2018 Aprilia RS4 50 Euro 4 Upgrade Project

Berkeley · Post by **Berkeley** » Tue Jan 15, 2019 5:20 pm

Hi guys.. thanks for the input and the maths!.

Yes the JM is a race pipe.. its hollow all the way through and is a massive improvement over the stock shite pipe!

My thinking is that it's not hitting 13.5k so something is holding it back. The JM pipe was designed for 50cc and not 70cc

If you look at the chart here for instance
https://www.racing-planet.co.uk/exhaust ... rettyPhoto
Then taking the same principle I have an R1 pipe and not an R2 which would be suitable for a 70cc.

From what I recall I've never hit over 11.5k with the 70cc kit (plus JM pipe) but before when I had the 50cc stock head ( plus JM pipe ) I recall seeing just over and around the 13k mark on the rpms...

I'm sure if I put a 15 front sprocket then will see a bit more top end gain but lose acceleration ...and will still not hit the 13.5k that you should get from this 70cc BBK.

I will ask JM that rpm question and see.

The stock bike came with an 11/59 sprocket ratio btw.

Cheers

kaldis12 · Post by **kaldis12** » Tue Jan 15, 2019 9:38 pm

A video with good sound quality could help tough. Maybe its just a carburation issue, but I dont think that is your issue.

About the cc's it does matter. Not just the rpm. More power with the same gearing can achieve higher kmh. 94cc at 13k rpm can reach 150kmh with gps quiet easily. At least when ported quiet well.

Altough if you can measure the exhaust inlet pipe inner diameter and the outer pipe inner diameter at the exhust chamber and the biggest outer diameter part of the chamber, then I can help a bit. Altough it wont be a perfect number but a pretty close.

Berkeley · Post by **Berkeley** » Thu Jan 17, 2019 4:31 am

Thanks Kaldis12,

Hopefully you can work with these figures!!

At the cylinder head the ID its 35mm      The exhaust manifold connection ID is 32mm

Then then the exhaust pipe ID is 29mm, and the chamber ID is 110mm approx.

I have not head from JM since I contacted them this week but this is what they said about the Pipe originally:

JollyMoto wrote:So, with the stock system the bike is blocked at 6000 Rpm, with the Jollymoto pipe it works until 9000 Rpm but there is a limit in the electronic brain.

At the moment many resellers talk about the 2018 version of a specific brain for the RS50 2018 but, as we know, isn’t available yet.

After changing the brain the bike with JM pipe could reach 12000 RPM with a big power gain.

Thanks

kaldis12 · Post by **kaldis12** » Thu Jan 17, 2019 4:46 am

As I get home will calculate things out. I forgot that I nees the pipe lenght from the cylinder to the expasion chamber end.

What they say is nuts. Anyway yours is not restricted so thats okay. Now as I see your pipe would start about on the 7,5k-8k rpm range. Which is kinda normal as I see these numbers. There is definetly more in that cylinder with a different pipe tough.

When you see the power coming in? Would be interesting to see. We could compare it to the calculated rpm and then we will know if its the pipe or not. But I would say it is.

Anyway please mesure that lenght and as I get home I will calculate it.

toratora · Post by **toratora** » Thu Jan 17, 2019 7:39 am

The bigger issue I see here is the desire to tune the bike for an advanced rider vs. who’s actually riding the bike—a new rider.

When one of these bikes is tuned to develop peak power at 13.5K it isn’t generally an easy bike to ride as they tend to not have any power below 10K. This makes it a challenge to keep it on the pipe. If this was a bike for an advanced rider that would be fine, but is it? No, it’s a bike for someone still very much developing the basics. Therefore isn’t it a mistake to be asking the bike to produce these sorts of numbers?

kaldis12 · Post by **kaldis12** » Thu Jan 17, 2019 8:47 am

When I started riding I was 14. I did my driving test on an old Simson. After that I got a stock Aprilia Rs 50(d50b) after a few months I sold it because it was too weak. My second bike was a SM with a pretty overkill 17hp, 14k rpm, inner rotor ignition, 28mm pwk carb. My first week was the learning. Not more. These are not that hard to ride. You need to start soon to feel what is like to be riding a real high rpm bike. You need to learn it as soon as it possible. I dont say that you dont need any driving experience, which you need, but you know. But Its my opinion and its not for me to be decided.

Anyway, if you manage to source some good pipe, which lets say would rev to 13k (which would be real) then your power band would be about from 9k to 13k. Or with an even better pipe it can go from 8.5 to 13k. (My exhaust was about this range with some comprumises)
I had the same metrakit cylinder once. Its not that hard to keep up the rpms. Small, fast accerating cylinder with a good pipe and sprocets.

Other than that I ran through the number even with missing sizes, but could be disappointed or not, the exhaust has a stop sing right here.

Berkeley · Post by **Berkeley** » Thu Jan 17, 2019 9:32 am

kaldis12 wrote: ↑
Thu Jan 17, 2019 4:46 am
As I get home will calculate things out. I forgot that I nees the pipe lenght from the cylinder to the expasion chamber end.

What they say is nuts. Anyway yours is not restricted so thats okay. Now as I see your pipe would start about on the 7,5k-8k rpm range. Which is kinda normal as I see these numbers. There is definetly more in that cylinder with a different pipe tough.

When you see the power coming in? Would be interesting to see. We could compare it to the calculated rpm and then we will know if its the pipe or not. But I would say it is.

Anyway please mesure that lenght and as I get home I will calculate it.

Hi Kaldis the length from the cylinder head to the very end of the chamber is 760mm approx and what you said about the power coming in.. it is around the 7.5 to 8k range.

Tora... Well noted, also if you see on pg 34 I did give a reason why the power increase would be good. Ps if it was my bike i wouldn't put fairy lights on!

cheers

kaldis12 · Post by **kaldis12** » Thu Jan 17, 2019 9:51 am

Oh nice quess from me, So I was pretty close.
In my countings I got the rpm range from 7k to 11.8k. But that could be due to some guessed numbers, and maybe a bit of a measuring errors. You has a doorstop right here because of the exhaust. Maybe with some carburation you can get a few hunder rpms more but not too much.

Berkeley · Post by **Berkeley** » Sun Jan 20, 2019 3:28 am

Yesterday I changed the Carb needle from a 14/22 to a 12/22 ( not sure how that affects things, is it a more gradual fuel delivery upon acceleration?)

This time the needle actually fitted.. was expecting it to be the same as before when it didnt.

Again doing some runs hitting about 11k rpm max as confirmation, forgot to setup the phone gps for speed though.

kaldis12 · Post by **kaldis12** » Sun Jan 20, 2019 4:02 am

You should see the numbers between 11-12k rpm. More like in the midway around 11.5k. That would be the perfect carburation. Cant really say it where it should be because the exhsust measurment are a bit off from the real but you know. You got the idea.

Also dont forget to check the Piston wash. It helps a lot.

Do you have a friend who could weld you an exhaust? If you have, then you could ask for someone to design it and you could make it. Could compare it to the Jolymoto exhaust, would be interesting to see though!

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