lou69

Hi there all

really stuck on this one,
I needed to change out the spark plugs in my 1969 corvette 350/300
matching numbers, I ordered ACDelco R43s but after removing the current plug I noticed it was a NGK BPR4FS and the ACDelco wont fit.
as I understand the R43s are the correct spark plug.
should I just keep using the NGK?

I would really appreciate some help on this one

Lou

toobroketoretire

It its truly a matching numbers car the R43's should fit. If however the heads are later heads that use taper seat spark plugs then that's what you'll need. I suggest taking a real close-up picture of the spark plug opening and see what you have or pull the valve covers and get the casting numbers of your heads. Its entirely possible one head got changed whereas the other didn't so you really need to check both of them.

Sayfoo

This is exactly what happened to me. My 69 390hp BB has 1971 lower compression heads to run lower octane non leaded gas.
OP, you should be able cross reference the existing plug # to get the brand you want or the heat range compatible to the R43's.
Xlnt idea about checking both heads.

lou69

thanks for your replies

this is what i have so far
cross referenced the NGK plugs and it seems that that the heads are from 76 through to 84 that fit these plugs,
and also contacted the original owner (from new) and he said that the heads were never changed, Mmmm

while the the car was off the ground i checked the transmission (T400) id tag
and it shows these numbers
(top right) 200
(bottom left) 73-CF
(bottom right) 1761

is this indicating that the trans is a 1973

regards
Lou