RS*R exmag on an na6ce, power loss?

[coreys]

I have recently installed an RS*R catback with the silencer in the tip on my na6. I had never read about anything negative, power wise. but for some reason my car feels as though it has lost responsiveness at low revs and feels rather flat afterwards. This is all seat of the pants, but i know i used to be able to get a bit of a kick when i booted it at 4000 in 2nd, now it appears to be flat. This could just be me, but i am wondering if anybody else has had this happen with any exhaust and maybe will be able to offer some advice? Not sure if this would have any effect, but my timing is set to ~17btdc. I also have a standard cat installed.

Thank you, Corey.

[Steampunk]

...but my timing is set to ~17btdc..

Can't really answer your exhaust question, but why are you running this timing?

[coreys]

To be honest, I have no idea. i guess i saw some things around saying people have run 18deg fine.
i have dropped it back to 14deg today though, and it feels a bit better.

[Steampunk]

14deg BTDC is the best compromise between better low-mid range torque without losing much top end.
Do some more research on the power/torque graphs different timing make, you will see that anything more than 15deg BTDC you start losing considerable top-end power. It's not the case of more is better.

This will explain part of your problem.

Another reason why you might think you are losing power is that people assume they will get a huge improvement with a freer-flowing exhaust, so when they install one and they don't feel a big difference then they instantly think they lost power.

You might notice the engine revs easier, but a 5% or even a 10% increase in engine power is pretty hard to discern with the "butt dyno"

[emex]

The factory unit relied on a bit more back pressure...The RS R seems to loose some of that, also yes the timing back to 14 should bring some seat of the pants results.

[coreys]

Thanks for the help, now i feel rather daft. hopefully some ignorant others can also learn from my minor mistake.

Thanks, Corey.

[NitroDann]

The factory unit relied on a bit more back pressure...The RS R seems to loose some of that, also yes the timing back to 14 should bring some seat of the pants results.

Wrong, backpressure is bad.

The problem is that the rsr is far too big for an otherwise stock car so there is no flow velocity, and the biggest restriction in the stock system is the headers and cat. Not the midpipe and tailpipe.

Dann

[A.Chen89]

^. Shortest and simplest answer if you don't want to do hardcore computational fluid dynamics.

[NitroDann]

Nothing complicated. Backpressure is bad, so is low exhaust velocity. Smaller the pipe the faster the gaaes must travel through it. Simple enough.

Dann

[ralt]

Hi.
I was talking to a fellow recently who has a lot of experience with exhaust systems. He was talking about velocity and the density of exhaust gases. According to him the difference in temperature at the port and downstream is significant and as the exhaust cools it becomes denser and slows down. He has been experimenting with a reduction in pipe size down towards the outlet. I mentioned to him i had a 2.25 exhaust pipe and he suggested i try a 2.00 inch from the resonator outlet to the muffler as he feels an increase in mid range torque would result and the smaller pipe will balance up the flow speed. He also thought 2.25 is to large for a 1.6 na motor and 2.00 inch is the size for standard cams and street driving. Interesting conversation.

[rossint]

Hi.
I was talking to a fellow recently who has a lot of experience with exhaust systems. He was talking about velocity and the density of exhaust gases. According to him the difference in temperature at the port and downstream is significant and as the exhaust cools it becomes denser and slows down. He has been experimenting with a reduction in pipe size down towards the outlet. I mentioned to him i had a 2.25 exhaust pipe and he suggested i try a 2.00 inch from the resonator outlet to the muffler as he feels an increase in mid range torque would result and the smaller pipe will balance up the flow speed. He also thought 2.25 is to large for a 1.6 na motor and 2.00 inch is the size for standard cams and street driving. Interesting conversation.

I went to a very reputable exhaust shop who work on a lot of fast street and race cars to get my exhaust done when my extractors rusted out. He recommended 2 inch, I was sceptical but went with what he said. As soon as I picked up the car I felt the power was down, got it dyno'd and it was confirmed that power was down about 8% from the old 2.25 system. The shop re-did the system with a 2.25 system and the power was back again.

[NitroDann]

What mufflers were on it? And what mods? And 8% peak or under the curve?

Dann

[rossint]

Cowl ducted intake, extractors and aftermarket cams. The 2inch system had a hotdog as the muffler. The 2.25 system has a luckey muffler, nothing between the cat and the muffler on both systems. 8% at peak.

[NitroDann]

Sounds about right to me. Exhaust guy underestimated the whp of your car id say.

Dann

[rossint]

I gave him all the info but I don't think he'd had any experience with MX5's and was shocked when what he'd done didn't work. We talked a bit before hand about options and what I thought would work (2.25inch) but he was adamant that anything bigger than 2inch on a 1.6 would be too big. He rectified the problem at no extra cost, you can't ask for more than that.