I was at my local auto parts store and they could not find in any of the manufacturers books a plug specifically for the 1965 327/365-SHP corvette.
I am currently running [ NGK B6S ], this number shows the stock application for the 327 - 300 HP. Is there any difference? I am running it now, but I would like to know if there is a different part number for the 365 SHP.

Mark

 

The OEM plug for ALL '65 Corvette 327 engines was the AC44, but the AC45 - one heat range hotter - is really better for normal driving. Of course, you can't buy these new anymore, but NGK and Denso both make non-resistor plugs that are equivalent to the original ACs.

You can check any manufacturer's catalog at a parts store or maybe check the web. You are looking for a 14 mm non-resistor, 3/8" reach plug with a 13/16" hex. This is the basic plug family. You can also look at manufacturer's cross reference charts.

NGK crosses the AC 44 to the B6S and the 45 to the B4. Looking at the heat range chart for this family they also offer, on the hot end, the B2 and two ranges colder than the B6S.

My suggestion would be to try a set of B4s and see how they work out. They should be less likely to foul, and since it's tough to run a SHP engine hard for very long on the street, they will be unlikely to overheat.

If you want to try a Denso, their equivalent to the AC 44 and 45 is the W16S-U and the W14S-U respectively, and their heat range offering is very broad with nine plugs covering their heat range 9 (hot) to 31 (very cold ), which should cover every need from easy cruising to endurance racing.

Too bad AC doesn't service our application anymore, but I never really liked them anyway because their shell coating was not very corrosion resistant. NGK and Denso both sell a high quality products with corrosion resistant shell coatings and good technical features in the electode design at a reasonable price, and based on my experience with some specialized applications, they both have outstanding customer service as well.

Duke

 

Thanks Duke.
I will try the B4's and see how the run.

Duke, do you glass blast your plugs, I have on snowmobiles, bilkes, etc.
In most of my cars if I go to the trouble to take them out, I just replace them.
I was thinking of cleaning the B6S's up and storing them incase I wish to use them in the future, since they are only a year old.

Mark

 

Yeah, over the years I've cleaned spark plugs. Back in the sixties I used to clean Corvette plugs every few months - had to keep swapping them with clean ones because of the marginal ignition.

On my modern cars I usually run them 30K miles and then replace. With modern ignitions and fuel mixture control they don't look that worn or dirty at 30K miles, but that's the typical manufacturer's replacement recommendation for copper core plugs and they only cost about two bucks apiece.

Duke

 

On your advice Duke, I installed the NGK B4. I gapped them at .045”.

On another note. I was changing my plugs and my dad walked by in the garage and saw me on the top side of the engine trying to get by the heater hose, engine shielding and battery. He told me it was easier to do it from the bottom of the car. Never occurred to me. I guess since I had the car on jack stands already I would give it a try. Heck, I could have changed all my plugs with an open/box end wrench, they were that accessible. I was probably just trained that it was a top of the motor job.

 

Looks like your dad know's his vettes.

:cheers: :cheers:

 

The OEM recommended gap is .035". I assume that the B4s are designed for this nomimal gap, but I'm not sure. What were they out of the box. The OEM single point ignition might have some problems firing through a .045" gap.

When I ran AC 43s for race track hot lap sessions, I gapped them at .025".

Duke

 

I am running the PROTRONICS IGNITOR ignition module in place of the stock breaker points. I also have an Accell Super coil, stock size, and I am bypassing the ballast resistor, so I am getting a full 13 volts at the coil. I am also using 8MM Accell Non-Suppression wires, (painfully hidden in all the shrouding :smash:). I was told this set-up was a little hotter then stock and would be ok up to .045 - .055 gap. The plugs were gapped at .035 out of the box.
Mark

 

Okay, if Pertronics or Accel recommend .045" that's the way to go. A higher energy ignition will work with wider gaps and wider gaps are better for marginally ignitable mixtures (lean, low density or exhaust gas diluted), which is the case at idle and low rev part throttle operation, however, you might want to try .035" and see if it has any effect on the backfiring through the carb.

Duke

 

I was just thinking about that before I finished reading your post. I will adjust the timing and bring it down a tad like as we discovered it was about 8 degrees to high on the total. If that does not cure the pop out the carb I will back the plugs down to .035 and try that. Like you said earlier it may well be the accelerator pump as it only back fires after the three or for snaps.
Mark-