Spark plug gap

[vilant]

I was told from the auto parts store clerk that NGK recommends .05" gap. But in Solutions it says .043" on a 91'. I have a '90. My question is: What gap size is correct .05" or .043"? TIA

[efnfast]

This was the answer I got from Mr. Haibeck

Hi Steve,

For high load operation I recommend a spark plug that is one AC heat range cooler than the OE plug. The best spark plug is the NGK TR7IX. Part number 3690.

It has a tapered seat. All LT5's are machined for both tapered and flat seat plugs. Carefully open the gap to .050"

Best of luck.

Marc

[vilant]

Thank you very much:cheers:.

[efnfast]

Thank you very much:cheers:.

Piece a cake. That's what I did, with no regrets.

[vilant]

He wasn't kidding about being careful. How're you suppose to bend the ground without breaking that tiny tip?:confused: I'll try needle nose.

[efnfast]

Don't break 'em, they're expensive. My gaping tool had an end to open the gap, but yes, be careful.

[efnfast]

I also read somewhere that not all the heads were tapped for both. The plan was to over torque by 25 pounds to kinda make a tappered seat.

Marc has seen plenty of heads and I would ASSUME he's right. I think I over torqued some, maybe not 25 pounds, backed them out and retorqued.

[scottfab]

As with many issues this has been covered as far back as 98 on the mail list. (and maybe earlier) Unfortunately the archives on the Club pages only go back to 2000.
This is the earliest found there:
http://maillist.corvettemuseum.com/cgi-bin/wa.exe?A2=ind0504&L=ZR1NET&P=R21105

[vilant]

Thanks, fellas. The new plugs had the same end as the old ones. I torqued them to 22 ft/lbs, per the FSM.

[scottfab]

At least you don't have to worry about the gap effecting the dwell or timing.
Ah the 60s ... =D>70s.
Some things really have improved.

[vilant]

I am not so sure it is not 22 Nm....which would be 16 ft-lbs Plug Torque (http://www.zr1.net/forum/showthread.php?p=125900#post125900)

A little antizieze on the plugs and a bit less torque ;)

Definitly used antiseize. Here's a pic from both manuals. The larger one says 22 ft/lbs, the supplement says 19 ft/lbs. Which one are you suppose to follow?:confused: The larger manual is under the 5.7 vin J engine too (ZR-1).
http://www.zr1.net/forum/picture.php?albumid=210&pictureid=1576

[Hib Halverson]

This was the answer I got from Mr. Haibeck

Hi Steve,

For high load operation I recommend a spark plug that is one AC heat range cooler than the OE plug. The best spark plug is the NGK TR7IX. Part number 3690.

It has a tapered seat. All LT5's are machined for both tapered and flat seat plugs. Carefully open the gap to .050"

Best of luck.

Marc

You have to be careful when you say that.

Actually, all LT5 heads were not "machined" for both types of seats. The heads were cast with spark plug mounting and threads designed for both, but on the 90-92 heads the taper seat is not there.

When you use taper seat plugs in early heads for the first time you purposely overtorque the plugs then back off a turn and retorque to the normal tightness. The "first-time-overtorque" forms the taper seat in the head.

Once you do that, then the head will accept either flat or taper seat plugs.

As for gaps, since my engine doesn't have a dual mass, in search of more stable idle and less gear rattle, I installed more powerful ignition coils, lower resistance MSD Super Conductor wires then opened my plug gaps up to .070-in.

As for plugs, I use a Denso IT-22 which, heat range wise is close to that NGK 7 which Marc likes. Use them in LS7s, too.