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Compression ratio

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Sullbren17

Proven Member
175
0
Nov 29, 2012
Chadron, Nebraska
Wiseco Forged Pistons Mitsubishi Eclipse RS 420A 2.0L - $509.99 : Real Street Performance Engine Parts, Pistons Rods Cams Valvetrain and More

I was looking to buy pistons for my build, but I don't understand the compression ratio part. The website says that I can order 10.5.1 ratio or 8.8.1 ratio. I think its the hight of the piston. But the only reason why I would think that would matter is if you were buying the right rods for it. But i don't see what the difference between the 10.5.1 and the 8.8.1 is. Is it for a different stroke or what? and i do have a turbo on my car but what would be best to do?

I watched this video on it.
[ame=http://www.youtube.com/watch?v=nveqCMNTth0]Compression Ratio - Explained - YouTube[/ame]
 
Compression Ratio is the value that represents the ratio of the volume of its combustion chamber from its largest capacity to its smallest capacity. it is the ratio between the volume of the cylinder and combustion chamber when the piston is at the bottom of its stroke, and the volume of the combustion chamber when the piston is at the top of its stroke Hence the 8.8-1 or 10.5-1


Going to try to explain the difference between the two rates...

Okay 8.8-1 is a "Normal" compression that most people go with on forged internals, good on pump gas.

10.5-1 is a very high compression. If your tune is spot on & you are running a larger turbo & e85 this is a great compression ratio. But the margin for error is a lot higher with a compression that high. The engine is a lot more prone to Knock & detonation if used with a low octane fuel.

Higher compression is more "desirable" i guess you could say because they are a lot efficient at extracting "energy"

Hope this helped you. Had some serious brain farts while writing this.
 
Well i was planning on running a hight octane in the motor its self does it matter the size of turbo involving the ratio?

and what is e85?
 
Well i was planning on running a hight octane in the motor its self does it matter the size of turbo involving the ratio?

Supposedly people say a higher compression helps spool the turbo, but I have yet to see a single post or article to support than theory.

& my personal opinion on the compression ratio is IF i where you I would just purchase the 8.8-1's. I have 10.5-1 in my car & the only fuel I run is e85, the car has never seen pump.

Running a higher octane is always better, but if you look at the octane in e85 & then your local highest octane 91 or 93 you will notice the difference in it. I would just go with the 8.8's, you will be happy with it.
 
E85 is a 85% denatured ethanol fuel and 15% gasoline
The average octane is between 100-115 depending on the blend & season
Most states have it at the pump.... But if you are unfamiliar with it I would research it on here. It isn't a "fill up & go" type deal. Need a fuel system to handle the %20 more fuel, A way to tune, etc etc.
 
Last edited by a moderator:
I had aftermarket pistons in my car but i dont know what compression ratio they where i spun the rod bearing and i trashed my crank shaft so im looking for a new shortblock i was suppose to get one from a guy but i sent the money and he never called me back or i never got my stuff sent to me so im going with plan b and boring my block and put a new crank in and get new pistons and rods i have a turbo on it but i dont know anything about it

Well i bought the car from a guy and he told me to run high octane fuel in it, i have 450cc injectors a wally 255 FP and i have a vortex FMU is that what your talking about ### i had some knock going on reving at about 2400RPMs and i didnt know what it was someone told me it was my end cap bolts on my rod but i wasnt sure
 
I had aftermarket pistons in my car but i dont know what compression ratio they where i spun the rod bearing and i trashed my crank shaft so im looking for a new shortblock i was suppose to get one from a guy but i sent the money and he never called me back or i never got my stuff sent to me so im going with plan b and boring my block and put a new crank in and get new pistons and rods i have a turbo on it but i dont know anything about it

Well i bought the car from a guy and he told me to run high octane fuel in it, i have 450cc injectors a wally 255 FP and i have a vortex FMU is that what your talking about ### i had some knock going on reving at about 2400RPMs and i didnt know what it was someone told me it was my end cap bolts on my rod but i wasnt sure

Alright going to try to cover what I managed to get from this

#1: If someone scammed you for a substantial amount of $ I would contact the police, they have dept that deal just in online fraud.
#2: Are you saying you don't know what turbo it is? Or you don't know anything about the engine build?
#3: 450's are not big enough to fuel a e85 powered car, you will lean out bad. Remember the car requires %20 more fuel than it would on say 91. So running e85 on a car that is set up to flow 91 will cause the car to lean out bad.
#4: if you are unsure on the condition of your engine or the cause of your knock, i would do a complete dis assembly to check the condition of your short block.
#5: I am not familiar with the 420a because I have never owned a car powered by one, but everything I am telling you transfers over to your platform, by no means am I a "DSM GOD" but if you do not trust anything I am telling you the search box will usually wield results to whatever questions you may have.
 
