4inch exhaust for the AU

**Stav** · 10-12-2005, 10:39 AM

Well ive been thinking about it an think a 4 inch exhaust may be my next move.
If 5 litre enigines run with 2 2.5 inch units well the area of piping is 5 inches. So we are essentially running each 4 cylinders off 2.5 inch pipes.

I might give this a go.1 inch per litre

INJECTED_250 · 10-12-2005, 10:46 AM

HAve fun with that.....Id love to hear that :>:>.. Is there even room to run a pipe that size.

Just dont go pulling the house drain pipe of the gutters of youre house...

Casper · 10-12-2005, 10:49 AM

Go for it Stav.. will be "interesting"

**Mechan1k** · 10-12-2005, 10:51 AM

I don't think it works quite like that though.

high-boost applications use 4" exhaust systems.

For N/A systems to work properly they need the right size for the exhaust pulses to scavenge the gases out of the system. It works on vacuum to suck the exhaust out ... each pulse has a vacuum behind it to suck the next wave of gas out.

Going too large in diameter will not allow enough vacuum ... which in turn doesn't allow to gass to get out quickly enough ... resulting in a loss power and torque.

Turbocharged vehicles are different ... needed as large as possible an exhaust (high boost applications) ... as the turbine wheel causes turbulence ... totally different to an N/A setup.

There's some excellent tutorials out there on the web about this that explains it better than I can.

The V8s use 2.5" for each side ... which is a decent size ... but it allows for exhaust pulsing to work efficiently ... going up in size too much can adversely affect this.

What are you currently running now on the 6???
With your power outputs .... you should be able to go up to 3" in diameter ... and gaining some ... but jumping up to 4" I think you will find you will lose power ... and definitely lose torque as well.

Casper · 10-12-2005, 10:53 AM

Quote:

Originally Posted by Mechan1k

I don't think it works quite like that though.

high-boost applications use 4" exhaust systems.

For N/A systems to work properly they need the right size for the exhaust pulses to scavenge the gases out of the system. It works on vacuum to suck the exhaust out ... each pulse has a vacuum behind it to suck the next wave of gas out.

Going too large in diameter will not allow enough vacuum ... which in turn doesn't allow to gass to get out quickly enough ... resulting in a loss power and torque.

Turbocharged vehicles are different ... needed as large as possible an exhaust (high boost applications) ... as the turbine wheel causes turbulence ... totally different to an N/A setup.

There's some excellent tutorials out there on the web about this that explains it better than I can.

The V8s use 2.5" for each side ... which is a decent size ... but it allows for exhaust pulsing to work efficiently ... going up in size too much can adversely affect this.

What are you currently running now on the 6???
With your power outputs .... you should be able to go up to 3" in diameter ... and gaining some ... but jumping up to 4" I think you will find you will lose power ... and definitely lose torque as well.

Shhhh, you're spoiling the fun. Sure it wont work... we all know that.. but imagine a wagon with a 3300rpm highstall and a 4" exhaust. You'd hear it coming from 4 miles away

:

INJECTED_250 · 10-12-2005, 10:57 AM

Here is somthing i find interesting.. I actually went from 103-104 to constant 107's gained 3-4 mph by dropping the exhasut at the colector on my 250 cortina .. THe system is 2.5 inch with only one semi/of set muffler. There for by fitting a 4 inch system wouldnt this just be kinda the same. There for no loss should be experianced. IT would depend on the CAM i was running a pretty hot 260@050 cam which i gues would like a very free flowing exhaust... ON an AU with a mildish cam (which they are in the world of cam shafts) i could see a power loss occuring but hey u never know. Mabie run it on a dyno with the exhaust of then on???

outback_ute · 10-12-2005, 12:10 PM

Sorry Casper but now that reality has intruded... It is not the diameter, it is the area of the exhaust that matters - 2 x 2.5" pipes do not have the same area as a 5", quite a lot less in fact.

I have a flaw in the theory though, I have a <1L car with a 2" exhaust... perhaps you should go 2" per litre and have an 8" exhaust lol

Casper · 10-12-2005, 12:12 PM

Quote:

Originally Posted by outback_ute

Sorry Casper but now that reality has intruded... It is not the diameter, it is the area of the exhaust that matters - 2 x 2.5" pipes do not have the same area as a 5", quite a lot less in fact.

I have a flaw in the theory though, I have a <1L car with a 2" exhaust... perhaps you should go 2" per litre and have an 8" exhaust lol

HOT DAMN! I have the VCT so I have room for twin pipes built in. Can I go TWIN 8"??? Should be cool so long as a couple bull elephants dont mistake them and do rude things to my car!

:

AnthonyQLD · 10-12-2005, 12:16 PM

Quote:

Originally Posted by Casper

HOT DAMN! I have the VCT so I have room for twin pipes built in. Can I go TWIN 8"??? Should be cool so long as a couple bull elephants dont mistake them and do rude things to my car!

:

: that would look interesting

12 · 10-12-2005, 12:41 PM

Quote:

Originally Posted by Casper

Go for it Stav.. will be "interesting"

Bhwaaa haaa haa

You meanie!

But after reading some of your posts of late useless, I say go for it too.. build that rocket wagon! Why stop at 4"?

stiddy · 10-12-2005, 01:25 PM

LOL 4in is too big... i wont say anymore..

