RPI GT exhaust GB thread.

[Beedub]

Originally Posted by trsbmw

Sorry, but that does not explain anything. Can you explain what "labouring the engine" means? I have never heard of that before. (Again, excuse me if I am being ignorant)

If it causes undue strees, wouldnt it be multiplied when it actually produces peak torque? (which I believe is at about 4500 rpm for the S54) Applied torque is applied torque, and I would imagine that the entire car is engineered to reliably tolerate the range of forces that the engine could produce throughout the entire RPM range...

their you go rusty cat explained it in the detail you require. google is your friend

[RPIpower]

Originally Posted by Beedub

their you go rusty cat explained it in the detail you require. google is your friend

We can think of it this way. Imagine being on a 10spd bike or 18spd, whatever. Now, your RPMs are how fast you are pedaling. Start off in a low gear and you can bring your RPMs up relatively easy. If you are in a higher gear and you try to take off, you are putting too much load on yourself and you will tire out, not to mention your acceleration would suffer. The engine works the same way. Other than 1st gear, there is no reason to be in such a low rpm range. If you are cruising and are at that rpm range, you are in too high of a gear........AND if you hear drone, most likely its because you are giving it gas and putting load on the engine at THAT rpm range. Drop down a gear or two and let the engine work a little easier. It will thank you

[Rustycat]

I'm happy to tell you that I had good success with the rigid insullation I fitted into the stepped own section of the trunk. I used Johns Manville rigid insullation 3 pound spun glass, number 814. It is 2" thick and comes in 2'x4' panels. Not easy to find. I made a template out of cardboard and cut the 814 on the table and band saws. It really was effective and removed a majority of the annoying frequencies---not all, but a bunch of them. The 2" thickness actually did a nice job of leveling out the floor in the trunk of the M Coupe. I'm sure more sound deadening will go further and I suspect placing more 814 along the back bulkhead behind the seats would really do the trick, but, for now, I'm going to take it for another test drive. Damn itchy stuff to work with when using saws.
Lew

[Rustycat]

Just came back from my short road test. The Johns Manville 814 continued to make me very very happy. I placed another piece on the floor next to the battery hump. The sound in the cockpit was very muted. To illustrate how muted the cockpit had become with the application of the 814, I would say that I could hear the fan at less than half speed settings consistently throughout the drive. In your face nastiness only reared its ugly head a couple of times and then only very briefly. I'd say the JM 814 specifically targeted the frequencies that I found annoying.
I couldn't be happier.
As a second step in this application I wrapped in the insulation in heavy mill plastic bags with strapping tape. This keeps the insulation from getting beatup and migrating around the trunk and cockpit. I'll probably overlay it with some carpeting to make things look a bit more finished. It works great, and I sort of think that at no load and cruising down flat highways the interior might be quietier than with the stock exhaust. This might be a slight exageration, but, if it is, it is only a bit so....
Regards,
Lew
Oh, the Johns Manville 814 was a substitute for Owens Corning 703, which at the time I was in the market to buy, was impossible to find. Here's a link to OC 703. I don't endorse it, as I've never dealt with them, but, if you come up stumped for a source for JM 814, it is a place to go for the OC 703:
http://sensiblesoundsolutions.com/pr...products_id=29

[Rustycat]

One final comment re RPI and Johns Manville insulation: A perfect synergy. The sound of the RPI exhaust is totally exotic to the max. Ferrari, eat your heart out. I'll never forget a comment by Sir Stirling Moss re the BMW straight six. He commented that it was hard to tell difference between a straight six and a V12 as they were going down the track. RPI's solution is totally sexy, totally, "OhMyGod, that is soooo good," Plus coupled with sound dampening via Johns Manville or Owens Corning and the SEX factor between Car, Driver and the incidental environment makes driving the M coupe a religous experience. I've commented to friends that driving the M coupe is more like dancing than driving. Well, driving the M coupe with the RPI and Johns Manville is more like great sloppy-wet pass out Sex.

[Nate2046]

nvm

[rcodea]

ok, so with all this talk of drone in the 1700-2400 range, and the insolation Rusty added, i still have just one question: are we saying this is mostly a COUPE issue, or do the roadsters have the same interior drone/levels?

~Ryan

[Rustycat]

Ryan, I've not experienced a roadster, so I can't answer your question specifically with an answer based on actual comparisons. But it certainly makes sense that the Coupe would amplify sounds coming through the rear floor, which has no sound deadening. The shape of the coupe is actually a very nice horn curve. Think of a trumpet where a small sound is created by the player's lips against the mouthpiece and a Huge note is
created through the mechanism of horn loading. This natural horn amplification combined with the hard surfaces that make up the roof of the M coupe are in effect horn loading any noise coming from the exhaust pipes.
Regards,
Lew

[rcodea]

Thats why I ask, with the lack of the harmonic amplification and 'horn' shape of the rear in a coupe, i wonder if the same issues arrise in the roadster, both with the top up and down.

