ESE's works engine tuner

[husaberg]

Are 'big bore' cylinders really that good?
At Aprilia some of the boys working with me fitted big bore cylinders to their Rotax engined bikes.
The result was always the same: less power.....
Because of the big bore made a mess of the transfer ducts!

likely true Jan an engine should be designed and engineered for its size, to limit space compromises.
The class where i was discussing their racing use is NZ F3. (Yeah i know its not the name now)
Due to a rule change a few years ago it now allows 2t multis up to 400cc as long as they have road based crankcases.
GP bikes are only allowed to be 125's
As most of the later 2T bikes are 250cc such as RGV250 or NSR250 this is why they go the big bore route.
the 4ts they compete against are 450 multis old VFR400's bored out etc plus 600/4 with one cylinder disabled. \or 650 twins SV650 etc
The RZ350 is one option Wob has done. He was also doing a NS400 with cr based cylinders for someone
I think you might have gone with the RG400 which is the small bore version of the RG500.

[Lef16]

Jan, can you tell us about the cylinder casting(aluminum type,casting procces,heat treatment after etc)?

[Tim Ey]

Are 'big bore' cylinders really that good?
At Aprilia some of the boys working with me fitted big bore cylinders to their Rotax engined bikes.
The result was always the same: less power.....
Because of the big bore made a mess of the transfer ducts!

Hi Jan, if you refer to the Polini cylinder for the Rotax 122 and 123 - the lower Power is caused by reduced port timings compared to Rotax barrels.
The timings are still quite low when you combine the Polini for the 123 with a 56mm crank. Without spacering the head insert...

[Tim Ey]

I can't see youtr picture but nsr125 heads don't bolt on to NSR250 even though the cylinders can be fitted to each other

That was a PDF. Did work for me?!
Anyway, this is the picture of the head I want to build.

Would be interested if NSR250 is a match and I do not need to do the CNC Milling.

Regards
Tim

[monkeyfumi]

Thats just silly much easier to use RG150 (i know the UK had them as Grey imports) ones or better yet modded Artic Cat ones

Have you tried finding RG150 or arctic cat cylinders? Absolute hens teeth compared to standard RGV250 (especially as most people use the ones they already have on the bike)

Off the shelf kits using 250 cylinders have been sold by a couple of places, 150 or arctic cat is all DIY.

As I said, it's all a big compromise anyway, as it makes an already oversquare engine more so, and as Jan commented, takes a big chunk out of the transfer ducts.

[1948rod]

Have you tried finding RG150 or arctic cat cylinders? Absolute hens tehieth compared to standard RGV250 (especially as most people use the ones they already have on the bike)

Off the shelf kits using 250 cylinders have been sold by a couple of places, 150 or arctic cat is all DIY.

As I said, it's all a big compromise anyway, as it makes an already oversquare engine more so, and as Jan commented, takes a big chunk out of the transfer ducts.

Hi I had hoped that I could use to 350 Pistons in the spare cylinders on my tza 250 engine hoping it would have better torque for hill climbing or second choice big bore on my rev. I wouldn't modify the Tz cases so it could be reused for historic bike races.

[wobbly]

Does anyone know of a TZ250G cylinder that is unusable.
I want to section one up the Ex port to look at whats needed for to add Aux for a LSR engine.

[kel]

I have a question: Does an owner of a Honda NSR250 cylinder or head may print this out
Attachment 331151
and check if bolt patern and other dimensions are a match?
TeZee probably?

Thanks a lot!
Tim

No they are not a match. See attached NSR250R MC21 cylinder and head gasket photos.

[2T Institute]

Thats just silly much easier to use RG150 (i know the UK had them as Grey imports) ones or better yet modded Artic Cat ones


I can't see youtr picture but nsr125 heads don't bolt on to NSR250 even though the cylinders can be fitted to each other



Google vincent crabtree rgv250 big bore
http://www.apriliaforum.com/forums/s...-Kit-E-Mids-UK
http://www.apriliaforum.com/forums/s...ankshaft/page4
https://sites.google.com/site/vpcrab...ki-rgv250-vj21
https://www.kiwibiker.co.nz/forums/s...post1130586696
https://www.kiwibiker.co.nz/forums/s...post1131030948





You were going to try modding a RG250 crank to go in a RGV weren't you?

Yes just the cylinder to do. Though I have seen in Italy a fellow fitted RS honda cylinders. RM 125 would be a good start

[TZ350]

MC21 stud pitch circle is 88mm, outside diameter 104mm with studs evenly spaced.

The MC18 is different to the 21 and the NSR125 has an uneven spacing of the studs compared to the 18.

[2T Institute]

Are 'big bore' cylinders really that good?
At Aprilia some of the boys working with me fitted big bore cylinders to their Rotax engined bikes.
The result was always the same: less power.....
Because of the big bore made a mess of the transfer ducts!

Have made a 288cc Rotax that was 6 hp/4 ft/lbs torque more than the 250cc that diminished down to the same peak power at the same rpm. A full 350 is under construction. Big bores tend to make way more mid range.

[2T Institute]

Does anyone know of a TZ250G cylinder that is unusable.
I want to section one up the Ex port to look at whats needed for to add Aux for a LSR engine.

Contact Craig Stafford on FB his dad Don was a Yamaha dealer for many years and was recently selling a big box of that era TZ stuff

[Ocean1]

Does anyone know of a TZ250G cylinder that is unusable.
I want to section one up the Ex port to look at whats needed for to add Aux for a LSR engine.

Is it difficult to justify this?:

https://www.dotmed.com/listing/ultra...be-3dx/2281218

[husaberg]

Have you tried finding RG150 or arctic cat cylinders? Absolute hens teeth compared to standard RGV250 (especially as most people use the ones they already have on the bike)

Off the shelf kits using 250 cylinders have been sold by a couple of places, 150 or arctic cat is all DIY.

As I said, it's all a big compromise anyway, as it makes an already oversquare engine more so, and as Jan commented, takes a big chunk out of the transfer ducts.

Ebay is full of zrt600 arctic cat cylinders.
for the RG150 cylinders try the asian countries where they were sold. Like Thailand
NZ had quite a few, More than the 125's but the 150 streetstock racing class has swallowed them.

[monkeyfumi]

Ebay is full of zrt600 arctic cat cylinders.
for the RG150 cylinders try the asian countries where they were sold. Like Thailand
NZ had quite a few, More than the 125's but the 150 streetstock racing class has swallowed them.

A moot point, as I'm not interested in big bore kits. Just wanted to correct your assertion that RGV300 are usually done with 150 cylinders, when overwhelmingly, they are not.