Cats and exhaust for L98

[sambo]

I'm after your thoughts on choice of cats for the L98 (6.0L) going into my Harrison. A sponsor on the LS1 forum has a sale on cats suitable for my car (4" body) and I have an opportunity to buy the pair for less than $500.

The question is what size inlet/outlet pipe diameter should I order for the cats? If my steering clears the VE Commodore factory headers that come with the L98 crate engine, then I'll present the car for rego with those in order to keep the noise down. If not, I'll be going with Harrison's custom headers which are a 4-into-1 design that presumably end in 3" pipe and I'll probably fit them later anyway (just for race days).

The cats are available in both 2.5", 3" and 4" inlet/outlet and can be ordered with different sizes on each side. They're 100cpsi meaning the cells are 4 times the size of standard ceramic cats and twice the size of stainless substrate cats. So they will flow nicely!

Since I don't plan on any more than 300kW, I'm thinking 3" inlet to match the custom headers and 2.5" outlet into a twin 2.5" system (possibly even more restricted for rego).

Or would it be better to go 3" outlet because I can always restrict down to 2.5" but still be able to go back up to 3" if I wanted to later?

I'm planning on cosmetic sidepipes and an underbody system exiting to the rear for rego, and for "race days" they might be shortened and directed out behind the sidepipes as I have seen on a number of cars.

Thanks in advance.

Paul

[Rebel1]

Sambo, for what it worth I'm using a similar system to you.

That is cosmetic side pipes and undercar exhaust out the back.

I'm planning on custom headers to a 3" collector to 3" in 2.5 out cat. x pipe under the diff to 16" mufflers either side of the fuel tank. Maybe room for a couple of small hot dogs before the x-pipe.

The pipe man claims he may have some problems with the 3" in pipe to the cat so may use 2.5" in instead of the 3".

[sambo]

Hi Les. I'm leaning towards the 3" inlet, 2.5" outlet at the moment too. It's plenty wide enough for a near-stock 6.0L and the flanges are likely to be smaller and easier to mount up high under the car. Hot dogs - is that a resonator of sorts?

[sambo]

Can anyone suggest a good exhaust shop in Melbourne? One that has been through the rego/compliance process with a Cobra if possible.

Thanks

[Rebel1]

Originally Posted by sambo

Hot dogs - is that a resonator of sorts?

Yep sambo .. small diameter mostly straight thru mufflers is a reasonable description. Come in a variety of lengths and usually round in shape.

[stiffy]

SAMBO,

Can anyone suggest a good exhaust shop in Melbourne?

My car has just come back from Yarra Valley Exhaust ( I wanted the side pipes connected for the NATS) They also fitted my tow bar last week and just completed another Cobra last week,,,,,

speak to Dave tell him Doug Pearce sent you.....


STIFFY

[sambo]

Stiffy, thanks mate. Yarra Valley hmmm... might have to stop at some cellar doors.

BTW, I just got the email confirmation that those LS2 sump kits are shipping tomorrow. It's going to be interesting when the mail room bloke drops them at my desk next week.

[Rebel1]

Originally Posted by sambo

Stiffy, thanks mate. Yarra Valley hmmm... might have to stop at some cellar doors.

BTW, I just got the email confirmation that those LS2 sump kits are shipping tomorrow. It's going to be interesting when the mail room bloke drops them at my desk next week.

Sambo...put up some pics when you can mate.

[ac andy]

i can recommend Yarra Valley exhausts as well. Have had work done there before and been very happy with the job and the price.

Andy.

[stiffy]

SAMBO,

It's going to be interesting when the mail room bloke drops them at my desk next week.

The mail girls are always afraid when I get international mail

STIFFY

[sambo]

Les, the sump hasn't arrived yet but I have pics of the race cats. These are 100cpsi (cells per square inch) which means the honeycomb is 4 times as big as standard. I ordered 4" body with 2.5" pipe size so they're definitely going to flow nicely. The metal substrate is welded in place which I'm told will have more longevity than the ceramic cats from the factory.





Paul

[sambo]

BUMP - here's a picture of our resident quality control supervisor.

[Rebel1]

Hey Paul, Taa loads for the pic. The substrate being welded in is a huge plus.

Supplier and costs?

Cheers

[sambo]

Les they're from Sureflo in Sydney and were bought through a special deal on the LS1 forum for $170 ea. You'll be able to get them at that price til end of the week. Here's the forum link.

[Rebel1]

Thanks Sambo, I'll contact them.

By the way, the hot dogs (as I call them), are mainly to provide a means of stuffing the exhaust with stainless wool to shut them up for rego.

After rego who knows what will happen with the steel wool.

[sambo]

Hehe, yes indeed my friend. I've heard of some very strange things happening after rego!

I've been advised to fit a copper plate between the exhaust flanges with holes drilled through to act as a restrictor. That combined with factory headers + cats down to a single 2" system with pressed bends and a large muffler should get me close.

Does anyone know whether removing (and deleting from the tune) the rear O2 sensors will affect the emissions reading? I believe there are certain variants of the Commodore (ute?) that don't have rear sensors, just the two at the front.

[Rebel1]

Sambo, I am led to understand that the second O2's do little but throw a fault to advise when the cats are completely stuffed and require replacement.

Maybe the whiz kids over the LS1 site can answer the question with more confidence.

[Rebel1]

By the way sambo I'm sure you are as eager as me to see how the 6 Ltr performs at the nationals.

I understand there will be a couple competing.

[sambo]

Most definitely mate. I won't be attending but I'm probably 50/50 for next year. A 1050kg Cobra with 270kw at the rear wheels will take some getting used to!

[Tenrocca]

Ive been 50/50 for the last 2 nationals too ....I reckon Im 99% for the next through. The 2nd O2's are definately just to detect bad cats, so shouldnt cause you to fail emmisions, however they are a requirment under the euro3 so will at least need to look like they are there for rego.