Shaving Vrs Rechambering

[jlsparky7]

I was told that shaving your head doesnt increase compression, only rechambering does. Is that true? Whats the difference?

 

 

Heres what im hoping to do this winter and I would like to keep the quad on 94 oct gas.

 

Shaved head (how much for 94 oct? I was thinking .025)

.020 mx port with wiseco pistons

PT mids

Welded crank

+4 timming if I can stay on 94 oct gas

500-1000 feet above sea level

The rest of my mods are in my sig.

[BenBB]

No not true. Shaving the head DOES increase compression, what you are doing is taking off the gasket surface thereby decreasing the combustion chamber volume. Rechambering may or may not alter compression, although without shaving or decking the gasket surface on a stock head it would almost certainly reduce compression, and in conjunction with shaving the head would either equal or increase compression...to clarify rechambering or reworking the combustion chamber involves changing the squish angle, radius and/or depth, the shape and characteristics of the combustion chamber itself. To get the very most out of a motor you want the squish set up just right, typically by whomever does the porting. It's not a dire necessity but it's one of those little things that adds up.

 

Mods sound good, you should be plenty safe with .025" and 94 octane (double check with your porting guy though because crazy porting can alter the compression ratio, which is what directly affects what octane you'll need NOT the static compression reading you'll get with a gauge). With no porting you're usually safe to go .030" down to 91 octane, but that's just a rule of thumb and there's always circumstances that might cause it to go boom (bad gas, going to super low elevation like the center of the earth, etc.). I think .060" is the most I've heard taken off but there again it needs to be set up right to do so.

 

You should also be fine with 4 degrees of advanced timing, again see what your builder says and see if he knows of any issues just in case. Definitely worth welding the crank while you're in there, also a good time for any other upgrades if you got the green; modded shift star, port match the cases, lightened flywheel, RZ shift drum & forks, new clutch (bet you'll need to run at least 3 aftermarket clutch springs and 3 stock ones, if not all 6 aftermarket), billet basket, lockup (mmm lockup :happy: ), etc. etc. etc. the list never ends. One thing you might seriously consider is reeds and/or some Vforces, ok well two things you might also wanna go with either bigger carbs or bore out the stockers to 27.5mm. Good luck.

[jlsparky7]

No not true. Shaving the head DOES increase compression, what you are doing is taking off the gasket surface thereby decreasing the combustion chamber volume. Rechambering may or may not alter compression, although without shaving or decking the gasket surface on a stock head it would almost certainly reduce compression, and in conjunction with shaving the head would either equal or increase compression...to clarify rechambering or reworking the combustion chamber involves changing the squish angle, radius and/or depth, the shape and characteristics of the combustion chamber itself. To get the very most out of a motor you want the squish set up just right, typically by whomever does the porting. It's not a dire necessity but it's one of those little things that adds up.

 

Mods sound good, you should be plenty safe with .025" and 94 octane (double check with your porting guy though because crazy porting can alter the compression ratio, which is what directly affects what octane you'll need NOT the static compression reading you'll get with a gauge). With no porting you're usually safe to go .030" down to 91 octane, but that's just a rule of thumb and there's always circumstances that might cause it to go boom (bad gas, going to super low elevation like the center of the earth, etc.). I think .060" is the most I've heard taken off but there again it needs to be set up right to do so.

 

You should also be fine with 4 degrees of advanced timing, again see what your builder says and see if he knows of any issues just in case. Definitely worth welding the crank while you're in there, also a good time for any other upgrades if you got the green; modded shift star, port match the cases, lightened flywheel, RZ shift drum & forks, new clutch (bet you'll need to run at least 3 aftermarket clutch springs and 3 stock ones, if not all 6 aftermarket), billet basket, lockup (mmm lockup :happy: ), etc. etc. etc. the list never ends. One thing you might seriously consider is reeds and/or some Vforces, ok well two things you might also wanna go with either bigger carbs or bore out the stockers to 27.5mm. Good luck.

 

Thanks, that answered all of my questions. Im trying to draw a line for mods and not cross it. Thats gunna be hard to do. lol. My quad has been completely stock up until this year and then I slapped on all the mods I have now.