Is it true that compression higher than 10:1, 91 octane gas is supposed to be used?

 

Should have the 5.3 in it. 9.4:1. Regular should be fine.

 

thunder550, So using 89/ 87 would be ok? The only performance done on my 5.3 engine is adding JBA Headers, Open air intake, and an exhaust system. What can increase my compression ratio? Just curious.

 

87 will be fine. Compression can be raised by shaving the heads, using a head with a smaller combustion chamber, or using domed pistons.

 

The owners manual will tell you what octane fuel to use. If I remember correctly it says to use fuel with an octane rating of 87 or higher.
To change your static compression ratio you need to make changes to your engine (mill the heads, thinner head gasket, etc) or your cam selection can alter effective compression ratio (there is an actual name for this but I am having brain lock) by changing your camshaft durations.

 

There's two types of compression ratios. Dynamic and static.

Static is just your bottom dead center (largest) cylinder volume divided by your top dead center (smallest) cylinder volume. The only way to change this is to change the relationship between these two values, like changing piston design, or changing to a cylinder head with a different sized combustion chamber.

Dynamic takes into account valve events. Most cams don't close the valves directly at bottom dead center, so there is a little bit of compression lost between the time the piston starts its upstroke and when the valve actually closes. You can change your dynamic compression ratio by changing valvetrain components, like a cam or rocker arms.

The SCR of my engine is 9.4:1, but the DCR may only be 8.2:1. DCR is always less than SCR.

Nothing that you have done so far will change your compression ratio.

 

All this time using 91 octane, I could of saved money on gas. Another question, if my mileage is really high, say over 100K. Do I need to use a higher ocatne. My co worker says, carbon accumulates in the combustion chambers which results compression ratio rises???? is that true?

 

I really don't think it's necessary. You could run a can of seafoam through your engine though, should clean out the top end of the engine really well and remove any carbon deposits that have built up.

 

do you think you save that much money between the two?

26gallon tank difference between 93 octane and 87 is 6 bucks!!!!!!!!!!

 

Sea Foam is supposed to be good (O'Reilly and others carry it). It's about $6 a bottle here. It has other uses,too...read label.

BG 44K is supposed to be very good at cleaning the fuel system and valves/combustion chamber. It's not avalable at regular AP stores as far as I know. Check yellow pages. It's $15 or more per can.