95 gt vert sparkplug questions

Nubbyless

Member
Apr 30, 2018
11
1
13
45
Zephryhills fl 33540
So I purchased a used 95 mustang GT convertible I got some factory copper sp-450 plugs to put in it when I pulled the existing plugs they were from bolt shoulder to the tip a half inch longer then the ones I bought turns out the plugs in it were sp-493 platinums but on research I find this to only be used in cobras not the gt so I started trying to Id the engine best I can tell it is not a cobra engine and I can not Id the 3 bars of a GT40 head which I think also uses these plugs so what's the story are they just the wrong plugs? they been it for a while so I guess they weren't hitting anything it was throwing random lean codes and breaking up around 5500 rpm so I decided to put in the plugs I bought figured there shorter shouldn't really hurt anything after a hard test drive it seems stronger pulls clean all the way to redline and no check engine light yet I'm just still kind of nervous if I have the right plugs in this thing it has the factory crimped headers on it and I can access plugs fairly easy on it if that helps at all
 
  • Sponsors(?)


Nubbyless

Member
Apr 30, 2018
11
1
13
45
Zephryhills fl 33540
Well after more reading I found you can identify GT40 heads by stamping near the corners near plug number 1 and near corner of the valve cover there is nothing there so I can only assume the plugs they had in it were incorrect I just hope they didn't do any valve or piston damage it still seems strong so maybe I'm lucky
 

Christian Cornwell

Active Member
Aug 31, 2016
86
20
28
Upstate NY
Sounds like someone put the wrong plugs in. I've heard of guys trying to go one step colder or hotter with their plugs and not checking to make sure that they're the same length as the ones they took out and having the Piston hit them.