Compression Ratio - Can't Decide

8.5 or 9.0

  • 8.5:1

    Votes: 22 59.5%

  • 9.0:1

    Votes: 15 40.5%
  • Total voters
    37
I have the 8.5.1 and after 3200 miles of driving I can honestly say I cant tell the freaking difference between the stock CR and this.
I did get a bigger cam, port the intake and some other stuff but my mileage and drive-ability are about the same my MPG did go down some but it is still over 30MPG highway.

Plus I feel good knowing I can ram the boost as high as I want...well to the end of the turbo's range anyway.

I have it tuned to around 18PSI now headed over 20 later on. I loves me my MPI piggyback :)
 
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Since you are going to use a high quality head gasket anyway (hint hint), you could comprimise and go in between. Get the 9:1's and use a .074" Cometic head gasket and CR will be around 8.65:1. You can find the gasket for around $100 + sh. Keep you AFR's a little rich this time tho. Big killer on these motors. Best of luck to you! Be ready for some head aches....lol
 
Why would you want 9.1 when you can go with 8.5.1 and run more boost?

I understand you only want roughly 250 wheel horse power but 8.5.1 is just the safe way to go.

Does the SS AFC have control over timing?

If the price isn't a big diffrence Id just do the 5 angle valve job but maybe you can get the 3 angle and put the rest of the money towards 505zooms IM :D

icespeed said:
8.5:1 or 9:1?

to bring everyone up to speed, old engine => boom. Building new forged engine. Not looking for crazy power, maybe mid 200's whp, mid 13's 1/4.

Upgrading/Adding: FMIC, EMS (prolly SS AFC), exhaust mani, intake mani (possibly) - P&P'ing either way and head work (can't decide on 3 or 5 angle valve job) by the time the engine's built.

Upgrading to GT28RS (possibly, may just upgrade t25's internals/p&p etc), fuel injectors/fuel pump, exhaust and s-pipe later on down the road

Thank you,
Click to expand...
 
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JDM Sam said:
Keep in mind you will run into the gear box breaking.
Click to expand...

Man, that is something I dont want to even think about :(
I will definitely not hook it up with sticky tires until after I get a built tranny or strengthen my tranny.
 
lol, already lost that in July. I'm pretty sure it's the LSD. But, rather than fix it, I just put a new one in... so I have the old one just waiting to be "built". muwhahahahahaha.
 
Signature Sound said:
what power level does this tend to happen at? I hear a ton of people are running into this, what are our options? GTX, PAR...??????? And what about cost????
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Big $$ , that's why there are so few people doing it and evrybody is so scared to break.
 
orng1 said:
Big $$ , that's why there are so few people doing it and evrybody is so scared to break.
Click to expand...

Actually, I'd like to know a price range aswell...

I keep hearing about cryo treating the gears and then either welding the stock lsd or putting in the quaife. Which I also understand that the quaife is not a "drop in" replacement and needs adjustments.

Anybody know a price range for cryo-treating the gears alone? (meaning that the tranny is already disassembled and just bringing the gears to a shop.. which begs the next question, what kind of shop would you take the gears to, to have cryo-treated?)
 
mspHtown said:
steve (turfburn) runs 8.8 to 8.9 CR on his mp3.


"306 whp at 16 psi. "
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keep in mind he does this only because he cannot break anything higher without detonation. he has a fully worked head so breathability is not the problem, he has a standalone tuned six ways to sunday and spent literally hours on the dyno trying to push the car past 306. the compression ratio is simply too high to go beyond that without detonation, regardless of what timing curve you set or what AFR you run.

sam and i fundamentally agree to disagree here. i personally tire of hearing 8.5 is undriveable or robs the car completely of power. with a proper engine management system and equally proper tuning, there is no reason why you should feel any loss of power throughout the powerband. its been done countless times by people on this forum and with the FS engine. you can run exponentially more boost on a lower compression piston, have a larger margin of error while tuning, run cooler combustion temps comparatively speaking at the same psi, and you have more potential down the road.

