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Post by stirling11 on Feb 17, 2023 14:42:28 GMT 1
Hi All
I was reading a story that I found by idly surfing the net
I have a LC2 and just fitted TSA's to it, beautiful craftsmanship and so light too
There is a definite power increase over stock ,however the power really starts coming in at about 68-7000 and keeps on going to 10000rpm
It's not quite in the range I want my bike to run at
So after a bit of research on reed spacers I put a set of the 6mm ? ones that Norbo sells, my initial result seemed to lower the revs at which the PB came in to about 6500
So I'm thinking I'm on to something here, it certainly perks the mid range up a bit with a better transition
I stumbled upon a subject that was talking about inserting exhaust spacers to drop even further the advent of the PB, they were talking about 1500 -2000rpm
Only problem the discussion was only about 2T singles and not RD/Z 2/350's
So the idea is to put a shim between the port outlet and the start of the exhaust thereby lengthening the first section of the down pipe, some use as little as a 1mm shim some go fatter to get their desired result
Personally I'd never heard of this idea and I could not find anything on DrG that remotely related to two stroke twins
What are the thoughts of the forum, good idea or bad idea or is someone just spinning furphies
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Post by midlifecrisisrd on Feb 17, 2023 14:49:31 GMT 1
I'm sure I'd heard of cutting and rewelding standard pipes in racing to make them rev more so suppose it would work in reverse making them longer
Steve
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Post by midlifecrisisrd on Feb 17, 2023 14:51:19 GMT 1
Oh and I run 10mm Reed spacers and v4 reeds
Still goes bat shit crazy at 7 but stronger in the midrange where before it lugged a bit between 5 and 6500
Steve
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Post by Tobyjugs on Feb 17, 2023 18:43:39 GMT 1
Yes lengthening the pipe slightly can alter the top and mid range.
I actually posted it on this site not sure if i posted the back to back readout with dyno runs.
If I remember it was 28 or 24 mm.
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Post by Gunny on Feb 17, 2023 19:52:31 GMT 1
Oh and I run 10mm Reed spacers and v4 reeds Still goes bat shit crazy at 7 but stronger in the midrange where before it lugged a bit between 5 and 6500 Steve Surprised you can remember, its been that long since you had it out. |
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Post by midlifecrisisrd on Feb 17, 2023 20:04:37 GMT 1
Oh and I run 10mm Reed spacers and v4 reeds Still goes bat shit crazy at 7 but stronger in the midrange where before it lugged a bit between 5 and 6500 Steve Surprised you can remember, its been that long since you had it out. Last summer ya cheeky git 🧐 Steve 🤣 |
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Post by muttsnuts on Feb 17, 2023 20:17:43 GMT 1
yes it lowers the power curve, but also lowers the peak power/rpm point, on the testing I have done (a fair amount), for every 25mm added to the header it moved the power curve down by around 500rpm, the amount does vary a little depending upon the tuning/porting of the engine and the exhaiust design of course, so that is just a guide, but one that seemed reasonably consistent to a point, be aware that you can lengthen it too much with disasterous results
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Post by muttsnuts on Feb 17, 2023 20:19:09 GMT 1
Surprised you can remember, its been that long since you had it out. Last summer ya cheeky git 🧐 Steve 🤣 aye, but that was only rolled out of the garage ontot he drive, I think what Gunny meant was actually riding it.........   |
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Post by midlifecrisisrd on Feb 17, 2023 20:23:38 GMT 1
Last summer ya cheeky git 🧐 Steve 🤣 aye, but that was only rolled out of the garage ontot he drive, I think what Gunny meant was actually riding it......... Ya cheeky big bass 🖕 And here was me about to place a massive order for 2 x 240 mikuni main jets with you I'll have to reconsider that now 😤 Steve PS - do you have them in stock 🤣 |
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Post by muttsnuts on Feb 17, 2023 20:45:31 GMT 1
LOL yeas, bloody loads of them !
