what top end do i have? HELP!

[ZSNOW]

ok, well i talked to the previous owner of my 250r and they said its a 265-270 and its a +4 mm stroker? my cylinder is a paul turner national mx kit, set up for midrange, but for somereason my compression is wayyy high at almost 290 with a duncan racing cool head 23cc dome +4 stroker and paul turner cylinder..

was there a motor kit set up like this?

why do i have so much compression?

what is my displacement if it was stock bore with the +4 stroker?

[86 Quad R]

the addition of 4mm's to the stroke will increase the compression a great deal but there are other things that would contribute to the compression your getting as well. like a thinner head gasket(if using a non o-ring head), a milled cylinder deck or a stroker setup that doesnt require a base plate, how the port timing is set for the stroked crank or any combo.

the last stroker i built using a stock virgin head was around 235#'s using a thin head gasket but, after switching to a oem gasket it dropped to about 195 or so.

btw: the cc's for a stock bore and a 4mm stroker would be around 260cc's