New exhaust = less power :(

[rossint]

The other week my extractors developed a large hole so I took the car to a reputable exhaust shop in Adelaide. They recomended some headers which they ordered, I asked about replacing the whole system and it didn't work out too much more for them to custom make something so gave them the go ahead. They recomended a 2inch mandrel system using my hi flow cat with no muffler and just a lukey resonator sticking out the back. (my cars mainly used on the track)
The car felt like it had lost power and today I got it on the dyno, 6kw down from the last run 1 month ago. So what do you guys recommend I should be aiming for in an exhaust? I thought the last one was to big and looked ugly (2.5 with lukey muffler and cannon sticking out the back) but seemed to have been pretty good in hind sight. It's an na NA6 with pod filter and cams done. I will be contacting the shop tomorrow to see what they have to say, I made it clear I didn't want to loose power.

[Okibi]

Post up the dyno charts, it might explain why your readings are different.

What's the difference in the torque figures?

[rossint]

I didn't get torque figures today (not sure why), just power. The graph looks exactly the same just lower, last time made just under 81kw and todays made just under 75kw.

[philz]

Same dyno? Same temp? Has the dyno been calibrated in the last month?

[rossint]

Same dyno, couldn't tell you if the dyno has been calibrated or not. Temp would be slightly colder than it was a month ago which should result in more power shouldn't it? I thought the car felt like it had less power as soon as I picked it up but you always wonder if you're imagining things. I put my foot down and it makes noise but dosen't pull as hard.

[philz]

So from what I can gather your last system was a 2.5", and now it's a 2"?

[Okibi]

Cooler air should mean more power but they might have adjusted the dyno figure to compensate?

[rossint]

So from what I can gather your last system was a 2.5", and now it's a 2"?

Correct, I did mention I didn't think 2 was big enough but the shop said it would be fine and would make the car really torquey.

[StanTheMan]

isn't that stock size?

I thought 2.25 was he sisze everyone goes on about......for N/A

[Hellmun]

I thought 2.25 was the happy medium where you don't lose the bottom end but still get gains up high. At the top of the range I'd expect the 2.5 to perform better though for peak figures.

[Jeo]

I thought 2.25 was the happy medium where you don't lose the bottom end but still get gains up high. At the top of the range I'd expect the 2.5 to perform better though for peak figures.

+1


I'm assuming since you said the car mainly saw track work that you explained to them what you wanted out of the car/system?

[rossint]

I thought 2.25 was the happy medium where you don't lose the bottom end but still get gains up high. At the top of the range I'd expect the 2.5 to perform better though for peak figures.

+1


I'm assuming since you said the car mainly saw track work that you explained to them what you wanted out of the car/system?

I sure did, made it clear that I didn't want to loose power and it was a track car. So it looks like it's back to 2.5 then.

[philz]

Yep I would go back to 2.5", 2.25" is okay as well, 2" is too small.

[Juffa]

Normally a 2.25 system on a N/A engine would be fine. However, with a pod filter and cams a bit more work may be required to get it right.

By the way, what is your timing set to? A number of us run 14 degrees, not sure it this applies with the cams you have.

J

[rossint]

It was at 14deg before the cams then was dyno tuned when the cams went in, I'm not sure what my mechanic set it at. Thats where I got the original power figures from, post cams tune.