| Motoring Discussion > Mimsing weather | Miscellaneous |
| Thread Author: Armel Coussine | Replies: 28 |
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New Fri 31 Jan 14 19:46
Mimsing weather - Armel Coussine
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Mimsing weather today. I went to Richmond/Ham and back in it and even I hardly exceeded the speed limit a dozen times. Big, very big, pools of standing water everywhere, rain between drizzle and tropical all day and all the roads awash. The jalopy is far cleaner than it was this morning although I guess the rear end might have a bit of fine filth on it. There are beavers more eager than I in Surrey but they weren't at their best today. Nor did that county's ridiculously low, widely ignored speed limits seem as unreasonable as usual. There seemed to be a lot of traffic. And as for the genuine, pitiful mimser in mimsing weather, the less said the better. Fortunately herself wasn't with me because the bawled c-word count per mile was a lot higher than usual. 35 in a 50 limit or NSL, I ask you FFS... On the way back there was a geezer tailgating me on the A29. I was doing a relaxed 45-65 depending on conditions, and there was less traffic although still plenty. But he kept coming up close behind. After he had missed half a dozen overtaking opportunities I irritably signalled left and drove closer to the verge than I wanted, but he still didn't pass and I started to think ill of him. Eventually I came up behind a real mimser going so slowly that I could tailgate him/her in perfect safety. Soon it did what I had done, irritably signalled left and pulled in and slowed a bit. I whipped past instantly. My tailgater followed, but after that stayed back 70 or 100 yards in more correct fashion. Heh heh... so he wasn't a total moron. All people need is to be set a good example. Terrible weather, bad visibility. I had to brake hard for an invisible fool of a young male pedestrian. Not even a small burp from the ABS with the new Avons on the front. It would have sounded all right with the old ones. Windscreen wipers can really get annoying. Mine work fine but they are noisy. When you are crawling you only need intermittent, but although the control has six or seven clicks on it there are only three intermittent speeds, one so rapid that it's hardly worth using and the others too slow for any speed in bucketing rain. I had to boot it in the gears a couple of times for one reason and another and rather annoyingly that has blown out a small bit of gunge from an exhaust joint and made the car noisier again (and doubtless not working properly owing to reduced back pressure). Gripe gripe kvetch kvetch... |
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New Fri 31 Jan 14 20:00
Mimsing weather - R.P.
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| Same here. Went out in my truck in the eye of the storm first thing, weather took a turn for the worse - when I was heading back to refuel and unload the wind was back, scared the living shampoo out of me to be honest. Mimsed back a scaredy cat. Trip home was different V40 festooned with passive/aggressive safety and four paws firmly planted on the road was a different bouilloire de poissons |
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New Fri 31 Jan 14 20:01
Mimsing weather - Dave_
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I'd like to take a passenger ride with you one day AC. On second thoughts... |
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New Sat 1 Feb 14 01:17
Mimsing weather - Armel Coussine
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>> On second thoughts... You wouldn't notice anything out of the ordinary Dave, boringly normal, not much aquaplaning, only a couple of involuntary wiggles. Just like all the others. |
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New Fri 31 Jan 14 20:07
Mimsing weather - bathtub tom
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>>blown out a small bit of gunge from an exhaust joint and made the car noisier again (and doubtless not working properly owing to reduced back pressure). Where has this myth of engines needing back pressure originated? The only useful purpose I know of is to improve fuel economy in a two-stroke. I recall an engine tuner stating "the best thing to do with the exhaust gas is get rid of it" (that was back in the days before turbos). |
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New Fri 31 Jan 14 20:31
Mimsing weather - Number_Cruncher
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>>Where has this myth of engines needing back pressure originated? No idea BT, of course, it's utter guff. In modern engines, the aim is to reduce back pressure to a minimum while complying with noise regs - it's effectively a trade off. When engine testing on rigs, one requirement is to use a valve in the test rig's exhaust system in order to match the installed system's back pressure in order that the test rig result doesn't artificially allow the engine to perform better owing to reduced back pressure. It also makes sure that EGR flow rates match those of the installed engine. I wonder if it (and many other motoring myths) began by malicious rumour spreading inbetween the pit crews of early motor racing events. I'm guilty of having believed too many motoring myths that when investigated more closely and peer reviewed evidence sought , simply dissolved away. |
