diff --git a/GameData/RP-1/Tree/ECM-Engines.cfg b/GameData/RP-1/Tree/ECM-Engines.cfg
index a67cce85f13..42a4e1ce2ea 100644
--- a/GameData/RP-1/Tree/ECM-Engines.cfg
+++ b/GameData/RP-1/Tree/ECM-Engines.cfg
@@ -637,6 +637,7 @@
     RL10C-1-1 = 45000,RL10C-1
     RL10C-2-1 = 45000,RL10B-2
     RL10C-3 = 50000,RL10B-2
+    RL10C-X = 25000,RL10C-3,RL10C-1-1
     RL200-200k = 146000,RL10A-3-1
     RL200-225k = 20000,RL200-200k
     RL200-230k = 5000,RL200-225k
diff --git a/GameData/RP-1/Tree/TREE-Engines.cfg b/GameData/RP-1/Tree/TREE-Engines.cfg
index e887db6c772..ecd5df42147 100644
--- a/GameData/RP-1/Tree/TREE-Engines.cfg
+++ b/GameData/RP-1/Tree/TREE-Engines.cfg
@@ -4189,6 +4189,13 @@
                 *@PARTUPGRADE[RFUpgrade_RL10C-3]/deleteme -= 1
             }
 
+            @CONFIG[RL10C-X]
+            {
+                %techRequired = hydrolox2019
+                %cost = 487
+                *@PARTUPGRADE[RFUpgrade_RL10C-X]/deleteme -= 1
+            }
+
             @CONFIG[RL200-200k]
             {
                 %techRequired = improvedHydrolox
@@ -19668,6 +19675,46 @@ PART
 {
 }
 
+PARTUPGRADE
+{
+        name = RFUpgrade_RL10C-X
+        partIcon = RO-H1-RS27 // FIXME Once we get dedicated model
+        techRequired = hydrolox2019
+        entryCost = 0
+        cost = 0      
+        title = RL10 Engine Upgrade: RL10C-X Config
+        basicInfo = Engine Performance Upgrade
+        manufacturer = Engine Upgrade
+        deleteme = 1
+        description = The RL10 Engine now supports the RL10C-X configuration for increased performance. Unlock it in the VAB/SPH through the engine configs interface.\n\n
+}
+
+PART
+{
+    name = RFUpgrade_engineConfigSource_RL10C-X
+    engineType = RL10
+}
+
+@PART[RFUpgrade_engineConfigSource_RL10C-X]:AFTER[RealismOverhaulEngines]
+{
+    %MODULE[Module*EngineConfigs] {
+        @name = ModuleEngineConfigs
+        %CONFIG[RL10C-X] {
+            &specLevel = operational
+        }
+    }
+}
+
+@PARTUPGRADE[RFUpgrade_RL10C-X]:AFTER[RealismOverhaulEngines]
+{
+    %description = #$description$\nAvailable at specLevel $@PART[RFUpgrade_engineConfigSource_RL10C-X]/MODULE[ModuleEngineConfigs]/CONFIG[RL10C-X]/specLevel$
+    // TODO: could add any number of other useful fields from the CONFIG here. cost? description?
+}
+
+!PART[RFUpgrade_engineConfigSource_RL10C-X]:AFTER[RealismOverhaulEngines]
+{
+}
+
 PARTUPGRADE
 {
         name = RFUpgrade_RL200-225k
diff --git a/Source/Tech Tree/Parts Browser/data/Engine_Config.json b/Source/Tech Tree/Parts Browser/data/Engine_Config.json
index 2ac72a9ba7c..03d660958d2 100644
--- a/Source/Tech Tree/Parts Browser/data/Engine_Config.json	
+++ b/Source/Tech Tree/Parts Browser/data/Engine_Config.json	
@@ -13849,6 +13849,27 @@
         "identical_part_name": "",
         "module_tags": []
     },
+    {
+        "name": "RL10C-X",
+        "title": "RL10C-X",
+        "description": "",
+        "mod": "Engine_Config",
+        "cost": 487,
+        "entry_cost": "0",
+        "category": "HYDROLOX",
+        "info": "",
+        "year": "2024",
+        "technology": "hydrolox2019",
+        "ro": true,
+        "orphan": false,
+        "rp0_conf": true,
+        "spacecraft": "",
+        "engine_config": "RL10",
+        "upgrade": true,
+        "entry_cost_mods": "25000,RL10C-3,RL10C-1-1",
+        "identical_part_name": "",
+        "module_tags": []
+    },
     {
         "name": "RL200-200k",
         "title": "RL200-200k",