Modern Vespa

Keeping this brief. Spec of scooter is px125 MY 2003 with DR177, 24mm carb.

I had a sip 2.0 road on it which drove fine but the exhaust was a couple of years old and passed it best, had become rusty and very noisy. It was jetted to 116 main and was spot on with plug colour (running on an NGK 8 short reach plug, so cooler. I was hitting indicated speed of 110 kmh and always without fail got 105. The GPS revealled top speed as 63 mph

So, a polini box was put on it. Upjetted to 118 main. When i checked the plug it was rich. So ive taken the plug down to a 7 short reach. Still the plug colour was too rich so taken jet down to 116 and now the colour is fine, albeit a tad rich on the pilot circuit. Due to winter weather i have only just gotten around to giving the scooter a thrashing with the polini box on. Its a great sounding exhaust, more like the original, sounds a bit like a p200 now and the torgue and pick up are very good; its particularly good at 50mph overtakes, really punchy, more so than the sip road 2.0 It flies really quickly up to an indicated 100kmh which on the GPS was 57.5 mph however it will not push over 100kmh (new speedo cable and drive worm also fitted).

When the scooter was a standard px125 with the sip road 2.0 i would regularly see 105kmh indicated so although i have a lot of power with the polinibox i cannot get the top speeds i was getting before as 125cc and 177cc.

Is there anything im missing here? Is this the nature of the exhaust, a compromise of having loads ot torgue. Before i revert the exhaust back to the sip road 2.0 to check if the top speeds return, can anybody advise?

I know i am quibbling over 5mph top end speed and maybe i should just live with this but its irritating when i was getting higher speeds before. Any pointers you can give me will be most appreciated. Thanks.

I’d be moaning too if I lost the last 5 on the top end. It makes me think because I just put the Polini box on my PX!

One thing I recently ran into, what color air filter are you using? Buddy of mine had the blue LML mesh and it choked him down on the top end. Switched to a white mesh 24mm filter and he’s gained it all back. Might be worth a quick look.

If the air filter doesn’t do it, I’d absolutely spend the money to swap pipes.

Just spitballin’

Put on any weight recently?

Checked tire pressure?

The air filter is a brand new original piaggio white mesh filter drilled out. This was present when i was using the Sip Road 2.0. Not a problem. Always hitting 105khm indicated and would regularly see 110km. It would always hit 105kmh, even when it was a 124 cc, its had a dr 177 in since last summer which is now settled in nicely.

I have two brand new Michelin S1 tyres fitted at one up tyre pressures.

As to my weight, im a light weighted 6 footer weighing 12st 4 lbs. Ive actually lost 7 lbs.

The polinibox has loads of power for racing about town, so being able to hit 60mph plus around town is not an issue. If i didnt travel then the polinibox is a good setup for blasting about and buzzing past cars. But when you head out to another town or city, not being able to get to 60 plus is an issue for keeping ahead of cars and the have a go racers on their auto peds. UK speed limit is 60mph on open road and 70 on dual carriageways, so i need that speed back. When i had the Sip Road 2.0 i was revving out, running out of gearing. My next job was to have a clutch upgrade and whilst at it, split the engine and have the cruciform replaced (its fine but due a change) and seals etc. But as it is with polinibox, i wouldnt even be able to take advantage of that clutch cog change.

I bought the polinibox having read reviews surrounding the new sip road 3.0 and established the consensus that the road 3.0 was pretty much a copy of the polinibox. I needed a new exhaust as the sip was too loud and i like the tone of the polini, doesnt annoy my neighbours when i had to work early. So now having had a chance to give the PX some tougher riding im having this top end issue and the scoot is not revving out. Its happy at 57mph sure, it gets there very quickly, its not straining or sounding rough but it feels like you are holding back on the throttle. Increasing Jetting to 118 just causes rich plug and no difference. I even sat back on the seat prone scooterboy style and still it would not increase on the speedo. Im at a loss as the plug colour is good. Ive taken the filter off to visually make sure the throttle slide is fully opening. MJ Rally, have you taken your PX for a full throttle thrash yet, notice anything different?

