Is 11.2:1 compression too much for pump gas.
Is 11.2:1 compression too much for pump gas. Do to my current motor issue I'm have to put a motor together from spare parts. I have a 6.0l short block and the 59cc stage 2 ls6 heads off of my 5.7 and the compression will be about 11.2:1 with a .060 headgasket. Will that be too much for 93 octane or should I get a .075 headgasket to lower it to 10.9:1. The only other thing I can do is to put my stock 5.7 heads on it but I would really like to have my ported heads on it.
Teching In
Joined: Jan 2004
Posts: 17
Likes: 0
From: Marietta, GA
Here's my experience with an LS6 427 running 11:1 compression at the
dragstrip. I use a 50/50 mix of 93/100 octane. I had the engine apart after a couple of hundred runs and no sign of detonation on the piston tops.
dragstrip. I use a 50/50 mix of 93/100 octane. I had the engine apart after a couple of hundred runs and no sign of detonation on the piston tops.
i at 10.98:1 here in Texas. 93 is what i run. it also has a lot to do with how high you DCR is. if its in the high side will be more prone to knock, but your F13 you should be fine.
There are some here such as Patrick running close to 11.5:1 on pump gas even with a mild cam. To safely run this high, you need to be careful to details such as quench and cam overlap. A tight quench allows more compression because the burn is more complete.
Jason
Jason
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TECH Senior Member
Joined: Mar 2004
Posts: 14,620
Likes: 17
From: BFE
Originally Posted by racer7088
It depends on the cam but with the larger ones I run 11-11.25 all the time with no issues. On the smaller cams I wouldn't run quite as much.
BTW, running colder plugs help too
TECH Senior Member
Joined: Mar 2004
Posts: 14,620
Likes: 17
From: BFE
Guys, just so thaT it is clear:
DCR- DYNAMIC COMPRESSION RATIO
Is the determining factor, not SCR (not completely)
You could have a 13:1 motor run on pump gas if the DCR is low enough.
On average:
<8.5 OK on 91
8.5>8.7 Higher octane recommended (but not absolutely necessary)
>8.7 93+ Octane
Ways to combat detonation and run higher compression:
> Colder plugs
> tighter quench (squish)
> More quench area (dual like AFR)
> Tuning
DCR- DYNAMIC COMPRESSION RATIO
Is the determining factor, not SCR (not completely)
You could have a 13:1 motor run on pump gas if the DCR is low enough.
On average:
<8.5 OK on 91
8.5>8.7 Higher octane recommended (but not absolutely necessary)
>8.7 93+ Octane
Ways to combat detonation and run higher compression:
> Colder plugs
> tighter quench (squish)
> More quench area (dual like AFR
)> Tuning
TECH Resident
Joined: Jul 2005
Posts: 861
Likes: 0
From: Midland
Originally Posted by PREDATOR-Z
Guys, just so thaT it is clear:
DCR- DYNAMIC COMPRESSION RATIO
Is the determining factor, not SCR (not completely)
You could have a 13:1 motor run on pump gas if the DCR is low enough.
On average:
<8.5 OK on 91
8.5>8.7 Higher octane recommended (but not absolutely necessary)
>8.7 93+ Octane
Ways to combat detonation and run higher compression:
> Colder plugs
> tighter quench (squish)
> More quench area (dual like AFR)
> Tuning
DCR- DYNAMIC COMPRESSION RATIO
Is the determining factor, not SCR (not completely)
You could have a 13:1 motor run on pump gas if the DCR is low enough.
On average:
<8.5 OK on 91
8.5>8.7 Higher octane recommended (but not absolutely necessary)
>8.7 93+ Octane
Ways to combat detonation and run higher compression:
> Colder plugs
> tighter quench (squish)
> More quench area (dual like AFR
)> Tuning
Originally Posted by 91Z28
If 8.7 requires 93, what is the limit to what 93 octane will be sufficient for? I've never found this kind of info before.
Coolant Temps
Ambient Air/Inlet Air Temps
Underhood Temps
PCV System - Oil/Carbon deposits in the combustion chamber
Coatings on the valves/pistons/combustion chambers
I'm sure there's more than that - but there's lots of good reading in these two articles.
http://www.popularhotrodding.com/tec...power_squeeze/
http://www.popularhotrodding.com/tec...ression_ratio/
