Exhaust Issues HMMM

G

Guest

Unregistered
Hi Peeps,

Just wondering if ny one elde has had similar issues with their Exhaust System - I Recently got Custom Made Dumps 2.5Inch into 3 Inch Full Exhaust High Flow Cat & High Flow 3inch Muffler (hurricane) with Sexual Mandrel Bends but can't feel any difference in acceleration or power?
Whathefudge?
Maybe my leggie is sick - I'm sure it needs a tune but I expected to see some noticible power gains?......
 

Mac Dog

Leaving Skid Marks
Location
South Australia
First Name
Macca
Drive
Red 1997 Legnum
Do you have a boost gauge or anything? On my 200sx, after I replaced the stock exhaust with a full 3" system I only felt a slight difference in power gain, and my boost gauge verified that there was a slightly noticeable power increase.
 

godzilla

1 AYC Bar
Location
QLD / Tweed Coast
First Name
Trevor
Drive
1/19 2002 FL Legnum Type 'S' Manual in Black with Suede Recaro's!
By rights you should have noticed quite a big difference going that full stystem over the stock one but there might be another problem somewhere i.e. maybe the O2 sensor has had it and after throwing it into an even free-er flowing system it is going nuts on over fueling? I am sure others will have maybe more realistic responses.
If you dont mind telling us, how much did said system set you back? And who did you get it done through?
 
G

Guest

Unregistered
That'll be my next purchase - Yea I had a Silvia few years back with Blacktop SR20DET & responded brillianty to Full 3 inch exhaust...Very noticable power gain - 16kwatw to be excact:p
To be honest i'm i little dissapointed in the Leggies performance :mad:
Maybe after a Auto Box service & Tune it might respond a bit better...
 
G

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Unregistered
Yea Sensor is possible - I'm getting a resonator put in 2moro cause it's a bit too loud - being auto it's a little Droning...]
I paid 1200 Smackos
 

godzilla

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QLD / Tweed Coast
First Name
Trevor
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1/19 2002 FL Legnum Type 'S' Manual in Black with Suede Recaro's!
Thats a good price including front pipes, highflow cat and mandrel. Where did you go?
Best price i have had so far is $880 for a Highflow s/s cat, 3" mandrel and a 3" cannon stlye muffler.
 

Soldat

Hesitantly Boosting
Location
AU
First Name
Blake
Drive
R33 GTST (S2)
get a tune. My R33 actually got worse when I put on a 3" high-flow turbo-back system but it went like a rocket with a retune.
 

godzilla

1 AYC Bar
Location
QLD / Tweed Coast
First Name
Trevor
Drive
1/19 2002 FL Legnum Type 'S' Manual in Black with Suede Recaro's!
You cant just "tune" the car, if you want to tune you have to look at piggy backing the ecu with either fuel controller or fuel/timing controller.
 

eddyvr4

Leaving Skid Marks
Location
SA
First Name
Eddy
Drive
2001 Legnum Type S, 2007 Kawasaki ZX14
it wont be o2 sensor, the ECU ignores the o2 sensor under heavy throttle.
 
G

Guest

Unregistered
Got Exhaust done at Hannam Street Mufflers in Cairns

Thanks for the info guys - I'm not sure which way to go in the way of tuning- don't want to spend a fortune but need my leggie to run sweetly
I might research on Fuel/Timing controllersetc etc 2nite
 

SiliconAngel

1 AYC Bar
Location
Perth, WA
First Name
SA, Trevor
Drive
'99 Legnum VR4 Black MT
Replacing your exhaust is not just about going for bigger pipes, its about maximising flow. The best way to do this is designing pipes tuned for maximum flow at a given RPM range. If done right you can get substantial performance gains from upgrading your exhaust. But just throwing larger pipes at the problem may actually make things worse, not better.
 

jungle

3 AYC Bars
Lifetime Member
Location
QLD
First Name
Simon
Drive
1 PFL & 1 FL Legnum
Replacing your exhaust is not just about going for bigger pipes, its about maximising flow. The best way to do this is designing pipes tuned for maximum flow at a given RPM range. If done right you can get substantial performance gains from upgrading your exhaust. But just throwing larger pipes at the problem may actually make things worse, not better.

Thats a bit general Trev.

A better answer is what boost are you running? i'm guessing stock,
Did you do a dyno pull before the exhaust was fitted? doesn't matter if you didin't but you'd be able to tell from that.

