[Marko_SJ]

JrZook wrote:

MacDaddy wrote:

alien wrote:

lol 1 7/8 vs 2" =)

Oh and no need for another "back-pressure" argument

Backpressure

[JrZook]

Marko_SJ wrote:

JrZook wrote:

MacDaddy wrote:

alien wrote:

lol 1 7/8 vs 2" =)

Oh and no need for another "back-pressure" argument

Backpressure

NO

[Marko_SJ]

JrZook wrote:

Marko_SJ wrote:

JrZook wrote:

MacDaddy wrote:

alien wrote:

lol 1 7/8 vs 2" =)

Oh and no need for another "back-pressure" argument

Backpressure

NO

In any case I wonder how Heidiisacat's new exhaust is. maybe he likes the note so much he's still driving it.

[BigRay]

It used to scream because it was straight piped hahaha
Before I cut the muffler off and straight piped it I had to rev it higher to get the power but not anymore.
I love the sporty note!

[alien]

its still only a 1.3L engine =)

here, have some reading:
http://www.exhaustvideos.com/faq/how-to ... -diameter/

[MacDaddy]

Yeah, i think we have flogged that topic of back pressure enough here in AZ... there is a thread all about it here somewhere...

But, if you want to read up on/about it, then have a read here -

Back pressure: The myth and why it's wrong.
http://www.gomog.com/allmorgan/exhaustbackpressure.html

[Marko_SJ]

MacDaddy wrote:

Yeah, i think we have flooged that topic of back pressure enough here in AZ... there is a thread all about it here somewhere...

But, if you want to read up on/about it, then have a read here -

Back pressure: The myth and why it's wrong.
http://www.gomog.com/allmorgan/exhaustbackpressure.html

Nice article... It reminds me, I need to do something about the muffler tips on my commodore.

Too lazy to bust out the welder.

[Heideisadog]

Heidiisacats exhaust is in 2 peices on the floor. Stock as a rock and lame.

So thanks for all the helpful info. I have been soaking in all this information for the past couple of days and come to the conclusion that the best option will be 4.5inch fully hektik dual truck stacks.

You can't stop me!!!!!!

But more seriously, I haven't made it to the exhaust shop this week which was a bummer! But considering all this information I'm pretty sure I'm going to go a 2inch exhaust from extractors and then see what the specialists recommend for the sound management side of things... Something that sounds good while increasing performance is desired. But I'm always going to want better performance over sound. I know for a fact I will get sick of a noisy exhaust but I can't get sick of upgraded car ability. Though balance between them would be good!

I'll keep you posted when I eventually get around to going to the exhaust shop! Maybe on Saturday, if I'm lucky!

[Heideisadog]

So ah this never happened. But I'm hoping it'll be done soon.
I got a quote for $800 to fit and make a 2 inch system with hi flow cat. Though I have to provide extractors.
Does this sound a little steep to you guys??

Thomas.

[atari4x4]

unless that is for a mandrel bent stainless steel system with s/s cat & s/s muffler, i'd be shopping around.

[matth27]

I got a quote for $450 in Fyshwick for a 2" if i supplied extractors. not sure about a cat or muffler if you like pm me and i can get you the number

[Dec]

Having done my rear main seal on my Zook 3 times now, you may wish to ask for a flange prior to the gearbox to make life easier. I certainly will be:)

[Heideisadog]

matth27 wrote:

I got a quote for $450 in Fyshwick for a 2" if i supplied extractors. not sure about a cat or muffler if you like pm me and i can get you the number

That's where I went. Out too powatone in fyshwick. If you went somewhere else please let me know! 800 minus extractors is a fair bit.

[atari4x4]

was it just a mild steel system or stainless steel that he quoted as a stainless steel system could easily cost $800.

[Heideisadog]

I'll have to find out. I'll give them a call tomorrow!

[Bozy97]

QUAD CARBIES!! WHATS THAT WORTH TO SETUP?

[alien]

[henno]

[atari4x4]

Bozy97 wrote:

QUAD CARBIES!! WHATS THAT WORTH TO SETUP?

some tech for you viewtopic.php?f=14&t=29378

[jimny_timmy]

My 2" system including the factory cat and I supplied the headers was $280... That'd be worth the 5hr drive to get it by the sounds of it lol

[losfer]

MacDaddy wrote:

Yeah, i think we have flogged that topic of back pressure enough here in AZ... there is a thread all about it here somewhere...

But, if you want to read up on/about it, then have a read here -

Back pressure: The myth and why it's wrong.
http://www.gomog.com/allmorgan/exhaustbackpressure.html

really ? that article must of been written by a university student who studied gas flow and has no idea on how an internal combustion engine works !!

I would like to write a brief article of my own having a lot of experience with this sort of thing . this is more relevant to a twin cam engine rather than a single cam but you will get the idea ...

intake stroke : the inlet valve opens and sucks in a charge of fuel and air (the exhaust valve is still open at the start of this and this will come into play later) . in theory , the more air and fuel in a stoichiometric consistency you can get into a cylinder the more power you can make so for this reason the inlet valve closes well after bottom dead centre of the intake stroke so it can suck in as much fuel and air as possible.
compression stroke : the piston compresses the air/fuel charge , both valves are closed . just before top dead centre of the compression stroke ignition occurs , it occurs before top dead centre so that the flame front is allowed to propigate to make the most power , if ignition occurs too late all the air fuel mixture will not be burnt and will push some unburnt air fuel mixture out the exhaust and cause you to lose power . if ignition occurs too early then it is generally called pre-ignition , detonation , or most commonly known as "pinging" , as general rule of thumb in making power is to advance base timing until pinging then back it off a couple of degrees . if ignition occurs too late then you will not burn the entire air/fuel charge and either way will lose power. i should write another article about ignition timing ...
combustion stroke : I like to call this the power stroke , its the only cycle in a 4 stroke engine that makes the car go forward , all the other cycles are like a prelude to the main event . so your fuel and air has been ignited this is the big moment to lay down some rubber . the octane level of your fuel also plays a big part of this main event , too low of an octane and the fuel air mixture will be a sudden explosion rather than a more controlled burn of a higher octane fuel. near the bottom of the power stroke the exhaust valve will start to open , on a standard gti engine it is 42 degrees before bottom dead centre , the engine has made the power and burnt all the air fuel mixture
and now it needs to start pushing it out , opening the exhaust valve early will "scavenge" some of these gases before the piston even decides to make the exhaust stroke. it does this because we need a "fresh" charge of air and fuel in the cylinder for the next power stroke.

