RSF Posted June 13, 2013 Share Posted June 13, 2013 I have a '72 MC with the original/rebuilt 402 that I purchased a few months ago and decided to change the spark plugs today. I bought the "correct" AC Delco plugs which are part # R44T. The plugs that came out of the car are NGK R GR5's which are significantly different. According to a little research I have done it seems that the GR5's are for a 396. Can anyone shed some light here??? Thx in advance!!! Quote Link to comment Share on other sites More sharing options...
RSF Posted June 13, 2013 Author Share Posted June 13, 2013 this MC was built in the second half of '71 and delivered in November '71. Is it possible that it actually has a 396? Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted June 13, 2013 Share Posted June 13, 2013 the car is 42 years old, have the heads been changed or are the they originals? 396 heads would use a gasket plug and 402 heads will use a tapered seat plug Quote Link to comment Share on other sites More sharing options...
gprimm Posted June 13, 2013 Share Posted June 13, 2013 The "396" in Chevelles were actually 402's after 1969 so unless the heads were changed (check the date on those) or the engine was changed, it doesn't make a difference. A 402 was just a bored out 396. Quote Link to comment Share on other sites More sharing options...
Mike 57 Posted June 13, 2013 Share Posted June 13, 2013 Like Sam said, early heads use a gasketed plug and they are 3/4 inch reach Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted June 16, 2013 Share Posted June 16, 2013 your best bet is to pop-off a valve cover and check the casting number to see what you actually have Quote Link to comment Share on other sites More sharing options...
RSF Posted June 19, 2013 Author Share Posted June 19, 2013 thanks for the feedback! the plugs that are in the car are definitely not the tapered seat style so I am going to pull a valve cover and see what I find. I was led to believe the entire engine was original but I bought it from the 3rd owner so who knows. Assuming I have heads from a 396 - are they better, worse or no difference than the 402 heads?? Quote Link to comment Share on other sites More sharing options...
LS5 Posted June 19, 2013 Share Posted June 19, 2013 I believe in the 70 chevelle/454 I ran an AC Delco plug green stripe 45 RT's... They didnt use the 402 in the Velle's until 71 as the velle in 70 as an SS option was a 396 or the 454. They had the L78 chevelle that was also a 396 but it was the 375 hp engine. The 402 came in the Heavy Chevy chevelle but not in 1970. Darren. Quote Link to comment Share on other sites More sharing options...
RSF Posted August 1, 2013 Author Share Posted August 1, 2013 so after a long delay I finally had time last night to pop a valve cover off and found what I think is the casting number.....8872702. I am a novice and have never done engine work myself so can you guys help me out here? Is there date coding within this number or do I need to compare/match it to other numbers on the block? where would i find the number on the block? Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted August 1, 2013 Share Posted August 1, 2013 sure that's not 3872702? if so they are 1965-66 oval port, closed chamber, 98cc chambers and they will used a gasketed plug 3/4 reach, like a R44XLS Quote Link to comment Share on other sites More sharing options...
RSF Posted August 2, 2013 Author Share Posted August 2, 2013 You are correct Sam - the first digit is a 3 not an 8. Based on your info these are obviously not the original heads. Do you know where to find the block number and any others so I can try and figure out what the heck i have in this thing? Comparatively speaking, are these heads decent? The entire motor was rebuilt and the valves and springs were upgraded so i guess that is a good thing. Quote Link to comment Share on other sites More sharing options...
Sam (Bones) Posted August 2, 2013 Share Posted August 2, 2013 you want to find the "stamped" numbers, and they should be on the block where the passengers side head sits on the block behind the alternator with the stamped numbers we can find out what is was when GM built it Quote Link to comment Share on other sites More sharing options...
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