1g pistons vs. 2g pistons

[blueberry_dsm]

now im not new to dsms at all, but i have seen multiple different people run 2g internals in a 1g block. i am picking up a parts car, and im going to rebuild the engine, but i am trying to decide pistons and rods, thinking about wiseco pistions with oliver rods, but for cost effective results right now, i am considering running 2g internals.

now i heard that the difference between thm is that the 2g have a higher compression, thus making the 2g engine push a wee bit more power. now im goin to be doing a turbo '90 2.0L 4g63 engine swap into a 93 eclipse, and i was wondering if it would make more sense to keep the 1g internals or run 2g internals? looking for some advice here, thanks.

 

[95GSXBLUR]

most people run the combination of the two..

1G 6-Bolt Crank/Block/1G Head (flows more, minorly more aggressive cams)
1G Rods
95 Pistons

the pistons have to be machined to fit the 1G rods though. 1G pistons are 7.8:1 compression 95 Pistons are 8.5:1. It's a proven combination that has lasted on several cars I've had close personal experience with. I'm currently running more boost with the lower compression 1G pistons... stock internals are good for roughly 400AWHP.. some have done more, others have roasted their motors with less. Hoped this helped.

 

[99gst_racer]

As stated above, the 1G rods are known to be stronger and the 2G pistons make a higher compression ratio. It makes for a great combo. The difference between the two is the diameter of the wrist pin. 1G's ran a 1mm larger pin diameter, so you will have to have it opened up on the piston end of the rod.

 

[WhiteTsiAwd]

In all honesty, it is a good combination but for the amount of money you will probably end up spending, your better off just keeping the stock 1g pistons and rods. Ya they have slightly less compression, but you will be able to run more boost slightly. And really for the money, I dont think its a good idea unless you can get stuff done cheaply.

Cody

 

[staticbrainwash]

i totally agree. 2g pistons and 1g bigrods are a good combo, but for the money youll spend WAY less on just sticking with stock pistons. espically if the stock pistons are ok to go back in.

i was planning on doing the 2g piston mod when i do my rebuild, but honestly, unless you can get it cheaper, youll end up spending just as much to get them to fit as you would for forged pistons (wiesco or ross).

it's really up to how much you want to spend and how well you trust your machine shop.

 

[Mike1992]

It cost me roughly $150 to have my 1g rods machined for 2g pistons/ $150pistons + $150 Machining + $0 for 1G Big Rods = $300 $300 is cheaper then any set of forged pistons out there. Stock motors can handle the power all day long. Build it once, build it right, build it to what your budget allows.

 

[staticbrainwash]

did you use mitsu 2g pistons? cuz anywhere i've found them they are about 200 without shipping or tax.

i know topline and ITM are cheaper, but i don't really trust though. i havn't heard many people have too good of experience with them.

 

[Malero5]

I came across this same question when I went to do my rebuild 3 months ago. If you look at the topline 1g pistons and 2g pistons you will notice thy have the same compression. Both of them come from cast and are reliable. I decided to save the 150 dollars and go with the 1g.

 

[Stapl3]

Just get some used OEM pistons online. You can snag 4 of whatever generation you want for like 25 bucks.

 

[Matts95TSiAWD]

so they are not the same strength?

 

[Mike1992]

did you use mitsu 2g pistons? cuz anywhere i've found them they are about 200 without shipping or tax.

i know topline and ITM are cheaper, but i don't really trust though. i havn't heard many people have too good of experience with them.

I used the "ITM" pistons from partsdinosaur.com I haven't heard any complaints from the "ITM" brand users here or anywhere else. Theres a couple guys on the board running these pistons and all is well.

 

[blueberry_dsm]

well i was told that the 2g pistons have a higher compression so they would be better for a n/a application. however, isnt it better for the turbo engines to higher lower comprssion pistons rather than high? so would be staying with the 1g be a better idea?

 

[Mike1992]

If your rebuilding a NT and want no future with a turbo just use stock 1g pistons and ignore this entire thread.

 

[blueberry_dsm]

^^^ummm, did you read my first post? its a turbo rebuild.




im still not fully answered. i was told that a n/a engine gets more power from higher compression pistons, and turbo cars get more power from lower compression pistons. and since the 2g pistons have a higher compression than the 1g, would it make any sense at all to put 2g pistons in a turbo 1g rebuild? or should i just run stock internals?

