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Note: This authoritative compendium is not yet finished, or even edited to reduce verbosity. This will be fixed at roughly the debut of community warefare.
Ever since going into production in 2579, the Extra Light engine has drastically changed warfare in the Inner Sphere, allowing half of a BattleMech’s engine mass to be put towards better use with the cost being 4 times the price in C-bills and twice the bulk in critical slots.
Not all XL engines are created equal, and with the price of XL engines as high as some assault mechs, one must educate themselves on these venerable engines to avoid spending money unwisely.
XL Engine Basics
This guide aims to provide a comprehensive view on XL Engines by providing references on the XL engines most needed in building mechs.
In general mechbuilding, the XL engines you should be relying upon the most are the XL200, XL225, XL255, XL280, XL300, XL 325, XL350, XL375 and XL400. These XL engines are the most useful because they are the lowest weight engines that provide a certain amount of heatsinks.
The Most Versatile XL Engine
Out of those XL engines, the absolute most important is the XL255, this should be the starting engine to consider on any non-light mech that you wish to put an XL engine in. The reasons for this mainly center around this Engine providing the most value for heat-sinks verses weight. You may note that the XL250 is of a lower rating and it does provide all 10 engine heat sinks, but oddly it weighs the exact same as an XL 255. There is absolutely no reason to ever buy an XL250 as the 255 is always a little bit faster for no cost in weight. To take full advantage of an XL engine, one should have double heatsinks equipped. This allows an XL255 to have the equivalent of 20 single heat sinks inside of it. Any double heat sinks located outside of the engine are only valued as 1.4 heat sinks, even if they are “extra” heat sinks that can fit inside the engine and not use critical slots.
Two More Important XL Engines
The next most important XL engines are the XL280 and the XL300. These engines allow a mech to go faster than an XL255 and still fit most chassis. The XL300 in particular is well balanced in terms of weight verses engine power and among the largest engine that can fit in many weight classes. After the XL255, the XL300 is probably the next most versatile XL engine. These engines also poise a special relationship because they are each 1.5 tons apart in weight (not including any extra heat sinks) Above the XL300, the weight of engines increases exponentially.
XL Engines XL200 to XL255
To quickly contrast engines in ratings below XL255, the XL 225 and XL200, each with 9 and 8 heatsinks respectively, follow a pattern of reducing weight by 2.5 tons. This is actually only a 1.5 ton reduction due to all mechs requiring 10 heat sinks to launch. These engines are commonly encountered in medium mechs with heavy loadouts. The odd engine sizes between XL200 and XL255 that are most encountered are the XL210 and XL235. This is mostly because the XL235 is one ton lighter than the XL255, including the ton in the mandatory extraenginous heatsink. The X210 is because it is one ton more than an XL200, but mostly because many people have an XL210 sitting around from the days when it was the max engine size of the commando or from the stock engine from buying a raven 3L. Don’t run an engine lower than an XL200 unless you’re in a locust or you’re running a very bizarre build. That being said, I do offer advice on the bizzare in the section on engines below XL200.
XL Engines XL300 to XL400
For XL engines above an XL300, the main consideration often turns to how many heatsinks can be stuffed in the engine, at least in heavier builds. This causes the engines that are multiples of 25 to predominate all the way up to the XL400 that can fit a whopping 6 extra heatsinks. The jump from an XL300 to an XL325, not factoring extra heat sinks is 3.5 tons, with a further 3 tons to fit an XL350. This unusual jump between the 300 and 325 often means that when people choose to build mechs with engines above an XL300, they tend to jump into the 340-360 range when possible. The 4.5 ton jump up to the 375 is usually the last sensible jump in engine weight in all but the heaviest of mechs, as one needs a full 7 tons to go from a 375 to a 400--which is rarely worth the few extra kilometers in speed--with 3.5 tons from just the jump from 390 to 400.
Special Overview of XL Engines in Light Mechs
Light mechs and the Cicada require special rules regarding XL engines. In general, one always runs the highest rated XL engine available to that chassis, as the light’s primary advantage is speed.
Locust: the XL engines of choice in this mech are the XL170 and the XL190. The XL170 with speed tweak lets you go 151.5kph and the XL190 at 169.3kph.
Commando:The commando is of two varieties in regards to maxmimum XL engine, with the 2D varient only able to fit an XL210 while all others able to fit an XL 240. Generally commando 2Ds will run an XL200 due to the XL210 not allowing more than one ton of streak SRM2 ammo when running 3xSSRM2, ECM, full armor and a medium laser. With speed tweak, maxspeeds with the XL200, XL210, XL225 and XL240 are 142.6, 149.7, 160.4, and 171.1kph respectively. Similar to running an XL200 in the 2D, an XL 225 is often used with the other variants as it allows one more ton, often used for more ammo or another heat sink and still maintaining a respectable speed of 160kph, enough to outrun mechs over 30 tons.
Spider: Similar to the Commando, the 5D variant has ECM and can only run an XL255 instead of an XL285. This limits its top speed at 151.5kph instead of the 169.3kph of the XL285. Many spider builds run the XL255 instead of an XL285 as this speed rating is necessary to run more than one ton of ammo with a large laser in the center torso on a SDR5K. Also, due to the spider’s height mobility, the extra boost in speed above 150kph is less needed than in the non-jumping commando and locust. A late trend is to run an ECM-carrying spider 5D with dual ppcs or ER lasers sacrificing speed or armor , often carrying an engine a few ratings lower than an XL255.
Jenner: Virtually everyone runs an XL300 at 152.7kph. Dropping down to an XL270 to go 137.5kph is sometimes used in sniping loadouts.