NOW MOST IMPORTANT
exhaust stroke: the piston pushes the gases from the combustion cycle out , as the piston nears top dead centre the inlet valve opens to suck in a new "fresh" charge of air and fuel , both valves are open! without some backpressure the charge would be allowed to escape out the exhaust valve and cause loss of power.if all the exhaust gases arent expelled from the cylinder you will have a mix of exhaust gases and the new fresh charge of air/fuel

now with single cams theres not a lot you can do to change where and when the opening and closing times occur apart from a custom cam grind , but with a twin cam engine you can dial in how you want the events to happen. you can make the power occur in different rev ranges and also change the lobe centres for n/a or forced induction . with sohc you can only dial in to make the power in a different rpm range. The type of headers also play a big part on where you want to make the power . I see most are 4 into 2 to 1 these days , just a generic cheap option , no tuned length , no split pulse , just cheap ebay shit that appeals to the general cheap arse joe public.

[JrZook]

losfer wrote:

without some backpressure the charge would be allowed to escape out the exhaust valve and cause loss of power.if all the exhaust gases arent expelled from the cylinder you will have a mix of exhaust gases and the new fresh charge of air/fuel

If fresh charge was drawn from the intake into the combustion chamber and pulled out through the exhaust how does that constitute a power loss? With a descent head design that would indicate that almost all the spent charge was expelled therefore the cylinder would have almost 100% fresh charge ie the cylinder was fully scavenged. I would have thought that the only negative of an over scavenged cylinder (fresh charge escaping out of the exhaust) would be a loss off efficiency and fuel economy. The same thing that happens on a 2 stroke with early designed tuned pipes that only have a diverging cone "megaphone" setup.

[Gwagensteve]

X2 to jrzook. According to that theory, changing to a bigger cam with more overlap would require an exhaust with more backpressure in order to prevent all the power from falling out. Or something.

Even if this was correct (and it's not) there would be sufficient "backpressure" in the exhaust ports due to friction and turbulence in the head to provide the backpressure required at the back of the valve to do the job. But it's not correct, which is why the worlds most efficient N/A engines based on hp/litre minimise backpressure with very open, unrestrictive exhaust tracts, from the valve onwards. Increasing exhaust valve size would also let the power fall out, as would porting the exhaust side of the cylinder head, increasing overlap, or swapping to a set of extractors from the stock manifold.

Steve.

[AckerDackerly]

Back to the topic at hand...

I have a 2.25" exhaust with a Thorley header (extractor) on my 1.6 8-valve SJ413 Samurai. It runs and sounds great

The most expensive single part was the Thorley @200.00 US back in 2002.

The exhaust system installed - complete with a universal-fit catalytic converter and muffler - was around 350 US (2002).

@ $800.00 AU even at today's prices sounds like someone needs to make a fishing boat payment...

[Gwagensteve]

I think the misunderstandings about "required" backs pressure re very relevant to the topic at hand because excessive noise and cost are all tied to some of the faulty misconceptions about "required" back pressure. However, 12 year old exhaust pricing from the US might not be relevant to the OP's question.

In any case, when I build a 2" exhaust, the parts alone always seem to cost around the $400 mark, and I've done a few. That includes a new cat, triple flow muffler a resonator, some mandrel bends, bolted flanges, and the header. If I was trying to make any money from building it I could easily see charging another $400 for the job. I can't make the decision whether the car justifies the cost, but perhaps it's worth seeing some of the shops other custom work. I've find it hard to locate an exhaust shop these days that's able to do high quality work regardless of cost, which is why I now make my own exhausts.

The $800 job should have bolted flanges with gaskets, not saddle clamps and silicone. It should have proper hangers made for the job, not those horrible universal hangers that are a mess of flat bar and bolts. Most importantly, it should be put together by someone with thought to clearances and use in an off road application. I add braces from the bottom of the muffler to the pipe (an old rally trick) that prevents the ends of the muffler cracking from fatigue. It's stuff like that you should be paying the extra $ for.

[Heideisadog]

Basically I called the shop up, wasn't too helpful but he said it's about $350 for the hi flow cat, then the rest is for the pipe and labour. Which is mandrel bent hi-temp steel.

Thinking I should probably look around a little more...

[alien]

FYI i paid about $120 for a 2" Cat to suit a commodore/falcon... brand new, metal core thingamajig welded in and all.

[droverdave]

"mandrel bent high temp steel"

Did he actually say this?

I would forget mandrel bend. There is alot more work in welding on mandrel bends, cutting them and welding pipe on again, as opposed to press bending one bit of pipe from one end of the car to the other and cutting out sections to put mufflers/cat in. And just get mild steel, cheapest there is.

[atari4x4]

^ huh, weld in mandrel bends.... my exhaust shop can mandrel bend on a length of exhaust pipe.

eg.


with something like this.

[jonno_racing]

That's a press bend or crush bend gus