VVRC 40cc Twin

[49dimes]

As far as other "super-cub" cowls fitting......Give the people you mentioned a call or email. Fiberglass specialties probably has one.
I did a world models 1/3 scale v1 ( not the one they have today) and fiberglass specialties had a PA-11 cowl (forerunner to the super-cub) that worked perfect for the OS 300 twin I had in it.

 

[witchfingers]

I did already open the front inlets wider and I will be flying it in the next hour or so. I honestly believe it was vaporlocking due to the fuel line being real close to the rt muffler and to fresh cool air not getting to the carb. Another thing I just noticed last night, one muffler pipe is 1/4 inch shorter than the other. They must have jigged it up wrong when they welded it up at the factory. I will post a picture of that later.

 

[witchfingers]

Here are the exhaust differences. Right side

 

[witchfingers]

Left side.

 

[witchfingers]

I flew it today 3 times and had no problems but it was only 66 degrees out. Temp gunning after landing said 170 degrees at the heads.

 

[AsphaltPilot]

I was always told the longer the pipes the better the performance .. but running cold fuel though a hot motor can cause vapor lock also like a frying pan put cold water in it will steam put hot it will get hotter

 

[witchfingers]

So the 1/4 inch longer pipe on the right is better? As far as cold fuel, I addressed that issue by putting a tunnel inlet on the front of the cowl so outside air blasts directly onto the carb. We figured that might be the case when it would deadstick and then would not immediately start. It acted like it was starving for fuel or it had been boiled off.

 

[witchfingers]

I'm no expert but id say the angle of attack of your cowl is actually deflecting air away from that cylinder head and not into it, the holes you have might not be helping as much as intended, being so close to the prop hub it may not be getting much air if any at all through there as the closer the hub you are the flatter and more solid the prop is effectively making a barrier where air cannot pass and is forced along the prop to its tip, that combined with the angle of the cowl towards the cylinder head might be creating a "vacuum" of sorts inside the cowl effectively blocking air penetration

are there other holes to allow air to exit the cowl, further back than the cylinder head?

I am thinking the prop blocking the holes is a good possibility. I widened them and it seemed to be better but I will have to try it on a hot day to be sure.

 

[49dimes]

The difference in the stacks is so small I doubt it has any thing to do with performance. Now your carb getting hot that can be definitely an issue. Might try and see if you can make a thermal deflector that shields the carb from muffler heat. Balsa and aluminum foil works good for making them.

Your cowl inlets look much better.

 

[Lojik]

Agreed those holes look much better, and they are now over the angled part of the prop so should be getting some forced air intake