what octane can it run?

[herbiehind]

if i build to a scr of 10.06 and dcrof 8.64 and .043 quench , what's the lowest octane i can run ? will it do 87?

[SilverXJ]

93

[Muad'Dib]

Depends on your elevation too... with that high of DCR you might ping at lower altitude. There are a lot of factors .. including quench, chamber polishing, heat etc.

[herbiehind]

k cool . what's the highest dcr that will handle 87 octane? then there's quench /. is there a formula to determine how much octane quench recovers?

[dragginwagon406]

I would say stock dcr is where you would want to be for 87, i.e., stock cam = stock compression for 87 octane.

On my '98, I run 93 for stock cam, 9.3 CR/7.68 DCR and it is good for towing and all in 95 degree heat but if you find the lean spot (above 4000 rpm with little throttle opening), it will ping on 93. I did not polish the chamber, use a lower temperature thermostat or anything else.

[dwg86]

If I remember correctly my stoker was 9.25 SCR and 7.8 DCR, zero deck, .041 quench, polished combustion chamber, 180 thermostat, ford 24# injectors. I ran 87 octane without a hint if pinging ever(95 deg, towing, ect). I think the tight quench and polished CC may have been the key. If I were going to build another stroker, I would go higher on the comp ratio maybe 9.5 scr, 8.0 dcr.

[gradon]

I'm at 10:1scr and 8.57dcr, polished CC and .062" quench(cause I used a .051"HG)and it pings a little in closed loop when kept to 14.7:1 AFR. My recommendation w/o proof is shoot for under 8.0:1dcr if you want to use 87, under 8.25:1 if you want to use 89/91, and under 8.4 if you want to use 93, while having a .040-.060" quench. Read this: http://www.empirenet.com/pkelley2/DynamicCR.html

[herbiehind]

I'm at 10:1scr and 8.57dcr, polished CC and .062" quench(cause I used a .051"HG)and it pings a little in closed loop when kept to 14.7:1 AFR. My recommendation w/o proof is shoot for under 8.0:1dcr if you want to use 87, under 8.25:1 if you want to use 89/91, and under 8.4 if you want to use 93, while having a .040-.060" quench. Read this: http://www.empirenet.com/pkelley2/DynamicCR.html

great read and bookmarked , thanks !! i think i can get below 8 dcr easily and into high 7's and still have decent quench . i dont mind running 91 or better. it's just that who knows what the future will bring regarding fuels and the green police .

[herbiehind]

I would say stock dcr is where you would want to be for 87, i.e., stock cam = stock compression for 87 octane.

On my '98, I run 93 for stock cam, 9.3 CR/7.68 DCR and it is good for towing and all in 95 degree heat but if you find the lean spot (above 4000 rpm with little throttle opening), it will ping on 93. I did not polish the chamber, use a lower temperature thermostat or anything else.

thanks but no way i can get into the 6's . i'll try for best quench and definitely run stock cam and i'll just have to see . thanks again .

[dragginwagon406]

What you can get away with is not necessarily what you will get away with as conditions change over the life of the engine. I would by no means build a low compression turd, but I would be honest with yourself too. Small cams do not need high compression and compression will not give that "much" horsepower due to the smallish cams.

Also, where you drive could be as important as what you are pulling. High elevation will get away with more compression too but will you always be in high elevation? Will you drive it to sea level or below?

Pinging will surely shorten the life of the engine, even if you can't hear it. Give yourself a little cushion - either by using a slightly higher than necessary octane fuel or by using modest compression for the desired fuel. Your engine will thank you with a nice, long life.