| Author |  Topic  |
Morticus
V4 Beginner
United Kingdom
59 Posts |  Posted - 25 Jul 2010 : 09:50:53  
| Has anyone got any suggestions for reducing the Jetex reverberation at c. 60 mph? I drove 200 miles yesterday, and the only speeds which allowed conversation without raised voices were 40 mph and below. Has anyone tried inserting a flexible section?
Kenny |
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Morticus
V4 Beginner
United Kingdom
59 Posts | Posted - 25 Jul 2010 : 09:52:06
| | Perhaps this should be in the "Idle chat" section! |  |
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Woody
V4 Guru
United Kingdom
1209 Posts | Posted - 25 Jul 2010 : 10:20:38 
| I think it is in the right place.
I don't have any experience of the Jetex system. Is it the resonance sound of the exhaust you are experiencing or do you think you might be getting some vibration back through the body? | |
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Jon
V4 Beginner
France
60 Posts | Posted - 25 Jul 2010 : 11:07:15 
| I used to have a Jetex exhaust which had the ennoying resonance at 60-65mph. I since had a stainless steel exhaust system built for my car to fit my twin port heads, and thought that the resonance would disappear BUT oh no it didn't.
So I've concluded that it's the body that's resonating by a LOUD sound frequency generated by the exhaust system. The standard system doesn't do this if I remember (it's been 20 years since I've had a std system!) as it's not loud enough.
At 70-75mph all goes quiet - in a manner of speaking!!
Jon
http://www.dutton.co.uk/saab/ | |
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IAN
Starting Member
Spain
36 Posts | Posted - 25 Jul 2010 : 14:05:04
| | Just a thought. I had my exhaust replaced and used mini exhaust bobbins to fit it. They are much more rigid than the genuine SAAB item and I then suffered a resonance that wasn't there before Ian | |
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Morticus
V4 Beginner
United Kingdom
59 Posts | |
pchristy
V4 Mad
United Kingdom
511 Posts | Posted - 25 Jul 2010 : 16:48:02
| My Jetex is noticeably louder in the 60-65 region, but then quitens down with increasing speed. Many years ago, I had a SAH system that didn't seem to suffer from this, and was remarkably quiet inside the car.
Having said that, the noise of my current system is not excessive - at least, not compared to the Highgate it replaced....!!!
--
Pete
"Duct tape is like the Force: It has a light side and a dark side, and it binds the Universe together!" | |
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Derek
V4 Mad
United Kingdom
815 Posts | Posted - 25 Jul 2010 : 23:45:26
| My standard system does give some resonance at about 60-65 so I guess it's some sort of body boom. I bought a new front box and long pipe from Brian at Saab Sanctuary, both genuine Saab. The long pipe had the mounting cross bar in the wrong place to match the bobbins. Brian said he had been telling Saab for ages that they were wrong. It was welded to the pipe so I made up 2 short extenders to bring them inline. This probably makes the mount a little more flexible but it's still likely too stiff, along with the rear box mounts. Remounting it at both the bobbins and the rear with softer rubber loops might do the trick. Anyone want to disconnect the bobbins and have a whizz up the motorway to see if that helps? Maybe a thick bar/plate across the bobbins, inside the car. might stiffen the floor up. Yes I have thought about giving it a try....................
The site linked to for the flexi connection does have a range of alternate bobbins. Not too far away from me in Staplehurst. | |
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jdt
V4 Fanatic
United Kingdom
223 Posts | Posted - 26 Jul 2010 : 18:10:45
| | Make sure the exhaust system has no "tension" - slacken all the joints and allow to hang in place then tighten them bearing in mind the exhaust will expand when hot by a siginficant amount when hot. This should cure the annoying resonance but may take a few adjustments to get it right. | |
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v4admin
Forum Admin
United Kingdom
119 Posts | Posted - 26 Jul 2010 : 20:33:30
| | the early V4's had a clamp that went around the downpipes and connected to the top of the engine mounts, from what I have heard this helps stop the vibration resonance | |
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Derek
V4 Mad
United Kingdom
815 Posts | Posted - 26 Jul 2010 : 22:51:12
| | You say "early" but my '76 has them. I've also read that they are best removed but I haven't on the basis that there isn't much else holding the front box on. The 2 head clamps aren't exactly precision joints. | |
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Smokey six
V4 Beginner
United Kingdom
56 Posts | Posted - 27 Jul 2010 : 07:39:56
| My 73/74 Hasn't got clamps either.
Any chance of a picture to see what they are like. I don't like the idea of the front box just hanging on manifold clamps.
Len quote:
Originally posted by Derek
You say "early" but my '76 has them. I've also read that they are best removed but I haven't on the basis that there isn't much else holding the front box on. The 2 head clamps aren't exactly precision joints.
Broke it? Me? it came orf in me 'and
Len W | |
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Derek
V4 Mad
United Kingdom
815 Posts | Posted - 27 Jul 2010 : 11:15:42
| I'll see what I can do but it's just made from 1"(?) wide flat steel which wraps round the pipe and then is bent off at right angles, with a couple of holes to allow it to go under the nut on the engine mount and bracket. When I fitted mine it didn't clamp up very well and I stuck a couple of adapted bolts in the junctions to allow it to be tightened properly. Neat but a bit of a bodge. It was as if the clamps were made for a slightly bigger downpipe but I don't think they ever changed that.
Saab should have brought out a revised Sport/Monte Carlo version of the 96 in the early 70's. That would likely have had a much better exhaust which could have also been fitted to all models. The standard front box can only be described as "functional". | |
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Borstlap
V4 Fan
Norway
139 Posts | Posted - 27 Jul 2010 : 12:34:24
| quote:
Originally posted by Morticus
Has anyone got any suggestions for reducing the Jetex reverberation at c. 60 mph?
I clamped up the first part of the exhaust, which did give a noticeable improvement. This was about twenty years ago, when I didn't have internet or knowledge about flexible exhaust pipes. Today I would certainly go for a piece of flexihose. Underneath some pictures of the clamps I made.
It's not good to see, but the first bobbin surely did suffer from the movement; it is quite cracked up.
Alex | |
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Derek
V4 Mad
United Kingdom
815 Posts | Posted - 27 Jul 2010 : 17:05:58
| | That looks like Jetex?Simons. I'd guess that you're the one that posted that he'd added extra mounts just below the front bulkhead? Read that some time ago, somewhere. Do you get any resonance now? | |
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Borstlap
V4 Fan
Norway
139 Posts | Posted - 29 Jul 2010 : 08:08:47
| quote:
Originally posted by Derek
That looks like Jetex?Simons. I'd guess that you're the one that posted that he'd added extra mounts just below the front bulkhead? Read that some time ago, somewhere. Do you get any resonance now?
Derek,
Yes and yes. The resonance became markedly less, but if I remember correctly there was still a bit around 3500rpm. The car has been a restauration project (= not roadworthy) for more than 15 years so the memory has become a bit faded, but the clamping did help.
Alex | |
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| Topic | |
Jetex; "The Noise"
