Generally speaking:

4-stroke for scale--slow flying.

2-stroke for speed.

I use 2-strokes in my 3D planes. I know this goes against the grain and people will swear that the only way to 3D is with a 4-stroke, but thats BS. A 2-stroke is your best power/weight ratio. They generally turn more RPM than a 4-stroke--so if you want speed--then you put a smaller diameter prop on it and more pitch. Let 'er rev.

Thats why Dave is using an 11-7.5 on his rocket ship. I use a 13-5 on the same engine for 3D.

Dave, is that a Patriot? If so--could you advise on your setup? I've been wanting a go-fast airplane, but don't know what servos to use. Retracts? Hobbico mechanical?

BTW--one of my TH .75 engines pooped the bed last weekend.[X(] It's about 1.5yrs old and has about 10 gallons of fuel through it. I had to set my low end again because I changed tank location, prop and plug. I had my low end set up and i went to full throttle and re-checked the high speed needle again. Set it about 1/4 turn rich and went back to low end again. All was well---plane was at idle. I picked up my TX and the plane and took a step towards the runway when BANG!! The engine loet out a loud noise--but kept idleing. I shut it down and went home. Removed the backplate and saw that the crankcase was full of metal shavings.[X(][&o]

I got it boxed up. Need to send it to Hobby Services. I'm sure they will just give me a new one. I'm a Super Club Member at Tower--so it's under warrenty for 4yrs from date of purchase.

Too bad though. I like this engine. Good thing I had 3 NIB engines (all TH .75) sitting on the shelf. I just pulled one outta the box and dropped it in the plane. Took 5 mintues. I have 6 of the TH .75 engines--altogether.