Troy-RCU

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I am running a K&B 6.5 rear exhaust that I am told was an old Formula 1 motor. It originally had a venturi carb on it and just a header for a straight pipe. I modified it to use a Magnum Pro .45 throttled carburetor (it works and fits) and also a Mac quiet pipe with matching header. It runs decent but I am trying to get it tuned better. I am searching for anyone who has had experience running this motor in years past as I hear the porting/timing is set pretty high. Also mentioned was that it may not run well on a tuned pipe and low nitro (under 20%). The one thing I do read is that this motor likes to be rev'd and that's all I'm trying to do.

Currently I am running a 7.5X8 APC Q40 carbon prop on a delta. I am able to squeeze about 19,500 RPM but in the air it still feels like it is not unloading all the way. Here is a video of one flight, keep in mind the needle setting in this was a bit rich, about 18,250 tached on the ground.

Any help, hints, or good links to more info would be appreciated.

http://www.youtube.com/watch?v=TPnXLDbEO9M

freeair

i used to race one of these K& B 40,s in r/c powerboats and yes they do have high port timings which is needed for maximum rpms, what you need to get sorted out is Head Clearance, Pipe Length, prop size and nitro content.

garys

Troy,
If it's a Formula One engine, and the timing hasn't been modified, the exhaust timing is probably too mild for a full tuned pipe. F1 engines were meant for the constant diameter "mini pipe" of about 3.5" length, not a full tuned pipe.

For example. The Nelson Q500 engines used the same liner and port timing as the F1 engines, while the Q40 liners were the same as the FAI liners for the tuned pipes.

Troy-RCU

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OK, so I am new to 'over-haulin' race motors. So if I do have the F1 timing, would I have a chance of getting better performance with adding shims, subtracting/machining clearance on the head... or maybe a new liner from K&B? I don't think a straight pipe would make friends at my field and surrounding neighbors but if I have to do some work to the motor I'm happy to learn. I guess this is what guys converting to electric systems feel like and want to get the best performance. I was spoiled all those years with excellent running YS and OS motors that just fired up and ran for me.

ChrisAttebery

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Hey Troy,

The MAC's airplane pipe is very mild. If that motor has "low" timing you need to make the pipe alot shorter to make it rev up. Another option would be to get a marine pipe that will have steeper cones and hit the tune harder. What's the distance between the center of the plug and the peak on the pipe? It looks really long to me.

The McCoy #9 or K&B HP plus will be your best bet.

To be honest it didn't sound like the motor was working that hard. You may be able to prop up with your current setup. Maybe try an 8x8 or Q500 prop.

You either need to raise the load or raise the RPM. It will sound rich and burrbly if the motor hits its tune and there's not enough load to burn the fuel.

If you can measure the timing you be able to get a better idea about what rpm range to prop the motor for. You can also decide to raise the liner, lower the head, etc.

When I raced boats the K&B 7.5cc motors would turn about 25-28k with timing in the 170s. This was on 60% nitro with a short marine style pipe.

Good Luck!


Chris

Troy-RCU

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I will measure the distance tonight. I really appreciate the info. So how do I measure timing?

update... it is currently 10 1/8" from glow plug center to apex of pipe. I am cutting off another 1/4" of header and will tach again tomorrow. So I guess if worse comes to worse, I can also cut some of the length off of the front of the pipe since it has a constant OD section there as well. So far my needle settings aren't too touchy. I keep having to lean out more and more and haven't had in flight issues yet.

HighPlains

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Make a degree wheel to put on the crankshaft and fix a pointer from a solid mounting point.

Troy-RCU

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OK, found this too: http://www.rcfaq.com/ANSWERS/ENGINES....HTM#clearance

PylonDave

Troy , We used to run the 6.5 front intake in the Q500 class with the tuned pipe in the late eighty and early ninties before the nelsons came out. I dug out some old wooden rev up props we used to run , and they are 83/4x 8 in pitch. They would tack about 19000 if i remember right. the pipe lenth was 9 3/4 to about 10 1/4 i believe. You have the Form 1 enging there and they used a smaller diameter prop and less pitch I believe. They were turning 21000 to 22000 i believe. Highplanes would know i think.

