modded stock exhausts?

can anyone tell me how much mucking about is needed with the tuning of the rocket if you drill three or more holes in the muffler end caps or is a really bad idea and i am better off putting aftermarket exhausts on it?trying to pinch pennies whilst blowing money on prog susp. & some s/bags!

[starman]

hello hipporider,I have modded the stock pipes,its relatively cheap,it works,(better than the TOR's) but it takes time and patience, access to tools, a bench and vise and some practical skills,so if you're adventurous and up for a challenge, read on! first,dont bother drilling holes in the endcap - this does nothing, behind it is a closed chamber 3 inches deep, the next chamber is approx 6 inches deep containing wadding surrounding a 1 inch dia perforated tube which is reduced to approx 0.75 inch as it meets the exitpipe. this I know because the entire contents of the stock pipes are in a bin next to my workbench. So, the stock pipes force your engine to exhale through 3x 0.75" pipes, or roughly 1.3 inch squared in area for the 3 pipes. the TOR's are a bit better, the exit pipe is 1.14 inch dia,or about 3 square inches in area for all three pipes.for comparison a 2.3 litre 16 valve 4 cyl cosworth mercedes engine makes about 185 bhp at the crank at 6200rpm, this exhausts through a 2.5" dia single pipe system, or an area of nearly 5 inches.
Before the pedants reply I know this is not a scientific comparison, exhaust system design IS "rocket science" and the above does not consider any of the principles of "mechanics of fluids" I studied while partying my way through university in the late 1970's, it's just to illustrate how severely restrictive the stock silencers (apt name!) are.

I fitted the de-cat pipe and TOR's re-mapped and was happy with the performance boost but the sound of the TOR's seem to lack character to me personally, I decided to experiment with the stock pipes, they now sound so good the TOR's are not going back on. ever. This modification takes a bit of sweat,not a lot of buck's and sounds incredible!

purchase 3 accessory exhaust tips,type A or B, your choice,total cost about $150
remove silencers/"pipes"
put 2 M8 thread bolts about 75 to 100mm long into stock mount points on pipe use an M8 nut to lock in place, now you can mount pipe in a vice on a stout bench without hurting chrome by clamping on both bolts simultaneously.
remove slash cut tip
use a dremel or equivalent with a cut-off wheel to carefully grind through the 4 welds securing end plate, prise out plate
get a 2 inch steel holesaw 4 inch deep (I made mine by welding in a extension piece)you need to locate a washer with a 22.5mm hole inside the holesaw, about half an inch below the cutting teeth, this will center the holesaw over the exposed exit pipe which is 22.2mm o/d. (access to a lathe usefull for this)
using the holesaw cut through the next disc at the base of the exit pipe
yank out the baffle you have just freed(the hidden end has a slight bend so a bit of strength/force needed-big vise-grips usefull), now the wierd bit;
you need some threaded bar at least 26" long, I used M24 metric as I already had some, M20 would be better, or a similar size in UNC etc,and 4 nuts to suit. hold the pipe vertical,and drop a nut into the 90 degree bend (where the pipe meets the cat box)
ideally the nut should be between 30 and 36mm across flats,(if you use M24 bar the nuts will 36mm a/f and the gaskets that mate to the cat-box will have to be removed from the pipes,M20 nuts are 30mm a/f so the gaskets can remain in place) with a bit of finnagle-ing make the nut drop into the recess in the entry to the first baffle, just around the bend.
pass the threaded bar up through the pipe from the other end and thread the bar into the nut-not easy but possible-I did it three times!!! I used a small inspection mirror to help the first time, just by 'feel' next two times.
mount the pipe back in bench vise
I then used a piece of aluminium plate 3/4" thick with a 1" hole, passed over threaded bar now sticking out the end of the pipe
thread on a nut using plenty of lube
thread two more nuts and lock them to-gether
using two spanners/wrenches,one to stop the threaded bar rotating, other to draw the remaing (pressed in) baffles out-slow process, but worked like a charm for me!
you now have a gutted, much lighter pipe!

buy some 2" dia. perforated pipe about 68 inches long if you use the 'A' tips, 76 inches long if you use the 'B' tips- iwent to an auto exhaust place cost me $25 cash for stainless steel

cut to length 22.5" for 'A'tips, 25" for 'B' tips
pass perforated pipe into R3 pipe and tap home to seat (prevents rattles)
trial fit your tip choice-remove small amount of metal from perforated tube to achieve a snug, neat, end cap fit

