moehorsepower

iTrader: (3)

What I don't understand is why people come on and say I want to make X amount of pounds of boost instead of a horsepower goal. Who cares if you are making 5lbs but have 600 HP!!, My car which is a 95 LT made 648 RWHP on Pump with only 12lbs and 722 RWHP on 14Lbs with the Fast Gas, This was with the D1...and all by 6000 RPM

98transguy

iTrader: (7)

true statement, but what was the point of your comment.nice numbers by btw.maybe the people that make the x amount of boost comment are just saying how much boost they want to make on pump gas or how much boost they can make before hurting the motor or lifting the heads.

ls1290

iTrader: (20)

They have seen the fast and the furious too many times......

Keith

landonew

I always wondered that too. Seems to me that your goal should be too boost as little as possible for your target HP. That would mean that your system is flowing good and not very restrictive. I guess a better measurment would be volume-of-air(at atmospheric density)/unit-of-time.

MIGHTYMOUSE

iTrader: (59)

we dont have a horsepower gauge in the car in front of us to use as a reference.. but we do have a boost gauge.

MIGHTYMOUSE

iTrader: (59)

i disagree with this.

if you want to make as little boost as possible then build a n/a motor and dont boost it at all. you will end up with a radical set up that sucks gas and is irritating to deal with on the street.

OR leave it all nice and conservative.. throw some psi to it
and keep all of those things you like about your car around to enjoy.

I spend the money on the engine to be strong, i spend the money on the FI to make the power.

DMH Fabrication

iTrader: (126)

PSI really doesn't mean much at all in terms of pump gas. It is about hp and generaly people will say you can make xxx hp on 93 with a good tune and not hurt the motor. They don't say you can make xx psi on pump gas. 10# out of a PTE 88 isn't going to be the same as 10# out of a PT106.

As far as wanting to run the least amount of boost, I think you are really looking for a middle point. Tuning window, off boost hp, turbo spooling time, etc. are all affected by the choices you make when you build the motor and design a turbo set up.

landonew

I sorta understand. But at the end of the day its how MUCH air you are moving right? I thought the point of FI was to force more air into the engine. Now you achieve this buy increasing the density of air through compression, but at the end of the day you can be making 20 psi w/o any power if you have a bottle neck somewhere in the system (i.e. poor flowing heads or intake).

With boost, you don't really know how much air is going through the system, only what pressure the system is operating under. If you measured the volume-of-air(at a standard density)/minute, wouldn't that give you a better understanding of how well the system was performing as a whole?

ls1290

iTrader: (20)

No, that is not correct. All the head units I know of have a know CFM flow rate. You can easily calculate the amount of air generated at a specific RPM based on the head unit, blower and crank pulley, and engine RPM. A boost gauge is just a simple indicator of the air that is not making it into the engine.

Keith

Slvr00Bird

iTrader: (2)

Very good point.
Since when does psi not involve what grade of gas? Of course hp and psi fall hand in hand, but in order to run certain psi's, you have to up the octane and take into account compression. I mean that's why there is race gas. To up the psi.

As far as saying I want to run _# of boost vs. hp. I think many people have their engine in a position that they would only feel comfortable running so many #'s. So at this point, they think they'll run the most boost they feel comfortable with and hope it nets them a good hp number. Funds limit a lot of things. So if you say I want to make XXX hp, that might entail a lot more money than if you said "I want to run 8# of boost (atleast until I can build my motor and then I'll up it)."

DMH Fabrication

iTrader: (126)

You can look at a compressor map and figure out the mass flow rate for a given turbo at a given condition. Here is an example:
http://www.turbobygarrett.com/turbob...o_tech103.html

DMH Fabrication

iTrader: (126)

You have to take into account alot of things for the grade of gas and boost really does not tell you much w/o knowing alot of other things. SCR and DCR both play a role also.

By your assumption if I run a PTE88 at 15# on pump gas, I should be able to run a PT106 at 15# on pump gas

BLNLS1/RX7

iTrader: (2)

Whats your point?

otherwhitemeat

iTrader: (3)

I think the boost reference comes on because if you know the motor is an Lt1 or ad Ls1 or a 4 cly .....and then they say they run about xxboost you can get a good idea what hp they make. It just from seeing other peoples combs, that to start to know that if a certain motor/F.I. comb make xxxboost then I should make about xxxhp.

landonew

assuming SC. I was actually thinking turbo.

ls1290

iTrader: (20)

Even today's turbo have well known flow characteristics. Determining the flow rate for a specific RPM should not be too hard.

Keith

landonew

Exactly. But with only one point of reference (boost pressure) you don't know whether or not you are on the surge line or the choke line, or somewhere in between.



I am not experianced at reading turbo compressor maps (but i am an engineer) so correct me if i am wrong.
The Y axis is boost pressure in atmospheres (1atm = 14.7PSI). The X axis is the amount of air/unit-time in lbs/minute.

Say you are boosting 3 atmosphers (or 2atms above normal = 28PSI) on the above turbo. Without knowing the resitance of the system you could be pushing anywhere from 34-70 lbs/min of air. The resistance of the system (i.e. the intake, heads, ext.) determine how fast the turbo is spinning. See, it is a 3 variable equation. You need 2 variables in order to figure out the 3rd.

If you have boost pressure AND turbo speed, you can determine mass flow. But if you only know boost pressure, you can't figure out mass flow.

Am i on the right track?

landonew

but how do you know the RPM of the turbo? Is there an equation? Garret suggests that you can interpolate it, but that seems as if it would require the knowing a lot more variables.

moehorsepower

iTrader: (3)

My point being is that I have had people come to me for tunes saying I want to make 15llbs of boost, I ask how much horsepower are they looking to get and the answer was I just want X pounds, Such as I have had customers saying I want to spin my motor to 7500RPM....WHY?? Just to say Oh I make 15lbs or Yea I spin my motor to 7500. But again they could be asking your answer, on how much they can have before lifting the heads..

nuclearxp

i may be completely off here but doesnt the engine pcm use the MAF, IAT, MAP etc to generate a fairly accurate air flow rate (lb/min) assuming your MAF table is properly tuned and calibrated? isn't air flow the main way to determine power output (negating N20, timing etc)?

i.e. i know when i dyno my car that in 3rd gear at 6000rpm and 15psi the motor made about 430ish whp. this is backed up by analyzing scans from the run: the maf frequency was ~11,000hz which equates to about 53 lb/min of air in my maf xfer table. granted the computer will also apply the IAT to this base number to compensate for air density to get, let's say, an actual air flow rate of 50 lb/min going in the motor. i was always under the impression that 1 lb/min of air is roughly 10hp at the crank, which is pretty much verified by my dyno results