Mitsubishi Eclipse 4G Forums banner
1 - 20 of 31 Posts

·
Use it or loose it
Joined
·
844 Posts
Discussion Starter · #1 ·
So I've been trying to find info on this and am coming up short. Few things I wanted to know about it.
I guess one is that I heard the max to bore it out to is 4.0 liter(4mm) is that correct?
Another is that(and this is to the guys who have done this) has there been any downsides to doing this? Ie.. Cracked block,clearance issues with internals etc..
I'm eventually wanting to do internals and go all motor(like the idea of keeping it all motor)so when the time comes to do this,is boring it a viable option? From what I know,we have to get custom pistons n rods made up anyway(I think. I could be wrong!)and if that's the case,then why not bore it out!
Any advice and knowledge on this,good or bad,would be greatly appreciated :bigthumb:
 

·
resident crossplatformer
Joined
·
1,407 Posts
Well, yes and no
Simply boring a 6g75 out by a millimeter (a millimeter increase in radius, so a bore of 97 mm) will give you 4 liters in displacement
if you go the supposed max 2 mm overbore (99mm bore), you land at 4.2 liters, that 99 mm figure I just stated is the estimated max safe overbore (from what I've read on aussiemagna), I don't recommend going this far as if you need to rebuild the engine, you don't have enough sleeve to safely bore the engine out again and if you do, you may run into sealing problems (which you may still run into with this amount of overbore to begin with)
Regardless, yes, boring out the engine is viable as it leads to more displacement, which gives you more power and so on
 

·
Use it or loose it
Joined
·
844 Posts
Discussion Starter · #3 ·
Well, yes and no
Simply boring a 6g75 out by a millimeter (a millimeter increase in radius, so a bore of 97 mm) will give you 4 liters in displacement
if you go the supposed max 2 mm overbore (99mm bore), you land at 4.2 liters, that 99 mm figure I just stated is the estimated max safe overbore (from what I've read on aussiemagna), I don't recommend going this far as if you need to rebuild the engine, you don't have enough sleeve to safely bore the engine out again and if you do, you may run into sealing problems (which you may still run into with this amount of overbore to begin with)
Regardless, yes, boring out the engine is viable as it leads to more displacement, which gives you more power and so on
Thanks fox brand. So I could safely bring it to a 4.0 liter with some room to spare,just means that f/I would not be an option anymore really,correct? And just build my engine around those specs. As well as suspension and driveline of course!
 

·
Registered
Joined
·
96 Posts
Would this be totally worth it?
 

·
Use it or loose it
Joined
·
844 Posts
Discussion Starter · #6 ·
Would this be totally worth it?
Ha ha,that's what I'm trying to find out!
If I was to upgrade all the internals anyway,why not go the extra mile to bore it out. I'd like the idea of all motor. I haven't seen any numbers put up of all motor and bolt ons yet unless I've missed something.
Basically I'm just throwing it out there to get some input,both good and bad as well as achievements and failures.
 

·
Use it or loose it
Joined
·
844 Posts
Discussion Starter · #7 ·
And just so everyone knows,I do realize that this is not going to be cheap! I take pride in owning my eclipse and plan on keeping her for years to come. I'm sure I won't be the first to do a project like this,but I like the idea of taking a path less traveled when it comes to our eclipse
 

·
chucknasty
Joined
·
558 Posts
i would just do .20 over and order pistons. try going with 11.5:1 ratio but you will require a reflash (actively nto shipping out) as timing has to be adjusted carefully.
 

·
Use it or loose it
Joined
·
844 Posts
Discussion Starter · #9 ·
i would just do .20 over and order pistons. try going with 11.5:1 ratio but you will require a reflash (actively nto shipping out) as timing has to be adjusted carefully.
If I may ask,your saying .20 of a mm? And if so,what's the reason behind that chuck? Have you done this or know of somebody and got great results? Just .2 eh!
Oh yah,there's no doubt about a reflash! That will be done once I'm full bolt on. Mabe even sooner. :bigthumb:
 

·
chucknasty
Joined
·
558 Posts
.20 an inch. standard measurement many shops do when rebuilding an engine so that the cylinder walls are nice and smooth. every engine can be bored .20 over. also a standard measurement that many piston companies use when you buy overbore pistons. it would bring you to 4.0 or 4.1
 

·
Registered
Joined
·
5,034 Posts
The calculation are that accurate. 1mm is closer to 3.9 2mm is a 4.0.

Is it worth it...if your not running boost or juice...no is not. Unless you're doing it yourself and yours only changing pistons and rods your prob looking at 2000 in pistons,rods, bolts and gaskets and another 2000 if not more in labor/machining. Make sure you talk to Joyb and rent the torque plate for the bore ns hone. You can followy build to see what all is needed to donor right and ill have about $12000 in parts, labor and machine once I have the motor installed.
 

