Re: 1990 Spark plugs
As is often the case, Marc H. is right about the proper heat range for the LT5 plug.
Just before the cars went on sale in 1990, GM changed the spark plug recomendation from the FR-1LS to the FR-2LS. The reason for this was concern on the part of the dealer network about "pre-delivery fouling". What this means is the AC "1" heat range really is the proper type of plug to run as long as the engine doesn't see a lot of duty where it is started, run at idle and low speed for a very short period then shut off.
Needless to say, the AC 2 heat range is too hot a plug for most LT5s. The AC 1 heat range is equivalent to the NGK 6 and the Denso 20 heat ranges and that should be the hotest plug anyone should consider unless the most you ever run your LT5 is a few minutes.
I've run the Denso IT-22 (crosses to the NGK TR7IX) in my LT5 for a number of years. It's a great street performance spark plug. The IT-22 uses a very fine, iridum center electrode and a u-groove ground electrode.
As for running taper seat plugs in heads which have previously used only flat set plugs, to convert to the taper seat, the first time you install taper seat plugs you have to torque them to 22-ft/lbs to form the taper seat. Then loosen the plug and re-torque it to 15 lbs/ft
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Hib Halverson
Technical Writer
former owner 95 VIN 0140
current owner 19 VIN 1878
Last edited by Hib Halverson; 05-03-2015 at 10:21 PM.
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