LZY13B build thread

**sambb** · 28-10-2015, 02:08 PM

Yeah I was quite swayed by his arguements. Plautos as well swore that the stock cat had great flow and he incorporated it into his system. I was planning then on just doing a 3'' dump into the stock cat. That had the extra benefit that I wasn't very likely to get a CEL with the stock cat with a dump and phase 1 tune. After it was removed though I made up my mind. Looking (or trying to!) through it versus through a 200 cell was night and day. I think the simple fact that you will generate high flow CEL's with 200 cells versus the stock cat that won't, is proof enough that high flow cats do work better than stock ones.
My 3'' dump and 200 cell that then cones down to the stock 2/1/4 works realy well. I've logged 190g/s with a phase 1 tune and stock intercooler which I think is pretty good. The K03 is all about midrange torque and an agressive ramp up. Enough volume is built into the system before it cones down to standard pipe, that back pressure shouldn't become a major issue until higher in the revs anyway and when you drive these cars you just don't hold sustained high rpm anyway. I don't think I loose anything compared to cars that have a mandrel bent 2/1/2 back section.

**sambb** · 28-10-2015, 05:30 PM

you might be interested in this story mate RX9 has landed!

Tokyo Motor Show: Mazda rotary powered RX-Vision announced

**LZY13B** · 29-10-2015, 06:36 AM

Yeah my fb exploded with the new RX lol thanks for the info mate might see if I can get a cheap hiflow cat spoke to the mechanic and said it would be less than $500 for the dump so I'll start sussing things out

**sambb** · 29-10-2015, 12:04 PM

You see a lot of cats placed right up the front quite close to the downpipe section. My guy explained that to get a front section only to work well you need to build maximum volume into it by going no less then 3 inch and also by positioning the cat as far back as practical. That way you extend the 'filling time' of the front section before back pressure starts to ramp up. If you place the cat right up at the start of the system you are just taking the component that is singularly most responsible for causing restriction and moving it into a position that cuts unrestricted 'volume' out of your system and causes backpressure rise to occur sooner. That was the theory anyway. Tradeoff would be that it'll take longer for your cat to heat from an emissions perspective. anyway food for thought.

**Slow_Polo** · 29-10-2015, 03:14 PM

Is that $500 including the cat or just the pipe without? If its with that's a good price! I cant find anywhere near me to go that low.

Where is that at?

Luke

**LZY13B** · 29-10-2015, 05:22 PM

It would just be a cheap hiflow cat nothing special he said around $500 with cat and he is just a local mechanic in silverwater just up from my work he does all our work cars I told my boss I'll send him the bill haha

**seangti** · 30-10-2015, 11:06 AM

Originally Posted by sambb

You see a lot of cats placed right up the front quite close to the downpipe section. My guy explained that to get a front section only to work well you need to build maximum volume into it by going no less then 3 inch and also by positioning the cat as far back as practical. That way you extend the 'filling time' of the front section before back pressure starts to ramp up. If you place the cat right up at the start of the system you are just taking the component that is singularly most responsible for causing restriction and moving it into a position that cuts unrestricted 'volume' out of your system and causes backpressure rise to occur sooner. That was the theory anyway. Tradeoff would be that it'll take longer for your cat to heat from an emissions perspective. anyway food for thought.

My car has a 4" expansion chamber as part of the dump pipe on it, done by the previous owner, Anthony. There's quite some detail in his thread on the theory behind it, which supports what you're saying. As I understand it, it's essentially a high pressure system behind the turbo which allows it to spin freely, leading into a lower pressure (exhaust) to suck/accelerate the exhaust gas out. You want as much capacity in the exhaust before introducing a restriction.

In talking with a race shop when getting other work done, he did say for the power produced by these cars, it's pretty useless, if making double the power, say 300kw, yeah absolutely go for it. That's in reference to the 4 inch expansion chamber. 3" is more than adequate on these cars IMO. Even the stage 3 cars, in reality we're not making big numbers anyway.

**Paazuzu** · 31-10-2015, 12:21 PM

I've been running a custom 2.5 inch downpipe with a xforce cat on stage 2 tune and it performs very well.

I don't think I'd bother going to 3 inch unless I was going stage 3.

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**h100vw** · 31-10-2015, 12:26 PM

Originally Posted by Paazuzu

I've been running a custom 2.5 inch downpipe with a xforce cat on stage 2 tune and it performs very well.

I don't think I'd bother going to 3 inch unless I was going stage 3.

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Probably nothing much to be gained with the 3 inch on a std turbo. Scene points maybe. I got mine knowing that I'd be doing the turbo soon enough.

PS Wasted no time getting the MCAs in the signature Dan