Wondering what a good starting point is for tuned pipe on a ops 90.

Personally have no idea I never ran nitro that large (thats what gas is for ) BUT here is a copy and paste from cooper pipes that MAY (or may not) help you out
http://www.cooperpipes.com/

Starting pipe lengths measure down center of header to weld at widest part of the pipe

21-pipe QHP _____________7-8in
45 pipe QHP_____________9 -10.5 in
67 pipe QHP_____________10-11.5 in
90 pipe QHP____________10-12.5 in
QHP-2 Gas pipe __________13.5-14.5in
21 S-pipe ______________7-8.5 in
Cooper Cobra ___________ 13.5 to 15 in.

Thanks Mike Hey how would this work in general. The mork the engine is modded the longer the pipe. Or wondering if it would be the other way.

Here is what Im talking about pipe too short.

What is the distance from your engine glow plug to that mounting bracket that you show in your picture?

My O.S. 91, when set up with a "pipe length" of 12.5 inches, has a total length of 18 3/4" measured from the glow plug to the very end of the pipe. The pipe is a AA muffled 80/90 from Al Hobbs.

OOPS That's why they make erasers. looks like a engineering mistake. My wood hulls have wood dowels epoxied in were I made mistakes. I sand the outside back flush,then reseal Or go down to Ace hardware and get some more Alum.

Just noticed your pipe is not muffled. A muffled pipe might get you the length you need...

Ya my pipe was suppose to be an unmuffled pipe 18in bought from Al Hobbs I have an email in to him to return it. Its not right he sent me a chopped pipe that only measures 14in total pipe length. I even asked him what the length was of the pipe before I bought it.

I dont know what your talking about the was no mistake made on my part. I bought the boat from my LHS and it had the same pipe on it but the owner needed it so, I bought boat without pipe I just bought the same pipe from Al Hobbs which was suppose to be 18in. but he sent me a chopped up 14in pipe. My Bracket is at about 17in and would work perfect if he sent me the 18in pipe.

The pictures I posted I was showing Mike AKA Toyota Truckin how I got a bum pipe 14in and he said it was 18in from Al. Maybe he made a mistake I don't know. Im waiting to here from him.

Hey dave, if you end up keeping the pipe an add on muffler should put it right back to the mount, OR make a longer arm to reach back to the pipe I wouldnt move whats mounted the hull looks like its in very nice shape I wouldnt bugger up the hull with plugs unless its a last resort, work on your deal with al to see what happens before anything

Good news Al has sent me a message that he made a mistake and will be putting the 18in pipe in the mail. And then after running it I will add a muffler on it to save my ears

OK I'm with you now.I was off on another universe.

OK I got the new pipe but have a few issue's to work out. Build thred is here http://www.rcuniverse.com/forum/fb.asp?m=9012357

I've started with one pipe ended up with another. use the kiss principal. I've had more than one pipe not preform to my liking. I also cut em or extend em depending on the temp & humidity.