Expension chamber modification or piston modifications to increase rpm

Hi moped army

I’m looking to break 10.5-8krpm it seems to be a barrier on my e50 Athena large reed maxi build.

After much head scratching I’ve come up with a couple ideas to push the Rpms

I’m wondering increaseing the exhaust timing by making a small ramp on the exhaust side of the piston crown. Currently myexhaust timing is at 185’ I’m unsure how high is to high on a e50

Re: Expension chamber modification or piston modifications to increase rpm

Or

shorten the header on the exhaust slightly

1inch or so. I’m reading lots about exhaust design at the moment and this seems the problem. But I may try and lengthen the stinger on the rear of the pipe see if that will change how it hits.

Any other advice would be appreciated and thanks for reading :)

I’m doing lots of reading on exhaust design

Re: Expension chamber modification or piston modifications to increase rpm

Just my opinion,

But 185 is plenty high for an e50.

Clutch munching high depending on your blowdown.

You can mirror polish the exhaust, that can often get you more rpms up top.

That being said, shortening the header is easy, one inch will get you about 400rpm.

Re: Expension chamber modification or piston modifications to increase rpm

Stinger most likely won't change your rpms much at all. I never had much of a change, though the bike would run better/worse with longer or shorter stinger

Re: Expension chamber modification or piston modifications to increase rpm

Shorter header, larger dwell diameter, larger diameter stinger, will affect the rpms where your pipe is hitting. A less radical angle of converging cone will give a little more over rev.

I've gone as high as 185 on a single speed, but the clutch had to slip to 8k and the gearing was so low it only topped out at 47 at 13k.

Is your intake duration at 360°? Are you running stock, dual stage, 4 or 8 petal reeds in the Athena? Single ring piston? What carb are you using?

For your exhaust mods, the puch simonini is the hardest hitting highest revving pipe made for mopeds, I would look there and maybe modify your pipe to have some of the same characteristics.(edited)

Re: Expension chamber modification or piston modifications to increase rpm

My clutch slips till around 5.5k

No it is heavily opened up, I did wk see about windowing the intake side of the piston,what do you think?

Stock 2 petal with carbon reeds all ported inside as they’re not great for flow stock.

I’ve started making a riser for a 8 petal from a AM6 engine

Carb is Mikuni TM24 currently 160 main jet 10 idle

I’m running a homoet p6 PSR and it hits hard!

Re: Expension chamber modification or piston modifications to increase rpm

> JBOT Admin Wrote:

> -------------------------------------------------------

> Just my opinion,

>

> But 185 is plenty high for an e50.

>

> Clutch munching high depending on your blowdown.

>

> You can mirror polish the exhaust, that can often get you more rpms up

> top.

>

> That being said, shortening the header is easy, one inch will get you

> about 400rpm.

Mirror polish the inside of the exhaust port on the cylinder

I’ve had the top end off over winter and cleaned it all back to shiney it’s seen 500 miles this year was quite a layer of gunk and crud!

Re: Expension chamber modification or piston modifications to increase rpm

Also my earlier post was for you but it didn’t tag I run 17x41 and I’m hitting 58mph. I really want to break 60mph without going upto 18

M> Daniel '' Wrote:

> -------------------------------------------------------

> Shorter header, larger dwell diameter, larger diameter stinger, will

> affect the rpms where your pipe is hitting. A less radical angle of

> converging cone will give a little more over rev.

>

> I've gone as high as 185 on a single speed, but the clutch had to slip

> to 8k and the gearing was so low it only topped out at 47 at 13k.

>

> Is your intake duration at 360°? Are you running stock, dual stage, 4 or

> 8 petal reeds in the Athena? Single ring piston? What carb are you

> using?

>

> For your exhaust mods, the puch simonini is the hardest hitting highest

> revving pipe made for mopeds, I would look there and maybe modify your

> pipe to have some of the same characteristics.

Re: Expension chamber modification or piston modifications to increase rpm

> JBOT Admin Wrote:

> -------------------------------------------------------

> Just my opinion,

>

> But 185 is plenty high for an e50.

>

> Clutch munching high depending on your blowdown.

>

> You can mirror polish the exhaust, that can often get you more rpms up

> top.

>

> That being said, shortening the header is easy, one inch will get you

> about 400rpm.

Sorry should’ve posted

Exhaust 185

Transfers 128

Blowdown 29

This was the initial reason I avoided the Simioni pipe. As it doesn’t perform well with high blowdown

Re: Expension chamber modification or piston modifications to increase rpm

Again, just my opinion, but that blowdown sucks for an e50.

