joz8968

iTrader: (13)

Specifically, I need an emission-friendly one that will temporarily swap in their own supplied cat (either downpipe or centre section), in order to get it through the emissions.

In the Leic. area -- but would travel (within reason).

Cheers

Vxr2010

would it in the long run , not be easier to put a 200 cell downpipe cat on and no more mot hassle , and a map check , it’s a minimal power difference

joz8968

iTrader: (13)

Yes, it would! As I have just had full engine and turbo rebuild and will no doubt seize the opportunity to do that before a remap (after running in).

But, right now, that's not an option.

stockcar

we have just convinced another customer to fit a 'sports cat' and just as we have seen on many previous occasions it has made the same power whilst actually gaining response and torque in the mid range........

just to add, correctly mapped to suit.......

jaygsi

iTrader: (46)

What cell sports cat is this? In reality the car will be setup to have a cat in place unless remapped.

stockcar

this particular one was 100CEL but we see it with all sports cats..........
this is going from a correctly mapped car with no cats to fitting a sports cat and then adjusting the map to suit

Vxr2010

two of mine have 200 cell sports cats , the third still on its standard cat but has not been mapped yet , both sports cats making good power , i have a japspeed down pipe on mine since pre 2019 and not had an mot issue as long as it’s warm pre test , and they are not a lot of £ to buy , i expect hayward and scott one is better but it’s also ££ , but quite a few sports cat down pipes come up on ebay ie a prodrive ones 👍😁

jaygsi

iTrader: (46)

I struggle to get my 100 cell Ninja sports cat to pass is mot. It does but takes ages off revving and warming. Want to swap to 200 cell. But I'm running some cat cleaner through it, to see if that helps.

lockheed

iTrader: (1)

Why do you think this happens in regards to the cat gaining torque and response Alyn ?

Vxr2010

im sure alan knows more than me , my theory is all exhausts need some back pressure , my na 6.2 v8 ran really bad without some exhaust back pressure , it was very loud 😁😂 but terrible running , i expect a scooby has the same need of some but not too much back pressure 👍😁

lockheed

iTrader: (1)

I always thought the quicker you can get the fuel in then burn it effectively and get it out the better .
thats what all this exhaust and head porting is all about surely .?
Could be wrong , i often am. Heard the get spec manifold might work better if it were a smaller diameter .

hedgecutter

iTrader: (5)

Just to clarify; the OP is looking for an MOT station that provides their own sports cats ( obviously various different cat lengths and bolt patterns) to temporarily bolt on to his car to pass emissions?
Why would a business do this, on any planet?

stockcar

exhaust design just as head / manifold porting is a science rather than simply some bloke tying a few bits of scrap pipe together (as at least one competitor found out who tried to copy our 'trick' up-pipes.......)

if there is little or no back pressure then it reduces the scavenging effect and therefore is less efficient

joz8968

iTrader: (13)

Alyn

Do you stock the GT Spec1 un-equal single-scroll two-bolt manifolds? If so, how much?

Can they also be supplied by you, DEI heat-wrapped? Again, what price?

John

stockcar

your far better off emailing the office direct as random messages like this tend to get missed (and we aren't supposed to post biz stuff.......)

the first Gen - GT spec headers were a 2bolt flange that was basically poorly designed and generally these don't exist anymore albeit we have seen some random copies here and there of varying quality / we do stock later 3bolt options and always have as well as a 'trick' up-pipe to match

RetroPug

I have a genuine WRX downpipe cat you can buy in Leicestershire if you like.

It won't be cheap though, they can be scrapped for hundreds.

jaygsi

iTrader: (46)

I was going say same, will be down to back pressure.

Other things that can effect it are increasing the bore of your exhaust, mine off full 3" bore, not always the best on some cars, can damage performance.

ALi-B

iTrader: (1)

Well that's the basic theory, which if extremely restrictive, opening things up is a benefit. Problem most exhaust systems are already well designed straight from the production line (ignoring miss aligned ports ). And if gases were a constant smooth flow this would be mostly true.

But. Exhaust gases are in pulses that create shock waves that bounce around the exhaust system. Get it wrong be it length, diameter or restrictions and those pulses can bounce back into an adjacent cylinder at certain rpms/loads. Certainly on V8s with a dual plane crank which creates uneven pulses so exhaust system design is more important than a inline 4 cylinder, even then a good 'ol 4-2-1 manifold/downpipe was always favoured amongst some over a 4 into 1.

The science gets even more important with 2-strokes that rely on exhaust port scavenging to make good power. Hence expansion chambers and tuned length runners the size of pea shooters

Of course I pretend I know what I'm on about. But I do know a full decat doesn't make a huge difference to overall power, put can improve spool; I've often theorised that a cat could be made more beneficial if re-positioned on a straighter section of exhaust system as the honeycomb straightens the gas flow which should remove turbulence on straight sections after the cat*


* Of course this could prove to a utter load of bollox

stockcar

if you want to be proper nerdy then modern 2stroke tuning started at Peenemunde in the 2nd world war (V2's had a small 2stroke engine fitted)
Walter Kaaden continued his work at MZ in East Germany after the war - most specifically on the "expansion chamber" - and they became very dominant in early GP racing until his protege, Ernst Degner defected to the west and sold the secrets to Suzuki........
hence the rise of the far Eastern motorcycle world started in earnest (pun intended.....)

ALi-B

iTrader: (1)

It's always fascinating me the engineering technology that was developed to fight world wars, especially tank and aero engines. I'm pretty certain alot of two stroke technology is buried in a dusty archive room somewhere.

Whilst talking of resonated exhaust tuning (or any form of tube that flows gas) another interesting thing is resonated silencers, or for speakers tuned ports to create more sound at specific frequencies (bass ports ).

I stumbled upon that with my old Land Rover that had a fabricated system taking a 4into1 downpipe off each bank into a unequal 2 into 1 collector and back out as two pipes with two straight through baffled back boxes. No idea if power as it was a half dead engine with worn camshaft and stretched timing chain. But sounded positively evil with a proper V8 lope at idle, and a lot more powerful than it actually was (130bhp when new, probably 100bhp after 30 years included 10years sitting and rotting on a welsh hillside).

I fell foul of it being a bit too noisy for some, and found that temporarily plugging the one tailpipe pretty much made it silent through the remaining open tailpipe! The closed dead end branch must have been just the right length and size to cause the sound pressure waves to cancel each other out by the time it reach the other open tailpipe.

Also after rebuilding it, it sounded totally different smoother and quieter; EFi camshaft with even lobes (rather than worn and uneven) with higher lift and less overlap, higher compression, accurate cam/ignition timing (no chain flapping about altering the timing on the overrun ) and thinner valve stems made it sound much more boring, even if it was more powerful it didn't sound like it was.