Hopefully someone will chime in, but i will say, i dont hear it in the videos posted thus far.

[crfine88]

Originally Posted by rcodea

ok, so with all this talk of drone in the 1700-2400 range, and the insolation Rusty added, i still have just one question: are we saying this is mostly a COUPE issue, or do the roadsters have the same interior drone/levels?

~Ryan

I drive a coupe and have put 2000mi on my rpi exhaust now. The Low RPM drone everyone is talking about was abrupt at first. This drone is now almost none existent. The Exhaust tone has deepened a bit and I experience no rasp at all. The sound is very exotic. IMHO RPI got it right with this exhaust. I was a skeptic at first, but this has been one of favorite mods so far.

[Beedub]

Originally Posted by crfine88

I drive a coupe and have put 2000mi on my rpi exhaust now. The Low RPM drone everyone is talking about was abrupt at first. This drone is now almost none existent. The Exhaust tone has deepened a bit and I experience no rasp at all. The sound is very exotic. IMHO RPI got it right with this exhaust. I was a skeptic at first, but this has been one of favorite mods so far.

thats the same experience as me to be honest!! very happy with mine!!

[Chuck I]

Originally Posted by rcodea

Thats why I ask, with the lack of the harmonic amplification and 'horn' shape of the rear in a coupe, i wonder if the same issues arrise in the roadster, both with the top up and down.

Hopefully someone will chime in, but i will say, i dont hear it in the videos posted thus far.

I have a Roadster and to be honest, it's not bad.... I can't use my bluetooth with the top down... but I couldn't use it with the top down before... It's not an issue with drone, it's the damn wind noise... With the top up, there's no issue at all... With the top down the exhaust sounds so good. I keep stepping on the gas just to listen to myself... I'm starting to think I'm weird!

It may be the the way the trunk is made for the roadster that it isolates the noise. Looking at it though, it looks to me that if you wanted to you could insulate the area above the heat shields. They have a natural shape to deflect the noise... I haven't really looked at it but mine is up on the lift and I'll explore it further... Chuck I

[Rustycat]

Chuck, there might, and probably are, some effective sound dampening sheet material that might hold up to the heat without danger of degradation, but off hand, I don't know what they are. Thicker is always more effective than thinner in sound dampening. The JM and OC 2" panels are great and give a lot more sound insulation than anything else I can think of that is 2" or less in thickness. Dynamat might have some firewall insulation that might hold up to the heat being thrown off by the RPI resonators, but it won't be as effective. If the mufflers break in and tone down as several posters have indicated, then, I'm looking forward to the combined decrease in
cockpit noise that I'll be experiencing.
Lew

[trsbmw]

Originally Posted by RPIpower

We can think of it this way. Imagine being on a 10spd bike or 18spd, whatever. Now, your RPMs are how fast you are pedaling. Start off in a low gear and you can bring your RPMs up relatively easy. If you are in a higher gear and you try to take off, you are putting too much load on yourself and you will tire out, not to mention your acceleration would suffer. The engine works the same way. Other than 1st gear, there is no reason to be in such a low rpm range. If you are cruising and are at that rpm range, you are in too high of a gear........AND if you hear drone, most likely its because you are giving it gas and putting load on the engine at THAT rpm range. Drop down a gear or two and let the engine work a little easier. It will thank you

Thanks, I understand the logic behind that. I was just a bit more interested in technical specifics behind why the engine is ill suited under those conditions. The only thing that really makes sense to me is that the oil pressure would be less than optimal at lower RPM's and therefore offer less wear resistance given the extra load.

[Palantirion]

Originally Posted by trsbmw

Thanks, I understand the logic behind that. I was just a bit more interested in technical specifics behind why the engine is ill suited under those conditions. The only thing that really makes sense to me is that the oil pressure would be less than optimal at lower RPM's and therefore offer less wear resistance given the extra load.

Load = resistance to the engine's ability to rotate the crank. The more resistance, the more mechanical strain on the internals of the engine. In Eloy's example, it would be knee strain that over time develops into an injury.

