Can an Astron 2 litre block be bored and stroked to 2.6?

[BAD-SIG]

Can an Astron 2 litre block be bored and stroked to 2.6? Stroking should be easy just by fitting a 2.6 crank i think, but can it be bored out to 2.6 or more? Are 2 litre Astron blocks the same as 2.6 ones but with more meat between the cylinders on the 2 litre ones?

I decided to keep the original Astron 2 litre in my car so all the numbers match, but when it comes time to recondition it I would like to bore and stroke it and have a worked head plus high compression to get as close as possible to 200hp...

[A112H]

I am pretty sure the crank is about the only difference between 2.0 and 2.6
As for larger, I have heard of 2.8 but I think that is about as far as you can go safely.

[BAD-SIG]

Ok, after some research, I found some more info from my workshop manuals, Wikipedia (http://en.wikipedia.org/wiki/Mitsubishi_Astron_engine) and Sigma Turbo Register (http://www.sigmaturbo.com/Specifications.htm). The four Astron engines we will be looking at today are: 4G51, 4G52 (and G52B), 4G53 and 4G54.

4G51: 1850cc, 112.89ci, bore=81mm vs stroke=90mm, 8.5:1 non-turbo

4G52 (G52B): 1995cc, 121.74ci, bore=84mm vs stroke=90mm, 9.5:1 non-turbo, 7.8:1 factory turbo

4G53: 2384cc, 145.48ci, bore=88mm vs stroke=98mm, unknown compression ratio

4G54 (G54B): 2555cc, 155.92ci, bore=91.1mm vs stroke=98mm, 8.2:1 non-turbo (Australia), 8.8:1 (overseas non-turbo, carburated) and 9.2:1 (overseas ECI-multi injected)

So basically, the 4G51 and 4G52 share the same crankshaft but have different bores. The 4G53 and 4G54 also share the same crankshaft but again have different bores. The 4G53 was only available overseas (outside of Australia).

This has been discussed in the past here in these forums but I could not find where. From memory, the blocks are all exactly the same on all Astron 1 engines, which are all small block. Only Astron 2 engines came as big/wide block on factory manual cars (Sigma, Scorpion and Triton). Not sure on the Pajeros.

So from what I could work out in my research, it is indeed possible to fit a 2.6 crankshaft from an Astron 1 engine onto any other Astron 1 engine. The blocks are all the same too except for the size of the bore and compression ratio depends more on which pistons are used (flat tops, etc).

So in short, fitting a 2.6 crank into a 2 litre block with stock bore would give you an engine size of 2172.7cc or 2.2 litres.

The largest Astron 1 engine I found online was 3 litres, but that was a full race motor. Most street going vehicles had engines enlarged to about 2.7 or 2.8 litres.

So here is what I'm thinking when it comes time to recondition the engine: fit a 2.6 crankshat to it and enlarge the bore to make it at least a 2.6 litre engine but with at least a 10:1 compression ratio with forged pistons. This should get us close to 200hp, but to be honest I think I would be happy even with just 175hp or 180hp.

RPW in Perth did quite a bit of research and development on their drag racing Galant coup. They started out with a 2.6 and got it as big as 2.9 litres before going turbo! http://www.rpw.com.au/shop/index.php?op ... &Itemid=40

[RaptorReed]

Now if you were Destroking a 2.6l, there is a difference between main bearings and you would need a g54 with narrow main bearings to suit the g52 crankshaft.

[Cottees]

From the 2L and 2.6L blocks I have seen, it might not be possible to bore a 2L out to 91.1mm for the 2.6L pistons. If it is possible, it might not be recommended since the bore walls would end up much thinner than in a 2.6L. If you look inside the 2.6L block through the welch plug holes, you can see there is no internal space between the bore walls, where as in a 2.0L, there is a gap.

[84GKSIG]

defiantly not possible to bore out a 2 liter block to a 2.6, the 2 liter block casting has a physical gap between the cylinder wall castings ( as cottees mentions above ) on the 2.6 the cylinder walls are butted right up to each other, if you have 2 blocks, a factory 2 liter and a 2.6 pop the welche plugs out on the exhaust side of the block and you will see what im talking about.