Superspec/rover Dramatic Performance Change.

[alanrichey]

Ever since I have had my Superspec it has been marginal on the emissions test and this year, even with a completely new exhaust system it only just scraped through. At the same time I have always felt that something wasn't working properly. Although she idled OK there was a bit of hunting. When I pulled away she occasionally hiccupped, when I put my foot down there was sometimes a bit of hesitation before the revs picked up, and she would regularly have a small uncommanded surge for no apparent reason (lamda sensor switching mixtures?). Finally, there was lots of popping and banging on the overrun.

 

But up till now I have lived with that, as with a non-programmable ECU and the fuel injection I didn't think anything could be done or adjusted. I just assumed some of the sensors were a bit iffy.

 

But while I was asking for help on the forum regarding my catalytic converter Nigel Evans (n.r.evans) told me of a trick a mechanic had recommended to him when he was trying to pass the emissions test, which I don't recall reading on the forum before, and that was to block off one of the 2 exhaust outlets. So, willing to try anything I shoved the remains of an old tea towel up the exhaust.

 

 

What an amazing transformation. She now idles perfectly, and there is no hesitation during acceleration. The power (apparently more than before) comes on smoothly when I put my foot down, and there are no more unexplained surges. She is now working as you would expect. There is also no more popping and banging on the overrun (which is a pity as I quite liked it )

 

So what is the explanation for this dramatic improvement? Nigel's mechanic reckons that when the system was designed there was no attempt made to match all the exhaust components, they were just picked because they fitted together in the right space available. In particular he thinks the lamda sensor needs some back pressure before it will work correctly and with the exhaust as designed there just wasn't enough. Blocking one of the outlets is just enough to provide the necessary back pressure to make the sensor work. Obviously I can't prove it but it seems very logical?

 

I haven't had a chance to check if it has improved the emissions yet but based on Nigel's experience I am very confident. Meanwhile I am enjoying a much improved performance. I just need to find a more professional way of blocking it than an old tea towel.

 

Hope other Superspec/Rover owners find this useful. I would be interested to hear from anyone else who tries it.

 

Al

 

 

[Guest 2b cruising]

I would sujested a simple job of removing box, take to a welder and remove one pipe.

If you want to keep the looks, just patch the box and refit the pipe.

It might even be worth drilling a smaller hole into the patch so overall port size matches the exhaust pipes on the inlet side of silencer.

[Snapperpaul]

With twin exhaust you can get a strange back flow occurring, air sucked in one side as the other ejects the exhaust gasses.

Popping as fresh O2 meets in burned fuel and as the Lambda measures O2 it could confuse the ECU

IMHO

[Guest Tim Norman]

Or just put a new can on with a slightly larger bore and get a better sound as well!

[Al Milton]

What a good spot for you Al - I wonder if this was a contributing cause with the emissions problems for all of the Rover engine 'Specs?

 

As a simple semi permanent fix, if you don't have access to a welder, could you get a 'plug' to match the ID of the exhaust, or slightly smaller?

You could secure semi permanently with a domed headed bolt & nut through the exhaust & 'plug'.

A glug of exhaust sealant around the plug should help as well.

 

Just a thought

Cheers

Al

Edited August 25, 2015 by Al Milton

[alanrichey]

What a good spot for you Al - I wonder if this was a contributing cause with the emissions problems for all of the Rover engine 'Specs?

 

Nigel's mechanic deserves the praise But it would explain a lot wouldn't it, when it appears all Rover-engnied Superspecs suffered the same. I'll report back when I can manage to get the emissions checked properly with and without the plug just to confirm it isn't just my imagination,

[bullfist]

Marvellous - I'll have to try this.

Did the rag not blow out as you sped along the road? When is your MOT due - as would be interested to see if it passes emissions test (as I have issues too)?

-steve

[alanrichey]

I jammed it in The MOT was last week and as I said in my original post, it just scraped through the emissions (as it has done for the last 3 years) even though this year I had a new cat. Haven't had a chance to get the emissions checked yet.

[Guest 2b cruising]

Always go for a good run in a lower gear before testing.

This gets the cat over normal running temperature and clears off any soot traces allowing the ceramics a better reaction process.