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How much horse power is in 1 psi?

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There are too many variables (cylinders, displacement, comp ratio, turbo size, etc) to set a 1 PSI= X HP, but for most of our applications, I think your number is acceptable. Somewhere around 5-7. Your relationship of the 99 NT and 99 T is justified by this.

However, like I said before, it's definitely motor specific, and pretty much turbo specific. Imagine a V-10 Viper, do you think if you added a turbo with 5 psi you would only add 30 or so HP?

As such, it's a pretty broad generalization to begin with, unless you have the same displacement, compression ratio and turbo as someone else and are comparing between the two cars.

My .02

edit: I realize now we are talking about the 420a and 4g63 T, but the relationship of the motors is similar enough, I suppose.
 
^ Very well said, and he is 100% right on that. There is more variables to it, not all setups or motors will make the same HP-PSI ratio.
 
2G Non-Turbo has 11:1 compression
2G Turbo has 8.5:1 compression
1G Turbo has 7.8:1 compression

There are entirely to many variables to contend with for this kinda of question. At least for me. Not to mention it's Monday and I'm not going to wake up until at least Wednesday.
 
^^^ Gonna have to agree. Unless you are wondering how much more HP you will get from more PSI with your setup, or comparing the exact same setup in two identical cars, you'd be better off not saying this around anyone, as you will either get made fun of or pollute other newbie's minds with information that is only true in some specific context. Then they will go on saying it's BS that "some dude" made 1000 hp on his 1g (ahem) running 40 psi, because 195 + 40x6.25=445. Get the drift?
 
Yes, Your doing the math right, but the second gen DSMs non-turbos use the 420A Chrysler built engine, rather than the 4g63 Mitsubishi engine in the turbo models. Coincidently both the engines have the same liters, 2.0, and have the the same valve train system ,DOHC. So they are very comparable in terms of power gains with PSI because the PSI is distributed to the same 2.0 liters of displacement. :thumb:
 
well i looked into it more and your are right

http://truetex.com/aircompressors.htm

that site says everything and explains what you guys said but in more detail and they show and explain using formulas and everything.

I think that 6.25 hp is a good estimate on what 1 psi will give you or no?
 
I think it's better to speak in terms of percentage of original horsepower vs a flat number. Lets assume in N/A form a car makes 100hp. If you conveniently ignore external factors by using the physics "magic vacuum" you can assume that by doubling atmospheric pressure (14.7 psi) you would double power output. The 100hp original engine would produce 200hp or 6.8 HP per PSI.

If you started with a larger engine that produced 200 HP in N/A form it would be double that. 14.7 PSI would produce 400 HP or 13.6 HP per PSI. And so on...


In the real world it doesn't quite work this way. We have air flow restrictions, friction, turbo size, etc... reducing efficiency. These intriduce huge variables which makes the percentage increase hard to guess at. I might suggest a range of 60-80% efficiency depending on the set-up, but it is just a guess. Only a dyno can tell you exactly. :)
 
dont forget that volumetric efficentcy must also be considered, and if your turbo is being overflown... ie at a psi that your turbo cant support full time...
 
ddavisaf said:
2G Non-Turbo has 11:1 compression
2G Turbo has 8.5:1 compression
1G Turbo has 7.8:1 compression

There are entirely to many variables to contend with for this kinda of question. At least for me. Not to mention it's Monday and I'm not going to wake up until at least Wednesday.
11:1 !!!!!!!!!! wow dude did you pull that from your butt. try 9.5:1 but you were close though ;)
 
How much horse power is in 1 psi? I was told that 1 psi = 6.25 hp

99 Eclipse GS = 140
99 Eclipse GST = 210

what is the stock boost - 12 stock PSI (not to sure what it is)

6.25x12=75

so then 140+75=215 (Close Enough)

Does any one think this is correct?

Ref: http://1000q.dsm.org/

Thanks Brandon

The GS with the 140HP will be much different than the GST if it was non-turbo. The 4G63T motor has a lower compression compared to the 420A motor. So if they were both non-turbo I bet the 420A will make more power.

And for 1psi = 6.25HP It all depends on the turbo.

Maybe a T-25 will make around 5.5 HP for 1 psi where lets say a T3/T4 60 trim maybe make 20 HP per psi. It all depends on the flow of the turbo or CFM.
 