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New Fri 31 Jan 14 20:59
Mimsing weather - Old Navy
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| I just knew that the screwdriver through the silencer tune ups of my youth increased performance as well as aural presence. :-) |
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New Fri 31 Jan 14 21:03
Mimsing weather - No FM2R
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| That's why I took the baffles out of my FS1E. Clearly made it a stage one tuned racing machine. |
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New Fri 31 Jan 14 21:51
Mimsing weather - Westpig
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>> That's why I took the baffles out of my FS1E. Mine came out involuntarily. My mate behind saw it briefly. Never did find it. |
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New Fri 31 Jan 14 21:57
Mimsing weather - Ted
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My Bond, with it's 250cc Villiers mill used to spew the contents of it's exhaust out regularly. When it got too noisy I used to stuff a load of steel wool in with a broom handle.......part of the toolkit ! HO |
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New Fri 31 Jan 14 23:47
Mimsing weather - bathtub tom
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>> My Bond, with it's 250cc Villiers mill used to spew the contents of it's exhaust >> out regularly. When it got too noisy I used to stuff a load of steel >> wool in with a broom handle.......part of the toolkit ! No! What you had to do was fill the silencer with a caustic soda solution to dissolve the stuff. I recall having a 2-T with a Burgess silencer you could dismantle. The centre tube was perforated and surrounded with a wire-wool jacket. Perhaps that was where you got the idea of stuffing it up the end? |
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New Fri 31 Jan 14 22:14
Mimsing weather - Kevin
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>That's why I took the baffles out of my FS1E. Still can't remember to put the cat out before you go to bed though? tinyurl.com/kpdjs8r |
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New Fri 31 Jan 14 22:22
Mimsing weather - Old Navy
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| That is a serious moggy, it would sort out the tough dogs in the area. |
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New Fri 31 Jan 14 22:34
Mimsing weather - Zero
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>> That is a serious moggy, it would sort out the tough dogs in the area. Yeah, lets see Pat rescue that one! |
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New Fri 31 Jan 14 23:44
Mimsing weather - Armel Coussine
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>> myth of engines needing back pressure originated? >> No idea BT, of course, it's utter guff. Well that's me told in no uncertain terms. I thought if the exhaust was wrong that Lambda sensor at the bottom of the downpipe wouldn't do its stuff for the engine tune 'reprogrammed several hundred times a second'... but on reflection I suppose that only happens if the leak is upstream of the sensor. Anyway the damn exhaust is blowing again and I don't like the noise. Of course for ultimate performance open exhausts were always best, although I believe having them the right length gave the best results (hence the incredible sort of sheepshank tangles seen sometimes in racing cars). But noisy cars are a bit tiring when you're my age especially if they lack the yee-hah! factor. |
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New Fri 31 Jan 14 23:53
Mimsing weather - bathtub tom
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>>Of course for ultimate performance open exhausts were always best, although I believe having them the right length gave the best results (hence the incredible sort of sheepshank tangles seen sometimes in racing cars) Now you're entering a whole new ball-park. Tuning an exhaust for maximum torque's a science I never fully understood. Something to do with pressure waves? I (briefly) looked into 2-T expansion chambers, tail-pipe diameters and exhaust gas flows, but it gave me a headache! |
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New Sat 1 Feb 14 01:37
Mimsing weather - Armel Coussine
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>> whole new ball-park. Motor park... goodness how nostalgic that term makes me feel. You have to have seen a Nigerian - or actually any other West or East or any other African - motor park in all its seething glory to know what it means. But I mustn't make you all envious. Last edited by: Armel Coussine on Sat 1 Feb 14 at 01:41
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New Sat 1 Feb 14 16:30
Mimsing weather - Cliff Pope
