JimiHendrix

Notice a number of people with the bigger cams use thinner head gaskets with bigger cams like the G6x3, Vindicator, Brian Tooley stage 3+. Usually to get about 11.4:1 compression or better.

How much better are the manners and horsepower with this seemingly small amount of compression increase from 10.9:1 to 11.4:1? Assuming the usual bolt-ons?

JimiHendrix

Bumpy bang bang...

Dano523

As long as you have the valve clearance to the top of the pistons, the higher the compression, the more power you are going to make.

But at the same note, the higher the compression, the higher the octane fuel you will need to run.

Hence the reason for the drop in compression on the LS3, was it allows the motor to only need a octane rating of 91 to run it best. On the LS2 with higher compression, it requires a octane rating of 93 to run it best instead.

Note, if you are going to run a blower, leave the compression low, and bring the pressure up with the blower isntead.

JimiHendrix

Thanks Dano! Anyone else wanna chime in? bump!

Kingtal0n

Depends on the fuel you are comfortable using for the distance you drive. For example I drive everywhere, 100miles+/day, so the car needs to run on 87 in a worst case scenario. 9.5:1 compression was more than enough for me. When 93 is available, I can use boost 12~psi and when Methanol is available 18~psi is fine. If E85 was available I could use 25-30psi of boost. See how the fuel choice gradually opens up options for more boost?

Without boost its kind of a nickle and dimes thing. You nickel yourself a couple percentage of power but at the same time it shoe-horns you into this car that only takes the most expensive fuel, and leaves you stranded if you can't get it, and all without the additional 400~ or whatever horsepower that boost provides at lower compression ratio.

z06scentair

To answer your question about driving manners is Yes, it will help with low end cruising. The bump in compression by .5 point will assist in making in less slugish on the bottom end.

The higher compression will also allow for less timing up top.

xBoostx

Compression Yes it works great check with ptv clearance.

Kingtal0n

When the auto manufacturer designs an engine, the engineers know all about compression and the extra power and economy. That is why it tends to go up year to year. But if they know about it already, why didn't that use "all of it" in the first place? In the first year?

Q: What changed that allows them to use more compression as years increase?

A: List of some things that changed, as 'old' combustion tech becomes 'new':
Direct Injection
Combustion chamber shape tech
piston surface shape tech
piston materials science
heat transfer to cylinder wall and valve properties
heat transfer from ring to wall property
Aluminum heads
fuel quality (got better? got worse? it changed some ways, maybe both)
general materials science and manufacturing tolerances, better alloys

...Add to the list a fun favorite if you want


Once we account for all this possible tech, you get a range of acceptable ratios for best and worst case situations. Best case is best fuel, what 91? 93? 97 in Japan on the pump I think is normal for them. So it depends where you live, that is a factor of compression. If you happen to own a plane and a hanger with 30x 55 gallon drums of aviation fuel, well, it only really helps you in the range of the hanger, which affects the range of the vehicle, since you can't go farther than the return trip uses all of the fuel that is in the hanger. So now you also need to consider how far you want to go with it, and where you will get the fuel along the way, or else how to carry more fuel. Or use lighter fuel. Or tune the engine and gearing for better Miles per Gallon, which means the fuel lasts longer, you have increased vehicle range.