less power after exhaust upgrade

Hey guys. I just got my nice aftermarket exhaust put on and its not as quick as it was stock?

Should i check timing mabey as less power with less backpressure seems wrong

Cheers. Ian

 

How much less.....

.....back pressure compared to the stock system?
How much power have you lost?

 

Hard to guage it but i would say about 20% less

 

How much of your exhaust system did you replace and what is it for everyones reference.

 

2.25 H pipe. 3inch tails with straight thru mufflers.
It was off my 2 seater. Got.it fitted to my 4+0. My 2 seater flew with this system...

Mabey it needs a tune

 

Could be a collapsed cat

 

NA right?

At a guess the exhaust velocity is out of sync with ideal scavenging potential.

You need more back-pressure. :zlove:

Using more fuel too?

 

Is your car an NA by any chance? Because sticking a 3" exhaust on an NA will definitely rob power.

Contrary to population opinion you do not need back pressure. What you do need and what a smaller exhaust (or rather a properly matched exhaust) will deliver is higher velocity and hence higher momentum exhaust gasses. This creates the scavenging effect as the older exhaust gasses get out of the way of the newer exhaust gases quicker (hence actually reducing back pressure).

But if you go too small you will lower the exhaust velocity again due to resistance from the pipe walls (air next to the wall is supposedly stationary and velocity increases as you got toward the centre so too small a diameter restricts flow and creates back pressure). You need the right size exhaust - not too small or too big that achieves maximum exhaust velocity for the amount of air your engine needs to flow.

 

I wonder if you could try a restrictor and get an improvement.
OR

 

Exhaust flanges lined up properly?

 

I just remembered... It originaly had restrictor plates between the H pipe and tails.

it is NA aswell. Ill make up some plates and see how it goes.

Cheers guys

 

This :agree:

 

There you go

I am guessing that the loss of power is being measured by the ass in driver's seat as you drive on a familiar piece of road? I also notice that you haven't complained about backfire.

Your new exhaust might be giving you more at higher revs and you are just noticing the loss at lower revs. While you have the chance do some runs at overtaking speeds on the highway.

Since you have a drop in torque, have you recently done anything with instrument lights at back of speedo, or checked that the cable in back of speedo is plugged in for the vtc.?

 

Please explain....

......the advantages & benefits of installing a larger diameter exhaust & then reducing the diameter with restriction plates?

 

20% loss of power??From and exhaust? Not on your life M8.

All due respect but unless there is a major defect/blockage then your arse dyno is way out of calibration.
Increased gasflow "may" enlean mixtures ssignificantly which will eventually self correct as time goes by so long as your O2' sensors are fitted and working.

"If" it feels that slow, Id suggest something far more sinister.

Fitting restrictors and valves?? baaahahahahah!!!!!!

E

 

Fixed!
Simply disconnected the battery over night. Let it warm up to running temp in the morning and away I went. it's amazing now. A definate good power gain compared with stock exhaust.

 

Good of you to put an update, but
How does that fix it? What else has changed?
New jeans? Dry road? Fresh petrol?

 

Our ECUs learn and trim their maps based on feedback from the O2 sensors and knock sensor, unplugging the battery for a while resets that. Either that or there was a knock code stored in there.