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We broke down a MR18 today for a customer to see if we could improve it for boost any. We made some interesting discoveries in there.

 

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So the wrist pins are smaller on the 1.8. but is the wall thickness the same between the two? I would think if they shrunk the pin size but either increased the wall thickness or at least kept it the same it should still be as strong as the 1.6, but just not stronger than it. Lighter weight pin, similar wall thickness and it should allow for or handle higher RPM while having a very similar tensile strength as long as they are made of the same material.
 

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Over all, the MR18 bottom end is just as strong as the MR16, until you make big power, then the wrist pin becomes an issue. This is easily fixed with just using an aftermarket piston and rod with a bigger pin, obviously. But, the only reason i don't think its worth even going that far in is because of the cylinder head. You would need to do a custom cam grind for sure to make it worth while, then have to deal with the lack of duel cam phasing to bring on boost faster and make more low end with the turbo. We did check to see if we could use a MR16 head, and while it will bolt up and probably work, your then stuck with a wrong sized valve area, so I am not sure how that would effect things. We have already asked our machine shop to get us that information. If we end up finding that we can get away with a MR16 head using the MR18 block, then we could easily make an MR20DDT hybrid engine.
 
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Over all, the MR18 bottom end is just as strong as the MR16, until you make big power, then the wrist pin becomes an issue. This is easily fixed with just using an aftermarket piston and rod with a bigger pin, obviously. But, the only reason i don't think its worth even going that far in is because of the cylinder head. You would need to do a custom cam grind for sure to make it worth while, then have to deal with the lack of duel cam phasing to bring on boost faster and make more low end with the turbo. We did check to see if we could use a MR16 head, and while it will bolt up and probably work, your then stuck with a wrong sized valve area, so I am not sure how that would effect things. We have already asked our machine shop to get us that information. If we end up finding that we can get away with a MR16 head using the MR18 block, then we could easily make an MR20DDT hybrid engine.
Typically, if you are bumping up the bore size while using the same head (1.6L), it will only help. It will make it flow better #s because there is more room in the combustion chamber to let the air flow out the valves. If you look at head flow charts, heads always flow better with a bigger bore and/or using a bigger flow tube on the exhaust side. Being a DI engine, I would prefer to see a custom piston made so that you can get the valve reliefs in the correct spot and the correct shape/location for where the injector squirts.
 

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The issue is the bore is much much larger than the compression area in the head. The “squared” off edge of the compression chamber would be susceptible to scoring or melting in high power applications. Again. I am going to have the professionals tell me the viability. As for a custom piston for di, the pistons we already have made can be very easily changed to fit these. But. If your doing this sort of budget big block deal, the 1.8 pistons would be fine. The 2.0 is DO so those pistons may be a drop in di swap for the 1.8. The atomization from the di would not be as efficient, but it would still be just as efficient as the atomization of port injection. I would still much prefer a stroked 1.6 over a bored out 1.8 for the torque benefits of stroking. Which is why we designed the stroker kit the way we did. But, since no one is opening these engines up to see if we can play the ej or b/k series games, we may as well. Really we want to see if we can take a 2.0 engine and make it work with the 1.6 head. Then you get all of the benefits of the di system, the bore, and the stroke, and you get the head flow benefits of the 1.6, and the cam controls of the 1.6. We are actively looking for a cheap 2.0 to take apart right now.
 
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