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 modifications

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Old 06-14-2007, 01:25 PM
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PHall
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Default Engine modifications

I have read where some of the faster planes have higher timed engines but I really have not found any information on specific numbers. I would be interested in .40 and .60 mods if anybody has any suggestions.

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Old 06-14-2007, 05:19 PM
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dclancey
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Default RE: Engine modifications

BUY A NELSON 40 OR JET 40. A STOCK ENGINE WILL NOT HOLD UP AFTER DOING ANY MODS TO MAKE IT FASTER. BEEN THER DONE THAT.
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Old 06-15-2007, 01:28 PM
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Default RE: Engine modifications

http://rcboat.com/past.htm
Some interesting stuff here, especially the Exhaust Timing, Combustion chambers and Tuned Pipe articles.

A few years ago I took a box stock (but broken in) TT40 pro and did some mods to it, I would need to go back and look at my notes but basically went from about 15.8k to 18.8k rpm on 15% fuel with an APC 8x8 prop. I also added a MACS tuned pipe and header. I did change out the back bearing, those were a problem on these engines. I also tried 20 and 25% fuel which gave a hundred or so rpm increase but didn't think it was worth the extra cost of the fuel. Basically I wanted to see how far I could take it before it blew up, it never did, so I built a plane for it, pictured, and those that saw it fly estimated it was doing between 130 and 140 mph.
All mods were done one at a time with several bench runs. I used two tachs, one hand held and one with a magnetic pickup attached to the engine and battery operated, they were always within 100 rpm of each other.
Some of the mods:
Raised exhaust port (more duration)
Chamfered the boost and intake ports
More clearance between crank pin and rod bushing
Set head clearance at .014 at first but kept blowing plugs at 18k rpm, increased it to .017 and that problem went away.
Drilled out the fuel nipple on the carb, the engine became hard to needle until I did this.
Set the tuned pipe length, ended up shortening it by an inch or so

Some observations:
As you go up on nitro and rpm, 3000 in this case, you need more head clearance. The engine will detonate (pre-ignition) if you don't do this.
If you can not get a steady tach reading, the engine is detonating, the rpm jumps around plus or minus 100 rpm. This shows up as pitting either on the top of the piston or on the combustion chamber.
The engines fuel consumption doubled, at least! A 4 oz tank lasted about 1 1/2 minutes at full throttle on the bench.

In the end it was an interesting experiment.


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Old 06-15-2007, 06:24 PM
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Default RE: Engine modifications

Thanks for the tips. We have been do the boats for a few years now and turning engines up between 17K and 25K. As far as the engines not holding up I would have to guess that the airplane engines are not the quality of those for boats because Novarossi, Picco, CMB, and MAC can all take the rpm. You should hear a Novarossi 21 hit the pipe's fourth stage. AWESOME.
I have a JETT 40 and it is great out of the box, I just thought a speed plane could turn well over 20K.
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Old 06-15-2007, 07:36 PM
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Default RE: Engine modifications

Q40 engines will turn well over that...well over 25,000 actually, and the FAI pylon (F3D ) IR and MB40's will go 32-33,000 or more...
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Old 06-15-2007, 07:44 PM
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Default RE: Engine modifications

Weigh the boat motors, they have a lot more beef in the case than a typical racing airplane motor. BTW, an open piped ST X-40 or Nelson F1 engine turned around 27-28K in the air and only weighed 12 oz or so.
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Old 06-15-2007, 09:56 PM
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Default RE: Engine modifications

There is nothing more fun than to show up at the flying field with a stock looking engine and watching heads turn when your engine is not what it appears to be. There is also much gratification in scaring the "woohaas" out of the guys that have had their wallets emptied by buying a thoroughbred racing engine instead of making it. You may not stay on top with your "labor of love" racing engine but you will send the "big boys" into a tizzy thinking that they have to go spend some more money! The Nelsons and Jetts are hard to beat..no doubt about it...but they can be beat. And when you do beat one, it infurriates them. Now that there's funny!!! Being on top is great but sooner or later, no matter how much money you have spent, you will get dethroned. I prefer the cheap and sneaky approach plus you get a better education on what makes an engine tick. We learn from our mistakes. That is why I'm getting smarter every day! Let's go flying!
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Old 06-16-2007, 12:43 AM
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Default RE: Engine modifications

Lowering the weight of the moving parts will show gains regardless of what rpm you prop the engine to run at.
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Old 06-25-2007, 01:56 PM
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Default RE: Engine modifications

Good to hear some big numbers. I had heard of these before. Now, how to obtain them and back to the question. How about some numbers. Exhaust, transfer, boost, intake open/close, head volume, head clearance

Either for a 40 or 60 will be fine and a good starting point is fine as well. I have seen the rcboat.com stuff and the software is great for telling you how much material to remove to get certain timings. But the numbers themselves can only come from experience. And from experience I know that a Jett or Nelson will have different timings than an OS or Thunder Tigre. MAC engines come with better timings than most engines, but with modifications to PICCO and CMB these engines will run with the MAC. And for the same life span. I am just looking for a little direction. Not trying to make a JETT or Nelson from an average engine.






combatpigg,
We ain't turn'n those brass flywheels anymore. The weight thing just ain't the entire case. As far as weight goes, my rear exhaust Rossi is a pig.


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Old 06-25-2007, 02:30 PM
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Default RE: Engine modifications

There are a few other guys (not me...not yet anyway ) that could give you some exact numbers...maybe they will chime in here before too much longer?

From what I have read, I have gathered that the racing boat and racing aircraft engines have fairly similar timing numbers?

I would think that r.p.m. is r.p.m. no matter what type of prop (air or water ) the engine is spinning, it's mainly the shape of the torque curve and where the peak(s) occur?
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Old 06-25-2007, 05:32 PM
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Default RE: Engine modifications

Does anyone also have tips to modify a 4-stroke engine?
Or know a link to a article or something like that.
I know that a 4-stroke won´t rev as much as a 2S, but I like very much de sound of a 4S in a warbird plane (or in my case it would go to a caudron C-460[&:])

Thanks
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Old 06-25-2007, 05:36 PM
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Default RE: Engine modifications

A four stroke would need modified cam shafts. Not so easy.
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