Sunday Ride Classic creates a 309-lb, 88-rwhp, two-stroke sportbike…
By the 1980s, the days of street-legal two-stroke sportbikes were limited. A combination of emissions regulations, noise ordinances, and the continued evolution of four-stroke performance engines would sound the death knell of the two-stroke streetbike. Today, rumors abound of smokers making a modern return — Kawasaki, in fact, filed a patent for a supercharged two-stroke four-cylinder engine just this year.
While we await news of a two-stroke rebirth, our new friend Jean Pierre Bonato (“JP”) — organizer of annual motorcycles events like the Sunday Ride Classic and Alpes Aventure Motofestival — has decided to take matters into his own hands. His idea was to create a modern two-stroke sportbike that would look and seem like a factory-made machine:
“The spirit of the 475 was to imagine a modern 2-stroke sport bike. The aim was to have a standard bike built exactly like a constructor’s catalog bike: street-legal with big mirrors, not a replica with race numbers plates and so on…”
In order to transform this dream into a reality, he enlisted the help of two friends with deep experience building race bikes, mechanic Varm’Up Moto and fabricator Kerlo Classic. They started with the chassis from a 1999 Aprilia RS250, one of the last street-legal two-stroke sportbikes. To power the machine, they went with a very special engine, the liquid-cooled two-stroke 90° V3 from a 1984 Honda NS400R. Like most engine swaps, it was easier said than done:
“It was easy to imagine and design the bike, but it was not so easy to organize enough room for the three carbs, for all of the electric parts…the bike is really full!”
They didn’t leave the NSR engine stock, either. It’s been bored to 470cc, complete with carbon reeds, digital ignition, Keihin carbs, Terry Shepherd exhaust, and more — good for 88 bhp @ 9885 rpm! The suspension and brakes have been brought up to modern spec as well, making the “SRC 475” a hoot to ride:
“The pleasure of a really light bike with the 2-stroke character and sound!”
We especially like how JP changed the logo from HRC to SRC, which is the name of the event he organizes each year: Sunday Ride Classic — and also mixed the Honda and Aprilia logos in a very slick fashion:
“Honda (engine) gives wings to the Aprilia (chassis)…”
All in all, the SRC 475 is the dream of a modern two-stroke sportbike brought to fruition. Below, we get the full details on the build straight from JP himself.
“Aprihondia” SRC 475 V3: Builder Interview
• Please tell us a bit about yourself, your history with motorcycles, and your workshop.
I’ve been organizing classic meetings since 2009. I’m a collector, but sometimes I also like to create special bikes. The 475 is one, for example I’ve also created a Scrambler based a 1000cc TR1 Yamaha.
The “spirit” of the 475 was to imagine a modern 2-stroke sport bike. The aim was to have a standard bike built exactly like a constructor’s catalog bike: street legal with big mirrors, not a replica with race numbers plates and so on…
If someone looks at the bike on a street close to a motorbike shop, he could be confused and enter the shop to ask about the manufacturer’s new bike. For example, we put the 2-stroke oil pump and small tank in the tail of the bike like a standard street bike…
The Aprilia RS250 was one of the best modern compact frames to start the project. And it also has the classic swingarm with the banana shape typical of the last 500 GP bikes.
To make a compact anonymous bike, I chose the V3 Honda 400 NSR engine because it’s light and compact, and also because there’s already a huge number of tuned bikes with the Suzuki RG500 or the Yamaha RD500LC engines.
It was easy to imagine and design the bike, but it was not so easy to organize enough room for the three carbs, for all of the electric parts…the bike is really full!
• What’s the make, model, and year of the bike?
Chassis: Aprilia RS250 (1999)
Engine: Honda NSR 400 (1984)
• Why was this bike built?
It was 50% a personal pleasure and 50% for event promotion.
• What custom work was done to the bike?
- Created a special subframe to install the engine.
- Ohlins shock.
- New internals for the forks.
- Beringer brake system with a hand rear brake at the handlebar.
- Tyga footrests.
- From 387 to 470cc with big pistons and special tuned cylinders.
- New carbon reed valves in the Boyensen spirit.
- New parts in the gear box: 2nd/3rd/4th are closer.
- New digital ignition.
- 32 mm carbs Keihin from 250 Honda NSR MC 18.
- 3 Terry Shepherd exhausts.
We’ve also created and tried a 120° “screamer” crankshaft and ignition with Guy Bertin, who was a big French GP rider with a lot of technical knowledge, but the power came on too hard, so we went back to the stock 90° “big bang” crankshaft.
The bike uses TYGA parts, with a lot of changes. For example, the little LED red light at the rear, just to give some room for the 3rd silencer.
• Does the bike have a nickname?
“SRC 475 V3.”
• Can you tell us what it’s like to ride this bike?
A huge pleasure. 140 kg for 88 bhp @ 9885 rpm, and with the new ignition the bike is easy to ride, with smooth throttle response.
The pleasure of a really light bike with the 2-stroke character and sound!!! The power is not so important but the feeling of the bike is really interesting because of the quality of the chassis and the weight/power balance.
• Was there anything done during this build that you are particularly proud of?
…to have finished it !!!
Also, changing the logo from HRC to SRC, which is the name of the event: Sunday Ride Classic 😉
If you look at the fairing, there’s a logo RS on the side, because RS is the only model name in common between Honda and Aprilia. And if you look at the logo on the tank I have mixed the two logos also: Honda (engine) gives wings to Aprilia (chassis).
Follow the Builders
The Mechanic: Varmup Moto
The Fabricator: www.kerloclassic.com
Pictures from me, and from Boris Meyer (the ones on the track)