i just got a asp 108 need to no what size prop please help

Throw the ASP108 away and get an engine to fit the prop you have. This is from an old asp108 owner.

I would tend to agree with Biplane.. I ran a 15x8 mostly, on mine. Mine was nearly perfect- 22 out of 23 flights deadstick.. Tried everything from header tank to a pump to make it run.. The only engine that I have never been able to make run in 30 years of modeling and I have had some POS motors..

hmmm..mine ran great with a 14x8......

Had one 4 stroke ASP when they first came out. Terrible metal. The crank bent itself out of shape while I watched running it in on the test stand. They replaced it and I sold it NIB.

Got a brand new two stroke in the basement (via trade) that I've yet had a reason (or desire) to run.

But your engine may be great ! Every one is it's own thing ya know ?

Prop it with a 15X6 to 16X8 and see what ya like.

Somewhat in defense of ASP, I bought a plane with a .46 on it, I took it off and threw it in my junk box. A year or so later I ran into the guy I got it from and he asked me how I liked it. I told him I had taken it off the plane. He said that it was one of the best running engines he had ever had. I put in on a POS profile hots I had, and it did truly run perfect. I did plant it once and bent the crank over about 45degrees in front of the prop driver, I bent it back, trued it with a dial indicator, and ran it for 3-4 more years till the rod finally started knocking.