Need a compression lesson...

There are some all motor FJ members out there that have experience with high compression Foci so I suggest you talk to them (or PM them)... mycannon and CTZX3 are nearly running 13's all motor with a ported head and hightened (mispell) compression..

From my experience, high compression is really good if you're going all motor. Usually when you're running turbo or even a supercharger it's actually better to take down your compression levels. I had a lot of experience working with all motor Hondas and I learned that changing your compression by 1 ponit or even .5 of a ponit well make a big difference. By "difference" I don't just mean dyno numbers but also horsepower mainly in the high rpm areas.
The higher compression doesn't only give you more "bang" on compression but also let's in more airflow as stated earlier by the other FJ member.

Disadvantages of higher compression is that you need more higher octane gas (as stated by the other FJ member). My friend's GS-R has 10.5: 1 compression and has to use 93 octane gas ( I think the Foci SVT does the same). There is also alot of work making an high compression motor run well such as camshaft timing but that's always an issue with any car when it comes to camshaft timing.

You're just getting the head milled? Have you seen the ports on a stock head before?, It looks like damn sidewalk concrete I'd suggest buying one of Tom's heads. [censored], get it ported somewhere...

But, as mentioned before in other threads, DO NOT take your head to someone who usually ports V8 heads. They will port into the water jackets and give you your head back looking like a piece of rat infested cheese, which is now trash.

for what's it worth...might clarify what dj said:

stock head:



My FC stage 3 head:





quiet a difference, ey.

You need to tell then how much to take off...This is what to tell them.

.0155 in. = 10.0
.0309 in. = 10.5
.04 in. = 10.8
.0459 in. = 11.0
.05 in. = 11.15

The higher compression doesn't only give you more "bang" on compression but also let's in more airflow as stated earlier by the other FJ member.

Click to expand...

<font color="red"> CAREFUL</font>.......higher compression does <font color="red"> NOT </font> allow for more airflow.......every engine can be "mapped" for power using a p-V diagram.......for those who do not know, this is a diagram plotting 1 cylinders changing volume and the "current" cylinder pressure at each time increment, usually measured in 0.1 crank angle degrees.......power of an engine is defined as the integral of pressure with respect to volume.....this can also be looked at as what would be the average pressure seen during the expansion and intake stroke - the average pressure seen during the compression and exhaust stoke(multiplied by the swept volume or engine displacemet)........now on to compression ratio.......increasing an engine's compression ratio increases the cylinder pressures near TDC......then you combust and the effect multiplys.......raising your "averaged pressure" and resulting in MORE POWER.........pros: you get more power.......cons: you might need to run a higher octane fuel to prevent auto-ignition (pinging).......also all that added pressure does indeed stress the engine components more and shorten their life, is it enough to notice?....only if you go wild with the compression ratio.....
...not sure if i explained this very well, let me know if it doesn't make sense.....

Usually during NOS and force induction the compression ration is usually lowered since they usually make the pistons work harder then usual. To keep this danger from happening many people lower their compression. For example the GM Caviliar Ecotec's motor has about 10:1 compression but they were forced to lower it to 8.6:1 to keep it from "knocking".

But since Ollie18's friend ran NOS without a lower compression I could be wrong but I doubt it.
Maybe it had to do with his stage 3 head?