Opinions on compression..

[BuiltMazdaTough]

Ok, i found a great deal on some of the 01-02 Miata Pistons.
as you should know, this would bump the BP up to 10:1 comp.

that's great, im down, but i also found a good deal(though not as good) on the 9.5:1 comp pistons.

the problem is that my head is fully machined, and shaved .20"
which means that my compression would either be(around)
10:1 with the 9.5's
or 10.5:1 with the 10's

so now, which is a good choice?
im leaning toward the 10's, honestly.

but im not sure how it would work out. im going to be running pump gas, the stock ecu, and never plan on boosting this GT.

would 10.5:1 even run on the stock ecu?

soooo discuss?
quickness is a virtue.

(when i say that i found a good deal, i mean turpro did) :lol:

[inferno94]

I knew a guy that ran an egt motor with miata cam(s), can't remember if it was just one or not, and pistons of the 10:1 variety on the stock ecu and it went well. I can't remember if he tuned the maf though. He was also a Mazda master tech.

[13thghost]

well the problem with to high of a compression and turbo is the fuel.i think there is a formula to find out about how much mep you will make at a given boost and rpm level.

[inferno94]

well the problem with to high of a compression and turbo is the fuel.i think there is a formula to find out about how much mep you will make at a given boost and rpm level.

He's not boosting it, it's all motor.

[13thghost]

ooh well in that case you will be a ok!

[jrally]

I'm running over 10:1 right now, no problem, just have to tweek the air meter a bit to get tuned in.

-Jon R.

[BuiltMazdaTough]

awesome. that's what i was hoping for.
i am no stranger to tuning my (and a couple friend's) VAFs
it looks like tomorrow i will be ordering the 10:1 pistons...
10.5 : 1 here i come!

[whistler]

what kind of a deal are you getting on the pistons, if u dont mind me asking?

[Shades]

Go with the 10.5:1... now is that .200" or .020"?
Cause I believe that .200" is quite a lot, you may even be hitting the seats at that much...
.020" is fine, that's the limit on a stock head before it changes your valve timing and what not... and also if fine with your compression cause .020" doesn't change the compression enough to even jerk off about.

With the higher compression tho you might have to run mid to high grade gas... but you won't need more than just high grade pump gas.

You may have to play with the air sensor to make it run more efficient, but it will run and prolly run pretty great.

Good luck!

[dave0r]

get adjustable cam gears if your taking alot of the head

some site mentioned per .mm = x degress changes so what you think it sweet is out a few degress

just a thought

[Turpro]

what kind of a deal are you getting on the pistons, if u dont mind me asking?

http://cgi.ebay.com/ebaymotors/Mazda-01-02-Miata-BP-1-8L-Pistons-Rings_W0QQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247QQcategoryZ33623QQihZ003QQitemZ130202982248QQrdZ1QQsspagenameZWD1V

http://cgi.ebay.com/ebaymotors/JDM-Mazda-Miata-1-8L-BP-Pistons-MX5-NA-NB_W0QQcmdZViewItemQQcategoryZ33623QQihZ005QQitemZ150232464413QQrdZ1QQsspagenameZWDVW

[Mazda_Powered]

Go with the 10.5:1... now is that .200" or .020"?
Cause I believe that .200" is quite a lot, you may even be hitting the seats at that much...
.020" is fine, that's the limit on a stock head before it changes your valve timing and what not... and also if fine with your compression cause .020" doesn't change the compression enough to even jerk off about.

With the higher compression tho you might have to run mid to high grade gas... but you won't need more than just high grade pump gas.

You may have to play with the air sensor to make it run more efficient, but it will run and prolly run pretty great.

Good luck!

How do you adjust your valve timing if you go over .020"? I was going to do a total of .030"....020"head and .010"block.

[BuiltMazdaTough]

Yeah, it's only shaved .020"
i planned on getting adjustable gears.
only after i get the new head on and tuned, im going throw in a simple stage 2 clutch and try my luck with the exintake cam.

on a side note, i thought you could take .020 off the head and then another .020 off the block before anything in the head had to be changed?

[Mazda_Powered]

I actually heard we can go a total of .050" before it changes our engine to an interference....or something like that....

JACK.

[almighty4wd]

at what CR was that 0.050" quoted?