"Small bore" kits?

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5/5/2021 9:19 PM

With the popularity of KTM's 350 platform i'm surprised i've never seen a "small bore" 380-400cc kit offered for any of the Japanese 450s. Not everyone wants a KTM. Most people don't need the full 450 power and would rather have a quicker and higher RPM spread like the 350s. A 400 kit would probably have more low-mid torque then the 350 but more Rideable and rev happy then a 450.

Am i alone? Has anyone attempted to make something like that?

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5/5/2021 9:34 PM

I think one issue is that the ceiling for rpms is dictated by more than just the bore and piston, so an engine designed for 450 type rpm limits couldn't handle higher RPM just by switching to a small bore. Whereas redline stays the same on big bore kits.

But I’m not an engineer or skilled mechanic. This is a really cool idea though.

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5/5/2021 9:42 PM

I don't remember the backstory, but do remember that Jeff Alessi rode a CRF 350 several years back.

I think an Italian company built it?

No idea what happened with that project.

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"Sorry Goose, but it's time to buzz the tower."

5/5/2021 9:50 PM

RedMoto Honda in Italy makes a 400 cylinder (413cc) for 2017+ CRF450R/RX. It’s a Athena cylinder and Vertex piston. You can buy them from the USA importer Check Point Offroad. They also make a 300 kit (295cc) for the 2018+ CRF250R/RX. they also include mapping.

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5/5/2021 10:13 PM

TheGetFresh wrote:

I think one issue is that the ceiling for rpms is dictated by more than just the bore and piston, so an engine designed for ...more

If anything should be less inertia, quicker revving and with some mapping and maybe different cams, valve springs,etc, i'd have to imagine more RPM should be safe.

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5/5/2021 10:17 PM

I'd get a 250F and send it to Tom Zont for a big bore kit

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5/6/2021 5:08 AM

Way back when the Honda 450X was released, quite soon after, there were 400cc kits. I think they may have come out when just the R was available. A de-bore kit.

So, it's been done before, and, as noted above, about Redmoto Honda, it's being done now. I'd be surprised if a few other companies don't offer de-bore kits.

In this day and age of EFI and so much E tech on bikes, with a little bit of effort, often with just a tuner app, or even a throttle cam or flywheel weight, you can make a 450 into a mellow, yet still very fast, Teddy Bear, or going in the opposite direction, a fearfully violent Monster.

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5/6/2021 5:20 AM

Beta currently builds a 390, the only remaining manufacturer at that size currently. The Honda XR 400 and KTM's 400 EXC were some of the last bikes built in that size.

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2015 Beta 500 RS, history: 99 KTM 300, 87 CR250, 84 KLR 600, 82 GPZ 550, 81 KX 250, 80 KX 250, 79 Montesa 414 VE, 78 250 VB, 77 360 VB, 76 360 VA, 75 YZ 125, 74 TM 125, 72 TS 125, 60's West Bend Go Boy Kart

5/6/2021 5:33 AM

griddle922 wrote:

RedMoto Honda in Italy makes a 400 cylinder (413cc) for 2017+ CRF450R/RX. It’s a Athena cylinder and Vertex piston. You can ...more

I don't know what is more ridiculous, the fact that a company sells an item that reduces the power of your motorcycle or the fact that for 99% of the riding public it is a great performance improvement.

I race a YZ250FX with a 270 kit in it so I'm in that bikes target market. I may have to start looking for a CRF450.

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5/6/2021 5:41 AM

griddle922 wrote:

RedMoto Honda in Italy makes a 400 cylinder (413cc) for 2017+ CRF450R/RX. It’s a Athena cylinder and Vertex piston. You can ...more

McG194 wrote:

I don't know what is more ridiculous, the fact that a company sells an item that reduces the power of your motorcycle or the ...more

How do you like the 270 kit on the Yz? I love my 21 YZ250F engine feel stock. Did it lose that light, aggressive, zero vibration, super fast revving feel at all? Seems like that kit should probably add 3-4hp without doing anything else.

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5/6/2021 5:55 AM

Johnny Depp wrote:

Beta currently builds a 390, the only remaining manufacturer at that size currently. The Honda XR 400 and KTM's 400 EXC were ...more

That 390 engine i heard is amazing too! The rest of the bike not really call my name. I like that they do both the 390 and 430. I wish more would follow!

