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Does anyone know this? I can't remeber were I saw this but what I remember is something like for each pis of boost equals 16 hp. Let me know what's up.
 

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Thinking Man's Engine
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From talking to one of Craig Paisley's crew members:

For every 14 psi of boost, you double the horsepower (from a naturally aspirated engine).
 

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so how much horses do you think the rex would have without the turbo? just curious
 

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The engine in the WRX is made for a turbo. It runs lower compression than say a honda engine. In the WRX it is about 8:1 and a Honda is about 11:1. If you took the turbo out and actually got it running well it would get beat down by a Yugo. This is one heavy little car made to be turboed.
 

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I know this is probably stupid to revive this incredibly old thread, but I found this query kind of interesting.

First off, I agree with Tan 14psi = doubled hp over natural aspiration

Baluch on the other hand...thats an overgeneralization and psi/hp is relative to the original performance of an engine.

Here's the theory.

Assuming tuning is done correctly, you get a stoichiometric mix of O2 and fuel igniting in the combustion chamber. We can establish that we have a set ratio of oxygen and fuel and it should never change. So if we dump in twice as much gas then we MUST have twice as much oxygen for proper combustion.

On planet Earth, there is a constant air pressure, 14.7 psi at sea level (this is the base air pressure in the combustion for all non turbo vehicles). So without turbo on a car, people can honestly say they are running their cars slightly over 14psi (relative to the vacuum of space anyways).

We indirectly measure amount of gas particles with pressure, so if we turbo our cars to lets say 14.7 psi (on top of the 14.7 psi the Earth already gives us [totalling 29.4psi]) then we effectively have twice as much oxygen before ignition. Therefore the amt of fuel being pumped in is doubled, then at ignition we should theoretically get doubled the explosive power. So yeah, as Tan said if you do a 14 psi boost then you've nearly doubled the amount of oxygen in your turboed engine for double the power.

Of course you lose potential power the higher you go because you encounter more resistance in the change of inertia of the internal components.

So if your NA car makes about 100 hp
-Boosting it to 14.7 psi will theoretically give you 200hp
-Boosting it to 7.35 psi will theoretically give you 150hp and so on
[ (HP of NA car) x (1 + (boost psi/14.7)) = HP at boost psi ]


As for Baluch, his numbers are close enough but not for all engines. If you want an easy psi to hp conversion just divide your NA hp by 14.7 and that's it.

-If your Suby is 147 hp NATURALLY ASPIRATED stock then, sure, 1psi boost = 10 hp (147/14.7)
-But for a car that is 240 hp NA stock, a turbo would yield an equivalency of 1psi = 16.3hp

To put it more accurately for Baluch, every 1 psi will get you approx 6.8% extra hp over a naturally aspirated setup (again, theoretical).

Cheers
 

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Friendly Neighborhood Spider-Admin
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Just think, many of our younger posters were in 4th grade when this thread was started.
 

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Friendly Neighborhood Spider-Admin
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tan hasn't posted since 2005..our loss; he was a wealth of knowledge, IIRC.
 

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LOL, actual responses. Yeah, I did a quick search on the topic and this one was one of the first ones that came up. And since I am a proud new Suby owner, I decided to check this thread out.

So is that true a pound of boost equals 10 hp?
I suppose, but remember its only guess. I would ask other members that has played around with turbo. Although there's only a handful that are brave enough to turbo their NA cars, we can calculate backwards what a WRX or STi might have in terms of a NA HP.

It'd be nice to get some real numbers. All that is really needed is just Dynoed HP and corresponding air pressure. Then the rest is basically algebra. In fact if people are willing enough to dump enough numbers in this thread. We can actually calculate the rate of inefficiency turbo gets as the PSI values go higher.

I hope none of you guys are one of those that think having a turbo makes your car run more efficiently.
 

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LOL, actual responses. Yeah, I did a quick search on the topic and this one was one of the first ones that came up. And since I am a proud new Suby owner, I decided to check this thread out.