A few words of warning here, these modded pipes are loud,really really loud when you gas it,but you CAN trickle through urban areas on a pace with traffic and not attract attention, theres no going back of course and it's a fair bit of sweat and work, but for ME personally, none of the accessory pipes looks as good as the stock R3 pipes with the accessory end tips.
I didnt take pics during the work, but if anyone is interested i'll try to post pics of the finished pipes and the guts of the stock pipes so you know what you're up against.
marty. :-D

[ This message was edited by: starman on 2005-08-19 10:11 ]

[hlw3]

Does the modification you made still allow for plenty of back-pressure on the engine? I don't know too much about this stuff, but I have read that the engine needs a certain amount of back-pressure to operate correctly? I just glossed over the instructions you provided, but I will read them again a few times to try and understand what you have done. Have you taken your bike to get a performance tune? Have you checked for change in HP??

thanks for info, ride safe, take care...

[geofft]

Starman:
Thanks for the great reply, that had to take a while to write. I have done mods to stock pipes before and they worked out well. It might be possible to find some universal baffles that could be slid into the new pipes you put into the stock mufflers to turn down the volume some, but still sound good. Another thing that might help is to use a hole saw in the cat box, I am guessing that the cat box has some plates in it that are causing a restriction. When you did your exhaust did you look in the cat box, I have not had mine apart yet, so I don' know how it is put together.

[starman]

hi guys, taking a tea break, so got a minute to talk,
any restriction to the free flow of gas in an exhaust pipe(youmay use the often used phrase 'back pressure' to give a name to this restriction) will cause 'pumping losses' - this describes the power from a cylinder on the combustion stroke used to drive the cylinder on the exhaust stroke which has to force spent gas out of the cylinder past the exhaust valves, exh. ports and exhaust system.
highly restrictive exh. system= high pumping losses.
Tuning guru David Vizard goes into this subject at great length in his many excellent books on tuning theory and practice.
Im running modified airbox,K&N filter,no underseat trunking,20054 tune and PCIII on order.
hi Geofft, cat box was junked after 500mile service, mine had a catalyst inside, I had a good look at the cat box internals and as soon as isaw how bad it was for good flow I decided to junk it and fit the de-cat pipe,
plus it it heavy, my nephew uses the catbox now as an anchor on his rowboat :-D
the de-cat pipe is expensive but i got mine while on vacation in the U.S. saved a bundle, anyway I can sell it on when(if) I get my custom headers finished.
as for reducing the noise level on the gutted stockers, that's easy, fit a perforated blanking plug located inside the 2" perforated baffle tube halfway along, I made a set of these that bolt in/out easy tried them and they take the edge off but I like the sound without them. havent been on a dyno but throttle only wheelies much easier now,like my tuned RD350 Yamaha I raced/crashed/thrashed in 1975 - this bike makes me feel like i'm 19 again sometimes!! most fun i've had in years!!! :-D

[Froggo]

Great article Starman , can I ask you though , what is a " TOR " :???:

[starman]

TOR's =" Triumph Off Road" silencers, the alternative,accessory, louder, non EPA approved factory 'track use only' pipes,look like the stock pipes, slightly less restrictive, louder, and shorter in length(bout 70mm) than stock.

[originalice]

You git a wet one, babiee...now, that is a way to write. Very good information. I have just bored 4 7/16 inch holes into the first set of plate. Nadda...as you said. No help.'
I then put one into each of the next plates....one hole in each mufflet. It made a differance in sound. I broke my drill tip and the long ones are very costly. So.....be a pay day until I buy another. It would be very nice to see a picture of the insides of the stock pipes. My weekly budgets is not too much so, I need a cheap way to go faster and louder. Thank you very much and thank you in advance for pictures if you post them. Merci beaucoup.

[macmolly]

I did the same thing with the stock pipes. I'm running them now. Took off the TOR's. You can order 13in Vance and Hines baffels which cost about $13.50 ea. from V&N direct. The ones that you want are the two inch that fit the V&H Big Shots.They are a stright shot through with louvers cut into them. You can run them either way for the sound level you may want. Use one of the end tip holes to go through the muffler and secure the baffel so it wont rattle. Keep the inside muffler end caps, that you removed, you can reinstall when your completed and it make for a clean installation.

[starman]

good info macmolly! BTW, how did you gut your stockers??