motor mod question.

[ken t.]

<_<

I have noticed when looking at photo's of various engine modders works that many people polish the crank. I had always thought that internals of engines should not be polished since the rough finish will actually help the air and fuel to mix.

Does this not apply to nitro motors as well or does nitro fuel react differently to such mods than gasoline.

 

[NITROSNIFER]

<_< I had always thought about that as well. But after looking, thinking and then just doing it I found no adverse side affects to polishing any of the internals. The smooth finish I found actualy helps in the flow through the engine and ports. I looked at it this way, with a cranshaft, rod and piston flying around in the case I should never have a mixing problem. But with a smooth crank (.21 inside port) and other pieces the fuel/air will move easier past them and not slow down as much. I could be wrong but have had great success with doing this kind of mod and my engines sure seem to like it.

 

[ken t.]

<_< I had always thought about that as well. But after looking, thinking and then just doing it I found no adverse side affects to polishing any of the internals. The smooth finish I found actualy helps in the flow through the engine and ports. I looked at it this way, with a cranshaft, rod and piston flying around in the case I should never have a mixing problem. But with a smooth crank (.21 inside port) and other pieces the fuel/air will move easier past them and not slow down as much. I could be wrong but have had great success with doing this kind of mod and my engines sure seem to like it. 

91102[/snapback]

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Well that does make sense, I had read somewhere that gas can actually go back to a liquid state when it comes in contact with a polished surface. Perhaps nitro does not have this same tendancy.

The polished cranks sure look trick

 

[Rickracer]

I'm no small engine guru, but I've done a lot of porting in my years as an automotive technician, mostly on hot street andrace cars, and a few fullsize outboards. My opinion is that cranks and rotating stuff needs to be flowed and polished and stationary intake surfaces should be slightly rough to aid in keeping the fuel mix atomized. Exhaust surfaces should be smooth as possible, mirror finish would be ideal. I'm not sure if the same principles would apply to nitromethane and alcohol and the scale involved though. B)

 

[AndyBrown]

Rickracer is right in my opinion.

Some moddifers polish everything because their customers want to see Shiny stuff.

My engines look like roadrash inside. LOL.......but they hold lots of records.

 

[Don Ferrette]

My engines look like roadrash inside.  LOL.......but they hold lots of records.

91112[/snapback]

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Yup, you should see the inside of my record holding MAC45, the only thing shiny there is the sleeve. Polish is for the ouside of scale boats.

 

[AndyBrown]

Air/fuel ratio for gasoline is 16/1 , meaning mostly air.

Air/fuel ratio for 70% nitro is about 1.5/1 , meaning a hugh amont of liquid that needs to be busted up.

 

[rhomodel]

Strnage as it sounds, but very often a rough surface enhances flow. As the rough surface "holds" a little of the fuel-air mixtures, it forms a layer around the surface which allows a bit farther the fuel air mixtures to flow better without disturbing it too much. In nature a shark skin is a good example of this. However with a 25-30 K revving engine I don't know it this boundry layer will be kept in place.

Julius

 

[Rickracer]

What happens is the rough surface keeps the layer of air molecules closest to it tumbling, and any raw fuel that gets near the walls gets caught up in this turbulent layer and is atomized. I use 80 or 60 grit stones or sandpaper rolls on car and boat intakes and crankcase or heads, whichever applies. Given that alcohol evaporates more easily/quickly than gasoline, it makes sense that it would help. B)

 

[ken t.]

<_<

Sure would be nice to have a dyno to comare a polished engine versus a none polished one. B)

 

[Rickracer]

My engines look like roadrash inside. LOL.......but they hold lots of records.

What better proof do ya need?

 

[F.Orlic]

I have done some bench testing with Novarossi polished vs non polished.

This was done with constant load , RPM and temp were the only things recorded, than the engine was taken apart, sleeve and crank were roughed out and the engine was ran again within 20 min of the first run. Withhout any change engine RPM stayed within 100 RPM. I have done this test only with novarossi and I suspect because the distance fuel has to travel at the speed it travels polished or not makes next to no difference. All my engines have very good finish and they set many records, so it can be done both ways.

 

[ken t.]

I guess it comes back to being a small part of a bigger picture. A good motor is based on a number of aspects and stuff like polishing or not is more personal preference.