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Old 07-11-2008, 01:07 AM   #1
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Default modified motor

tell me about your modified motors
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Old 07-11-2008, 03:57 AM   #2
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Lightbulb Not Highly Modified but.........................

I read in this section somewhere a mod that caught my eye. The guy had taken a crankshaft and basically turned the outer most portion of the crank into an impeller blade to act as a compressor. I thought of doing something like that a while back but thought it was a bit too wild, but then again I love big horsepower and tall gearing. My driving sucks so at least I can make em wonder when I go past them on the long staight at Revelation. A lot of Team drivers come there so it's always a good place to "track test" anything I mod. Anyway, I dug through several boxes of Rossi stuff and pieced together a older 7 port motor, left my usual thinking behind and carved about 8 blades into the crank with a angle grinder and then finished them with the trusty old Dremel and hand file. Since I wanted a test of this mod only and nothing else it really didn't take long to do, and it will tell me at the track if it works or not. I through a RB card on it with a 8mm restrictor, a Foroni turbo blue glass clutch with 14 tooth bell and a J3 pipe on my well used Losi buggy. Boy was I surprised when I fired it up! It sounds like no other Rossi I've ever done, very crisp and spools up real nice. Can't wait to run it. I'm thinking Dana will probably be working on the track in the morning so I'll get him to run a couple of laps with it and let you know the outcome.
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Old 07-11-2008, 06:36 AM   #3
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heres mine inside pic's of 3port rb i modded
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Old 07-11-2008, 07:19 AM   #4
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LOL, I keep telling people if you can cut the correct angles and get the blades to compress 4:1, it actually DOES work and it works very well. I have been doing more and more lately and the harmonics decrease internally and the spool up time is FAST!! It doesn't take much throttle to kick it in the ass and get things moving. I make a believer out of people one person at a time. I also sent a turboed S5 to Xtreme RC for a dyno test and a field report in a car of their choice so stay tuned for that issue. I don't have an exact month yet but I sent it in back in April and Derek said it was in the works.
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Old 07-11-2008, 10:24 AM   #5
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Thumbs up Powerhouse Hesitant at first........

I was alittle hessitant at first mainly because I had recently built a flow bench based on the preasure differential method and a mod like this isn't really going to show dramtic results since it's a static test. Damn, I wish I had a dyno! I'm glad to hear you sent one to RC, that should be really interesting! What do you think or know about run time with kind of mod? Also, when I was in the development stage of the flow bench I spent quite a bit of time with Rick Blood at FloData Engr in Anaheim and learned quite a few things that I suppose some peole have a hard time with understanding. Mainly because since you can't see with your eyes, air moving, it sometimes becomes hard to understand. Anyway, he emphasized that the best lubricant for air, is air! the small amount of turbulance on the surface that air is moving across is the layer of lubricant in a port or against any surface where there is air movement. I won't go into all the details but you have embraced that and it is TRUE. The only thing I polish is the top fin of a motor!
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Old 07-11-2008, 11:23 AM   #6
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I don't know the boys in Anaheim but I certainly know what I have learned and experimented with myself and I do try my best to give people what works. It may not be the shiniest penny in the pot but it will work the way it was intended. I ran an experiment years ago about polished versus rougher surfaces and found that the rougher surface created less drag and didn't allow the fuel to touch the surface due to the tummbling of the air molecules along the surface acting like a bearing as oppossed to draging along the surface like a bushing would. Both polished and unpolished surfaces will still perform but the rougher contour will perform better. How much better? Its worth 5hp on a 1000cc pro-stock engine but at a scale this size it will be very minute. What I can say is, I have alot more time to focus on the important parts of the engine such as degreeing the ports, timing the ports, adding auxillary ports if needed, crank timing etc. I don't waste the time polishing because it will not outperform a non polished surface and I have proven it many times with different types of engines ranging from a 50cc y-zinger all the way up to a 502ci blower motor. If you are the type that a polished surface with unaltered ports makes you all warm and fuzzy inside, then more power to you but I want a motor that works!!
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Old 07-11-2008, 11:46 AM   #7
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Default It's easy.....................