Go and get one done with boost and AFR's

Generally at stock boost levels there's not much of a restriction, it's once you start loading up the engine and really making it work. What do i mean, The stock exhuaust might for example given 125kW at stock boost and 150 at 12psi.. Full replacement might be 125kW at stock boost but 165kW at 12psi.

Hope that helps
 
G

Guest

Unregistered
Thanks for info guys - Trev - I understand what you mean but my new exhaust no longer has half a dozen factory press bends, (very straight through with only 3 Mandrels) now has 3inch hi flow pussy & 3inch hi flow Muffler (not cannon) with no resonator so it's about as unrestricted as it gets... just can't figure how some people get 10% more power? hmmm

Jungle - yea I'm running stock boost (till next week) am booked in for dyno & putting in a boost controller - hope things improve - def. looking into getting piggyback tune if possible...

Cheers
 

trounced

Leaving Skid Marks
Location
NSW
First Name
Wes
Drive
1997 Mitsubishi Legnum VR4
dont turbos need some backpresure in the exhaust to get full potential and to work correctly.

or is that just high performance normally asperated cars ?
 

Kenneth

1 AYC Bar
Location
New Zealand
First Name
Kenneth
Drive
1999 Galant VR-4
The term is a misused one.
Back pressure does not help at all, in no way, shape or form.

What you DO benefit from on a normally aspirated engine is having high exhaust velocity. At the point at which you have the highest exhaust velocity with little or no back-pressure is where your engine will sing. (high torque)

This point is designed at driving RPMs on production cars so they are not a pain in the arse to drive. As a result, at higher rpm, you will get back pressure.

Another way of putting would be that to have a car tuned for good torque at low to moderate RPM, you must live with back pressure at higher RPM.


dont turbos need some backpresure in the exhaust to get full potential and to work correctly.

or is that just high performance normally asperated cars ?
 

VR-04-TT

1 AYC Bar
Location
NSW
First Name
Paul
Drive
2005 Liberty 3.0R Spec B
That's where the back-pressure myth comes from - exhaust velocity, because you can actually decrease the size of your exhaust towards the back to retain velocity. The air will be condensing as it cools and, with a large exhaust, will lose velocity.

Making it smaller will keep the velocity in line with the condensing air.

That's all theory though, in practice it probably doesn't cool enough to warrant downsizing the pipes. But it's where the back-pressure myth stems from.
 

Soldat

Hesitantly Boosting
Location
AU
First Name
Blake
Drive
R33 GTST (S2)
You cant just "tune" the car, if you want to tune you have to look at piggy backing the ecu with either fuel controller or fuel/timing controller.

Totally agreed. Had an ECU remap done a couple of weeks after the zorst went in.
 

SiliconAngel

1 AYC Bar
Location
Perth, WA
First Name
SA, Trevor
Drive
'99 Legnum VR4 Black MT
That's where the back-pressure myth comes from - exhaust velocity, because you can actually decrease the size of your exhaust towards the back to retain velocity. The air will be condensing as it cools and, with a large exhaust, will lose velocity.

Making it smaller will keep the velocity in line with the condensing air.

That's all theory though, in practice it probably doesn't cool enough to warrant downsizing the pipes. But it's where the back-pressure myth stems from.
Not really Paul. As you said, the effect of gas temp is minimal in real world applications.

The length of components in your exhaust in a NA car relates to the frequency of the standing wave you produce from escaping exhaust gasses. Basically in order to scavenge exhaust from the cylinder quickly, the exhaust is designed to promote a negative pressure difference which literally sucks exhaust out of the chamber as the valve opens. Back pressure is merely the inverse of the standing wave generated, which is optimal at a particular RPM range but cannot be overcome (as Kenneth stated), only traded off. So manufacturers design exhausts to provide maximum benefit at lower (normal) RPMs, performance exhausts are tuned for maximum benefit at the highest performance range of the engine.

If you're interested in reading more there is bucketloads of info floating around the interwebs, such as this. However if you wish to learn about exhaust design for turbo applications, this is a little more useful.
 

VR-04-TT

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Location
NSW
First Name
Paul
Drive
2005 Liberty 3.0R Spec B
Yeah I'll check that out Trev. As I said, it was all in theory as explained to me and I didn't think it'd work particularly well in the real world.
 
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