I rarely ride my 450s. On my 250fs i feel like i'm pushing it hard and really putting in effort to get through the track and clear everything which makes them a lot of fun. On the 450s i feel like i'm at 1/8 throttle and barely in the midrange half the track and even though i'm going faster, it FEELS like i'm going slow. Just gets boring to me not needing any effort to clear a big jump out of a corner and such. Also the heavy feel and huge power just wears me out so much faster. My 350s seem like the perfect compromise but the choppy WP suspension and high vibration is hard to ignore compared to the Japanese bikes.

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5/6/2021 5:56 AM

griddle922 wrote:

RedMoto Honda in Italy makes a 400 cylinder (413cc) for 2017+ CRF450R/RX. It’s a Athena cylinder and Vertex piston. You can ...more

McG194 wrote:

I don't know what is more ridiculous, the fact that a company sells an item that reduces the power of your motorcycle or the ...more

Ray Knight wrote:

How do you like the 270 kit on the Yz? I love my 21 YZ250F engine feel stock. Did it lose that light, aggressive, zero ...more

For me it was a great addition. I'm a bigger dude so I way too often found myself in 1st gear with all the abruptness that comes with it. I found with the 270 kit I could run 2nd gear in former 1st gear sections and the chassis was much more settled. It will still spool up quickly but I can ride way smoother. I really want a 350 but I don't want to be like every other vet racer on my line with a KTM.

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5/6/2021 6:14 AM

McG194 wrote:

I don't know what is more ridiculous, the fact that a company sells an item that reduces the power of your motorcycle or the ...more

Ray Knight wrote:

How do you like the 270 kit on the Yz? I love my 21 YZ250F engine feel stock. Did it lose that light, aggressive, zero ...more

McG194 wrote:

For me it was a great addition. I'm a bigger dude so I way too often found myself in 1st gear with all the abruptness that ...more

Good to hear! Owning both a 350sxf and YZ250F and riding back to back i can tell you the Vibration and engine braking of the 350sxf especially at higher revs feels insane after getting off the YZ! The power is great just not as aggressive and smooth balanced as the YZ. I've been thinking its probably because its based on the 250f bottom end with a much heavier piston spinning almost the same RPM. A 450 based engine with a smaller bore i would think would be more ideal. At least more ideal for the majority of guys not racing and riding 450s if they are honest with themselves.

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5/6/2021 6:21 AM

Small bored to 350, any decent engine's valves will hit the cylinder.

If they don't hit the cylinder the valve clearance cutout's will be somewhere in the piston rings.

Not happenin.


Upscaled 250: much, much more feasible.

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5/6/2021 6:27 AM

Aren’t most 250 rolling chassis slightly lighter than their matching 450? I thought that most were, which is why Service Honda used CRF250 chassis for their AF500 bikes.

If that’s generally true for most brands, it would seem to make sense that a big bore/upsize kit would make more sense than trying to downsize, especially if it’s due to a 450 being too tiring the more you ride.

I suppose that there would be exceptions to that idea, though.

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5/6/2021 6:38 AM

Ray Knight wrote:

How do you like the 270 kit on the Yz? I love my 21 YZ250F engine feel stock. Did it lose that light, aggressive, zero ...more

McG194 wrote:

For me it was a great addition. I'm a bigger dude so I way too often found myself in 1st gear with all the abruptness that ...more

Ray Knight wrote:

Good to hear! Owning both a 350sxf and YZ250F and riding back to back i can tell you the Vibration and engine braking of the ...more

I think the combination of a smaller displacement with corresponding less power along with the heavier rotating mass would make a ridiculously tractable engine. I'm excited about the prospect.

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5/6/2021 7:01 AM

McG194 wrote:

For me it was a great addition. I'm a bigger dude so I way too often found myself in 1st gear with all the abruptness that ...more

Ray Knight wrote:

Good to hear! Owning both a 350sxf and YZ250F and riding back to back i can tell you the Vibration and engine braking of the ...more

McG194 wrote:

I think the combination of a smaller displacement with corresponding less power along with the heavier rotating mass would ...more

Exactly!!!

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5/6/2021 7:03 AM

APLMAN99 wrote:

Aren’t most 250 rolling chassis slightly lighter than their matching 450? I thought that most were, which is why Service Honda ...more

I'm pretty sure chassis weights are the same these days. Definitely for KTM, i know the new YZ250F is using the 450 chassis, the Yellow bikes have the same chassis and the new KX250 is on the 450 platform as well. Bets the new 22 CRF 250 is using the new 450 chassis as well. I think this would be for the guys that already own 450s and want to tame them a bit but still want a lot more low-mid then a big bore 250/270F will have.

