The 50

[F5 Dave]

Gosh. Maybe Frits and engmod know more than me. Do ya think?

[richban]

Gosh. Maybe Frits and engmod know more than me. Do ya think?

Ha. Well I am going to re measure everything again soon. But looks like close to 20hp is not that far away.

[husaberg]

Google told me
http://www.mopedarmy.com/wiki/Moped_and_scooter_stud_spacings

he told me this too
http://www.apriliaforum.com/forums/archive/index.php/t-242814.html



http://www.mopedarmy.com/wiki/Moped_..._stud_spacings

Cheers Husa but this only tells me what wont fit , I already found that one. I was hoping that the Aprilia RS had the same spacings and one of our Euro friends confirmed it for me

Er....that second link half way down the page.

[cotswold]

My SR50 now has an RS50 cylinder, not too difficult to make fit, just a couple or three hours with a dremel, have been gifted an RG50 frame which I'll put my NF4 front into but the rear wheel is going to take some work

[sonic_v]

My SR50 now has an RS50 cylinder, not too difficult to make fit, just a couple or three hours with a dremel, have been gifted an RG50 frame which I'll put my NF4 front into but the rear wheel is going to take some work


What stroke are you running?

[cotswold]

What stroke are you running?

I'll stroke it to the stock Aprilia RS50 Bore x Stroke, 39,86 x 40 mm.
it has an after market crank in it but would want the big end upgraded so would stroke it at the same time to make things easier in the long term.

[dark art]

I'll stroke it to the stock Aprilia RS50 Bore x Stroke, 39,86 x 40 mm.
it has an after market crank in it but would want the big end upgraded so would stroke it at the same time to make things easier in the long term.

There are some AM6 engines that have the 40.3 bore x 39 stroke. Always thought the 40x40 is the piaggio engine on newer aprilias.

[Juho_]

I have just started getting my 50 into engmod. A few lessons already. My reeds don't have enough area to make the power I want. Also pipe needs a small adjustment. But that timing of 192 / 130 is hard to beat.
What reedvalve are you using?

Could you tell us, how much your cylinder has blowdown area?
Just curious, because I'd guess the cylinder must have a lot of blowdown area (very wide exhaust port) to be able to reach approx. 20bhp @ 14krpm.
Based on my tests.

And how much power does the engine lose with e.g 198 degrees duration exhaust port, compared to 192 degrees?
If I understood correctly, you meant peak power?

[richban]

What reedvalve are you using?

Could you tell us, how much your cylinder has blowdown area?
Just curious, because I'd guess the cylinder must have a lot of blowdown area (very wide exhaust port) to be able to reach approx. 20bhp @ 14krpm.
Based on my tests.

And how much power does the engine lose with e.g 198 degrees duration exhaust port, compared to 192 degrees?
If I understood correctly, you meant peak power?

Hi There.

Reeds are a Stage 6 setup. Not the vforce version.

I need to go over all the port measurements again to get everything more accurate. The first measure up was not that accurate. More time is needed. I have put the engine back together to go racing. The only change I made was adding lots of exhaust port side angle area. I will also order the Vforce reeds and then dyno it. I will let you know how I go. Re 198 V 192 timing. From memory ether way you went it lost 2 hp on top and 1 hp everywhere.


Thanks Rich.

[Juho_]

Yes, the 'regular' Stage 6 reedvalve is about the same size as stock Minarelli AM6 if I remember correctly.
VForce reedvalve (Stage 6 or Top Performances.. they are very similar, expect the stuffer is different shaped) will make a great difference.

I did some small and quick tests.. and with the VForce (Top Performances) reedvalve power improved everywhere.
Peak power improved +7,6%, running very lean WOT (with stock reedvalve it had been jetted for the best peak power, when hot engine).. ran out of main jets, so ended the testing 'till I get larger jets.


But very interesting results. Thanks for sharing them!
Especially the exhaust port timing. Got me more inspired on trying different exhaust port timings (transfer timing @ 130 degrees) on my engines.

