It is currently Fri 23 Feb 2018, 11:19 pm

All times are UTC + 10 hours [ DST ]




Post new topic Reply to topic  [ 29 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: 2.5" or 3" exhaust
PostPosted: Mon 02 Feb 2004, 1:48 pm 
Offline
Forum Regular
Forum Regular

Joined: Sat 13 Dec 2003, 6:00 pm
Posts: 59
2.5" or 3" exhaust
To get this fitted on a 87 colt how much would I be looking at?

_________________
I need help


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Mon 02 Feb 2004, 1:57 pm 
Offline
This forum is my life
This forum is my life

Joined: Thu 30 Oct 2003, 12:49 am
Posts: 1785
Location: Adelaide
im hoping your not planning to put a 2 1/2" or 3" exhaust on a standard colt.....if thats what your planning i think u need to think harder. we cant tell you what is the best to put on without some details bout your car like is it Turbo or modified in any other way? take it to an exhaust shop...


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Mon 02 Feb 2004, 4:18 pm 
Offline
Moderator
Moderator
User avatar

Joined: Tue 02 Sep 2003, 10:22 pm
Posts: 2339
Location: Wellington, New Zealand
If its a standard N/A then 2.5" is probably too big, 3" is way too big. There's no real benefit to an excessivly large exhaust, it reduces low down power and sounds horrible, droning on acceleration (think hondas with 3" exhausts) and excessive popping on deceleration, not to mention it attracts unwanted attention from the coppers.

2-2.25" is about where you want it I think. Go to an exhaust place and talk to them, they'll know what size will give you the best power increase without being excessivly loud and dronny (Is that a word?? :? )


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Mon 02 Feb 2004, 4:58 pm 
Offline
Resident Cyclist
User avatar

Joined: Tue 02 Sep 2003, 6:40 pm
Posts: 2428
Location: Canberra
Your car: 3 Litre Magna
a 3" exhaust will not reduce low end power. all it will do is reduce that nasty thing called back pressure. and be loud as fark.
Quote:
2-2.25" is about where you want it I think. Go to an exhaust place and talk to them, they'll know what size will give you the best power increase without being excessivly loud and dronny (Is that a word?? )

that part I agree with. 3" will shit you to tears with its loudness for minimal gain over 2" or 2.5" on an n/a colt motor.[/quote]

_________________
Gallo 24 all the way


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Mon 02 Feb 2004, 5:31 pm 
Offline
Resident Antichrist
Resident Antichrist
User avatar

Joined: Wed 03 Sep 2003, 1:39 pm
Posts: 2367
Location: Canberra
Having too large an exhaust on an NA car will slow down the speed of the gas through the entire system (including all the way back to the valves) which will drastically affect exhaust scavenging, in turn reducing the amount of clean fuel/air mix that enters the engine... this will reduce power numbers quite a bit.

I put a 2.25" exhaust on my NA 1.5l carby lancer and it was too big... a 3" on a colt is going way overboard. The lancer probably would've been happy with 2", maybe even so low as 1.75"... when we put the 2.25" I lost about 10kw and a shitload of torque (poor thing didn't have much to begin with)... but it sounded so damn good I left it on lol ;)

Astaroth.

_________________
[size=75]Ich will die Ruhe stören

Bones heal, chicks dig scars, glory lasts forever.

Image


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Mon 02 Feb 2004, 6:44 pm 
Offline
Resident Cyclist
User avatar

Joined: Tue 02 Sep 2003, 6:40 pm
Posts: 2428
Location: Canberra
Your car: 3 Litre Magna
you lost a dyno proven 10kw with a too big exhaust?, show the paperwork and i might beleive it. slow exhaust velocity = good flow = less back pressure = greater scavenging and more power. fast exhaust gas velocity = restriction = huge back pressure = sfa getting out of the cylinder. :?

_________________
Gallo 24 all the way


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Mon 02 Feb 2004, 8:15 pm 
Offline
Super Cordia Guru
Super Cordia Guru
User avatar

Joined: Wed 03 Sep 2003, 8:17 pm
Posts: 898
Location: Cordialess (Melb)
Hehe, you guys have stirred up one of the big automotive debates (in my opinion, the subject of back-pressure is debated almost as intensely as BOV's).

