I have read that the Fox 35 weighs 7oz and did well on the Sig Twister. I have a Tower 40 C/L engine, many thanks to Bootlegger, that I want to put on a Twister but would like to know the weight of the engine with muffler if anyone knows it? Thanks, Tim

  Tim, here are those weights, the engine alone weighs 8.5 ounces, the stock muffler weighs 2.1 ounces and a tongue muffler weighs .7 ounces..

  Hope that this helps...

Or make the tail longer 

Knactually Y'd still need a shorter nose . Though a TONQUE MUFFLER would loose an ounce forward .
Bit of everything maybe . A Profile it'd be easy to locate engine when the planes finished , to give the correct C of G .

I could be wrong, but I think you will find the 40 a bit much for that plane. Especially if it flew acceptably with the Fox 35.  If you don't shorten the nose or lengthen the tail, as others already suggested, you will at least be adding weight on the tail to get your CG correct.  You didn't state what tank you have, I could be that you might need to enlarge this as well depending upon how it's fuel consumption compares to the 35.

INDEED .
If its a ab initio type device , you WANT it Nose Heavy .

tho maybe , if youre a quick learner , put a second set of holes ( or two ) BEHIND the std engine posn ,
as in use the std back holes for the new front holes , so six holes give two engine positions  ,

C G right aft , itll go all over the sky.
C G right Fwd , it wont - turn or move away from impact , when required .

Muffler Weight'd be a big bit . The little Tongue / chip mufflers weigh diddly squat .





To Clarify , a inch or more nose heavy , or 1/2 inch aft , are about whatd get it NOT companiable