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.
- Turbo Size
- Compression Ratio
- 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
Psi, in short is the positive pressure created by forced air into the engine by a turbo or supercharger. With a higher air volume and increased fuel, we can see a huge jump in power output. 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 so much more air, resulting in much more power.
Fuel and Compression Ratio:
These 2 directly influence one another. But let's 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 of 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 compression motor on pump gas 93 octane, detonation may not happen at all until you are making some serious power (600 +) But with 10:5:1 compression motor you will start detonating at a much lower power rating (probably much closer to the low 400hp range), because of the increase in cylinder pressure and normally an increase in heat. 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 or q16 on a high compression motor with turbos, to keep the engine happy.
A vast majority of people who own turbo cars, have probably heard in passing about the limited power they can make on stock parts, such as injectors, exhaust, intercooler etc. assuming a stock turbo car such as a 300zx tt, or stock supra, has no supporting modifications they will run out of fuel injector relatively quickly as they increase boost/psi. Now as soon as they upgrade injectors, intercooler, downpipes, exhaust, intake, clutch etc, they will no longer be limited to that mid 300hp range, and will be able to run "more psi."
One question I've gotten a lot is " How much power can I make at (blank) psi?" well I can't 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.
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 turbo car will make the same power with the same modifications. Your engine health, air temp, altitude, quality of fuel, humidity etc all have an effect on the power you make.
By: Ocean Nickel
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