I think the only way if nobody can advise is to take the polinibox off tomorrow, refit the old Sip Road 2.0 and see whats happening. The jetting will be exactly the same on the Sip Road 2.0 as is in it now. If the speed returns then i will know the polini box is not right for me. I will then have to refit a new Sip Road 2.0 so more cash. Just shelled out 100 pounds for the polini, bloody annoying.

I feel your pain, I was using the same DR177 setup. I was also trying to get to 60 mph sustained not peak. You have to pay very close attention to dyno graphs and peak power rpm when you can. I was pretty much ringing every little bit out that I could. You'll find for instance, exhaust to exhaust peak numbers maybe the same but one peaks 500 - 1000 rpm sooner than the other. The Polini peaks lower in the rpm range about 5000 and levels out and falls off at 5500.
A sip road 2.0 or sito box is better in the 6000 - 6500 rpm range and that is where I was running. They're almost 12% better in hp at the higher 6500 rpm range.

If the sip 2.0 puts you back to 60 mph you'll be confirming this graph is correct for your scooter.

This is one source that I referenced.

Box-type Exhaust comparison for 125 and 200

You've not mentioned ignition timing, so guessing it's still stock. Reduce it 2 degrees and go for another run.

Trying to move the power band up by reducing timing?

Creating better over-rev.

Hope this helps.

Reference to Eric Gorr

Thanks Christopher for that really useful link to the exhaust chart and narrative. That narrative (translation) aptly describes what i put in my post. The polinibox is a good exhaust for hacking about with and fast bursts in urban, winding country back roads but its falling over on the open carriageway. So they are saying at around 5500 RPM the sip road 2.0 will out perform the polini on top speed.

As to the timing, my mechanic reduced it by 2 degrees couple of weeks ago to see if this would help, it made no difference on the top end issue.

I kept asking myself why isnt the scooter reaching the same power and high revs, the chart provided pretty much explains why. Thanks all for replying. Will put the SIP r2 back on to test and if conclusive proof will order a new road 2, probably the sport version going by the information provided in that link. Cheers all

Same here on my LML with standard cylinder: went from an old and noisy SIP Road 2 to a Polini Box and lost a couple of mph at the top end.

I was a little underwhelmed by the Polini Box after reading how peppy and quiet it supposedly is- it's only a little quieter than my Sip Road 2 and not as nice sounding as a standard box imho.

I think I might be getting old.

I will be curious to see how this works out for you, and if the change back, gets you back to where you were before. I'm sure if this gets you back to where you want to be you can sell the Polini and get part of your money back.

I had been looking at various exhaust pipes for the P200 I put in last year in the fall, I bought a used sip road XL with it. The XL gets poor reviews because of the peak power being mostly 5500 rpm and above. This just happens to be where I want it for cruising at 60 - 65 mph. I haven't found anything better with dyno graphs to back it up for my setup.

If you have or can get a tachometer it helps to see exactly what rpm your turning while cruising at 60- 65 mph. Keeping that RPM in mind for any changes or tuning helps. When making any changes I always ask myself what happens at that rpm range?

As far as I know, there is no published testing for these 125/150cc box exhausts on a 177, which is too bad since that is such a common configuration. How do results from a stock 125 translate to an aftermarket 177? Beats me, but at least it’s the same part. Other tests are on exhausts for 200s, which have a slightly different header pipe, making extrapolation even more dubious.

I have a Polini box which I ran on a stock LML 150 cc jug for a while before going to a Malossi 177 kit. On the 150, there was a significant increase in low and mid-range power, but no discernable impact (up or down) on top speed. I’ve never run the 177 with anything else, but I am getting a top speed of 65 mph (GPS) sitting upright, etc. Mind you that is more of a testing parameter than a useable cruising speed.

Changing exhaust back to road 2.0 tomorrow morning as got the morning off so i will report my findings as soon as i can. Thank you all for your really helpful pointers, i really appreciate it. Drive safe everybody.