**FTE217** · 10-12-2005, 01:34 PM

Stav I love your mental battles to get more power !
Ever thought up there about buying a faster car ?

JC · 10-12-2005, 01:38 PM

Does he mean 4" long, or 4" diameter. 4" long may work, but not diameter.

To get the same area as dual 2.5" on a 5L for your 4L, 3.1" is the optimum size, so 3" is the size you could go.

stiddy · 10-12-2005, 01:41 PM

ive got 3inch on my car, and i think thats boarderline, feels a little gutless under 2500rpm, but having a manual im not overly fussed...
but for an auto, i think it would make it slower off the line..

Dark Horse · 10-12-2005, 01:49 PM

Quote:

Originally Posted by Casper

HOT DAMN! I have the VCT so I have room for twin pipes built in. Can I go TWIN 8"??? Should be cool so long as a couple bull elephants dont mistake them and do rude things to my car!

:

A JATO pack you mean?

jabba · 10-12-2005, 01:49 PM

OMG. I can't wait to see the result on the track...... Stav were does your knowledge come from. Have you been talking to 18 year old kids with there mother's auto Hyundai's and big exhaust.

jonbays · 10-12-2005, 02:11 PM

A good twin 2.5' system could be worth while but I doubt it. A 4" single system just won't fit and really has no hope as it will be too hard to run properly on a street car.

**Stav** · 10-12-2005, 02:37 PM

Ok then why do cars with no exhaust gain big power?
For all the smart guys.

dansedgli · 10-12-2005, 02:41 PM

Quote:

Originally Posted by useless

Ok then why do cars with no exhaust gain big power?
For all the smart guys.

Not all cars do.

My bike is slow as walking with a dropped exhaust.

**Stav** · 10-12-2005, 02:43 PM

If the air fuel ratios are corrected it should run good

**Stav** · 10-12-2005, 02:44 PM

Quote:

Originally Posted by Bluedriver

Stav I love your mental battles to get more power !
Ever thought up there about buying a faster car ?

If I got a faster car I would have to play more sports.

:

**Stav** · 10-12-2005, 02:48 PM

Quote:

Originally Posted by INJECTED_250

Here is somthing i find interesting.. I actually went from 103-104 to constant 107's gained 3-4 mph by dropping the exhasut at the colector on my 250 cortina .. THe system is 2.5 inch with only one semi/of set muffler. There for by fitting a 4 inch system wouldnt this just be kinda the same. There for no loss should be experianced. IT would depend on the CAM i was running a pretty hot 260@050 cam which i gues would like a very free flowing exhaust... ON an AU with a mildish cam (which they are in the world of cam shafts) i could see a power loss occuring but hey u never know. Mabie run it on a dyno with the exhaust of then on???

Injected 250.Run a twin exhaust man..I have seen this done on a 250 2v motor and it flew!!If you would like more details pm me.

stockstandard · 10-12-2005, 02:55 PM

Quote:

Originally Posted by useless

If 5 litre enigines run with 2 2.5 inch units well the area of piping is 5 inches.

Your maths skills could use a little work.

Id LOVE to see the look on the faces at the exhaust shop when you ask them to fit the 4" pipe.

**Stav** · 10-12-2005, 03:04 PM

Quote:

Originally Posted by stockstandard

Your maths skills could use a little work.

Id LOVE to see the look on the faces at the exhaust shop when you ask them to fit the 4" pipe.

Ill take a photo. :Reverend:

EDXR8 · 10-12-2005, 03:05 PM

Firstly cars without exhausts do pick up power but its at the expense of the low end. Secondly twin 2.5" isn't the same as a 5" exhaust, its far less than that, some simple maths will show you that. Thirdly, V8's with twin 2.5" or even single 3" systems do suffer from low end power loss compared with smaller pipes.

A 4" system on a NA 6cyl running 15's is an absolute joke, but I guess it will give all those genIII's you keep beating something to look at as you pull away from them.

**Stav** · 10-12-2005, 03:06 PM

What do gen3s have to do with anything.

NEG · 10-12-2005, 03:10 PM

i say get a single 2 1/2 or 3'' and put a 4" tip on the end, or why not a 5" :P

jonbays · 10-12-2005, 03:11 PM

Quote:

Originally Posted by EDXR8

Firstly cars without exhausts do pick up power but its at the expense of the low end. Secondly twin 2.5" isn't the same as a 5" exhaust, its far less than that, some simple maths will show you that. Thirdly, V8's with twin 2.5" or even single 3" systems do suffer from low end power loss compared with smaller pipes.

A 4" system on a NA 6cyl running 15's is an absolute joke, but I guess it will give all those genIII's you keep beating something to look at as you pull away from them.

Don't laugh too hard there were plenty of genIII's at WSID lining up against useless' wagon and no word of a lie there were a few that didn't get away till well past the 1/8th mile. And these genIII V8Owners guys are serious about their drag racing!

Lukeyson · 10-12-2005, 03:15 PM

go the 4", if your putting a 460ci in it

DanXR6T · 10-12-2005, 03:18 PM

I really think Useless needs some help in the maths department.

area = 3.14 x (radius^2)

therefore 2.5" = 4.9 square inches
2 x 2.5" = 9.8 square inches

4" exhaust therefore has an area of 12.56"

applying your "4L/5L" theory the optimum area for a 5L is then 15.7 square inches or twin 3.1"