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Would hang too low and look like $hit. It has to be 6" wide and about 3.5" high to fit right and look right. Furthermore, big ducts like that can resonate so you don't want to have sharp corners, sharp corners mean flat surfaces that resonate like drums and break over time. Even a 6" x 3.5" oval pipe without any sharp corners will need support rods every 4 inches or so to not resonate like a drum and eventually crack from the welds.
I think this flows quite naturally with the shallow cone. The expansion should have no turbulence. Also, feeding the wastegate circuit (1/3 to 1/2 of mass flow) to the inside turn of the pipe will minimize turbulrnce and prevent the back flowing vortex.
Hopefully with this change you can drive the car. And show pictures from that.
For me, it's more of a science experiment and less of a car. However, I'll be sure to take some pictures of me driving it. I'll get a hair cut for you, too. Any preference on what I should be wearing? ;-)
Originally Posted by BC
Is he he going to be offering these changes to the kit?
The car was basically ready earlier this spring with the 3" dual exhaust. The problem was that although the exhaust was about exactly right sized for the little over 700 rwhp that the car was making, it would've been too small for higher power runs.
I don't know what John will do with his kit, but if I were him, I'd go with the dual 3" exhaust for cars that are built for that about 700-800 rwhp target. Then go with the dual 3.5" exhaust for cars that aim to make more power. The dual 3" is lighter, easier to fit, cheaper to fabricate, ultimately easier to muffler, and has much more muffler options than dual 3.5". I'd only go to dual 3.5" if it's absolutely necessary.
Then there's the question about the number of cross-overs and their location. A true dual without any cross-overs will sound like a muscle car V8. About half the people love that sound, and about half the people don't. It's a personal preference. A long single merge in the middle and a joint tail-pipe muffler will make the sound much less divisive in terms of opinions. It'll be more neutral, with more of the half firing engine order frequencies cancelling. Over the years, so much work has been done on 90-degree cross-plane exhausts that I'd classify this as a fact.
One thing to note about the 928 exhaust geometry is that the distance from the exhaust manifold collector to the center resonator is such that at low loads and low rpms, that pipe length resonates at some frequency I'd guess is at the 140-150 Hz range. Breaking that pipe section up with a large merge pipe or other changes in cross-sectional area should by my logic (not experience) reduce the drone. This is not a fact, it's speculation on my part.
Hopefully with this change you can drive the car. And show pictures from that.
Is he he going to be offering these changes to the kit?
With dual 3.5" exhaust I am not sure he has the nerve to drive the car uphill to his place. Maybe he will tow the car to keep the neighbours happy.
Åke
With dual 3.5" exhaust I am not sure he has the nerve to drive the car uphill to his place. Maybe he will tow the car to keep the neighbours happy.
Åke
This is a car thread but seriously- I have always questioned this noise thing about neighborhoods, etc. when people have dogs and crying babies I can hear at 2am all the time and I'm supposed to be worried about a loud car sound that last 20 seconds as I leave or return? And? What can they do?
With dual 3.5" exhaust I am not sure he has the nerve to drive the car uphill to his place. Maybe he will tow the car to keep the neighbours happy.
Åke
We'll try it with this exhaust and three mufflers first.
If it's too loud, then I'll try making some adjustments. One idea is to combine Slate Blue's and Speedtoys's exhausts:
That is, place an exhaust valve in one of the 3.5" pipe legs. Furthermore, place it in a spot that creates two quarter-wave resonators with the valve closed that are tuned to take out some of the problem low frequencies.
Originally Posted by BC
This is a car thread but seriously- I have always questioned this noise thing about neighborhoods, etc. when people have dogs and crying babies I can hear at 2am all the time and I'm supposed to be worried about a loud car sound that last 20 seconds as I leave or return? And? What can they do?
This is a car thread but seriously- I have always questioned this noise thing about neighborhoods, etc. when people have dogs and crying babies I can hear at 2am all the time and I'm supposed to be worried about a loud car sound that last 20 seconds as I leave or return? And? What can they do?
That was a joke, Tuomo and I have discussed how to silence a dual 3.5" exhaust the best way using both built in Helmholtz resonators and absorption mufflers. What can the neighbours do if they find your car too loud - well they can stop saluting you.
Åke
For me, it's more of a science experiment and less of a car. However, I'll be sure to take some pictures of me driving it. I'll get a hair cut for you, too. Any preference on what I should be wearing? ;-)
Maybe a frilly little see-thru number........ Oh wait a minute, wrong forum.
06-18-2017, 11:46 AM
