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BHP Calculation from MAF?

dsrr

dsrr

Full Member
Oct 23, 2004
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I have been doing some logs on my car since getting the APR remap and based upon the results and a known comparison have com up with the following conclusion.
A lot of us on here believe that the BHP of a car can fairly accurately be calculated from the MAF by varios simple calculations such as G/sec x 1.31.

However I have don runs in 3rd and 4th gear to the redline and found a maximum Maf reading of around 170 - 174 G/sec and at using GaryM's car as a comparison ( sorry to pick on you Gary) his car is almost identical in spec to mine and is running custom code 2, his Maf reading is around 187 g/sec and I have recently seen a maf log of DPJ on here getting similar MAF figures but running only 188bhp and 109 lbs ft torque.
Here raises a question......Gary's car runs 19PSI boost and DPJ with Revo is running 21PSI my car is running around 16-17PSI why is the Maf reading consistently lower?
My power and torque curve was plotted by awesome against Gary's car and they are almost identical.
Mt thoughts on this....and I stand to be corrected by some more knowledgeable guys on here....is that the Turbo is a compressor and as such the faster the turbo spins ( within it's efficiency envelope) the more boost pressure it produces and the more volume is moves through it.
It it well documented that more boost ( hence more volume through the MAF ) does not always equal more power so this brings me back to the MAF,

if my car is producing 212 ATW and producing 250 lbs ft torque but only moving 170 G/sec through the MAF @17PSI boost,
GaryM's car is producing 216 ATW 255lbs torque moving 187g/sec through the MAF @19PSI Boost and
DPJ's car is producing 188 ATW 209lbs torque Moving 186g/sec through the MAF @21PSI Boost

Then the correlation between MAF reading and BHP goes completely out of the window so how can the BHP be calculated from the MAF figure?
all these readings are from Awesome's RR so there is consistency in the RR.

Open to discussion.......
 
Interesting points. I don't think mine is a great comparison - there's some other reason why my car isn't doing the business on Awesome's rollers. (but I'm not saying the rollers are wrong.)

Here is a graph of Zboyd's LCR on Awesome's rollers against plotted g/sx1.31. Note rollers are ATW - I 'extracted' an average figure from his runs as I didn't know which run g/s was done on.
ZboydBHPAwesome1.jpg
 
Last edited:
ibizacupra said:
temperatures?
timing?
Click to expand...

exactly my point Bill, there are just too many other influencing factors to be able to use the 'simple calculation' to estimate power.
Oh, the MAF is almost brand new before anyone points a finger at it.
 
Last point on my car here ................ I've been logging 60-100s and am coming up with consistent 8.9s. I understand that equates to around 238bhp flywheel with my weight of car. Now if 238bhp fly = 188 ATW then it does...... :shrug: I'm going to try to get some acceleration calcs done to calculate bhp on the track.
 
Assuming the MAF measurements are correct, that volume of air has got to be going somewhere - namely through the combustion chambers. If my car is that less efficient, then surely it's got to be running incredibly lean - or stacks of fuel are being dumped in to compensate.

Vag-com suggests my fuelling is correct - so what else - does my flywheel weigh loads more than yours? :confused:
 
what blow by does yours have...
what other losses are on yours...

what compression does yours test to

what wear and tear is there internally.


Are you not calculating figures to the point of confusion and sticking a pencil up ya arse? (not meant to be demeaning by that last bit)

Several parts of the "power" game equation not known. insert x & y & z as req'd to make the figures as you would like them.

and the benchmark is a RR Dyno....

"Dyno Lottery" (TM)
 
what gear are you starting to log the data for the power graphs in?

Mine recorded 180.1 bhp which cant argue with that really from a std lump
 
DPJ said:
No, simply trying to understand (from a more limited viewpoint than you have).
Click to expand...

I know where you are coming from... been there myself.
my engine was always lesser powered compared to identical spec'd other ones.. Oettinger chipped back in 2001. Never knew why.

I went IHI and was again less powerful than others for the same spec and boost levels? To this date I do not know why.

So many parameters in the engine spec alone could contribute to the differences... wastegates, cams, timing of cams, fit and clearance of component tolerances etc etc etc..........

There is no datum which can be reliable when trying to log and makes sense of this as you are just unable to know or record all of the parameters and components which contribute to the end figure... and the end figure is measured on a .... Dyno? and taken as gospel? - which as has been done to death, is simply not possible.
 
dsrr said:
( sorry to pick on you Gary)
Click to expand...

LOL, no worries Dave.
I doubt you'll be finding an answer anytime soon though :confused:

As you correctly pointed out though, higher boost does not necessarily create more power. I keep seeing people quoting 20psi and upwards yet don't make the power I do, its all a fine balancing act.

Hope James (JBS) doesn't upset that balance next Saturday when he makes some fueling tweaks, after looking at various vagcom logs I sent him he thinks there's more to be had.
 
Gary,

If James is doing some fuelling tweaks do your vagcom logs indicate that you are running overly rich? I think that my catr may be so am going to be doing some fuelling related vag-com logs and seeing if this may present a possibility of upping the power further. Have you though about doing the inlet and exhaust manifolds, I am considering the APT exhaust and the Dahlback inlet
 
:) Easy..........

The said calculation, is very accurate on a standard map, with standard boost........ask Uwe @ rosstech who wrote the brilliant software:)

Problem as such is consistancy whith other maps/boost etc, and other stuff bill has quite rightly pointed out, remember boost aint linear to output if it was people who write code would not have much of a job to do, and thats before you throw volumetric effiencey and dyno accuracy in the equation, where is the datum point? answer there is no known one, only comparisons........ works for most though as the dyno's i had done and g/s readings more or less matched up:blink:
 
DPJ said:
Last point on my car here ................ I've been logging 60-100s and am coming up with consistent 8.9s. I understand that equates to around 238bhp flywheel with my weight of car. Now if 238bhp fly = 188 ATW then it does...... :shrug: I'm going to try to get some acceleration calcs done to calculate bhp on the track.
Click to expand...
60-100 in 8.9? That seems slow, what what you getting Gary and you other k03 lot?
 
DPJ said:
60-100 - isn't the time for a standard 225 LCR a fraction over 10 seconds? (Weight about the same as mine)
Click to expand...
You want to take the bodykit off it's slowing you down! ;) It's that spolier!:whistle:

EDIT: Oh 10 secs sounds about right for standard LCR cupra is around 40Kgs lighter than LCR IIRC
 
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