Way too peaky.

You kinda boxed yourself in with the porting. But to make more power go V reed.

Problem with going full 360 intake is that that's gonna make your shit even more peaky. But fuck it, it'll make more power up top.

Window the piston so that ex is open all the time 360 deg, and then rejet.

Re: Expension chamber modification or piston modifications to increase rpm

Ignore me(edited)

Re: Expension chamber modification or piston modifications to increase rpm

> JBOT Admin Wrote:

> -------------------------------------------------------

> Again, just my opinion, but that blowdown sucks for an e50.

>

> Way too peaky.

>

> You kinda boxed yourself in with the porting. But to make more power go

> V reed.

>

> Problem with going full 360 intake is that that's gonna make your shit

> even more peaky. But fuck it, it'll make more power up top.

>

> Window the piston so that ex is open all the time 360 deg, and then

> rejet.

Or intake side? Should I leave the sides of the window in

Re: Expension chamber modification or piston modifications to increase rpm

The 360 term means that the cases are open to the intake post reeds all the time, the full 360deg of the crank.

This allows a maximum mix to get into the cases, but at the expense of a wider band that many cyl reed kits have utilizing the piston to shut off the intake for a time, even with reeds

Re: Expension chamber modification or piston modifications to increase rpm

> JBOT Admin Wrote:

> -------------------------------------------------------

> The 360 term means that the cases are open to the intake post reeds all

> the time, the full 360deg of the crank.

>

> This allows a maximum mix to get into the cases, but at the expense of a

> wider band that many cyl reed kits have utilizing the piston to shut off

> the intake for a time, even with reeds

Interesting yea that’s more or less what I took away from it. But how much material would you leave on the intake side of the piston. I already smoothed the inside and made the window bigger. Maybe if you could possible send me a picture I might get it more ?

Re: Expension chamber modification or piston modifications to increase rpm

If your piston is windowed the intake is most likely already open all the time. Just run the piston thru the barrel and look thru it to see if it's open for the whole stroke.

As far as shape, you can experiment. Some folks chop the whole intake side out. The whole friggin side of the piston.

Not saying to do that, just emphasizing that much can be done. Go at it

Re: Expension chamber modification or piston modifications to increase rpm

Joe Schuitema /

From doing some dyno experiments, just changing the convergent cone of the exhaust moved both the peak torque and maximum rpm of the engine. If you can roll cones, I'd suggest going a couple degrees steeper on the convergent cone. you should pick up a bit more topend at the expense of the bottom, and the tuned length will probably be shortened by an inch or so, moving the powerband up 500 rpm.

Re: Expension chamber modification or piston modifications to increase rpm

Chöschi21 C.K. /

Are you still running the Stock Point's Ignition? I could never hit more than about 11'000 RPM with one, could never get over it until i tried lighter points and a stiffer Spring.(edited)

Re: Expension chamber modification or piston modifications to increase rpm

I'm pretty sure hes got the kokusan ignition? Been wanting one of those on a puch for a while, my peugeot loves it.

Re: Expension chamber modification or piston modifications to increase rpm

> Chöschi21 C.K. Wrote:

> -------------------------------------------------------

> Are you still running the Stock Point's Ignition? I could never hit more

> than about 11'000 RPM with one, could never get over it until i tried

> lighter points and a stiffer Spring.

I’m running a kokusan ignition. I blew the original cdi by poor wiring (will attach pic)

Currently it’s running one from a Derbi sendr am6 I believe it’s limited to 12k rpm

Top performance make a derestriced unit for around £45 that people put on their modern Aprilla rs50’s and use them too 14-16krpm... or so they say

https://www.racing-planet.co.uk/unrestricted-performances-minarelli-derbi-senda-ducati-kokusan-ignition-p-184189-1.html?utm_source=google&utm_medium=google_merchant&utm_campaign=google_products&gclid=EAIaIQobChMIuPr-vaHI3wIVUkTTCh2ImAxrEAQYAiABEgJpYPD_BwE#.XCkY6KSnyEc

Something like this (edited)

23752A1F-D174-4F4F-BC24-452D9DD13C88.jpeg

Re: Expension chamber modification or piston modifications to increase rpm

> Daniel '' Wrote:

> -------------------------------------------------------

> I'm pretty sure hes got the kokusan ignition? Been wanting one of those

> on a puch for a while, my peugeot loves it.

I’ve yet to utilise the pickup at the for a rev counter. Only realised that’s what it was for a few weeks ago

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