My understanding (which could be really bad, I'm happy to admit that) is that if the engine is tuned properly after the exhaust is put on, then lower back-pressure will result in more power.

Having said that, putting a big exhaust on a N/A car and not retuning it properly could well result in a reduction in power. Turbo car's are a whole different story - basically, as big as possible after the turbo is best!
But, keep it reasonable - there's no point putting on 4" instead of 3", the back-pressure difference won't be noticable.

I think in terms of flow, a larger cross-sectional area means that for the same flow velocity, a greater amount of gas can escape.

Just my 2c worth.

Adrian

_________________
Was: Powered by EVO
Now: Powered by pedals


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Mon 02 Feb 2004, 8:57 pm 
Offline
Forum Regular
Forum Regular

Joined: Sat 13 Dec 2003, 6:00 pm
Posts: 59
ok i'll talk to the exhaust dudes, cant anyone just give me a rough cost?

_________________
I need help


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Mon 02 Feb 2004, 9:49 pm 
Offline
Resident Antichrist
Resident Antichrist
User avatar

Joined: Wed 03 Sep 2003, 1:39 pm
Posts: 2367
Location: Canberra
Yer, dyno-proven 10kw ish loss (think it was 9kw). That was a few years back though, so I don't still have the sheets. I might be able to dig them up from the old dyno shop... if they're still open :?

Low exhaust gas velocity through pipe means low exhaust gas velocity from cylinder as well, causing a drop in scavenging speed. Not to mention that you lose any sonic tuning* the exhaust had, which further slows scavenging.

The exhaust needs to be small enough to keep the gas moving at a good speed - the faster the exhaust gas moves towards the rear of the system, the more low pressure is created in the manifold and when the valve opens, this low pressure zone sucks the exhaust gas out and creates low pressure in the cylinder, which in turn sucks more fuel in.

If the exhaust gas is way too slow, this backs up the system and slows the gas coming from the valve... in turn more gas is left behind and less clean fuel/air mix in the cylinder.

That's what I've discovered based on 4 years of 42 weekends a year racing gokarts at national level. While I understand a 100cc piston port two stroke is not quite the same as a cordia motor, the theories are fairly universal.

However, when it comes to turbo's, the 'bigger is better' theory is pretty much right. The turbo wheel acts as a valve and nullifies any sonic tuning and also means that the exhaust gas can slow down after the wheel with no ill effect to the motor.

Astaroth.

* Sonic tuning : when the exhaust valve opens, a sonic 'pop' travels down the exhaust, hits the tip opening and bounces back towards the cylinder. Sonic tuning involves tuning the exhaust length so that this 'pop' hits the exhaust valve at the precise time it opens... this creates a HUGE sucking effect and helps scavenge gasses out. The disruption to sonic tuning is one cause of popping noises in exhausts that are too large.

_________________
[size=75]Ich will die Ruhe stören

Bones heal, chicks dig scars, glory lasts forever.

Image


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Mon 02 Feb 2004, 10:10 pm 
Offline
Super Cordia Guru
Super Cordia Guru
User avatar

Joined: Sun 26 Oct 2003, 8:36 pm
Posts: 518
Location: Melbourne
I think u'd be looking at around-about $1000 for the system...

-Loss

_________________
Think of the average person. Half the people in the world are below that.


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Mon 02 Feb 2004, 10:51 pm 
Offline
Super Cordia Guru
Super Cordia Guru
User avatar

Joined: Wed 17 Sep 2003, 8:55 pm
Posts: 526
Location: Werribee, VIC
1000!!!....for that thing, bring it to me and ill make one for about half that...

astro is pretty right on his theories i must say.

but again turbos are different.

Dylan

_________________
Is there anything better in life than boost...??


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Mon 02 Feb 2004, 10:54 pm 
Offline
Resident Antichrist
Resident Antichrist
User avatar

Joined: Wed 03 Sep 2003, 1:39 pm
Posts: 2367
Location: Canberra
I wouldn't bother with mandrel bends, although if there are some bends more than about 45deg I'd get those particular ones done in mandrel. Similarly, don't bother with stainless... a mild steel exhaust should last a good 5-10 years and will most likely (if looked after) will probably outlast your colt.

Press bent mild steel system shouldn't cost more than about $300 including a muffler.

