Compression Ratio - Can't Decide

[icespeed]

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,

 

[ProtoType5]

Why not 8.5:1....That's my only question...Good luck with the rebuild...and push that boost...

 

[shane02pro5]

I say 8.5 since once you get that gt28rs in there or whatever you will always want more!! I'm at 13psi and around 250whp and get a little flickering from my J&S from the timing control kicking in and I'm not running out of fuel with afr's around 11. Stock is 9.1:1

 

[orng1]

I don't think you need the 8.5's unless your above 300. A few people have lasted at 250 with the stock set up so a forged set will be just as good amd better. It is a slight diff of .1 but I guess it does help.

 

[AcolyteMSP]

just do the 9s then and use a thicker headgasket

 

[03.5MSP]

I say 8.5, you will be able to run more boost safely. You deff dont want another blown motor.

 

[icespeed]

just do the 9s then and use a thicker headgasket

I ran the numbers on both already, there is a .91mm difference between the pistons. So, I *could* go with a headgasket that is ~1mm thicker and get the same results as an 8.5:1... hmmmm

 

[shane02pro5]

What would be the point wouldn't it be the same difference!?

 

[2.0t03speed]

run the 8.5's if your going over 16 psi there resistance to pre-ignition is better at higher boost levels. but for what you say you want 9.0 should be more than enough.

 

[icespeed]

lol, yeah, but I don't know if there is such a headgasket that is 1mm thicker.

 

[JDM Sam]

For your hp goal use 9. You have more low end power and torque with the 9 which will be more driveable on the street.
If you take your car to get the EMS tuned properly by a professional you shouldn't have any tuning issues. Don't use a piggyback either. You can run race gas if you want to run 20+psi on it. You will be buying tires frequently if you think you can can daily drive 20+psi.

 

[03.5MSP]

Kicker22705 is running 8.5cr, he is tuned at 11psi and if he tries and run anything above that he has detonation problems. Each setup is deifferent.

 

[2.0t03speed]

if you will see he fixed that.....

 

[Alejo_NIN]

the guy with the gloves says 8.5:1.....so, it must be done!

 

[JDM Sam]

Kicker22705 is running 8.5cr, he is tuned at 11psi and if he tries and run anything above that he has detonation problems. Each setup is deifferent.

something is very wrong with the tuning.

 

[03.5MSP]

if you will see he fixed that.....

As of the 6th he was still having that issue. I'm not sure if he had taken care of that since then, he and Dana were talking about changing plugs and stuff.

 

[03.5MSP]

something is very wrong with the tuning.

They(dyno shop) retarted timing and added fuel around the points where it pings a little and he cant seem to get rid of the ping.

 

[icespeed]

For your hp goal use 9. You have more low end power and torque with the 9 which will be more driveable on the street.
If you take your car to get the EMS tuned properly by a professional you shouldn't have any tuning issues. Don't use a piggyback either. You can run race gas if you want to run 20+psi on it. You will be buying tires frequently if you think you can can daily drive 20+psi.

lol, well, I wouldn't say "no" to 300whp, I just didnt think it was plausible given my "projected" build. If someone comes out and tells me, "Yeah, you'll hit 300 w/ the mods you're going to do.", then I would politely reply, "Great! How much boost do I set it to?" lol

 

[Fudgie]

They(dyno shop) retarted timing and added fuel around the points where it pings a little and he cant seem to get rid of the ping.

Whats he using for knock detection?

 

[03.5MSP]

Whats he using for knock detection?

The shop was using an knock amplifier of some sort, plus he can hear the ping as well.