Hey, I'm in the middle of a build and was wondering if I could run 11.5/1 compression on 93 octane. You can look at my signature and see what my setup is. It's just time to buy the head gaskets and was wondering what size to buy. Also if anyone has any HP estimates after it's done, please share what you think. And some track times if you want, I'm gonna be spraying 175 at the track.

 

1 very important aspect of a high compression motor is the piston quench demention of about .040 to prevent detonation. Your head gasket thickness, and deck height are the things to look at here.

To get that kind of CR to live on pump gas, your intake closing degree on your cam plays a very big part.

Educate yourself on dynamic CR and keep that under control

 

I dont think it will run with what is in your sig

 

You're going to need a huge cam to bleed that compression off at an acceptable level. 10.5:1 is pushing it in general, and 11.5:1 with optimal timing is going to send you using very high octane fuel. Pay close attention to your dynamic compression ratio (like mentioned before with intake closing point, as well as taking LSA and duration into account).

 

http://cochise.uia.net/pkelley2/dcrvb6.zip

Download and install that DCR calculator.
Input all the required details of your engine and see what DCR you come up with

For a explanation of DCR read
http://members.uia.net/pkelley2/DynamicCR.html

 

You'll be fine running 93. If anything your carb might be a bit big for street use. 355 are good street engines if you ask me.

 

i run mine a 10.3 cr (8.2 dynamic cr) on 87 octane and doesn't ping, quench, cam, aluminum heads, cooling system, ignition advance makes all the difference specially that stiff spring on the mechanical advance

 

Guys he has iron heads according to his sig....Atleast gutted cast heads with afr valves makes me believe its a iron head... If truely aluminum, it may have a chance but we dont even know what piston you have or what head chamber size you have. You dont have gaskets picked out yet but claim to know compression already? To get that much comp, you have either a dome piston or very small head chamber cc's

 

"gutted cast heads with AFR 2.05 aluminum valves"

Yep, I would say he is at least a point to high in compression. Probably more like a point and a half.

 

I like to see a DCR at 8.5.Now we have seen some guys push it to 9.0,but then that gets to be touch and go.The range of pump gas at the same octane,same brand name,can result in some ping and others don't.

 

Middle of your build..

what do you have so far?

 

shortblock done, heads at a machine shop, just havent bought a head gasket yet. i was gonna let him tell me what size head gasket to get for what compression, because this motor was at 12.5/1 at one point. the whole point was to ask if you can run 11.5/1 on pump gas if your motor can run at it. mostly all suspension and rear end work is whats done though.

 

if the block is done now it depends on your deck hight

 

In most cases - no. There are a few exceptions, but you'll be making some compromises by doing that. It will take careful planning on your part if you do manage to get it to run on pump gas. Like Gary said - different gasoline will react differently as well. This is also why I only fill up at ONE pump, so it's always consistant (minus seasonal changes with winterizing and all that).

 

I took my 12:1 iron eagle head car on a 20 mile round trip on 93 octane. I just cruised though. It's hard to hear pinging with open headers.

 

I personally think that 11.5:1 is to high. Specially if you are using iron heads and plan on using nos. I'm currently at 11 with my 383, AFR ported 190cc heads. SuperRam fuel injection and have issues with some detination WOT 4500-5000 rpm. With the base timing set a 8 degrees. If I add some octane boost I can get away with it. But you never really know what your getting at the gas stations around here. I stopped at Sunoco and put 10 gallons in of their best gas. Engine was spark knocking bad, added some 110 octane boost knock went away. Good luck!