double decat question....

Right, I have everything needed to do a double decat but there is a problem. Someone has tried to get the first cat off before and almost rounded the studs so I have a question....

Why do people do both decats?

If you decat the second and leave the 1st cat in place instead of a restrictor ring, with standard turbos you get the same boost as a double decat right? Basically using the 1st cat instead of a restrictor ring.

If that is the case, why do people do both decats? A double decat is only needed if also chaging the turbos or going single, is that right?

i don't think you can get the 1.2bar boost with the first cat in but not 100% sure!

The first cat is very restrictive, you would need a boost controller to raise the boost if it is left in. Running BPU levels of boost through the 1st cat will generate a lot of heat that could potentially be damaging.

The second cat is less restrictive, you could run with just the 1st decat fitted, but if you are going to the trouble of removing the 1st cat you might as well replace them both.

Removing the restriction of both cats will allow the turbos to spool up a lot quicker and keep exhaust temps to a safe level.

If the bolts are seized, time to get the angle grinder out.

and how would I get an angle grinder in that little space?

drilling them would take ages,

if its too tight to get the angle grinder,

maybe have to remove the whole exhaust from the downpipe,

and PS yea get rid of the 2 cats,

I don't really understand the angle grinding technique. Surely if you grind the stud off you are left with a hole that is full of old stand and needs to be drilled out and tapped again?

Can you not get vice grips on them? Which bit is rounded off? You say the studs? as you shouldn't have to touch them, just wind the nut off.

nuts are rounded and heat has been applied to one of the studs which is now seized and twisted. Basically buggered

also, once this is done I will have to get my valve stem seals done as I have the slight smoke on start up....which with no decats will become more smoke I am sure

that made everyone quiet. lol

I'm doing the first cat hopefully next week. I've been running it with just the first cat for 3 1/2 years now but saying that only done 5k miles in that time.

I just bought my 1st decat from mikeyb10supra so when i get it next week it'll be going in. I'll let you know how hard it is to get mine off and what tools i needed if you've not done it by then

Already know its hard to get mine off because someone has messed up the studs.

How has yours been running with one cat on? wht boost have you got out of it?

dont worry about the studs, remove the bolts a little further up and remove thenext section (the bit the cat bolts to)... then remove from car and grind the studs/bolts to get the cat off and fit new studs etc.. Job done

My studs needed burned off it took the poor bloke 40mins to get the little fecker off!

Running perfect at 1 bar boost.

Were you going to put the RR just after the first decat?

Running perfect at 1 bar boost.

 

Were you going to put the RR just after the first decat?

yup

Yeah getting that first cat off is a real pain, I was on with mine for hours.

But as afore mentioned, undo the elbow that the 1st cat is bolted to and all will be easier.

When i was running twins, i just sprayed a shite load of WD40 on mine and left it to soak for a few hours.The nuts came of the studs pretty easy then.

As for de-cats, you should achive 1.2 bar with the first cat removed, and the second cat still in place.But you'll probably struggle to get 1.2 bar with the first cat still in place, unless it's fooked!

I think it's recommended to fit the R/R after the second cat, not the first

Hum can you not just unscew the stud with a star on the end or are they rounded too?

This is one reason I always go to my local trusty Kwik Fit for 1st cat changes. Places like that are always equiped (and the people trained) for dealing with issues like rounded bolts and snapped studs. Breaking off the bolts and replacing studs is pretty much daily work for them and I've never had any issues, even when studs need changing.

The first time this happened, one stud snapped, but they had the thing drilled, replaced and the new decat fitted in 40 mins. Only charged £20 for it too (ahem, though that was cash in hand ). Was still fine 4 years later when it was changed to single turbo.

I wouldn't recommend any Kwik-Fit or exhaust place for it, there's a massive variation between them, just find one that has decent staff.

Sounds good to me Homer

This is one reason I always go to my local trusty Kwik Fit for 1st cat changes. Places like that are always equiped (and the people trained) for dealing with issues like rounded bolts and snapped studs. Breaking off the bolts and replacing studs is pretty much daily work for them and I've never had any issues, even when studs need changing.

 

The first time this happened, one stud snapped, but they had the thing drilled, replaced and the new decat fitted in 40 mins. Only charged £20 for it too (ahem, though that was cash in hand )

 

I wouldn't recommend any Kwik-Fit or exhaust place for it, there's a massive variation between them, just find one that has decent staff.

You are a lucky man. Most quickfit garages I know staff in just want to sell you pads and discs and everything else and fook you off out the door.. As one manager said to me once "hit em hard hit em once as they will not come back":blink:

Sorry to thread steal:innocent:

but i just need to know that putting the 2nd cat back in and having the 1st decat and RR put in will be ok ? how much power will i lose ?

im prepared to lose a few BHP and .0 bar to stop my turbos from destructing

You could remove both cats, and fit a 1.2 bar RR, and your turbo's will normally be fine mate.(providing your turbo's are in decent nic)

So yes, >

You could remove both cats, and fit a 1.2 bar RR, and your turbo's will normally be fine mate.(providing your turbo's are in decent nic)

 

So yes, >

Good stuff, cheers dude. thats exactly what i wanted to know