I’m sure someone out there smarter than me can crunch the numbers to tell what RPM the transfers on a Puch Gila are capiable of flowing. I’m hitting a wall and thinking this is my issue. Hitting the wall at 12,700. 24mm carb. When I’m at 12,700 then hit a decline it doesn’t rev out more, it pops and sounds restricted. Anybody know?
Puch Gila theoretical max RPM
Re: Puch Gila theoretical max RPM
It can go way higher.
What cdi?
What pipe?
What gearing?
One ring or 2?
Re: Puch Gila theoretical max RPM
And did you push back the transfers outer walls as far as possible?
Re: Puch Gila theoretical max RPM
Max rpm on 2 strokes is calculated from the stroke and bore size.
And uses piston speed to determine the maximumm
Have a google about I’ve found calculators before and worked that out, the, before you start suffering from the need of more expensive materials is around 15,500 rpm
Re: Puch Gila theoretical max RPM
I know that most of the Guys racing in 75cc classes cap off their Gilas at 14-14'500.
Re: Puch Gila theoretical max RPM
JBOT - none of those questions have anything to do with the ability of transfer flow, but I'm happy to answer. HPI inner rotor, 2.1mm BTDC. MLM BK100. 17x42. 2 rings on stock piston, so 1 dykes, 1 regular. I have ported the cylinder slightly and feel the transfers are "pushed back" as far as possible w/o welding the cased, I'm already getting into the bolts deeper in so anything more at the deck would just bell out at the top. I'll list the port numbers later.
Adam Smith - not talking max RPM before the engine scatters, talking about the ability of transfers to flow air.
Chöschi21 - I wonder what their porting looks like.
To add a little more to this here are the area numbers I came up with for certain things, I assume these would all be listed as millimeters squared
Carb and Intake manifold 452
Intake port 510
Transfers 491
Exhaust port 600
I'm pretty simple minded when it comes to some of this but when you have a smaller port like the transfers the port velocity is higher than a larger port so depending on the size of the port vs port velocity you could have larger or smaller ports at different velocities that flow the same.
Port durations in degrees
Exhaust 192
Main transfers 130
Auxiliary transfer 118
Intake 152
Blowdown 31
Squish is at 1mm.
This is the same cylinder that hit 77.6mph in 2014 that has been massaged a bit. At that time I was only spinning it to 10,700 relying on the torque to pull the gear. Now I'm trying to get it to breath better in hopes of getting in the 80's. I'm kinda working against myself here because I have gotten more RPM out of it since before but haven't put a load on it with more gear to verify it pulls the gear to a higher RPM. I should do that to see if it breaks 80. But, for street use and everyday practicality it would be nice to spin 14k to have a wide power band/speed range. With 17x42 its in the low/mid 60's but 70 would be ideal. Still has great takeoff at that gearing.
This is getting long winded. I think I need to gear up and see how fast this thing goes then mess with RPM. I'm convinced the transfers are the issue but still appreciate any input. Talking gets the ideas flowing.
I'll post a picture of the transfer to cylinder from my phone, can't figure it out on the computer.
Matt
Re: Puch Gila theoretical max RPM
Re: Puch Gila theoretical max RPM
I should add that those numbers are only at the surface, I don’t know what the volume is like inside the ports. Also, stock reeds surface area 1,080.
Re: Puch Gila theoretical max RPM
I don't think it's necessarily the transfer timing. Soooo going off the numbers on the wiki Gila is 123' transfer and 178' exhaust, blowdown of 27.5.
I don't have much Gila experience so ima go off my experience with polini. Wiki numbers on polini are 114' transfer, 164' exhaust, 25 blowdown. I haven't modified my transfer timing, but I did open up the transfers at the base and ground out some of the webbing in the intake, as much as I could while preserving the boost port angle. I also cut auxiliary ports into the exhaust, without raising it. With a simonini pipe, I'm revving out over 13k. So with less transfer and exhaust timing than gila, it's still revving higher. Ik cutting those auxiliary ports did increase the blowdown even tho it didn't increase the duration.
If it's the same setup I remember you having, that monster Gila bk100, I bet there's more to be had in different pipes. Like with that 14k metra 65 ya had, what pipe and transfer or decking did ya do with that? Like you've done it before, maybe there's some direction to be had from that
Euro drag dudes rocking fat short pipes, I bet that's where it's at
Re: Puch Gila theoretical max RPM
Shorten the pipe. Bk100 is looonnngg.
Re: Puch Gila theoretical max RPM
Agreed. You should shorten that bad boy or try a better top end pipe.
12k is pushing it for that tuned length .
Re: Puch Gila theoretical max RPM
Jordan - I had that 65 Metra spinning 14,300 I turned it into an open transfer cylinder. I have a buddy with a Gila and it’s turning more but it has an 8p on it and is more of a horsepower set up where it needs to wind out. My situation is the exhaust port is so large that the pipe has to hit hard enough to fill it and make torque down low that if I run a real high horsepower pipe I never get in it. I have ran a Putt Putt and St Ripper on it and both made the bike unrideable. A Circuit pipe is a blast but it shuts down even earlier, but the hit is harder.
Daniel and JBOT - I’ll have to shorten it and see what happens, I can always weld it back together.
