Install:

1:Copy the "update" folder to 
"Grand Theft Auto V\mods\"

2:If you haven't done it yet, copy the file 
"Grand Theft Auto V\update\update.rpf"
to the mods folder

3:Open the file 
"Grand Theft Auto V\update\update.rpf\common\data\dlclist.xml" 
then use notepad to edit it and add the following line

		<item>dlcpacks:\rx7tunable\</item>

Save it and use OpenIV to replace the original one 


4:Use OpenIV to extract 
"Grand Theft Auto V\update\update.rpf\common\data\extratitleupdatedata.meta" 
then use notepad open it,add new line 

		<Item type="SExtraTitleUpdateMount">
			<deviceName>dlc_rx7tunable:/</deviceName>
			<path>update:/dlc_patch/rx7tunable/</path>
		</Item>

Save it and use OpenIV to replace the original one 

OPTIONAL(If you have a lot of car mods)
5:Use a modded "gameconfig.xml" file


You can use the Simple Native Trainer to manually spawn it using the name "rx7tunable"