HighPlains

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21,000 - 21,500 was typical

8 1/4 x 7 1/2 props

HighPlains

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Oh yeah, 65% nitro

Troy-RCU

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So is this length from the glow plug to the high point of pipe? I was browsing at some high nitro fuel at the LHS but most were for cars. Any pointers there? I am going to try the new pipe length and then a lower pitch prop to let it unload more. No chance this weekend to fire it up[&o]

You guys are great, thanks! I just want to out run the Pico .60 Shrike at my field on glo power.

PylonDave

Yes , from the center of the glow plug to the high point of the pipe.

PylonDave

you might try a small unload prop to find out what rpm it comes on the pipe.

Troy-RCU

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Sounds like a plan. I have some other Q40 props to play with... 7.2X7.7 and 7.2X8 I also have a thinner blade 8X8 I can eventually trim down to 7.5 or something. I really need to build a cowl for aerodynamics over the motor/pipe but want to get the motor running well first.

freeair

it might also pay you to buy an R.P.M. conrod for the K&B engine, the standard rods break easy.

Troy-RCU

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Got a link?

ChrisAttebery

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RPM has been out of business for about 10 years. Good luck. Richardson used to race boats in my area, but I haven't seen him in a long time. You might try asking someone from NAMBA District 9 if anyone knows how to get hold of him.

proptop

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Every once in a while an RPM rod pops up on epay...
The last one I was watching sold for 75 bucks...(too pricey for me )

I've been flying a couple of Quickie 6.5's this year, and they both have the old style rods. I've been told that they'll be o.k. until you get to around 21-22K or more on a regular basis?

I have been using an APC 8x8 with a "Newton" muffler and 15% Powermaster, a K&B HP plug, and can get about 19K R.P.M. (I am also using a backplate Perry pump and carb from a 7.5 DF )

PylonDave

Ahh the newton muffler. That is a name from the past!!!! We used them on the west coast for a number of years. I thought they were a west coast thing. Were you on the west coast back then.

Troy-RCU

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I did a little more tuning today at the field and made some nice improvements. I am now taching at 20,400RPM on 7.5X8 and the pipe sounds like it is kicking in. Haven't measured timing just yet (forgot to pick up protractor at store) but will be opening up motor this week to inspect a few things. I finally have a working low end transition to high end with a decent idle. Looks like I need to stock up on glow-plugs. I'm burning through quite a few on those long flights on 8oz of fuel.

proptop

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Hi Dave,
No...I got it in a box of stuff from Brad Young...through epay...he used to race with Dave Shadel in team Samurai (did I spell that correctly? )

Troy...you might need to add a shim or two if you're eating plugs? But I hear the F-1 6.5's used to go through a plug per run? (that was on 60-70% Nitro though )

BarryReade

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Wow, nice thread. I ran the motor being discussed back in the middle 70's in my F1's. I ran 60% nitro fuel and made sure I was tacking 22K rpm on the ground by carving the prop pitch until I got the desired results. It would unload an additional 3K in the air. 19K is not enough on the ground with the timing in that motor. You are lugging it. It really needs to turn. Whoever said one gp per run is correct. If your fuel mixture was correct and not to lean the gp glow wire would be scrambled but still in the plug at the end of your heat. If you tried to run the plug again you either had a hard time getting a decent needle setting or you would lose the plug in the air and flame out. We ran the shorty exhaust pipes and then found if we got another pipe about 1" longer than stock and tuned it by cutting 1/8-1/4" off at a time until you got peak rpm it helped. I usually went through 2-3 rods a season. Just one semi lean flight and the rod end would really wear. Just like most 2 strokes the small end first amplifying to the big end. The engine new really needed to be disassembled flushed out and the bearing hand fit. Not like the new motors being produced today. The fuel I mixed back then by volume was 20% Klotz synthetic red can go kart oil, 20% methanol and 60% nitro. If you go over 60% nitro it doesn't like to ignite and you need to add some propolyne oxide to help it at 2-3%. But then your needle settings became really cranky and you needed to be spot on. One click to lean and it was to much. With the 60% mixture I had a 2-4 click range that the motor really ran strong even if it was a bit fat on mixture. Clarance Lee was the big builder of custom K&B's back then. He had a deal with K&B and built a good engine. Several guys in my group had his engines but they didn't run any stronger than mine.