I am upgrading my savy engine for an STS .28. What % nitro would be best to use? I currently use 20% on my star s-25. Should I stick to the same for the STS or Should I go higher?

20% is okay. wanna more low end torque then choice more nitro.

I run 20% and could not be happier. Watch out the .28 has crazy power.

If I go up to 25% would the extra nitro just be compensating for the extra room for combustion, being a slightly bigger engine, or would it actually give it extra power? If any of that makes sense!....lol

How many % nitro...it is just like how many compression bar to a turbo engine. There are two main fuels of your engine. One is methyl alcohol another is "AIR". Higher nitro % = more air

I am using RACE 30%.

And it runs ok with 30%, right? What temp plug do you use & have you modified the engine? Or does it run just fine with no modification with 30%?

So far so good. I am still breaking it in. An excerpt from the manual indicates they have planned on people using %30

FUEL
Total thickness of head shim
Under 20% Nitro
0.3 mm
25% Nitro
0.4 mm (±0.1 mm)
30% Nitro
0.5 mm (±0.1 mm)

It appears that it is okay to run the 30%

EDIT I am using an OS 8.. but don't follow my example. This is only my 2nd engine and my first engine, the k 4.6 lost mad power on the start of the 3rd gallon.