The moster i plan on biulding

:twisted:
Ok here is what i have decided to build
its still going to be the 650 head BUT
going to have the head milled down 1.5MM to increase compression
Replacing stock valve with the XJ900 valves as long as they fit if not the 700 valves. they will be
700:

Intake: 34mm
Exhaust: 28mm

900:

Intake: 36mm
Exhaust: 30mm

then i am going to fun a XJ700 intake cam increase of .5 lift
and a XJ900 non-X exhaust cam increase of .5 lift. that will be the beast plan on getting light weight pistons.

that is all i know as of now. what you guys think. will be a Frankenstein for sure. Should give me better low to high end power along with a higher RPM range too. Will look into stringer valve spring to help with floating the valve. i will also perform a clay test to make sure valve will have proper clearance if not i will have my mechanist shave the stems down to give me proper clearance.

what will be some good names for her? thinking some sort of bomber theme...

 

sick tank, you built that, right?

 

Bigger valves (even if they actually seated) will give you NO improvement if they are put into standard ports, and in fact may shroud things and restrict air flow.

If you play with cam changes, it would be nice to get a dyno reading before and after as performance changes can be deceptive. I have seen a few seat of pants changes that feel much faster, but when put up against a standard engine get shown up badly.

Are you serious about chasing performance or just tinkering for fun?

 

i plan on tinkering for fun and performance i have time and its my toy. i have to collect all the parts first. i will be porting the intake end exhaust to match the larger valve. i will get a dyno before i start all this major modification.

the Tank yes i am custom building it.

 

Make sure you check the piston reliefs with those larger valves. Be carefull not to lose port velocity when porting for the bigger valves

I am sure it is a typo, but the 900 exhaust cam will not work in the 650/750 head. The 900 used a 4 point cam support over the two point on the 650/750.

Ghost

 

Sorry to sound negative, but porting will not increase the diameter of the valve seat which is what will stop the larger valves from being a benefit to you.

Before removing 1.5mm from the head I would recommend calculating the new compression ratio before doing it. Go too high and you will have problems and by the time you retard the timing so it runs you may have less power. And yes I have seen it done before.
Go past 11:1 comp and you will have problems unless you get wild cams to decrease the effective compression.

1.5mm machined off the head will retard the valve timing (changing the distance between the cams and crank) If you do want to do this, buy a degree wheel and a dial gauge and degree the cams in. You will need to modify the cam sprockets to get it all to happen.

 

i prob going to just polish and port. I will be using 750 intake cam with 700 non-X exhaust cam. (Your right Mighost Type-O) I thinking of going to the 700 intake valve its 1mm larger in diameter. My machinist said that would fit since it will only increase .5mm on each side of the valve. I will do a clay check to make sure everything is good.

My question is are the timing marks the same for the 700 as they are for the 650/750. will they line up or ill i have to figure that part out as i go.

Prob not going to plain the head not worth what i would gain. i would prob be easier to get forged pistons with higher comp. and would allow me to modify them to allow for the larger valve.