Something I expected with my mods was when the bike hit the higher RPMs that I’d catch the next power band of the pipe. I wonder why that’s not happening. With my Cali on my 65MK I went through 3 or 4 distinct power bands between 10-14k. I even put the Gila on a down hill to help push it in but it wouldn’t do it. I was running something like 210 exhaust on the 65MK, not sure if that would do it.
Re: Puch Gila theoretical max RPM
If you're header shortening,
Inch cut out is about 400rpm.
Might sound crazy but have you ever thought of running a dual switchable exhaust or a slipper adjustable pipe?
That would take care of lows and highs real time
Re: Puch Gila theoretical max RPM
You need to look into the world of scooter exhausts. I think you are kind of neutering your tuning by only using off-the-shelf moped exhausts.
Re: Puch Gila theoretical max RPM
77 with that gearing at 10k sorry bud, but you had to have a glitch in your gps.
BK100s are great for low to mid. Like crazy power. But if you want to wind it out you will need a much higher revving pipe.
Re: Puch Gila theoretical max RPM
Take a look at some of the shorter pipes:
Homoet 8P
Simonini (some even shorten them)
Doppler for Peugeot SPX (needs a flange and cutting/welding)
Re: Puch Gila theoretical max RPM
Yasuni, Malossi, Polini, Stage 6, they all make better pipes that are suited for the output you're hunting after.
MLM is a rad, but their pipe designs are not overseen by teams of engineers and refined for actual racing on the track.
Re: Puch Gila theoretical max RPM
throw a gianelli black gun on there and see what it does!
Eric you gotta read his whole post, he was saying he had taller gears to hit 77 but has geared shorter now.
this thread is pretty awesome all around! I haven't ever even tried to get a moped over 70 mph, 80 is bonkers.
Re: Puch Gila theoretical max RPM
+1 for mlm pipes being meh. Not only are they kind of made generically for bike to bike without much change in design other than fitament, but also they arent made for any specific cylinder. For example; stock magnum peoples pipe, it really sucks on a stock magnum. What are they doing over there? Also I think they use too thick of gauge steel. I know most road racing pipes are 20 or 22 gauge and I think mlm uses 16 and 18.
I would try a simo if someone has one laying around. The black gun isn't great on 74cc, its also discontinued, and if you hack up a perfectly good French is pipe I'll cry. It has close dims to a 6p, but for whatever reason it doesnt want to over rev as much. Ive only ever gotten to 57mph at +13k, cant run tall gears here in Seattle.
Re: Puch Gila theoretical max RPM
> Graham Motzing Wrote:
> -------------------------------------------------------
> throw a gianelli black gun on there and see what it does!
>
> Eric you gotta read his whole post, he was saying he had taller gears to
> hit 77 but has geared shorter now.
>
> this thread is pretty awesome all around! I haven't ever even tried to
> get a moped over 70 mph, 80 is bonkers.
There is is...that is what I get for looking at posts between classes. Makes sense now.
Re: Puch Gila theoretical max RPM
What reeds you running ?
Re: Puch Gila theoretical max RPM
My current Gila revs out way farther with a 8p or G104 then it does with the BK100, not sure how far though as I don't monitor speed or rpm. I know I can keep up with city freeway traffic no problem with BK100.
Re: Puch Gila theoretical max RPM
I think what your looking for is beyond any production pipe. You may need to bust out the two stroke hand book and and do some mathssss. Then see if you can get someone to build what you want.
I am with Derek on the pipe situation. My Gila with a BK100 rips hard all over but leaves something to be desired up top. The Gila I have with a Motomatic N8P revs out super high. I need to put a tach on there and see where it revs out at. If you could get your hands on one I would try that or maybe a Simo just because?
It would be cool to see someone hit 80 on a non variated bike.
Re: Puch Gila theoretical max RPM
yep porting and pipe, as discussed i went there(into the magic 80's) many moons ago
Re: Puch Gila theoretical max RPM
> Daniel '' Wrote:
> -------------------------------------------------------
>
> I would try a simo if someone has one laying around. The black gun isn't
> great on 74cc, its also discontinued, and if you hack up a perfectly
> good French is pipe I'll cry. It has close dims to a 6p, but for
> whatever reason it doesnt want to over rev as much. Ive only ever gotten
> to 57mph at +13k, cant run tall gears here in Seattle.
I have a Simo on my A55 Gila! it works great, BUT as I mentioned its a damn Tomos, it hits 13k, but anything over that and it blows the head off, because tomos use fucking pot metal for there cases, even re-tapped to m7 studs the head comes loose on me above that point, soooo I dont let it run at wot for long, or at all (edited)
Re: Puch Gila theoretical max RPM
You could always lower the compression
Re: Puch Gila theoretical max RPM
> Daniel '' Wrote:
> -------------------------------------------------------
> You could always lower the compression
I added a slightly thicker base gasket, but its a Tomo, so mehhhhh (edited)
Re: Puch Gila theoretical max RPM
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Re: Puch Gila theoretical max RPM
Sorry I know that link is garbage, but I think it'll get you to what you need to see. Some Psychos in Europe somehow did a bridged exhaust and made the exhaust mega wide on a gila. Amazing stuff Ive seen done only with a sleeve prior.
Check out "MST Performance" on Facebook to see some of their stuff. (edited)
Re: Puch Gila theoretical max RPM
Thats some interesting porting, nice looking work. They must have to re-plate the cylinder after that work on the exhaust.
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