For duning the turbo is excellent. It has amazing torque at low rpms. You only see the problems below 25-2800rpms and mainly when launching. The stock internals, minus the piston hold up well to duning. When you start racing back to back and pulling the really high rpms and holding them for long periods maybee more internal work is needed. I never had overheating problems or any other signs of the engine working hard when duning. I rode one of the first 730's out west and it was not near as powerful as the turbo. It would take a turbo off the start but be reeled in quickly. It may be different now. If I was to start over right now I would probably go with the 730/nos combo for reliability. I thought I had the turbo figured out and felt it would last 2 seasons of riding. I still think it would if the a/f was dialed in. My machine was dialed in for 7-9lbs of boost. When it was sneeking into the mid teens the last trip I am sure it was detonating even with the methanol.

 

Only last two seasons? That is a lot of dough for a short life span. Are there those longevity issues on the big bore also?

 

Anytime you start modifying engines you lessen the longevity. Higher horsepower always creates more wear. I would venture to guess I will probably get about 80% out of my current setup. Theres always a price to pay!

 

Ok, understand that. However a lot of you are on 2000-2002 Very modified. Still running it would seem [img]i/expressions/face-icon-small-smile.gif[/img] Do you all have a lot of costly repairs? I am on very tight budgets, and just want to run as long as possible before huge issues......But I want more power also. Hmmm stuck somewhere in the middle

 

If you are on a tight budget just do all the bolt on's you can and don't mess with the motor. The 730 w/nos is great. It took me a long time to get things right with $$$$$ spent. I think everyone hear will tell you. You never just spend the $5000 to get the stuff. There is always something to spend more money on. I think I said I was done about 2grand ago. Very easy to put $10000 into these bikes. HP=$$$$$$$$. With all the bolt on from HPR and better shocks you will love the dunes. Keep it simple if the budget is tight and you will love to ride the dunes and your bike will run every trip.

 

I am guessing that every two years you would have to freshen up the motor. I don't think anyone can be sure. The turbo and EFI will last a long time but the piston/valves will need some love now and then. If the system managed the fuel perfectly you would maintain 80-90% of the engine life at 7 lbs. Mrhp feels 14 lbs is not a lot of boost. He is definitely very knowledgable. (so if he wants to argue, I give but....) At 14lbs and with the proper a/f you would be at around 110 hp with 650cc motor. In my opinion that is alot to ask of stock internals.

 

IF you run aftermarket cams. . .
You should run aftermarket springs. . .

If you run the above you should change your springs AT LEAST EVERY-OTHER SEASON!

Some suggest yearly change.

This means pulling the head and having someone pull the valve springs. New valve seals would also be recommended at that time (about $7 each). You'll need to re-shim the valve-lash too.

Having a built engine costs time and money.

 

Well I am thinking Cams, Pistons, and clutch springs would be my next moves. Along wiht a ported intake to complement the larger carb. After that I can save up for bigger engain mods. Of course the nos shot will be in there for when you just want to have a little fun [img]i/expressions/face-icon-small-smile.gif[/img]

A lot of great information from everyone, thanks!

 

Nobody asked about nitrous, but if they did, you know what my choice would be! As for turbos, once they are setup, not just on your machine, but once they are correct, and I mean they run just like they do on my cummins, no bs about changing maps, more fuel, less fuel, bigger injectors, smaller injectors what haveya, they would be the ones to reckon with. Now if you want a machine that can hammer the hill as long as it wants, then go tear up the dunes, fill up, then hammer the dunes somemore, then go over to the hill for the evening races and hammer the hill for three more hours, there is no choice but Big Bore, (besidesnitrousuhemm). For me my 650 is plenty in the dunes, dont need anymore, its just when I]m lined up that I want all I can get. For duning a stock machine with an end cap and carb is a blast.

 

With 15PSI boost and a stock bore your engine now thinks it's a 1300cc engine. Now that's a "big block!!!"
I would go with the big bore turbo on some juice. Turbos and juice are like peanut butter and jelly............ they just go together.