packaging is possible. but dropping stroke 2mm and shorter rods only gives 7mm. seems much easier to contour hood 7mm higher. I will keep looking for a good answer.

 

If any of you read magazines like Car, R&T, etc., you'll find that manufacturers often refer to external dimensional changes in terms of mm. Packaging is more important than ever due to increasingly stringent CAFE standards, and having to raise the hood by several mm wouldn't be as trivial as it might seem.

It costs a great deal of money to make the changes Mitsubishi made. However, the internal changes to bore, stroke, and RS ratio are insignificant to engine output and durability given its specific output and operating range in the most clinical of settings. If the 4B11 head had to be designed taller (?), that would definitely be a big reason for engineers to look at reducing the deck height. And if this engine isn't intended to configured in larger displacements (longer strokes), the extra deck height isn't needed.

Anyway, you have my $0.02.

 

While I would agree that this is probably the case often, I doubt it is the reason behind a performance oriented car like the Evo. Considering the block is essentially the same as in the 2.0 Turbo Genesis, I think like I have previously stated the the block dimensions for the block in its 2.0 form where determined long before any heads where designed for it.

 

That is a significant observation. If the engine is used across different platforms, then packaging is of even greater importance.

 

Packaging is important to OEMs and since this engine has its roots as a "world" design for literally dozens of applications amongst (initially) three different manufacturers - what the skunkworks team of Evo designers wanted would be secondary at best.

However, I think hood designs because of the whole pedestrian safety thing made cars chunkier with taller hoods, so I'm not sure how that would play into it.

I always thought square engines revved better.

 

You also have to take into consideration the lateral dimensions. Fitting this engine with the gear box between the "frame rails" if you will. By having a larger bore size you have to make the engine bay wider or siamese the cylinders (like Honda)

Same reason why chrysler chose to keep the bore size the same from the 2.0L to the 2.4L but increase the stroke by a grip. The width of the engine and transmission was already as wide as they could go given the chassis they were dumping the engine into. The SRT-4 had a widened chassis up front to fit the improved T-850 gear box. Packaging dictates bore in a transverse setup. There is certainly a maximum bore that can be achieved given their limitations.

Kinematics still proves that a longer rod is advantageous in terms of forces applied to the rod bearings and con rod fasteners... especially if you're going to be revving the crap out it.

 

One of the most vivid examples of minimizing packaging lies in BMW engines. BMW 6-cyl engines have annoyingly tight bore spacing, in some cases necessitating the blocks to be sleeved for higher hp forced induction applications. This was done purely for packaging considerations to minimize the length of the block. Already, BMW's short deck height is such that their larger displacement 6-cyls have short RS ratios (e.g. 1.5-1.6).

With 4-cyl engines, because bore spacing becomes important where transverse mounting creates spatial limitations, the most practical means of leaving room for increasing displacement is increasing the stroke, which requires sufficient deck height. If there are no plans to increase displacement, there is no reason to have a deck height taller than that required to accommodate the desired RS ratio. With a smaller displacement engines in heavier vehicles, shorter RS ratios improve VE in lower rpm ranges, which makes the engine feel more torquey, which is something that appeals to prospective buyers. But always in this day and age, OEMs minimize engine packaging so that it works across the intended platforms and will be suitable for future generations of body/chassis revisions.

 

Tighter packaging would also mean lower center of gravity.

 

I'm not saying that packaging consideration isn't taken into consideration on a lot of cars. What I am saying is I doubt that is the reason for the square bore in the Evo...Highly doubt. Unfortunatly unless we get a Mitsu engineer that was involved in the building of the Evo X everything said here is simply conjecture.

 

Believe what you will. The writing is on the wall. I know for a fact that this is the reasoning used at GM, Chysler, and Ford. Directly from the horse's mouth. I haven't met an engineer who worked on the Evo... or a mitsubishi engineer for that matter yet. Maybe I'll run into one in Death Valley, Silverthorn, Denver, or Baker grade... but as of yet... nope.

I bet they wanted to keep it a 2.0L... lowered the deck height...adjusted stroke and rod length. And then changed the bore size to meet their 2.0L high level requirement.

 

Remember, this is a world engine. The blocks are used in Chryslers and Hyundais. So they probably decided on a block that would be suitable for many different applications. The whole engine wasn't designed specifically for a Lancer Evolution / Lancer Ralliart. Every engine in this family has an 86mm bore besides the 4b12 which has an 88mm bore.

 

My point exactly, while overall size of the block I'm sure was accounted for I am saying that it wasn't sized with the Evo's cylinder head specifically in mind. As it wasn't probably even desgined at the time.