How big can i go xt500

Hi All, I have a question regarding engine size. I have seen a number of kits for these bikes ranging from 540 up to 700. How much can the bottom end handle? I know that the bottom end was over engineered but i don't want to destroy the bottom end. Also i want to keep the decomp lever attached for obvious reasons. I have three motors and two bikes, i was thinking of keeping one stock one maybe a 540 then the other maybe 600. Any advice would be apreciated.:thumbsup:

I'm not sure exactly how big you can go however I do know I used to race a TT500 with a 580 kit for sidecar ice racing. The bike was an absolute monster with the 580 kit in it and would easily wheelie with the sidecar and two riders all the way into the first turn. I'm not sure I'd even want to find out how fast a 700 would be LOL :thumbsup:

The bike competed for years in sidecar ice racing with absolutely zero bottom end problems. I also knew quite a few other riders with hopped up TT500s and none that I know of blew out the bottom. I know you can definitely pump the engines up pretty high before you hurt the bottom end. I'm sure others with more experience will be able to provide more info.

thanks father time. I have never heard of a bottom blowing up neither, just wanted to see if anyone has.

Powroll used to sell a 605cc kit. 92mm bore and 91mm stroked crank. They did porting, used a big cam with a Supertrapp exhaust (3") and a 38mm carb. I have a road test somewhere where Powroll admitted that the engine life was pretty finite and they knew that they were on the ragged edge when it was run hard. Powroll dyno'd their engine at about 42hp which at sea level would have been about 48hp. They ran it to 8k rpms on the dyno but it peaked at 6k and fell off pretty hard after that. That said, there were a number of 650 and a few 700 kits that were built. Both of them ran hard but they typically ran longer strokes and dropped the rpms a fair amount. Torque monsters, but not revvers! On the really big engines it was typically the cranks that came apart when they were over-rev'd...

The big Hyperkinetics engines were very expensive for their time, but they were full out Blueprinted race engines.

Swiss

Powroll used to sell a 605cc kit. 92mm bore and 91mm stroked crank. They did porting, used a big cam with a Supertrapp exhaust (3") and a 38mm carb. I have a road test somewhere where Powroll admitted that the engine life was pretty finite and they knew that they were on the ragged edge when it was run hard. Powroll dyno'd their engine at about 42hp which at sea level would have been about 48hp. They ran it to 8k rpms on the dyno but it peaked at 6k and fell off pretty hard after that. That said, there were a number of 650 and a few 700 kits that were built. Both of them ran hard but they typically ran longer strokes and dropped the rpms a fair amount. Torque monsters, but not revvers! On the really big engines it was typically the cranks that came apart when they were over-rev'd...

The big Hyperkinetics engines were very expensive for their time, but they were full out Blueprinted race engines.

Swiss

Powroll still does strokers and big bores. Most of the racers that I know usually just go the big bore route. Along time ago I had a stroked TT with the Powroll cam. You get 40 cc with the bigger bore or 40 cc's with the 1/4 inch stroker and the cases, rod and crank will need to be modified with the stroker.It sure makes for a very good running machine but like Swiss says they do tend to get weak when built up and pushed hard. Probably ok on the street though,but I think I would install an SR clutch basket if you build it.

I had a short tracker with a cheater 4mm stroke Powroll crank I think it made it a 540cc ran great off the bottom Mega Cycle cam...I believe 605 is maxfb9de708.jpg

All the big air cooled Yamaha singles have the same stroke - 84mm.The XT500 has an 87mm bore,the XT600 has a 95mm bore,the early SRX600 had a 96mm bore,and the XT660 has a 100mm bore.I don't know how big you can go with the 500,but a 101mm piston is available for the XT600.

I ran the 605 kit in mine back in the late eighties. It was a monster but on hot days it would overheat to the point that it would loose power. I ran it for about 1500 miles.

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