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i heard that if ur pushin about 14 psi ur gaining 100% more horse becuz atmospheric pressure is 14. something is this true? just tryin to see how much power i got
 

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Hates: Liver. Loves: Diesel
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5,659 Posts
Basically, yes but there are several factors involved.

The compressed air from the turbo is much hotter than the intake air, so the molecules spread out. The intercooler (which is present in any serious turbo setup) pulls some of that heat back out regaining some of the density.

So, theoretically, if you put a turbo on that is capable of a pressure ratio of 2:1 (double atmospeheric) and an intercooler that is 100% efficient, then yes you'll approximately double your power.

Problem is, intercoolers are rarely 100% efficient, and turbos are tend to heat the air more than usual at the very edges of their performance band, so you'll actually need more pressure to double the power.
 

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Hates: Liver. Loves: Diesel
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5,659 Posts
Yes, but the effect I outlined above is cumulative... the more you ask from your turbo, the more it heats the intake charge.

So, theoretically speaking... If it takes 14 psi in a perfect world to make 100% more power, then it might actually take 16 psi to achieve that number. But, that same idea taken to 28 psi might require 33 psi to get the 200%.

What kind of engine are we talking about here? Most stock engines won't take more than about 8 psi without a complete re-engineering of the internals.
 

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Buick Hybrid Guy.
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I do alot of turbo setups and tuning. By text book your both correct. In a perfect world where you have 14-15psi your engine will act like it doubled the cubic inch. Or in other words you've packed in twice the air/fuel that could normaly be pulled into the combustion chamber.

Tuning is 90% of the work on a turbo setup. It's much easier with a good system (FAST/Accell/Big Stuff) ect. When you hack into the factory ECM it's more challanging but you can acheive the same results.

I'll give you a example. My daily driver is a 89 Maxmia Not a performance car by anyone's standards. Car and driver states it runs 15.70'[email protected] with a good tail wind. I put on a TA49 GN style turbo and stock GN intercooler,made all my own pipes/to/from and hacked the factory ecu for fuel/timing curves. It now runs [email protected] That's 100% stock engine with over 222,000miles on the clock! I make new GTO's and normal muscle scratch their heads most days.. I get 21mpg in town and 28 highway.
I run 13psi on pump gas.... I've had this setup on there for over 40,000mi.
I've made a new downpipe and plan to re-visit the track in the spring to get my first 12sec. pass.

My point being ... if it's not tuned or a matched setup you will not get good results. I've seen alot of guys in the Turbo Buick world spend top dollar getting all the latest goodies and parts and their car still runs 12's. It's not the parts most of the time it's how it's tuned.
What engine are you talking about? (as asked above)
~Scott
 

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Yes, you can use the pressure ratio as an estimate.

(boost + 14.7) / 14.7 = pressure ratio

pressure ratio x normally aspirated hp level = boosted hp level

So, if 10 psi of boost was added to a 260 hp/300 ftlbs GM Goodwrench 350 it should make 1.68 x 260 = 437 hp and 505 ftlbs of torque.

Another way to add a turbo is to use a FMU to increase fuel pressure to the injectors during boost. This works well to 10 psi of boost, but requires enough fuel pump to make 100 psi of pressure with good flow. I run a system like this on a 76 280Z (see photo album) and it runs 108 mph in the 1/4 mile with 12 psi of boost. Yes, it runs a little lean at 12 psi at high rpms but makes more power in the midrange.
 

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Buick Hybrid Guy.
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255 Posts
You'll need the following things:

Live edit: Free on internet
Pocket Romulator or chip from me.
Sockete'd ECU for chip/romulator
370cc injectors
AFPress.regulator
Warbro 255lr/hr fuel pump
Z32 MAF
Good timing belt/tensioner
GN style turbo
Pipes to/from stock manifolds
Intercooler
I've got complete pictures of my build with all the information you'd need to dupicate it.
E-mail me if you've got questions. Be glad to help. :thumbup:
[email protected]
 
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