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2nd burned out resonator

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Old 07-19-2004 | 10:33 PM
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2nd burned out resonator

I've just gone through my second resonator. Good thing
this isn't really costing me anything. The Jun-BL hi-flow
resonator just isn't built tough enough to withstand the
massive amounts of heat the rotary pumps down the
exhaust pipes.

I'm getting a replacement resonator on saturday that
is tougher.

So anyway, if you do decide to get a resonator for a custom
exhaust , make sure it is racing toughness.
Old 07-19-2004 | 11:22 PM
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Did you do a mid-pipe as well?? I thought you just did the rear muffler assy?

Cheers,
Hymee.
Old 07-19-2004 | 11:31 PM
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It depends on what you mean by mid pipe. The setup goes :
Cat -> small 3.5" dia pipe -> high flow resonator -> another 3.5" dia pipe splitting into -> 2 x JunBL racing spiral mufflers -> 3.5" tapered tips.

The entire custom job is about 1.5m long from end of tips to under the car if that helps (as the bird flies).
Old 07-19-2004 | 11:41 PM
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OK. You cut the "mid pipe" after the cat, and did a true "cat-back".

3.5" pipe is interesting. Since it is all 2.5" before the cat anyway.

Cheers,
Hymee.
Old 07-19-2004 | 11:53 PM
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the pipes might actually be 3", but they are definitely bigger than 2.5".

All I know is that without the resonator it way waaaay too loud, you know how it goes -> setting off every car alarm in the carpark and being able to hear the thing a couple of kilometres away when revving high.

now, because I have cooked the resonator, the car farts out the side at idle. People still think it sounds cool, but they don't have to listen to it constantly.
Old 07-20-2004 | 02:07 AM
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post some pics of the set-up I'm interested in see'n it.
try ausrotary.com they will be able to sugest something that can handle the heat.
Old 07-20-2004 | 02:48 AM
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I can post some pics of the resonator itself, sorry for the strange angle, but I am just shoving the camera under the car and taking happy snaps. You can also see my lovely driveway and side fence.
Attached Thumbnails 2nd burned out resonator-res1.jpg   2nd burned out resonator-res2.jpg   2nd burned out resonator-res3.jpg   2nd burned out resonator-weld2.jpg  
Old 07-20-2004 | 06:05 AM
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I like the look of the two mufflers. is it the resinator or their welding thats blowing through?
Old 07-20-2004 | 05:34 PM
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Two of the guys from Exhaust Technologies, where I got the initial work done, could tell by listening it was the resonator that had gone. But, looking at those photos more closeley, it does appear that the weld at the front of the resonator might also / be coming apart a little bit.

I suppose I will see on Saturday when the car gets up on the car-lifting thing.

Until then, I can out riceboy any other car on the road in terms of noise when I decide to rev until the beep.
Old 07-21-2004 | 11:32 PM
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I did check out ausrotary, and a recommendation was made for the "rotaflo" glass pack resonators. Specially designed and built (here in SA) for rotaries. $125 AUD.

http://www.rotaflo.com.au

So, I have spoken to Mark at Exhaust Technologies , and he already had the same idea. He initially thought the JunBL could handle the heat (since it is ok for GTRs and Supras).
Old 07-23-2004 | 09:34 PM
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It is fixed now. Sounds sweet again. The resonator wasn't proper cooked, the back of it had cracked, but the resonator itself was ok. Notice the new weld at the rear of the resonator? They have done that to fix the crack and add extra strength to the entire unit.

