Power Restriction?

[bj0rn]

well, i realise dyno's are only a means of measurement, but i'm convinced that my setup has seemingly less power than almost everybody elses thats similar, so im just trying to figure out what the restriction could possibly be.

here's a list of what's been done:

unopened s1 rb25det

ems stinger ecu

hks gt2835 pro-s

3" flexi pipe intake hose

nismo 740cc injectors

walbro pump

hybrid cooler

stock coils

exhaust that goes from 2.5" to 3", 2 mufflers no cat

18psi - 315rwhp

13.1 @ 109mph on 205 rubber

compression test came up as 150psi across all 6 cylinders

it holds boost through to redline, and im assuming the coilpacks are working as it doesnt miss. it has a stock fuel pressure regulator.

the most obvious thing i can think of is either the exhaust is restricting it, or my tuner isn't putting any timing into it?

any thoughts please punt them at me

cheers in advance

Edited January 24, 2011 by bj0rn

[snozzle]

drop your exhaust and see how much of a difference you feel - if its alot then thats probably your answer

post up dyno sheets if u have any

[R31Nismoid]

2.5" exhaust - your issue is staring you in the face.

3" or bust at a minimum.

Also 230rwkw/109mph, is pretty close. So it's not down on power, its just restricted to the heavens.

You'll probably get 20-30rwkw out of an exhaust change easily.

[bj0rn]

ok, forgive me if this is a stupid question but would dropping the exhaust affect my afr's ?

possibly lean it out quite a bit ?

heres the dyno sheet

[R31Nismoid]

There are no AFR's on that sheet.

It might affect the tune - either way mate you with such a restriction, attention to the tune is a given.

[bj0rn]

yes i know there are no afr's on the dyno readout,

i'm pretty sure if the restriction is the exhaust and i remove it, theres a definite possibility it may go pop ?

[R31Nismoid]

What will go pop?

The motor?

Mate - get the exhaust fixed. Drive sedately to tuners (or have them do the work on-site if possible), run it up and have a look.

There is no way around this. Your motor will simply not just up and die from an exhaust change, however the tune MUST be looked at with such a restrictive exhaust. You will hit load points that you weren't previously.

Also that tune, is honestly looking pretty average. The curve should be much smoother. Is the right axis is toruqe, then its 100% a poor tune as its dropping around 104-120, but then that could also be the exhaust.

Overall moral of this story? Get the exhaust fixed, and get the tuner to have another look at it all.

[bj0rn]

yeah i was thinking just simply dropping the pipes and taking it for a thrash was generally a bad idea.

cheers for your help

Edited January 24, 2011 by bj0rn

[R31Nismoid]

That often doesn't work, or give you a good idea.

Cause it's louder, you've made a change - often a bit of placebo kicks in.

Hence on the same dyno/tuner etc, you'll soon see whats going on.

That turbo is good for 260-280rwkw, and should be up around 112-114mph once you get that power.

I was racing regularly years ago with 220rwkw and I was running 12.9 @ 109mph consistently.

[R31Nismoid]

Also where does the 2.5" start?

If it's a 2.5" dump, and then 3" after the cat - then dropping it wont show much until you actually replace it

[Harey]

I would also change to a 3" hard intake pipe. Not sure what flexi hose you mean but most likely it will suck shut as you increase the power.

[bj0rn]

nismoid: funnily enough, its only 2.5" where the hks dump flange meets the front pipe. and its only that small for about an inch, then immediatgoes to 3 inch. it has a hollowed out cat, then two mufflers. are you sure it'd be the exhaust?

heres a photo;

harey: the intake has wire which stops it from flexing. im fairly positive thats not the issue.

[Harey]

nismoid: funnily enough, its only 2.5" where the hks dump flange meets the front pipe. and its only that small for about an inch, then immediatgoes to 3 inch. it has a hollowed out cat, then two mufflers. are you sure it'd be the exhaust?

heres a photo;

harey: the intake has wire which stops it from flexing. im fairly positive thats not the issue.

That looks terrible. Is that 2.5" section part of the dump pipe or the front pipe? Either way it is most likely the cause and should be changed immediately.

The intake wont be causing the issue yet at that low power level. I had a flexi intake with wire and it still twisted and did nasty things above 250rwkw.

[75coupe]

that exhaust looks dodge, get it done properly

[GTScotT]

The exit of the HKS dump is 70mm from memory. Redo that to be something a little nicer than what youve got, yours looks more like 65mm ID, even if it were 68mm it could potentially hold back a lot of power.

The other issue is the flexi intake pipe, its GOT to be an issue.

Redo both ASAP. You WILL need a retune.

[bj0rn]

the hks dump bolts to the factory exhaust flange, then after the flange it goes to 3". i agree it looks dodgey

so what i'll do is unbolt the flange, take an ID reading off both the dump flange and front pipe flange and report back

[HEKT1K]

I had a front pipe like that, but I had the small bit cut off and a 3" offcut welded on. Fix that shit ASAP

[Rolls]

Im betting who ever dodgied up that exhaust didn't cut it properly and also didn't clean it up hence it has bits and pieces sticking out on the inside cause flow obstructions.

Edited January 25, 2011 by Rolls

[Brezza]

+1

for getting the 2.5in section replaced.

On my WRX years ago the owner had a terrible exhaust on it, pieces were 3in, some still had stock mufflers and resonators. it was all welded together horribly and the dump pipe had a big dent in it from where it was bent into shape. after i had the catback section replaced the car was louder, but still didnt gain any power because of the dent in the front pipe. this dent was quite big and was definitely restricting it.

The exhaust bloke said its like when you step on a garden hose, the amount of water that comes out the end is less because it cant flow past the restriction of your foot on the hose.

moral of the story,

had the dent fixed, welded in a new 3in section and gained power all over the power band.

[Harey]

Why the hell do big companies make exhausts like this???

Greddy:

http://cgi.ebay.com.au/Greddy-Nissan-Skyline-R33-GTS-t-RB25-MX-Front-Pipe-/200563900514?pt=AU_Car_Parts_Accessories&hash=item2eb28a4062

Apexi:

http://cgi.ebay.com.au/APEXi-GT-Spec-Front-pipe-Skyline-R34-ER34-RB25DET-/380277809380?pt=AU_Car_Parts_Accessories&hash=item588a52e0e4

Surely it would cost more to have a change in diameter then just straight pipe??