Raven: The raven has two varieties of maximum engine size, with an XL295 for the raven 3L and an XL275 for the 4X and 2X. The most popular raven 3L build remains the triple medium laser with two streaks running an XL295 at 150.2kph. The sniper build with 2ER LL is usually found in an XL295 as well due to the 3L’s ability to carry both ERLL as well as ECM and almost full armor with that engine size. The 2X and 4X max out at 140.0kph with an XL275, but there is a variety in building styles from a RVN-4X with an AC/20 to snipe builds on the 2X. Even so, heavy builds stick to common engines such as the XL210 found in the stock RVN-3L as these variants are often sold after the 3L is mastered.
Cicada: Every variant of the Cicada can mount up to an XL340 at 151.5kph. It is not uncommon to see a slow cicada, but these builds are usually mounting large ballistics and are oftentimes ineffective. The XL330 remains popular on the CDA-X5 due to that engine coming with the stock build and little needed to optimize that mech’s loudout besides upgrading the dual SRM2s to Streak SRM2s.
Largest XL Engine per variant
XL400 - AWS-PB VTR-DS BLR-1D-1G-1S AS7-BH
XL390 - CN9-A TBT-3C VTR-9B-9K-9S
XL385 - AWS-9M
XL375 - WVR-6K
XL360 - GRF-1N-1S-3M KTO-18-19-20 SHD-2D2-2H-5M WVR-6R-7K DRG-1C-1N-5N-FANG-FLAME QKD-4G-4H-5K ON1-K-M-V-VA-P AS7-D-DDC-K-RS
XL355 - CPLT-J
XL340 - CDA-2A-2B-3C-3M-X5 JM6-FB CTF-1X-2X-3D-IM
XL330 - HGN-HM
XL325 - TBT-5J-5N-7K-7M HGN-732-733-733C-733P
XL315 - CPLT-A1-C1-C4-K2 JM6-A-DD-S TDR-5S-5SS-9SE
XL310 - STK-3F-3H-4N-5M-5S-M
XL300 - JR7-D-F-K-O CN9-YLW AWS-8Q-8R-8T-8V
XL295 - RVN-3L
XL290 - KTO-GB
XL285 - SDR-5K-5V
XL275 - RVN-2x-4X CN9-A-AL HBK-4G-4H-4J-4P-4SP-GI
XL255 - SDR-5D CTX-4X
XL240 - COM-1B-1D-3A-TDK
XL235 - BJ-1-1DC-3
XL210 - COM-2D
XL190 - LCT-1V-3M-3S
XL Engines found inside stock mechs:
XL210: RVN-3L
XL250: TBT-7M **
XL255: STK-5S
XL260: JM6-DD **
XL275: GRF-3M SHD-5M WVR-7K**
XL280: CTF-3D
XL300: CN9-D TBT-3C ON1-M AS7-K
XL320: CDA-3M AWS9-M
Champions/Hero/Special
XL200: HBK-GI
XL220: KTO-GB
XL235: BJ1©
XL255: SDR-5K©
XL275: HGN-HM **
XL280: JM6-FB CTF-IM
XL300: JR7-D(S)-F© DRG-5N©
XL330: CDA-X5 VTR-DS
XL340: CDA-2A© AWS-PB
XL400: AS7-BH
** = Non-optimal XL engines because there is a rating that is faster for the same weight
XL Engines to avoid purchasing because there is a rating that is faster for the same weight:
XL205
XL215
XL230
XL240
XL250
XL260
XL275
XL290
See engines under XL200 for engines under XL200.
XL engines below 200.
Unless you’re in a locust, these are of very little use: for the locust, XL 170 and XL190 are the engines of choice, with the XL 190 being of the maximum rating allowed in the chassis and the XL170 being the highest rated of the 4 ton XL engines. The XL170 in a locust usually allows for heavier builds, like running large lasers with other weapons. The XL engines of note in this range are the XL125, XL145, XL170, XL180 and XL195 because these are the engines that are the highest rated for their weight. If you’re running any other engine (save the 190 due to the locust’s limitations) you could be going faster for no cost to tonnage! The only reason to run these engines lower than an XL200 is if you have extremely specialized builds, like for some awful reason you want full armor on a cataphract-4X with dual AC/2s and dual AC/5s and want to write home to Mom about the 14 tons of ammo you can pack now.
The only XL engines under 200 worth considering:
| Engine Rating | Weight | Internal Heatsinks | Needed Heatsinks | Weight with 10 Heatinks |
| XL100 | .5 | 4 | 6 | 6.5 |
| XL120 | 1 | 4 | 6 | 7 |
| XL125 | 2 | 5 | 5 | 7 |
| XL145 | 2.5 | 5 | 5 | 7.5 |
| XL170 | 4 | 6 | 4 | 8 |
| XL180 | 5.5 | 7 | 3 | 8.5 |
| XL195 | 6 | 7 | 3 | 9 |
I have yet to encounter a good reason to ever run an XL100. I have never seen anything that actually needed that extra half ton in even the trolliest of builds. Of note, from the XL100, you can gain 6 crit slots and the ability to lose side torsos by going with a standard 100, or an extra internal heatsink and 25 points of engine rating from going with the XL125. Note well, you should see that the XL120 and the XL125 weigh the exact same after heatinks. If you’re going to use something this lowly rated, XL125 is the way to go. Of all of these super low rated engines, the Xl170 is probably the best in terms of weight vs engine capacity, as it’s rated 70 points higher than a STD100 for only a 1 ton weight increase factoring in required heatsinks.
Edited by One of Little Harmony, 02 February 2014 - 06:07 PM.