[richban]

Yes, the 'regular' Stage 6 reedvalve is about the same size as stock Minarelli AM6 if I remember correctly.
VForce reedvalve (Stage 6 or Top Performances.. they are very similar, expect the stuffer is different shaped) will make a great difference.

I did some small and quick tests.. and with the VForce (Top Performances) reedvalve power improved everywhere.
Peak power improved +7,6%, running very lean WOT (with stock reedvalve it had been jetted for the best peak power, when hot engine).. ran out of main jets, so ended the testing 'till I get larger jets.


But very interesting results. Thanks for sharing them!
Especially the exhaust port timing. Got me more inspired on trying different exhaust port timings (transfer timing @ 130 degrees) on my engines.

Thanks for the info on the reeds. +7 percent would be nice.

[husaberg]

In the words of the immortal Dave.
Bump..........

[cotswold]

I know it's been pointed out that Aucklands F5 class has started to pick up, mainly due to Team ESE supplying half the field at some of the rounds and me banging on about how cool they are, but there are a couple of others putting bikes on the track this year.
Its a bit tough sourcing donor bikes for the class and lets face it most of the motors used are out of the 80's and are scarce on the ground. My old Honda shitter has been built using custom made parts at some expense as there are no hop up kits, I have had lots of help getting it up to a reasonable standard. I would love to see more screaming 50's on the grid and one way of doing that would be to allow so called race parts to be used, the KTM 50 cylinder is a work of art and fits straight onto the KTM 65 bottom end, parts are cheap and plentiful and lets face it these are kids bikes not works 125's.
There are loads of Aprilia and Derbi bits on the market that are banned because it says race on the box, big end bearings fail on standard crankshafts because they were spec"d for 4 1/2 hp not 14, silver cage bearings are out there but are race parts on a vast majority of them.
How do people feel about a Free Tech class ? the only rules 50cc normally aspirated, 98 pump gas and up to 6 gears.

How cool would a grid full of 2T screamers sound, I know I have not mentioned the 100cc foul strokes and to be honest not sure how free tech would be any benefit to them.

[TALLIS]

I don't think anyone has a problem with a free tech class, as long as it's not the f5 class. Drebis would benefit and it would create new breed of 50 machines, but the other f5 bikes including the 100 4t would be boat anchors there after. Looking forward to see how these things go.

[Bert]

I know it's been pointed out that Aucklands F5 class has started to pick up, mainly due to Team ESE supplying half the field at some of the rounds and me banging on about how cool they are, but there are a couple of others putting bikes on the track this year.
Its a bit tough sourcing donor bikes for the class and lets face it most of the motors used are out of the 80's and are scarce on the ground. My old Honda shitter has been built using custom made parts at some expense as there are no hop up kits, I have had lots of help getting it up to a reasonable standard. I would love to see more screaming 50's on the grid and one way of doing that would be to allow so called race parts to be used, the KTM 50 cylinder is a work of art and fits straight onto the KTM 65 bottom end, parts are cheap and plentiful and lets face it these are kids bikes not works 125's.
There are loads of Aprilia and Derbi bits on the market that are banned because it says race on the box, big end bearings fail on standard crankshafts because they were spec"d for 4 1/2 hp not 14, silver cage bearings are out there but are race parts on a vast majority of them.
How do people feel about a Free Tech class ? the only rules 50cc normally aspirated, 98 pump gas and up to 6 gears.

How cool would a grid full of 2T screamers sound, I know I have not mentioned the 100cc foul strokes and to be honest not sure how free tech would be any benefit to them.


I don't think anyone has a problem with a free tech class, as long as it's not the f5 class. Drebis would benefit and it would create new breed of 50 machines, but the other f5 bikes including the 100 4t would be boat anchors there after. Looking forward to see how these things go.

Good thing is that bucket racers aren't as precious as big bike riders; one could run a class within a class. As long as supplementary rules are written and MNZ are appeased.

