L-series cat

Post by **Alex** » Mon Mar 13, 2006 10:18 pm

hi all,

ive got a 90 l-series wagon, the first with a cat apparently!

they tell me the best(and cheapest) way to get more power out of her is to axe the cat! I went to wreckers, and had a look at a piece of y-pipe from a 89 wagon(no cat), all looked good, until i told them that i had a 2.5 inch sports exhasut on it, they reckon there wont be enough back pressure and i'll loose power!

Is this true(and i know its illegal)

cheers, alex

Gannon · Post by **Gannon** » Tue Mar 14, 2006 5:13 pm

Back Pressure only decreases power, what the wrecker told you is a common myth.

It is true that with no exhaust pipes at all,.. you will lose power (especially bottom end)

Having exhaust pipes on your engine creates a "scavanging effect", where the pulses of air from the exhaust ports creates momentum in the exhaust pipes which then kinda sucks the next pulse of hot gas from the engine, thus creating more power. Properly designed header pipes (extractors) are where this phenomon comes into play.

Yes you must have a cat to be legal.

Your best bet would be to get the y pipes or use your own and get an aftermarket cat welded to it.

I have the factory y pipes and cat, and a 2.25" cat back with a straight through muffler, definately made more power.

Gannon.

smoov · Post by **smoov** » Tue Mar 14, 2006 6:49 pm

all L series have cats. its a requirement when it runs on unleaded fuel.

many L series don't have cats, as they are expensive to replace - the cat is actually part of the header pipes, and non original aftermarket replacement cat/headers sell for $700~ !!

most people replace them with catless headers, which go for around $200~.

They are integrated with the headers in order to keep it close to the engine, to have enough heat for them to actually work. some exhaust shops will bung one further down inline, and in actual fact, these don't work, and only tend to choke your exhaust.

MUDRAT · Post by **MUDRAT** » Tue Mar 14, 2006 9:00 pm

Bernoulli is your friend.

But to cut a long story short: 2.25" with a turbo muffler is tried and true.

mattims · Post by **mattims** » Tue Mar 14, 2006 10:34 pm

yeah i have catless headers and the cars makes lots of fun pops and cracks. I think it did have noticeably more power at top end but was probably losing power down low.

smoov · Post by **smoov** » Wed Mar 15, 2006 11:17 pm

with the hitachi, i had the crackles and pops, but with the weber, it dissapeared.

waggaclint · Post by **waggaclint** » Sat Apr 08, 2006 11:39 am

yeah i too have headers [genie headers] pops and cracks only after you give heaps but the rest of my exhaust is stock. i have noticed more power up high from say about 3000rpm up and its better on fuel to an extra 80km per tank

dree · Post by **dree** » Sat May 06, 2006 1:25 pm

What the wrecker told you could be true if the exhaust SYSTEM is poorly designed, no myth, although back pressure is a fairly simplified description. Any exhaust designed properly is tuned to produce a scavenging effect in the cylinders which helps suck the exhaust gases out of the cylinder on the exhaust stroke. So the exhaust pulse that is already in the pipe, creates a suction that sucks the next pulse out of the next cylinder. So a change in the exhaust configuration can often decrease this scavenging effect, and decrease power as a result, because instead of the gases being sucked out of the exhaust, the piston has to push them out. What is a common myth is that simply increasing the diameter of the exhaust will give more power, this is only true if the design of the exhaust also increases the scavenging effect.

This is where the term Extractors comes from, a set of tuned extractors combine exhaust pulses from two cylinders, increasing the scavenging effect in the next cylinder that opens it's exhaust valve, increasing power.

So if you are going to put a non standard system on your car, make sure there is some evidence of it improving power output.

I believe there are heavy penalties in some states for running without a Cat.

dree · Post by **dree** » Sat May 06, 2006 1:33 pm

Whoops that was a late post, only looked at the last date. Oh well.

suby87 · Post by **suby87** » Wed Jun 07, 2006 3:32 pm

Hey guy's,

I know I am adding to a old post but with the cat when I rev my engine I can hear what appears to be a sound likes rocks rattling around inside a washing machine I pretty sure it's coming from the cat. Does this sound right or is the problem in other places.

mattims · Post by **mattims** » Wed Jun 07, 2006 3:54 pm

very likely is the cat. They tend to break up inside and bits come away. You can either replace it, bash it out entirely.. or replace it with a straight bit of pipe.. or put up with the noise. depending on how much it bothers you, how much you car for the environment and how much $ you want to spend

suby87 · Post by **suby87** » Thu Jun 15, 2006 3:56 pm

thanks for the reply mattims.

If I hollow out the cat will it decrease performance and use more fuel. Just that I did this in me 98 EL Falcon and it ran like a dog. I had a look under there how hard is it to hollow out the cat. It appears to be a long way from the cat back to the first flange. Is this a easy job or hard. Thanks.

mattims · Post by **mattims** » Thu Jun 15, 2006 4:47 pm

actually ive never done it on a suby. I have a custom exhaust and manifold. It probably wont affect performance noticabley but it will make it pop and crackle a little.

suby87 · Post by **suby87** » Fri Jun 16, 2006 7:02 am

Ok. It already pops and crakles after you come off the throttle anyway when its cold so it couldn't get much worse. Does anyone out there know how hard it is to hollow out the cat. I have to take the car out tonight to blackwood.

YouTube · Post by **El_Freddo** » Wed Jul 12, 2006 9:46 pm

Hey Suby87,
Here's my cat story/theory:
I recently went 4wd'n and hit my cat on a rock. I don't know if i shattered the internals of the cat but my car ran like a dog after i let it cool down... it ran like this for two days and was fine once at speed, it had the rattling noise you talk about too.
The first flange behind the cat created a hissing noise, i presume it was the build up of the gases in the exhaust cos the cat pieces had clogged the rear muffler.
It all came good while i was delivering pizzas, saw another neat suby and thought i'd catch up to it and pushed it really hard (due to the lack of performance), at about 3 and a half on the taco (not the first time that night), something must have been blown clean cos after that it ran better than it did before i hit the rock, but it now has a tinnier note to it

i can't afford to do anything with my zorst at the moment and probabily won't. It seems to perform better through out the rev range, and rev's easier too.
I think the easiest way to clean it out would be to have a hammer and something solid, putting the solid object on the other side of the cat from where your hammering, moving around the cat. Idea being to shatter the internals with some small hits - without making huge dints. Then take off the rest of the exhaust pipe at the next flange down, start your engine and blow all the bits out of it. You might need to warm the car up then let it cool and do it again to get all the loose bits out through heating and cooling. Put it all back together and see how she goes.
I don't experience any popping sounds... that to me would indicate an air leak that sucks air in and burns unused fuel on down rev's.

Bennie

Post by **Alex** » Tue Jul 18, 2006 10:57 pm

haha i love the crackling and popping my L makes, and would never want to get rid of it! its good when you revv her hard and then suddenly take the gas off and it sounds like its backfiring a little bit!