Hi all,

I have searched and read various posts but couldn’t find the information I’m looking for.

Are the benefits of race exhausts just weight saving and top end power/speed?

If I’m looking for best overall setup for a road bike with good low end and mid range power would that be OEM chambers with some aftermarket silencers on a stock mc21R.

Any info appreciated.

Personally I'd say standard exhausts are good for road use. There are some Dyno graphs in the tuning section. A standard wire spliced bike that is set up correctly will be perfect on the road. After market pipes are lighter, but I think most people fit them because they crackle more
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Why do things simply when you can complicate them

As Rob says, stock NSR chambers are actually very good, particularly on a standard or delimited bike.

R5K, MC21, and MC28 silencers are increasingly restrictive model-on-model, so a set of silencers is well worth fitting. If still available, I can highly recommend Swarbrick carbon silencers for a direct fit to standard MC21 chambers.

The key benefits of aftermarket chambers are weight saving and over-rev. Race systems generally produce peak power around 11,500rpm, and will over-rev beyond 12,000rpm (inadvisable!), whereas peak with standard exhausts is often closer to 10,800rpm. Delimiiting the airbox will free the motor up somewhat more.

Standard chambers absolutely destroy race pipes in the bottom-end and mid-range!

This graph shows a well-maintained, stock delimited MC21R with Swarbrick silencers before and after our airbox mod.



However, a race system (both chambers, cans -- even alloy ones, and manifolds) weigh less than one bare stock chamber.
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Andy.
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Thanks RobH and Andy.

My MC21R with new top end rebuild and Jolly Moto exhausts feels weak/sluggish at bottom end till about 5000/6000 rpm and a big difference when I compare the low end/mid range power to my mc18 R2J with OEM chambers and Tyga silencers.

I think I will revert to the stock chambers with some aftermarket silencers as I truly miss low end /mid range acceleration.

Jolly Motos are one make that we've never tested, but seem very comparable with early Jha in appearance. Normally I'd steer well clear of visual comparisons, but both the early Jha and the JM's are noticeably fatter in the belly than other brands, and the similar Jha pipes seem to perform just how you describe.

If it's for the street, I don't think you'll be disappointed reverting to the OEM chambers on an otherwise standard bike. As the graph in my previous post shows though, modifying the airbox can make a noticeable difference too.
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Andy.
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Andy,

Was the power gain after the air box modification with the same jetting?

Is the loss in power in bottom end/mid range due to race exhausts being free flowing and therefore a loss in back pressure?

sami1 wrote:
Andy,

Was the power gain after the air box modification with the same jetting?

I'm sorry, but I can't/won't comment on the jetting of any particular setup. Besides, there are no jetting notes on the run file of that bike, and it was done way back in 2006 at our very first ever Dyno Day, so there's no hope of me remembering specifics! As with all topics of this type, I will simply say "every situation is different. Always check the jetting after every mod!"

Is the loss in power in bottom end/mid range due to race exhausts being free flowing and therefore a loss in back pressure?

No, not really. It's due to the physical shape of the expansion chamber.
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Andy.
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This has got me wondering about putting stock chambers on my Mc21 now! I bought the bike with Tyga pipes on and the carbon Airbox top and it now goes very well but it’s only a road bike so maybe that lower end drive would come in handy.

Zeus, if it's running well and your happy is it worth changing? You may need to re-jet if you do
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Why do things simply when you can complicate them

Zeus wrote:
This has got me wondering about putting stock chambers on my Mc21 now! I bought the bike with Tyga pipes on and the carbon Airbox top and it now goes very well but it’s only a road bike so maybe that lower end drive would come in handy.

Difficult to say. If the bike's set up well and you're happy, and the noise doesn't bother you, then I don't see any reason to change.

Just be glad you're riding an NSR, which in comparison to other 250s, pulls like a 4-stroke from the bottom, even with race pipes! 🤣🤣🤣
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Andy.
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If possible, maybe Sami1 would be able to weigh the OEM system and TYGA system while all the parts are in limbo during the swap-over?!

It's something I've never got round to doing, and the "stock" pipes I have have been gutted and all the sound deadening removed, so are lighter than standard. (Previous experiment, rather relative to this thread!)
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Andy.
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Andy,

I have the JollyMoto exhausts which I could weigh but need to sand and paint my OEM chambers and order some silencers which probably won’t be a direct bolt on. Could be a while till all this is accomplished.

I read somewhere that Jim Lomas has bought JM. I’ve only ever heard the sound of Jim Lomas exhausts on You tube.

RobH / Andy,
since sorting out the front cylinder it runs and goes very well but I suppose because I’ve not rode a bike with standard pipes on it makes me wonder if I’m missing out on some bottom end!
I’m pulling it out for mot next week so I’ll refresh my memory but I’m always surprised at just how quick these bikes are.
Chris.

sami1 wrote:
Andy,

I have the JollyMoto exhausts which I could weigh but need to sand and paint my OEM chambers and order some silencers which probably won’t be a direct bolt on. Could be a while till all this is accomplished.

Yeah, sorry, I meant Jollies, but "autokeyboard" entered TYGA! 🤣🤣🤣

I have a set of stock MC21 silencers somewhere that I can weigh.
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Andy.
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Zeus wrote:RobH / Andy,
since sorting out the front cylinder it runs and goes very well but I suppose because I’ve not rode a bike with standard pipes on it makes me wonder if I’m missing out on some bottom end!
I’m pulling it out for mot next week so I’ll refresh my memory but I’m always surprised at just how quick these bikes are.
Chris.

As I say, if it's running well, personally I'd leave it well alone. However it's getting more and more popular to restore them now, and the more original [looking], the better [and more valuable]! So if you want to go that way, at least you know there's plenty of performance still to be had.
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Andy.
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