 

[xveganxcowboyx]

Higher compression = more power. It doesn't matter if it's N/A or F/I.

The reason some people use lower compression pistons in F/I vehicles it it allows higher boost on the same octane gas. Higher compression and higher boost both require higher octane or you'll have knock. You just have to choose between the two. Neither piston will give really high compression though.

Another thing to keep in mind is the power curve. Higher compression will probably yield lower gains than higher boost, but it will give you more low end torque whereas higher boost will give you more top end power.

Did that make sense?

 

[Deez]

There are generally two pathways you can take:

A) Lower compression and higher boost or
B) Higher compression and lower boost

Both can yield similar but different results. If you choose A, then when running on pump gas, you'll be able to run higher boost levels without knock. As it was mentioned before, the yield will come in the form of more top end power with a sacrifice in low end torque. More top end power because you'll have more boost but because of the lower compression ratio, the turbo will take longer to spool and build full boost hence full power.

If you chose the later, then low end power will be better because of the higher compression (which creates more pressure in the cylinders naturally aspirated) but boost pressure will be limited to the gas being ran. In essence, you'll be able to run less boost but still make good power.

Lets look at both situations, both running on pump gas <93 octane. In situation A, you have 7.8 to 1 compression which yields decent throttle response and spools up your 14B turbo at roughly 3300 RPMs (hypothetically as this threshold will vary depending on boost pressure, etc). You notice that your car feels pretty good even with the boost jacked up to 19 lbs and surprisingly it doesn't knock. You try and jack up the boost to 23 lbs but notice that the car starts to knock, which could be because not only are you taxing the little turbo out of its efficiency zone, but also taxing that little stock side mount intercooler and heat soaking it, or maybe because you're running out of fuel running stock injectors, fuel pump, pressure regulator. At any rate, let’s keep things in relation to boost vs. compression ratio. Let’s say that this hypothetical situation yields 240ish whp on a dyno.

Let’s not look at situation B. In this situation you have your brand-spanking-new OEM Mitsubishi 8.5 to 1 pistons on 1G rods. With the higher compression running pump gas, you notice that if the boost is over 16 lbs, the car starts to run sluggish and much slower. This could be due to the higher pressures in the cylinders even though you're not running your 19lbs of boost but now have a higher dynamic compression ratio. This higher pressure causes knock which the stock ECU picks up and retards the cars timing accordingly as its purpose is survival. So hypothetically, you turn the boost down until the car doesn't knock, say 14 lbs and notice that the car is equally fast as in situation A.

Couple of things to mention here. With higher compression you'll have better throttle response but you won't be able to run as high of boost without reaching the knock threshold (on pump gas). You'll also have better low-end torque due to the higher dynamic compression ratio while in naturally aspirated mode. The higher compression is essentially why Honda motors can run low boost levels but put down over 3xx whp. This not only gives better low-end response but also aids in spooling a turbo up faster. Remember that turbo spool is created by the pressure, heat, and sound energy within the motor. With higher compression, the heat is higher as is the pressure and possibly the sound. The higher compression will also help you make more power by designing the motor to the turbo you want to run. If for example, the 14b starts to knock like the 4th of July at 15 lbs with higher compression but you switch to a more efficient turbo whose efficiency island is in the 78 percentile range from say 13 - 18 lbs of boost, the better efficiency of the turbo will aid in the anti-knock index of the motor. Simply put, the more efficient the turbo is, the less of a difference the compression ratio change will make.

One more thing and that is the higher the compression, the harder it is to tune. Your error margin decreases from a little bit to slim to none.

 

[Stapl3]

Both have their pros and cons, one isn't better than the other.

The difference between 1g and 2g pistons isn't enough to notice in real life.

 

[eclipsegs98911]

Dimension Drawing

http://hometown.aol.com/rcm1061/myhomepage/auto.html

 

[95GSXBLUR]

Basically, it'd be cheaper for you to just leave the stock 1G internals and spend the money elsewhere.. turbo, frontmount, DSMLINK, etc.

 

[gsxtacy]

I thought about this for awhile....and decided to go low compression/High Boost.

The 1G pistons in the block I got were like brand new, so I cleaned them up and reused them.

I figure if I can safely run 20 psi on 90 octane with 750's here at 3000 ft above sea level, that will be great.

I will sacrifice a bit of low end loss for some top end gain.....