Exhaust Woes

[G0DZLR]

after hmming and harring for months now i finally decided it was time for a new exhaust. simple, 2.5" straight through, couple of mufflers to hush it a bit but keep a note.

to cut a long story short, the 2.5" has taken away some of (enough to be quite noticable) my pickup. what i dont get is how a 2.5" can get worse performance than the stock 2 1/14" one that had a blitz cannon on it and a aftermarket resonater (EPA )

in more detail, the new system, 2.5" catback, what looks to be a big f**koff resonator (about 40cm long? :S) to a single muffler in the back (apparently one they use on 5.0L commodores) feeding to twin medium sized tips. just below 2k revs, it has the distinct sound of a clapped out VN commodore .

im not happy anyway cos its way too loud, my exhaust dealer said the same, hence why havnt actually got a quote for the system as of yet, but i want to know why iv lost performance and what i can do to get it back and then some. i go back to the shop monday arvo to sort it out (getting a second muffler put in somewhere), so any ideas before then would be appreciated.

car in question is a bone stock SI R33 GTS25 non-turbo. RB25DE.

people have already said to put my cannon back on it to free it up a bit, its half tempting at this stage.

cheers

[Moodles2]

Since it's a N/A engine, I'm actually not suprised you might be losing power, N/A engines create torque with backpressure in the exhaust , the RB25 isn't exactly a torque monster in N/A form either. There might be a more simpler answer, resetting your ECU or a leak somewhere in the exhaust

[(OO)SKYLINE(OO)]

If your car is N/A, I would not go anything larger than 2.25" (2 1/4) and thats for the In-pipe.

Your muffler out let can be 4.5" or however big you want it but as long as the In-pipe is 2.25" you should be fine.

[G0DZLR]

Since it's a N/A engine, I'm actually not suprised you might be losing power, N/A engines create torque with backpressure in the exhaust , the RB25 isn't exactly a torque monster in N/A form either. There might be a more simpler answer, resetting your ECU or a leak somewhere in the exhaust

i always thought it was the other way round, smaller exhausts on turbos otherwise the turbo would lag....hmmm.

so in theory, my old exhaust, with its one really weird bend, creates more backpressure, therefore is better for my performance now?

other issue i thought of was heat soak, seeing as it has been 40+degrees the past 3 days down here

[MrStabby]

i always thought it was the other way round, smaller exhausts on turbos otherwise the turbo would lag....hmmm.

Nah exhausts on turbo cars have a big f*ckoff restriction in them already - the turbo's turbine. You want everything beyond to the turbo to be the lowest back pressure possible so the turbo's turbine sees the maximum pressure difference across its blades that it can.

[(OO)SKYLINE(OO)]

i always thought it was the other way round, smaller exhausts on turbos otherwise the turbo would lag....hmmm.

Nah buddy, bigger the better for turbocharge cars. 3"or 3.5".

so in theory, my old exhaust, with its one really weird bend, creates more backpressure, therefore is better for my performance now?

Whatever brand / made exhaust system you had last time was probley designed for a N/A that was why its was good or suited your car very well.

other issue i thought of was heat soak, seeing as it has been 40+degrees the past 3 days down here

You don't really have to worry about it so much as you car is N/A.

Just make sure you engine oil and radiator fluids are up. If you have an airpod, then you can sheild it off to block out the heat or stick to your stock air box.

[Guest 40th-edition]

Since it's a N/A engine, I'm actually not suprised you might be losing power, N/A engines create torque with backpressure in the exhaust , the RB25 isn't exactly a torque monster in N/A form either. There might be a more simpler answer, resetting your ECU or a leak somewhere in the exhaust

not true, cant be bothered explaining read this if interested http://www.uucmotorwerks.com/html_product/...etorquemyth.htm

the only thing i have seen that has needed back pressure is some cars that get to faster flow will not let the O2 sensor get a accurate reading resulting in prolems.

may just feel slower? dyno it and see, would need to swap back to test

Edited January 30, 2009 by 40th-edition

[G0DZLR]

well interestingly enough, now the weathers cooled down a bit, took it for a spin after work, seems to be a bit quicker now. plenty of top end grunt but still lacking a bit in the lower revs.

taking it back to the shop Monday to get a second muffler fitted as it wasn't quite finished the other day, so hopefully with the addition of the second muffler, and addition to restriction, should regain me some back pressure

moral of the story i think is i shouldve got a 2.25" system instead. either way the stock system had to go (had the annoying metallic sound that all 33s get)

ED: 40th ed, the first part of that article is true, a stock engine with modified elements is bound to unbalance the rest, which is what iv done by the looks

[Guest 40th-edition]

yeah i didnt read the whole thing, spent 4 yrs learning all that shit.

its good to know so you dont waist money trying to gain hp with no rewards

[Godzilla32]

Bolt on exhaust is the way to go. Tried, tested and proven.