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I have an older Sullivan Model 4 starter powered from two 12V SLA batteries. One of the batteries died and needs to be replaced. Has any one tried running one of these starters off a Lipo battery or similar? Thinking there might be something smaller/lighter than the lead batteries. Thanks in...

How much pressure does the exhaust gas exert on the fuel tank pressure line? Has anyone put a pressure sensor on the tank pressure line for a 21 size engine? Mike

What is the best, or most economical, material to use for placing a weight slug in a crankshaft? I know tungsten is often used in full size crankshafts but looking at some of the crankshafts in 21 engines, it appears to be more like copper or bronze slug. Also how much press fit is required...

On a standard glow plug, it is common to pull the wire out slightly from the plug to "advance" the ignition. This has been discussed before on the forum. However I could not find if this practice is used on the turbo type of glow plugs too. Has anyone tried it? Mike

A friend of mine asked if I could machine him a .21 size head button for a turbo glow plug for an RC drag car application. I can machine the chamber side with no issues. I am trying to figure out how to machine the threaded hole and mating seat for the turbo glow plug. Was hoping someone on...

I am just about to begin finish work on a fiberglass/carbon hull. The hull will be eventually be color painted and cleared. What is a good primer to use on the fiberglass/carbon before the paint? On wood hulls I have used PPG DPLF40 epoxy primer. I was planning on using this again but wanted to...

For a 90 size boat, what is the general distance from the water's surface to the bottom of the tub? Thanks in advance. Mike

What is the typical face width of a 90 size outrigger rudder blade? Looking for the face width - leading edge to trailing edge. Thanks in advance. Mike

For those interested in Drag Boat racing, tune into CBS on Saturday (9/22) at 1pm CST. The race from Wheatland MO several weeks ago will be on. Mike

On the CMB drum, see photo, there are two holes in the "disk" section. One is for the drive pin on the crankshaft. What is the other for? The diameter of the other hole is larger than the drive pin one. I am guessing it was using in the machining process but wanted to ask the group. Thoughts...

What is a recommended rudder servo for a 90 outrigger? Prefer Futaba but open to others. Would like to stay analog instead of digital. Thanks in advance. Mike

Does anyone have a used CMB 91VAC they want to sell? Looking to build a 90 outrigger. Thanks in advance. Mike Rappold

For sale: brand new OPS 5270 tuned pipe. i have had it for several years and never got around to using it for a project. $50.00 plus shipping. Mike

For carburator barrels, has anyone used a plastic material like Delrin (Acetal) with good success? I have used brass but looking for other ideas for something lighter in weight. Aluminum barrel in an aluminum housing eventually sticks. Thanks in advance. Mike

For sale: SpeedTech SM-28 Weather Meter. Measures wind speed, air temperature, relative humidity, dew point, barometeric pressure. Good for keeping track of weather conditions after a run. More details can be found at the Speedtech website if needed. http://www.weatherhawk.com/wind-meters...

I was thinking of machining several head buttons for a MAC 67 to try. Was curious what volume of the head buttons others found works well - even if not on a MAC? This would be 50 - 60% nitro fuel in an outrigger application. Also what about head clearances? Thanks in advance. Mike Rappold

What is the idea behind some outrigger designs having the last several inches of the tub's bottom curved or ramped upward towards the transom - as opposed to a perfectly flat bottom tub? Does the curved bottom work better with a single center ski over the drive shaft or more the traditional...

For those that are interested, drag boat racing will be on CBS this weekend (Saturday, 8/20) at 1:00pm EST. The race was taped a few weeks ago from Wheatland, MO. Lucas Oil owns the track and built a man-made lake dedicated to drag boat racing. This is the first race from the facility. Look...

What is theory/purpose behind a piston top that is dished slightly? Like the MAC 67 piston. Thanks in advance. Mike

For those that are making their own head buttons, how are you machining the combustion chamber? Are you using a custom ground form tool or a ball end mill on the lathe? Or something else? Thanks in advance. Mike Rappold