Polini Speed engine, DR43mm or Polini 46mm?

[Dea_944tTopic starterBerichten: 87]

I’ve decided to get a Polini Speed engine and if I understand correctly they work with both 43 mm and 46 mm cylinders, correct?
I have a new-in-box 43 mm DR Evo but will using a 46 mm Polini give much better performance?

/Dea

[QuicklyHeizerBijdragerBerichten: 135]

Hey,
its correct, both cilinders work and from both the layout fits perfect to the speed engine. The 46mm does not really have a better performance. When you look at the exhaust port of those cilinders, you see that the one of the DR Evo is way bigger. Both cilinders will work very good. If you already have the DR and no Polini, I would just use it. Note, that you need the fitting crankshaft for the case! A original crankshaft for “Mofa” in Germany for example does not work in the Speed Engine. But if you would use the 43mm DR Evo, the Speed Engine would just make sene, if you can’t mill an original Crankcase. So it’s your decision, 43 oder 46. Just one more information, I saw some 46mm Polini cilinders, where the piston broke, which I think never happened to any DR Evo.

[Dea_944tTopic starterBerichten: 87]

Thanks! great info, Iäll use the 43 mm DR Evo.

What versions of the original crankshaft, if any, works in the Speed engine?

/Dea

[freddy kBijdragerBerichten: 456]

Original crankshaft do work on speed engines.
But a moped crank is better then a mofa (better timing.
mofa crank

moped crank

race crank

If you go for a race crank, keep in mind that the TopRacing cranks may break after a while.
mfg Freddy.

[ritzeBijdragerBerichten: 3421]

do not mill your crankshaft, it is good as it is
otherwise your timing wil be to long. and you have to make 13.000 rpm to get any good power at all

the 43 dr evo is a hi rev cilinder but the 46 polini give`s up tons of torque

De budget beun tjoener: geen geld is te duur of het werkt nog niet
Link naar Mijn collectie / Projecten.

[Dea_944tTopic starterBerichten: 87]

Interesting, I didn’t even know that there were different versions of the crankshaft… I have a couple of original crankshaft in my garage, let’s hope at least one of them is for moped…

I thought that low-end torque increased if the opening intake timing was increased slightly?

I want torque 🙂 no variator and a lot of hills where I live, so maybe I should go for a 46mm cylinder. What other good 46 mm cylinders are there except Polini?

I actually broke a Top Racing crank last summer…. after reading on some forums it seems that a modified original crank is better that any race crank?

/Dea

[ritzeBijdragerBerichten: 3421]

when the inlet is opening earlier jou will have more torque in the lower end of rpm range
that is why a snor crank has a earlier timing than a brom crank

i also broke a top break race crank after 630 km so they suck very hard
original cranks are the best en will survive a comet strike 😀

there are 3 46 mm cilinders
a malossi (got one but it is not all that great but it has some torque )
pinasco (really expensive but really bloody fast
and the polini all round the best i thing for that kind of money 😀

De budget beun tjoener: geen geld is te duur of het werkt nog niet
Link naar Mijn collectie / Projecten.

[Dea_944tTopic starterBerichten: 87]

I couldn’t decide so I’m building two engines 😀
One with the Speed engine carter and the 46 mm Polini and one with a “belgian” carter and the DR Evo 43 mm.

I opened the engines I had and the only moped crank was an old one without needle bearing…..
Looking at the difference it should be possible to change a mofa crank into something that should work. If I increase the opening on the outlet side it will be the same as a moped crank with increased intake timing?

EDIT: Somehow I confused Ritzes pictures….. 😕 what I have are three moped/brom cranks and one old mofa/snor crank so no modifications needed 😀

/Dea

[ritzeBijdragerBerichten: 3421]

Your s.e. Engine already has a long inlet timing if jou tune it too far you will loose engine case pressure or you have to let it run 15 k rpm
Iam curius to see wat you are going to do
Please make a perso topic so we can follow it

De budget beun tjoener: geen geld is te duur of het werkt nog niet
Link naar Mijn collectie / Projecten.

[Dea_944tTopic starterBerichten: 87]

EDIT:

Just disregard the part below, I confused the moped/brom cranks and the mofa/snor cranks….
“”
I will measure the cranks and put up some pics on how I plan to modify them, if it doesn’t work I will try to get hold of a a moped crank (unfortunately almost impossible in Sweden as only the mofa version was sold here) or get a good quality race crank (if there are any…)
“”

I’ll make a person topic showing the modifications. The Polini parts arrive in a few weeks so I’m starting with the DR engine.

Btw, what’s the best way of getting the bearings off the crank?

/Dea

[Gebruiker]

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