Scooterotica

Adspeed wrote:

156 D wrote:
Looks as though you`ve covered everything then?........

Not exactly - I did ask what the theory is behind this crank producing a better gas flow........?

I suppose really its easiest if i think about it this way......reduction of crankweb mass = increased area for more mixture/gasses.....vs increased web masss = less area for mixture/gasses. Also, as the crankcase is housing the mixture that flows thorough the engine....it needs less 'flat' faces and surfaces (restricting flow) and more smoother/rounder edges and corners to aid flow in....and flow out of crankcase.

The crankcase area is not a sealed unit, and is not excluded from the gas flow process.....its part of it, so anything that eases that transition must therefore help. So its surely arguable that a reduction in crankweb mass will increase area for mixture, plus the reduction of 'flat' surface faces (the crank web edge) that restrict flow, and the use of tapered edges that to increase flow (reduction in an area of resistance) should........well.....improve gas flow.

Combine that with a small reduction in PCR and a reasonable reduction in rotating mass and we should see an improvement over a standard crank...........maybe?

Anyway...................we can be judged by the forum-masses, based on the results of my back to back dyno run when i compare the same engine with 2 cranks.

Avantone wrote:So Guys, will you be doing a direct comparison between the modded crank and a full circle item when completed in the same dyno session to properly assess it?

The crank is a fine piece of work, and it would be really interesting to see how it does.

Yes mate, my new dyno is arriving in approx 3 weeks.....which should be about the time the scooter is built and getting run in.....so we'll get stuck in with some tests.

Looking forward to the dyno results

bit excessive thou, a dyno for home use

Well, from what I have read here, I can see one common factor, every one appears to agree that Primary Compression has an Influence on the Tunning of a Twostroke engine. and most are in agreement that the modified crank will have an effect on the running of the engine (balance/vibration). but as these crankshafts webbs are fitted to all lengths of rod and all makes of pistons currently fitted to RB's, TS1's, Rapidos etc, surely they are rarely balanced to suit any one application. (I would hazard a guess that it's no better or worse balanced now than in its original unmolested state). With this modification I would expect it to rev higher due to it having a lower rolling mass and being more gas flowed. I also think if its a high revving motor, a high primary compression would be a dissadvantage. but we wont really know till its run. I for one have never thought of doing this type of modification not because I wouldnt do it just cus ive never thought of it, I like what I see here... I hope it goes well...

davidblythe wrote:bit excessive thou, a dyno for home use

Says who?

Its not just for home use.....will be as much for customer dyno runs as out own development time.

J1MS wrote:Well, from what I have read here, I can see one common factor, every one appears to agree that Primary Compression has an Influence on the Tunning of a Twostroke engine. and most are in agreement that the modified crank will have an effect on the running of the engine (balance/vibration). but as these crankshafts webbs are fitted to all lengths of rod and all makes of pistons currently fitted to RB's, TS1's, Rapidos etc, surely they are rarely balanced to suit any one application. (I would hazard a guess that it's no better or worse balanced now than in its original unmolested state). With this modification I would expect it to rev higher due to it having a lower rolling mass and being more gas flowed. I also think if its a high revving motor, a high primary compression would be a dissadvantage. but we wont really know till its run. I for one have never thought of doing this type of modification not because I wouldnt do it just cus ive never thought of it, I like what I see here... I hope it goes well...

A believer!!!!

you going into business then Dan

drunkmunkey6969 wrote:

Adspeed wrote:

156 D wrote:
Looks as though you`ve covered everything then?........

Not exactly - I did ask what the theory is behind this crank producing a better gas flow........?

I suppose really its easiest if i think about it this way......reduction of crankweb mass = increased area for more mixture/gasses.....vs increased web masss = less area for mixture/gasses. Also, as the crankcase is housing the mixture that flows thorough the engine....it needs less 'flat' faces and surfaces (restricting flow) and more smoother/rounder edges and corners to aid flow in....and flow out of crankcase.

The crankcase area is not a sealed unit, and is not excluded from the gas flow process.....its part of it, so anything that eases that transition must therefore help. So its surely arguable that a reduction in crankweb mass will increase area for mixture, plus the reduction of 'flat' surface faces (the crank web edge) that restrict flow, and the use of tapered edges that to increase flow (reduction in an area of resistance) should........well.....improve gas flow.

Combine that with a small reduction in PCR and a reasonable reduction in rotating mass and we should see an improvement over a standard crank...........maybe?

Anyway...................we can be judged by the forum-masses, based on the results of my back to back dyno run when i compare the same engine with 2 cranks.

Thanks for that Dan, I'm not so sure, but thats what forums/discussions are about hey

davidblythe wrote:you going into business then Dan

I'm hedging my bets David.

I'm buying a dyno for personal use/tuning development, and installing it at Seans very busy scooter workshop and offering a full dyno service. I have a Mon-Fri job that is difficult to walk away from, as i'm a family man with the usual wife/kids/mortgage to support.....so working in a scooter workshop in evenings and weekends, on something that i enjoy will be a pleasure.

Im a technically profficient chap, i understand tuning theory to a good level, i work with Sean as he applies his skill to my engines and i race them, i also build my own engines, and i will revel in the combination of technology and engine performance/tuning that only a dyno can provide.

So its win-win....i get to ease my way into the scooter business at the level of both work and pleasure, without compromising my home commitments, and Seans customers get a cracking service!

Adspeed wrote:Thanks for that Dan, I'm not so sure, but thats what forums/discussions are about hey

No worries bud.

Out of interest (dare i ask!!!) what are your objections/opinions as to why it wont work?