New ZO6 C/R

[Pontiaco]

How can the new ZO6 handle 11.0-1 C/R on pump gas? can a ls1 do that?

[Lunatikgixxer]

i couldnt tell you but ill take a guess maybe because its a bigger motor?

[ls1camino]

How can the new ZO6 handle 11.0-1 C/R on pump gas? can a ls1 do that?

It's all in the tune...to run high compression on pump gas, some timing has to be pulled. The trick is to not pull so much timing that you're actually loosing power. My new 427 LS3 is 11.8:1 compression, and I'm planning on running 93 octane pump gas.

[Pontiaco]

you can tune it, but you will make more hp with higher octane fuel!! 11.8:1 is way too high, I run that on my 9 sec. 70 goat

[PFM]

Mine is 11.5 to 1 and it runs fine on 93 octane.

[Firebirdjones]

you can tune it, but you will make more hp with higher octane fuel!! 11.8:1 is way too high, I run that on my 9 sec. 70 goat

A pontiac engine is a completely different animal. I've built quite a few pontiac engines for myself and others. You didn't mention whether you had aluminum or cast iron heads, that's a huge factor.
Pontiac iron heads have a crappy combustion chamber, they require alot of ignition lead for best power, so they tend to get finicky on pump gas if the compression is high.
I built a 455 for my father 10 years ago, it was an 11:1 motor with a cast iron head. It ran on pump gas but the tune had to be spot on. Just for safety sake at the strip we would mix 50/50 110 octane with 94 pump.
About 3-4 years back I built another 455 for my father, this time with aluminum heads and dropped the compression to 10:1. That thing would run on cat pee. As a matter of fact, we dynoed that one on 87 octane and it made 603 hp.
Now he is building a 499 cubed pontiac with same aluminum heads, but looking at 11.5:1 compression on this engine. It too will run on pump gas just fine.

It has alot more to do with cam timing and dynamic compression ratio that can be dictated with intake valve closing after bottom dead center. Generally speaking,,,,with a cranking compression of about 190 psi you can make that particular engine run on pump gas if the tune is spot on. I've found 190-200 psi seems to be about the limit with 94 octane pump gas and a cast iron head.
Aluminum heads are more forgiving, especially if they have a more efficient combustion chamber like the LS heads do.

[Firebirdjones]

To touch on these LS engines and pump gas, it's relatively easy to do with aluminum heads. We've run several aluminum headed engines with 11:1 compression and pump gas without complaints.
The first LS engines in 97 had 10:1 with very small camshafts that build cylinder pressure. They still ran on pump just fine, again, aluminum heads that dissipate heat along with a very efficient combustion chamber that doesn't require much ignition lead at all, 24-28 degrees in most cases make the best power.
Now all your aftermarket heads, both cast iron and aluminum are using this combustion chamber design (heart shaped) that promotes better flame travel and turbulance with a tight quench area. This style of chamber runs best with less total timing. Makes them much more tollerable to pump gas.

[Pontiaco]

ok I guess I'm 4 years behind, so what is the max C/R on 93 oct?

[ls1camino]

ok I guess I'm 4 years behind, so what is the max C/R on 93 oct?

Most engine builders will tell you 11.5:1, because not all tuners are the same, but I have complete confidence in Frost to tune my car perfectly for my 11.8:1.

[Firebirdjones]

I depends alot on the type of engine used, the camshaft, cylinder head design etc...

Anything in the 11:1 range is easily doable with a good aluminum head and modern combustion chambers along with a camshaft that has some overlap.

The real question though is do you really want to push that envelope?? The quality of gas has gotten progressively worse over the years and it's not going to get better. An engine you build today that's on the edge may not run that great on pump gas 5 years from now. For some people, their engines aren't together that long before they are torn down for a refresh.

To be safe, I prefer a little fudge room, especially if the car is driven alot. You never know when you might get a bad batch of gas when you fill up in unfamiliar areas. This crap varies at the pump from station to station. It's not very consistent at all. Just something to think about.

To give you an idea, I built the engine in my 70 formula 12 years ago. I was living in Ohio at the time where 94 octane was easily obtainable. Factory compression was 10.25 to 10.5 depending on who you ask.
I built the engine with 10:1 compression with the stock ram air III cast iron heads, stock ram air III camshaft etc...
I was able to get this combo (which was basically a true to form stock rebuild) to run fine on 94 octane with good tuning.

I moved out here to AZ and all that changed. Pump gas is only 91 at best, and the firebird complained like crazy. I had to dial it back so far it really doesn't run like it should anymore, to the point I'm contemplating taking the engine back apart to make some changes. The combination of 3 points less in octane plus the fact that AZ sources their gas from California completely screwed up what I had built 12 years ago. Now I need to drop back and punt.

[Firebirdjones]

I'll give another example.
I built a 406 several years ago with 10:1 compression, cast iron Dart heads (that didn't have a modern combustion chamber) and I ran a custom 230/240 at .050 cam in it. It ran fine on the 94 octane pump gas with a good tune. But I kept timing to 32 degrees total to be safe and because it was finicky, on the dyno it liked 36. I drove it daily for 3 years putting 30,000 miles on it before pulling the motor to sell the car as a roller.

I kept the engine as it sat for 2 years. I decided to toss it in my 71 Ventura. Before I did I pulled it apart to have a look at things, and decided to swap the camshaft to a Mutha Thumper while I was in there. This camshaft has alot of overlap and bleeds off low speed cylinder pressure. Just the ticket for a 10:1 motor with cast iron heads, especially since I was now in AZ with only 91 octane.

Nothing else changed, just the camshaft, which changed the dynamic compression ratio to the point that it ran beautiful on 91 octane with the timing back up to 36 total.

Just shows how other things can affect what you get away with.

[Pontiaco]

so on a stock bottom end ls1, how many cc's I need to get 11.5:1?

[Firebirdjones]

Without actually measuring anything a rough cc estimate for 11.5:1 compression on a stock LS1 would need in the neighborhood of a 60cc chamber.

[PFM]

ok I guess I'm 4 years behind, so what is the max C/R on 93 oct?

The DCR has more to do with what octane fuel you have to run. The SCR like we are talking about here can have a lower or higher value depending on the valvetrain setup.