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5/6/2021 7:10 AM
Edited Date/Time: 5/6/2021 7:20 AM

SilverSpurs wrote:

Small bored to 350, any decent engine's valves will hit the cylinder.

If they don't hit the cylinder the valve clearance ...more

Ports will also be too big and you can't get around the larger stroke(the rev killer) without a different crank.

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5/6/2021 7:19 AM

SilverSpurs wrote:

Small bored to 350, any decent engine's valves will hit the cylinder.

If they don't hit the cylinder the valve clearance ...more

This is exactly what I was going to say. I highly doubt you'd have the clearance to run a smaller bore netting you -100cc's.

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Tomac and/or Anderson for 2020.....

5/6/2021 7:21 AM

SilverSpurs wrote:

Small bored to 350, any decent engine's valves will hit the cylinder.

If they don't hit the cylinder the valve clearance ...more

BobPA wrote:

This is exactly what I was going to say. I highly doubt you'd have the clearance to run a smaller bore netting you -100cc's.

I'd think +/- 30-50cc should be possible with just about any.

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5/6/2021 7:26 AM

Piston speed limits RPM ceiling. A shorter stroke will allow more RPMS and keep piston speed down. So a shorter stroke and smaller bore would be needed.

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Take it to the limit, one more time!

5/6/2021 7:46 AM

Anybody ride the YZ400f from the late 90s? Those bikes were smooth!

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5/6/2021 8:00 AM

I keep wishing a company would release a kit like RedMoto's 400RX for my KX450X. I have both, a KX250X and KX450X, and I'd like more than the 250 gives me, but the 450 is too much in the tight enduros.

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Shout out to: Fly Racing, X Brand Goggles, Kenda Tire, Nuetech Nitromousse, ProTune Suspension, Motool, Sunstar Sprockets, and Rehmerts Kawasaki KTM

Instagram: WoodsRacer126

5/6/2021 8:14 AM

WDSRCR wrote:

I keep wishing a company would release a kit like RedMoto's 400RX for my KX450X. I have both, a KX250X and KX450X, and I'd ...more

You guys are wanting exactly what Beta is already doing...if they offer the 390 in their new MX line you will see a ton of them at the track:

Photo

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5/6/2021 8:15 AM

WDSRCR wrote:

I keep wishing a company would release a kit like RedMoto's 400RX for my KX450X. I have both, a KX250X and KX450X, and I'd ...more

I'd buy one for my KX450 as well!

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5/6/2021 8:20 AM

Someone was offering something like this for the YZ400 or YZ426 back in the day. Can’t remember who, or what displacement it was... but I definitely remember one of the magazines testing it.

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5/6/2021 8:24 AM

WDSRCR wrote:

I keep wishing a company would release a kit like RedMoto's 400RX for my KX450X. I have both, a KX250X and KX450X, and I'd ...more

Black Diesel Bomber wrote:

You guys are wanting exactly what Beta is already doing...if they offer the 390 in their new MX line you will see a ton of ...more

Yes, Beta is offering a 390, and Husaberg offered one in their 70* engine some years back.

I have rode the Husaberg 390 and it wasn't bad.

I have only rode 2 stroke Beta's and I won't be buying one. I'm sure it is a decent bike but the 3 people near me who have them have all had problems with the electronics on them.

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Shout out to: Fly Racing, X Brand Goggles, Kenda Tire, Nuetech Nitromousse, ProTune Suspension, Motool, Sunstar Sprockets, and Rehmerts Kawasaki KTM

Instagram: WoodsRacer126

5/6/2021 8:38 AM

mx317 wrote:

Piston speed limits RPM ceiling. A shorter stroke will allow more RPMS and keep piston speed down. So a shorter stroke and ...more

To illustrate your point, using KTM bores and stroke to give piston speeds in metres per second. Threw the YZ400F in at the end for comparison too.
Hope I got those formulas right. unsure
Photo

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5/6/2021 8:52 AM

WDSRCR wrote:

I keep wishing a company would release a kit like RedMoto's 400RX for my KX450X. I have both, a KX250X and KX450X, and I'd ...more

Black Diesel Bomber wrote:

You guys are wanting exactly what Beta is already doing...if they offer the 390 in their new MX line you will see a ton of ...more

WDSRCR wrote:

Yes, Beta is offering a 390, and Husaberg offered one in their 70* engine some years back.

I have rode the Husaberg 390 and ...more

Which model and what years for the electrical problems?

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