Over size pistons on a 4g63

[sb7775]

Just wondering what the biggest bore some of you guys are running. I have a spare block with some 4g64 .20 over wiseco 87mm piston and i was think of stuffing them into the 4g63 block. I think thats a pretty big increase in bore and should move some serious air. It is .80 over for our block and i know its more than the factory reccomend but there is plenty of meat there. Just wondering if anybody has tried anything like this, and just for your info there is a .80 piston for the 93 newer 4g63 in the wiseco book so i don't think it will be a problem

Steve

 

[blackGSX2g]

On our motors I would only use overboring to ensure a smooth and straight cylinder wall. If you want to build a motor that pumps alot of air, look at doing a stroker motor with some good headwork and upped compression.

 

[sb7775]

On our motors I would only use overboring to ensure a smooth and straight cylinder wall. If you want to build a motor that pumps alot of air, look at doing a stroker motor with some good headwork and upped compression.

I have a stroker allready i was just thinking of trying this. I have collected all the parts for free so beside boring and some new bearings and rings its free. Just something i figure i would try.

Steve

 

[Caithness]

It gives you a 2092.6cc displacement. However, you don't gain the torque advantage from the longer stroke of a 100mm crank, and .1 liter isn't that much of a gain. Perhaps some work on the combustion chamber to take advantage of the larger bore by unshrouding the valves combined with your extra .1 liter might make it worth your while.

 

[boostedinaz]

As already show the gains in displacement will be small and not worht it. You will also have to worry about the longevity of the block. All in all, yes the stuff if free, but that doesn't mean it shoud be done.

 

[alqatan]

I don't think 4g64 pistons can be used with 4g63 block, because the compression will be different, I think the 4g64 block is higher than 4g63, that's why we need to use stroker piston type for 4g64 on 4g63 combo, I think if we use the 4g64 pistons on 4g63 block the piston will be littel bit out.

There are 4g63 stoker pistons which are .040 over and Mitsubishi head gasket wasn't designed for more than 86mm, but I'm sure wiseco could make custom 87mm pistons for 4g63 with 4g64 crank and custom comtic 87mm piston bore to fit.

But if I were you I won't go more than .020 which I'm running right now, bore won't give you that much power noticed, it's all about the crank in our case

 

[T9S1i]

weisco makes .60 over in 8.3 CR
You can get cometic head gaskets to fit too. Also, i think the mls is big enough for .60 over, dont quote me on that though.
Hope this helps

 

[Caithness]

I don't think 4g64 pistons can be used with 4g63 block, because the compression will be different, I think the 4g64 block is higher than 4g63, that's why we need to use stroker piston type for 4g64 on 4g63 combo, I think if we use the 4g64 pistons on 4g63 block the piston will be littel bit out.

There are 4g63 stoker pistons which are .040 over and Mitsubishi head gasket wasn't designed for more than 86mm, but I'm sure wiseco could make custom 87mm pistons for 4g63 with 4g64 crank and custom comtic 87mm piston bore to fit.

But if I were you I won't go more than .020 which I'm running right now, bore won't give you that much power noticed, it's all about the crank in our case

The stroker pistons have the wrist pin moved up to compensate for the extra stroke in a 4G63 block without the extra deck height of a 4G64. You don't use this type of piston in a 4G64 block unless you're doing a long rod 2.4.

I would only overbore an engine to get the cylinders back into round. Other than the possible gains from unshrouding the valves (not worth the overbore IMO) I don't think the minimal displacement gain is worth the downsides of taking that extra material out.

 

[alqatan]

The stroker pistons have the wrist pin moved up to compensate for the extra stroke in a 4G63 block without the extra deck height of a 4G64. You don't use this type of piston in a 4G64 block unless you're doing a long rod 2.4.

I would only overbore an engine to get the cylinders back into round. Other than the possible gains from unshrouding the valves (not worth the overbore IMO) I don't think the minimal displacement gain is worth the downsides of taking that extra material out.

Yeah this is what guys on the forum have told me by the time I was doing my stroker kit but I thought as much as I increase the bore I would get alot of power!

 

[sb7775]

They are the same part number for a .80 over in a 93 and up 4g63 and a .20 over 4g64. As far as the compression goes it shoudn't be a problem same exact specs. The head gasket is a off the shelf cometic. I know many of people people in the DSM community think that a 87 mm bore is to much but don't you think that weisco and cometic would make these parts if it wasn't ok, these we not special order but of the shelf parts. After some inspection and measuring there seems like plenty left and it shoudn't be a problem. Well needless to say i assembled the short block today with some eagle rods and it should be up and running by next weekend.

 

[Maglin]

The biggest reason to stay away from overboring to the limit is heat. When you go .020 over it isn't that much and their is still plently of clyinder wall left to hold and transfer heat. Once you go to .060+ overbore your clyinder walls are just to thin to hold the heat and most gets transfered very quickly and that ends in a car that has a tendency to want to overheat all the time. And of course the chance for hot spots in the walls to crack and even blow out. I wouldn't waste a block tring this out.