380 BHP/Liter...40 years ago

[Jinx]

The amazing Suzuki RP 68 50cc Grand Prix Triple



Rotary Valve two-stroke with 3-cylinders in a V configuration (2 horizontal...1 vertical)..each yielding 16.6 cc (that's 1 cubic inch) of raw stump pulling torque



Actually, all 3 couldn't pull the cap off your head....but at 20,000 rpm it made 19 BHP

And it had a power band narrow and sharp enough to cut diamonds

So how to keep it on the boil? How about a 14 speed gearbox



Specs?

Bore = "Not much"



Stroke = "Pretty much fuck-all"





Racing record....nada. Never raced in anger as the FIM changed the rules that year to limit 50cc bikes to one cylinder and six gears.

Pity

[Bloodweiser]

that's cute

[WB-PDX]

Stellar! Thanks for posting this!

What is it using for fueling? I don't see any carbs...

[Jinx]

Originally Posted by WB-PDX

Stellar! Thanks for posting this!

What is it using for fueling? I don't see any carbs...

Sadly, there are almost no photos of the complete bike available...it is the holy grail of teacup GP bikes. Since the bike itself had no racing history, Suzuki probably crushed it when the rule changes made it a technical dead-end

But you can see where the inlet manifolds mounted over the rotary valve covers...



...(the other rotary valve is, of course, on the other side of the engine)

The previous year's twins used carbs with remote floats, but the triple used Mikuni VM monoblocks. And I am going to crawl out on a limb here and guess that they were...

...really fucking small

Here is a picture of the LH side of an RS 67 (125cc V-4) which shows how the carbs were probably arranged



The bike was an amazing piece of engineering: The shot below shows how oil lines fed all the critical parts directly (Main bearings, gears, transmission, etc). A far cry from pre-mix and hope for the best. I count 9 lines coming off a single pump



A pity it never turned a wheel in anger. It was reported that Suzuki had plans to develop it to 25K RPM, though they thought the powerband would be so narrow (less than 500 RPM) that an 18 speed gearbox would be required to achieve those speeds. Cheers.

[WB-PDX]

I love this thread.

[norton73]

Originally Posted by WB-PDX

I love this thread.

Me too. There was some amazing stuff coming from out back then.

[ROSKO]

I've been chasing shadows with the classic 50cc racing itch for a few years now. Finally started building my own chassis this year. Really amazing to see the technology that came out of a world class 50cc series. Imagine moto gp with 50's. Crazy stuff. Lots of homebuilt specials up against the big companies, think jamathi, hemelya, etc. Space frames, monocoque, crazy gearboxes and retarded engine speeds. Shite, the landspeed record for 50cc was just broken this year, kreidler held it since their one visit to bonneville 60's! In europe they are seeing a resurgence of this class in classic road racing and here in the states the USCRA has the only classic/ supervintage/ modern 50cc classes that I know of. WERA also runs a 80gp class which is mostly cr80's dropped into rs/tz125 chassis. Very cool. If anyone is interested to find out more there is an AWESOME thread on the whole era over at the f1 forum: http://forums.autosport.com/showthre...threadid=98711

I can't even imagine the sound that came out of this little thing at 20,000+ rpm... pound for pound it puts an f1 to shame I'm sure.

[Jinx]

So what drove the Suzuki lads at Hamamatsu to such flights of engineering extremes?

Well, we would think that Yamaha would have been their natural rival. But for some reason Yamaha never had much interest in 50cc racers.

Nope...it was mighty Honda. Specifically the RC115 50cc Twin...all 130 lbs of it



And the later, even faster, RC116



Think Honda was playing around? That is not a giant front brake...that is a wheel fairing. The actual brake was a bicycle type arrangement that acted on the aluminum rim. And deep sumps are not something people invented in the last decade



But Honda was always about the engines, and they reached their pinnacle in the 1960's with the RC116

Bore = 35.5 mm

Stroke = 24.14 mm

16.5 BHP @ 21,500 RPM...Redline at 22,500 RPM

And that is 320 BHP/Liter





Yes...that's a dry clutch

Yes...those are flat-slide semi-downdraft carbs (And, yes, they are Keihins. Just 40 years older than the FCR model they sell today)

And yes...it is mostly magnesium (except, obviously, the cylinder head)

And just because the cylinders were little didn't mean Honda was going to go all cheap-ass and crude. It is still a four valve per cylinder design...they just happen to be very small valves (13mm In / 11.5 mm Ex...3.5 mm stems)



It amazes me today when I see sharp edges on piston crowns...Honda knew better. They were also making the transition to much narrower valve angles...56 degrees by now. Yes, even narrower is better...but not in an air-cooled engine. Close the angle between the valves of an air-cooled engine much less than this and you can't cool it properly.

