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Horsepower gains from pounds of boost.Weird question

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Old 09-24-2007, 01:36 AM   #1
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Default Horsepower gains from pounds of boost.Weird question

well after talking with a few friends that have nissian 240sx with a sr20 det they say that you will gain 7 horsepower for every pound of boost you have .I was telling them how i seen some Turbo setups running 6-7 psi and putting down 400-415 hp at the wheels ,They said their is no way that is possiable on a bolt on car with that little boost .So is that about the goin rate of hp gain for each pound of boost you bolt on ls1s guys see. they said i was full of it when i told them i seen a ls1 put down 300rwhp then put a turbo kit on and hit 400+ with around 6-7 psi .
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Old 09-24-2007, 01:43 AM   #2
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There's an equation to figure it out, but I don't remember what it is.
Basically the more power a motor make N/A the more it will make per pound of boost pressure. 7 hp/psi is total BS. It might be close on their 4 cyl engines, but it's not going to work for everything.
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Old 09-24-2007, 01:46 AM   #3
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id say it might be double that for a v8 and remember your car has twice the power maybe more and twice the cylinders....

also every cars differant
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Old 09-24-2007, 01:51 AM   #4
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Every setup and tune combination is different, but 90 crank hp from six pounds of boost is very possible.
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Old 09-24-2007, 01:51 AM   #5
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ya thats what i told them but they wouldnt here it ,they was he must have been spraying bla bla bla you know how those import guys are.i guess he was mad cuz he is running 14 psi and only hittin about 250-260 rwhp lol.but i was just trying to get some more insight to it im still new to forced induction and readign up trying to learn a little about it
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Old 09-24-2007, 01:55 AM   #6
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i called procharger about this a while back and they told me each psi is about 15-20 horse.
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Old 09-24-2007, 02:04 AM   #7
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Doesn't it depend on how much power the engine makes naturally aspirated at a given atmospheric pressure? Say at sea level, you have 14.7 pounds of atmospheric pressure. Therefore, adding 14.7 pounds of boost pressure would double the engine's power output.
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Old 09-24-2007, 02:04 AM   #8
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The Incon kit I have gets around 30 hp per/lb of boost, so adding 3psi was like adding almost 100hp, when I went from 7-10psi.
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Old 09-24-2007, 02:11 AM   #9
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damn mike 100hp for 3 extra psi thats nice. I have looked into the Incon kits before how do you likes yours so far .Regardless of brand i go with my car is making 365rwhp now, i dont see any reason why i shouldnt be able to pul 430hp with 6psi
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Old 09-24-2007, 02:14 AM   #10
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of course physics is impossable and the world is not perfect... but if it were:

perfect pressure at see level is 14-14.5 psi. that is just natural atmospheric pressure (if youre running n/a then this is your "boost" haha!). now there are hundreds of factors that effect power output, heads, cam, displacement, stroke, bore, rpm, ect., not to mention timing, engine and air temp, humidity, ect... but a given engine in a perfect world will double its output with 14.5psi of boost. so you cannot put a numbe on it because...

a 400hp motor will make 800hp at 14.5psi, but a 200hp motor would only make 400hp at the same boost level... see how it works. like i said these are perfect world numbers and that is why all "boost" manufacturers rate their systems in percentages. pro-charger for example says "up to 70% increase" that is dfrom your n/a baseline, and please note the "up to" part of the equation. that is your nod to all the variables, the biggest probably being elevation, and heat.

hope this helps you out. and yes an import with a 150-160hp motor will probably only make 7-8hp per lb boost. thats why they run 20psi to equal ours at 9psi. so really there is still no replacement for displacement!!!
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Old 09-24-2007, 02:18 AM   #11
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maybe they meant that every pound of boost is equal to 7% of the engine's n/a power.