Kinda where F4 has already gone, GP spec and production.

[Grumph]

As i see it, you're simply reactivating a class already on the books - open 50cc.

If you want to run it with F5 as it stands, yes, class within a class works.

[F5 Dave]

I'd love to build one but I think the 50 class is not big enough to be divided. I also don't think many will have the aptitude or the budget to build enough. Let's just hope the resurgence wave keeps going and more old bikes can be pried out and more new bikes found.

The RG50 was the FXR of the F5 class. My first GP in the late 80s I came 13th on a borrowed RG. Most of the class was RGs. Going back to my MB was hard but it was all I could afford.

A damn shame more euro 50s weren't imported thereafter.

[lodgernz]

Just a heads-up: Last time I looked at the European Freetech 50 class rules, it seemed that they don't allow any oversize. The limit is 50.000000cc.
That eliminates most old engines, and also means that a seizure bad enough to need a rebore (in an iron cylinder) signals the death of that cylinder you've put 300 hours work into.
What I'm saying is the Freetech rules in their entirety might not suit our culture, and we'd need some Kiwi amendments if we did adopt them.

[lodgernz]

As i see it, you're simply reactivating a class already on the books - open 50cc.


Don't think it is on the books any more Grumph.

[Grumph]

Don't think it is on the books any more Grumph.

Not as such - but as i understand it, if you apply for the 50cc GP title race - as distinct from the F5 GP - that's exactly what you'd be running.
And of course there's precedent for the open 50 GP.

There's also so much precedent now for running multiple classes simultaneously now, it shouldn't raise an eyebrow...

[cotswold]

Time to resurrect the 50cc discussion as it's gone way too quiet of late.
Watch this

https://www.youtube.com/watch?v=HA3nvqRDvxg

Pay especial attention to the revs and water temperature
I think this debunks the oh you have to run the temps higher than that or it will seize debate, I talked to Henri and he is happy to let it run as low as 30 degrees and has done in wet races with no issues apart from having lots of power.
He has dyno checked and tells me you would be saddened by how much you lose by running your bikes at 65 degrees instead of 45
this cold seizure thing from what I can gather happens when the piston expands quicker than it's surroundings, so it makes sense that if you warm the engine up to a good operating temperature in the pits it would be a non problem
enjoy the video, it's how 50cc racing could be out here if we tweaked the rules a little

[F5 Dave]

I have been driven by myths starting with Bell.
But I've never seen that much degradation on the dyno. Often last of three runs is the best and the bike is always hotter then.

But sadly we don'thave the droves of 50 base stock Europe has. I of course think 50s are the best class for sheer willpower to retain speed.
MB5, RD and GT50s were popular with students and apprentice lads. Then the RG50s followed and we're the FXR of the day.
Sadly importers didn't get to the groove of Euro imports and Japs stopped making them.

[sonic_v]

The ACU - Governing Body of Motorcycle Sport in the UK - has sanctioned an official ACU 50cc championship this season.

Recently Mallory Park Circuit had 28 entries for the 2nd round of the championship. This is a full size circuit where the maximum allowable grid size is 32 bikes.

https://www.youtube.com/watch?v=lHITC_-SnPU

First 6 bikes doing 74 mph laps.

[diesel pig]

The ACU - Governing Body of Motorcycle Sport in the UK - has sanctioned an official ACU 50cc championship this season.

Recently Mallory Park Circuit had 28 entries for the 2nd round of the championship. This is a full size circuit where the maximum allowable grid size is 32 bikes.

https://www.youtube.com/watch?v=lHITC_-SnPU

First 6 bikes doing 74 mph laps.

That was some cool racing, At the start I thought the bike we were riding with was much faster than the other two it was racing by the way it caught the other two hand over fist thou the long sweeper but down the straight there was not much in it and in other set corners it got left behind which got me thinking may each bike had a set of gear ratios that really suited one particular corner really well.