Astaroth.

_________________
[size=75]Ich will die Ruhe stören

Bones heal, chicks dig scars, glory lasts forever.

Image


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Tue 03 Feb 2004, 12:03 am 
Offline
Moderator
Moderator
User avatar

Joined: Mon 17 Nov 2003, 10:56 am
Posts: 3040
Location: Christchurch, New Zealand
If it's on a naturally apserated mirage, 2" with press bends should be fine.

Resonator in the middle and a big chrome cannon on the back for pimping.


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Tue 03 Feb 2004, 7:48 am 
Offline
Resident Cyclist
User avatar

Joined: Tue 02 Sep 2003, 6:40 pm
Posts: 2428
Location: Canberra
Your car: 3 Litre Magna
I beleive you if you'ce got it dynod to prove you lost power no finger pointing there. just think there might be other factors. exhaust tuning (sonic tuning as you say) being a critical one.
Quote:
the faster the exhaust gas moves towards the rear of the system, the more low pressure is created in the manifold and when the valve opens

the only reason the exhaust gas moves fast through the system is because it's under very high pressure because the pipe is too small.
so you're suggesting that it doesn't matter in terms of how much power you're making how much pressure it takes to force the exhaust gasses out of the cylinder. It only matters if it effects scavenging or not? A sonically tuned set of headers going into one large pipe would be the best solution you might think. not that any exhaust shop on the planet can successfully tune an exhaust. that' why i vote for larger is better, the skill to not only mathematically but practically tune a set of headers correctly is very, very, very, hard to come by. or leave it as stock, it costs $500,000,000 to design cars for a good reason. you think they just whacked a piece of pie on it from the factory (yeah I know it's a colt, they probably did). but you see my point.

_________________
Gallo 24 all the way


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Tue 03 Feb 2004, 8:58 am 
Offline
Moderator
Moderator
User avatar

Joined: Mon 17 Nov 2003, 10:56 am
Posts: 3040
Location: Christchurch, New Zealand
Ok, what you want in an exhaust on an NA car is for the pulse to suck out the next pulse, and the remader of it's own pulse.

If your exhaust is too big, this isn't going to happen as your exhaust speed will be lower than the exhaust gasses coming out your valves at low RPM, making the engine actually have to push out the gasses.

At high RPM, a excessivly big exhaust may make more power, saw with a 3" on a small engine 9000 rpm, but at low RPM it's going to be doughey as fudge!

So with a 2" exhaust, this will be good for the whole rev range in which your car is operating.


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Tue 03 Feb 2004, 11:57 am 
Offline
This forum is my life
This forum is my life

Joined: Thu 30 Oct 2003, 12:49 am
Posts: 1785
Location: Adelaide
okay, i also have a cordia GSL, it was completely stock. i was thinking a 2" system from the flex point back. i got down to the exhaust shop (complete Exhausts,Main North Road) and the guy told me 2 1/4" would be better. i already picked up a muffler with tip so i saved money there.
Price:
$120 Piping
$70 labour
$40-300 depending on wether u want just a tip or a good cannon style muffler.

so all up id say u are lokin at around $250-$300 for 2" system with a cannon style on there. the guys get carried away talking technics, but here is what u wanted to know.


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Tue 03 Feb 2004, 3:45 pm 
Offline
Resident Cyclist
User avatar

Joined: Tue 02 Sep 2003, 6:40 pm
Posts: 2428
Location: Canberra
Your car: 3 Litre Magna
put that down to my love of a good argument.





btw: i'm right :P

_________________
Gallo 24 all the way


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Tue 03 Feb 2004, 5:49 pm 
Offline
Forum Regular
Forum Regular

Joined: Sat 13 Dec 2003, 6:00 pm
Posts: 59
lol thanks guys, so i'll be looking at about $300 to $400 depending on what i pick.

_________________
I need help


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Tue 03 Feb 2004, 6:52 pm 
Offline
Resident Antichrist
Resident Antichrist
User avatar

Joined: Wed 03 Sep 2003, 1:39 pm
Posts: 2367
Location: Canberra
Quote:
so you're suggesting that it doesn't matter in terms of how much power you're making how much pressure it takes to force the exhaust gasses out of the cylinder. It only matters if it effects scavenging or not?