to get sidetracked! 100% with you on the surface prep. I went as far as actually flow testing different grit numbers in rolled legths of tubing to ascertain the best "Reynolds" number but it was tedious and there was little difference. Rick at FloData builds benches for Nascar Teams. Very very nice guy and has had lots of experience with small two stroke motors too. OK, back to my original, got sideracked again, question. Do you think this compressor crank effects run time? Back to being sidetracked, the age old controversary about Flow Testing a small 2 stroke engine, some say it can't be done, and you don't end up with numbers like "my HD EVO heads flow 185 cfm with 20 inches of water". But with the preas. differential method you can definately compare before and after mods or use as a tool o verify you are producing a duplicate of the last hot rod motor. It always amazes me how much goes on in a motor, less than 1/4 cubic inch, with 3 moving parts that makes 12 HP per Cubic Inch!!!!!!!!!!!!!!!!!! Would love to build a opposed twin .24 single carb major compressor crank mid section, layed out flat on the chassis screaming monster.
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Old 07-11-2008, 12:29 PM   #8
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Originally Posted by randy snyder View Post
to get sidetracked! 100% with you on the surface prep. I went as far as actually flow testing different grit numbers in rolled legths of tubing to ascertain the best "Reynolds" number but it was tedious and there was little difference. Rick at FloData builds benches for Nascar Teams. Very very nice guy and has had lots of experience with small two stroke motors too. OK, back to my original, got sideracked again, question. Do you think this compressor crank effects run time? Back to being sidetracked, the age old controversary about Flow Testing a small 2 stroke engine, some say it can't be done, and you don't end up with numbers like "my HD EVO heads flow 185 cfm with 20 inches of water". But with the preas. differential method you can definately compare before and after mods or use as a tool o verify you are producing a duplicate of the last hot rod motor. It always amazes me how much goes on in a motor, less than 1/4 cubic inch, with 3 moving parts that makes 12 HP per Cubic Inch!!!!!!!!!!!!!!!!!! Would love to build a opposed twin .24 single carb major compressor crank mid section, layed out flat on the chassis screaming monster.
Looks like you are looking at modding from all angles and want numbers to prove it I think that is awesome. my question I guess its a question maybe more of a statement you tell me is that if you put two engines same engines side by side one flowed more air/fuel the other flowed less air/fuel but did it more efficiently. That the engine with less flow would be fastter.So it's not how much it flows but how well it flows. Just my thinking looking forward to reading everyone's thoughts.
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Old 07-11-2008, 12:43 PM   #9
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Default side by side

I would have to agree with that. Everything else being equal, the one that is more effiecent would run better, more power and longer run time. So if you took two identical motors, theoritacally, left one alone and did a proper surface prep to the other one it would improve, but, it WOULD probably flow a better number. Dana at Revelation told me a story about McCoy bringing in 100 identical motors, dyno testing every one and found, 3 really good ones, 3 really bad ones and everything else somewhere in the middle. The major difference being the sizing of the piston and liner!
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Old 07-11-2008, 01:12 PM   #10
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I also read somewhere else and think it is a great point that far as a surface being polished it is different for example fuel flowing of a polished intake port on a 4 stroke engine the fuel would drag or not be atomized but it would not be the same on a nitro engine because the fuel/air is moving as well as the crank so you would see gains by polishing the crank .I agree do you?
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Old 07-12-2008, 02:06 PM   #11
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Cool polishing

From everthing I've tested I would have to stick by the non polished surfaces. On the Flow bench I ran a test by taking a motor and polishing the crank, case, liner so that everything was like pretty and shiny. I flowed it that way and then re-did the whole thing with about a 120 grit finish. It flowed better with the rough finish! So these days if someone wants a polish, I polish the top fin of the head!
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Old 07-12-2008, 03:25 PM   #12
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From everthing I've tested I would have to stick by the non polished surfaces. On the Flow bench I ran a test by taking a motor and polishing the crank, case, liner so that everything was like pretty and shiny. I flowed it that way and then re-did the whole thing with about a 120 grit finish. It flowed better with the rough finish! So these days if someone wants a polish, I polish the top fin of the head!
Well the flow bench does not lie how much better did the rough flow 5% 10%
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Old 07-12-2008, 05:22 PM   #13
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To properly flow test a polished crank vs a rough crank you would need to spin the motor up to speed....Many variables can change when the crank is spinning 30 000 RPM......I do know a rough surface flows better when the surface is static, but I am not quite positive that holds true for a surface moving as fast as the barrel of the crank.....
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