Polini 130 with zirri pipe

My polini kitted smallframe easily pulled 70 with a leo vinci pipe on. Just fitted a zirri silent (considerably better expansion) and now it wont pull any topend in 4th and acceleration is suffering noticeably.

are there any tuners out there who can figure my problem ?

I’m running standard primary drive and it feels like there could be a prob with not enough back pressure with the new pipe . I want to rectify this with being able to keep the zirri pipe on. I’ve mucked about with the jetting but with no postive results.

Someone out there in smallframe land must have had this problem themselves, so please advise me ( I can’t afford the zirri short 4th so that option is out the question).

The zirri is supposed to match the 130 polini and this has come as a real surprise to see a leo vinci out perform it ! [:@]


very good idea to use Polini 130 the way it is best: a reliable and powerful GT engine.
Your carb. is a good choice.

As far as concerned SIP, I wouldn’t be so hard.
You know it is difficult to put in few lines a summary of the pruduct. ( They don’t pay me !)
It is like if I try to describe the taste of meat.
From my description you may like it but then you don’t cook it right or maybe you discover you don’t like meat at all.
And your taste can change too !

My tastes over the years for tuned vespa engines changed.
Before I used to like furious engines that would rev. as high as possible and short gears. Small target power range, but when the target was reached was like a kick. Very poor city drivebility but fun.
Now I still like this kind of engine but just everynow and then or for race.
For everyday use a prefer a good GT lot of torque and good power on low medium - medium range and long gear with the right exhaust not with the best one!


Oh and finally how would you spec the engine fo the best usage on polini 130

„The exhaust for either original or souped up small frame Vespas in the 125cc class. Zirri is the best in“

The above quote is taken directly from the english translation of sip catalogue and it goes on to say „most commonly used with polini 130 or standard 125 cylinders“

I believe what it should say is " this exhaust won’t perform as good as cheap alternatives unless you go for a balls out tunig job"

25 phbl, d22,264. 95 main. I;m taking the zirri off as 1,2,3 acceleration suffers also. I like the idea of the short 4th, but will aim to put that in the malossi engine i plan to build over winter.

With the new engine i hope to utilise the zirri pipe and i’ll keep the polini,leo vinci engine as a useable gt machine…

So for now zirri can hang up in the garage next to the simonini d&f.

If I’d already had the information to hand that you have imparted I could have saved my money and ordered the short 4th. I now view sip reviews with a diferrent scepticism after purchasing this pipe [:drink:]


the Zirri exhaust is a racing one and not a Gt.
This means that it has to be treated this way.
It is made to go fast, to rev high, not to drive nice and smooth.
It performance it is no compromise so you can’t make compromise in gearing either.
All the power curve is shifted about 1500rpm higher then other high performance exhausts. To drive in this condition is difficult.
Often people make this mistake. A pure racing thing is good for street use too. No, it is not true.
My most tuned racing engine it doesn’t pull at low rev not untill get to 5000 - 5500 rpm. It has to go as fast as possible so I don’t stay at 3000 3500rpm just because I have to pass from it to get higher rpm. It is a very bad street engine. Also a bad GT engine, but a great racing engine.
So everything has to follow. If you expect having a smooth engine with Zirri, forget about it. If you want a fast one yes.
I love Polini 130 kit, it is one of my favorite kit of all time all frames.
Be ready to buy the right gear, the right carb, the right crankcase porting, the right crankshaft and you will go fast, but not smooth power deliver.
If you can’t for economic reasons go for another exhaust.
You will be much happier.
But if it is for pure racing…


Thanks for your information

I have 2 questions based on your comments.

Will zirri short 4th be a suitable solution ? rev happy motor is what I’m after.


Can the polini kit be tuned to produce higher rpm. ?

(if sip advertise the zirri pipe as „the“ best pipe for either the standard 125 or for use with polini, then based on your knowledge, there marketing is misleading.

I’ve fully ported the casings so didn’t just build a plug n play motor.



Cheers Curare,

Guess I’m gonna have to stick with the Leo Vinci and hold onto the zirri until I build a monster engine. As I said it seems to run great with this pipe on and pulls a good accelaration with the front end lifting as i change to 2nd.

