Spark Plugs for 1968 327

[CaptainK]

I have a 1968 327/300hp engine. Mostly standard, except Edelbrock intake and carb.

I want to change the spark plugs as its been a while, but no idea what plugs to use. Last time I had the plugs changed I bought what the internet says is the plugs for me to use - some big fat ended short ones. Even some well known Corvette suppliers list the fat plugs as the ones for my car, weirdly. Turns out they were wrong as I had a garage replace them, and they didn't physically fit as the ones in the engine were thinner and had a longer screw part.

Below is a new plug (the clean one) I bought wrongly many years back (B6S), and next to it is an original plug that was in my engine when I got the car (AC Delco 45TS).



I have no idea what plug is currently in my engine, as the garage sorted out new plugs when they said mine were too big.

So fast forward to NOW and I want to change plugs again. I could go for the AC Delco 45TS again as evidently they fit, but thought I'd ask you for any recommendations as they weren't in the car long before I had them changed.

Also as the "TS" says, I'm guessing I need "Tapered" plugs. But do I need "S" plugs? Can I got for a 44 instead of a 45? What would be the NGK or other manufacturer equivalent? The AC 45 TS also seems to be "resistor" plugs - do I need them? I've read up on this, and the more I read the more it confuses me.

I've also read it also depends on driving style and kind of driving you do. Apparently if you drive more in town you need a hotter plug or something. I have no idea. But I drive mostly A and B roads and some duallies / motorways. Try to avoid city driving.

Please recommend me a plug. Thanks.

 

[teamzr1]

I attached below right from GM engineering archives the complete design specs for 1968 Corvette
This is 140 pages as PDF and includes total design and specs.

Notice for the 327 CI is AC44 spark plugs (A/C Delco)
you could cross-reference to other brands

S Resister types are to limit static sound of radio to speakers

 

[teamzr1]

Could use AC45 which is one step hotter than the 44s whereas a AC43 is one step colder than the 44s

A hotter plug is more resistant to fouling than a colder plug (higher number on an AC plug is hotter, lower number is colder). 43 is a cold race plug, 44 is a medium heat range, 45 is a city/cruising plug.
A "cold" plug is designed to transmit combustion chamber heat faster to the cylinder head than a hotter plug

Cross-reference website

spark plug cross reference

www.sparkplug-crossreference.com

OR

1964-1970 Chevrolet Reproduction AC Delco Spark Plug Set #44

1964-1970 Chevrolet Reproduction AC Delco Spark Plug Set #44

www.ss396.com

 

[Mr. Cricket]

I and many mates use these guys for great advice and service

Green Classic & Vintage Spares - Home

www.gsparkplug.com

 

[Chuffer]

My C3 runs with 1985 IROC- Z 305 cu inch motor with Edelbrock Torker 2 inlet manifold and Edelbrock 600 cfm Performer carb and I use AC Delco 45 plugs . It runs fine as she is only doin` the cruzin these days .

 

[Chris Sale]

I have been using NGK BP5S plugs in my '64 327 300HP for many years. Excellent plugs.

Chris Sale
'64 Coupe

 

[CaptainK]

That is excellent, thanks everyone - and especially teamzr1 for the excellent description of what everything is. I'd spent ages on the internet looking to see if I needed resistor or not, hot or cold plugs and so forth and just got myself confused.

 

[CaptainK]

I have been using NGK BP5S plugs in my '64 327 300HP for many years. Excellent plugs.

Which is a little odd as the sizes on those are a little too short reach compared to the AC 45s, and the hex spanner size is much bigger. They also look a lot like the "fat plugs" I have pictured above, that I've been told don't fit in my engine.

I did read something online about the 1968 327/300hp engine having some oddities compared to other engines and also different plugs etc. Could just be internet talk though.

It seems that gparkplugs (a site I've used before thanks) seem to think that the AC45 TS plugs are obsolete, so out of stock. I've been using the cross reference to find other suitable plugs, and the NGK ones I've tried are also listed as obsolete and thus no stock. Hmmm.... I might fire them off an email, or just look on E

 

[Roscobbc]

Why not take a look at the NKG comparison and see that other vehicle used the same plug and search from that point. I'm using NGK BCP7ES plugs which I think was an OEM spec' for a Seat Ibiza of all things. This is a relatively cold plug. The BCP8ES originally spec'd by the engine builder was certainly a race spec' plug and would foul-up given time driving in urban conditions......the '8' is just about Ok. The ES relates to a extended tip to the plug. Your '5' number is a hot plug I believe.

 

[CaptainK]

Yeah I've been on the NGK comparison site a lot. Unfortunately all their plug recommendations as the same (UR4 / 6630) seem to be more expensive / out of stock as getting AC 45TS over here. I've looked into Champion plugs, but no idea about them. Might try Bosch.

I probably ought to find out what is in the engine currently too, for comparison. (time and effort to find to dig one out... and a 14mm spark plug tool)

 

[Roscobbc]

Cylinder heads.......OEM?

 

[CaptainK]

Cylinder heads.......OEM?

I believe so, I checked all the numbers when I got it. It also tallies up with the spark plug referencing - the engine was specced for AC Delco 44 as per teamzr1's document above, and I had 45TS in them too.
These are 14mm threads, with 16mm hex socket and a reach of 10.9mm. Whereas the plugs I accidentally bought, as recommended by most sites, are the right diameter of 14mm, BUT are 20.8mm hex size with a reach of only 9.5mm. I guess that's why they don't fit.