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>> >> >> Where has this myth of engines needing back pressure originated? Perhaps from confusion with the concept of evening out the inevital pressure pulses from the individual cylinders? Accepting that for other reasons an exhaust pipe is necessary for ordinary road use, then I understood part of the art of exhaust tuning was to try and make the pulses merge so as to minimise the combined pressure? That is said to assist the flow from an exhausting cylider by absorbing it in a pressure trough from another. Isn't there a critical point downstream of the engine where it is important to site, or perhaps avoid siting, the first silencer? From my observation of ordinary cars, a leaking exhaust pipe or one missing its back end detracts from rather than improves performance. Or is that an illusion? |
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New Sat 1 Feb 14 16:48
Mimsing weather - Armel Coussine
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>> Or is that an illusion? I don't think it is. Cars run better with the correct exhaust. Modifying exhausts was a popular and cheap thing to do, but it usually made more noise than speed. And despite having been trumped by N_C, I still have a suspicion that back pressure is taken into account in the basic tuning of cars, and if the back pressure is reduced other aspects of its tune may need to be adjusted accordingly. The point has been well made that tuning exhaust lengths (for example) can alter the balance between an engine's low-revs torque and flat-out 'power'. Now that it is droning a bit, my jalopy seems to be going less well. But perhaps that's because if it makes a noise I am unconsciously expecting it to be going faster than it is... be that as it may, I feel a grovel and knuckle-bruising and gungefest coming on. Damn. I hate that even in decent weather. PS Of course the universal, fragile, obstructive catalyser, placed warmly just behind the Lambda sensor and before the rest of the exhaust, is a new expense and performance hazard for us all... Last edited by: Armel Coussine on Sat 1 Feb 14 at 16:51
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New Sat 1 Feb 14 17:23
Mimsing weather - NortonES2
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I have a vague recollection that exhaust performance (or more likely, absence of deterioration) is linked to gas speed in the exhaust system. Entrained gases reduce exhaust port pressure, but introducing resonances (whether a hole in the pipework, or too short a pipe) can reduce output by creating standing waves which affect the flow. Good standing waves were harnessed by expansion chambers (two-stroke racing engines) but were rpm dependent, with a narrow power band. Boy racer plumbing (dustbin exhausts) are not necessarily beneficial to power.... I have now reached the limit of anything semi-sensible and it's time to make prawn curry! |
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New Sat 1 Feb 14 19:54
Mimsing weather - Number_Cruncher
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AC, forget back pressure - it's a "bad thing", which should be minimised for both efficiency and power. The standard description of the four stroke cycle gas movement is OK for explaining behaviour at cranking speed, but, once the engine is turning at any speed, the dynamics of the gas in the manifolds and the acoustic pressure waves dominate. During engine design, these effects are dealt with using a so-called one dimensional analysis, where the whole gas flow path from the start of the inlet system to the end of the exhaust pipe is modelled as a one dimensional system. For a readable introduction to this, the books by Gordon Blair are worth a look - some computer algorithms for simulation are also included. Using this modelling technique, the interplay between manifold lengths and valve timing can be tuned. Most aftermarket modifications don't look at the whole system in this way, and can, therefore, give indifferent results. |
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New Sun 2 Feb 14 00:31
Mimsing weather - Armel Coussine
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>> forget back pressure - it's a "bad thing" Yeah, OK, point taken... no doubt I am confusing back pressure with harmonics, standing waves and other musical considerations. But I do seem to remember that cars don't go better with their tailboxes missing. I'm worrying about my own jalopy. When I started it this morning I put my hand over the exhaust to no effect whatsoever. When the rich mixture backed off after half a minute the noise diminished slightly. It doesn't sound too anti-social on the road but can only get worse... The tailbox on the car is a replacement for the old one, which rusted apart internally and got blocked by huge wads of glass fibre wadding. If that's happened to the new one inside 30,000 miles I won't be best pleased. Have to peer up the damn thing with a torch tomorrow. Whatever, I'll get the garage man to do it. He's got a lift and a pit, does good work and isn't a thief. But what a PITA. Last edited by: Armel Coussine on Sun 2 Feb 14 at 00:33
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New Sun 2 Feb 14 13:22
Mimsing weather - Robin O'Reliant
