Imagination and thought experiment – Page 4

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Imagination and thought experiment

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Thread: Imagination and thought experiment

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08-16-2011, 11:55 AM #46

Stuboy911

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you can compensate with a different design, shape look at the old Gp250 / 500 bikes. the rear pipes at the top of the rear seat. the length is a lot different. its all about the centre chamber. take a standard V twin ( rs250 / VJ22 / 23 ) chamber size is different to take into consideration the difference in distance from each cylinder to the rear.. or a Moto cross bike.. it can be done, and has been done.
plus a CR500 standard engine is about bottom end grunt.. where a road bike tends to have more top end.

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08-16-2011, 12:30 PM #47

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Damn…..that guy might as well chuck the whole project in the trash!! http://2wheelwiki.com/wp-content/uploads/2014/12/

Seriously if virtually every twostroke bike with an expansion chamber has pipes with kinks and curves to fit the bike, then a few extra will just be par for the course! Just looking at the squiggles needed for the KTM Mito project! Guess he’s lucky to only have a V twin without the extra pair of cylinders to fight for space over!! http://2wheelwiki.com/wp-content/uploads/2014/12/

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08-16-2011, 12:46 PM #48

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something like this…

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RS250 2000
RS250 2001

http://www.youtube.com/watch?v=Dn0o3tc6T_s

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08-16-2011, 08:24 PM #49

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plus a CR500 standard engine is about bottom end grunt.. where a road bike tends to have more top end.

Tuned length is longer for lower RPM, so for that rear pipe it’s going to look like a snake swimming

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08-17-2011, 04:11 AM #50

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Yes, that’s another question the owner of the prototype didn’t ask himself.

Why put a low-grunt engine on a road bike ?
Road bike you want mid-top end power, of course low-end is always good ( throttle response since low-revs ), but the main is mid-top end.
The gearbox for that kind of engine must be a 6 wide

Another problem, that the owner probably didn’t ask himself, the vibrations .. if 1 CR 500 vibrates a lot .. how would it be 2 x CR 500 ? Even with crankshaft balancers ..

This is the length of my tuned pipe for Polaris ” 400 ” ( 86mm x 70mm ) for 8600rpm max with a 14cm belly diameter. ( FMF / Pro-Circuit etc for CR 500 has a maximum ~12cm – 12.5cm belly diameter )

It would fit on the front cylinder of that Aprilia RSV ” 1000 “, but it would be almost impossible to fit on the rear cylinder .. there’s simply no space available, even making like a ” snake ” ..

If that pipe, with short length because of 70mm stroke & 8600rpm ( a CR 500 doesn’t rev until 8600rpm ) would have problems fitting on that prototype .. how could a 79mm stroke engine and length to ~8000rpm fit .. ? http://2wheelwiki.com/wp-content/uploads/2014/12/

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08-17-2011, 06:33 AM #51

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I say ditch the subframe, compress the rear suspension to max and start playing with those crayons!! Might have to double back a bit like the ones on scoots and old peds!!

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08-17-2011, 06:46 AM #52

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http://2wheelwiki.com/wp-content/uploads/2014/12/ Originally Posted by scottydog http://2wheelwiki.com/wp-content/uploads/2014/12/

Might have to double back a bit like the ones on scoots and old peds!!

Yep that’s how HRC increase the length of the rear cyl pipe on the RC212v
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(Yes i know that’s a 4 stroke http://2wheelwiki.com/wp-content/uploads/2014/12/ )

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08-17-2011, 07:20 AM #53

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Another approach to the rear pipe would to be point it straight up from the end of the fairing and fly a flag from it – it’s going to be tall enough!!

But I do feel a little guilty making fun of it like that because it dismisses the simply brilliant quality of his work

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08-17-2011, 09:32 AM #54

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It’s a complete different league building 2-Stroke performance pipes comparing with 4-Stroke headers ..

4-Stroke headers are simply tubes with little variations on diameters, the artwork are in the curves itself and the welding.

On a 2-Stroke pipe, you have to respect not only lengths of the sections ( initial curve, pre-belly, belly and final cone ) but also the respective diameters.