 

[teamzr1]

Best for you drivestyle is just getting the A/C 45TS, make sure gapped correctly
Being S type will help reduce static sound of radio output

 

[Chuffer]

Yeah I've been on the NGK comparison site a lot. Unfortunately all their plug recommendations as the same (UR4 / 6630) seem to be more expensive / out of stock as getting AC 45TS over here. I've looked into Champion plugs, but no idea about them. Might try Bosch.

I probably ought to find out what is in the engine currently too, for comparison. (time and effort to find to dig one out... and a 14mm spark plug tool)

AC Delco 45 TS plugs on Ebay UK for £44 for a set of 8 .

 

[CaptainK]

AC Delco 45 TS plugs on Ebay UK for £44 for a set of 8 .

Thanks. I spied that the other day, but was holding off until I heard back from some people, and also wanting to find out what plugs are in my engine. I don't know if the 45TS plugs are any good, as they were only in the engine a short time when I first got the car, and back then it didn't run very well until I changed a lot of stuff and had it tuned.

Hopefully dig a plug out at some point and see what it is.

On further research I think actually my heads have been swapped over the years. It turns out GM didn't start using "Tapered" seat (the T in 45TS) plugs until the 70s. Mine being a 1968 should be using gasket seated plugs. So this would explain things. If true, it would also explain why my engine is only running 250ish bhp when I had it tuned. It should be more, but I put it down as "not bad for a 50+ year old car".
I know I checked the block number and that is correct, but I suspect I forgot to check the heads and assumed it was all numbers matching as that is how it was presented to me. I guess I need to lift a valve cover at some point to find out. Anyone any recommendations for valve cover gaskets? Or will any SBC gaskets work fine? If my heads are wrong, and possibly from the "lower power" era of the 70s, then I feel an upgrade may be needed in the future. Thing is, my Corvette seems quick enough for me though.

 

[Roscobbc]

'IF' the cylinder heads are from a later mid/late 70's car they importantly will be of a lower compression - that will confuse any spark plug choice heat range selection (let alone your potential fitment type)

 

[CaptainK]

'IF' the cylinder heads are from a later mid/late 70's car they importantly will be of a lower compression

This was my concern when the thought of a 70s head on my Vette entered my mind. Coincidentally, on a forum I was reading, it turned out another 1968 owner found out the exact same thing happened to them. Turned out the previous owner wanted to use unleaded and found a set of 70s heads cheap, so it was much easier and cheaper to swap em over.
Still, like I said, car is fast enough for me. But its the "knowing its not right" just erks me if that's the case. Maybe when I have money I'll be looking for head recommendations...... I wonder what heads Andy is running on his 383? Granted its a 383, but it sure goes well.

 

[Roscobbc]

This was my concern when the thought of a 70s head on my Vette entered my mind. Coincidentally, on a forum I was reading, it turned out another 1968 owner found out the exact same thing happened to them. Turned out the previous owner wanted to use unleaded and found a set of 70s heads cheap, so it was much easier and cheaper to swap em over.
Still, like I said, car is fast enough for me. But its the "knowing its not right" just erks me if that's the case. Maybe when I have money I'll be looking for head recommendations...... I wonder what heads Andy is running on his 383? Granted its a 383, but it sure goes well.

Seem to recal they were Trick Flow or AFR?...........I'm sure Andy will let us know soon.

 

[Forrest Gump]

This was my concern when the thought of a 70s head on my Vette entered my mind. Coincidentally, on a forum I was reading, it turned out another 1968 owner found out the exact same thing happened to them. Turned out the previous owner wanted to use unleaded and found a set of 70s heads cheap, so it was much easier and cheaper to swap em over.
Still, like I said, car is fast enough for me. But its the "knowing its not right" just erks me if that's the case. Maybe when I have money I'll be looking for head recommendations...... I wonder what heads Andy is running on his 383? Granted its a 383, but it sure goes well.

AFR Eliminator with Magnum 270 cam

 

[teamzr1]

Thanks. I spied that the other day, but was holding off until I heard back from some people, and also wanting to find out what plugs are in my engine. I don't know if the 45TS plugs are any good, as they were only in the engine a short time when I first got the car, and back then it didn't run very well until I changed a lot of stuff and had it tuned.

Hopefully dig a plug out at some point and see what it is.

On further research I think actually my heads have been swapped over the years. It turns out GM didn't start using "Tapered" seat (the T in 45TS) plugs until the 70s. Mine being a 1968 should be using gasket seated plugs. So this would explain things. If true, it would also explain why my engine is only running 250ish bhp when I had it tuned. It should be more, but I put it down as "not bad for a 50+ year old car".
I know I checked the block number and that is correct, but I suspect I forgot to check the heads and assumed it was all numbers matching as that is how it was presented to me. I guess I need to lift a valve cover at some point to find out. Anyone any recommendations for valve cover gaskets? Or will any SBC gaskets work fine? If my heads are wrong, and possibly from the "lower power" era of the 70s, then I feel an upgrade may be needed in the future. Thing is, my Corvette seems quick enough for me though.

If in doubt, take one spark plug out and look at the head where the plug installs
If the surface is flat than not seated ,and if the surface shows tamper than for tapered type

Some people if the heads were aluminum and not for tapered would over torque a seat type once and that would cause
that area to press inward and then allows for tapered plug