·
Registered
Joined
·
5,034 Posts
The calculation are that accurate. 1mm is closer to 3.9 2mm is a 4.0.

Is it worth it...if your not running boost or juice...no is not. Unless you're doing it yourself and yours only changing pistons and rods your prob looking at 2000 in pistons,rods, bolts and gaskets and another 2000 if not more in labor/machining. Make sure you talk to Joyb and rent the torque plate for the bore ns hone. You can followy build to see what all is needed to donor right and ill have about $12000 in parts, labor and machine once I have the motor installed.
 

·
resident crossplatformer
Joined
·
1,407 Posts
I disagree that just boring the engine out is not worth it
if you aren't concerned about the cost, on the very fact that the engine is then larger, it will push out more power and torque (while your at it, the rotating assembly must be balanced, which will allow you to rev a little higher, but as is mentioned above, more machining is required with more new parts) will be available or even simply the same power and torque can be achieved sooner in the rpm range, however unless you do additional mods like porting the heads, upping the compression ratio from the oversized pistons, regrinding the cams and so on and any combination there of, you won't be reaching the engine's potential, but I do also somewhat agree with twilson, on the basis of just expecting massive amounts of power to be unlocked by a 5.263% increase in displacement, it isn't worth it without having a means of increasing power per liter, but in what I described above, in the makings of an N/A near race engine (or maxing out any built N/A engine), anything that can be done to an engine to make it more powerful out of the gate is a must, the question is with you if you think you want to spend the money on something like this and have your car inop until the engine done, or spend it elsewhere
I now declare this run on sentence over
 

·
Use it or loose it
Joined
·
844 Posts
Discussion Starter · #14 ·
@ twilson. Holy shit man! I just read your build thread and I gotta say that's pretty god damn impressive! Not to mention a little discouraging too! Lol. I like the route you went with getting another engine so you don't sacrifice your dd.
Thanks for your input too fox-brand. Your guys inputs and reading twilsons thread really opened my eyes. I knew that by upgrading components ,it would lead to changing other stuff,but had no idea of the extent. Guess I know now who to pm if I have any questions...gentlemen.
 

·
Use it or loose it
Joined
·
844 Posts
Discussion Starter · #15 ·
@ twilson. Holy shit man! I just read your build thread and I gotta say that's pretty god damn impressive! Not to mention a little discouraging too! Lol. I like the route you went with getting another engine so you don't sacrifice your dd.
Thanks for your input too fox-brand. Your guys inputs and reading twilsons thread really opened my eyes. I knew that by upgrading components ,it would lead to changing other stuff,but had no idea of the extent. Guess I know now who to pm if I have any questions...gentlemen.
 

·
Registered
Joined
·
18 Posts
There's a guy here who bored out a 6G75 to 4.2L

Obviously, not enough meat for Forced Induction, but this guy did his measurements and found that you could go 4.2L (with space to rebore/hone for rebuild in the future)

This guy was one of the engineers at the Australian Mitsu Factory in South Australia.

Made really good power too!
 

·
resident crossplatformer
Joined
·
1,407 Posts
Hmm, I thought someone went 4.0 liter with a 6g74 and that was were that bore size calculation came from, at least that is how it sounded to me from Aussiemagna
In all honesty, I won't go that large on the stock sleeves for a car that would spend a good deal of time on the street going to and from a track, maybe with a little bit of block filler, or coughing up the money for aftermarket sleeves, but that's just me
 

·
chucknasty
Joined
·
558 Posts
cast iron blocks dont use sleeves. i have seen 3.7 on a 6g74.
 

·
resident crossplatformer
Joined
·
1,407 Posts
our blocks have either steel or ductile iron sleeves, if you look at any engine in the 6g7 family with a cylinder head taken of and if the deck isn't machined, you can clearly see the block and the sleeves are different materials (sleeves have somewhat shiny top surfaces while the deck is a dull grey), you can get replacement sleeves for a 6g72 from 3sx
if you bore a 6g74 to 99 mm, it will displace 3962.8 cc's, I fully belive someone bored a 6g74 to 3.7 liters
 

·
chucknasty
Joined
·
558 Posts
when i removed heads from my old 6g72 and a 6g74 didnt see any. looked like one solid surface. normally if a cast iron block has severe cylinder scarring you bore it out then insert a sleeve so oyu have new cylinder walls. but i will take your word for it.

greg almeida at ucs performance made a built 3.7 liter 6g74.
 
1 - 20 of 31 Posts
Top