84oldsDelta88

So i been hearing different things regarding spark plugs for my setup. Some say to use spark lugs for a 70 350 cause they would be a colder spark. And some say to use plugs for a 77 and up with hei but have heard they produce a hotter spark then what my engine should have.

I've also heard various things about which brands are better (NGK, ac delco, bosch, autolite).

Also point gap some say .045 others say .065 or even .035

So i wanna get your advice.
For a 1970 olds 350 (2barrell version i think stock compression was around 9.0:1) with a gm hei distibutor and egr.
What plugs should i use, what gap and what brand?

Thanks

380 Racer

With points in my 350........ .030, with the HEI or the MSD...... .035 With 14:1 and MSD......... .035 and NGK.

SBORule

I bought the NGK's V Groove for a 1970 Cutlass with a Olds 350, don't recall the part number but they are a resistor plug R5 heat range gapped @ .035".

You don't have to run a wide gapped plug with an HEI distributor.

84oldsDelta88

Is your 70' 350 using HEI too?

O ok wow didnt know that i figured you had to widen the gap with an HEI conversion.
So i guess i should be shopping for spark plugs for my 1970 engine and not looking up for a 77+ 350 right?
Are there any improvements from going with a .035 gap.

I heard the NGK plugs you listed are well recommended for olds 350s with lower compression, give good idle and good throttle response. Any of that true.

I think i have a misfire when accelerating from a dead stop but seems to go away at higher rpm (usually above 1500 its smooth).

I'm thinking its either something with the spark plugs or maybe even the ignition control module under the cap. It comes random 1 day its running fine then the next its running like crap, and sometimes when i'm accelerating from a dead stop it will take off kind of sluggish and then outa nowhere the power will come in without me even pushing the pedal anymore, and itll be running great and amazing performance after that.

Also noticed that when i'm cruising at a steady 50+ mph on a highway my a/f gauge rides in the lean zone, but if i start to accelerate some it will jump back up the ideal/rich.

I already got 55 rods and 73 jets in the carb. should i go to 75 jets instead to richen it up some more, or could my possible misfire be causing this and not igniting the fuel properly? Gonna pull all the plugs tomorrow and see what they look like.

Currently I'm running ac delco r46sz plugs gaped a .065

Will performance be better with a lower gap? How but Mpg will I gain a couple, lose some or remain the same.

SBORule

Yes, I'm running a HEI distributor I got off ebay for $59 from China to replace my worn out 28 year old Accel HEI distributor. I'm still using the Accel Cap and adapter kit, which allows the use of an external Accel Super coil. I still have the red cap and 50,000 volt coil that came with the ebay HEI for back up.

My car has a 1971 Block with 1970 #6 heads, so if you have number 6 heads on your 350 then 1970 is the year you should be buying plugs for. You don't have to run plugs designed for 1975 or later engines that used an HEI distributor. You'll probably see a major difference using NGK V Groove plugs for a 1970 Olds with the plugs gapped at .035".

Don't know what kind of gauge you are using that tells you if you are running rich or lean, so I wouldn't know if it's accurate or not. I'm not up on what number rods to run with 74 -78 jets, my Q-Jets had special made metering rods from an unknown aftermarket supplier. If you are using metering rods made by GM, you need to find the ones they used in the higher Horsepower engine combo's like a W31 that made 310HP or the Big Blocks that made 350HP or so and that should get you in the ball park.

Make sure that rod that goes to your accelerator pump on top of your carb is in the top hole, that will give you more pump shot/more fuel when you push down on the gas from a dead stop and might help that hesitation you feel.

Nasty455

I use the larger gap,as the higher quality spark shouldn't have trouble jumping the gap.
I don't think it makes a ton of difference,but I run the .60 gap.
Buy the plugs for your 70,and use the gap of the later HEI.
What matters on the plug is the thread size and the reach into the combustion chamber.

cutlassefi

You run a .60 gap? Wow! You must have a great ignition system in order to jump a gap that's over a half an inch wide!

Run a plug that's right for a '70 or '71, whatever you have and gap it at .035. HEI's really aren't that strong in stock form.

70Wcars

Try 71 or 72 Jets with 49 Rods. CV or AU Secondary rods. And yes, check your Accel Pump Rod position as stated above.

Just my experience/suggestion

Danny

Intragration

I've heard a lot of people talking about running earlier plugs and narrower gaps when running HEI on earlier motors. I've got a '70 455 with a '76 HEI and I run '76 plugs gapped at .060, .020 NARROWER than the '76 HEI factory spec of .080. It runs great. The HEI might not have been THAT powerful, but it was apparently powerful enough to power a spark across .080. If lighting off the compressed air/fuel mixture as efficiently as possible is the goal, I don't see how a wider gap with HEI on an earlier motor can hurt. Seems to me this is part of the BENEFIT of running an HEI. This is just my opinion. If someone has a definitive answer on this, please chime in.

ThePackRat

Don't know how true this is so standard disclaimers apply ...

But I thought I read somewhere that new cars on dealers lot's at the time were "loading up" with the .080 gaps & the often quickie start/stop/not fully warmed cycles such cars sometimes go thru.

Thus ... the gap was cut back to .060.

Again standard disclaimers apply.

BILL DEMMER

gm introduced hei to reliably fire the lean mixtures with egr they were running back in the mid-70's and later. the hei is a very powerful system if in even halfway decent shape. i run my gap at .045-.050, never a problem. i use the correct plugs for a '67 hc 4-bbl. 425.

it sounds like your mixtures are right, when cruising, you should be a little lean, and when you push the feed a little, it should richen.


bill

cutlassefi

While they were ok to fire the lean mixtures, those were also coupled with low compression, that makes a difference.
However the power level on the stock HEI's falls off pretty quickly up around 5000rpm or so. Obviously the tall geared cars of the 70's and 80's didn't see those Rpms too often.

captjim

The reason those gaps were .080 is because the cars ran so lean that the gap was required to increase the chance that it would find a molecule of fuel to ignite.






J/K, Sort of..........................

380 Racer

^^^ lol ^^^

Redog

I ran a .060 gap on my 1968 350 with HEI.

I was using ACDelco RS45 plugs or was it 43's? I can't remember but one was for the 455 and the car didn't run that good with those plugs in place. It made a "struggling" and pinging noise so I swaped out the correct plugs and it was fine

BILL DEMMER

i didn't glean from the op's post that he was racing the car.
there was the vette and gn's, they used hei.
if you're racing the car, sure, get a better module, etc. for the typical vehicle on co, stick with the proven factory hei-unless you've money to burn.


bill