What if I want to KEEP the cat? What performance mods are still worth it?

FlyingBasset · 10-30-2021, 10:49 PM

So I recently hooked up a new eBay exhaust to my Raven / BSR 250 (works and fits great - I'll post a separate thread about it).

But as expected - it's a lot louder and smells worse than stock - like they all do. Also, you'll of course have a lot more emissions without a cat. Obviously in the grand scheme of things it's negligible, but it is something. And I expect to be taking this in a lot of national parks where I don't want to piss off any rangers.

So hypothetically speaking - what would I still do to maximize performance (top speed) while keeping the cat? Here are my ideas:

1: keep eBay exhaust and rear stainless pipe (much lighter, better flow)
2: grind out inner welds in stock header pipe
3: port head inlet and outlet?
4: tt250 head gasket?
5: pwk30 carb?

OBVIOUSLY the stock cat is going to limit the benefits I see from these mods - but the question is how much? If I just have to lose 2 mph top speed from keeping the cat I can live with that.

Thanks in advance!

China Rider 27 · 10-30-2021, 11:18 PM

I have never had a Ranger encounter but I believe what will make them reach for the citation book first is the fact you have no spark arrester on that E bay muffler you are going to run. I don't know that they know much or care about CATS.

The issue with keeping the CAT is that it bottle necks exhaust flow retaining heat and limiting engine flow into and out of the cylinder. In my opinion if you keep the CAT all of those mods are questionable as to whether they are cost effective and even achievable (PWK30).

The question is really about what are the goals for the bike and keeping a CAT is a good goal if it fits with the overall bike goal. We strive for performance, but the reality is we use just half the power these engines are capable of producing most of the time while we obsess over a couple of miles of top end speed.

If I was to keep the CAT, I would keep the stock muffler and enjoy it for the quiet exhaust note.

DualSportDude · 10-30-2021, 11:42 PM

Keep the performance exhaust & add a baffle & spark arrestor. Sounds better and satisfies the Ranger. I have been checked, just ran a rod into the pipe and made sure something keeps the rod from going all the way down the pipe.

https://carcustomonline.com/tt250-pe...park-arrestor/

http://chinariders.net/showthread.ph...804#post367804

FlyingBasset · 10-30-2021, 11:55 PM

I appreciate the suggestions so far, but I already have a cheap spark arrestor on the ebay exhaust. That's not really going to reduce the noise, smell or emissions - even if it is the only NFS requirement.

I don't really want to mix my work (chemical engineering) with this friendly forum - but I'll just say small engines like these are actually pretty terrible for the environment (even compared to cars). So the idea of this thread is what's the best you can do without making the bike a much worse polluter.

DualSportDude · 10-31-2021, 12:21 AM

Stock exhaust, 112 main jet, stock slow jet, needle one slot down from highest position, air mix about 1 1/4 to 1 1/2 turns out or so.

DualSportDude · 10-31-2021, 12:24 AM

Better but still kinda slow and starves for fuel at about 7k rpm.

Boatguy · 10-31-2021, 06:48 AM

You don’t want to hear this, but get a different bike.

It’s so illogical to get a 250 then try to make all these changes to get an extra 5% power from it. If you want more power, buy a bike that has more power.

Save your money and time (your time is worth a lot per hour as a ChemE) and get a bike that delivers the power you’re looking for stock.

Then you don’t have to modify anything at all.

China Rider 27 · 10-31-2021, 11:00 AM

Being as tinkering is a major skill set here on the China Forum, maybe building a better CAT and attached exhaust that flows more air to make up the difference? See if you can find another larger motorcycle CAT and pipe it in?

FlyingBasset · 10-31-2021, 07:30 PM

Quote:

Originally Posted by Boatguy

You don’t want to hear this, but get a different bike.

It’s so illogical to get a 250 then try to make all these changes to get an extra 5% power from it. If you want more power, buy a bike that has more power.

Save your money and time (your time is worth a lot per hour as a ChemE) and get a bike that delivers the power you’re looking for stock.

Then you don’t have to modify anything at all.

I don't mind hearing that at all and you're absolutely right. If I had known what I know now, I would have just bought a Hawk DLX or similar from the start. But this bike was super cheap and I had never ridden before - so if I didn't enjoy it I was only out $1k and would enjoy the learning/ tinkering regardless.

Even now the logical thing to do would be buy a Versys-X 300 and be done with it - but I think it's more than just the price that attracts the people on this forum to these bikes.

