ok some people already know that I have forged pistons 40 over with 10.5-1cr. now here is my question. Since my pistons are forged will they always have a lower compression then the stock pistons with a cold engine? Do the pistons expasnd more when they heat up and give more compression? The reason I am saying this is becuase I compared my old engine to the new one AI just built and it seems like the old engine with 221,000 miles has more compression then the new engine cold. I only checked it by hand so far.
checked by hand????? when mines cold with 20 thous over with forged 10.5:1 i get 250psi hot is slightly higher but not much about 255psi what are you getting for psi???
Compression on an old engine can have a few things that affect it. worn rings will make it drop, but at the same time carbon build up on the pistons and in the combustion chamber will raise compression. The material its made out of it won't affect it. With an older engine normal wear and tear will make it have more resistance when trying to turn it over then a brand new fresh motor all covered in assembly lube and what not.... but either way the debate is kinda pointless cause you might as well be talking out of your ass if your "checking compression by hand"
I havent checked my pressure yet but when I turn them over by hand using a wrench it seems like the engine I just built turns easier like there is less compression.
Do forged pistons expand more when they get hot? <------------ was what I should have asked. No i'm not checking the compression the engines are on engine stands. The new engine isnt even broke in yet so I was just wondering why it seems like the engine with 221000 miles feels like there is more compression.
Darkstars wrote: but either way the debate is kinda pointless cause you might as well be talking out of your ass if your "checking compression by hand"
He said it best right there. Come back when you have done a real compression test!
Edited 1 time(s). Last edited Thursday, October 04, 2007 6:51 PM
FORGET GIRLS GONE WILD WE HAVE GOVERNMENT SPENDING GONE WILD!
Wade Jarvis wrote:Darkstars wrote: but either way the debate is kinda pointless cause you might as well be talking out of your ass if your "checking compression by hand"
He said it best right there. Come back when you have done a real compression test!
I never said I did a compression tes tor even said I was going to! However I'm still wondering if forged pistons expand more then oem pistons when they get hot.
One more time, like I said before I didnt check my compression but yes I can turn the engine over with a wrench. Anyone could!!
I don't think anyone is going to be able to give you an answer on if they expand more... it really doesn't matter. Its pistons that are cam ground, they are oval shape when cold and when hot they expand to there proper size and shape... cold doesn't make a difference. and once again
Darkstars wrote:Darkstars wrote:With an older engine normal wear and tear will make it have more resistance when trying to turn it over then a brand new fresh motor all covered in assembly lube and what not....
mabey your spark plugs were in when you turned it over last time?????
Did you measure the head Volume (cubic centimeters), measure piston height, and calculate the proper head gasket thickness for a 10.5:1 CR. Also, did you properly bed the rings in (break-in)?
Also, your rings are going to do the sealing so I wouldn't worry about your piston expansion. I believe that the forgings do expand more than a stock hyper-eutectic piston.
You need to do your compression test with a warm engine, full throttle, (pull all the plug wires so you don't start the car ) crank a minimum of 3-4 revolutions in case you're mid cycle.
heavyclutch wrote:Did you measure the head Volume (cubic centimeters), measure piston height, and calculate the proper head gasket thickness for a 10.5:1 CR. Also, did you properly bed the rings in (break-in)?
what do you think.... hes checking compression by hand
What you have to worry about with forged pistons on a cold engine is piston slap. Mine do it like crazy till it warms up. And yes the piston to bore clearance is right. Theres actually a way to get more power from forged pistons with offset wrist pins but you will have even more piston slap on a cold motor. You just put the offset the oppsite way that the piston company says.
http://www.cardomain.com/ride/2090440
heavyclutch wrote:Did you measure the head Volume (cubic centimeters), measure piston height, and calculate the proper head gasket thickness for a 10.5:1 CR. Also, did you properly bed the rings in (break-in)?
Also, your rings are going to do the sealing so I wouldn't worry about your piston expansion. I believe that the forgings do expand more than a stock hyper-eutectic piston.
You need to do your compression test with a warm engine, full throttle, (pull all the plug wires so you don't start the car ) crank a minimum of 3-4 revolutions in case you're mid cycle.
Thank you..... Now I need to actually do a compression test when I get the engine back in.
Nitrous Nate wrote:What you have to worry about with forged pistons on a cold engine is piston slap. Mine do it like crazy till it warms up. And yes the piston to bore clearance is right. Theres actually a way to get more power from forged pistons with offset wrist pins but you will have even more piston slap on a cold motor. You just put the offset the oppsite way that the piston company says.
and thank you nate, you two answered my question. Its much apreaciated.
what do you think.... hes checking compression by hand
um no I didnt say I was checking my compression by hand. I was comparing the two by turning them over using a wrench. How can you really check the compression with the when its on an engine stand with a wrench? I simply said it feels like there is more compression. I dont want to sound consisending, and I dont mean to if I do. However it seems like you didnt read everything and your making assumptions. In your defense I should have worded my first post better. I hope that helps you understand what I was actually doing.
