Not sure what to do!

[LukeG]

So currently I have a 1990 KX250 completely torn down to be turned into a motard road racer. The thing sat for about eight years so the engine also has been completely torn down.
So here is my current dilemma, I need a bike with at least 55hp to run with the tractors, I have collected parts to make the 250 engine into a 295. The 90 cylinder has a steel sleeve and from research 265 seems to be the biggest they are taken out to but I picked up a 93 top end complete and they can be bored to 295. In the states this usually costs 600 to 700 bucks, there doesn't seem to be too many places in Australia that really advertise their work on 2 strokes and by the time I post and exchange Aussie pesos for greenbacks, I am looking at a bit over a grand. I have an Aussie company that will do a 295 top end full rebuild for $1100 so I think I will talk to them. Also since I have a 93 top end I need a 72mm stroke crank as the 90 Stoke is 70mm. I picked up a 92 crank that needs a rebuild which I was planning on doing anyway with a new rod and a balance. Dimensionally the cranks are the same except for the stroke. I have mocked them together and they look like they will go together alright. I also have a KDX transmission to go in as I also need to be able to do 180-190kph down the straights. All up I am probably looking at $2000 for the full rebuild.
But there is an 86 500 engine for sale near me for $1500, it's a runner and comes complete. Also has a lectron carb. I have the skills to fit the 500 engine into the 90 frame, I just don't know what to do!

What do you guys think?

[sandblaster]

I don't know buddy... 190 kph or 118 mph is gonna be tough enough for a 500cc,
A 300cc or less?
I just don't think your gonna get there... And if you did how long will that engine last?
So, I'm leaning toward the 500 with a large bore, lots of port work, re-cut head, full rebuild, and a balanced crank.
Anyone else?

[LukeG]

When your running with 450s that are doing nearly 200kph down the main straight at Phillip Island you need all the help you can get.

[umberto]

The 250 is going to be wound pretty tight to get that kind of speed. You wouldn't have to spin the 500 engine as hard, which should make it last longer. In the hot rod world they always say, "There's no replacement for displacement.".

[Brute]

"Cubic Horsepower" was another one.
My brother and I Drag Raced a lot in the late '60's and '70's with small block Chev's. While it was fun to go up against the bigger stuff and beat them it was also disappointing to see how much easier it was to get lots of power out of the big engines. AND they were not working as hard either.

[don46]

I would NOT go with a 86 motor, while it may be a runner today, when you need parts it may be a nightmare to get some of them as some have already been discontinued. I think even if you do go to 295 you may have balance issues. I think I would look for a newer 500 motor.

[Foxx4Beaver]

But there is an 86 500 engine for sale near me for $1500, it's a runner and comes complete. Also has a lectron carb. I have the skills to fit the 500 engine into the 90 frame, I just don't know what to do!
What do you guys think?

I posted several K5 motors just a couple weeks ago if you're looking to spend that kind of money on an engine...

http://www.kxriders.com/forums/index.php/topic,13918.0.html

I just looked, and 3 are still available...
it would be better to try and find a blown '89-'04 K5 motor for a couple/few hundred bucks, and then completely rebuild it yourself...then you know what you have

[LukeG]

I missed the 86 motor, in Australia they are rare on the best of days. A clapped out complete bike will still set you back around $3000. I have seen a CR500AFX for sale for $21000 and there is a CR500E for $14000, this one is street legal in Australia.
Shipping an engine from the states to Australia is also a real pain in the arse. I will keep searching, you never know what might pop up.