I think what I'll probably end up doing is continuing to ride and learn on this for a while as it's a great beginner's bike. But I'll be keeping an eye on the group working to crack the code for tuning the Hawk DLX - because it would be really cool to join that effort and experiment.

FlyingBasset · 10-31-2021, 07:39 PM

Quote:

Originally Posted by China Rider 27

Being as tinkering is a major skill set here on the China Forum, maybe building a better CAT and attached exhaust that flows more air to make up the difference? See if you can find another larger motorcycle CAT and pipe it in?

Yeah, it's a shame because emissions technology has come a long way since these engines / cats were designed - nowadays cats barely impact performance if they do at all.

I don't know if it's reasonable to find a replacement cat, but I have been browsing on facebook to see if anyone has a more modern exhaust they are getting rid of. That would be nice if possible.

Wild Dog · 10-31-2021, 07:51 PM

Quote:

Originally Posted by Boatguy

You don’t want to hear this, but get a different bike.

It’s so illogical to get a 250 then try to make all these changes to get an extra 5% power from it. If you want more power, buy a bike that has more power.

Save your money and time (your time is worth a lot per hour as a ChemE) and get a bike that delivers the power you’re looking for stock.

Then you don’t have to modify anything at all.

That's always seems to be logical reply "Get a different bike". But think about this, for every single motorcycle out there, you have the aftermarket world.

Even sometimes when folks mod out real racing motorcycle the gain is not that impressive yet it's done.

Is not just about the 5%, it's the fun of doing it.
Porting a head is not going to make a 300cc be a 650cc or a 650cc a 1200cc
But it's fun and nice to do.

Of course this is not the cup of tea that everyones like, some people don't care nor want to mod anything and that's fine.

Boatguy · 10-31-2021, 08:57 PM

Quote:

Originally Posted by Wild Dog

That's always seems to be logical reply "Get a different bike". But think about this, for every single motorcycle out there, you have the aftermarket world.

Even sometimes when folks mod out real racing motorcycle the gain is not that impressive yet it's done.

Is not just about the 5%, it's the fun of doing it.
Porting a head is not going to make a 300cc be a 650cc or a 650cc a 1200cc
But it's fun and nice to do.

Of course this is not the cup of tea that everyones like, some people don't care nor want to mod anything and that's fine.

I definitely don’t want to drink that tea, but I’ve gone down the path before when I would have been better off selling and getting a different whatever (not just bikes). So I wanted to make sure the OP didn’t lose sight of that option. It’s easy to lose sight when deep in the projects.

If you enjoy working on bikes, it’s a completely different story of course. I do not enjoy working on the bike. I prefer the riding. I kept mine so stock it’s almost a joke. Ha ha ha.

Aftermarket items include: USB port for phone, holder for phone on handlebars, top box and panniers. Accessories, really. That’s it. 100% stock otherwise. That’s because I don’t want to work in the bike. I have enough other things to fix/build.

I even run the crappy Chinese chain. After you tighten it 10x it stops stretching by the way. Ha ha.

China Rider 27 · 10-31-2021, 09:40 PM

Quote:

Originally Posted by Wild Dog

That's always seems to be logical reply "Get a different bike". But think about this, for every single motorcycle out there, you have the aftermarket world.

Even sometimes when folks mod out real racing motorcycle the gain is not that impressive yet it's done.

Is not just about the 5%, it's the fun of doing it.
Porting a head is not going to make a 300cc be a 650cc or a 650cc a 1200cc
But it's fun and nice to do.

Of course this is not the cup of tea that everyones like, some people don't care nor want to mod anything and that's fine.

Absolutely! This is a Mechanics forum, whether you realize that or not most become mechanics and appreciate the mechanical application of principles by your own hand. The majority of the people here have been "mechanic--ing" for years. Something about turning a wrench to fix something or create something better generally gets in your blood and stays there.

These inexpensive chinese motorcycles are great fun to mod and experiment with because they are affordable. Not possible on a mainstream bike with anything like a budget.

XLsior · 10-31-2021, 11:33 PM

Advanced timing key and weight reduction are about the extent of "performance" mods without engine fettling. Maybe a different carby but that can get a bit hands on as well..

But yeah...an exhaust port and uncorking pretty much gets you the bulk of untapped power mods on this 250ish chonda bike engines.

