Looking on the OS Engines, stumbled upon the news of a new Shimo edition of his engine. Still 9 ports but not so much information about it. They talk about new process for piston and... seems they put some shims to move the sleeve height and change the timing.

Wondering what differences among the visible ones (different cooling head - smaller, different color). Crankcase looks like the same as 2106 but without the manual and the parts list for the engine is somewhat difficult to see what's different.

https://www.os-engines.co.jp/osspeed...oad/1fg01.html

Edit: Forgot to include the link.

Probably based on the R2106 which its crankshaft has a much larger timing than all previous models.

The shims are no sleeve shims but exhaust shims to lengthen up the exhaust a tiny bit for a little bit more bottom torque w/o the need for a different manifold. Funny thing is that a year ago I placed this on my FB page, just quick and dirty made for a test and nu I saw this Shimo model. Makes you wonder where he got his idea from....

Roelof Placing shims there, alters the manifold lenght... but differences of half and one millimiter makes me wonder... ¿found enough difference between them or was just splitting hairs?

Looks like engines will be available on Europe about half January. Wondering if Rody took a look on the guts of it to comment?

Remember the Novarossi 5/6/7 fin manifolds? Those fins are just about 2.5~3mm separated and you could feel a huge difference between them. I made them from 1mm teflon and can stack up 2 of them behind the rubber seal. On the exhaust side the dimensions are different but if I make them for there too I could go up to 4mm extra length, that for sure will be a lot to notice.

But I believe the MR05 manifold that is in the combo package is a short one so I believe with these shims something will be noticeable. And as the tekst says, it is a finetune.

and OS sells mr02, 03, 04 and 05 manifolds now

Yep, but I have not seen any list of the length or what kind of performance is linked to those manifolds. Also the topicstart talks about a combo package, you can buy a 50 dollar manifold not knowing what to get or you can get a few dollar shims with which you know you get some better low rpm performance.

This is something that I hate: Lack of details from the manufacturer. Nothing like lenght or whatever about it. So basically they list it and you mighty test them by trial and error? a somewhat expensive trial and error for 50 €/US$ a test.

VS_Rody can you assist with technical info on the various OS manifolds and how they compare to each other?

Hello,

The SHIMO3 comes indeed with some extra shims to play with the manifold length, but since I have not received them I cannot tell you more in detail for how its made and applied. So we have to wait a little untill I have them in my hands.

As for the OS manifolds, yes indeed I agree that there is no real clear measure and of what they should really gain
MR02 is the one which is bend down and gives you the usual look with the pipe horizontal.
MR03 is the horizontal manifold quite long and make the pipe touch and melt the body very often in that area. This pipes gives you a better low-mid RPM but less top rpm
MR04 is also horizontal and shorter then the MR03 shold give better mid and top rpm
MR05 is for me almost the same, cannot see a lot of difference but according to to OS works the bes with their 2196 pipe.

In the beginning we used a lot the MR02/2165 combination.
Now the best combination is for me the MR05/2196 combo but also uses a little more fuel.

Many combinations are possible but I suggest you try and keep things as simple as possible to get a relaiable engine and power.

Probably Rody can but I think it is a task for OS to do this. As mentioned the 5, 6 and 7 fin manifolds from Novarossi were very clear

This is what AI has to say about the different OS manifolds:

O.S. Speed Exhaust Manifold Differences
The manifolds vary in length and angle, which changes the power band of the engine they are paired with.

• MR02: This manifold is designed to provide a quicker response in the low-to-middle power range.
• MR03 (WC): Used by the 2019 World Championship winner, this manifold is designed for a smooth transition of power delivery from low speed to high speed, making it easy to handle. It has a revised shape compared to the MR02.
• MR04: This version features an adjusted angle from the MR03, further improving the mid-range power characteristics and extending smoothly into the high-speed range without compromise.
• MR05: The newest in the series, the MR05 has a different length and angle compared to the MR04. Its design goal is to make carburetor adjustments easier across any power range.

Interesting for sure. I have been extremely happy with the 2106 just wondering what is different on shimo 3 now that it is 9 port and ceramic rear bearing.

I run the 02 header only when I need to make fuel miledge. Mostly run 04 or 05 header with the tr03 pipe. I usually try both at every race and see what feels better. The 05 to me sometimes runs rich on an infield straight no explanation just know when I go to 04 that goes away usually.

Seems to be the same as a 2106 but unless someone gets one and starts measuring it (Roelof, Rody, ...) we cannot say anything that doesn't falls into speculation. What seemed strange is lately (from Black friday to today) the 2106 is getting discounted (not much but... some).

Maybe an hypothetic 2107 is around the corner?

If I look at the older Shimo-2 then the main difference was a higher exhaust port and I believe it was more like the R21-Euro edition (regarding its story that it was made for the longer Euro tracks) but I can not tell because I never had an Euro in my hands. It would not surprise me if the Shimo-3 has a same timing difference over a stock R2106.

Here a list of most OS I had in my hands with also the R2106 and the 5 port R21-v2 listed.