thanks gents,

Going for a Pre Cat Eliminator seem to be a good option to begin with, keeping the main Cat in place,

With just the PCE fitted, can someone tell :
- how much power increase ? torque ?
- what impact on the noise ?

[steve matthews]

Axel, will you also upgrade exhaust size?
I would expect to see some improvement 5 to 10 HP.
But the exhaust is still restricted with the 2".
No additional noise but maybe a little deeper tone.
Steve

[Axel-F]

Axel, will you also upgrade exhaust size?

Not yet, may be later, but I have to change damper / tyres, and also think about brake upgrade...

I would expect to see some improvement 5 to 10 HP. But the exhaust is still restricted with the 2".

Thats not too bad, do you think I could face overboost issues ? (I won't risk overboost issues for 5 hp more ...)

No additional noise but maybe a little deeper tone.

Thats perfect !!

By the way, does a Cat need replacement after some years or miles of use ? does it obstruct when get old ?

[steve matthews]

Axel, no over boost when I first fitted mine even with 2 1/4" exhaust.
Over boost showed up upon removal of main cat and then only when cold damp air present.
This is per a Fed. car.
Cats do clog and break up inside. They make a metallic rattle sound.
Steve -w- new lady

[tigerdog]

I can confirm, a clogged or broken cat will SIGNIFICANTLY hamper performance. Smaug's main cat became knackered after running a short while on 2 cylinders (shorted ignition after coolant bottle crack). The excess unburnt fuel was enough to overheat the cat and crack the ceramic substrate. Once the rattling started, the abilty to make boost went away and performance suffered. New cat installed (2.5") fixed the problem and restored the boost.

[bratboy_y2k]

ok my brain needs some clarity on this one. so the theory is if you clear the precat and remove the main cat, even if everything else is stock, boost creep might happen. i dont get this since the european se's didnt have cats of any kind and i havent heard of them having boost creep. why would north american cars be affected by something that their european counterparts dont have when the circumstances are the same-no cats?

[GeoffSmith]

so the theory is if you clear the precat and remove the main cat, even if everything else is stock, boost creep might happen.

I don't think anyone has suggested that.

the european se's didnt have cats of any kind and i havent heard of them having boost creep. why would north american cars be affected by something that their european counterparts dont have when the circumstances are the same-no cats?

Correct.

[Axel-F]

... is if you clear the precat and remove the main cat, even if everything else is stock, boost creep might happen...cats?

From what I understand boost creep apend when removing CAT and fitting 2 1/4 exhaust, not with stock exhaust,
as it has been said there's a flatened section of the stock exhaust, that reduce flow ...

By the way, any adress were to get a Peco PCE ? Didn't find with Google...

[steve matthews]

Piper pre-cat.

[Axel-F]

Piper pre-cat.

Thanks!! Find it !
Do you think the 2,25" PCE will fit the 2" standard exhaust ? (no 2" pce...)