[Rustycat]

RPI,
I've been experiencing your exhaust for a week now and wanted to share my impressions. I'm driving a Coupe,and as you have noted, I've surmised that the build of the Coupe-- lack of insulation and the curvature of the metal roof-- all work in concert to amplify the cockpit noise coming from the exhaust. My solution was to insulate the interior with sound absorbing spun glass insulation. Towards that end I've now insulated the entire floor of the trunk, sans battery hump and the back wall behind the seats. By far, the most effective area was the recessed floor directly above the exhaust. After that it was sort of diminishing returns.
So, at this point I notice that the "loudness" factor in cockpit noise is very complicated.
It is totally unable to be described by RPM alone, but is more dependent on aggressive acceleration and load. I do get the dash air vents rattling at some points, which seems
uncorrectable with insulation (I can moderate my right foot, but where's the fun in that?). I have noticed that the smaller of the tail pipes look to be unused, judging by the difference between the color between the smaller and larger pipes, and wonder if they work as a back pressure siphon or are simply 99% cosmetic. I love the sound of the exhaust, BTW, as does everyone that hears it. I used to get comments like "nice car" from passerbys, now it is more apt to be "nice sounding".
Regards,
Lew

[Beedub]

heres mine from over the pond at my local sprint track!
http://s75.photobucket.com/albums/i2...t=MOV00321.flv
http://s75.photobucket.com/albums/i2...t=MOV00338.flv
http://s75.photobucket.com/albums/i2...t=MOV00329.flv

[laidback]

by far the best description of the RPi exhaust

Originally Posted by Beedub

heres mine from over the pond at my local sprint track!
http://s75.photobucket.com/albums/i2...t=MOV00321.flv
http://s75.photobucket.com/albums/i2...t=MOV00338.flv
http://s75.photobucket.com/albums/i2...t=MOV00329.flv

[Beedub]

yup the change up a 7900 rpm with a lovely pop describes it perfectly!!!
i absolutly love this exhaust, the weight saving, the power increase the sound, the looks, is just what i wanted, my sprint track the people were saying what exhaust is that it sounds fantastic!!! very very happy with my rpi!!!

[Rustycat]

Very nice, and by far the best clips yet at capturing the sound quality that is produced by the RPIs. I thought it was very accurrate. Just want to mention, as a follow up to my previous comments re sound proofing the Coupe with the RPIs. Since my initial efforts, I've tried adding poly pillow fill and even a BMW car cover. These helped, but took up all of the space in the trunk. I had a couple of rolls of 3/8's" cork lying around and I cut them to shape and taped them onto the Johns Manville rigid spun glass I had
already placed in the trunk. Fantastic results without losing all of the trunk space, as I've added only 2.5" inches to the back of seats and the same to the floor in the trunk.
I'm busy for the next week, at some point, I'll post some detailed pictures. I highly recommend this treatment to anyone with an aftermarket "track" exhaust.
Lew

[RPIpower]

Originally Posted by Rustycat

RPI,
I've been experiencing your exhaust for a week now and wanted to share my impressions. I'm driving a Coupe,and as you have noted, I've surmised that the build of the Coupe-- lack of insulation and the curvature of the metal roof-- all work in concert to amplify the cockpit noise coming from the exhaust. My solution was to insulate the interior with sound absorbing spun glass insulation. Towards that end I've now insulated the entire floor of the trunk, sans battery hump and the back wall behind the seats. By far, the most effective area was the recessed floor directly above the exhaust. After that it was sort of diminishing returns.
So, at this point I notice that the "loudness" factor in cockpit noise is very complicated.
It is totally unable to be described by RPM alone, but is more dependent on aggressive acceleration and load. I do get the dash air vents rattling at some points, which seems
uncorrectable with insulation (I can moderate my right foot, but where's the fun in that?). I have noticed that the smaller of the tail pipes look to be unused, judging by the difference between the color between the smaller and larger pipes, and wonder if they work as a back pressure siphon or are simply 99% cosmetic. I love the sound of the exhaust, BTW, as does everyone that hears it. I used to get comments like "nice car" from passerbys, now it is more apt to be "nice sounding".
Regards,
Lew

The secondary tip is still used but the larger inner pipe is definately the one that gets the most flow through. We didnt change it entirely because this exhaust shares the same production line as our Porsche 996 exhaust. Keeping the tips the same enabled us to keep the price of the production down. Plus, I really like how it looks with the rear bumper.

The thing with vibration is that if you put the engine under heavy load at a low rpm, even with the stock exhaust, youll hear things in the cabin vibrating. Its just amplified now with the new exhaust.

Our exhaust is not for everyone. Those looking for a quiet sound with no drone at all would have a hard time with our system.

[jonanator]

Originally Posted by Rustycat

Very nice, and by far the best clips yet at capturing the sound quality that is produced by the RPIs. I thought it was very accurrate. Just want to mention, as a follow up to my previous comments re sound proofing the Coupe with the RPIs. Since my initial efforts, I've tried adding poly pillow fill and even a BMW car cover. These helped, but took up all of the space in the trunk. I had a couple of rolls of 3/8's" cork lying around and I cut them to shape and taped them onto the Johns Manville rigid spun glass I had
already placed in the trunk. Fantastic results without losing all of the trunk space, as I've added only 2.5" inches to the back of seats and the same to the floor in the trunk.
I'm busy for the next week, at some point, I'll post some detailed pictures. I highly recommend this treatment to anyone with an aftermarket "track" exhaust.
Lew

Please post those pics and instructions when you can! I am very interested in doing this to my car!