If a block is sleeved to 85 mm, yet the combustion chamber of the head is 81.5 mm how does that work? Does machining have to be done on the head?

 

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It doesn't have to be opened up but some people like to. If you do plan to open it up I would cc the head and then order the pistons so you end up with the compression you are looking for. I have never opened up the combustion chamber on my heads and have never had any detination problems.

 

Quite a few people on here will tell you that it will cause more detonation, but if you have a good tuner then that can be dealt with.

 

Opening up the chambers will reduce the compression of the motor. BUT it will make up for the lost compression with more flow, The only way it will increase detonation would be if u were to cc the head and up the compression to what it would be prior to the chamber work. In that situation you would have more compression, and more air = more chance for preignition.

 

id like to know also,is it possible for the pistons go into the head? I'm not sure if i'm understandable, but are the rods tall enough that they can push the pistons into the head? or do all honda engines only push the piston to the end of the block?

(sorry if my writing is not understandable.)

 

Im not positive, but i believe that they only go to the top of the block, unless they are high compression pistons, with a dome. Then, i think the dome can go reach into the head. Correct me if im wrong.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by L33T &raquo;</TD></TR><TR><TD CLASS="quote">id like to know also,is it possible for the pistons go into the head? I'm not sure if i'm understandable, but are the rods tall enough that they can push the pistons into the head? or do all honda engines only push the piston to the end of the block?

(sorry if my writing is not understandable.)</TD></TR></TABLE>

if the dome is big enough, its possible for the piston to go high enough to hit the spark plug, but you're going to have other problems to worry about if that happens.

Clay your motor before you start it.

 

I doubt i'll ever do that but I was just curious if people have ever done that to get more compression and more volume from each of the chambers.

 

ya i was askin about this a couple days ago...i would think you would want to match the head with the block,but im no expert on this subject...i would like to be someday..

 

this is somewhat true and not true. even with big oversized 84mm+ pistons usually they are made with enough clearance .020 or higher so u dont need to open the combustion chambers. now remember this is piston to deck height not piston to head height.
right now we r in the process of finishing my block and just based on calculations not actual measurements we need to shave the blocks deck .030 for 0 PTDH (piston to deck height). usually the manufacturers of pistons want .030 piston to head height and that right there is the thickness of a OEM gasket crushed. food for thought, enjoy.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 1 2 NV &raquo;</TD></TR><TR><TD CLASS="quote"> usually the manufacturers of pistons want .030 piston to head height and that right there is the thickness of a OEM gasket crushed. </TD></TR></TABLE>
so if they're calculating thier compression assuming a 0 PTDH won't that throw actaul compression way below advertised comp. given stock PTDH usually between .020 and .030?
...scary

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by thad &raquo;</TD></TR><TR><TD CLASS="quote">
so if they're calculating thier compression assuming a 0 PTDH won't that throw actaul compression way below advertised comp. given stock PTDH usually between .020 and .030?
...scary</TD></TR></TABLE>

yes, this is what ive found to be true using more than 1 compression calculator online. i thought i got 12.5:1 pistons originally and when u crunch the #s i actually have 11.6:1. then u add a B16 head to my setup and it drops me to 11.3:1. i think its pretty cheap. ppl think they are gettin this huge compression piston when in actuality they are gettin something much less.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mentat Ghola &raquo;</TD></TR><TR><TD CLASS="quote">If a block is sleeved to 85 mm, yet the combustion chamber of the head is 81.5 mm how does that work? Does machining have to be done on the head?</TD></TR></TABLE>

most stock head chambers are around 79mm or so including GSR quench. You dont need to modify when going bigger bore because most piston domes fit into the head when using a 36 thou gasket or thicker. As for detonation, its a myth, if it were true honda would have made the cc 81mm to match stock bore.

the only other mod is to ensure you have the correct bore headgasket, so 85mm bore = 85mm headgasket

greg

 

Are these 85mm gaskets manufactured or strictly custom bored?