New Exhaust, Less Backpressure, More Fuel!
Thread Starter
Joined: Oct 2006
Posts: 6,603
Likes: 15
From: Toronto, Canada
New Exhaust, Less Backpressure, More Fuel!
So I finally got a nice new straight-thru titanium exhaust to replace my Racing Beat dual-tip. I also had setup an exhaust backpressure sensor last week for comparison testing. So I went out tonight to do some testing.
Last week when I went out to test the backpressure sensor, I was putting out about 10 PSi of backpressure with the Racing Beat dual-tip catback still on at full bost. Now with my new exhaust, I'm only putting out 3-4 PSi of backpressure at full boost. That is a pretty decent drop in backpressure but with it came some required changes in the fuel.
My boost controller settings were unchanged and the boost curve was identical as with the old exhaust. However, what happened was it would go lean at high RPM. So I added more fuel and retuned the up top area to do what I was doing before. By the end of it I realized I had added 5% of fuel at exactly 7200 RPM and 1-3% in the cells surrounding that.
This new exhaust has really opened up my top-end and lowered my backpressure noticeably. Here is a comparison of my fuel curves....
OLD Racing Beat dual-tip exhaust
New Amuse Titanium exhaust
Full boost is roughly on the blue line (4th one down). As you can see the change is quite noticeable. I was pulling the car to 8300 RPM because it felt so much better up top now.
However, even with this change, I'm still not satisfied. I still ahve 3-4 PSi of backpressure and the Amuse exhaust had something unexpected. Which is it goes from 80mm piping into 70mm inside the canister (doh!). So I continue my search of a new exhaust that is true 80mm all the way through. Here is a picture of it, its literally like its made of paper in regards to weight
...
thewird
Last week when I went out to test the backpressure sensor, I was putting out about 10 PSi of backpressure with the Racing Beat dual-tip catback still on at full bost. Now with my new exhaust, I'm only putting out 3-4 PSi of backpressure at full boost. That is a pretty decent drop in backpressure but with it came some required changes in the fuel.
My boost controller settings were unchanged and the boost curve was identical as with the old exhaust. However, what happened was it would go lean at high RPM. So I added more fuel and retuned the up top area to do what I was doing before. By the end of it I realized I had added 5% of fuel at exactly 7200 RPM and 1-3% in the cells surrounding that.
This new exhaust has really opened up my top-end and lowered my backpressure noticeably. Here is a comparison of my fuel curves....
OLD Racing Beat dual-tip exhaust
New Amuse Titanium exhaust
Full boost is roughly on the blue line (4th one down). As you can see the change is quite noticeable. I was pulling the car to 8300 RPM because it felt so much better up top now.
However, even with this change, I'm still not satisfied. I still ahve 3-4 PSi of backpressure and the Amuse exhaust had something unexpected. Which is it goes from 80mm piping into 70mm inside the canister (doh!). So I continue my search of a new exhaust that is true 80mm all the way through. Here is a picture of it, its literally like its made of paper in regards to weight
...thewird
Thread Starter
Joined: Oct 2006
Posts: 6,603
Likes: 15
From: Toronto, Canada
The exhaust is already called for before I even decided what exhaust I was gonna buy hehe.
thewird
This is very interesting.
Where is your BP sensor installed?
Was the RB a chambered muffler? 10 psi is way too much back pressure for any straight through muffler or resonator.....
Where is your BP sensor installed?
Was the RB a chambered muffler? 10 psi is way too much back pressure for any straight through muffler or resonator.....
A couple of observations from my considerable experience with flow benches: If the 70mm section is perforated internally like a resonator, then it probably isn't much of a restriction, if at all, since perf sections usually have less internal friction to flow than solid walled pipe. In fact, I use a resonator with a 64mm internal section (24" long) that is better flowing than an equivalent length of 3" pipe. It gives better sound control with no flow penalty.
I will assert that the bends, or radii, if you will, in your exhaust is your biggest restriction followed by the friction of the longer 80mm sections.
I will assert that the bends, or radii, if you will, in your exhaust is your biggest restriction followed by the friction of the longer 80mm sections.
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Thread Starter
Joined: Oct 2006
Posts: 6,603
Likes: 15
From: Toronto, Canada
The Racing Beat dual-tip exhaust is indeed a chambered catback.
thewird
A couple of observations from my considerable experience with flow benches: If the 70mm section is perforated internally like a resonator, then it probably isn't much of a restriction, if at all, since perf sections usually have less internal friction to flow than solid walled pipe. In fact, I use a resonator with a 64mm internal section (24" long) that is better flowing than an equivalent length of 3" pipe. It gives better sound control with no flow penalty.
I will assert that the bends, or radii, if you will, in your exhaust is your biggest restriction followed by the friction of the longer 80mm sections.
I will assert that the bends, or radii, if you will, in your exhaust is your biggest restriction followed by the friction of the longer 80mm sections.
I know it seems counter-intuitive; however, the best and simplest analogy for this effect is the same as that of dimpled golf ball. There is simply less frictional loss vs a solid surface.
Joined: Feb 2006
Posts: 3,162
Likes: 1
From: London, Ontario, Canada
If it was just a straight pipe then it would no longer be a muffler. It would be a pipe with the body of a muffler welded on, and it would be loud as hell.
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