boring an engine .40 over

[jmartinez1228]

hey my friend just rebuilt his engine and bored it .40 over. What kind of performance gains would he notice from boring it that much? How much boost would the engine handle ? He put in JE pistons and eagle rods by the way. Its in a 1g gsx thanks

 

[jmartinez1228]

also is there any downside to boring the engine out that much?

 

[V8Hunter]

One downside to boring it out that much is that if his cylinder walls get misshaped due to whatever reason, he might not be able to bore it out to correct the problem because it might bust into one of the coolant passages that run by the cylinders to keep them cool. Im not sure exactly how far you can bore a 4g63 out until you strike the passages but .40 over is higher than alot of people go (.20, .30 are common). So right now there is no downside as his cylinders just got bored out so they will be in good shape for a while. As for performance, its debatable, there is obviously that much more A/F that the cylinder can hold now so there will be a performance gain, was it enough gain for the money he spent? thats the debate

 

[jmartinez1228]

Originally posted by V8Hunter
One downside to boring it out that much is that if his cylinder walls get misshaped due to whatever reason, he might not be able to bore it out to correct the problem because it might bust into one of the coolant passages that run by the cylinders to keep them cool. Im not sure exactly how far you can bore a 4g63 out until you strike the passages but .40 over is higher than alot of people go (.20, .30 are common). So right now there is no downside as his cylinders just got bored out so they will be in good shape for a while. As for performance, its debatable, there is obviously that much more A/F that the cylinder can hold now so there will be a performance gain, was it enough gain for the money he spent? thats the debate

ah so your saying he may have been taking a chance boring it out that much because if it busts into the coolant passages he may as well start be starting to look for a replacement block am i right?

 

[dsmturboawd]

its stupid to go that much right away. go .020 if you need it, then if you need to bore over again, your block isnt trash. you can then go .030 over, and so on.

.040 over isnt going to give you shit for power.

 

[dsmturboawd]

Originally posted by jmartinez1228
ah so your saying he may have been taking a chance boring it out that much because if it busts into the coolant passages he may as well start be starting to look for a replacement block am i right?

giong .040 over is completely safe, shit they make oem parts to go that high. i personally wouldnt go higher.

 

[jmartinez1228]

Originally posted by dsmturboawd
giong .040 over is completely safe, shit they make oem parts to go that high. i personally wouldnt go higher.

hey i was just asking if it would be any good. He himself wasn't sure either, the guy at the machine shop suggested it and that itll make more power so thats why he did it. He is going to be running a buschur racing 20g turbo on that motor so he figured the .40 over would be good, i myself have never seen any dsm with .40 overbore so thats why i asked if its safe and not harm the engine in any way . thats all.

 

[dsmturboawd]

Originally posted by jmartinez1228
the guy at the machine shop suggested it and that itll make more power so thats why he did it.

*shakes head* did you pee on him? i would have pee'd on the guy and taken my motor elsewhere.

 

[jmartinez1228]

Originally posted by dsmturboawd
*shakes head* did you pee on him? i would have pee'd on the guy and taken my motor elsewhere.

Yea maybe i should kick him in the head and tell him he's ugly. :laugh:

 

[Rogue_Ant]

A 4G64 is essentially .060 over... so I wouldn't worry about .040"...


Rogue

 

[Colt2.0]

.040" (actually .039", 1mm) is the maximum overbore according to Mitsubishi for the 4g63 engine block. Going over this may not get you into the water jacket, but it will severely lower your power potential in the long run due to thin cylinder walls. Think about what pre-det does to pistons. What do you think will happen to a thin cylinder wall? .040" is a poor choice for a first oversize. You have virtually no room for error #1, and if anything ever happens to your cylinder walls (knock on wood) you won't be able to refinish (safely) over .040

I would have pee'd on him too. must be used to 8 cyl domestics.

 

[jmartinez1228]

welll i guess he should start looking for another block then, how much would a block cost?

 

[Rogue_Ant]

Originally posted by Colt2.0
.040" (actually .039", 1mm) is the maximum overbore according to Mitsubishi for the 4g63 engine block. Going over this may not get you into the water jacket, but it will severely lower your power potential in the long run due to thin cylinder walls. Think about what pre-det does to pistons. What do you think will happen to a thin cylinder wall? .040" is a poor choice for a first oversize. You have virtually no room for error #1, and if anything ever happens to your cylinder walls (knock on wood) you won't be able to refinish (safely) over .040

I would have pee'd on him too. must be used to 8 cyl domestics.

Are the 4G64 blocks the same casting? If so then I'm going to have to disagree with your opinion. Like I said, the '64 blocks are 1.5mm (~.060") more stock. I doubt the power potential is lessened at all.



Rogue

 

[Rogue_Ant]

Originally posted by jmartinez1228
welll i guess he should start looking for another block then, how much would a block cost?

If he already had the machine work done, then it would be silly to not use it.

Rogue

 

[Rogue_Ant]

Well since the '64 is 6mm taller, the casting wouldn't be identical... I still don't think much else was changed though.



Rogue

 

[pneumo]

Going 0.040" over gives you 47 cc more displacement. That's nothing to brag about. To put it in perspective, if the added dispacement were equal to added HP then it would give a 200 HP engine an extra 5 HP. If the engine made 300 HP before being bored over, then the extra 47cc would add 7 HP. Of course the extra displacement does not equal extra HP, so the gains would be less than that.

