Exhaust Change

[Guest pmacleod]

about 3-4 weeks

It's usually a good idea to run your car in a bit before you change the exhaust but given that the Cat Converter is usually the major restriction in an exhaust system there's probably no pressure change to the engine.

Are you able to get copies of the Dyno Sheets from the other car and post them - a 17KW increase at the wheels would mean a greater power increase at the fly wheel as you would get more loss of power in the drive train from heat/friction etc etc.

A strictly linear equation would peg fly wheel power to be 262 KW however the equation would actually be exponential so it would probalby be a bit more power than that.

Any word about how that affects the warranty?

Drive train loss is a fixed value, it's not proportional to power output. This has been done to death a zillion times (really) on various Subaru forums.

CJF - GO SON ! Good to see you didn't restrain yourself too long :D

Cheers,

Paul.

02 STi with stock exhaust for about 4 weeks :D

[Guest driftin]

about 3-4 weeks

It's usually a good idea to run your car in a bit before you change the exhaust but given that the Cat Converter is usually the major restriction in an exhaust system there's probably no pressure change to the engine.

Are you able to get copies of the Dyno Sheets from the other car and post them - a 17KW increase at the wheels would mean a greater power increase at the fly wheel as you would get more loss of power in the drive train from heat/friction etc etc.

A strictly linear equation would peg fly wheel power to be 262 KW however the equation would actually be exponential so it would probalby be a bit more power than that.

Any word about how that affects the warranty?

Drive train loss is a fixed value, it's not proportional to power output. This has been done to death a zillion times (really) on various Subaru forums.

CJF - GO SON ! Good to see you didn't restrain yourself too long :D

Cheers,

Paul.

02 STi with stock exhaust for about 4 weeks :D

That's not correct.

Think of a 1000kw GTR or something similar. A standard GTR might put down 150kw at four wheels and 230kw at the flywheel. Hence, by your reasoning, GTRs lose a fixed 80kw from the flywheel to the wheels.

Obviously, the 1000kw GTR does not have 920kw at the wheels.

Also, by your reasoning, it would be quite possible to have a car that has a negative power

output to the wheels if it were say, running badly and down on power.

Adam

[CJF077]

Im a bit confused about this whole flywheelKW and KW, what is the difference? And how is it measured?

[Guest MrSparkle]

Im a bit confused about this whole flywheelKW and KW, what is the difference? And how is it measured?

Flywheel kW is the power measured at the flywheel, ie. before the gearbox, clutch, drive shaft, diff, etc. Each of these experiences a loss in power due to friction, etc. Hence, the power that reaches the rear wheels, has gone through many components with frictional losses - which is why it is less than at the flywheel. Automatic transmissions experience more loss than manual boxes, which is why a manual car will have a sniff more power at the rear wheels. There is no fixed figure for the actual drivetrain loss for a car, the only real way to measure power absolutely correctly, is to take the engine out and put it on a proper engine dyno.

I can't stress enough, that chassis dyno figures are only RELATIVE - conditions of the day, the dyno, and the operator, will differ between locations and dates. It is absolutely meaningless to quote a figure from one dyno on a particular day, to a dyno in a different place on a different day. If you want to see what effect a modification has had to your car, use the same place and the same operator, and try and find similiar conditions to do it in, ie. don't do the first run on a 15deg day, and the next one on a 40deg day Alternatively, if you want to see how your beast compares to other ones, organise (or join in with) a dyno day with other guys. Not only is it a great day out, but you get a set of meaningful comparative results.

Check out our last club dyno day results HERE --> http://nsw.tickfordclub.com/images/2002-03...10/dynoday.html

BTW mine is the 3rd one in the V8 mod class, Michael H :lol:

Ballpark figures for drivetrain loss are approximately 20-25% for a manual box, and 25-30% for an automatic.

Nothing is set in concrete when it comes to the issue of dyno figures! (Unless you're talking engine dynos)

Cheers!

[Guest DZ.]

That's not correct.

Think of a 1000kw GTR or something similar. A standard GTR might put down 150kw at four wheels and 230kw at the flywheel. Hence, by your reasoning, GTRs lose a fixed 80kw from the flywheel to the wheels.

Obviously, the 1000kw GTR does not have 920kw at the wheels.

Also, by your reasoning, it would be quite possible to have a car that has a negative power

output to the wheels if it were say, running badly and down on power.

Adam

Agreed. Your frictional and heat losses will increase as you try and put more power down to the increased energy that each component has to transfer. It may appear to be a fixed percentage loss - however in reality a formula incorporating an exponential factor would be more accurate.

[Guest MattK]

In regards to the computer detecting changes ive been told that the cat is in the same place within the chain so the computer should not notice any difference at all. (this is what they told me). I had a look at the Dyno sheets from the car that was for City Ford 180 Rear Wheel KW and after with the exhaust 197.. im not too sure how they work things out but im pretty sure that means the car is now 257KW? maybe someone can

correct me?

Where the cat is in the chain shouldn't affect anything for the ECU (it shouldn't even care if it's not there at all), the important thing is that the O2 sensor is before the cat - and I've never heard of any exhaust shop stupid enough to move it. The only reason I can think of that the ECU would come into play with an exhaust change is that it may be boosting a little higher now, but I doubt that'd happen either.

Cheers,

Matt

[CJF077]

Here are some pics of the exhaust ...

[CJF077]

#2

[CJF077]

#3

[CJF077]

And a Video fo the sound.. can't really hear it the best.. but you can tell its alot deeper..

MOV00146.MPG