I finally also took the opportunity to photograph the system whilst it was up high.
Attached Thumbnails 2nd burned out resonator-x1.jpg   2nd burned out resonator-x2.jpg   2nd burned out resonator-x3.jpg  
Old 07-24-2004 | 12:32 AM
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Just an aside, but when I had my Hymee cat back fitted, the fitter -- a rotar fan -- said it was probably wise I had chosen the aluminised steel over stainless steel as, in his experience, stainless steel did not handle the heat generated by rotaries. Dunno if this means anything to your guy, dbb, and I'd also acknowledge the NA Renesis should be cooler than a turbo rotar, but may be a thought
Old 07-27-2004 | 01:42 AM
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Originally Posted by timbo
said it was probably wise I had chosen the aluminised steel over stainless steel as, in his experience, stainless steel did not handle the heat generated by rotaries.
Stainless will handle it much better. The issue is usually when someone doesn't properly weld stainless. It needs to be treated a little differently. Stainless will expand and contract with heat more than other steels and this can really stress the welds if not done properly. This is why many people have issues with stainless. They just don't weld it properly.
Old 07-27-2004 | 02:03 AM
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One thing I have noticed with the all stainless system on the XR8 is the incredible amount the damn thing "grows" when hot....tailpipes hang out the back at least an inch more when up to temp.....a higher coefficient of expansion.....?

Gomez.
Old 07-27-2004 | 04:35 AM
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Hehehe - as long as it doesn't push the engine forward into the radiator
Old 07-27-2004 | 04:39 AM
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Seriously now, here is some info on the coefficients of expansion (last bit)

http://www.azom.com/details.asp?ArticleID=1175

Thermal Expansion
A further property that can be relevant in high temperature applications is the thermal expansion of the particular material. The coefficient of thermal expansion is expressed in units of proportional change of length for each degree increase in temperature, usually x10-6/°C, μm/m/°C, or x10-6cm/cm/°C, all of which are identical units. The increase in length (or diameter, thickness, etc) can be readily calculated by multiplying the original dimension by the temperature change by the coefficient of thermal expansion. For example, if a three metre long Grade 304 bar (coefficient of expansion 17.2 μm/m/°C) is heated from 20°C to 200°C, the length increases by:

3.00 x 180 x 17.2 = 9288 μm = 9.3 mm

The coefficient of thermal expansion of the austenitic stainless steels is higher than for most other grades of steel, as shown in the following table.

Table 2. Coefficient of thermal expansion - average values over 1-100°C


Coefficient of Thermal Expansion
(x10-6/°C)

Carbon Steels
12

Austenitic Steels
17

Duplex Steels
14

Ferritic Steels
10

Martensitic Steels
10

* or micrometres/metre/°C


This expansion coefficient not only varies between steel grades, it also increases slightly with temperature. Grade 304 has a coefficient of 17.2 x 10-6/°C over the temperature range 0 to 100°C, but increases above this temperature

The effect of thermal expansion is most noticeable where components are restrained, as the expansion results in buckling and bending. A problem can also arise if two dissimilar metals are fabricated together and then heated; dissimilar coefficients will again result in buckling or bending. In general the quite high thermal expansion rates of the austenitic stainless steels mean that fabrications in these alloys may have more dimensional problems than similar fabrications in carbon or low alloy steels, in ferritic, martensitic or duplex stainless steels.

The non-austenitic stainless steels also have somewhat higher thermal conductivities than the austenitic grades, which may be an advantage in certain applications.

Localised stresses from expansion during heating and cooling can contribute to stress corrosion cracking in an environment which would not normally attack the metal. These applications require design to minimise the adverse effects of temperature differentials such as the use of expansion joints to permit movement without distortion and the avoidance of notches and abrupt changes of section.



Source: Atlas Steels Australia



For more information on this source please visit Atlas Steels Australia
Old 07-27-2004 | 06:32 AM
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Well there you go.......Austenitic, a new word into the Gomez lexicon....! Ta!

I can see the 1000 deg Celsius EGT of the Renesis would cause a fair amount of thermal growth over the full length of a stainless system with a coeff of 17......

I imagine it would be impossible to have the rear muffler assy rust out on a rotary when they generate this amount of heat. The old Magna's would fair dinkum rust out a rear muffler every 12/18 months due to retained acidic moisture generated on short trips....

Gomez.
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