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Post by midlifecrisisrd on Feb 17, 2023 20:53:22 GMT 1
LOL yeas, bloody loads of them ! I'll take 2 please, I'll send you a text 👍 |
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Post by stirling11 on Feb 21, 2023 12:49:02 GMT 1
I don’t think I would like to cut Kenny’s pipes to put in an extra section of, say, 25mm, Kenny would kill me if I did
The article I was reading describes a thin spacer where the exhaust exits the port, they were talking in 2-4mm, and clamping down on that
I suppose I could replicate that with another exhaust washer in place
10mm reed spacers are an easy do, however I have standard carbs that have been upjetted and standard reeds
Might be worth a try
Thanks for all the replies, it’s interesting stuff this 2T tuning business
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Post by Chewie01 on Feb 21, 2023 13:37:26 GMT 1
As good as the TSA pipes are, and they are very good. I can't help but think they're not the solution for your needs. Maybe have a look at the Alonze pipes, they maybe a better fit for your needs. www.alonzecustom.co.uk/stock-expansion-pipes.php |
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Post by Tobyjugs on Feb 21, 2023 14:50:49 GMT 1
You don't need to cut the TSA's.
You just make a sleeve tha fits between your pipe and the flange or a new flange with a longer sleeve.
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Post by beardy on Feb 21, 2023 14:56:48 GMT 1
As good as the TSA pipes are, and they are very good. I can't help but think they're not the solution for your needs. Maybe have a look at the Alonze pipes, they maybe a better fit for your needs. www.alonzecustom.co.uk/stock-expansion-pipes.phpI have the Alonze mid range pipes on mine. Love em 👍🏻 |
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Post by steve63 on Feb 23, 2023 7:14:34 GMT 1
yes it lowers the power curve, but also lowers the peak power/rpm point, on the testing I have done (a fair amount), for every 25mm added to the header it moved the power curve down by around 500rpm, the amount does vary a little depending upon the tuning/porting of the engine and the exhaiust design of course, so that is just a guide, but one that seemed reasonably consistent to a point, be aware that you can lengthen it too much with disasterous results What's the disastrous results Dave? Complete collapse of power or something more exciting than that? Is the extra length best added to the middle section? That also adds more total volume to the pipe than lengthening the downpipe. I know that's more difficult to do than adding an extra piece at the cylinder. |
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Post by muttsnuts on Feb 23, 2023 10:14:18 GMT 1
I just added at the front of the header, there is a limit to what I can test and do in a sensible time frame !  |
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Dave B
Drag-strip hero
Posts: 240 
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Post by Dave B on Feb 23, 2023 10:28:40 GMT 1
Surely the LC2 is a power valve motor. On my 'used to be an F2' machine I have a Zeel with two mappings which allow me to have the leading edge of the power band where I want it, and to have a sharp edge or a gradual taper to the valve opening.
You need to remember that expansion chambers are to do with the relationship between the reflecting length of the pipe and the time for which the exhaust port is open. It takes an hour of metalwork to alter the length of the pipe, but five minutes of programming to alter the exhaust open time.
Incidentally, there have been bikes that have variable length exhausts, but all the successful ones had the telescopic section in the belly of the pipe.
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Post by reedpete on Feb 23, 2023 11:21:32 GMT 1
I’m there with Dave, easiest way to do what you are trying to do is remap the exhaust port PV max. opening.
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Post by steve63 on Feb 24, 2023 14:34:51 GMT 1
Surely the LC2 is a power valve motor. On my 'used to be an F2' machine I have a Zeel with two mappings which allow me to have the leading edge of the power band where I want it, and to have a sharp edge or a gradual taper to the valve opening. You need to remember that expansion chambers are to do with the relationship between the reflecting length of the pipe and the time for which the exhaust port is open. It takes an hour of metalwork to alter the length of the pipe, but five minutes of programming to alter the exhaust open time. Incidentally, there have been bikes that have variable length exhausts, but all the successful ones had the telescopic section in the belly of the pipe. I think Gordon Jennings mentions making a slip joint in the belly section that can be adjusted on the dyno. It would be a headache getting it to seal but doable. I'll put it on my list ☺️ |
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