# Naturally aspirated nissan gets new pistons



## yiotis (Dec 23, 2004)

As i stated above a have no turbo engine but i intend to install a turbokit later when my car is ready to accept it(still have to change lots of things)
Anyway are the new pistons going to help the car's performance increase and by what margin? Also i will probably need more fuel to the engine so i will need a new fuel pump and bigger fuel injectors correct? Also please tell me if there is something else i need to know on this specific upgrade.
THX


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## psuLemon (Apr 23, 2003)

Detail, they elude you right now. what kind of car, what motor, etc.. come on, we can't say without info


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## yiotis (Dec 23, 2004)

What's the point oh knowing the motor since all cars follow the same philosophy?Anyway the motor is QG15DE(GA15DE American version)


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## psuLemon (Apr 23, 2003)

yiotis said:


> What's the point oh knowing the motor since all cars follow the same philosophy?Anyway the motor is QG15DE(GA15DE American version)


there is no american ga15de, there is a south african and mexican. secondly, motors like the sr20 have pistons already out, while the ga16de you would have to get custom pistons. plus the ga16de has very thins walls in which you can barely bore so there would not be much of a point. lastly, unless you are running extreme boost (as wes is hittin 252whp on 14 psi on stock internals) there really is no point.


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## alexnds (Oct 1, 2005)

*New pistons and adding turbo later*



yiotis said:


> As i stated above a have no turbo engine but i intend to install a turbokit later when my car is ready to accept it(still have to change lots of things)
> Anyway are the new pistons going to help the car's performance increase and by what margin? Also i will probably need more fuel to the engine so i will need a new fuel pump and bigger fuel injectors correct? Also please tell me if there is something else i need to know on this specific upgrade.
> THX


This is general advice. A car that will run with alot of power, without a power adder, has a compression ratio of 10:1 . Any higher than that, such as 11:1 and you risk serious pinging or knock. you'd need gasoline of over 100+ octane, or race gas, if your compression ratio was let's say 11:1.

Now then, any motor that has a power adder, such as super charging, or turbo-charging, usually has alot lower compression ratio of 8:1. Since you're stuffing the cylinder with more pressure from the Turbo or SC, you need lower compression.

If you use regular pistons for your motor, and the machine shop measures the valve clearence and other factors, and tells you your compression ratio is 9.5:1, let's say, you're generally limited to a maximum of 6PSI of boost and any more boost than than will blow up your motor. However, if your compression ratio is 8:1, you can probably use 20 PSI of boost and you'd be ok. That's the point I'm trying to make.

The ignition timing may need to be retarded as well, and bigger fuel injectors. You'd need a different ECU map for air-to-fuel ratio for a car under boost than on motor alone.

The oil control ring is different for a turbo car than a regular car. It's slightly different distance from the other 2 rings. 

Basically, before you rebuild the motor, decide up front if you want a naturally aspirated motor or a boosted motor. If you are going to go for a boosted motor, make sure you have a strong bottom end and a crank that's been magnafluxed.


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## psuLemon (Apr 23, 2003)

and the problem with generalizing is that many cars act different due to head and block combinations. for example the GA16de, has a cast iron block, i believe the crank is forged. it runs 9.1:1 compression and can run at least 14.5psi putting out 252whp and 220whp (this is proven by Wes) and the only restriction so for is the MAF and ECU air/fuel set up. this is why i initially asked what the motor was and the car its goin into because there are other variables. Secondly, lowering the compression to 8.1:1 seriously degrades the driveability as you will have to run higher octanes and sometimes even leaded race fuel on certain setups.


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## alexnds (Oct 1, 2005)

*Lower compression vs Higher compression*



psuLemon said:


> and the problem with generalizing is that many cars act different due to head and block combinations. for example the GA16de, has a cast iron block, i believe the crank is forged. it runs 9.1:1 compression and can run at least 14.5psi putting out 252whp and 220whp (this is proven by Wes) and the only restriction so for is the MAF and ECU air/fuel set up. this is why i initially asked what the motor was and the car its goin into because there are other variables. Secondly, lowering the compression to 8.1:1 seriously degrades the driveability as you will have to run higher octanes and sometimes even leaded race fuel on certain setups.


