Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Engine help needed

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Old 08-10-2013, 05:55 PM
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speedracerntrixie
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Default Engine help needed

Here is the deal, Im great at tuning an engine and can get everything it has to offer and can do mild mods. I just came home from a race series that I usually do very well in with a 3rd place finish. Even after that disappointing finish I am the points leader in the series but the guys are nipping at my heels. Bottom line is I need more power but have taken the engine to the limit of my knowledge. What I think I want to do next is extend the exhaust and intake duration. Exhaust I have done some and it,s at close to 140 degrees. My biggest question is the intake. Do I want it to open earlier or close later? Here are the particulars:

Rossi .45 VP, 10mm carb, Ultra thrust muffler, 15% nitro. Currently spins an APC 8.75X 7.5 at 17K. Any help is appreciated
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Old 08-11-2013, 04:54 PM
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lfinney
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i would extend exhaust duration to 170-172 degrees, more duration intake on the closing side maybe 3-5 degrees more, then use a very cold plug and start with shim adjustments
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Old 08-11-2013, 06:19 PM
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speedracerntrixie
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That sounds like a good place to start. I can take the sleeve into work and have the exhaust port raised on a mill. Knowing that the intake needs to somewhat match what I do on the exhaust, I just didn't know which side to open up. The engine does have a fairly new piston and liner in it. At this point it has 3/4 gallon through it. I'm curious about the cold plug and head shims. Right now it has a single copper shim of .1mm. I have not had any plug issues running either and OS #8 or an Enya #3. After 5 rounds of racing yesterday the plug was a slight gold color, exhaust residue was a faint pink. This tells me that the combustion is not getting too hot. I will try some 20% nitro after I make some mods. If I have an issue with pre-ignition I will remove some material from the combustion bowl so I can retain the squish band. The RPM figures with the prop previously mentioned are fairly good but I think the airplane has too much drag for the prop.
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Old 08-11-2013, 07:16 PM
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Speed
I assume this is the white macci, in which case nice job. You brought the plane home in one piece. I guess this means the trash talk will commence in that other thread.
Cool, we need to keep those people with engines that have valves and cams and stuff at bay.

A couple of questions. Do you have to run a muffler.
If not, run the exhaust timing up to 175 or so and run a full length tuned pipe.

If you have to run a muffler, call Dubb Jett, tell him what RPM you are running and he will hook you up with a tuned Jett muffler for your RPM

I must admit, 17K with 140 exhaust timing is pretty impressive.

Shoot me a PM and we can talk particulars.

Scott Mooney
Scott Mooney Racing Engines
Reno NV
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Old 08-12-2013, 11:51 AM
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Exhaust timing has some play in it but really need to know the blowdown, For that size engine .100-.105" is a good area to start. Some engines have to have a high exhaust port (180 degrees) to reach this number because of the transfers being higher. a ultra thrust is the same design as the "Jett" mufflers. They are both 1/4 wave pipes. what is the crank timing on that engine?
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Old 08-12-2013, 02:08 PM
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the low end of timing exhaust wise is 154 on the small rossi's 4-45 size, the gold colored jett pipes are for higher revs, and the black one is for 19-24k plus range, if you don't have the exhaust duration, you are losing the boost time that the ultrathrust or pipe system needs, I run the rossi 40 at 18-19 k with stock timings with pipe on 16 percent fuel effortlessly, cold plugs help with detonation prevention are you running a spacer between engine and pipe if so you need to find a way to remove it from the equation
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Old 08-12-2013, 02:27 PM
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Ifinney, that post is a little confusing to me. My understanding is that to get the most out of the Ultrathrust muffler that I need to increase exhaust duration but that you run a .40 with stock timing at 18K+. What size prop and what muffler or pipe are you using? I am not running a spacer as I knew it would mess with the timing. Knowing that plug temp adjusts the " ignition timing " so to speak I know that if I was having a detonation issue I could go to a cooler plug, reduce compression or run less nitro. At this time I do not have that issue. To me it sounds like two things should happen. Increase both intake and exhaust duration to get the potential out of the Ultrathrust muffler and 10mm carb. Correct me if I am wrong and thanks for all your input to this point.

