Cat bypass pipes
Discussion
I'm due to have a set fitted next weeked, and I was wondering what people think of the mod - positive & negative - I've done a search but no real views either way other than it is louder - won't need these to :ears: it coming then.
Its a standard 4.5 with a sports exhaust - just after views really from others who have had it done - thanks
Depends on the type of sports pipes you already have and also whether you have the joined or separate bypass pipes. It will be VERY VERY VERY loud. Mine is so loud that I cant now take the kids in the back without fear of damaging their hearing (really!).
I might shove a standard rear on at some point.
But they do sound like a pure race car! And the flames are great.
I might shove a standard rear on at some point.
But they do sound like a pure race car! And the flames are great.
gazzab said:
Depends on the type of sports pipes you already have and also whether you have the joined or separate bypass pipes. It will be VERY VERY VERY loud. Mine is so loud that I cant now take the kids in the back without fear of damaging their hearing (really!).
I might shove a standard rear on at some point.
But they do sound like a pure race car! And the flames are great.
I have a sports exhaust that was also decatted by Joo and my kids love it to bits..!
They have no problems hearing each other and we have sing-a-longs to their Bob The Builder CD.
There are many advantages and disadvantages to decatting:
For:
- Sounds f*****g awesome (The way a TVR SHOULD sound)
- Spits flames every time you lift off
- The quicker you get the gasses in and out(fuel and air), the quicker the engine goes.
Against:
- Can't think of any, apart from waking up the neighbours at 4am
Cooky
>> Edited by cooky on Monday 31st October 03:07
Cerbera and emissions tests. Conjecture on my part, but I'm not sure how the link between the pipes would help performance. If anything I'd expect the pulses from one bank to interfere with the other bank via the link. My reasoning is since we don't have a 90 degree V8 and we don't have a regular interval between pulses. It's probably more complicated than this, so can anyone enlighten me where I'm going wrong in my thinking?
Cheers,
Steve.
>> Edited by Steve_T on Tuesday 15th November 13:47
Cheers,
Steve.
>> Edited by Steve_T on Tuesday 15th November 13:47
Steve_T said:
Conjecture on my part, but I'm not sure how the link between the pipes would help performance. If anything I'd expect the pulses from one bank to interfere with the other bank via the link. My reasoning is since we don't have a 90 degree V8 and we don't have a regular interval between pulses. It's probably more complicated than this, so can anyone enlighten me where I'm going wrong in my thinking?
Cheers,
Steve.
>> Edited by Steve_T on Tuesday 15th November 13:47
I'm sure Track will be along in a while to share his thoughts...
just because the Vee isn't 90deg doesn't mean there isn't an overlap period where there's higher pressure going down one decat pie and a lower pressure down the other .. it's the sharing of the pressure down the rest of the system that contributes to the sound reduction (absorption silencers are better silencing a steady flow rather than individual bangs) and also if there are any pipe area changes down the system they're less noticeble to a smooth flow that a varying high/low pressure flow.
there *is* a hp advantage to be had from decats, but it's very small .. single figure increases typically 3-5hp on an otherwise fully functioning high flow cat .. the linked decats add very slightly more again .. i use a rolling road that has recorded hp readings on separate days for the same car to withing .5%! (405 one day, 403 the next day) so we can detect hp changes on back to back sessions of 2-3bhp repeatedly, tho the sample of cars so far doesn't allow us to properly decide what the average hp increase is, but it is there the main problem is getting hold of cars with fully functioning catalysts, as even a small blockage in the cats can sap hp and artificially inflate apparent hp gains so fudging results 
if you took a decat hp increase as maybe 3-5bhp then linked decats would be maybe 7bhp on the same car. once i get my own rollers i'll get some better results for you, not long now
there *is* a hp advantage to be had from decats, but it's very small .. single figure increases typically 3-5hp on an otherwise fully functioning high flow cat .. the linked decats add very slightly more again .. i use a rolling road that has recorded hp readings on separate days for the same car to withing .5%! (405 one day, 403 the next day) so we can detect hp changes on back to back sessions of 2-3bhp repeatedly, tho the sample of cars so far doesn't allow us to properly decide what the average hp increase is, but it is there
the main problem is getting hold of cars with fully functioning catalysts, as even a small blockage in the cats can sap hp and artificially inflate apparent hp gains so fudging results if you took a decat hp increase as maybe 3-5bhp then linked decats would be maybe 7bhp on the same car. once i get my own rollers i'll get some better results for you, not long now
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