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Novarossi Mephisto 21 running 25% fuel

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Novarossi Mephisto 21 running 25% fuel

Old 08-19-2019, 02:49 PM
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Default Novarossi Mephisto 21 running 25% fuel

The spec of the Mephisto 21 said the recommended fuel is 16% nitro, if I run it on 25% nitro fuel, do I need to shim the head up? If so, any idea by how much? Might be hard over here to get the 28025 head button for 25% nitro fuel. Thanks
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Old 08-19-2019, 03:00 PM
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Wasn't a 2nd button delivered with the engine?

But yes, it is wise to add an 0.1mm shim or maybe 0,05 by replacing an 0.1 for a 0.15
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Old 08-19-2019, 07:22 PM
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Originally Posted by Roelof View Post
Wasn't a 2nd button delivered with the engine?

But yes, it is wise to add an 0.1mm shim or maybe 0,05 by replacing an 0.1 for a 0.15
This engine is delivered only with the 28038 button. The 28025 button must be purchase separately.
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Old 08-19-2019, 07:28 PM
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Originally Posted by blackshark3 View Post
The spec of the Mephisto 21 said the recommended fuel is 16% nitro, if I run it on 25% nitro fuel, do I need to shim the head up? If so, any idea by how much? Might be hard over here to get the 28025 head button for 25% nitro fuel. Thanks
I finally got my Mephisto to perform. It turns out I had a damaged bearing, probably from breakin. But now that I replaced the bearing and have the piston seated in the liner, it runs very well. Wish there was a radar available as I think this is the fastest straight speed I have ever had. Now working on headers and pipes to get the car around the track in better times. This new header 41013S perked up one of my old Flash Specials, so it might be the ticket for the Mephisto. Trying this stuff is fun.
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Old 12-16-2020, 09:14 AM
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Originally Posted by davidl View Post
This engine is delivered only with the 28038 button. The 28025 button must be purchase separately.
sorry for the question, it's an old topic ..
I am in the same situation, I have bought the 28025 cylinder head for nitro 25% but I don't know if I have to put washers on it or leave the ones with the 16% cylinder head on
What washers should I put with the 28025 cylinder head (25% nitro), none?

thanks!
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Old 12-16-2020, 02:52 PM
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Just swap in the 28025 head, use all the shims
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Old 08-25-2021, 12:55 PM
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So, I received today 2x Novarossi Mephisto gt5 .21 engines and as always I open my new engines, dissemble them, clean them and prep them for hot oil bath break in..
But with those 2 something really odd is going on, its like they are 2 different engines.
On the one the headbutton has a bigger dome than the other and 0.8mm stack off shims, and the other has smaller dome and 0.95mm stack of shims, different crank opening and crank weights material and different front bearing, and backplate. On the one crank it says 09/18 and the other 01/20. The headbuttons, crankshafts and conrods don't have part numbers on them.













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Old 09-02-2021, 11:48 PM
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Does any of you have a Novarossi Mephisto gt5 .21 to upload some pics to compare it with mine?
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Old 09-03-2021, 03:38 AM
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My experience is that between production series there can be differences. Also keep in mind that at the end several engines were just assembled with left over stock parts.
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Old 09-03-2021, 09:08 AM
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Yes I know but its like 2 different engines.
Nevertheless I wanted to stock up for my GT so it doesn't matter, I will use both, eat them and go to werks GT..
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Old 09-03-2021, 12:07 PM
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Visible They are different, performance wise they can be (almost) the same. The smaller burn room looks like a 16% model but then it is also shimmed higher to work with 25%
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Old 09-03-2021, 02:35 PM
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Thanks for the info!! I will change the 16% headbutton and shim it for 25% and run them to check if they are any different!!
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Old 09-05-2021, 09:49 PM
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My GT5 Mephisto had a DLC coated crank, the smaller bowl volume head for 16% and came with 1 alloy and 2 copper head shims. The head and rod were both laser etched with NR details. I cant post pics as my post count isn't high enough.

It would be wise to measure the squish clearance on both of those engines prior to running them, just for piece of mind more than anything. (in other words, not just counting shims and trusting it. Particularly with the one with a 16% bowl if you plan on running 25% in it.) 17 to 25 thou (0.45mm to 0.65mm) for the large volume bowl on 25%. I'm not a fan of shimming up for higher nitro personally but add 4 thou (0.10mm) to those numbers with the small bowl if that's the way you go. My preference is to go for the tighter values for squish clearance in GT's as the cars are heavy and the effective pipe length is longer, meaning less impact on peak rpm.
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Old 09-05-2021, 10:50 PM
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Originally Posted by rc_hydro View Post
My GT5 Mephisto had a DLC coated crank, the smaller bowl volume head for 16% and came with 1 alloy and 2 copper head shims. The head and rod were both laser etched with NR details. I cant post pics as my post count isn't high enough.

It would be wise to measure the squish clearance on both of those engines prior to running them, just for piece of mind more than anything. (in other words, not just counting shims and trusting it. Particularly with the one with a 16% bowl if you plan on running 25% in it.) 17 to 25 thou (0.45mm to 0.65mm) for the large volume bowl on 25%. I'm not a fan of shimming up for higher nitro personally but add 4 thou (0.10mm) to those numbers with the small bowl if that's the way you go. My preference is to go for the tighter values for squish clearance in GT's as the cars are heavy and the effective pipe length is longer, meaning less impact on peak rpm.
Thanks for the reply. I have the optional 28025 button head for 25% so I will change to those and shim the at 0.7 as their manual says for 25%.
When you are able to and if its easy to post some pics of the internals so that I can compare them I will really appreciate it!
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