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Bore and stroke I6 

 

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 Post subject: Bore and stroke I6
Posted: Sun Oct 09, 2005 6:47 pm 
Getting Side Ways
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Just a curiosity thing really as I don't have the money to do it, but I can't seem to find any info about boring and stroking the I6.

Seems just about everyone, prefessional companies or otherwise, focus on increasing power from the 4.0L and I've never seen anyone mention, or sell an stroking kit for the engine.

I would find it very hard to believe that you can't take the engine out to 5.0L, so why hasn't enyone done it?
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Posted: Sun Oct 09, 2005 6:57 pm 
Getting Side Ways
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your right in they seem to specialise in the head work - JMM doesn't seem to touch anything below. That mob in sydeny do though - IPS ot ITS or something like that - maybe try to have a chat to him?
i asked about it a while ago aswell, quite a while now. turned into a bag twr7cx thread "as he wanted to know how to stroke it".
someone however did mention something about fitting the EA pistons or rods or something like that - the 3.2 ones I think. I dunno, i kinda gave up on it and still don't really understand it.
waggin/brad did however did make his bottom end into a 4.2 - but maybe that was bored (which I presume is different - larger pistons while the other increase the travel of the pistons?)?
i'm still interested to learn more so i'll also be following this thread.

 

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Posted: Sun Oct 09, 2005 7:03 pm 
Getting Side Ways
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you can't bore them out that much because it has to be efficient. What would happen would be the bore would be way out much wider than the bore is high and wouldn't make as much power. I can't remember but i think there was like two ratios that a bore and stroke had to be within. If you bore out a lot and still have a short a** stroke the torque would not be as high, therefore lower power. Thats like the 3.2L EA had the same with bore as the 3.9L however the stroke was way shorter and it ended up inefficient and gutless, therefore it was abandoned after one year of production.

Think thats right. :oops: please be right

Cheers
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Posted: Sun Oct 09, 2005 8:13 pm 
Getting Side Ways
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The DMac wrote:
you can't bore them out that much because it has to be efficient. What would happen would be the bore would be way out much wider than the bore is high and wouldn't make as much power. I can't remember but i think there was like two ratios that a bore and stroke had to be within. If you bore out a lot and still have a short a** stroke the torque would not be as high, therefore lower power. Thats like the 3.2L EA had the same with bore as the 3.9L however the stroke was way shorter and it ended up inefficient and gutless, therefore it was abandoned after one year of production.

Think thats right. :oops: please be right

Cheers



they dont have a short stroke at all. the have a stroke that is already to long.
wich is the reason why they don't like to rev. the AU I6 has a slightly longer rod to help witht this but it doesnt fix the problem of a very long stroke and high piston speeds.

aside from reducing it's already limmited ability to rev you can't get kits to do it because there just isnt room in the engine to stroke it any more.

you may be able to get an extra 1mm in stroke by offset grinding the crank and milling 1mm of the top off the pistons.
but it would hardly be worth the cost and effort

with the stock stroke/bore you get 3982.6cc
with a 1mm over bore you get 4069.4cc
with a 1.5mm over bore (60thou) you get 4095.6cc

add to that a 1mm offset ground crank (if at all it can be done with this engine) and you get 4136.8cc with the 60thou pistons

there are some people on here that claim to have 4.2L engine by only over boring. you would need a 3mm overbore to get to 4245.cc
though that would need custom pistons and custom head gaskets not to mention how thin the cylinder walls would be. i personly have not seen any proof at all that either of the claimed 4.2L engine are infact that big.
and considering one of them claims it was done using only a 1.5mm over bore it would need a 3mm offset on the crank. I personly don't believe the engine to be a 4.2L

take what you will from what i have said as it is only my opinion

 

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Posted: Sun Oct 09, 2005 8:19 pm 
Getting Side Ways
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tickford_6 wrote:
The DMac wrote:
you can't bore them out that much because it has to be efficient. What would happen would be the bore would be way out much wider than the bore is high and wouldn't make as much power. I can't remember but i think there was like two ratios that a bore and stroke had to be within. If you bore out a lot and still have a short a** stroke the torque would not be as high, therefore lower power. Thats like the 3.2L EA had the same with bore as the 3.9L however the stroke was way shorter and it ended up inefficient and gutless, therefore it was abandoned after one year of production.

Think thats right. :oops: please be right

Cheers



they dont have a short stroke at all. the have a stroke that is already to long.
wich is the reason why they don't like to rev. the AU I6 has a slightly longer rod to help witht this but it doesnt fix the problem of a very long stroke and high piston speeds.

aside from reducing it's already limmited ability to rev you can't get kits to do it because there just isnt room in the engine to stroke it any more.

you may be able to get an extra 1mm in stroke by offset grinding the crank and milling 1mm of the top off the pistons.
but it would hardly be worth the cost and effort

with the stock stroke/bore you get 3982.6cc
with a 1mm over bore you get 4069.4cc
with a 1.5mm over bore (60thou) you get 4095.6cc

add to that a 1mm offset ground crank (if at all it can be done with this engine) and you get 4136.8cc with the 60thou pistons

there are some people on here that claim to have 4.2L engine by only over boring. you would need a 3mm overbore to get to 4245.cc
though that would need custom pistons and custom head gaskets not to mention how thin the cylinder walls would be. i personly have not seen any proof at all that either of the claimed 4.2L engine are infact that big.
and considering one of them claims it was done using only a 1.5mm over bore it would need a 3mm offset on the crank. I personly don't believe the engine to be a 4.2L

take what you will from what i have said as it is only my opinion


I'll go with yours because it sounds more decent than mine and i am not a enigine sort of guy. But would you be able to look at my post called "Cylinder 6 makes the car shudder" beccause you sound like you know what your talking about.
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