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theageofindustry

Mugello 200 Setup

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I am in the process of setting one Mugello 200 of the two I have to do. Here's my specs and quandary:

Intake: 152°

Exhaust: 180°

Transfers: 128°

Blow down: 25°

As I have said before, those numbers mean very little to me as I don't know what it all means.

Squish: 1.16mm

That number is good as it it sits torqued up without any gaskets so I can play with it if I need to. Now my bigger question is using a standard GP 58x107 crank, with no gaskets at all, the piston drops at least 2mm below the exhaust port at bdc. I understand that is considered an absolute no no so now what are my options? Lower the exhaust port more to at least make it meet the edge of the piston? Gaskets are only going to make it worse.

Maybe change to a longer rod on the crank? What's everyone think?

post-24-0-21390300-1458697475_thumb.jpg

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Not sure what your deck height is, but if you drop the barrel by 1mm (definitely check my measurements, as I'm working backwards to make you numbers fit), you'll have 176, 122, 154, which I personally like better. Except the 154 intake. I'd shoot for 150 but that's not possible. 

 

You could certainly run it as is, but drop the exhaust to match the piston. That may be best actually. If you are 2mm too high in the exhaust, matching the barrel to the exhaust at bdc should give you 172, 117, 158 (again, double check that). That may very well be where the barrel was designed to run at. That only makes the intake worse, in my opinion. 

 

Of course, changing anything will mess with your squish clearance, so I think in this case, if it were me, I would probably run it as is and open the exhaust to match the piston at bdc. 

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Compare those numbers to page 41.

https://issuu.com/scooter-center.com/docs/sck-lambretta-2007_e

A lot of kits run something in the neighborhood 175/125/25 with an intake of 150. Of course kits designed for touring and race differ wildly.

I'd lower the exhaust port at a minimum, but first take some measurements with various gaskets to see what gets you close to those figures.

And please note this is the blind leading the blind. I have very little experience in this stuff.

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What sort of exhaust and gearing are you using? If using an expansion chamber I would try to get a higher blow down period like 26-26.5. But that means you'd have to raise the transfers (by removing material) and I wouldn't go higher than the 128 you already have. Or, if using an expansion, I would raise the exhaust port (by removing material) which would help increase blow down, and just keep the transfers as they are.

 

However, I would zero out that piston at the bottom of the ports before I did anything. Are the bottoms of the ports all level with each other? I wouldn't like the bottom of the exhaust port to be below the transfers. My best advice would be to get a longer rod and raise the barrel. Mugello's have a head that sets into the barrel, so you have room to play with. How close to the edge of the cylinder is the piston a TDC? If it is 4mm and the longer rod is a 110, will that head drop 6.8mm into the cylinder? Your head may need machining. A longer rod and a cylinder base packer will be the best way to get the real estate necessary to put your port timings where you want them.

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And that big divot/casting flaw in the exhaust port? I would make them swap it out with another kit. 

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I have thought about the 110 rod and if I went to a 60mm stroke it would it pretty much line up the exhaust port perfectly but that would leave the head needing about 4mm to be shaved off.  I chatted with Patrick at P-town and he also said to drop the port to match the piston and call it done.

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Paddyfitz knows tuning

Easy route or not....?

If the head is the type Chris mentioned above that drops into bore then the top of the barrel should be milled a few mm so head remains unchanged. That way you can play with head gaskets of different thicknesses (alloy) to get squish spot on. Machining that head doesn't seem best option.

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The port timings you originally posted aren't bad -

Take a .5mm off the top of exhaust port to add 1.5 degrees to blow down and remove the material from bottom of exhaust port to match piston.

I think not having the bottom of the ports lining up will make it messy. I would have just used a crankshaft w/longer rod, not increased stroke.

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Also: The guide I use is multiplying the blow down period by 2 and then adding it to the transfer duration. Yours is 50+128 so you'd need a 178 exhaust duration for it to be complimentary. However, since you aren't wringing it out at 10,000rpm I don't think such a high transfer duration is useful. So even though the numbers look good, I think those ports as set up will just be kinda crappy.

If all you are doing is bolting it up, why buy a $600 kit?

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If I spend 600 bucks on a kit, I'd expect it to be as close to perfect as possible. Otherwise, why not buy a crap SR kit for $150, have someone tune it (I do the whole thing for less than $180), and have a bolt on kit the way you want it for $330? 

 

 

Also: The guide I use is multiplying the blow down period by 2 and then adding it to the transfer duration. 

Also, where is that guide from? I'm not suggesting it's not a good rule of thumb, but I don't recall ever coming across that information in my studies. If there's evidence it works, I'd be more than happy to adopt it myself!

 

My biggest concern for those timings, not knowing the rest of the information on the tune, is the intake timing approaching too long of duration. Blow back can become very difficult to control once you approach 155 deg. That makes starting hard, filters clog, and poor low end, which if I remember is something quite high on Peter's list for engine tunes.

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If I spend 600 bucks on a kit, I'd expect it to be as close to perfect as possible. Otherwise, why not buy a crap SR kit for $150, have someone tune it (I do the whole thing for less than $180), and have a bolt on kit the way you want it for $330? 

 

 

Also, where is that guide from? I'm not suggesting it's not a good rule of thumb, but I don't recall ever coming across that information in my studies. If there's evidence it works, I'd be more than happy to adopt it myself!

 

My biggest concern for those timings, not knowing the rest of the information on the tune, is the intake timing approaching too long of duration. Blow back can become very difficult to control once you approach 155 deg. That makes starting hard, filters clog, and poor low end, which if I remember is something quite high on Peter's list for engine tunes.

 

This one is just getting a PHBL 25 and a big bore exhaust. You've done a lot of tunes for myself and the MN crew so you definitely have your finger on how I like to build my engines.  All bottom and mid-range!

 

That said, this is the scooter that Tino will be riding at the jammy this year and the same kit I am building for the raffle scooter so it's all Mugello up in this joint right now.

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What about pressure? The intake pressure is pretty low in these engines, so won't the scavenging effect be knocked with the exhaust port starting to close before the transfers start to close? This is the reason I am asking about the whether or not the bottoms of the ports all match.

 

 

I wish I would have the opportunity to go back in time and start school doing something worthwhile, but everything I do now is about applying the guidelines I read about. I like to create a complimentary relationship between the different parts based on what I get when I ride. The 128˚ transfers duration is meant for highs (10,000 rpm). The 180˚ exhaust is meant for middle (8,000 rpm). The 25˚ blowdown is meant for low-middle. If I am not mistaken, that Mugello kit has a slightly tapered shape to the top of the exhaust port, right? I imagine they do that to support the rings, but that also means that higher RPMs can be more difficult to get. 

 

I run a BGM RT225 kit with reed and Franspeed Super Tourer exhaust. I have my barrel set up to:  178˚ exhaust / 126˚ transfers / 26.5˚ blow down. My exhaust port is pretty square at the top. I recently set up a piston port Casa 185 kit with a peakier tune and the waste gas is a big problem, because the intake is 144˚.

 

 

My judgement on your cylinder, if the ports' bottoms are all lined up, is to raise the barrel 1mm and raise the piston 2mm. This will be better than just removing material from the exhaust and hoping for the best. Is the crankshaft new? Didn't Tino make these kits? What does he say about this? 

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 Didn't Tino make these kits? What does he say about this? 

 

On the one I built with similiar unique port timing I was told just to run it and it'd be fine. So far I've just got it running on the lift but it sounds good.

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Here you go:

Fit piston

Torque hardware

Measure squish

Profit

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