Octane

hello all!!! I have a pretty simple question (I think). i have a 67 440cid built to stock specs, with a mopar purple cam and a edelbrock 750 cfm carb. i was wondering what octane gas to use for best performance??? i've been using 93 for most of the time i've had da car, and it seems to run well, but a few of my gearhead friends say that it would run better on 87 any comments???? thanks in advance---- MJ

What is your compression ratio? Which "purple" cam. ALL Mopar Performance cams are "purple"

hello all!!! I have a pretty simple question (I think). i have a 67 440cid built to stock specs, with a mopar purple cam and a edelbrock 750 cfm carb. i was wondering what octane gas to use for best performance??? i've been using 93 for most of the time i've had da car, and it seems to run well, but a few of my gearhead friends say that it would run better on 87 any comments???? thanks in advance---- MJ

If it is in fact a stock rebuild with stock compression which was supposed to be 10.5:1 per factory specs (and they seldom were and usually are around 9.5:1) 93 Octane is the MINIMUM you would want to run. Unless there was signifigant head work done and you have a "quench" engine which typically allows a high compression engine to get away with less octane.

87 is a standard grade octane and is not for high comprssion engines.

thank you for your comments.... id have to look up the specs on the cam, i don't remember off da top of my head, when i get home today i'll look it up on the spec sheet the previous owner gave me. i'll post it later, thanks again!!!

your friends are morons. must be chevy guys. or your mopar intimidates them.

:rolling: BOTH!!!! :rolling: didn't get around to lookin at da spec sheet i'll def. look tonite...

ok so da spec sheet is not too specific...don't know da cam specs :sSig_noob: but it is a claimed 10.5:1 compression, with 906 heads (ported and polished) and a pretty lopey cam she thumps real nice.... makes me smile!!! :grin::grin:

If it's really a 10.5 then you'll need the 91-93 gas to try and make it live. Course, if you work your advance over so it doesn't advance real fast under a little load you MIGHT be able to run it on less.

maybe

I adjusted my timing last year when i first got the car, it was at 2 deg. advance, i bumped it to 5 deg. advance and it has been running ok, but i think if i go to 7.5 like the manual calls for, it will run like a raped ape. :grin: only prob is if i bump it to 7.5 i think it will run hotter, and she runs kinda hot right now. :sad: i did buy an 18" mopar perf parts viscious fan from summit a couple days ago, i think it will help... i'd like to sneak anothe question in this thread if i could...:blush: what idle speed should i run her at? it's at 850rpm and 650rpm on load right now----confused: :sSig_thankyou: :sSig_thankyou:

last thing you want is detonation,talk to us and dont listen to the little boys with bow ties.

I'm talking less about initital timing as I am advance in the distributor. You need a dial back timing light or a timing tape on your balancer to figure that out

i advanced my timing by shooting the timing light at da balancer; it has little piece metal attached to da back of it with little teeth on it so you can see the advance or retard, and turning the distributor cap, and shooting the timing light again and adjusting that way--is that what you are talking about?

Sorta. You're total advance should be 36-38 degrees and you won't see that with the factory marker. You need either a timing tape on the balancer which will be marked up to 45 or 90 degrees, and should also be marked every 90. I haven't used one in a long time cause I've got a digital dial back light which also has a built in tach so you're sure what RPM you're looking at

thats initial timing and should be set with vacumn advance plugged at a specific rpm found in the manual. with performance mods with all your timing in you want 32-35 in most mopars. this is with your vacumn advance and centrifugal advance .you find this with an advance timing light by dialing in what you want say 35* on the light and bring rpms up to say 2500 to 3k and turn distributor till balancer mark 0 and timing tab 0 line up. this would be 35* total timing

Otay! I will take your guys advice and also i will read da manual. it's going to take me a little while to wrap my head around all this, but i'll get it!!! :yes:
thank you guys soooo much for your help, if i get stuck you all will be hearing from me!!!!! :head_smack::rolling::sSig_thankyou: can u tell i love these little smile thingys!!!! Later!!!!!!!!!!!!!!!!!

thats initial timing and should be set with vacumn advance plugged at a specific rpm found in the manual. with performance mods with all your timing in you want 32-35 in most mopars. this is with your vacumn advance and centrifugal advance .you find this with an advance timing light by dialing in what you want say 35* on the light and bring rpms up to say 2500 to 3k and turn distributor till balancer mark 0 and timing tab 0 line up. this would be 35* total timing


The problem with doing it this way is determining how much advance is in the distributor itself. If you use the light to dial up (or actually back) to zero from wherever your total runs to, you will know how much advance is built in to the distributor...once you subtract your initial timing setting. You should also use the light to tell you at what point your advance starts to kick in, and at what RPM maximum is reached. THEN you will know what needs to be done to the distributor to optimize it to your motor

ok, i'm starting to understand this timing thing a little better, but i'm still at work slingin meat,:banghead: so i will try to put all of this together when i get home and in the comfort of my garagemahal. :cheers2: i'l check back later and post some questions; cause God only knows i'll have them!!!!:reading:

BTW the idle speed thing, i probably shouldnt worry about that until i get the timing straight, right?

if your marker is at 0 with your balancer this is no advance no retard so 35 has to be total. with the light on 0 youl see distributor advance on the tab with vacumn advance in and total will be off the tab. or initial with vacumn plugged

if its runnig hot you mite make sure your not running to lean also