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As a non-techie I always puzzled over this "Back pressure" business. As the exhaust is only there to cart away all the stuff the engine has already burnt and ejected as past it's sell by date, one would think that an unobstructed straight pipe would be the best way to go about it. Course the neighbours might moan... |
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New Tue 4 Feb 14 01:46
Mimsing weather - Armel Coussine
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>> Whatever, I'll get the garage man to do it. He's got a lift and a pit, does good work and isn't a thief. His man said he couldn't book me in till next Monday when we will be in London, so I went to see him since he hadn't rung me back. He agreed to squeeze me in on Friday afternoon to fit a new tailbox, damn. If the worst comes to the worst he works on Saturdays too. Great cat from a family of garagistes. Fingers crossed though. I always worry until all is normal again. |
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New Fri 7 Feb 14 17:55
Mimsing weather - Armel Coussine
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>> I always worry until all is normal again. And... it isn't. Turned up earlyish. There was a horsebox over the pit that wouldn't start. Eventually a forklift driver from across the way - it's a sort of small industrial suburb - came to tow the horsebox out. It went briskly towards the open garage door and stopped in the doorway with a terrible crash. The top of the forklift tower was about six or eight inches too high, ripped the roller door and its entire frame out diagonally and brought down a lot of brickwork, around a hundredweight of which was left resting on top of the forklift. No cars were damaged but it's hard to imagine the garage being made secure in less than a day or two... meanwhile the forklift can't be moved until the big lumps of broken brickwork are supported or removed. Aaaaaargh! My exhaust parts are there, I saw them. Have to collect a nipper from the station later so I'll take a look and see how they are getting on. Just hope the exhaust stays together in the meantime. I don't want to be hanging about for the AA in London next week. No peace for the wicked. |
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New Fri 7 Feb 14 18:20
Mimsing weather - Armel Coussine
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I wasn't the only person standing about watching when that happened. No one thought to look carefully at the height of the forklift's tower, although of course its driver bears prime responsibility, poor fellow. I can see how it happened. The forklift rushes happily in and out of the very similar industrial buildings across the road. Everyone assumed it would be all right. It's fortunate no one was injured by falling brickwork, not even the smart blue Jaguar whose nose was only a couple of feet away. I feel very sorry for the garage man who is nice. I wonder if his insurance will cover it, or the forklift man's? Those roller doors must cost quite a bit. |
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New Fri 7 Feb 14 18:32
Mimsing weather - NortonES2
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| I knew someone who did something very similar, on a slightly larger scale. At the Valor factory Bromford, Brum. He never lived it down:) Last heard of running jazz gigs in the Northwest, so he survived the barracking. |
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New Fri 7 Feb 14 19:40
Reversing through flood water - bathtub tom
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There seems to be a number of drivers complaining they were going slowly through floods when a vehicle speeding the opposite way created a bow wave high enough to stop them. What do we think of reversing through flood water to prevent this happening? Would the exhaust be more likely to fill? |
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New Sat 8 Feb 14 17:30
Mimsing weather - Armel Coussine
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>> I wonder if his insurance will cover it, or the forklift man's? Those roller doors must cost quite a bit. I am told the forklift driver's employer - a wine merchant - will pay. I wonder if the driver will keep his job... probably I think. The garage man says he asked him not to drive in having noticed that the forklift was too tall, but the driver had forgotten. Poor guy. My car still hasn't been done but the exhaust is holding together so far. They can't use the garage for a week or two until the doorway has been properly repaired. Meanwhile they are working using axle stands in one of the buildings opposite. He says he can do my car on Monday, maybe. I think the door is a steel concertina job, not a roller. Probably still costs a lot to replace or straighten. It's been sort of pulled to, but there's a big wine merchant's van parked across it up very close. As I thought, security is a big worry - two or three vehicles in there and of course costly equipment. Last edited by: Armel Coussine on Sat 8 Feb 14 at 17:31
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