this is the situation

my first mods were fuji headers, y pipe, exhaust and injen cai, installed a few months ago the car sounded tuff under acceleration and seemed to open up a lot at about 4k rpm deff got power and torque increase, last week i got hfcs installed and now it sounds a little more raspy but it seems i have lost power and torque.

i know this because when the car was stock i used a g-tech and got a 14.21 1/4, and now i got a 14.6

im thinking it could be one of two things

1) a/f ratio has been affected causing a decrease in power.

2) lost back pressure due to hfc's

Any suggestions???

 

What HFCs did you get?

Not all HFCs are actually high flow.

 

I thought the point of importance for needing back preassure is where the three header tube meets...

Here is a convo between myself and a friend:

Me: I heard back preasure is a myth... still confused on the subject

Friend: HAHAHAHAHA, no its not a myth

Me: It's a huge debate all the time in the forums

Friend: First consider something, think about how an engine works. The cylinders fire in an order, each firing results in an exhaust pulse that travels down the primary to the collector, etc. However each pulse is followed by a negative flow, designing the headers so that these flows converge at the right point will make power. Moreover the length of the primaries and where they meet will dictate where the exhaust system will make the most power. But a poorly designed system will look more freeflowing but actually hurt flow by causing collision of exhaust pulses, make sense?

Me: honestly... no

Friend: hahaha

Friend: BTW: the only case where zero backpressure is the best way is in a turbo car because the turbo exaust housing provides all the backpressure

Me: So test pipes are bad for my N/A car?

Friend: Not much point in a NA cars, moreover in comparison to a modern highflow cat, you wont see a huge improvement with a testpipe.

 

Tell me why pressure in the cylinder as its trying to push the air out is good?
Back pressure is bad, it dosent create power.
BUT
Having the largest diamater pipe is not going to help you any.

THe object of an exhaust is to be the right diamater so that the air has plently of space to flow freely, but the air does not slow down which will cool the air down and make it more dense which will increase the pressure required to push the air out.

 

ECU could need to be reset, that's usually the source for power lost

 

Your ECU timing is off... not reading mods.. have to reset then you should be good... just check your plugs to be safe also

 

The mods that you've listed will alter the torque curve. You may have traded low end torque or peak horsepower. Any analysis is just a guess. I recommend a dyno run.

 

You have probably lost low/early mid range power but have gained upper mid to higher rpm power. Chances are a good ECU tune would help out quite a bit to get that balance back. Another thing to check is your air filter to make sure its not filthy.

 

Yeah I went from a 14.0 stock to a 14.0 modded. Course I got 19's as well.... Also when tested the car on a dyno my HP and torque maxed out at like 3700 RPM's. I also think this is due to lack of fuel... Reflashing the ECU with all of your mods will without a doubt should be your next step. You will see uber loads of gains from that if done correctly.

 

Most, but not all Z's, after adding the parts you have start to run lean in the 3.0-5.0k rpm range. Since this is the beefy part of the Z's torque curve you would most likely feel it.

A dyno, then a re-flash, then another dyno to prove the reflash worked is what I would reccomend.

 

cool thanks guys,

ive installed custom magnaflow HFCs.

so a re-flash of the ecu is what i need, will a uni-chip do the job???

 

EDIT

 

Yes, and it will do a better job. Use a load dyno and Unichip authorized tuner though.

 

is there even someone here in Aus that can reflash the ecu?

i think the only option we have is a piggy back like the unichip

 

There is someone who can do a limited re-flash in Sydney but no A/F or Timing, just rev limit, speed limiter etc.

Your better off with a UTEC or Unichip for timing and A/f on a load based dyno as mentioned.

 

Your friend wouldnt happen to ride sportbikes would he? That is how motorcycle exhausts and engines are tuned. Cars are a little different. Back pressure is a myth for cars and a myth for motorcycles too. What he is talking about is properly tuned exhausts and headers. The pulse he is refering to isnt caused by backpressure. Its more like how when you create a siphon how the exiting gases create suction for the newly created exit gases to be pulled out quicker. Im not very good at explaining this but thats why these parts cost so much. They need to be designed correctly so the pulses work together. You hf cats could be the problem, what kind are they? Also your a/f might be too lean causing your ecu to pull alot of timing thus losing power.

 

He drives an imported Supra and an IS300. His cousins own a Greddy TT Z33. He's a huge car guy and does all the car work himself. He's taught me a lot and He has some contacts from Stillen and Megan Racing so I listen to his mod advice and sometimes gets deals from him

 

Despite my limited knowledge of exhaust system design, I’m going to join the “anti-back pressure” crowd. If resistance to a free flowing exhaust system is good, them why don't the racing teams above put a plug in the end of the headers? Please explain? Thanks.

 

that guy is getting back pressure and exhaust pulse mixed up. In fact thats where most of the confusion comes from.

 

I had the same issue

JWT Intake
Headers
Crawford cats
Nismo Exhaust

Car felt slow... and sluggish. Went back the the OEM intake... its like a new car. Now I'll go back to the JWT intake after a reflash...