I suppose, but remember its only guess. I would ask other members that has played around with turbo. Although there's only a handful that are brave enough to turbo their NA cars, we can calculate backwards what a WRX or STi might have in terms of a NA HP.

It'd be nice to get some real numbers. All that is really needed is just Dynoed HP and corresponding air pressure. Then the rest is basically algebra. In fact if people are willing enough to dump enough numbers in this thread. We can actually calculate the rate of inefficiency turbo gets as the PSI values go higher.

I hope none of you guys are one of those that think having a turbo makes your car run more efficiently.
You will only be able to possibly calculate for specific turbos with specific operating parameters, but it will still be close to impossible. A larger turbo will push more CFM. Air/fuel ratio ,timing, and temperature changes will also change the outcome. There are too many variable to even fathom a solid number.

And yes, a turbocharger does increase the efficiency of an engine by using the engine's waste product to increase power.
 

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So is that true a pound of boost equals 10 hp?


I would say no. Of course in some instances it might, but there are also cases where your hp will go down. If you're out of the efficiency range of your turbo adding more boost isn't going to do you any good. And some turbos will make 100hp more with the same, or even less boost than a much smaller turbo.

Compare someone running a td04 @ 17psi to someone else running a 35r @ 14 psi. I guarantee the car with the 35r will be making much more powa.
 

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I'm gunna have to agree with MainFrame on this one.
 

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And yes, a turbocharger does increase the efficiency of an engine by using the engine's waste product to increase power.
Ah ha! Another person who uses the "waste product" explanation. While we automatically think that turning "waste" into power is actually being efficient, it actually isn't. Don't forget your car still has to fight against the backpressure the turbo is making. Having a bigger exhaust can't help too much since your bottleneck is the turbo. The turbo in itself is an obstruction and your engine still has to fight against it.

So I am sorry, I have to whole heartedly disagree with the efficiency issue.

In this instance , I agree that the hp gains that I theoretically calculated is too simple. In fact, the turbo being a burden itself as backpressure just proves itself as a huge factor that keeps you from getting that ideal hp to psi ratio of a perfectly frictionless world.
 

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Super Modulator
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lol I've never seen a bump like this before...

Henry H, while you're down there, mind digging up a few dead sea scrolls?
 

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Ah ha! Another person who uses the "waste product" explanation. While we automatically think that turning "waste" into power is actually being efficient, it actually isn't. Don't forget your car still has to fight against the backpressure the turbo is making. Having a bigger exhaust can't help too much since your bottleneck is the turbo. The turbo in itself is an obstruction and your engine still has to fight against it.

So I am sorry, I have to whole heartedly disagree with the efficiency issue.
You are correct that the turbocharger creates more backpressure, but the simple fact is that the turbocharger adds much more power than what is needed to run itself by using the waste product of the engine.

It's really not a debate, it's a fact, so I'll try to explain it to you.

1: Take an atmospheric square 1.5L 4cyl engine that produces 250hp which is about the limits of today's technology without forced induction.
2: Simply bolt a small turbocharger to the engine and tune for correct fuel and timing under low boost (lets say 6psi) with no other modifications. This engine will now produce approx. 300chp.

Lets say the turbocharger added 70chp. I'll give you the benefit of the doubt and swing a guess that the engine needs about 20hp to overcome the added backpressure of pressurizing the intake. That leaves a 50hp power gain and much better efficiency as the topped out NA engine is now making much more HP that it was capable of without the turbocharger. Is a turbocharger 100% effective? No, but it does increase efficiency. You're confused by the laws of physics. There is no such thing as free power, but using the hot gasses that simply get vented in the atmosphere to spin a turbine and increase efficiency is brilliant.

The turbocharger has increased the engines volumetric efficiency. Forced induction engines always have better VE than NA engines. If the turbocharger only made a 1% increase in power over the power it took to spin it, it would still be more efficient.

So to reiterate, there is no debate, just a lack of understanding on your end.


Here, I also gave you a free Google search. Read up a little before you mis-inform any of my members here Sonny. Turbocharger - Wikipedia, the free encyclopedia
 
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