 

[crankbender]

its stupid to go that much right away. go .020 if you need it, then if you need to bore over again, your block isnt trash. you can then go .030 over, and so on.

Actually if you do the math he gains almost a tenth of a liter or 5% on displacement. I do see how this can be made to make say 4% (20 horsies on a race engine) more power.

Why are people so set against doing something just because it isn't popular. I mean most people on here don't even understand that a bigger turbo won't always flow more air.

 

[dsmturboawd]

if you reread the thread, we have clearly stated why we are against it. popularity was never brought up.

 

[crankbender]

SHITE i quoted the wrong part of the response

.040 over isnt going to give you shit for power.

That is what was ment. As for people being against something because it isn't popular.


In all reality there are many many reasons to use a large bore short stroke engine.
#1 you keep the piston velocities down. (the pistons produce viscus friction against the walls and keeping their velocity down means less power loss)
#2 many believe that the filling and evacuating of the cylinders is better with a shorter stroke. This may or may not be true but there is analytical arguments for both and few experiments proving either.
#3 smaller rod angles with the same length rods.


Please don't just assume that the machinist was an idiot and you need to piss on him. Take a look at pro engines (F1 etc where turbos are allowed) and you will find some really large bores compared to stroke.

That said the machinist was probably right and he will gain power. On top of that the cost of a new block is very small when it does blow as compared to new internals to match the new bore when you continually re-machine (assuming he doesn't destroy all the pistons).

NOT FLAMING to those who are saying you may hit the water jacket have you done it? have you seen somebody do it with your own eyes? have you gotten the engineering drawings from mitsu showing that the water jacket is that close? ever taken a mic to one after it had a hole in the side and found that it was that close? I have heard of people boring .08 over.....havn't seen it tho

 

[Colt2.0]

Originally posted by Rogue_Ant
Are the 4G64 blocks the same casting? If so then I'm going to have to disagree with your opinion. Like I said, the '64 blocks are 1.5mm (~.060") more stock. I doubt the power potential is lessened at all.



Rogue

I'm not saying the immediate power potential is lessened, I'm saying if you weaken the cylinder walls too much you're limiting your potential for power. Also, boring to .040 will allow the extra air/fuel, but your compression ratio will also be lessened.

 

[Colt2.0]

Originally posted by crankbender
SHITE i quoted the wrong part of the response



That is what was ment. As for people being against something because it isn't popular.




Please don't just assume that the machinist was an idiot and you need to piss on him. Take a look at pro engines (F1 etc where turbos are allowed) and you will find some really large bores compared to stroke.

That said the machinist was probably right and he will gain power. On top of that the cost of a new block is very small when it does blow as compared to new internals to match the new bore when you continually re-machine (assuming he doesn't destroy all the pistons).

NOT FLAMING to those who are saying you may hit the water jacket have you done it? have you seen somebody do it with your own eyes? have you gotten the engineering drawings from mitsu showing that the water jacket is that close? ever taken a mic to one after it had a hole in the side and found that it was that close? I have heard of people boring .08 over.....havn't seen it tho

It would have to depend on the application. you'd have to get pistons custom made #1. Either that or find ones with the correct dia. and wrist pin dia. To have a machinist suggest to bore an engine to the boundary of the factory maximum, is quite ridiculous for a street engine. Of course, I'm sure there are reasons for the factory maximum. Maybe you can bore over .040 safely without comprimising the cylinder wall integrity. Try finding pistons on the shelf for a .080" over 4g63 block. I haven't seen over .040".

 

[pneumo]

If you want to go bigger than .040 look up Weisco pistons for the 4G64 motor. ImportPerformanceParts.net has them.

Here's another way of saying what Colt2.0 is saying; if you bore it out too big the walls may be too thin to hold combustion pressure and they may crack in a short time.

They didn't invent cylinder sleeves for nothing.

 

[crankbender]

I'm not saying the immediate power potential is lessened, I'm saying if you weaken the cylinder walls too much you're limiting your potential for power. Also, boring to .040 will allow the extra air/fuel, but your compression ratio will also be lessened.

????

Your compression ratio is the volume at max stroke divided by the minimum volume. Both of these have the cylinder area in them and it falls out. Your cr is a function of stroke and dead space above the top of the piston at tdc.

If you want to go bigger than .040 look up Weisco pistons for the 4G64 motor. ImportPerformanceParts.net has them.

Here's another way of saying what Colt2.0 is saying; if you bore it out too big the walls may be too thin to hold combustion pressure and they may crack in a short time.

Isnt .040 the max from mitsu tho. At that I am sure you are in no way endangering the wall at street pressures.

yeah wiseco also sells the .060 over specifically for the 4g63.

It would have to depend on the application. you'd have to get pistons custom made #1. Either that or find ones with the correct dia. and wrist pin dia. To have a machinist suggest to bore an engine to the boundary of the factory maximum, is quite ridiculous for a street engine. Of course, I'm sure there are reasons for the factory maximum. Maybe you can bore over .040 safely without comprimising the cylinder wall integrity. Try finding pistons on the shelf for a .080" over 4g63 block. I haven't seen over .040".

check out http://www.wiseco.com/PDFcatalogs/2003_sport_mit.pdf like the 5th on on the list. they are just 4g64 pistons. Luckily with the dsm you don't have to find custom internals.