KA24DE lower compression pistons

I just had an Epiphany. But shoot me down if I'm wrong. If I put 8.5:1 forged pistons in a KA there is more room for air and fuel that can be forced in there. So I will have to run more boost but that also means I can run more fuel also. More fuel+more air=more power...right? :naughty:

yes... but theirs always exceptions... like the engine itself and tuneing

What kind of exceptions? and why do they say 8.5:1 pistons are the best for turbos?

Folks lower compression ratios so that the engine is more boost-friendly. In most cases, high compression and boost do not mix. You might see a few cars with 10:1 ratios and boost. Many VQ-powered Maximas do this.

However, most folks go with a lower compression if they can, and 8.5 isn't the only ratio used. For example, I believe the Evos use 8.8 or something. Honda guys typically just go down to 9:1.

Anyway, if you want low comp pistons for a KA, look in the Nissan Motorsports catalog.

Ok, here goes... try to follow allong.

If you get 8.5:1 compression pistons then yes, you are going to have more room in the combustion chamber for more air. Keep in mind though that since you lowered your compression, your going to need to boost more to get the same power out of a higher compression lower boost setup. If you get 8.5:1 compression pistons then you are going to have approximately 0.5725 in³ more room in the combustion chamber assuming that these are going into a DOHC KA that was previously equiped with the stock 9.5:1 compression pistons. This is figured out using the displacement volume along with the clearance volume. In N/A form, compression is referred to as static compression which means the amount that the air inside the cylinder is compressed. When a form of forced induction such as a turbocharger or supercharger is added, compression is referred to as effective compression.
How to figure out your efective compression:
(Boost / 14.7) + 1) x Stock Compression = Effective Compression

A general rule that you should follow is that you should not exceed an 18:1 or 19:1 Effective Compression while running on available "premium" piss gas. With very good tuning, a 20:1 effective compression is achievable on pump gas. On some C16 race gas, effective compression ratios of 25:1-26:1 can be run on street cars with good tuning and proper preperation.

So say that you are running 8.5:1 compression pistons. To get an effective compression of 18:1, you are going to need to run approx. 16.5 psi of boost.
If you were running 9.5:1 compression pistons, then you would only need to run about 13 psi to achieve the same amount of power.

I'm not saying to go out and buy super high compression pistons so that you can run low amounts of boost and still get the same power, because at a certain point, the high compression:low boost ratio would no longer be worth it. With a higher compression, it will have more low end torque and power due to the higher compression before the boost starts building.

I don't care what anybody says. You are the man. This is exactly what I was looking for. :biggrin:

hey jspec u math wiz, whats about the most Compression you could run, with good tuning, on pump gas for N/A applications? this would be some good knowledge for the peeps too.

yeah does anyone know how fast you would run if you get new pistons for lower compression, turbo, intake+exhaust and headers how fast that would run you in a 1/4 mile?? My friend said my car could run 11s but that seems kind of stretching it

I hope that was a joke, if not thats the stupidest thing I read all day

hey jspec u math wiz, whats about the most Compression you could run, with good tuning, on pump gas for N/A applications? this would be some good knowledge for the peeps too.

i'd like to hear that too.

im too rusty in math to figure it out, last time I did anything more complicated then 2+2 was back in High School lmao. I also have noticed my writing skills have diminished since Im not writing essays everyday and taking tests.

hey jspec u math wiz, whats about the most Compression you could run, with good tuning, on pump gas for N/A applications? this would be some good knowledge for the peeps too.

hehe, I don't believe in N/A power.... ;) haha j/k. The highest compression on a N/A street car I've seen is 13:1 on a Type R. That's pretty damn high for a street driven car running on 93 octane pump gas. For race applications you can go crazy. Some race cars like drag cars or those oval drivers, run compression as high as 17:1. Don't even THINK about running this in a street car unless if you have some super low specific gravity fuel. I'm talking about fuel like C46 which has a specific gravity of .68 at 60 degrees Farenheit I think.