I have been testing some new products from World Champion Products. They have a range of standard turbo heads and high compression heads to fit the OS engines and others. They fit better than OE and also have a high compression heads available.
If your old engines are getting a little tired or you don't fancy modifying your existing engines, they do there own marine version ready to go, just add a carburettor!
I have also tested there range of glow plugs in my 21 hydro, with some very successful results. The C5 and C6 I have now used in temperature conditions of 35C using 60% Nitro and I am still on the same glow plug after approx. 45-60 minutes running. They are very strong and hot, so this makes it much easier to use the higher nitro fuel.
They also do a very neat and compact remote fuel mixture base that uses the very popular OS main-needle. I have used one in my KEPS T2-21 Hydro for a while now and it has proved very reliable with accurate fuel metering.
Check out these products and many more at - http://www.worldchampionproducts.com/en/