Calculate Your GXP's HP

[Jack B]

For those of you that have access to a DashHawk or scan tool it is fairly simple to calculate your hp. It is similar to how GM would calculate torque/hp for torque limiting purposes. When they designed the GXP they claimed they could calculate the power via the MAF sensor within 2% of true flywheel hp.. We are not going to be that accurate, but, close enough for tuning purposes. The only variables are the a/f and the MAF magnitude. The a/f for a stock car is 12.745 at max hp.The max MAF number usually comes near max HP. The rpm for the max mass air flow might vary if the boost is peaky. On my car it is near 5800 rpm. I have seen some stock cars where it is lower due to reduced boost at the higher rpm's.

With all that said, it is very simple:

HP = 8.58 X MAF.

The MAF value is in lbs/min. This formula is set up for the stock a/f of 12.745. There may some minor inaccuracies in this, but, like a dyno, you are looking for relative changes, in this case, changes in mass air flow.

I have a scan for a stock car and it shows 248 hp peak. I have dozens of logs with my car. The latest with the MBC from Dejon, plus, his intercooler. If I play devils advocate and do min/max, my HP is between 298 and 317. An even bigger difference is the area under the MAF curve, the stock car takes a long time to climb to peak, a car modded similar to mine has the MAF climb almost vertical immediately then tapers into a peak.

[lil goat]

OK got the Dashawk, and the IAT2, and the Dejon IC. Give me details on the Dashawk set up, do I need to download the data or can I read it as I drive? I think my AFR is less than stock, Wester did the tune. This is interesting, I will do this then check it on the dyno soon.

[Jack B]

Originally Posted by lil goat OK got the Dashawk, and the IAT2, and the Dejon IC. Give me details on the Dashawk set up, do I need to download the data or can I read it as I drive? I think my AFR is less than stock, Wester did the tune. This is interesting, I will do this then check it on the dyno soon.

Set up your dashhawk to log. In the logging config set up the following:

rpm
boost
maf
wideband a/f
Knock Retard

You can only log five PIDS, but, the above five give you a lot of information on how your car is running. You can substitute throttle position for the wb or the KR, after you are sure of where your a/f is.

The next step is to find a road (a safe road) where you can take the car to at least 6000 in 3rd gear. You want to start the log and get into second gear, roll to about 3000 and then go wot. Run thru second and all the way thru third. You might want to get a couple of runs, When you are done hit the menu button and it will stop the log. Afterwards attach the cable to your computer and download/save the file, then, open it and get the following data:

Max MAF
rpm for max MAF
a/f at max MAF

If the a/f differs frtom the 12.745, it will not affect the calculation that much. That is one of the variables, we don't know where the a/f gives max hp. The factory setting of 12.745 may give max hp, but, may not be safe at the higher boosts that we are now getting. Here are some benchmarks:

1. Stock cars: 28 lbs/min at 5300-5500 rpm

2 Rod Mod or MBC: 34-36 lbs/min 5600-6000 rpm. This is based on my car which has an intercooler in addition to the MBC.

Another benchmark is Dave at Dejon, he is over 40 lbs. with the 16G turbo upgrade.

[lil goat]

Thanks Jack, now I just have to find that road.

[shabby]

You might wanna use this conversion chart since the dashhawk only reads in g/sec instead of lbs/min.

[BaldTurboFreak]

VE lbs/min (in hpt)has been shockingly close to RWHP on my land and sea dyno. I'll say that much. With the fully variable cam timing, Id wager the VE lbs min is the fueling part of the equation. With the Gt30R the dicrepency in VE/MAF has grown considereably yet ive had to continue to add MAF signal offset to get the stft/ltft's in line. (getting the table right for blowing thru the MAF/3" pipe)
I belive this discrepency represents the greatly increased amount of overlap flow from the reduced TIP.
Yet CMD/ACT a/f stays true all the way thru.

We need a stock or lightly modded but stock turbo soltice on my dyno same day, same conditions. hell, do our best here same tire psi, position on the roll, strap tension. all play factors But I bet logging the Ve/lbs min you'll find it matches the rwhp # spit out pretty close.

[Deepbluegxp]

I'm going to have to try this, thanks Jack B