Subtraction by Addition: CHECK! Sometimes I hate my car - Page 7 - The Unofficial BMW M5 Messageboard (m5board.com)

E55AMG2 · 8th July 2009, 01:20

Has anyone considered the fact that he was dynoing w/o fans? The april vid you posted has what seems to be a miniscule amount of airflow (judging by the tape blowing) and the later one you posted seems to have none. Just sayin

jrhaile · 8th July 2009, 01:23

Quote:

Originally Posted by E55AMG2

Has anyone considered the fact that he was dynoing w/o fans? The april vid you posted has what seems to be a miniscule amount of airflow (judging by the tape blowing) and the later one you posted seems to have none. Just sayin

Nope but now that you mentioned it, I could see that as an issue since our beast pulls timing VERY quickly when it gets warm and it was hovering around 90 degrees outside and probably around 100 degrees inside or hotter

E55AMG2 · 8th July 2009, 01:29

Quote:

Originally Posted by jrhaile

Nope but now that you mentioned it, I could see that as an issue since our beast pulls timing VERY quickly when it gets warm and it was hovering around 90 degrees outside and probably around 100 degrees inside or hotter

you can rent carpet dryers (and split the cost between you and your buddies) for like $25/day. I typically get 3 of them

gsfent · 8th July 2009, 04:46

Quote:

Originally Posted by jrhaile

haha you're crazy... I love it

Why don't you two guys simply swap MAF's and check the results after a few miles of driving for the computer to adapt? It wouldn't take more than 10 minutes for each switch.....
Regards,
Jerry

jt2ma71 · 8th July 2009, 05:05

Never noticed that. In my maxima, i dynoed like 15whp lower and 20wtq lower because my car was heat soaked. My car sat for 30 minutes outside, but it did like 7 runs to tune before we went for power numbers.

Given how tempermental the M5 is to heat, that could definately cause it!

jrhaile · 8th July 2009, 05:25

Quote:

Originally Posted by gsfent

Why don't you two guys simply swap MAF's and check the results after a few miles of driving for the computer to adapt? It wouldn't take more than 10 minutes for each switch.....
Regards,
Jerry

Because I already know how my car runs with VW Mafs... poop

churious · 8th July 2009, 05:35

I wanted to get OEM Mafs anyway... plus James is loaning me the money for em...

jt2ma71 · 8th July 2009, 05:43

Quote:

Originally Posted by jrhaile

Because I already know how my car runs with VW Mafs... poop

Whtat LPH were you able to pull with the VW compared to the BMW? I have VW MAFS and i pulled 138L/HR corrected. Other then K&N filters, i have the powerchips 93gold reflash if that makes any difference.

jrhaile · 8th July 2009, 07:05

Quote:

Originally Posted by jt2ma71

Whtat LPH were you able to pull with the VW compared to the BMW? I have VW MAFS and i pulled 138L/HR corrected. Other then K&N filters, i have the powerchips 93gold reflash if that makes any difference.

I didn't even bother. Car run sluggish and my MPGs were below 14 average. I ditched them quickly.

CSBM5 · 8th July 2009, 15:59

Quote:

Originally Posted by churious

Someone please tell me what the Dinan 3.45 gears do.. besides cost alot of money...

They have literally no gain on my car... James and I have rolled in 1st gear, 2nd gear, 3rd gear... etc

And my diff hasn't helped at all... Im actually thinking about selling it. Now that it has 1800 miles on it.... and make a 3.62 from my OEM diff.

Unless you change the operating rpm range for max volumetric efficiency of the S62, changing the rear gear does essentially nothing to acceleration. This argument has been going on for years on the board with both Cartest simulations (which I did extensively a few years...which have proven to be pretty darn accurate btw) and board members real world experience. The 3.15 diff is VERY well matched to the powerband of the S62 (note this has RARELY been the case with American muscle over the years as they were almost always, in the past 30 years, forced to compromise with obtaining better economy as opposed to max acceleration across the operating range).

Now if you alter the peak torque rpm and peak power rpm (i.e. moving them higher like the S2 mods do), then you will benefit from changing rear gearing to match. However, on a relatively stock engine, just changing the rear gear does about nothing for acceleration performance as proven time and again over many years here. If you look at the other thread along with the link to my Cartest simulation runs, you'll see that stuff like 1/4 mile trap speed being essentially identical across a wide range of diff ratios? Why? Because you haven't changed the power output of the motor, and trap speed is a profoundly robust measure of total power to weight ratio.

The other thing that pops out in my simulation tests is that as you go toward steeper rear gear ratios, said car will then end up needing to shift more (and earlier) resulting in time lost to the lower gear car. In net what the sims all showed was that one or the other was "ahead" at any given point in time typically based on where it was in relation to shifts. People who are "in favor" of steeper rear gears all point to "more torque to the wheels" at some point but they ignore "less torque" to wheels at other points in the acceleration curve (i.e. like after every time the steeper geared car shifts up), etc.

A stock diff car will beat the identical 3.45 diff car to 100mph by about 0.3 seconds. How? Because it doesn't have to shift to forth gear to get to 100mph...otherwise they'd be essentially equal.

See my modeling results from years back. These have been shown to be pretty accurate in board members actual tests (like the modeling results I did for PhillyM5's D/A supercharged car which were essentially spot on). Also, reading Lscman's post in that other thread might prove useful to some too.

Chuck

P.S. James I wouldn't fret over the dyno runs. Your car appears to be running normally strong, and you gave up a tad at the top of 1st when you touched the limiter too.

We all have to focus on shifting 1st when the tach needle gets to about 6200-6400 rpm since it lags so much in 1st, due to rate of change, behind real engine speed at WOT. This still catches me at times, and I've been driving the M5 for many YEARS now...