UPDATE

So, got out early this morning and removed the polini box. Picked up the old Road 2.0 and was amazed how perfectly lined up it was with the cylinder exhaust stub and the under floor frame bolt. The easiest most hassle free exhaust installation you could ask for. She fired up second kick and off i set, roads were a bit wet so i was a bit cautious as i run S1 tyres which can be a bit slippy. I took her out on a 60mph road and with no messing about the speedo went up to 110kmh and was still climbing but had to slow down as 50mph zone.
Pulled over and the max speed on my phone GPS stated 64.7 MPH. So my speed issue resolved. Bare in mind with the polini the max speed on GPS was 57.4.

So here is my conclusion for my setup an a PX125 MY DISC 2003 MODEL with standard gearbox and clutch configuration from factory.

DR177 24MM SI CARB, SIP ROAD 2.0 - Top speed of 64.7 mph, upright riding, slight side wind, rider weight 12st 3 lbs. As apposed to Polini Box, top speed 57.4 and it would not go past this speed despite many runs. 7mph top end gain for road 2.0 over polini.

Would i use the Polini Box again? -

Well this is clearly horses for courses. The polini box has the edge over the Sip Road 2.0 around urban roads, windy back roads, inclines and pulls pretty well two up as well. Its a fun exhaust that gets up to 50mph very quickly with very little effort; so if you were having a hack with mates you would have the edge out front on short run roads. You do not have to rev it through each gear to get there which is not the case for the Sip Road 2.0. This concludes with the graphing provided by Christopher earlier where the polinibox loses peak power after 5500 RPM. However, for open roads, dual carriage ways, the polinibox on my setup falls flat on its face. It would not go past 58 mph. Its actually slower on top end than having a Road 2.0 on a standard 125 barrel, bare in mind i have a 177cc in now. In terms of noise, yes the polini box is a little quieter but at higher revs there is not a lot of difference in noise.

If anybody in the UK has done the Isle of Wight Scooter Rally, you will know how challenging the hilly roads are; some are very steep. A polini box would be perfect for my setup in tackling these roads. If you have ever driven a T5 on the isle of wight, you will know how this feels, you cannot reach the high revs to climb these really steep inclines that the T5 needs.

So, im glad ive sorted the issue and of course this works for my setup and a DR177. It doesnt mean to say the polini box wont work for others, but for me im very disappointed with reviews on youtube etc that the polinibox is the way to go. For me it clearly isnt. 7mph + top end is a considerable difference for a bolt on setup with no tuning. Thanks for all your help guys, glad ive got it sorted.

Hi,

As mentioned earlier, there are some differences in the "behaviour" for Polini Box and Sip road...

The Polini Box is more of a "tractor", meaning that the power is lower down the rpm's. -more tourqe than high rpms.
The SIP Road is more a general exhaust, giving you a little of everything... -both a little torque and a little more rpm's...

Both compared to a standard PX box...

I'm runing several PX engines with both Polini and SIP boxes, dependent on the cylinder fitted. Polini and Malossi, but the behaviour is how you describe it.

My suggestion to utilize the low-down power of the Polini Box is to up-gear the engine. You now have 21/68, and I would have tried 22/68, even a 23/65 should be good with that setup. -then you will have the whole benefit of the Polini box with an angine pulling from the bottom, decent top speed without the engine screaming....

Just my tip.

I agree with Svint1. I run a Pinasco 225 with a Polini box and love it. I have upgeared to 24/63 and use the RPM restricted ignition system from a 2013 PX125. This combo means that it never sees more than 7000 RPM, but still reaches a genuine 70 MPH. The low down pulling power is amazing and carrying a pillion and/or luggage is what it's all about. For this profile, the Polini box is hard to beat. For a higher RPM profile, I would choose a different exhaust eg. BB Sport........and a different cylinder!!

I dont doubt that the polinibox works well for certain setups and of course the distances you are travelling. So the type i riding i do is about town, go to work which is 8 miles away and an occasional hack to Brighton or Portsmouth on the south coast which is 26 miles away and I need to be hitting 60 plus on those dual carriageways. Im going to keep the polinibox because if i get the chance to head to the Isle of Wight Rally in August, covid restrictions permitting/lifted, the polini will go back on just for that weekend. Cheers all for your replies.