shaving heads or high comp piston

[JKWGA400EX]

how much more compression do u get from shaving heads,and does it effect the reliability(sp)alot.whats the price difference on the both and the price on shaving them?

thanks yall

[chad502ex]

In general, shaving heads 1mm or 0.040" is good for about 1 point of static compression. Lowering the head closer to the crankshaft will also slightly retard your cam timing a few degrees. Nothing to worry about. Decking heads run about $50 from your local machinist. A high compression piston can cost between $150-$250; so, compression being equal it is cheaper to deck for an equivalent 1 point of compression gain. Care must be observed doing either modifications when considering piston to valve clearance. It's just that most piston manufactures have already considered P-V cleanances with proper flycutout depth in the piston dome. As far as reliability of decking, no issues there IMO

[cals400ex]

chad, if you shave 1mm on the 04/05 450r does that equal 1 number increase in compression?? right now i am running only 2 layers of my head gasket and i have no idea how much compression it is. i thought about getting it shaved and run a full head gasket.

[leadfoot_52]

I think That shaving your head is a bad Idea because it puts the spark plug closer to the piston, so it gets hotter. And its cheaper to buy a good piston rather than ruining your head. JMO

[GIXXER1KR]

Jetting compensates for the temp change!And theres nothing wrong with decking the head if its done right!!!

[chad502ex]

Originally posted by leadfoot_52
I think That shaving your head is a bad Idea because it puts the spark plug closer to the piston, so it gets hotter. And its cheaper to buy a good piston rather than ruining your head. JMO

not any more. HONDAs heads brand new are $200 in the box.



cals: I can't recall right now, but if my memory serves me decking 1mm or 0.040" is about 7cc reduction. I have the info written at home somewhere,...

[mattonln]

shaving your head is not a bad idea, but it is irreversable. yes, a piston may be $100 more, but the piston is also quite a bit lighter than stock and they claim they are "stronger" you will get more performance out of a piston than out of a shaved head at the same compression ratio just because of this aspect. plus most piston companies have taken valve clearences into aspect, as he said...

[440ex kid]

more performance out of a piston than out of a shaved head at the same compression ratio


Dan over at dasa was claiming different. Care to elaborate on how you came to that cocnlusion?

[DirtDevilBT]

I think the best advantage of decking your head is to improve scavaging during valve overlap. You take a 12:1 with a low dome and deck the head. Now you have a low dome running 13:1. Better high rpm revs. All and all it's up to you.


With air cooled motors it's easier. Take out the bottom gasket and run a liquid gasket. No water jackets, only oil. You get a hair over 1 point. Mostly I've seen this with 400ex's

[buck naked-r]

Originally posted by chad502ex
In general, shaving heads 1mm or 0.040" is good for about 1 point of static compression. Lowering the head closer to the crankshaft will also slightly retard your cam timing a few degrees. Nothing to worry about. Decking heads run about $50 from your local machinist. A high compression piston can cost between $150-$250; so, compression being equal it is cheaper to deck for an equivalent 1 point of compression gain. Care must be observed doing either modifications when considering piston to valve clearance. It's just that most piston manufactures have already considered P-V cleanances with proper flycutout depth in the piston dome. As far as reliability of decking, no issues there IMO

so one point on 14.1...will make it what?14.5 or 15.1?

[chad502ex]

Originally posted by buck naked-r
so one point on 14.1...will make it what?14.5 or 15.1?

1 point = from 14:1 to 15:1

[buck naked-r]

Originally posted by chad502ex
1 point = from 14:1 to 15:1

thanks

i may look into that,im looking to get as much power out of the stock bore as possible.........i wanna save the head porting for the last and final step.