Scooby B

iTrader: (2)

Back last year I went down to EngineTuner for a full remap, the car is a 2002 Bugeye STI prodrive style. Standard engine with normal bolt on mods, including alcatek ecu, sc42 turbo, injectors, fmic etc.

The graph: 412bhp|355ft/lbs


Whilst I was very happy with this result Martyn said the 2.5" exhaust was holding it back.

So a months later I finally got round to fitting a 3" Miltek and headed back down to EngineTuner for a map tweak and re-run. (The exhaust was the only change to the car.)

The graph: 430bhp | 396ft/lbs


Thats a 17bhp & 41ft/lbs increase. I was amazed at the difference in results. Who said size didn't matter

Trinity

iTrader: (28)

Size doesent matter, but set up does.

On a twinscroll 3" are pretty rubbish on a standard set up, and increase lag on standard single scrolls...but as youve shown over 400, the 3" starts to become useful!

DantheMan2605

Nice results bud.

I had 407/430 on a 2.5 inch

Changed to a 3 inch and added fmic and now sat at 470/470

Amazing the results attained through installing certain parts

Scooby B

iTrader: (2)

Impressive^^^

What engine and fuel?

ScottishRayman

Excellent improvement, probably 50/50 from those 2 parts on your increase as seems to be going 2.5 to 3 is pretty worthwhile. Must have be a fun drive home from mapper

DantheMan2605

Thanks.
Im cheating a bit, it's a 2.3 with t36 on the larger exhaust housing. Built and mapped by the Jeffery gang

DantheMan2605

Sorry, vpower only. Currently working towards Syvecs and toucan then a splash of meth

scooblet

iTrader: (5)

It was a pleasure to watch it on the dyno!

b3nmw

Gd results there m8

jaygsi

iTrader: (46)

I fitted a 3" system to my standard impreza, may have slightly increase turbo lag, but power wise really improved power delivery

Scooby B

iTrader: (2)

LOL

Was going to say 470 on a 2ltr is going some!

d4nnyc

Increased turbo lag? shouldn't it reduce turbo lag?

XDevil666

Less back pressure so increase of lag I believe, don't quote me on it

Paben

iTrader: (5)

I think a point that's being missed here is the large variation in results that can occur with rolling roads. There are many instances of the same car being retested within an hour on the same RR and getting quite different readings. While it seems to be accepted wisdom that 3" is better than 2-1/2" there are plenty of cars with 2-1/2" systems achieving high power levels.

Zuber

Turbos don't like back pressure, a true 3" system from turbo back will always be better than a 2.5" system for reducing back pressure alowing the turbo to spool much quicker and producing more power/torque.

gazney101

iTrader: (5)

Wrong!

Zuber

Well prove I'm wrong then, been tuning turbo cars for over 20 years and I know I'm right!

d4nnyc

Care to explain?

Dyno results? Scientific explanation? Own experience?

The Pink Ninja

iTrader: (23)

It's the headers and upipe that produce spool isn't it, The down pipe/exhaust is on the hotisde of the turbo to let the gasses out? Can someone explain how a more free flowing downpipe an exhaust will increase lag or decrease spool ?

gazney101

iTrader: (5)

If the diameter of the pipework is too big the gasses will gain pressure and slow down after leaving the turbo, whereas having the smaller diameter pipework limits the volume of air that can pass through it it also retains velocity.

Fitting a 3" exhaust to a car that doesnt require that amount of volume will cost a certain degree of performance even if it has the ability to make more topend power.

Back pressure is the enemy of turbos but no back pressure is bad aswell, a certain brand of exhaust which has no silencers in it at all underwent some testing (i was told this by someone who is very well respected by the subaru and ralliying communities) and didnt turn out well on dyno testing and showed issues with spool up and i was advised not to remove the silencer from mine, as i said this wasnt my experience but the physics dont lie.

Have a read up about the venturi theory as it displays what im talking about