Recommendation on spark plugs

[Michael L.]

Guys,

I'm looking to get a set of spark plugs for the 69 350/350 that I just had rebuilt. I upgraded the cam to the comp cams 280HR (hydraulic roller) and am planning on having the car judged. I've looked at the vendors and they seem to offer a couple of different varieties of plugs, some of which they refer to as "hot" plug or "cold" plug. Anyone have any recommendations? Thanks.

Mike

[Joe C.]

Re: Recommendation on spark plugs

AC Delco "45" plugs were the all-around plugs used, so I'd put these on the engine during judging in NOS form. "44" plugs were recommended for off road/racing use and "46" plugs we're recommended for stop and go city driving.

If you drive your car between judging events, then you have numerous choices.

[Jeffrey S.]

Re: Recommendation on spark plugs

The plug that was installed at Flint in 1969 350 Corvette engines was an R44. The 1969 AC Delco Spark Plug replacement catalog lists R44 as the recommended service replacement. However, a "5" heat range is a great plug to use for light, around town driving so an R45 is a good choice. A hotter plug will generally stay cleaner in light driving and is fine unless there is "pinging" and then a colder plug is necessary. I have used both in my 300 hp '69 (now a 383 with head work and cam) and both do fine. hope this helps.
Jeff

[David W.]

Re: Recommendation on spark plugs

So basic question, but which is the colder plug if I have pinging, the 44 or 45?

[David W.]

Re: Recommendation on spark plugs

I am assuming higher number is higher heat range. Correct?
Also, what is difference between the 44 and 45 and their XLS variants?

[Joe L.]

Re: Recommendation on spark plugs

I am assuming higher number is higher heat range. Correct?
Also, what is difference between the 44 and 45 and their XLS variants?

David------


Yes, for AC plugs, a higher number= higher heat range.

R44XLS and R45XLS spark plugs, as far as Chevrolet goes, are long reach, extended tip spark plugs used for in-line 6 cylinder applications.

R44S and R45S spark plugs are extended tip versions of the normal R44 and R45. I recommend the extended tip versions for most small block applications.

[David W.]

Re: Recommendation on spark plugs

Thanks Joe, I will pull my plugs to see what I have and think about trying R44S if I am running R45S.

[Richard K.]

Re: Recommendation on spark plugs

The 1969 Owner's Manual specification for spark plugs for the L46, 350hp are AC R-44. For "city driving only", the recommendation in the chart is AC R-45 (the "hotter" plug).

In prior threads, the Champion RJ12YC is highly recommended for the 1969 350 c.i. engine. However, when I pulled the original NOS AC R-44's to replace them with the recommended Champion's, I noticed that the reach was much longer with the Champions. The AC's measured approximately 52/100 inch from the seat to the tip. The Champion's measured approximately 77/100 inch from the seat to the tip, approximately 25/100 inch more reach into the cylinder.

Can anyone confirm that the Champion RJ12YC will not contact the piston in my 1969, 11:1 compression L46 (stock spec), 350hp when the engine is turned over.

For what it's worth, I have a Champion 1970 Supplement, and it shows that the RJ-12Y can be used in both the 300 & 350 hp engines, but the 370 hp (LT1) calls for an RJ-10Y, the same plug that is called for in my 1969 Champion booklet for the L46, 350hp. Were the same configuration pistons used in the '69 & '70 350 c.i., 350 hp engines, i.e. flat top vs a domed piston?

Again, just want to confirm that the RJ12YC won't interfere with the '69, 11:1 comp piston.

Thanks Much

[Joe L.]

Re: Recommendation on spark plugs

The 1969 Owner's Manual specification for spark plugs for the L46, 350hp are AC R-44. For "city driving only", the recommendation in the chart is AC R-45 (the "hotter" plug).

In prior threads, the Champion RJ12YC is highly recommended for the 1969 350 c.i. engine. However, when I pulled the original NOS AC R-44's to replace them with the recommended Champion's, I noticed that the reach was much longer with the Champions. The AC's measured approximately 52/100 inch from the seat to the tip. The Champion's measured approximately 77/100 inch from the seat to the tip, approximately 25/100 inch more reach into the cylinder.

Can anyone confirm that the Champion RJ12YC will not contact the piston in my 1969, 11:1 compression L46 (stock spec), 350hp when the engine is turned over.

For what it's worth, I have a Champion 1970 Supplement, and it shows that the RJ-12Y can be used in both the 300 & 350 hp engines, but the 370 hp (LT1) calls for an RJ-10Y, the same plug that is called for in my 1969 Champion booklet for the L46, 350hp. Were the same configuration pistons used in the '69 & '70 350 c.i., 350 hp engines, i.e. flat top vs a domed piston?

Again, just want to confirm that the RJ12YC won't interfere with the '69, 11:1 comp piston.

Thanks Much

Rich------


You are correct. The original GM spec for the 1969 L-46 was the AC R44. However, the R-44 is not equivalent to the Champion RJ-12YC. The RJ-12YC is equivalent to the AC R44S. That's why you found an overall length difference between the R44 and RJ-12YC.

The pistons used for 1969 L-46, 1970 L-46, and 1970 LT-1 were the same. These were a domed piston versus the flat tap with 4 reliefs used for 300 HP.

I used the Champion RJ-12YC for years in my original owner 1969 300 HP. They worked great and better than any other plug I tried, including and especially AC spark plugs. I highly recommend the RJ-12YC. I believe the RJ-12YC (or the RJ-10YC which is simply a colder plug) will work fine for an L-46 or LT-1 even though they use domed pistons. Apparently, Champion agrees with me. Further evidence could come from someone that's used the RJ-12YC OR an AC-R-44S in an L-46 or 1970 LT-1.

By the way, Champion has revised its nomenclature system for spark plugs. The RJ-12YC is now known simply as 14.

[Michael L.]

Re: Recommendation on spark plugs

Joe you think these 14 champions are good for my L-46 that I put the hydraulic roller comp cams 280HR in? Does changing the cam change things at all? I read in the TIMJG that plugs are not judged so I'm going to go with whatever works best.

[Joe L.]

Re: Recommendation on spark plugs

Joe you think these 14 champions are good for my L-46 that I put the hydraulic roller comp cams 280HR in? Does changing the cam change things at all? I read in the TIMJG that plugs are not judged so I'm going to go with whatever works best.

Mike-----


I don't think the cam makes much difference in this regard. It does not affect spark plug-to-piston clearance.

The best info on such clearance would come from someone that's used the RJ-12YC or R44S plugs in an L-46 or LT-1. However, I really think they'll work fine.

[Lawrence M.]

Re: Recommendation on spark plugs

Mike and Joe,
I am running R45S plugs in my 1969 L46. No problem with piston clearance. I believe these plugs were recommended by John Hinckley for use in the L79 L46. My engine has .030 TRW L-2304 pistons which I believe are the service replacements for the LT1 piston. It still has the original pink rods and forged crank.

[Michael L.]

Re: Recommendation on spark plugs

Thanks, Lawrence. Good to know.