Lawrence_Z Posted August 27, 2002 Share Posted August 27, 2002 Can someone please measure a K series 4 2 1 exhaust pipe for me? I need to know the diameter of the pipe between the collector and the main box and the diameter of the tail pipe. TIA Lawrence Link to comment Share on other sites More sharing options...
F355GTS Posted August 27, 2002 Share Posted August 27, 2002 tis 2.25" for both as I know to my cost cos I bought a BTB box with a 2.5" inlet ☹️ Powerspeed are just adjusting it for me!! Mark Link to comment Share on other sites More sharing options...
Lawrence_Z Posted August 27, 2002 Author Share Posted August 27, 2002 Many thanks Mark.... so I'm on the 2 inch box SLR is 2 1/4 ..................thats 26 % larger and a new R4HUN is 2 1/2......that's 56% larger does anyone have more than 190 bhp and a 2 inch system? apart from Mike Bees, who is only 1700 cc Lawrence Link to comment Share on other sites More sharing options...
AMMO Posted August 27, 2002 Share Posted August 27, 2002 Not 100% sure but I think some VX cars had more than 200 bhp with 2" silencers. Not a very good idea though. 2.5" would be better. The rule of thumb I use is 2.25" up to 200 bhp 2.5" over 200 bhp. Seems to work. Recently went up to 2.25" from 2" on my 1800 Zetec and the extra urge can be felt through the seat of the pants. Also Foxy Smith went up from 2" to 2.5" on his VX and is very happy. AMMO Link to comment Share on other sites More sharing options...
Lawrence_Z Posted August 27, 2002 Author Share Posted August 27, 2002 Thanks Ammo I had some feedback from a VX driver agreeing with your comments, looks like that's whats needed then Anybody got a 2 1/2 system for sale? now didn't I see a spare one at the weekend? in a trailer? cheers Lawrence Link to comment Share on other sites More sharing options...
scooby dooby doo Posted August 27, 2002 Share Posted August 27, 2002 i've got the opposite problem - 150 bhp and a 2.5" exhaust. but 200+ bhp upgrade going in over the winter HOOPY CYCLE WINGS CUCUMBER Link to comment Share on other sites More sharing options...
Mike Bees Posted August 28, 2002 Share Posted August 28, 2002 Going from 2" to 2.5" made not a scrap of difference on my ~230bhp K, back to back tests measured on the rollers. The 2" is quieter... Oh sorry Lawrence, you said apart from me Mike Link to comment Share on other sites More sharing options...
Lawrence_Z Posted August 28, 2002 Author Share Posted August 28, 2002 Yeah Mike, I've read your archives and feel that your car is exceptional, and therefore may not indicate a trend. I'll pass the power run over to you, if you'd like to comment Lawrence Link to comment Share on other sites More sharing options...
Nobby Posted August 28, 2002 Share Posted August 28, 2002 Lawrence, I dont think he's taking the bait. R4HUN Link to comment Share on other sites More sharing options...
Mike Bees Posted August 29, 2002 Share Posted August 29, 2002 Eh 🤔 I don't understand 😳 Link to comment Share on other sites More sharing options...
