Where to set the rev limit?

Stock GPZ750 top end on a KZ650 bottom will go up to 11/12K rpm? :woohoo:

Interesting.... Images as you progress, most definitely...

With a stock head, it wont breath past stock red line anyways.

hardr0ck68 wrote:

But at least my project is more than a worn out picture of an empty frame.

Should have said you needed a pic of an empty frame

mark1122 wrote:

With a stock head, it wont breath past stock red line anyways.

yeah that will probably prove to be the case. Unfortunately there is only so much money for the motor this year...


anyway with the 6 speed, lightened crank, 750 top end I should notice a little more get up and go than the stock 650.

I will add valve springs to the shopping list (any brand you recommend?) as they are relatively cheap and I want to replace the valve seals anyway.


I will set the rev limit at 11,000. I have had the stock 650 hulk up to ~9500 - 10,000 a few times already, so 11K should not be world ending.

77 650 motor with vm26 carbs, k&n pods, lightly baffled MAC 4-1, with home polish job on the head would spin 12K all day long, unfortunately the stock valve springs didn't like that much at all. Listen to these guys and get aftermarket heavy duty springs, then set your limiter at about 12K and let her scream!

I will be running pods on bs32's a full stainless 4 into 1 system from a zr750s, gpz head and cams (with springs APE now!)stock 750 jugs and pistons over the bottom end previously mentioned...

of course that is subject to change slightly, those are just the bits I have on the shelf now. 11,000 should be a good start.

Thanks for the input and advice.

just get the ape springs for a 1000. cheap enough and will fit right in a 750 head.

you are spending money on the bottom half ( which is a good thing ) but you are neglecting the biggest restriction in your motor.

CAN'T GO IF IT DON'T FLOW!

please listen to me here rocco.

spend most of your money on the head.
it is assnine to build a killer lower end if it can't breath.

it's like building a killer small block chevy and running 1.94 valve heads on it.

please for the love of god let us help you!

you can go with me to buffalo and meet the guy who will do this for you.

you are going to be so dissapointed with the performance of this motor, with all you are doing to it, if you run a stock head.

please let us help you or i have no choice but to rename you hardhead instead or hardrock! :laugh:

Oh don't worry Steve ( I know it is spelled Stephen or something like that but Steve is shorter :lol: )

I will build the top end. I am thinking about 72mm pistons for 860cc's of course custom liners in a stock 650 block. Then for the head I am not sure.... I would sure like Ti valves, but I haven't found a source of reasonable sized blanks yet... and I was quoted in the relm of $1600 for custom bits. New valve guides and probably new seats, some port blending and what ever porting the experts recomened. Top it all off with some nice hot cams, hopefully a bit hotter even than the factory gpz.


I have big dreams for the top end... my issue is I have an idea of what I want and it is not cheap. I will not settle, and I see no point in spending $1,000 to do it half way (ending up pissed cause it is not what I wanted) when I could spend $3,000 and have it make me happy.

Unfortunately, this winter I only have the time/funds to deal with the bottom end. I have been told it is better to start with a solid bottom end; which makes sence... If I do the top end and blow out the trans because it was not undercut what have I done for myself?

Believe me I know the head is "where the magic happens" but for the time being I will have to make due.

As a side note, my "road map" to success with this bike involved suspension mods and frame gussets this winter... Unfortunately I could not take the bike up to Maine with me in the move... but I could take a spare engine.

So I will do the bottom end this winter. Ride the piss out of it for a year; then tackle the top end. Then hand on to it as it tries to kill me for a year; then finally in the winter of 2012 I will get around to re-doing the suspension. Unfortunate but such is life.

1 thing about doing the frame last, it's more exiting to ride.:woohoo:
u don't have to go as fast to get that adrenaline rush.:woohoo: