Oh ya, when I bolt my exhaust on, engine temps go up 20° , plugs foul, stumbles ect.. I know tuned for open exhaust, I have the 3" flow master system under my B-body, hooker comp's.. 1-7/8" into 3"... Had super comps on it (got run off return road & crushed passenger side tubes flat) they were 2" primary into 3.5" - & could tell difference in power just test driving down road, back pressure & roots blower = canned napalm in my opinion