Help with a cat bypass

Hi there I'm hoping that someone may be able to help me. I bought Andy 43's VR4 recently and apart from it being a fantastic vehicle he kindly threw in a cat bypass pipe. Now it probably would have sat on a shelf in my garage for a little while longer had not what looked like a superchaged (sticking out of the bonnet) Nissan Navara given me a run for my money yesterday and upset me a little.

The questions I have are these;

1, Will bypassing the cat give me a noticeable increase in power or has that been already taken care of as far as is possible with the cat back jp exhaust that is fitted?

2, If I do fit the bypass is it legal and do I need to swap it back for the MOT?

3, Will I need gaskets or can I use some type of sealant when I fit the pipe and if so which ones?

4, When I did a search for "cat bypass" I found Sullis original ad from when he sold it to Andy and I liked the tiltle "300 BHP Ralliart Galant (Legnum) VR4 " I noticed that the only difference bar the cat bypass was a "Titanium backbox with removable baffle." Would this have made much difference to the power do you reckon and should I try to recover it or get a new one?

5, How do I persuade my better half that a boost controller is a necessity rather than a luxury?


Sorry for all the questions but I've always played with bikes before so it's all a bit new to me, especially how quickly and badly I have been bitten by the power bug! I'm amazed at just how much faster four wheels with AYC can get you around a corner than can two!

Thanks very much in advance

Removing the cat will release horses. It is illegal, I think? That hasn't stopped me in the past. And yes, you will have to refit it for your MOT, unless by some amazing feat you can get your emissions in to spec without it.
Basically, your turbos should spool faster, giving more low down power, but also the turbos will have less resistance to push against along the exhaust, so you will notice a big difference at high revs.

Not sure how to convince your better half that a boost controller is a necessity!

1, Will bypassing the cat give me a noticeable increase in power or has that been already taken care of as far as is possible with the cat back jp exhaust that is fitted?
I found mid range pull increased considerably but it lost a little of the off the line urgency.

2, If I do fit the bypass is it legal and do I need to swap it back for the MOT?
It's not legal, you probably would need to swap it back for the MOT due to the emissions test.

3, Will I need gaskets or can I use some type of sealant when I fit the pipe and if so which ones?
Camskill, and Mitsubishi make the proper gaskets, or you can just use some exhaust sealant/gasket, any brand name stuff should be alright

4, When I did a search for "cat bypass" I found Sullis original ad from when he sold it to Andy and I liked the tiltle "300 BHP Ralliart Galant (Legnum) VR4 " I noticed that the only difference bar the cat bypass was a "Titanium backbox with removable baffle." Would this have made much difference to the power do you reckon and should I try to recover it or get a new one?
I think 300bhp is stretching the truth a little. If you remove the baffle it'll be louder but I doubt you'll see much, if any hp gains

5, How do I persuade my better half that a boost controller is a necessity rather than a luxury?
Don't tell her

Thanks guys, thats helped me loads. But why I didn't think of not telling her about the boost controller I don't know, after all that how she persuaded me to bring our daughter into the world :thinking:

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Originally Posted by Dishuldog

after all that how she persuaded me to bring our daughter into the world :thinking:

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Sounds like leverage to me mate, let us know how you get on with that.

;) Ah but you see I already used the Baby card to get the car in the first place. it went something like this "You know, now I can't just go for a ride and unwind on my bike it would be good if we had a car that the whole family could come out in that I could enjoy driving" seemed to work ok.
I did notice that yesterday with the Navara she did seem a little bit miffed he kept up so well so we'll have to see.
What was it Andy Dufresne said in the Shawshank Redemption.......All it takes is time and pressure! ;)

Funny enougth i have just put my cat back in for it's mot and did notice alot of difference in performance just lost the urgency
But have found a friendly MOT station that may help me out for next year /lol
On ours it is not illegal to not have the cat but to fail a emmisions test is so in principle it is not illegal but in reality it is DOH
but to change it back is only a 30miniute job i have never used any sealant but can see where it blows a little. soot witness marks
all the usual mods would get nearer 300 not just an exhaust boost inlet and full exhaust. Have a look at some of the std graphs on uk fuel on WRC's day i made a poor 170wbhp with standard car and intercooler and hks inlet(bad) 230ish at the fly, last one boost controller 0.8 bar full exhaust and arc inlet 280 fly
DOn forget a big loss is down to poorer fuel (102 to 98?? )and age

a boost controller plus decat will definitely increase your power output, especially in the mid range. go for it!

All you need to do is slot the decat in in place of the cat, and use a bit of exhaust paste gasket stuff - it was hand made to fit exactly, changed it myself for Andy, alhough why he didn't keep the decat on I don't know. The baffle for the backbox will have restricted flow too, again Andy wanted it in - he was very under the thumb/pan

The decat allows the exhaust gas to flow freely, instead of being blocked by the catalyser, increasing power, and with it being a proper Ralliart VR4 @280 Bhp standard (although they only say it's that because of the gentleman's agreement), and the performance filter on it (Green I recall) it should be 300 Bhp.

You may want to fit 3" turbo downpipes to match the exhaust bore, as well as a remap, to get a good hike in power.

I really miss that car by the way. The only things I would have changed, had I kept it, would have been Brembos and possibly LPG, as the reason I sold it was the ridiculous fuel consumption - killed me then, I dread to think now.

Anything you need to know on it, let me know, i'd be pleased to help.

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Originally Posted by Sulli

...with it being a proper Ralliart VR4 @280 Bhp standard (although they only say it's that because of the gentleman's agreement), and the performance filter on it (Green I recall) it should be 300 Bhp.

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That's a little optimistic I'm afraid... Don't forget that the 'Ralliart' cars are just Cold-Area Jap Imports that were just SVA converted and undersealed by Mitsubishi UK and as such they're rated at 276bhp just like any other facelift VR-4. Over the past couple of years we've found that more often than not you get these beasties on a rolling road and if you get the quoted 276bhp (280ps) out of them - and with standard boost and no other mods you'll be some way off 300bhp.

Wang up the boost however............. ;)

Take your point, but I seem to remember Pezza recording times as quick as SGHOM, and the other bloke with a highly modded VR4, in Stratford. Mine was a very fast VR4, as well as feckin gorgeous - lucky new owner!

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Originally Posted by Sulli

Take your point, but I seem to remember Pezza recording times as quick as SGHOM, and the other bloke with a highly modded VR4, in Stratford.

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What event was that? I don't remember that?

Some meet up in Stratford just off the A46.
I think Pezza went out in a few and mine was one of the, if not the quickest - some chubby bloke called Dave and grey haired bloke called SGHOM were there/haz
Bernard (I think) from Nuneaton was there too/pan

Oh riiiiiiight - I remember reading about that..