question about compression and piston specs

[the mooch]

well my head and block are now apart, cleaned up and drained so it's time to start looking at ordering parts. I'm wanting to do forged pistons/rods but i have absolutely no idea what size to get. how in the hell do i figure out the right rod length, rod weight, and piston to match it? i know the stock piston is bored to 81 mm and stroked to 89mm. is it possible to get factory sized pistons only forged for strength? the motor is a b18b1, and some dude told me to up the compression to 10.5. i always understood that for turbo you want lower compression. does this sound right? how would the thickness of the head gasket affect compression? i'm not really wanting to over-bore the block, just replace the factory parts with better quality parts to run about 12-15 lbs. boost. also, would the stock crank hold up to this?


thanks.

chris

 

[Billy.]

yes you can get aftermarket pistons with the same compression ratio as stock. you will want to keep the same length rods if youre keeping the stock crank, else your basically stroking out the motor. 10.5 is a high compression to be running boost on, like boosting a b16, but you'll get the same power with less boost and thus less lag. some people like to run low compression with high boost and some people run high compression with low boost (which is typically less reliable as the motor makes more power more often = more stress across the rpm band). ideally you should run like 9.2-9.5 cr to boost. but it all depends on what your power goals are

what youre doing is what i already did. i rebuilt an ls block with factory compression forged internals and ran on 7 psi which made me 280whp

 

[DetainedCivic]

I'd go with a 9.1 or a 9.5 compression piston. They are good for daily driving. Anything of less compressions tends not to be a good daily driving motor.

Like stated get the same length rods. I would also put better sleeves in while you have it apart. Balance the crank, rods and pistons. I would also do head work.

 

[the mooch]

thanks for the replies....

i thought 10+ comp. was a little too high, i dunno....something about that shop was a little wierd anyways. how do i know what the rod length is? just bust out a tape measure? and who would i contact to get ahold of something like this? and while i have your attention, should i hit the head with some crower 62402T cams?

 

[DetainedCivic]

thanks for the replies....

i thought 10+ comp. was a little too high, i dunno....something about that shop was a little wierd anyways. how do i know what the rod length is? just bust out a tape measure? and who would i contact to get ahold of something like this? and while i have your attention, should i hit the head with some crower 62402T cams?

You can find stock rod lengths by doing a search. I know they are located in Virginia and are a distance away from you. But call up inlinepro out of Springfield, VA and talk to them about what you want in a motor. They can give you ideas of what you should do to build a healthy motor. www.inlinepro.com

They built a friends b16 and tuned it running 15lbs daily and 25lbs high boost. He is running stock sleeves, better rods and low compression pistons, stock crank, balanced and blue printed. Stock si head and runs high 10's all day in the 1/4mile

 

[nurevEKcivic00]

the longer you make the rods the more torque you have the shorter rods u have the more high revving youll have. the thicker the headgasket the lower the compression youll get. in other words the farther away the head is from the deck the lower the compression will be. if u run high compresson pistons with a turbo, youll most likly blow your head gasket down the road do to to much compression. lower your compression of the pistons

 

[Billy.]

the longer you make the rods the more torque you have the shorter rods u have the more high revving youll have. the thicker the headgasket the lower the compression youll get. in other words the farther away the head is from the deck the lower the compression will be. if u run high compresson pistons with a turbo, youll most likly blow your head gasket down the road do to to much compression. lower your compression of the pistons

you cant just throw shorter rods in a motor block. the crank is made to match a rod length. a b16 has a 77.4mm stroke. throwing 89mm b18 rods in a b16 and you wont make it much past startup before a piston is blown through the cylinder head or a rod gets blown through the oil pan

http://www.phearable.net/tech/wiring/enginecodes.html

 

[stealthy]

buy my 9:1 pistons

http://www.clubcivic.com/board/fs-je-9-1-t126524.html?t=126524