Quick Note: Lowering compression in fact requires LOWER octane fuel and Higher compression requires HIGHER octane fuel to avoid ping. In fact, you have it backwards. The only reason I mentioned that compression needs to be signficantly lowered is if the person plans to run SIGNIFICANT boost. Since the power in the engine is tied heavily to boost, to protect the engine from detonation and knock or pre-ignition, on such a motor, it 's built with lower comression. Now then, a motor with low compression doesn't have poor driveability problems. It's simply low on power if not boosted in relationship to the same size motor that is running higher compression.

THe basic idea is volumetric efficiency. Whether is naturally aspirated, and high compression and uses variable valve timing, or it's boosted by turbo or SC, your goal is higher volumetric efficiency.

A volumetric efficiency of 1:1 was considered good in the old days. So for instance, if I developed 1 HP per 1 Cubic inch of displacement, I had a volumetric efficiency of 1:1. So, a 350 Chevy (5.7 Liter) with 350 HP was good. So a 302 Cubic inch (4.9 Liter) Mustang at 302 Horsepower was likewise good.

These engines were limited in their ability to produce more than 1 HP per 1 cubic inch because they are OHV , or pushrod engines. Our Nissan engines are SOHC or DOHC. So you're seeing the Nissan Maxima at 3.5 Liters, or about 189 Cubic inches, putting out 235 HP!! So if you do the math, it has a volumetic efficiency of almost 1.4:1. How does it achieve so much power from so little displacement? Simple: higher compression combined with optimized breathing and variable valve timing give higher volumetric efficiency. By contrast, a lower compression motor, but the same size, say 3.5 Liters, like a truck motor, with 9:1 compression ratio instead of 10.5:1 compression ratio, and no variable valve timing might only give out 190 HP.

So basically, the answer comes down to volumetric efficiency. In a pushrod engine, bigger is better. If you can do volumetric efficiency of 1.1:1, and your motor is 454 Cubic inches (8.0 Liters) you'll be doing better than 454 HP.

By the same token, if your motor is small, say 3.0 Liters, but turbocharged, you have a smaller displacement creating more power, because of higher volumetric efficiency than a bigger motor that is naturally aspirated. So, a 3.0 Liter turbo, (toyota Supra) can put out same horsepower, roughly, as a 5.7 Liter Chevy Camaro. So the difference of 2.7 Liters, or almost twice the displacement, is overcome by raising the volumetric efficiency via turbo.


The lower compression suggestion was given as an idea for the person that wants to do alot of boost. Lowering compression in fact, LOWERS volumetric efficiency, but it is then raised back up significantly via boost, but the motor is protected from destroying itself during high boost levels, since it was built to rely on boost as power adder.


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## snowcrash1984 (Sep 22, 2005)

MMM, it’s kind of incorrect to compare a 3.0 inline 6 from Toyota to a 5.7 v8 Chevy. I just don’t see a fair comparison if any between a turbo 6 and NA 8 in volumetric efficiency. Besides, how would you explain then that people get all kinds of gain out of 3.0 and 5.7L? I’ve heard of 5.7L getting as much as 600hp NA with solid roller bump sticks. You just lost me in comparison.


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## psuLemon (Apr 23, 2003)

snowcrash1984 said:


> MMM, it’s kind of incorrect to compare a 3.0 inline 6 from Toyota to a 5.7 v8 Chevy. I just don’t see a fair comparison if any between a turbo 6 and NA 8 in volumetric efficiency. Besides, how would you explain then that people get all kinds of gain out of 3.0 and 5.7L? I’ve heard of 5.7L getting as much as 600hp NA with solid roller bump sticks. You just lost me in comparison.


his comparison is just comparing the efficiencies of non turbo vs turbo. a turbo is a more efficient way of bring power to a car. But lowering compression, you will enable a car to become more efficient.


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