Would my current setup benefit from a zirri short 4th though.? when I say benefit , i mean would I get higher speed in fourth through letting the engine rev higher and reach the necessary power curve


I don’t think SIP is doing a misleding marketing for Zirri exhaust.
Saying it is the best, depends for what you think it is the best.
The best is who gives the more power? Or the more torque? or the better power spread?
The best will be something that can do all this thing togheter but it doesn’t exists.
For example for a Polini 177 (for PX) it is very good for city and touring to use a Sito plus, it will pull easy, climb without changing gears. But on pure power is far behind the SIP, Taffspeed, RZ and so on. But none of them is better on low rpm. Or power spread.
The Zirri is the best for power at high rpm. For me is the best race exhaust.
Polini 130 is a very reliable kit, you could use also for touring.
For race you should do some barrel porting.
You should make the exhaust port a little higher. And the bases ports larger and then enlarge crankcases to suit. If you want to keep some reliability it is enough, it will help the kit rev higher.
If you want a killer machine then you have to work the barrel more. And the piston too. And many other things has to follow.
But I don’t know if you want to push it that far.

The Zirri short 4 is essential. If not they wouldn’t have made it.

Vespa has only 4 gears and with engines that don’t pull at low rpm you need a shorter 4. If not the engine will not reach the power target zone where it pulls better.
If you are building an engine to rev high then you need big carbs.
Standard Polini 130 with race crankshaft and ported cases with normal pipe not a radical as Zirri one, it works beautifully with 24.
In a racing engine 26 it is minimum. I used succsefully Mikuni TMX27 - 30, Keihin PWK28 and only for highly tuned PWK 33. And no filter of course. Even the best filter is restrictive and in a race engine we don’t want any restrictions.
For racing I prefer these giap. carbs cause are smother then dell’ortos. But they are big and need frame cutting. But if it is for racing it is not a problem.
But with bigger carb your lows will suffer more, so reed is in this case good. With a Polini 130 you won’t get more power from reed but better drivebility.
But I think that all this modification will kill the real nature of this beautiful kit.
I think to get the best from a kit we have to go its way.
Polini 130 was not made to rev high. It is a very very good compromise of power, torque ,high rpm but not radical in any of them.
It is not a radical kit. As Zirri are and Malossi.
But globally for me is the best one. It is the best balanced.

For me the best cooking for this kit is: race crankshaft, ported cases, Polini exhaust or some equivalent, and 24 - 26 dell’orto carb. This will give the best compromise.

Any other modification as the use of a more radical exhaust, bigger carb ecc, not followed by the right compensation either will make it slower or globally worse even though potentially more powerfull.

Can you immagine you make a modification in your engine that will make it gain 25%more power at 9000rpm, but less power at 8000 then standard. You will be very happy! But for too long gearing or other reason you will never get to that target rpm. Result : you will go slower. You will never see that power, it can’t be expressed in practice. The engine can’t get at that rpm. So I don’t think in practice you will be very happy to have more power.

You said you like reving engine but how far you want to go?

Tell me what you are ready to loose for power and high rpm, and I will be able to be less panoramic in my answer.



yes, I wouldn’t say that your engine will benefit from Zirri short 4th gear, I say that it needs to have it !

You don’t need to build a monster engine to put the Zirri on, but you need the short 4th.
(maybe just talked too mutch in my previous answer and made myself not really clear)

I say the more tuned your engine is the more will be the advantage of the Zirri exhaust. But if you don’t put the short Zirri it is better not to use the Zirri exhaust. 1, 2, 3 will be ok but you shift to 4th and it is like he can’t go up on high rpm.

What would I do in your situation will be:

put the other exhaust you have untill you can buy the Zirri short 4th.
Then put the Zirri on.See how do you like it and then consider the future of your engine. Maybe will be enough… who knows…

Which carb have you now ?
If it is a 24 will be ok
If not will be too small and you need togo for a 24 or 26.



for your next engine.
Remember that the Zirri exhaust will start giving some real power at about 7000rpm, will give the most power at around 8500rpm and will be useble up to around 10000rpm where you will get about the same power that you had at 7000rpm.

So your engine has to get to 7000 easy. It means: not long gears.