Jeff, I don't know what the crank timing is, I need to pull the engine out of the airplane and measure.

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Old 08-12-2013, 08:21 PM
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lfinney
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the ultrathusts come in three rpm ranges, the red is standard next up is the gold, then the black one. the different rossi's used the same timing on crank and intake ports, the exhaust duration was the only thing changed, I just examines some of my stock and this is the norm..so raise exhaust to 168-172 degrees, I checked my nelson sleeved Os 61 sx setup and they all use stock factory intake timing on sleeve, and they do rev like crazy and make tons of power, with excellent idle and transition , if you have more shims measure them all as you raise timing you lose dynamic compression, so check deck height 10-12 thou should be good/
I use the macs wizard, and the standard open pipe, I can post a pic of the header if you like, for length approximation..
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Old 08-12-2013, 08:38 PM
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Default clarence kee specs on rossi 40 class engines

the ultrathusts come in three rpm ranges, the red is standard next up is the gold, then the black one. the different rossi's used the same timing on crank and intake ports, the exhaust duration was the only thing changed, I just examines some of my stock and this is the norm..so raise exhaust to 168-172 degrees, I checked my nelson sleeved Os 61 sx setup and they all use stock factory intake timing on sleeve, and they do rev like crazy and make tons of power, with excellent idle and transition , if you have more shims measure them all as you raise timing you lose dynamic compression, so check deck height 10-12 thou should be good/
I use the macs wizard, and the standard open pipe, I can post a pic of the header if you like, for length approximation.. here is the Clarence Lee review with timing specs for the .40, so its a good starting point, he advises the 170 degree timing mod for full pipe performance as well. i am trying to post Clarence Lee's review of the .40 rossi, it has all the timing spec as well as prop data
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Old 08-12-2013, 08:50 PM
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Default Lee review

here is the pdf
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Old 08-13-2013, 08:29 PM
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Finney the Ultrathrus mufflers were made by nelson and were one color "natural". The colored ones are from Jett and have different colors.
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Old 08-14-2013, 06:38 PM
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Originally Posted by airraptor View Post
Finney, the Ultrathrust mufflers were made by nelson and were one color "natural". The colored ones are from Jett and have different colors.
Eeee-Yup......
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Old 08-21-2013, 06:29 PM
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Ok I did some of the suggested mods. I raised the exhaust port .030 and cleaned up the crankshaft. This included cutting a bevel into the sides of the intake opening and making it .015 larger on the closing side. I also cleaned up the passage and cleaned up the crank case under the carb. I had a 12mm Picco carb so I threw that on to see what would happen. After running a tank through it at a rich setting I fired it up and peaked it out some. With an APC 9X7.5 I was able to get a constant 17K. This is actually quite a power boost. Although the numbers are the same, the 9X7.5 has more blade area then the 8.75X7.5 I was running previously. Now all I need to do is get some free time to fly it. One never really knows if it's faster or not until you are rounding pylons with 3 other airplanes though.
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Old 09-08-2013, 04:24 PM
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I finally got time to fly the airplane today. The mods seemed to give me a noticeable speed increase. Realizing this is somewhat subjective, the airplane was popping through the turns harder. We fly a 700' course and I was averaging between 9.5 and 10 second laps. Last time out it was closer to 11 second laps. At the end of 2 flights I looked at the plug and it had just a light gold tint and the element looked new so I think I can bump up the compression a touch more or throw some 20% nitro at it.
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Old 09-09-2013, 01:58 PM
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Would you like to try one of my modified piston-rod & liners ? I did one for a guy in england - 19500 on the test stand 8.8 x 8.75/9 pylon blade,
K&B 1L plug 15%coolpower all syn. diffrent pipe & carby arrangement -
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Old 09-10-2013, 03:06 PM
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speedracerntrixie
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Originally Posted by scoeroo View Post
Would you like to try one of my modified piston-rod & liners ? I did one for a guy in england - 19500 on the test stand 8.8 x 8.75/9 pylon blade,
K&B 1L plug 15%coolpower all syn. diffrent pipe & carby arrangement -

I have tried some of those narrow blade pylon props. My airframe has a bit too much drag for them to work well.
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