Some areas I touched upon but did not really address...
A lot of the speed that can obtain is effected by many issues.
One of the most important of these is the weight, and the COG.
If your plane is heavier it will not fly as fast as the others.
If your COG is set up different and you have to use more elevator trim this will slow you down as well.
Everyone thinks that more power is the only way to get ore speed out of an airplane, while that is true to a point, it is not the only factor involved.
Sometimes something as having you high end a bit rich on the ground will buy you some more rpm's in the air.
If you have wire gear rather than a flat metal or composite type this will be more draggy.
A big spinner rather than a prop nit will give you better penertration.
The same plane with a few different items will perform much better with out all the fancy stuff you can do to the motor.
Look through the speed plane forum and pylon you will get some ideas.
I have found that sometimes something as simple as cutting down the unused portion of my control horns will give me a couple more knots of airspeed.
So look over your airplane carefully and see just what may be slowing you down.
The first thing I would look for is added weight, and were the COG is set, that along with the other things I mentioned in the prior post.