BAIN

iTrader: (5)

Just checking if the lbs. of air sucked/pushed through the engine correlates to what rwhp should be produced. I saw a thread about this a while back and to me it had some mixed results.
Lets get this started again. Post your lbs/min airflow, rwhp, and if it's an m6 or a4.

My MAF lbs/min is 50.65 on an a4 cam only(T-Rex), 90/90 car. I was wondering what rwhp could be possible.

RedHardSupra

iTrader: (1)

you got a right idea, but there's few more steps to it:
1. convert airflow to cylinder fill (easy)
2. convert cylinder fill to torque (hard) (as dyncylair is directly related to compression, and compression is related to torque)
3. convert torque and rpm to hp (easy)

i haven't tried to quantify it yet, but i've seen enough data that i approximately can tell with what dyncylair at what rpm makes what power.

50lb/min is a very healthy car, what's your max dyncylair at what rpm?

HumpinSS

iTrader: (1)

Pretty stout my g5x4 sees 52 lb/min @ 6k but i dont put to much faith in these figures since they are/seem to be dependant on how your injectors are dialed in. Mine are dialed in via the injector spreadsheets that are floating around so I guess they should be pretty consistant providing everyone uses them


Edit looking over a few logs IAT and Baro seem to have an affect also

RedHardSupra

iTrader: (1)

well, it's an issue with how much AFR you're gonna end up. a bad IFR calibration will throw it off.

HumpinSS

iTrader: (1)

I dont think its so much an AFR issue most people tuning are shooting for 13.0 if you muck around with the IFR table that can drive your ve values up or down and since that is a representation of dynamic air and the PCM is using these values to figure out air this can either inflate or deflate your numbers at WOT as far as Lbs/min is concerned

RedHardSupra

iTrader: (1)

ok ok...ASSUMING everything is dialed in proper, it should be very consistent.
but than again, how many cars are tuned properly...

shizon

iTrader: (1)

The other things we're not considering is how much power the engine loses from pumping the air. For instance, the idea of DoD is to cause the engine to make less power at a certain throttle position so that to make more power, you have to open the throttle more creating less of a restriction.

This should apply all the way down the line I would think in some capacity. An engine could flow the same lbs/min but work harder to do it creating more error in our "equation". I'm not sure it's a HUGE amount of error, but nonetheless something to think about.

I think the real question we're trying to answer is how much energy can realistically be released by 13.0 lbs of air and 1 lb of fuel mixed together, compressed, and burned. I'm sure we can get this calculated somehow maybe? Then we can take into account engine efficiency and friction loss of engine internals even across different engines.

BAIN

iTrader: (5)

Max dycylair comes in at 6200 rpm = .82 g/cyl

dycylair @ the max 50.65 lb/min (7000 rpm) = 0.74 g/cyl

The logs were done @ WOT with an unlocked converter if that makes any difference. Oh and my 28# injectors are seeing 101-103 % cycle duty.

ringram

All these calulations are available in various text books. An interesting point based on what max power you can get from a lb of air, or fuel for that matter is that engine losses are as follows in an NA Diesel (SI Engine will be a little less efficient due to fuel having less energy, plus less compression, but you will get the idea)

Losses

Combustion 22.5%
Exhaust 14.4%
Heat transfer 13.5%
Aerodynamic 4.7%
Friction (mechanical) 4.8%
TOTAL LOSS 60%

Available power 40%

So thermal coatings, good valve timing and good heads can make a significant difference. Look at the power from the rotary valve engines to get an idea of how inefficient the current cams are.

I recommend John Heywoods MIT text book for those interested in such things.

Phil99vette

iTrader: (11)

My formula says 50# of air = 417rwhp in an automatic.
3500# curb weight and the ET/MPH say 411rwhp
Phil

Phil99vette

iTrader: (11)

HumpinSS:
4.33 12 bolt rear
6 speed
52# = 436rwhp

BAIN

iTrader: (5)

How did you calculate the drivetrain loss? I know the drivetrain loss of a stock converter is around 20%, but my 4800 looses 46hp form locked to unlocked.

Phil99vette

iTrader: (11)

I used 17.5% driveline loss.
Phil

Bombguy99z28

How much does dynamic compression ratio effect dynamic cylinder air? My logs show my camaro having less MAF air and more cylinder air than the example posted earlier. Could be I just suck at tuning... lol DCR is something like 9.3 or .9.4.

shizon

iTrader: (1)

Wow, I had no idea that much power is lost. Thanks

HumpinSS

iTrader: (1)

At 6700 i see 51 lb/min and .87 gm/cyl

mr2guru

iTrader: (16)

I am seeing 1.16 at 5200 and 1.08 at 6900.

oztrack

I am seeing in EFIlive 44.3lbs/min (VE Table says 50.9lb/min) - so its 87%.
6600rpm and 0.85g/cylinder at peak
The max dyncylair is 0.92g/cylinder at 5400rpm. It is above 0.82 at stall speed of 3600rpm.

216 220 Cam 114lsa with 1.8s 555 lift. Ported Heads at 10.7:1

The other values include the SVo injectors IFR table rated at 40 psi - so 36.1lb injectors and they are going as high as about 80-83% at 12.75:1 AFR.

I dont know rwhp - but i know the car does 11.76 in 85 deg F and 115.3mph at a race weight of 3650lb with driver.

oange ss

iTrader: (50)

so what would be the cause for a relativley low gm/cyl air reading for a H/C 6 speed car ? hypothetically speaking

RedHardSupra

iTrader: (1)

h/c cars usually have headers. headers usually leak (90+% of car i've tuned went back to get that fixed) at the block or at the collector.
another usual suspect is intake, and the gaskets. don't reuse them, get new ones, they're cheap enough.
if you're logging, look at O2 readings at wot, and the moment they go lean under wot you know you got a leak.