Help me choose heat range etc.

[Stupidquestionspro]

I don’t quite understand carburetors or heat range on plugs or otherwise that well yet and my motor is modified enough I’m not sure stock specs will work

68 sbo 350 bored .30 over with number 5 heads but unfortunately modern stock replacement cast pistons so dropped compression.

The guess compression is about 7.5:1 it has also been converted to HEI with MSD ready to run distributor.

Right now I’m running the 68 factory recommendation ac Delco plugs with a .45 gap.

I just want to ensure I wouldn’t need to change heat range or gapping due to the HEI, lowered compression and added ethanol in modern fuel.


Sent from my iPhone using Tapatalk

 

[paul.m]

.45 is what you want

 

[Stupidquestionspro]

.45 is what you want

So I want a 45 heat range. It’s currently a 43 I think


Sent from my iPhone using Tapatalk

 

[TURNA]

Being it is such a low compression engine you may want to run a plug that was made for a low compression engine

A number 5 head 1969/70 calls for 3 different plugs with a 30 gap

Now move up to a low compression engine like a 79 Olds 359 and the gap changes to 60 and in 1980 it changes to 80

 

[MrSony]

Heat range will be told by the heat mark on the strap, the piece of metal going over the electrode. Should be halfway up the strap. Start with ac Delco factory spec plugs at .045 gap and see what your engine likes.

 

[Stupidquestionspro]

Right now it’s ac Delco r43ts which if I remember was the factory for a 68 gapped to .45 it didn’t seem to like .5

But it’s just not running right and when I had researched the lower compression HEI engines I saw they ran hotter plugs do I’m thinking I should do the same now gap wise I don’t think I’d go 60 but I’m definitely considering hotter plugs.

I’m kinda torn because I know I’ve seen HEI olds v8 I think it was a 307 with compression close to mine it called for a 46 heat range.

I’m thinking about trying the 46 to make sure it’s right and from what I understand that will help burn off the deposits I’m sometimes getting on the plugs and the one cylinder I have a small amount of oil getting into.

So which should I do 45 or 46? And what happens if the heat range is too high?


Sent from my iPhone using Tapatalk

 

[pontiacgp]

a too hot a plug with cause pinging....

 

[olds307 and 403]

I usually run the NGK XR45 plugs, lower number for them means hotter. I had only bucking at low speeds on 87 with 9 to 1 compression 214/214 cam at low speeds with nearly 60 degrees part throttle, around 50 at idle. I changed from a 30 to a 20 degree vacuum advance, problem fixed. On my 8 to 1 stuff, those numbers worked fine. You could try XR5 plugs but should not be necessary. I gap a loose .045. I find they idle nicer than the new AC Delco and Autolite plugs now made off shore.

 

[Stupidquestionspro]

I usually run the NGK XR45 plugs, lower number for them means hotter. I had only bucking at low speeds on 87 with 9 to 1 compression 214/214 cam at low speeds with nearly 60 degrees part throttle, around 50 at idle. I changed from a 30 to a 20 degree vacuum advance, problem fixed. On my 8 to 1 stuff, those numbers worked fine. You could try XR5 plugs but should not be necessary. I gap a loose .045. I find they idle nicer than the new AC Delco and Autolite plugs now made off shore.

I was thinking about a set of NGK.
A 1980 sbo 350 looks like factory recommended a 46 heat range which it is an HEI set up and closer to my compression than a 68 obviously so I am seriously considering trying that and then for giggles trying out a .60 gap and working it down from there if it runs rough.

Would there be any reason not to go range 46 considering that Is what the factory recommended plug is for a motor fairly close to mine?


Sent from my iPhone using Tapatalk