The Top Mitsubishi Galant VR-4 Resource

Join the best E39A 1991-1992 Mitsubishi Galant VR-4 community and document your GVR4 journey.

  • Software Upgraded - Reset Your Password to Login
    In order to log in after the forum software change, you need to reset your password. If you don't have access to the email address you used to register your GVR4.org account, you won't be able to reset your password. In that case, follow the instructions here to regain access to the forum.

Opinions and Experiences with 9.0 CR on a DD

matt92vr4

Well-known member
Joined
Oct 3, 2010
Messages
676
Location
Venice, FL
Greetings, I'm in the market for a new set of pistons and I'm trying to decide on the compression ratio. I currently run 2G piston with 8.5 and really like the difference over 7.8. I notice that 9.0 seems to be offered by many piston companies. What are your experiences with 9.0 pistons on a 4-5 day per week daily driver? The details are:

93 pump gas 90% of the time with occasional 110 gas at the track
EVOIII 16g (as big as this car will ever see)
ECMLink v3
Cyclone intake
HKS 264/272 cams
EVO 8 valves, springs, etc.
EVO 9 FMIC

Also, what pistons do you like? Thanks for your help.
 

CutlassJim

Well-known member
Joined
Jul 17, 2006
Messages
1,699
Location
Manchester, NH
I have Weisco 9:1's in my motor and I love them. That's coming from a 2G piston'd engine before that. I'll never probably go back to under 9:1 on a 4G63.
 

Dan D

Well-known member
Joined
Feb 27, 2001
Messages
1,171
Location
Brownsburg, IN
I have Weisco 9:1's as well. I was surprised at just how much timing I had to pull in low-mid throttle to avoid knock. This is with a an E3-16G so it's pretty spool happy. It seems like with a small turbo the expected grunt pickup from the compression bump is negated by the timing that has to be pulled. Probably a different story with a turbo that doesn't spool so early.

I'd go 8.3:1 if I were doing it again with the same turbo.
 

BogusSVO

Well-known member
Joined
Aug 29, 2013
Messages
232
Location
Pensacola, Florida
This is one of my pet peeves.... Just because you drop in a set of 9.0:1 CR pistons will not mean you you have a 9 to 1 engine.
That is just one factor. There are other factors that need to be measured and the math run.

Please read this.
click
 

theevozero

Well-known member
Joined
Oct 12, 2011
Messages
332
Location
Odessa, Texas
That's not really the point he asking about.

I have them in a stroker engine. I like them also, but I used e85 and do not have a problem with knock. I'm debated going back to 93, so I guess I'll find out when I get there.
 

ktmrider

Well-known member
Joined
Sep 10, 2007
Messages
3,128
Location
Tempe, AZ
DanD hit it perfectly, get your tune on.

Always the same thing I heard from Keydiver back in the day, 10x harder to tune out all knock events at higher compression levels.
 
Last edited:

matt92vr4

Well-known member
Joined
Oct 3, 2010
Messages
676
Location
Venice, FL
Thanks for the replies. Fortunately I'm familiar with the other factors that determine final compression ratio. I was mainly looking for a general consensus regarding an advertised 9.0:1 piston compared to an advertised 8.3 or 8.5.

I'm leaning toward Wiesco which is what triggered this post because they offer a 8.3 or 9.0. Any wiesco guys have the piston slap issue at idle? Any other good 8.5 options out there around $500?
 

EMX5636

Well-known member
Joined
Jun 28, 2008
Messages
1,631
Location
Bucks County, PA
I'm running the Wiseco 9:1 in the 2.0L in my Galant. Makes around 500whp on 28-30psi on straight pump gas now. Boost response is a bit better, and off-boost power is also slightly better.

I don't remember what my PTW was when I assembled the engine, but I don't have any slap issues hot or cold, idle, etc.
 
Last edited:

strokin4dr

Well-known member
Joined
Aug 30, 2005
Messages
2,770
Location
Savannah, GA
9:1 Wiseco 2.0L here. No slap at any temp either.
 

prove_it

Well-known member
Joined
Jul 3, 2008
Messages
4,201
Location
Sioux Falls, SD
Low end knock can be resolved using E85. /ubbthreads/images/graemlins/devil.gif
 

matt92vr4

Well-known member
Joined
Oct 3, 2010
Messages
676
Location
Venice, FL
I'd love to run E85. I have to drive 50 miles in the wrong direction to get some though. That's not an option for this DD /ubbthreads/images/graemlins/smile.gif Maybe one day we'll get some around here.

Anyone have any experiences with Manley Pistons?
 

mitsuturbo

Well-known member
Joined
Jun 2, 2008
Messages
3,551
Location
Near Seattle, Washington
Quoting strokin4dr:
9:1 Wiseco 2.0L here. No slap at any temp either.



THANK YOU!
THANK YOU!
THANK YOU for spelling Wiseco properly. I don't know how people screw this up. It annoys me to no end. I don't know how you can't just put WISE and CO together. I've seen this spelled so wrong, so many times. Are people saying it wrong? Because it's spelled exactly like it sounds.
 

matt92vr4

Well-known member
Joined
Oct 3, 2010
Messages
676
Location
Venice, FL
Yeah, I noticed I spelled it wrong after I posted it. It was bothering me, but not enough to change it. Sorry about that.
 