here is my take; if you plan on - at some point - wanting to be able to push 300 or more and have the option of going big numbers down the road, there is no compelling reason not to go with an 8.5:1 piston setup. the proteges and FS powered vehicles with the best quarter mile times run lower compression, end of story. so if the idea of, now or eventually, running huge numbers is compelling to you, go with the lower compression.

that being said however! however - if 300whp or less is enough for you, if you have no intention of beefing up the transmission, if you have no intentions of running a complex standalone, if you want to spend the money and just enough to put you at this point and be done with the car then factory compression forged pistons are fine. in the end it depends on your ultimate goals (think long and hard now!) and your budget.
 
icespeed said:
Actually, I'd like to know a price range aswell...

I keep hearing about cryo treating the gears and then either welding the stock lsd or putting in the quaife. Which I also understand that the quaife is not a "drop in" replacement and needs adjustments.

Anybody know a price range for cryo-treating the gears alone? (meaning that the tranny is already disassembled and just bringing the gears to a shop.. which begs the next question, what kind of shop would you take the gears to, to have cryo-treated?)
Click to expand...

i can cryo treat an entire gear set for $150
 
Has cryotreating proven successful with anyone in this tranny? I guess it certainly must do better but how much?

I debated long and hard and finally thought how much I put into this car and decided on the PAR 1-4 set. I think my original plan for 300whp may go up a little higher since that was pretty much my limiting factor. Payment went through today gearset will be here in a week!
 
Captain KRM P5 said:
keep in mind he does this only because he cannot break anything higher without detonation. he has a fully worked head so breathability is not the problem, he has a standalone tuned six ways to sunday and spent literally hours on the dyno trying to push the car past 306. the compression ratio is simply too high to go beyond that without detonation, regardless of what timing curve you set or what AFR you run.

sam and i fundamentally agree to disagree here. i personally tire of hearing 8.5 is undriveable or robs the car completely of power. with a proper engine management system and equally proper tuning, there is no reason why you should feel any loss of power throughout the powerband. its been done countless times by people on this forum and with the FS engine. you can run exponentially more boost on a lower compression piston, have a larger margin of error while tuning, run cooler combustion temps comparatively speaking at the same psi, and you have more potential down the road.

here is my take; if you plan on - at some point - wanting to be able to push 300 or more and have the option of going big numbers down the road, there is no compelling reason not to go with an 8.5:1 piston setup. the proteges and FS powered vehicles with the best quarter mile times run lower compression, end of story. so if the idea of, now or eventually, running huge numbers is compelling to you, go with the lower compression.

that being said however! however - if 300whp or less is enough for you, if you have no intention of beefing up the transmission, if you have no intentions of running a complex standalone, if you want to spend the money and just enough to put you at this point and be done with the car then factory compression forged pistons are fine. in the end it depends on your ultimate goals (think long and hard now!) and your budget.
Click to expand...


this is definitely interesting to hear about him not being able to go higher. when i spoke with him on the phone about it, he claimed the only thing holding him back was the transmission. he said that he ran that 306 whp on a 98 degree day as well.

im not saying you are lying or he is lying, basically im saying wtf....
 
Signature Sound said:
what power level does this tend to happen at? I hear a ton of people are running into this, what are our options? GTX, PAR...??????? And what about cost????
Click to expand...

On SUs website they sell gtx, 2,3, and 4th gears. It wouldnt be a ton to upgrade to those. I believe its like 680ish for all three.
 
kamon8404 said:
On SUs website they sell gtx, 2,3, and 4th gears. It wouldnt be a ton to upgrade to those. I believe its like 680ish for all three.
Click to expand...

where are they getting the gtx 4th gear? mazda doesnt stock these any more (or they ran out, however you want to look at it).
 
shane02pro5 said:
Has cryotreating proven successful with anyone in this tranny? I guess it certainly must do better but how much?

I debated long and hard and finally thought how much I put into this car and decided on the PAR 1-4 set. I think my original plan for 300whp may go up a little higher since that was pretty much my limiting factor. Payment went through today gearset will be here in a week!
Click to expand...

Well that guy with over 360 whp msp built by TBK has stock cyro treated gears.
 
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