for all you 84mm+ pistons guys, did you bore out the head to match the block? if so, what advantages does it do? some people told me that it drops compression. Up for answers. TIA.

 

Do you understand the concept of compression ratio?

 

dude, CC... come on.

some people match the combustion chamber up, some dont. some chalk up that extra 3mils as a 360 degree quench. others use that 3 mil as an opportunity to take come shrouding from around the valves.

you can just drop the head onto a b20 head gasket and you will be ok, if thats what you want to do. but if youre going to do some dremel **** to the head, just sell it to me instead.

 

Doesnt the B20 engine use a plain old PR4 head just like the LS engine?
I think if it were a concern, Honda would have enlarged the chambers to match the larger B20 84mm bore.
And yes, an "opened up" combustion chamber would have more volume, resulting in lower compression...

 

Why should I "come on" ? It was a serious question. If he understood the concept of compression ratio, he wouldnt have to ask the question. And if he doesnt understand the concept, then maybe it would be better to help him understand the concept itself, instead of answering this question specifically. Teach a man to fish...

 

some times its easier to just answer a knuckleheads question than to get philosophical on them.

 

sorry but i do not understand the concept, please explain. and also explain if someone does decide to bore out the head to match the block, should the person go for a high compression piston in a build such as a 12:1 in order to get a 11ish compression since it will drop the compression? TIA.

 

Yes, that is the correct approach. Some people actually match all the parts before they start the build.
Honda did make an 84mm chambered head for the B20 in Japan, the PR8 head, had larger intake valves also. There are advantages to opening up the head, if it is a B16, it needs to be done on a milling machine with a boring bar.

 

you me and everyone were knuckleheads at one point! don't you remember?

how do you think we all learn? a stupid question is better than a stupid mistake!

 

what are some advantages on opening up the head? also, is there a way to see how much compression will be dropped by matching the head bore with the block bore?

 

bump

 

play around with this compression calculator
http://www.c-speedracing.com/howto/c...c/compcalc.php

Basically when the piston goes up, it squeezes air and some fuel into a little tiny space before the spark plug ignites it and it goes BOOM and pushes the piston back down...

If you take that tiny little space and enlarge it, the BOOM isnt quite as powerful, because you didnt squeeze it or compress it as much...
Making sense so far?
Changing the size of the "combustion chamber" which is that little tiny space we were just talking about will raise or lower your compression depending....

 

yes it is making sense. so correct me if im wrong, but if I would to match the head with the block bore, I would need a higher compression piston? ex. If I would want to have a 11.5 cr, I would need to get a piston that has 12-13 cr to make up for the loss of compression? Or would I need to get a thinner head gasket help for the loss of compression? OR am I still approaching this all wrong? sorry if I sound like a dumbass, Im still learning...

 

you dont NEED to get a higher comp piston and the drop from opening up that chamber isnt 3 full points. the RS machines pistons are flat for 3 mils around the edge. this is part of the reason i think RS machine pistons equipped motors make more power than they "should". it makes this 360 degree quench with a 81mm head.

 

such great information guys, and a learning process. so if i decide to stick with 11.5 cr pistons, a thinner head gasket will help the little loss of compression? TIA

 

I had only the areas around the valves deshrouded to match the bore (85mm). The entire chamber on the head (PR3) remained mostly at 81mm. I don't have any flow numbers, but just opening up the area around the intake valves should increase low-lift flow by quite a bit.

 

i would suggest leaving in more sharp edges in the combustion chamber so deton ation will start even earlier. Of course a "good" tune with less timing and more fuel may solve the promlem.
To the OP if tou are not going to pay to get the head CC'd, to find the compression ratio, why bother asking, just guess like everyone else.

 

what are the pros and cons of keeping it 81mm and the pros and cons on matching the head to the block bore?

 

Pro's for 81mm. It's cheaper. Cons less flow, more chance for detonation. Compression only comes in if you do not know what you want or how to measure CC's. Opening the head, reverse the 81mm stuff.

 

you funny. "good" tunes robbing people of power and fuel all around the world. I wonder why it doesn't make power? I love detonation showing up early to dinner. OP, I'm running my b16 head stock bore chambers, but smoothed out. Mahle pistons.

 

Good for you, do you want a cookie?

 

back to my other question. when it comes to gaining the compression that is lost by opening up the head to match the block bore, would a thinner head gasket gain the lost compression?

 

saturday bump.

 

A thinner headgasket will certainly raise compression, but it is unknown how much compression was "lost" by boring the head.

 

Hmm, good info.