New 503cc 400ex bore kit

[400exrapes]

on the 400ex forum theres talk of this new 503cc big bore kit for the 400ex does anyone have a dyno of this ? i know one guy has an almost stock 400ex with the huge bore in it he just posted btu i cant find him

[Big - D Racing]

that bore would be ipossible on the 400ex atleast with the stock cylinder. It would bore it out way too far and couldn't be cooled. It run super hot and break real quick. There is a 500 kit ut it is a combo bore and stroke. I believe it is a 440 bore (89.00mm) and a +4mm stroke kit put you right at 499 I believe. Now if you do the 89.25mm bore it will take you to 503. That is probably what you are thinking about and is the highest I have ever hear of. Back in the day when the 400ex was the hottest quad Four Stroke Tech did make a bolt on top end that was a 500cc liquid cooled. That was a totally radical design that bolted to the stock bottom end. He stopped making them a while ago though. I think they ran for like $3000

[Wheelie]

A 440 Bore with a +4 stroker is a 460. I believe the 503 kits are a 92mm piston and a +7 stroker.

[400exrapes]

well if any of you find someone with one let me know i wanna see how those things perform

[browng31]

A guy on another popular site's name is Chad502ex, he might be on here too, he built them and he probably has some dynos.

[400exrapes]

thanks ill look that up now.

[Mickey Dunlap]

I still build the 500 kits. We start off with a 90mm piston and a 7mm longer stroke with 4 over bores up to 500cc with a 91mm piston. The 90mm bore is a 490cc.

[LT250_JOE]

Originally posted by browng31
A guy on another popular site's name is Chad502ex, he might be on here too, he built them and he probably has some dynos.

READ "GETTING CLOSER TO 60HP" POSTS CHAD 502EX IS ALL OVER IT.

[Benjithx]

How do you keep something like that cool?

[TURBO-530R]

I have a 502 for sale 8mm stroke and 90.5mm piston
Pm for info