Spark Plug Reach - 350 Vortec SBC and others

[eXodus]

The former owner of my P30 put in a  2002 ish  Vortec 5.7L Engine.   (presumable out of a Chevy Express Van)

It's running somewhat fine, but I'm chasing a misfire for few months.  I pulled the plugs before and they looked fine.
Now I ordered plugs to the engine code, and guess what came:



The new Plugs have more threads then the ones which are in the engine. So which are the correct ones?



It's hard to see, but I think those Iron Vortec heads have more threads then the old Small Block heads. 
Any suggestions how to measure the correct depth of the spark plug thread?  I'm a Electronic/Code Monkey and could need a idea how to measure the reach in the cylinder head.



What other issues could come from running the wrong plugs? 
I'm going to get a spark plug chaser and tap the holes in the cylinder head to get the deposits out of the threads.

Since this is a drop in engine conversion with no documentation, I don't know what plug should go in there.

[Elandan2]

That much difference would certainly affect the compression and with the spark plug so far from the combustion chamber would likely cause misfires. Maybe a 90° awl would be small enough to put down the spark plug hole and get an idea of the depth.

[eXodus]

What is a "90° awl" ?

Sorry I don't know that tool.

[Elandan2]

It's an awl with the end bent 90°. Kinda looks like a tool your dentist uses for torturing your teeth.

[eXodus]

thanks for the inspiration.



Built myself a depth measure device out of a twisty tie. With this high tech engineering marvel I've checked the wall thickness of the cylinder-head where the plug thread comes out.

Conclusion, the former owner used to short of plugs.
Put one long reach plug and started it up and it runs fine. For what it is - with those wrong plugs, it's surprisingly running well.  Only one cylinder is misfiring once in a while.

Next project- cleaning all spark plug holes with the tap, since at least 3 threads have carbon built-up from running the too short plugs...

[Oz]

Gotta love old time "necessity engineering."
That's one for the books, for sure!

[Eyez Open]

Here ya go, there are two plugs that run without failure in GM engines...20 yrs marine hot-rodding, they do not fail.

AC MR43T: Pre Vortec heads

AC MR43LTS: Vortec heads

M stands for marine, a alloy is used in there design

Nickel-chrome alloy sheathing to help prevent corrosion on center electrode

[Eyez Open]

The former owner of my P30 put in a  2002 ish  Vortec 5.7L Engine.   (presumable out of a Chevy Express Van)

It's running somewhat fine, but I'm chasing a misfire for few months.  I pulled the plugs before and they looked fine.
Now I ordered plugs to the engine code, and guess what came:



The new Plugs have more threads then the ones which are in the engine. So which are the correct ones?



It's hard to see, but I think those Iron Vortec heads have more threads then the old Small Block heads. 
Any suggestions how to measure the correct depth of the spark plug thread?  I'm a Electronic/Code Monkey and could need a idea how to measure the reach in the cylinder head.



What other issues could come from running the wrong plugs? 
I'm going to get a spark plug chaser and tap the holes in the cylinder head to get the deposits out of the threads.

Since this is a drop in engine conversion with no documentation, I don't know what plug should go in there.

It is all about the casting number on the heads themselves.

https://www.crankshaftcoalition.com/wiki/SBC_cylinder_head_identification

[eXodus]

It is all about the casting number on the heads themselves.

https://www.crankshaftcoalition.com/wiki/SBC_cylinder_head_identification

Thanks,  going to find the casting numbers and see what heads I got on that engine.  It's definitely some kind of vortec intake.

It has also huge exhaust manifolds on it.  I got also a Vortec 5.7 in my other truck and that manifold in this RV is about 1,5x the the diameter.  Just huge.  the intake is that of 8.1L Bigblock.   Very interesting what the PO cobbled together.

[eXodus]

I got the Spark Plugs changed to the Vortec ones. I measured the depth the Cylinder-head wall thickness and it's that the old spark plugs where the wrong ones.

And it runs great,  feels even a like it has tiny bit more power.  But that could be in my imagination.

My assumption is that when ever the engine swap happened they took a few parts of the old 350 (alternator, powersteering, starter)  and just bolted those to the new Vortec. Maybe during that time they also put in the old 350 sparkplugs. 

Alternative - they brought it to a shop to get it serviced.  They looked up parts according to VIN, and put in 350 plugs, instead of the correct ones for the current engine installed.

Going to have a longer trip in a few weeks and will see what it does to MPG.

[Oz]