I said nothing of the sort. Please read my posts before quoting me...

Sonic tuning and pressure levels are two VERY different things, you seem to think they are the same. Sonic tuning involves the exhaust length (including all the way to the cylinder) and has VERY little to do with the actual diameter of the exhaust. The sonic pulse takes a certain time to travel a distance, the diameter of the pipe doesn't affect this very much at all (if any).

Sorry man, but I'll argue this to the death. An NA car needs a certain level of pressure in it's exhaust system to keep the gas moving, if the gas slows then it slows the flow of gas through the ENTIRE ENGINE.

Basics... this is just an example, picture it in your mind... seal a piece of hose into a plastic coke bottle and suck like hell... what happens? A low pressure zone (vacuum) is created inside the bottle. Now, if you were to make a hole on the other end of the bottle, you can suck air through. NOW, if you put your hand over the hole (e.g intake valve closed) and without sucking on the hose, lift your hand off the hole for 1 second, then what happens? Shit all... not much moves. Lift your hand off for 1 second while sucking like shit on the hose, and a shitload of air will rush from outside the bottle into it. Following?

Bottle = cylinder, tube = exhaust, hole = intake valve. The first test (no sucking) represents what happens to your intake mixture when the gas in your exhaust is moving slowly. The second (sucking like buggery) represents the gas moving down the pipe VERY quickly. In the first example, there was higher pressure in the cylinder/bottle (close or at atmo) and in the second example, there was a vacuum in the intake/bottle which sucked the mixture (air only, in the example) into the cylinder/bottle.

Here's ANOTHER example to show you how air being slown down in a bigger tube (and if this doesnt explain it i'm going to bloody well give up) actually creates backpressure... blow into the end of a garden hose and feel how fast the air comes out the end... blow into a piece of 3" pipe and you will require MUCH more effort to get it to move at the same speed ... why is this? Because when you blow into the garden hose, there is less stationary air for you to blow down the tube... whereas you need to move more air in a 3" tube to get the same results... in short, there is more resistance to the efficiently fast flow of gas in the BIGGER tube than there is in the smaller tube, in otherwords, MORE backpressure.

Does that make it a bit clearer? I know these theories like my own nutsack.... as I said, I've spent a couple of thousand hours at the track testing the theories of exhaust size and sonic tuning... in road cars it's not usually set up very well but in a 14hp go-kart every TINY bit helps.

If you like, I can try to get some dyno time and actually prove these. I would need a GSL cordia donated for a couple of hours though... preferably with a stock exhaust. If that can be arranged, I should be able to get numbers with a stock exhaust, 2.25 (my current one) and a 3" (I'm buying a 3" soon, we could use that) and I reckon I could get it done for nothing... that's assuming a GSR exhaust will fit a GSL and I can sweet-talk the boys into letting me go wild on the dyno for a day ;)

JAPRCR - Yep, turbos are different... I'm rambling about NA motors, I don't really have any experience with turbo exhausts but I DO believe in 'bigger is better' on a turbo car, to a point... while I think there is such a thing as too big on a turbo car, I highly doubt you could fit it under a cordia ;)

Quote:
If it's on a naturally apserated mirage, 2" with press bends should be fine.

Resonator in the middle and a big chrome cannon on the back for pimping.


Sounds like a plan to me :)

Astaroth.

_________________
[size=75]Ich will die Ruhe stören

Bones heal, chicks dig scars, glory lasts forever.

Image


Top
 Profile  
Reply with quote  
 Post subject:
PostPosted: Tue 03 Feb 2004, 7:36 pm 
Offline
1800 CORDIA
1800 CORDIA

Joined: Wed 10 Sep 2003, 7:16 pm
Posts: 1260
My opinion on this is that a large diameter exhaust on a
naturally aspirated engine has less back pressure but
unfortunately reduced scavenging/cylnder filling.

This is fine for a vehicle setup for high engine speed ie.
Nascar but not much good for a standard GSL Cordia.

Slow air flow through the intake manifold/ports, has a
tendency for the fuel to collect on the manifold walls.

Matt


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 29 posts ]  Go to page 1, 2  Next

All times are UTC + 10 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron



Connect with Cordia Power on Facebook. Cordia Power 2000-2017. Cordia Forum powered by phpBB.