Not sure if this is true but it makes sense...

cuz ive seen a stock ls1(330rwhp) w/procharger at 5 psi make approx 450rwhp...and if you do the math that is about right...
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Old 09-24-2007, 02:36 AM   #12
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hey ray thanks for that ,ya i know you cant just take a givin number and say this is what hp i have like takign factory ratings for aftermarket parts that say 20 hp gain but in reallity you might get 10hp or so .I tried to explain to them that when they by parts turbos etc they cant just say hey it says 50 hp increase so i have 50 more hp .Like you said it has alot more to do with it timing,Fuel,Tuning etc but thats like talking to a brick wall most of the time with them.Yes i will agree i will take a ls1 running 7-9psi vs any just about any import running 15 psi lol thats just me thaugh
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Old 09-24-2007, 02:38 AM   #13
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another question guys im in the market for a good introductory turbo or supercharger system.I dont really need a huge complex system just a good system for a beginer .What would be some good companys to look at i looked at a few sponsers on her already.I know they say you get what you pay for but for my aplication i jsut dont thinka 6-7k system is what i need somthing around 3-4k would be great if thats posiable
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Old 09-24-2007, 03:18 AM   #14
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sts kits have a pretty low intro price, but everything is optional and cost!!!

procharger has a very complete kit but is more than you want to pay.

maybe a basic vortech kit, then upgrade to aftercooler later. that would get you in for around $4-$5k

honestly if your on a budget just go nitrous. im shooting 175 and others are shooting more all day long. seems kinda scary at first but you are doing the same thing as boost, just adding more air. only this boost is instant full boost!!!

decent kits can be had for about a grand with everything you need (window switch, bottle heater and purge) then just save up and get a nice turbo kit later!!! thats what im doing and its working out great!
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Old 09-24-2007, 03:21 AM   #15
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oh and i almost forgot...

on a 150 shot i dyno'd 507hp and 619tq with basically same mods as you but i have full exhaust and a very small cam. (crane 224/224 .551/.551 114 lsa)

good luck!
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Old 09-24-2007, 03:32 AM   #16
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Hp per lb of boost is total bs, as stated for the reasons above. The real numbers you need to look at are displacement and the airflow numbers of the cylinder heads. Remebember that an engine is basically a huge air pump. The more displacement, the more air the heads flow, and the amount of boost are all variables to be considered in total crank horsepower.

Of course running slicks, 4.88 gears, a detriot locker, TH350 with a 5000rpm stall and a trans brake will make a reliatively low beans motor run quite a bit faster
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Old 09-24-2007, 03:46 AM   #17
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GENERAL RULE:

Turbo (no drag on engine) = 20hp per 1# boost (approx)

Supercharger (drag on engine due to crank driven) = 15hp per 1# boost (approx)
supercharger compressor efficiency will affect the output.
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Old 09-24-2007, 05:00 AM   #18
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(Your hp) / (14.7) x (#lbs of boost) + (Your Hp)

example....350rwhp car with 7lbs of boost

350/14.7 = 2.80
2.80 x 7 = 166.6
166.6 + 350 = 516 rwhp roughly

Just kinda a rough idea on hp...this is the equation I have heard of.
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Old 09-24-2007, 07:08 AM   #19
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Quote:
Originally Posted by SuperSweet
GENERAL RULE:

Turbo (no drag on engine) = 20hp per 1# boost (approx)

Supercharger (drag on engine due to crank driven) = 15hp per 1# boost (approx)
supercharger compressor efficiency will affect the output.
THIS is NOT a General Rule. I have never heard of this before. There is no science behind it. The amount of power per lb of boost is going to vary depending on the amount of naturally aspirated power you have to start off with. A 500hp motor is going to make twice the amount of power per lb of boost as a 250hp car, keeping all contributing factors the same.

Someone already beat me to it and this is also just a GENRAL RULE because there are other factors affecting the formula, tuning (a/f and timing) being one of the biggest but: total power = na power / 14.7 x psi + na power.

Stock LS1 = 300rwhp /14.7 = 20.4hp x 18psi = 367 + 300 = 667. But an APS kit on a forged stock cube LS1 should make 850rwhp on 18psi which would equal over 30rwhp per lb of boost, which completely bothces this formula.

On the other hand, a built 408 = 500rwhp / 14.7 = 34.0hp x 18psi = 612 + 500 = 1112.

And a Honda Civic = 100rwhp /14.7 = 6.8hp x 25psi = 170 + 100 = 270.

So you can see that hp per lb of boost is all over the place.
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Old 09-24-2007, 07:10 AM   #20
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Update: LS1Chris, your friends are holding you back. Find new car buddies.
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