[Jinx]

Originally Posted by ROSKO

I've been chasing shadows with the classic 50cc racing itch for a few years now. Finally started building my own chassis this year. Really amazing to see the technology that came out of a world class 50cc series. Imagine moto gp with 50's. Crazy stuff. Lots of homebuilt specials up against the big companies, think jamathi, hemelya, etc. Space frames, monocoque, crazy gearboxes and retarded engine speeds. Shite, the landspeed record for 50cc was just broken this year, kreidler held it since their one visit to bonneville 60's! In europe they are seeing a resurgence of this class in classic road racing and here in the states the USCRA has the only classic/ supervintage/ modern 50cc classes that I know of. WERA also runs a 80gp class which is mostly cr80's dropped into rs/tz125 chassis. Very cool. If anyone is interested to find out more there is an AWESOME thread on the whole era over at the f1 forum: http://forums.autosport.com/showthre...threadid=98711

I can't even imagine the sound that came out of this little thing at 20,000+ rpm... pound for pound it puts an f1 to shame I'm sure.

Very cool...thanks

Never know what you will find on the interwebs

[norton73]

Edmucate the unwashed masses

[ADV8]

Great thread for sure.

Hugh Anderson

Year	Class	Classification	Machine	Victories
1960	350 cc	7th	AJS	0
1961	350 cc	-	Norton	0
1962	50 cc	7th	Suzuki	1
1962	125 cc	-	Suzuki	1
1962	350 cc	14th	AJS	0
1963	50 cc	1st	Suzuki	2
1963	125 cc	1st	Suzuki	6
1964	50 cc	1st	Suzuki	4
1964	125 cc	-	Suzuki	3
1965	50 cc	3rd	Suzuki	1
1965	125 cc	1st	Suzuki	7
1966	50 cc	4th	Suzuki	0

I wonder if any of the technology Suzuki "borrowed" from MZ went into the 50cc,the 125 certainly went faster overnight and later on, the RGB500 (two MZ 250's)

[Jinx]

What could we do today?

Maximum output of a 50cc engine using "today's technology"!

The expert:
"The best horsepower we attained at Aprilia last year (2007 125cc GP) was 53.9 HP at 13,000 rpm. This means a Pme of 14.88 at a piston speed of 23.6 m/sec. Using these same values means that a single cylinder 50cc would give 29.5 HP at 17,850 rpm and a 50cc twin would give 39 HP at 23,600 rpm, measured at the gearbox output shaft. I am 100% sure these values can be attained although it never will be proved due to lack of interest and money. Remember that 50cc development was stopped in 1983 and enormous progress was made in the following 24 years. Now, sadly, also the development of the 125cc two strokes has stopped, the two stroke will only survive in karting but there will be no progress because of the very strict regulations!" - Jan Thiel 2008

Soooo...anyone up for a 45 BHP 50cc triple?

A most excellent tiddler site

Superb site for 1960's GP Honda

[ROSKO]

for anyone humbled by the homebuilt specials of the day, Herman Meijer(sp?) who made the ENGINE, TRANS and CHASSIS of the hemelya 50cc GP bike has a website documenting the build, tech and design of the machine. For the weekend builder/ machinist/ welder/ racer this is very inspirational, pardon the long link site is dutch and I list the googledtranslation... check it out:
http://translate.google.com/translate?client=tmpg&hl=en&u=http%3A%2F%2Fwww.hermanmeijer.nl%2Fhemeyla%2Fver taal%2520uk.html&langpair=nl|en

monoshock:

rotary:

no factory, this is homeshop made:

watercooling:

how does a homemade six speed work?
http://www.50c.nl/animatie-2.html
and of course the chassis:


anyway, I could go on and on. I have over 400 50cc images saved on my hard drive. Talk about nerding out eh??

[mark1305]

Those 50cc machines fascinated me back in their heyday in the 60s, and still do. The Youtube clip from thre IOM TT is priceless.

In the mid-2000s Honda was selling a reissue of their CR110 labeled the Dream 50R. (For about $10 Large, IIRC). Strictly a race bike, I saw one in action when I rode in the 2005 True Grit Rally. A young man from Japan had managed to bring one over, get it tagged somehow for the event, and rode it.

Here are some pics that barely show it after the Rally

The owner/rider from Japan brought an interpreter with him from Japan since he spoke little or no English. That's dedication to an event!


My old YSR50 next to it Wish I had taken more pics of it. I was in awe of it. It looked just like the '62-67 CR 110 50cc GP bikes. (Except for the required legal stuff like mirrors and lights)

[Bloodweiser]

this is one of the greatest things I've been introduced to in a while

Rosko - that link didn't work for me. sounds really interesting though.