362Ryan

Well-known member
Joined
Aug 9, 2013
Messages
116
Location
Alaska
I'm in the process of building a 9.5:1 2.4L. I will let you know how that turns out in the next few months.
 

curtis

Well-known member
Joined
May 4, 2003
Messages
11,892
Location
Clarksville TN
Ok its like this and not going into all the math when you can plug and chug through the numbers yourself.....see link below. Easier to just punch in numbers and play than quote formulas. Plus you may actually learn


The old guys on here remember when Tom went over 500Hp on a 16G....what..... how .... Fuel and Compression
You have to have the fuel to make power British thermal units and all but a 16G cant boost and flow up top like a 37R, s366 hx40 etc. etc. Tom had his compression cranked up and then boosted it As I remember this setup on 20 something psi equaled the numbers of what a 7.8:1 was on 42 psi


Turbo doesn't know if its feeding a 7.8:1 or a 15:1 engine. All comes down to total compression but you have to remember total compression is the secret. To much total compression ratio and to much boost makes things go boom. Just like lean is fast right till a piston melts.

Use the formula calculator posted at the bottom and make a list for your altitude
7.8:1 8.5:1 9:1 9.5:1 10:1 10.5:1 and 11:1 playing with different boost levels and altitude. After you play long enough making a chart / spread sheet etc you see the relationship forming. Then you can play with the altitude and understand why Bandimere at altitude is slower than Pomona


Ever notice peoples video's where they're running around 50psi but never say what the total CR is. I did a Compression test on a friends turbo car a few years back and all four holes were right at 190 and he said the car had 8 or 8.5:1 pistons......... /ubbthreads/images/graemlins/rofl.gif Guess he forgot the part about the block being milled and the head being milled numerous times. Even though I did polish up the chambers its still up there. After you start plugin numbers you realize why some 18psi cars run so damn good and blow past cars on 30+. I personally like the feeling of higher compression turbo motors, Spin up faster especially with larger throttle bodies, great for driving around in traffic and as long as you do the homework set timing correcting and also have the tables set up right and run good gas no detonation best of all worlds and also works good to BS other racers. Give them a ride on 12psi and they're amazed because your 12 might feel like their 21. Plus the greatest benefit lower boost pressures exiting the turbo equals a cooler denser charge. I see mine with 9.5 or 10:1 plugs when I put it together.

Now think on this
Old top fuel cars use to run like 2:1 compression but ran like 100+ psi from the giant blowers. Those cars spin like 7500rpm and run 3 and 4 second passes..Now for math that will screw with you

a 7500 rpm monster engine in those cars only makes 250 full revolutions through all events on a pass
7500 divided by 60 seconds then multiple by 4 seconds then divide by 2 since its a 4 stroke.

Those engines suffer 10 times more starting and doing a burnout, idling back in reverse that ever making a pull.


Go play with numbers now. I had this all in Tom_N's old thread from back in the day but is gone now. If some one wants to do up a chart have at it. Now before someone asks when is to much to much do 7.8:1 at 11psi /ubbthreads/images/graemlins/rofl.gif

It all comes down to what you have for fuel and all the support components. a 16G powered engine with 10:1's and cranked to kill want live with 450's and 1680's may be to much....all depends.

I'm hungry and need food.

click me /ubbthreads/images/graemlins/rofl.gif
 

matt92vr4

Well-known member
Joined
Oct 3, 2010
Messages
676
Location
Venice, FL
Thanks guys, after researching this I've decided to go with 9:1 Wiseco. My old roomate is sponsored by Wiseco and he was able to set me up. Thank you.
 

prove_it

Well-known member
Joined
Jul 3, 2008
Messages
4,201
Location
Sioux Falls, SD
At 22psi and 8.5:1 (8.3:1 pistons and head milled with a 4 layer Mitus HG), my s16g engine is running 20.93:1 final compression. Hmm, no wonder E85 really woke it up. /ubbthreads/images/graemlins/devil.gif

stock 7.8 would be 19.18
9:1 would equal 22.18:1
9.5:1 would equal 23.42:1
10:1 would equal 24.67:1

Yikes. 10:1 would make a huge difference. hmmmmmm yep time to go 9.5:1. Sounds good to me. /ubbthreads/images/graemlins/grin.gif
 

cheekychimp

Well-known member
Joined
Apr 19, 2004
Messages
7,333
Location
East Sussex, U.K.
Okay but where does timing come into that? Surely you have to correlate the final compression ratio with your timing maps to ascertain if and at what point you are still safe and where potentially things could go boom?

Edit: Or to look at it another way what were the stock 1G and 2G timing maps based upon? If I put 7.8:1 and 8.5:1 into that calculator and set altitude to sea level is the final compression ratio I get what the stock Mitsubishi timing maps were based upon? How much leeway was built in by the engineers to account for people taking these cars to altitude? Or was it just left to the ECU and knock sensor to pull timing if any knock was detected?
 
Last edited:

prove_it

Well-known member
Joined
Jul 3, 2008
Messages
4,201
Location
Sioux Falls, SD
In my opinion the 1G timing maps are very aggressive, even on a stock car. There are times you can get up to 25* under boost. If you change compression, then the 1G map will not work. You will break things. Going to the 2G map is recommended up to 8.8:1. Its better, but the transitions aren't as smooth as the EVO mapping. I personally run with a modified evo map with LINK V3.

Pretty much the stock maps are limited to stock compressions, you can go higher, but then you'll knock suppression tuning/fuel/mods. I can push mine with E85 as much as I want. When I had pump gas, I did have to be careful on the EVO maps, but the 2G was fine.

Long story short, it's ill-advised to jack up compression past factory levels without actual tuning being done.
 
Support Vendors who Support the GVR-4 Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications RixRacing RockAuto RTM Racing STM Tuned
Top