The first gen runs about 11-12 psi and around 8.5:1 compression
The second gen runs about 13-14 psi and something like 8.7:1 compression
This is why it makes around 15 more crank horsepower out of basically the same engine.
I read this in Grassroots Motorsports a couple of years ago. :talon:
 
I will just agree with everyone else that has said there are to many variables to calculate how much horsepower 1 psi makes because it is true. Horsepower made on 1 psi changes depending on how efficient your setup flows. Oh and to correct the rookie first generation DSMs had a stock compression ratio of 7.8:1, second generations had a stock of 8.5:1.
 
greytalon26 said:
The first gen runs about 11-12 psi and around 8.5:1 compression
The second gen runs about 13-14 psi and something like 8.7:1 compression
This is why it makes around 15 more crank horsepower out of basically the same engine.
I read this in Grassroots Motorsports a couple of years ago. :talon:
:notgood:

2G Turbo has 8.5:1 compression
1G Turbo has 7.8:1 compression
 
Ultimatedsm said:
The GS with the 140HP will be much different than the GST if it was non-turbo. The 4G63T motor has a lower compression compared to the 420A motor. So if they were both non-turbo I bet the 420A will make more power.

And for 1psi = 6.25HP It all depends on the turbo.

Maybe a T-25 will make around 5.5 HP for 1 psi where lets say a T3/T4 60 trim maybe make 20 HP per psi. It all depends on the flow of the turbo or CFM.

So you are saying when I turbo my 420a, 8 lbs of boost off a t-25 would get me 44 hp but 8 lbs of boost on a t3/t4 60trim would get me around 160?

if thats true, 140 base hp, + 160 from the turbo + exhaust intake etc etc is already over 300 hp.
 
napkinthief said:
So you are saying when I turbo my 420a, 8 lbs of boost off a t-25 would get me 44 hp but 8 lbs of boost on a t3/t4 60trim would get me around 160?

if thats true, 140 base hp, + 160 from the turbo + exhaust intake etc etc is already over 300 hp.


I hope you aren't serious. This is what I was trying to avoid with my posts. You can't say this turbo + this psi = this much more HP. Otherwise you wouldn't see people on here with big 16g's and a dyno sheet that says 223 hp. Or see any threads "Just installed 20g ran a 14.4!" TOO MANY VARIABLES. One including setting everything up correctly and TUNING properly.

Arghh. :toobad:
 
Drop it!!!

You can not equate pressure to horsepower.
You can not equate a turbo to horsepower.
You can not equate a turbo to CFM.

Don't try. Forget it alltogether.
 
All of my posts have been to correct information and/or tell it to you straight.

Get over it you can not boil down a car to 1 psi = x horsepower....it can't be done.
 
nightstocker99 said:
I just wanted to know if what I heard was ture I am not trying to get anything else out of it I am not trying to bench race I just want the answer and now I do and now peopel are getting mad and are calling this bench racing.

were not getting mad, we're just simply telling the truth. there is no way you can calculate that sort of thing.
 
nightstocker99 said:
I just wanted to know if what I heard was ture I am not trying to get anything else out of it I am not trying to bench race I just want the answer and now I do and now peopel are getting mad and are calling this bench racing.


To answer your question succinctly then, what you heard was not true. PSI is one of MANY factors determining power out put. You CAN NOT determine power increase by looking at PSI alone.

I hope that's clear enough to end some debate.
 
crankbender said:
Get over it you can not boil down a car to 1 psi = x horsepower....it can't be done.

Exactly, I agree completely.

PSI (pressure) = heat

Airflow = power

Imagine running a T25 at 25psi, what is going to happen? You are so far out of the turbo's efficiency range, all you are going to do is increase the temperature of the intake charge without increasing the flow.

Higher IAT = more knock = less timing = less power.

Now think about running a 50 trim at 25psi. At 25 psi you are well within the 50 trim's efficiency range and while you are adding some heat, you are also increasing the airflow.

Once again, airflow = power.

Remember the equation PV = nRT

P = pressure
V = volume

The volume of the "system" is a constant in this case, as we aren't making any modifications to the vehicle other than increasing the pressure produced by the turbo. R is a gas constant and n is the number of moles of gas.

T = temperature

So, all we really care about is the relationship between T and P. As you can see, there is a direct relationship between pressure and temperature. This tells you that as you increase pressure, temperature will also increase. The result is that any increase in pressure is accompanied with an increase in temperature. This increase in temperature increases knock, pulls timing and ultimately reduces overall power.

Now for some "real world" numbers:

I was running my current setup (minus the UICP) at 17psi. Normally my airflow would peak around 28.5 lbs/min. After getting a good tune, I decided to increase the boost to 20psi. My airflow increased to about 28.9 lbs/min. Even with such a small increase in airflow, I started to see my timing get pulled on the logger. This was due to the corresponding increase in temperature. As you can see, no matter how high I turned up the boost, my airflow wasn't going to increase.

After installing the UICP my airflow increased to 30.26 lbs/min leaving the boost at 17psi. No increase in pressure (corresponding to no increase in temperature), just an increase in flow = more power. I then turned up the boost to 20psi and the airflow jumped to 32.15 lbs/min. Much better. :thumb:

I hope that helps demonstrate why increasing pressure isn't always the best. Most of the time, you are better off reducing flow restrictions, increasing your ability to cool the intake charge, etc.

Wonder what would happen if I got rid of the stock cat back. :D
 
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