What type of gas for 10.9:1 CR?

YoungCamaro · 05-26-2009, 05:49:15 PM

I was just wondering I'm running some keith black hypereutectic pistons that are 10.9:1 compression ratio and i'm wondering what type of gas would I be the safest running?

KevinsZ28 · 05-26-2009, 05:50:45 PM

93 premium octane.
thats what I run.

sooner · 05-26-2009, 07:44:33 PM

With Iron heads, you will probably be looking at 100 octane, or at least a mix of 100 and premium.

Lot of other factors involved, so just a rough estimate.

Cable Slacker · 05-26-2009, 08:13:32 PM

should be fine with 93 , I am at 11.7-1 on 93 with iron heads and no problems

jaywill · 05-27-2009, 10:03:22 PM

Quote:

Originally Posted by Cable Slacker

should be fine with 93 , I am at 11.7-1 on 93 with iron heads and no problems

DAMN!!! how u swing that curtis,,and here i'm worrying about running mine on pump gas w/10.86 w/iron heads

that good 2 hear.......

Mwilson · 05-27-2009, 10:16:52 PM

Quote:

Originally Posted by jaywill

DAMN!!! how u swing that curtis,,and here i'm worrying about running mine on pump gas w/10.86 w/iron heads

that good 2 hear.......

I put his motor together! His name is John, now youve called Chris Mitchell and John both Curtis! Is that an internet name?

Doug Jaynes · 05-27-2009, 10:41:00 PM

I wouldnt waste any money on the 882 heads camel hump heads are not much better in my mind.

find yourself a pair of used vortec heads and just run them as is till you can afford a valve job for them. heck you could just lap them in a little to get by. the difference will be huge over the 882's. I dont think head material makes much difference personaly , there are so many variables it would be hard to tell what the gains come from.

Has anyone out there ran a set of 1995 ish LT1 heads (same ports as vortec but aluminum) on a old school sbc ? isnt there a a mod for the coolant passages to make that work, that is probably more than you want to mess with Im just trying to think of cheap options

Doug

jaywill · 05-28-2009, 12:03:12 AM

Quote:

Originally Posted by Mwilson

I put his motor together! His name is John, now youve called Chris Mitchell and John both Curtis! Is that an internet name?

my bad

when i met him ..he said his name was curtis i think???

sooner · 05-26-2009, 08:24:30 PM

you must be running a GIANT cam then. I ran a 292 magnum comp cam in a 406 with a set of dart II iron heads and it would not even attempt to run on 93 with 11.2:1 compression.

kenny77 · 05-26-2009, 08:38:00 PM

I'm right at 10.5 to 1 maybe a bit higher with my 383 flat top pistons and 64 cc high lift Vortecs. When the heads were cc they were actually 62 cc. Not a daily driver. Weekend/nice nights/shows.

Compression is your friend on the street.

I run 5 gallons of 115 VP and mixed with the rest of the tank with 93 crappy pump gas. This mixture gives me 101-103 octane in a full tank. No problem for me to stop by and fill my 5 gallon jug once in a while. It's $10.00 a gallon but it gives me piece of mind.

BTW the VP 115 leaded is figured on the old Motor Octane standard not the RM/2 method...so by the new RM/2 method of figuring octane it's about 124 not 115. That's some serious fuel.>>>>>>>>>Ken

warped · 05-27-2009, 11:37:00 AM

we've had this discussion before. There is more than just static conpression that determines your engine's need for octane. Have you checked the actual compression your engine has or are you just using the published figures from KB? The cylinder heads you use as well as the head gasket will affect the final CR. If the engine is just going together, check the conbustion chambers and determine exactly what your static conpression ratio is. If the engine is built, why not try a few gallons of 93 octane premium to see how it runs. If that octane doesn't cut it, move up to additives and racing fuel. Good luck.

Doug Jaynes · 05-27-2009, 12:16:03 PM

I dont know what your motor combo is . What heads, pistons and cam are you running?

With a nicely prepped short block and the right cylinder heads it will run fine on 93 or 94 octane fuel.

the biggest factor is the combustion chamber design . The newer heads are much more efficient at burning the fuel mixture quickly. old school heads like the double humper and copys of them like the sportsmans and torquer heads have poor chambers and will need more timing and octane to run without detonation. Something like the 350 Vortec heads or a Dart Iron Eagle/ Pro-1 type chamber will be a better choice.

The piston shape is part of the combustion chamber, a domed pop up piston slows the burn down compared to a flat top or dished slug will.

If you can swing it, have the block zero decked so the quench height with a GOOD gasket will be .040" ish or so. Some guys will say just use a thin head gasket, I just dont like them. Do what your budget allows.

hhott71 · 05-27-2009, 12:44:44 PM

93 octane if your Quench is near 0.040"
Head material is IMMATERIAL.
At 6,000 RPM there are 50 cylinder firings per SECOND, Just how fast does heat travel away in that environment?
Aluminum, Iron, Titanium, Brass, Glass. Just as long as it doesn't burn, melt, or wasn't developed for the outer skin of re-entering spacecraft.

YoungCamaro · 05-27-2009, 03:23:47 PM

Yes the engine is not yet completed it's in pieces right now. Heads are chevrolet 882's, pistons are KB100 10.9 CR (64cc/ Flat top), cam is Crane Cams .467/.467, 278/278, 222/222, 110LC. The block is a standard 350 bored .060 and stroked to 383.

Simon@London · 05-27-2009, 03:45:22 PM

I am starting wo wonder about this also. I have so far ran 91/ 93/ 94 octane with no difference that I can hear or notice. In stock bottom end on flat tops with Vortec heads will this do damage. My compression should be 10.5:1.

Running lower octane with older heads was an issue but nothing so far with new heads.

Thoughts.