I've heard huge returns, up to 75 with a stage 3 heads and cams kit, but that they're very unstreetable that way
have you read any of the testimonials or emailed anyone from supersix motorsports? they're kind of the go to guys for 4.0 internals
super six heads and cams are said to be around a 90 hp gain, but yeah after installation your looking around 3 g minumum for the stage 3+. I know that rygan from mustang collective had his heads and cams done by powerhouse, so any tech questions i would try asking him, he has quite a bit of experience with such mods.
Tom morano Racing also specializes in all 4.0 mustang engines, he has a whole bunch of custom set ups Tom Morana Racing Engines
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