How to achieve a softer 4-2 break?

Guys,

Something else I want to improve. I run my engine in a classic setup with a 4-2-4 break but I feel the break is to abrupt and think my pattern would improve if the break was less marked. Some info:
-Engine Stalker .40SE. A classic loop scavenged engine but with ABC piston/liner. Ball bearings. I haven't measured port timing but as it is designed for stunt I gather it will have the neccesary specs.
-Prop 11x5 apc. Still looking for a much lighter prop as this one weighs in at a little over an ounce.
-Plug Enya #3, non idle bar.
-Fuel 20%oil 60/40 castor synthetic, 7,5% nitro 72,5% methanol.
-Fuel system. Uniflow on muffler pressure.

Things I tried:
-Different plugs, Enya's,Rossi's,OS's in different heat ranges. Anything cooler/different than the Enya 3 will give significant reduction in RPM when disconnecting battery.
-Lower compression ratio. Same as above reduction in RPM.
-Fuel:- oil content raised using castor to the above specs. Lower percentages of total oil content and/or castor makes the engine more sensitive to overheating.
- 7,5% nitro seem to be the lowest amount again in order to maintain revs. Only limited possibilities to further raise the nitro percentage because the tank volume can be raised only slightly to compensate for less milage.

Things out of my reach:
-change port timing or any other major modification to the engine's interiors.

What I don't want to loose:
-The amount of power available, I like/need what I have now.

Any suggestions?

Try a thinner head gasket, which you may have to cut yourself. You may need to reduce nitro content, maybe not.

If you want a softer break, you need to lower the compression. That means a thicker gasket (or more of them). Now I am talking three/four/five thousandths difference (in inches). With some engines you can get thin gaskets. The Magnum/ASP engines, for instance, come with .004 shims. Some engines have multiple shims in different sizes. With the FP engines which come with .016 shims, we use .010 shims. Two make .020. One of each make .026, (and so on.)

Now, you tried this and lost power. Open the venturi just slightly to regain the power. You can also up the nitro, but it may be counter productive. You need to lower the compression to raise nitro content anyway.

Alternately just go to a lower nitro content and open the venturi slightly. This, too, should restore the power with a softer break. If the weather cools down, go back to a smaller venturi. The cooler weather alone will restore the power. If the weather heats up too much, go to a slightly larger venturi over the one you just opened up. Or, in this case, go back to a slightly higher nitro content.

These are the simple solutions so long as you have access to several sizes of venturis.

Just to play devils advocate...

Couldn't he also go to MORE nitro, for more power, and eliminate the break all together, run it in a steady 4 4 4, maybe even load the engine up a little, more pitch... maybe a 3 blade...thoughts?
Eric Viglione

>Just to play devils advocate...
>
>Couldn't he also go to MORE nitro, for more power, and
>eliminate the break all together, run it in a steady 4 4 4,
>maybe even load the engine up a little, more pitch... maybe
>a 3 blade...thoughts?
>Eric Viglione

I guess you could say there are multiple ways to set up an engine, but you have got to watch it. Just like it has been said "There are three ways to talk to a woman......None of them work."

The question was a "softer 4-2 break". He could opt for 4-cycle all the way but would need to set it up entirely different. But the high nitro, nigh compression, 4-cycle routine takes considerable more fuel. He has already ruled that out.

A different prop will require an rpm change. I would advocate trying different props, but they will need to be tied to the break. You may end up too fast/too slow for lap speeds. Some engines are very user friendly. Some (Like the Fox 35) get very critical as to where they like to run.

On the pipe set-up, we pitch the prop to match the engine setting we like. We then adjust the head shims to get the amount of break. Then use venturi and nitro to adjust for changes in temperature. We are normally content to run 5% nitro, and in fact ordered ten cases of all 5% for this year.

>Just to play devils advocate...
>
>Couldn't he also go to MORE nitro, for more power, and
>eliminate the break all together, run it in a steady 4 4 4,
>maybe even load the engine up a little, more pitch... maybe
>a 3 blade...thoughts?

Sure - but that's a different question than the one he asked.

You might try adding castor oil. We've found, at least in the OS LA 40 and 46, increasing the oil to 25% or more softens the 4-2 break and smooths out the 4 cycle running. Doesn't seem to affect the horsepower, but it might reduce the mileage a bit.

Bram: You might try a lower pitch prop. We've been using the APC 12.25 x 3.75 prop (cut down to 11.75) on our LA 46s with great results. You can run the motor closer to a 2-stroke and the break won't be as abrupt with the lower pitch. My brother has also had good success with the APC 11 x 3 prop on his LA 40. I have also been using a Bolly 11.25 x 4 on my Thunder Tiger 36. We have good results with all these props.

I've done the usual things, more head gaskets, lower nitro, different props with some success. But recently, I had success with stuffing the crankcase. I took and old Enya 29 III and partially filled the bypass with JB Weld. I was getting 4-2-4 breaks that brought tears to my eyes. Yes, I was using 5% nitro and low compression head as well, but until I stuffed the crankcase, it never ran like this. I plan to continue this experiment on an Enya 60 and an OS 58, both potentially good stunt engines if they can be tamed.