TiCaL

ok, so i'm now building my D16a6 and i have already got most of my parts. i purchased eagle rods and srp pistons. the pistons are stock bore but i believe the compression is 9:1 which is for the d16z6, y8, y7, etc... i know stock comp. on my motor is 9:5:1. will these pistons give me any problems... i know all d-series ---- is pretty much interchangable so i'm guessing i should be fine, right? i mean i am lowing comp. a little which is boost friendly!?!? second, when you lower compression, does that change your a/f ratio, and what actually happens? how does the ecu react? i have a TE basemap on my ecu and it ran pretty damn good but will lowering compression change anything? will it run worse? i'm going to try tuning it asap and not beat on it until then but i would definatly like to know. sorry to sound noobish but this is my first major build-up.

TiCaL

this might not be the right forum but i know somebody has to know!? what actually changes when lowering compression and i should be good with these 9:1 comp. pistons right? stock comp. is 9:5:1 come on...Dr. Boost, Projekteg, Abaz, leed, xenocron, Whitey.. i know one of you top dogs can help me...

Dr.Boost

I'm a top dog?

There was a link posted somewhere recently that showed a very small change in both horsepower and A/F ratio from a drop in compression. You shouldn't have to worry about anything unless you're running Vitara pistons.

You will have to tune it regardless of how it ran before. It's a new motor now.

On the compression calculator I got a ~8.1:1 compression ratio with Z6 pistons in an A6. .............and that's stock Z6 pistons, not low compression Z6.

http://www.knology.net/~jediklc/D.htm
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TiCaL

oh ---- so if i use these pistons i will get a 8:1:1 compression or lower?... i still want to stick to 9's in the comp. i would like to stay stock compression but srp says their stock comp. pistons can handle nitrous but it doesnt mention a turbo? anything for turbo cars is 8:? comp. which is kinda low. the pistons i got which are for the y7, y8, z6 are 9:1 comp. and it says they can handle turbo and nitrous. will throwing these pistons in actually lower my comp. that much so it wont be 9:1 comp. then?!? ----...... my brain cluttered! i already bought these pistons so i hope i dont have to sell em and get another set...

TiCaL

i also checked and they are the same pistons for the D15b2/b7/z6/y8/y7/...etc 9:0:1 compression. so throwing the pistons in wont simply lower me to 9:0:1 why would it be in the 8's comp. i suck at this kinda ----!! i can turbo a motor to hell but building a motor anything other than stock is outta my league. i've never done a motor build up and i want to learn and make sure i do everything right, and why/how so many factors come into play when using other than stock parts....i hope you guys understand...

also, when building a motor for turbo...is it always necesarry to lower compression? am i wrong for wanting to keep the comp. in the 9's HELP...

Dr.Boost

All of those motors have different compression ratios so there is no way it will net you a consistant ratio in each motor.
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TiCaL

so, then what do you recommend i do?

Dr.Boost

Find out the exact specs of your pistons.
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TiCaL

what is the best compression to go with? i want to be putting down 250-300whp with the a6... i might just go with some 8:1 pistons if i have no other choice...am i wrong for wanting to keep it in the 9's??

boosted_b16

ok man, first off i would say that those pistons are going to give you way to low of c/r you should try to stay in the 9.0:1-9.5:1 area, c/r's in the low 8's is going to kill bottom end power, send those pistons back, and get the srp's that are stock bore/stock comp. (about9.5:1 i believe) made for the d16a6 motor, tell them you need pistons for a 1990 crx si, even if they say nitrous but not turbo they will be fine for boost, second before you go throw those h-beams in, you know that it requires machine work to the inside of the block casting for clearance with those rods right? if you didnt know that you should probably have a machine shop build your bottom end for you....