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Vortec 07-06-2012 04:30 PM

'93 Chevy 350CI spark plug depth
Hi ~
I recently purchased new Autolite APP 608 double-platinum plugs for my '93 350CI Chevy C1500 (Gen 1) engine. When I got them home, I noticed that they were about 1/4" deeper (from tapered seat to end of electrode) than the ones I pulled out (AC DELCO R43T). Also upgraded to MSD 48K volt coil & big wires (was getting some RFI on radio) so I could set 0.45 gap.

My question is... do I have that much clearance (extra 1/4") between TDC & plug for this to be safe? I'm kindof afraid to start the engine since I don't want the pistons to be hitting the plug, of course.

Has anyone run these plugs... and is there enough clearance??
Why would they sell these plugs for a '93 350 if there wasn't enough clearance?

Any help/opinion would be greatly appreciated.


lmsport 07-06-2012 04:46 PM

Autolite website says the double platinum plug is a APP 25.
Get the right plugs.

Vortec 07-06-2012 04:58 PM

Summitracing says these are (among) the right plugs... doublechecked fitment, etc.

Weird... how could they be so wrong (bought from them for years)??

lmsport 07-06-2012 05:10 PM

The plug for a later model GenI Vortec engine is an APP 605. It has the .705 reach whereas the App 25 is a .465 reach plug.
Do you have Vortec heads(8 intake manifold bolts, not 12)?

Vortec 07-07-2012 04:09 AM

Ahhh... that explains it!
No... not Vortec heads.


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