10-30-2021, 10:49 PM	#1
FlyingBasset Join Date: Jun 2021 Posts: 26	What if I want to KEEP the cat? What performance mods are still worth it? So I recently hooked up a new eBay exhaust to my Raven / BSR 250 (works and fits great - I'll post a separate thread about it). But as expected - it's a lot louder and smells worse than stock - like they all do. Also, you'll of course have a lot more emissions without a cat. Obviously in the grand scheme of things it's negligible, but it is something. And I expect to be taking this in a lot of national parks where I don't want to piss off any rangers. So hypothetically speaking - what would I still do to maximize performance (top speed) while keeping the cat? Here are my ideas: 1: keep eBay exhaust and rear stainless pipe (much lighter, better flow) 2: grind out inner welds in stock header pipe 3: port head inlet and outlet? 4: tt250 head gasket? 5: pwk30 carb? OBVIOUSLY the stock cat is going to limit the benefits I see from these mods - but the question is how much? If I just have to lose 2 mph top speed from keeping the cat I can live with that. Thanks in advance!
	0

10-31-2021, 06:48 AM	#7
Boatguy Join Date: Feb 2021 Location: Northeast Posts: 929	You don’t want to hear this, but get a different bike. It’s so illogical to get a 250 then try to make all these changes to get an extra 5% power from it. If you want more power, buy a bike that has more power. Save your money and time (your time is worth a lot per hour as a ChemE) and get a bike that delivers the power you’re looking for stock. Then you don’t have to modify anything at all. __________________ 2020 Lifan x-pect
	3

10-30-2021, 11:18 PM	#2
China Rider 27 Join Date: Dec 2018 Location: PNW Posts: 982	I have never had a Ranger encounter but I believe what will make them reach for the citation book first is the fact you have no spark arrester on that E bay muffler you are going to run. I don't know that they know much or care about CATS. The issue with keeping the CAT is that it bottle necks exhaust flow retaining heat and limiting engine flow into and out of the cylinder. In my opinion if you keep the CAT all of those mods are questionable as to whether they are cost effective and even achievable (PWK30). The question is really about what are the goals for the bike and keeping a CAT is a good goal if it fits with the overall bike goal. We strive for performance, but the reality is we use just half the power these engines are capable of producing most of the time while we obsess over a couple of miles of top end speed. If I was to keep the CAT, I would keep the stock muffler and enjoy it for the quiet exhaust note.
	1

10-30-2021, 11:42 PM	#3
DualSportDude Join Date: Jul 2021 Location: Georgia, USA Posts: 91	Keep the performance exhaust & add a baffle & spark arrestor. Sounds better and satisfies the Ranger. I have been checked, just ran a rod into the pipe and made sure something keeps the rod from going all the way down the pipe. https://carcustomonline.com/tt250-pe...park-arrestor/ http://chinariders.net/showthread.ph...804#post367804
	0

10-30-2021, 11:55 PM	#4
FlyingBasset Join Date: Jun 2021 Posts: 26	I appreciate the suggestions so far, but I already have a cheap spark arrestor on the ebay exhaust. That's not really going to reduce the noise, smell or emissions - even if it is the only NFS requirement. I don't really want to mix my work (chemical engineering) with this friendly forum - but I'll just say small engines like these are actually pretty terrible for the environment (even compared to cars). So the idea of this thread is what's the best you can do without making the bike a much worse polluter.
	0

10-31-2021, 12:21 AM	#5
DualSportDude Join Date: Jul 2021 Location: Georgia, USA Posts: 91	Stock exhaust, 112 main jet, stock slow jet, needle one slot down from highest position, air mix about 1 1/4 to 1 1/2 turns out or so.
	0

10-31-2021, 12:24 AM	#6
DualSportDude Join Date: Jul 2021 Location: Georgia, USA Posts: 91	Better but still kinda slow and starves for fuel at about 7k rpm.
	0

10-31-2021, 11:00 AM	#8
China Rider 27 Join Date: Dec 2018 Location: PNW Posts: 982	Being as tinkering is a major skill set here on the China Forum, maybe building a better CAT and attached exhaust that flows more air to make up the difference? See if you can find another larger motorcycle CAT and pipe it in?
	1

10-31-2021, 11:33 PM	#14
XLsior Join Date: Aug 2020 Location: Australia Posts: 1,318	Advanced timing key and weight reduction are about the extent of "performance" mods without engine fettling. Maybe a different carby but that can get a bit hands on as well.. But yeah...an exhaust port and uncorking pretty much gets you the bulk of untapped power mods on this 250ish chonda bike engines.
	0