All mechs have engines. there are 2 types of engines the standard (like the one in store purchased mechs) or XL engines (which are lighter, and much more expensive.)

all engines have heat sinks. the larger the number on the engine, the more power it produces. every 25 points for engine displacement increases the number of heatsinks by 1.

EX: a standard 150 will have 6 heat sinks. or a 300XL will have 12 heat sinks.

This being said if you upgrade your engine to an XL engine you need to be aware of a few things. A standard engine requires 6 slots and they all fit in the center torso. all XL engines require 12 slots, 6 in the center torso, and 3 in both left and right torso. this means that if the left or right torso take critical damage, you can have your mech knocked out of the fight for good.

XL engines are also very light as compared to their standard part. by adopting an XL engine, you may free up weight for more ammunition, or more weapons. you could always use the extra weight to upgrade the engine. this will make your mech quicker to move and quicker to respond. It's up to you

To expand on this point:

Right now the game is a bit broken. Only CT and Head shots will take a mech out. That and overheating causing an explosion. XL engines do give 3 crit slots to the right and left torso besides the center torso. Destruction of a Torso location (losing all Internal structure after your armor is gone on that location) will (is suppose to) kill your mech because it receives 3 engine hits.

This is the reason why Standard engines can technically be better, because they keep your R and L torso's clear for more weaps and equipment and makes your mech less vulnerable when its hurt bad.

Hence, XL's are more expensive because they are more vulnerable being bulky. They also cost a lot more when your mech is utterly destroyed. To clarify you can actually take damage in your R and L torso that is critical, it may not be the engine if you have other items equipped there such as heatsinks, ammo or even weapons.

If you wish to upgrade your speed the engine rating you need is the following formula. I use my Raven as an example.

Forumula : mech weight x desired walk speed = engine rating (Running speed is always 1.5 of walk)

Raven 2X has a speed of 5/8 or 50kmph walking, 80kmph running , tonnage is 35 tons
35t x 5 = 175. Means I need a 175 standard engine to obtain 50kmph walking speed

To upgrade the Raven to its XL version, (which has a standard speed of 6/9), I need a 210 XL engine
35t x 6 = 210. I want the XL because XL engines cut my engine tonnage in half, giving me more room for goodies.

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- rolly
(Former) SSI Co-Commander, Clan Admin
(Former) WoT Division Admin
Head of Office of Strategic Services [Retired]