i don't think the govenor on the cdi is 8000 because i have seen very
expensive tachometers redline at about 9500 RPM stock on a flat road. i have
gotten my 2000 targa up to 43 down a hill ( a very very steep hill). and
this guy even says, 98 sprint, 40-43. the numbers don't lie. and all these
speedometers aren't wrong.
>Subject: Re: Info on Tomos & Columbia
>Date: Sat, 07 Oct 2000 14:43:52 -0700
> >Before we go any further, I would just like to say that *officially
>speaking* Tomos A5 moped engines were designed specifically to be
>"tuning-proof". They are governed by the intake and exhaust system, thermal
>unit, ignition system and final transmission.
> >Now, theory is the only objective means of estabilishing the facts here..
>Calculated maximum speed at 8000 RPM limit for a Tomos with 13.3426 2nd
>speed total transmission ratio and a tire diameter of 548 mm is exactly 62
>km/h (38.75 mph), wether you like it or not.
> >You have to realize that the CDI in fact HAS to have an RPM limiter of some
>kind to pass the "Tampering Test" obligatory for homologation of the engine
>on the US and most other markets.
> >There is a possibility that your speed measurement isn't 100% correct, and
>in regards to the statements the dealer has made, they can be considered
>false (even provided he has a <1995 moped). Again, the theory shows that an
>engine of a moped with such aerodynamic properties as a Tomos A35 would
>to develop power exceeding 4 kW (5.4 HP) to achieve this speed, which is
>at approx. 10500 RPM. Unfortunatelly, even though the 70 cc cylinder has
>bigger cross-sectional area of the ports as the stock cylinder, the power
>limited by means of the cross-sectional area of the two crankcase transfer
>port openings (again, the "Tampering Test" compliance..).There is also an
>additional awkwardness of the 70 cc cylinder- it lacks the third T transfer
>port due to the non-reed valve design, additionally lowering the transfer
>port cross-sectional area.
>The engine simply cannot pump so much propellant through these two port
>openings to achieve 4 kW output, even though it has longer port opening
>timings after the tune-up.
> >Think of it this way- Imagine two halls (presenting the volume under and
>over the piston), connected to one another by three hallways (presenting
>three stock transfer ports). Each hall also has a massive wooden entrance
>(presenting the intake and exhaust port).
>Imagine 100 people walking through these two rooms (presenting the "stock"
>propellant flow dynamics at 6500 RPM). They go into the first room through
>the massive door, divide to three groups, go through the three hallways and
>exit through the massive door in the second room.
>Now imagine 275 people walking through these two rooms approx. 60% faster
>(presenting the "tuned" propellant flow dynamics at 10500 RPM). Of course
>you'll need to modify some stuff.. So you demolish the two wooden doors and
>build bigger ones. You demolish two hallways and build wider ones, but
>leaving the entries into the hallways unchanged. You also ruin the third
>hallway in the process, don't ask me why :-). You even enlarge the second
>And here they go, the crowd rushing through the awsome entrance and.. Oops,
>they're stuck at the two hallway entries. End of story.
> > >i don't think your right, because i know many people that have gotten
> >tomos with the new CDI to go 40 plus, i am one of them. i have even
> >to a dealer who got a true 50 out of his with the stock cdi and a 70cc
> >It is only implemented as a governor, but yes, it is also a "seizure proof"
>feature if you like. The speed improvement depends on your intake/exhaust
>tuned lenght and cylinder porting, but mostly depends on the resonance
>of the intake/exhaust system. For anything over 8000, the intake manifold
>way too long as it was designed to provide low end torque rather than high
>rev power (Tampering Test, yadda, yadda,..).
> > >Yeah I would also like to agree that you don't need to have a different
> >to go above 38mph. I have a 98 Sprint with Bi-turbo and it will go 40-43
> >on flat ground. However, I do have a question about the CDI RPM limiter.
> >this limiter part of the governing system for the us market like the
> >stock exhuast was or it it just there to prevent the rider from harming
> >bike. If I replaced it could i expect any speed improvement leaving my
> >the way it is?
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