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I fitted a 2.0 Golf engine into my T25 a few days ago, and we made an exhaust up out of one I bought off gumtree, that was fitted to an Astra.  (the flexy has now been replaced cos it was as shagged as it looked!) One of the boxes had RC40 stamped on it which I knew I recognised from somewhere - It's a bloody Mini exhaust system that had been bodged to fit an astra Anyway, all fitted on the van and on idle it's OK, but as soon as you put your foot down it rasps and unsurprisingly sounds like a bloody mini  Has anyone used these bolt-in baffle things to any success:  I'm obviously not expecting miracles - I don't mind it staying fairly loud but there's an ear splitting rasp at anything over about 1/2 throttle that I want to reduce as much as possible. |
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Last Edit: May 20, 2012 9:01:30 GMT by cobblers
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thats what they fit to bikes and they always do the job on them, so why not, not to much money to give it a go.......
can only help you ears:-)
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 1995 mk3 cavalier 1.8i 1972 1200 beetle 2010 1.2 fiat 500 "sometime's" 2000 suzuki gsxr 600 srad |
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May 20, 2012 10:01:19 GMT
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Deemon Tweaks do oval straight through silencers for £25 each. i fitted a pair to a GT40 due to limited space and it's amazingly quiet (one per bank with no crossover) the system does have some Helmholtz resonators. you could try a Helmholtz resonator in your system. it is just a short blanked off pipe at 90 degrees to the system. short for 1/4 wave or longer for 3/4 wave. it produces it's own noise (waves) to counteract the exhaust natural noise (waves). from what i read they do stop a lot of drone. Helmholtz Google search |
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May 20, 2012 19:37:42 GMT
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Hi,
I think the problem might be partly because an RC40 is designed for a lower capacity engine with lower gas flows. The 'rasp' you get in a mini doesn't usually come in until higher up the rev range, but because your bigger engine is creating higher flows you are getting that effect lower down the speed range. I'm afraid a Helmholtz resonator or a 1/4 wave resonator (two different things that work slightly differently) only work at specific frequencies and harmonics of those frequencies, therefore you would only get a benefit at a particular engine speed. The baffles you show would probably help (across the speed range) as they disperse the energy by passing the gas through multiple orifices, but they would put quite a restriction upping your backpressure and possibly affecting performance. You might be best to look for some boxes of something larger. Sorry if this is a bit anal, but its my day job!
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900 16v
900 16v FPT
Fiat 126
Austin Mini 1000
Mazda Mx5 Mk1
Rover P4
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May 20, 2012 20:00:03 GMT
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Hi, I think the problem might be partly because an RC40 is designed for a lower capacity engine with lower gas flows. The 'rasp' you get in a mini doesn't usually come in until higher up the rev range, but because your bigger engine is creating higher flows you are getting that effect lower down the speed range. I'm afraid a Helmholtz resonator or a 1/4 wave resonator (two different things that work slightly differently) only work at specific frequencies and harmonics of those frequencies, therefore you would only get a benefit at a particular engine speed. The baffles you show would probably help (across the speed range) as they disperse the energy by passing the gas through multiple orifices, but they would put quite a restriction upping your backpressure and possibly affecting performance. You might be best to look for some boxes of something larger. Sorry if this is a bit anal, but its my day job! That's a brilliant response, thanks. It pretty much confirms what I was trying to avoid though. I'm going to make a cheap bung out of an old holesaw and some spare 1.5" tube, but having had chance to really give the van a workout today, it would have to work an absolute miracle. It's not just a "bit too loud", it's absolutely completely stupidly loud. It's also running a bit rich so I get a hefty pop and flame out of the tailpipe on hard gearchange, so I reckon I'd end up firing a bung out and through someones windscreen. You say that exhausts are your day job, so get ready for a million and one questions as it's looking as though I'll be having to replace this exhaust. What effect do the various boxes have? The RC40 would normally have the large box as the backbox, and the smaller box as a mid-box (They were swapped by the previous owner of the system) What effect does the size and placement of a box have? Is it a case of sheer "volume" inside the box, or does the length/diameter matter? This is absolutely miles louder than the RC40 on my old fairly heavily tuned 1380cc mini was, and loads more raspy and annoying. When looking at boxes I see "straight through" boxes that you can literally see straight through, and ones that have the inlet and outlet at opposing corners, it looks as though the gases pass through the meshed tube and into another chamber? I'd guess these are more restrictive, which is no problem really, so long as they are quieter in the limited space I have available! |
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May 20, 2012 20:15:10 GMT
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are you planning on dismantling and re-assembling the box? if so putting some fibre glass wool packing inside may help.  |
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May 20, 2012 20:26:25 GMT
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No problem, however, although its my day job doesn't mean I understand it all yet!
Without knowing better I would hazard a guess that the small box is essentially just a volume change (the gas entering a larger volume slows and loses some energy - the straight through one you mention) and the larger box is the silencer (contains the baffles and any absorbent material like glass fibre - the indirect one) . I would think the smaller box would need to go first to actually do anything useful, the PO may have reversed it to deliberately make it louder!
Volumes of boxes can be deliberately sized for specific systems, but thats all getting a bit complicated. Perhaps you could shoehorn in the boxes from a golf system - although that might then be a bit quiet for you!
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900 16v
900 16v FPT
Fiat 126
Austin Mini 1000
Mazda Mx5 Mk1
Rover P4
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