i've searched quite a bit, and the topic has been touched on, but i still do not completely understand. if someone knowledgeable could help me out with this one i will appreciate it greatly.

okay, now, i've been researching the supertech phosphate coated pistons, found on ka24de.com.

there they explain, that, 8.5:1 / 9:1 pistons (with an oversize bore) , are ideal for turbo applications.

then it goes on to explain that the 10.5:1 (standard bore) pistons, are better for n/a + nitrous applications.

i understand how compression works, but for some reason this doesn't really make sense to me. further, what risks are associated with simply using the 10.5:1 pistons, for a turbo application, (versus an N/A application) and not having to bore the block..... i'm not looking for answers, simply direction.

help is much appreciated.

Mikhail

 

i had asked a similar question a few minths ago.... why is it that an s15 silvia has 11.1:1 compression and can make 250hp all day long? never got an answer. might want to post up on a few other boards.

 

detonation... its possible, just use good parts, and make sure it is welling tuned (timing and fuel!)

 

makes sense. tuning is key.

 

Early detonation..... Cramming air into an engine that now makes enough air for itself (10.5:1CR) will compress air making it really hot. Making it hotter than normal will just cause detonation which can blow a head gasket, throw a rod, or if enough fuel is added you can literally make the engine explode............
Even though it can be used for NOS, the NOS shots won't be as large if they could be at a 9.1:1 CR.

 

okay, so it would be much better to go with lower compression. a buddy of mine blew the ring lands at 14psi, stock internals, a few months back, and then strangely enough, rebuilt with ONLY cast pistons, (stock compression), and new rings. after the rebuild and sufficient brake-in, he immediately put her up on the dyno and threw the bearings. of course when i do my rebuild i'm gonna do it the right way.

 

what turbo and sh*t are you planning on running? I'd say go with 8:5:1 compression, only because you can run high boost on Street gas (93/94) with a higher compression like 9:5:1 you will need higher octane

 

the setup that i'm starting out with , on stock internals, w/ just under 100k on the motor.

t3/t4, 50 trim.
tial 38mm external wastegate
hks ssqv
safc2 (of course)
z32 maf
370cc injectors
walbro 255
msd ignition


i'm tuning very very safely and slowly until i blow up my motor, but i would like to tune to 10psi, on the stock setup. once i end up blowing up my motor, i'll build the block sitting on my floor. most likely up the injectors, and up the turbo to a gt28rs or equivelant. any stock block, stock head tuning tips?

 

Why wait till you blow the motor? You could cause more damage, if anything. Unlikely, but lets say that you crack the block? It'll end up costing more to replace the block, and you'd probably have to end up buying a new engine.

If you look in the dictionary:

Compression as an adjective means something is squeezed (in this case it's air and fuel)

Ratio as a noun means something is divided by something else. It is a math term meaning a quotient.


There are 2 kinds of Compression Ratios (CR):

1. Static

2. Dynamic

There is a big explanation for the two, but what is important is static CR.

Simply put, for static CR, the first number is the chamber volume at BDC, second number is chamber volume at TDC...the higher the first number is, the more squeeze you have. More squeeze improves burn up to a certain point. This point varies for each engine design.

If you know how to tune , you can go as high as 12.3:1 static CR in some all motor cars using 93 octane pump gas!

 

wow...well i understand what you are saying, and i appreciate you helping me out. i will take that into consideration. also though, i have a stripped block , in real good condition.... along with, a ported head, crank, oil pan, etc etc. i was planning on tuning the engine that's in the car, turbo, and slowly building the other engine outside the car, as i get the money. that way, when i blow up the motor, or get too "power greedy", which ever comes first, i'll be a few quick steps away from droppin the new engine in. once again, thankyou for explaning that to me, i kinda understand TDC a bit better now.

Mikhail