w8ye

My Feedback: (16)

Rock'N Ruben has a video of his own
http://www.rcuvideos.com/item/VGDGLHW3QHDSVZJQ

Flyboy Dave

My Feedback: (21)

....no, I didn't. Are the safety police wandering about in their usual stupor ? [sm=stupid.gif]

blw

My Feedback: (3)

Guess that's why he posted like he did.

MatheusC20XE

Hi friends!

Finally i got my tacometer, and did the vids.. well.. i really dissapointed with the results.. more screamer than result.. lol..

I got the tuned pipe shorter, like the tips of Dave, and the engines got screamer much more.. But here are the results:


K&B. 61, little worked, polished windows.. tuned pipe.. RitchsBrew 15% of nitro:

11x7 prop = 13200rpm peak

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

11x6 prop(Master) = 14670rpm peak

http://www.youtube.com/watch?v=C6MOs3X6TWg




What do you think? bad or good? or normal?




Cheers,



Matheus

Red Baron Mike

My Feedback: (287)

Max RPM on a K&B .61 ringed engine is 13,000. Go higher and you will shear off the crank pin. It is a 2-piece crank with a pressed in pin. If you want higher rpm, you will need to buy the one piece crank from the newer K&B "Twister" .61 along with a new rod. Go to the Mecoa website for more info...www.mecoa.com.

MatheusC20XE

Thank you for the tip.. but 14.600rpm is not so far from 13.000rpm.. i think i will take the risk..

I calculated the power from prop x rpm, and resulted exactly 1.9hp. Not so bad for a old K&B.. [8D]

blw

My Feedback: (3)

You may be outside of the h.p. and torque peaks with 14,600 RPMs. You can always write Clarence Lee for the exact figures.

MatheusC20XE

can you explain better friend?

Flyboy Dave

My Feedback: (21)

Matheus ....

....use an 11-7 Master Airscrew....don't worry too much about the RPM's.

...use plenty of castor oil in the fuel.

FBD.

MatheusC20XE

Hi Dave!

But tell me your opinion about my engine.. do you think it´s turning higher power than a stock K&B or pretty the same?

Flyboy Dave

My Feedback: (21)

....I can only offer my experience. I have been running those engines continuously
for 35 years. My second R/c engine was a K&B .61. I still have it. I have never blown
or broken a crankpin, nor have I heard of one breaking....but that doesn't it doesn't
happen. I wouldn't worry about it.

Run the heck out of it....when it blows, it blows. Judging from the fact that you have
worked on the ports, and installed a tuned pipe, it shows that you desire maximum
performance, and I would guess that you already know that stressing the engine could
result in a shorter engine life.

The actual RPM spec is for 12,000 in the manual. I would extend the maximum RPM
to 13,5000....even for extended use, as long as there is plenty of castor oil in the fuel.

The oil in the fuel is what keeps the engine alive. If you want to stress the engine beyond
the normal limit....extra oil would be a good thing.

FBD.

Red Baron Dave

My Feedback: (13)

Red Baron Mike is correct

I am the one with the 'old style' .61 that I had maxed out on a mini-tuned pipe in a pylon racer. Was peaking at around 14.5k rpm on average with 15% Power Master fuel with the APC prop and the large black perry carb.
She screammed long and hard - for awhile (like maybe 2 gallons total).
Then it happened durning a race - straight and level flight she just blew

landed safely and torn down the motor. The crank has a 'pressed' pin (vs. the new twister design which is all 1 piece milled from stock) which failed and chewed up everything inside: sleeve piston rod crank case. I still have what was left of the crank and rod - just as a reminder to me to define "sport" and "racing" engines. Ya get what you pay for

I have since aquirred another .61 with the C. Lee modifications and with the same pipe and prop I have NO fears of anything breaking again. I have 2 more .61s NIB and saving my pennies to have them 'altered' by Mr Lee as well

All the best and good luck

RBD

Red Baron Mike

My Feedback: (287)

14,600 RPM is significantly higher than 13,000. Max HP is at 12,000 so you will gain nothing by the higher rpm. The K&B .61 has a great deal of torque and can swing a larger prop. It is not a high rpm engine. If the crankpin fails because of your higher rpm, the rod, the piston and the cylinder can all be damaged. I witnessed a failure at about 14,000 and nearly scraped the engine. To get your speed, run a higher pitched prop so you will remain UNDER 13,000 on the ground.

It is your decision, but remember, you started this post to get information. If you don't like the answer, then possibly you should not have asked the question. If you don't believe me, contact Clarence Lee, the designer of the engine, or MECOA, the current manufacturer of the engine. Clarence Lee modifies these engines by "blueprinting" and changing the porting to give them more power. He is the one who told me to stay under 13,000 rpm. I didn't believe him either until I witnessed a crankpin failure on a fellow club member's engine.

There is one exception to this. If your engine is an early K&B .61 (pre-1970 vintage as I recall), it had a solid one piece crankshaft. Remove the rear case cover and look at the crankpin. If it is cylindrical with a hole through it, it is the two piece unit as I have been discussing. If it is solid, it is the one piece crank and you can disregard what I warned about above.

Good luck with your engine.

Harry Lagman

It's definitely stronger than a stock one, primarily because your one is on a tuned pipe. I'd expect a stock, muffled K&B .61 to pull somewhere around 12K with an 11 x 7 prop on it.

For an MA 11 x 6 comparison, I tached a stock, muffled GMS .47 on 5% nitro. It pulled 13,800 rpm. With a pipe, I'd expect it to pull at least 1000 rpm more, so your engine is performing in the same ballpark as a piped contemporary .46 schneurle ported engine, which is about what I'd expect.

Put an APC 11 x 6 or an APC 12.25 x 3.75 on it and I can give you very specific comparative data. Do you have access to either of these props?

Flyboy Dave

My Feedback: (21)

....K&B engines recommends one prop....an 11-8 for the 6550 engine. The RPM is
stated is 12,000 RPM....no more no less. Anything over and above this is in your
favor. Forget so called comparisons with .46 sized engines, and forget about
comparisons with APC props, because the results will not be the same. Forget
about 11-6, and 12.25 x 3.75 props. They are not suited to your engine.

FBD.