2 Inch Vs. 3 Inch

[JAP63]

Im making an exhaust dump pipe etc...

Its 2.5" Inch off the turbo down to the sump,seperate wastegate pipe etc...
Question,should i go three inch and merge the wastegate in and do it 3 inch from the front pipe back through a 3 inch flex etc...3 inch cat etc...


Or just do the whole thing up to my 3 inch catback at 2.5" inch?

I have the standard turbo.

would 1/2 an inch really matter with my setup?

 

[BobWrinkle]

Yes for 2 reasons, one even with a small turbo it will breate easier, two when you decide to upgrade you will already be setup.

 

[Entaran]

Simple answer here is...

full 3 inch will spool a little later due to less backpressure when the car is still under vacuum but will give better top end.

2.5 into 3 will spool a little earlier and give slightly reduced top end

 

[JAP63]

Simple answer here is...

full 3 inch will spool a little later due to less backpressure when the car is still under vacuum but will give better top end.

2.5 into 3 will spool a little earlier and give slightly reduced top end

So a 2.5 inch system is just simply not big enough?

Is standard 2 inch?

Have u seen a 3 inch dump pipe on one of these cars? i dont like it. there ridiculously awkward and dont line up with the flange anyway,especially when the back of the turbo is only a 57mm hole.they also get in the way of everything and are bulky,run closer to alternator and oil filter.

 

[matress]

mine is 2.5 inch dump pipe and flares into 3 inch where the dump pipe meets the front pipe... it seems to be fine.

if you do the maths, you will find that the area of a 2.5 inch circle is quite a bit smaller than the area of a 3 inch one.

i did have the cfm differences between the 2 sizes but i cant remember where it is now, but it was quite a considerable difference.

 

[JAP63]

yeah i suppose

2.5 x 3.142=7.855
3x3.142=9.426

Difference (1.571)

I see your point.
i dont think it will hurt my stock setup.

One thing i have found whilst making this is that its a c*nt of a thing to make..
Especially when the aim is good flow,it has to drop pretty shallow off the flange and at an fair angle,to clear the alternator and oil filter,it would have to be better for flow if it could come out straight off the turbo for a while then curve back...it becomes too close to the alternator though...and the oil filter etc..

 

[matress]

i think its pretty hard to get a decent radius on the dump pipe without relocating the alternator.

i wouldnt be too paranoid about it though... plenty of cars are making good power with 2.5 inch dump pipes with the tight radius... just look at the USA!

 

[JAP63]

i think its pretty hard to get a decent radius on the dump pipe without relocating the alternator.

i wouldnt be too paranoid about it though... plenty of cars are making good power with 2.5 inch dump pipes with the tight radius... just look at the USA!

serious...

People relocate their alternators?
where to?

As for instance,i seen this for sale a while ago.

Looks like a nice job but i dont know how in hell u would get the oil filter off....and it looks like it'd have to be real close to the alternator..it looks tight.

Another thing...does anyone know why some exhaust seem to have only the wastegate pipe made of stainless,and the main dump as mild?
ive seen it a few times.

 

[tharaka]

Simple answer here is...

full 3 inch will spool a little later due to less backpressure when the car is still under vacuum but will give better top end.

2.5 into 3 will spool a little earlier and give slightly reduced top end

it's a turbo car
it doesn't need backpressure



go 3"
bigger exhaust will spool earlier and give you more power throughout the rev range

 

[Entaran]

Simple answer here is...

full 3 inch will spool a little later due to less backpressure when the car is still under vacuum but will give better top end.

2.5 into 3 will spool a little earlier and give slightly reduced top end

it's a turbo car
it doesn't need backpressure



go 3"
bigger exhaust will spool earlier and give you more power throughout the rev range

I'm sorry tharaka, obviously you must know more than I do because you know, you are the master of this subject or something. :roll:

Increased backpressure will decrease the time it takes to spool but detract (in some cases significantly) from the top end. This is why a bigger exhaust ALWAYS nets LARGE gains from any stock exhaust. But as a result your car will ALWAYS spool 100-300rpm LATER.

 

[VR-4Squid]

I've actually tried both set-ups.