AMMO Posted August 29, 2002 Share Posted August 29, 2002 What Mike says is probably correct for his car. As I said only a rule of thumb. Generally speaking noise may increase with the increase of dimension of the silencer but not neccessarily. Depends on how the silencer is constructed. My experience with race bikes shows that bigger is usually better in terms of peak horsepower. A Ducati Supermono 580 cc single which won Daytona a couple of years ago worked best with the biggest diameter silencer available. Ducati twins have used exhaust exit pipes up to 60 mm O.D. That's one silencer per cylinder. Part of the sizing of the silencer is dependant on what you are expecting the exhaust system to do. There are returning waves from the primaries, the secondaries, if you have a four into two into one, and the end of the tail pipe. If you have a four into one, the end of the exhaust pipe is your secondary. By increasing the silencer pipe you may reduce the intensity of the secondary returning wave. This may be beneficial if the secondary is out of tune. The problem becomes even more complicated once you start looking at induction lengths, cam duration and timing. If the exhaust is really big you may even trick the engine into thinking that the end of the primary is the big outside world. I noticed Peter Carmichael's car at Curborough had a 3" pipe with a considerable step up from the collector. This was just to adapt an off the shelf silencer to his collector but it is probably having some sort of effect on the returning wave as well. If your exhaust is not perfect you can bring it back by changing the induction length or altering the cam timing. So what you end up with on your particular engine is dependant on many factors. Superbike manufacturers bring out new factory exhausts every year so you can't just say this works, that's it. These things are in a state of constant change. The theory remains the same but the solutions are always changing. Luckily for us who run road cars with mildish cams the exhaust length is not that critical. Things need to be more accurate when the cam duration goes up. I have seen a 7 bhp increase on a 950 cc twin running 320 degree duration cams by chopping one inch off the primary pipes. On the dyno you just chop an inch off at a time and when you have gone too far you weld an inch back on. With road cams the exhaust can be 10% out and you will have no measurable difference. Hope you find these ramblings intersesting. Personally I find most thing to do with four stroke engines fascinating as there is always something new to learn. AMMO Link to comment Share on other sites More sharing options...
scooby dooby doo Posted August 29, 2002 Share Posted August 29, 2002 wasn't the theory with WW2 aero engines just to have straight pipes from each cylinder. They then coated the outside with wax and ran them up to operating speed. The standing wave inside meant that the wax melted first at the antinodes. Then they just cut the pipe at the antinode. Is that just a very primitive version of what you've described? But missing silencers and collectors etc so its simple. OTOH it misses out on pulse tuning which is beneficial... HOOPY CYCLE WINGS CUCUMBER Link to comment Share on other sites More sharing options...
Rob Walker Posted August 29, 2002 Share Posted August 29, 2002 I am running a 230 BHP K with a 2" VX race silencer. 98dba at 4500 rpm. I would like to do some power runs with a bigger bore 4 2 1 system though ! Link to comment Share on other sites More sharing options...
Peter Carmichael Posted August 29, 2002 Share Posted August 29, 2002 The long run from the collector to the step up and the can was designed with the intention of giving a "secondary" effect. I did a load of calculations. Seems to work, but isn't quiet. Measured at 105dBA @6200 at Curborough. Link to comment Share on other sites More sharing options...
AMMO Posted August 29, 2002 Share Posted August 29, 2002 Hoopy Funnily enough the bike in question had straight tuned length pipes. This was when there were no noise restrictions. Didn't know about the wax business. I spoke to an engineer from Ricardo who said they put sensors along the length of the exhaust system at very samll intervals to monitor the returning waves. This way they could pinpoint what was happening in operation. AMMO Link to comment Share on other sites More sharing options...
AMMO Posted August 29, 2002 Share Posted August 29, 2002 Peter Must have misunderstood what you said. I though the exhaust was like that because the silencer was that size when you bought it and had to be adapted to fit. AMMO Link to comment Share on other sites More sharing options...
Lawrence_Z Posted August 29, 2002 Author Share Posted August 29, 2002 Wow!!!! Thanks Ammo, I now know that there's even more things I know nothing about Mike Brod is referring to Fred, who brought his new kit to Curborough, including a 2.5 system and who survived the many jibes, when repeatedly asked if I could try various bits of kit 😬 Lawrence Link to comment Share on other sites More sharing options...
Lawrence_Z Posted August 29, 2002 Author Share Posted August 29, 2002 Mike did you get my mail? Lawrence Link to comment Share on other sites More sharing options...
Mike Bees Posted August 29, 2002 Share Posted August 29, 2002 No! Link to comment Share on other sites More sharing options...
Lawrence_Z Posted September 6, 2002 Author Share Posted September 6, 2002 Ammo I've mailed you through blatchat, if you don't receive it ..... Can you mail me at Lawrence@hoymotorsport.co.uk Link to comment Share on other sites More sharing options...
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