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HKS Silent Hi-Power Info...

LuPix_S15

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For those that are interested, I was getting fed up of the silencing box on my HKS Silent Hi-Power exhaust between the backbox and decat catching on speed bumps and was also keen to see if it's removal will produce a more aggressive sound...

Dropped her into local Powerflow dealer yesterday and they chopped the box itself out (replacing the whole length would have cost around £250!!) and then welded a replacement 3" section.

The result is... not much difference lol!! Yes slightly louder and more aggressive when she's booted but on idle, no difference that I could tell :)


Suppose this is the best result if I still wanna do trackdays etc :thumbs:
 
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Thats good news, im thinking of doing the same to my Greddy some day as i have the same issue with it catching on everything. Its only the idle i worried about as i dont wont to be nusiance to the neighbours while warming the car early in the morning etc.

How much did it cost then ?
 

craig8585

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Same here with the speedbump issue, only usually on those little square ones though as the front wheels come down before the rears go up. The center box is by far the lowest part of my car with about 3" clearance, but the exhaust is loud enough as it is.
 

LuPix_S15

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Jez - Powerflow charged me £80 cash ;)


Craig - deffo recommend as the version in yours (believe it's the non-Silent version??) has an even more open flowing box than the one that was on mine... so I reckon there won't be a noticeable difference!!
 

DeanS15

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how did i not spot this - top work james. i'm pretty sure the centre silencer on mine is empty anyway due to a problem i had with very high egt's ages ago.....might get mine chopped out soon, after mot as i've got to swap the cat back over anyway :)
 

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lol nice1 Dean :)

For reference mine's got decat and all 1st stage mods etc... was noise tested at Curborough trackday 5000 rpm = 89.3 dB

So it'll sail through any noise tests and more importantly Der Nurburgring (which I've booked to go in June)!!! :D
 

DeanS15

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the 89db things good to know mate - nice one ;)
 
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Ill be doing the same as well mate to my Greddy. Let me know who you use as im trying to find someone that wil do it for a good price. Asked Haywood & Scott but they werent interested.
 

DeanS15

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Ill be doing the same as well mate to my Greddy. Let me know who you use as im trying to find someone that wil do it for a good price. Asked Haywood & Scott but they werent interested.
a local fabricator has quoted me approx 60-00 all in to do it, and his work is spot on. once i get it done i'll let you know :)

oh and i forgot to add jez - i think you are using an s13 decat same as me - i'm going to get him to add about an inch to the section he welds in to push the system back to where its meant to sit normally as this decat pulls it all forward a bit - also suspect it will make the car quieter inside on long journeys as the tip sits under the rear bumper a bit and i think this causes some sort of boomy echo under there on the motorway, with the tip further out it should get rid of some of the noise :)
 
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Ah great one mate, if its a goodjob then let him know ill deffo be down to have the same done :thumbs:
 

DeanS15

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got it done jez - cost 80.00 in the end due to the pipe being a couple of mm oversize in bore and needing a little more work. the welding is quality and doesnt look out of place on the exhaust at all. the section was a plain dull stainless that he welded in but a little time on the autosol and it looks the nuts :). the guy isn't an exhaust fabricator, he makes custom metal parts for bikes cars trikes etc and he made a jig on the bench so that the fitment would be 100% perfect but at the same time adding 20mm to the section to make the exhaust fit easier/not stretch the hangers. i left it with him for a day, but if you arranged it with him i'm sure you could drop it off and pick it up within a couple of hours. sadly the cars away at the moment so haven't had a chance to listen to it.....

heres the before pic


after (lots more clearance)




and the pipe itself




:D
 
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Nice one mate. If i cant find anyone local to do a good job then i may need to pay him a visit. Looks like his pretty nifty with the welder. Did you leave him with the car or just the centre section ? Has he got a ramp to use to remove the exhaust ?
 

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his welding is quality mate but he deals with sheet metalwork and building spaceframes etc hence no ramps.....

i dropped the section with him in the afternoon and picked it up the next morning, but if you needed it done in a day, provided you organised it with him he could probably sort it in a couple of hours :) it wont be wrong as he will drill two pieces of metal and bolt them to the ends of the system and then weld them to the bench before he cuts it, so it cant go wrong :)
 
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Got my car booked in to Pipecraft in Basildon for next sat to have same done. They didnt have any 3" stainless so they will order in a metre length for me. Quoted me £70, have a ramp and said i can wait while they do it. Actually a helpful bucnh of guys so far so hoping their work is as good.
 
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Ok so got my centre silencer cut out at the weekend and fook me its a fair bit louder now on idle when its cold and on mid - full chat. Hope its not going to drive me crazy. Dunno if its me but it also seems to rev quicker and spool quicker than before ?
 

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Ok so got my centre silencer cut out at the weekend and fook me its a fair bit louder now on idle when its cold and on mid - full chat. Hope its not going to drive me crazy. Dunno if its me but it also seems to rev quicker and spool quicker than before ?
i feel the same mate, i just didnt want to put it up here for fear of it seeming 'silly'. seems to go a little bit more nuts when coming on boost at full throttle.....

as for the loudness, i certainly think it makes the silent hi-power sound 'nicer' but in time maybe a decat silencer will put back some of the silencing taken away without compromising ground clearance like the original silencer does. its nice to be able to drive through my village again without wincing whenever a car comes towards me and forces me over a speed bump lol.
 

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I've also taken some inspiration from this thread. Currently I have the HKS Hi-Power cat-back (not silent version) so it has a different back box (with less sound proofing and no 2" restriction just prior to the tailpipe) and the pipework in between the boxes is mild steel.

HKS do a Spec-R version of the Hi-Power too which is titanium, has no mid-box and is single-piece design but costs over £1k. What I'm doing is buying a Hi-Power back box from HKS and getting a stainless 3" pipe welded onto it that incorporates the whole system up to and including the decat so the only flanged joint visible from under the car will be at the downpipe. Saves any unnecessary joins in the system and gives a bit of ground clearance too. Hope it's not toooo loud! :p
 

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I've also taken some inspiration from this thread. Currently I have the HKS Hi-Power cat-back (not silent version) so it has a different back box (with less sound proofing and no 2" restriction just prior to the tailpipe) and the pipework in between the boxes is mild steel.

HKS do a Spec-R version of the Hi-Power too which is titanium, has no mid-box and is single-piece design but costs over £1k. What I'm doing is buying a Hi-Power back box from HKS and am getting a stainless 3" pipe welded onto it that incorporates the whole system up to and including the decat so the only flanged joint visible from under the car will be at the downpipe. Saves any unnecessary joins in the system and gives a bit of ground clearance too. Hope it's not toooo loud! :p
what about mot my man? no cat, no ticket.......
 

craig8585

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Luckily I've never had a problem with not having a cat at MOT time. Infact I just got in MOT'd this Saturday and they did me a fast idle test for pre 1993 cars as they had no emissions data for my car as there is no UK equivalent.
 
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