If you have a CR 500 pipe starting with 52mm diameter ( almost the same as many 4-Stroke performance headers), then it grows to 100mm on the pre-belly, 150mm on the belly and then the cone goes to 35mm, this is very difficult to achieve in a ” snake curve alike ” exhaust ..

Also, you have to have in mind the available space bellow the frame and the bodywork .. the height bellow the frame and the road ..

That’s why that awesome GSX-R 800 snowmobile 2-Stroke engine has pipes with a ridiculous diameter .. like 11 – 11.5cm belly … lol

Each 400 cm3 cylinder of that bike could easily have fitted a performance exhaust with 14 – 14.5cm belly .. but then the pipe won’t fit the bike… http://2wheelwiki.com/wp-content/uploads/2014/12/

On 4-Stroke headers you can build them like in that HRC photo, making curves that the performance is not affected, the diameter of that final header just looks like the same, it doesn’t vary, the only concern on that header is the length …

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08-17-2011, 11:20 AM #55

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It just becomes a compromise in design, should be good to see what the pipe designer comes up with!

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12-29-2011, 01:13 AM #56

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As Ricardo says, it can be a challenge to fit 2T pipes to existing bikes fitted with aftermarket big-bore/long-stroke engines. Especially when trying to fit said pipes within the confines of stock bodywork!

And realistically this isn’t surprising, when what we are doing is fitting engines of double or triple the capacity of the original motor, to the same bike!

Take the example of the RS500 – with the max 123mm dia belly of the pipes, the only way to fit these pipes without compromising ground clearance was to make a new shock rocker arm (or mod the existing one) and new dogbones, to make enough room for the bigger pipes:

http://2wheelwiki.com/wp-content/uploads/2014/12/

If much bigger on the belly/much longer on the length – say for instance if we’d wanted to fit a 64mm stroke, 78mm bore monster in there – cor blimey it would have been a devil of a job to get pipes of optimum dimensions to fit.

And then there’s the inevitable choice – do you (A) Scale back on the bore and/or stroke of the mill so as to give yourself a chance to fit optimised pipes, or (B) Go ahead with the bigger mill but with the sure and certain knowledge that pipe design will need to be compromised.

In the case of engines of bigger displacement again – 1000cc or 800cc twins, there’s little hope of getting pipes to fit any ‘conventional’ motorcycle chassis without an obviously bulbous look, and even then the pipes are going to be too long to be legal for road or track use.

The only feasible way forward when fitting big 2T engines to existing bikes, I believe, is to employ direct-injected engines – which can get away with pipes that are not 100% optimised because with DI there is no escaping of fresh fuel/air charge into the exhaust. No longer is the pipe design the absolute imperative for getting good performance out of two-strokes.

The same basic rules of pipe design hold true for DI engines but the dimensioning is being done for different reasons, i.e. mostly to give a good hard scavenging ‘suck’ to bring as much air into the cylinder as possible/ to release spent exhaust gases. This is how come turbos can be used on DI systems, i.e. because there is no longer any danger of forced induction blowing fresh fuel/air mixture out of the exhaust port. The more air in there, the better. Providing the injection is calibrated to suit.

There are other considerations to be made when dimensioning pipes for DI engines and it depends on the DI system being used. I’m involved with a company that is developing an 800cc DI twin with a superbike transmission – this is more for fitting into bikes such as ZX-10Rs rather than RS250s – but there is the possibility of a 600cc version later on down the track. And possibly a DI version of the RS500, we shall have to see. In any case it would need two injectors per cylinder to achieve the required delivery rate for this application, i.e. 10,500rpm.

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12-29-2011, 05:40 AM #57

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Google ‘VW Direct Injection problems’ if you think DI is a way forward.

If jesus had ridden,he would have rode a two stroke

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12-29-2011, 07:55 AM #58

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Like the old adage says, “If it’s got tits or wheels, it’ll give you problems.”

Every fuelling system has its pros and cons. Only the individual owner can make a call as to which system to go for.

Early DIs did suffer carbon build-up issues but these appear to have been solved in later versions; and as the article on this page points out, the build-up issues were particular to poppet-valve four-stroke engines.

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12-31-2011, 02:01 AM #59

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How about V4?

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12-31-2011, 05:22 AM #60

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powers the martin jet pack

If jesus had ridden,he would have rode a two stroke

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