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Lets Talk About Boost

 

In any car community, you have your knowledgeable veterans, your active learners, and the guys and girls that have just bought their first car. No matter who or where you are, or how much you know, you are first and foremost a person and a car enthusiast. That being said im going to address a question i get on a day to day basis, and that question is this. "How much psi can i run?"

Well lets talk about this. There are 4 main things when considering how much psi you can run.

  1. Turbo Size
  2. Fuel
  3. Compression Ratio
  4. Supporting Modifications

The generic question of "how much psi can i run?" simply cannot be answered without knowing the above 4. Lets talk about turbo size first

 

Turbo Size:

Psi, in short is the positive pressure created by forced air into the engine by a turbo or supercharger. And we can all agree that the more air and fuel that is going into an engine will create more hp then less air and less fuel. But not all psi/boost is created equal. For instance a small gt2560 turbo at 20psi only flows half the air of lets say a gt3076 at the same psi.. Yes they are producing the same psi, but the larger turbo is flowing twice the amount of air, meaning it is creating much more power. 

 

Fuel and Compression Ratio:

These 2 directly influence one another. But lets talk about fueling first. When trying to figure out what psi level you can run you need to think about what fuel you are using. The simple way of explaining this is, the lower the octane, the less boost/psi you can run. This is because a lower octane level fuel will be more prone to pre-detonation which can shred a motor. Now how does this have anything to do with compression ratio you might ask. Well the higher the compression ratio the quicker you will detonate on low octane fuels. Here is an example: with a 8:5:1 (stock tt compression) on pump gas 93 octane, detonation may not happen at all until you are making some serious power 650+, But with 10:5:1 (stock NA compression) with stock twins you will start to pre-detonate at the low 400hp mark. Same fuel, but the massive difference in compression ratio increases chances of pre-detonation on low octane. This does not mean that a higher compression ratio is worse for a turbo application, actually quite the opposite. However you will need to run a higher octane fuel such as e85. 

 

Supporting Modifications:

Im sure a vast majority of twin turbo owners have at least heard in passing that with stock injectors you shouldnt run more then 14-15psi assuming everything else is stock. This is mostly because you dont have any supporting modifications to run more psi. If you upgraded your injectors, exhaust, smics, intercooler piping, intake ect ect, you would be able to make more power at the same psi and be allowed to up your psi higher without maxing out injectors. 

 

One question ive gotten a lot is " How much power can i make at (blank) psi?" well i cant answer that without knowing the above 4. Running gt3076 twins, 2000cc injectors with all supporting modifications with a 10:5:1 compression ratio on e85, can make over 1000hp... but your setup might be very different.

 

Conclusion:

In my opinion, especially if you are new to cars or boost in general, worry about supporting modifications for your setup, and running the right fuel for your needs before worrying about what psi you can run. Take all 4 points into account before trying to figure out what amount of boost you can run. Lastly not every single 300zx will make the same power with the same modifications. your engine health, air temp, altitude, quality of fuel, humidity ect all have an effect on the power you make. 

 

As always, continue to learn, continue to grow, and have an amazing day.

 

By: Ocean Christmas Nickel

 

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