LOL no i have my engine out and apart and i have my pistons and stuff out i know what a turbo is and i understand all that stuff yes.
I just dont know how a 57 trim and a 60 trim is any diffrent and i didnt know if your compression ratio mattered with any of that which im sure it does.
Im giving this guy until 4 tomorrow then il try giving him a call its been a week now but if he doesnt respond or his number is changed i already have it ready to be filed and stuff. but when i said i didnt know what it was i dont know the brand of turbo or trim or anything i think it was a turbo bought off ebay to be honest. Im very interested in this e85 stuff though. Can you run it with a 8.8.1 ratio?
 
LOL no i have my engine out and apart and i have my pistons and stuff out i know what a turbo is and i understand all that stuff yes.
I just dont know how a 57 trim and a 60 trim is any diffrent and i didnt know if your compression ratio mattered with any of that which im sure it does.
Im giving this guy until 4 tomorrow then il try giving him a call its been a week now but if he doesnt respond or his number is changed i already have it ready to be filed and stuff. but when i said i didnt know what it was i dont know the brand of turbo or trim or anything i think it was a turbo bought off ebay to be honest. Im very interested in this e85 stuff though. Can you run it with a 8.8.1 ratio?


The compression ratio is just for the engine, like i stated earlier some people say the higher the compression the faster the spool but I haven't seen any proof of that.

& Yes you can run E85 on pretty much any compression you want.
 
Higher compression will give you much better "off-boost" performance. It provides more torque as well. But plan on running less timing and/or e85 in a 10.5:1 car.
 
LOL no i have my engine out and apart and i have my pistons and stuff out i know what a turbo is and i understand all that stuff yes.
I just dont know how a 57 trim and a 60 trim is any diffrent and i didnt know if your compression ratio mattered with any of that which im sure it does.
Im giving this guy until 4 tomorrow then il try giving him a call its been a week now but if he doesnt respond or his number is changed i already have it ready to be filed and stuff. but when i said i didnt know what it was i dont know the brand of turbo or trim or anything i think it was a turbo bought off ebay to be honest. Im very interested in this e85 stuff though. Can you run it with a 8.8.1 ratio?

All turbo's have different compressor wheel and turbine wheel sizes. The compressor is the front section, and the turbine is the hot side. A 50 trim, 57 trim and 60 trim are all different, 60 trim being the larger of the group. If you look on your turbo compressor side you should see some markings indicating what your turbo is. If all it says is something like a.r 57 than it is probably a ebay chinese turbo. Most turbo manufactures engrave their turbo compressor's, cartridges and hot sides with a recognizable number or brand name.

If you do not have experience in tuning cars for high compression on boost, your safest bet is to go with a 8.5-1 or 8.8-1 from either JE or Wiseco. Piston compression is not affected by which turbo you use, but your pistons compression ratio will affect the amount of n/a power it will produce (off boost power, or while in vacuum).

If you are planning this car to be mainly a street car with the occassional track time, than e85 is not necessary and will require extra fuel upgrades. If you are not happy with 93 octane, then you can consider installing a meth injection kit. This will increase your fuel as well.

With a 420a the most recommended and common tuning device is MegaSquirt, which is a piggy back kit that comes with all the necessary sensors to allow you to tune much like DsmLink does for those who own a 4g motor. MegaSquirt ranges around $485.
 
Mi"sma;153270279 said:
All turbo's have different compressor wheel and turbine wheel sizes. The compressor is the front section, and the turbine is the hot side. A 50 trim, 57 trim and 60 trim are all different, 60 trim being the larger of the group. If you look on your turbo compressor side you should see some markings indicating what your turbo is. If all it says is something like a.r 57 than it is probably a ebay chinese turbo. Most turbo manufactures engrave their turbo compressor's, cartridges and hot sides with a recognizable number or brand name.

If you do not have experience in tuning cars for high compression on boost, your safest bet is to go with a 8.5-1 or 8.8-1 from either JE or Wiseco. Piston compression is not affected by which turbo you use, but your pistons compression ratio will affect the amount of n/a power it will produce (off boost power, or while in vacuum).

If you are planning this car to be mainly a street car with the occassional track time, than e85 is not necessary and will require extra fuel upgrades. If you are not happy with 93 octane, then you can consider installing a meth injection kit. This will increase your fuel as well.

With a 420a the most recommended and common tuning device is MegaSquirt, which is a piggy back kit that comes with all the necessary sensors to allow you to tune much like DsmLink does for those who own a 4g motor. MegaSquirt ranges around $485.

I thought that a piggy back system works with your factory ecu, and MS is a stand alone system and you dont need extra stuff Like FCD or anything like that. now im confused
 
Right sorry not piggy back LOL. But the system comes with everything required for it. Well worth the money.

Any piggy backs available for the 420a aren't worth the money, those $100 systems are a waste of money.
 
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