Originally I had stock exhaust to the flexi, then 2.5" back to 3" cat back (with no cat cos polution doesn't matter in nz :lol: ) (actually that's a lie, when i bought the car it had 2.5" flexi back into big ugly restrictive crap muffler, but i digress).

Then I went to 2.5" down pipe and top end was much better, boost went up 2psi, still came on at same revs.

Now I have a 3" front pipe, gained another 2psi, still spools up at the same revs - hauls arse! Oh, and sounds like a tractor off boost too :lol:

Back pressure is making it harder for the gas to exit, so how is that going to improve spooling time? :roll:

 

[bazeng]

its true mate
what lorry says is true

i've run the car with an open exhaust
3" out right after the turbo
vs a standard exhaust...

when its open.. down low its like a dog, but when it makes power u really feel it

with the std exhaust, much more torque down low.. but up top it really suffers..

remember, n/a's like some backpressure and turbo cars too are n/a's for a short period of time..

but in all seriousness.. it does effect it

but the best option for you is to go 3" dude...
the turbo is pretty small so lag is not an issue...

 

[rob323]

If you do make up a dump pipe, please make sure you bracket it to the block to take the weight of the turbo off the exhaust manifold studs.

Another thing to consider is how much ground clearance you will lose if you go 3".

I know its probably not possible to due to space restrictions, but it might be beneficial if the wastegate piping could join the main piping at a low pressure zone, such as the inside of the bend. Most of the ones I have seen seem to join on the outside of the bend where they would have to fight the flow of the main exhaust gases to get in. Maybe extend the wastegate pipe inside the main pipe alittle to help create a venturi effect.
(Feel free to set me right if my thinking on the above is wrong. I know that pressure is equal everywhere in the pipe however fluids will want to flow around the outside of the bend, maybe not so for gases)

 

[tharaka]

Simple answer here is...

full 3 inch will spool a little later due to less backpressure when the car is still under vacuum but will give better top end.

2.5 into 3 will spool a little earlier and give slightly reduced top end

it's a turbo car
it doesn't need backpressure



go 3"
bigger exhaust will spool earlier and give you more power throughout the rev range

I'm sorry tharaka, obviously you must know more than I do because you know, you are the master of this subject or something. :roll:

you're right, i do

 

[GSRSOL]

now who's acting like a child! :lol:



You cant do a 3" dump pipe off a BIG16G turbo anyway, the outlet even on the gtpumps enhanced turbine housing is only 7cm!

 

[SIVART]

Mines 3" straight off the 16g, it feels lag less, the boost is there as you want it, and I have a high flow cat, resinator, magnaflow muffler all in 3"

 

[JAP63]

Well people im halfway there.
Ill try an get some photos up,this thing looks nothing like any of the others ive seen,either im very wrong or im doing something no 1 else has tried.

I went 2.5 Inch,i know a 3" Inch will flow more but in all honesty it makes things harder to bolt up...theres F*ck all room down there.seriously,Oil filter clearance is a nightmare,even with the Z79.

Off the flange i went for a 90 deg cut shallow and straight down,this had the effect off the next pipe joining up almost straight,Its almost a straight pipe down to the base of the sump with a curve at the start.It mighnt have a great flow straight off the turbo but i think it'd make up for it with the fact its so straight..keeps it away from the alternator too,its nowhere near the alternator,which is a good thing.


Thanks for the advice with the wastegate,im going to plumb it in at about the 300-320mm mark.in a similar move to the pic shown,actually a bit further back from wats shown in the pic.

P.S.Lovely work Baz.It looks a treat. :!:

 

[Entaran]

Never -EVER- work on a car that's just up on a jack. Buy some jackstands unless you want to end up dead.

 

[bazeng]

that car is on 2 jackstands with the jack there just in case...

i dont trust jacks or jackstands.. lol
jackstands with pins are okay, i dont like the other types..

nice exhaust in that pic by the way!

 

[3zercrowd]

that car is on 2 jackstands with the jack there just in case...

i dont trust jacks or jackstands.. lol
quote]

:? Where Baz? I see only 1 jack stand and one jack?

I dont trust them either!

I usually use 2 jack stands and one jack just in case.

My life is valuable to me and my wife :wink: :lol: