SStolen

iTrader: (22)

How does this work exactly? If you are seeing full boost at 2800rpm on the street and 4600rpm on the dyno, it would seem that the tune would be way off..?? The way I understand it, when tuning with a MAF, the MAF is useless for reading airflow above 4000rpm's, so you basically set a tune for a certain boost level and then manipulate the data so that the timing and fuel is where it needs to be at every rpm level. Therefore, at x rpms, the car is expected to run x amount of timing and x amount of fuel. If you are spooling earlier on the street because it is under load, what timing and fuel you have entered in for 4000 rpms on the dyno would not be the desired timing and fuel for the street because at 4000 rpms on the street you are at 10lbs of boost and on the dyno you might have only been seeing 7 or 8lbs. So, at 4000rpms on the dyno, you have way less airflow and enter x amount of fuel. On the street at 4000rpms, you now have way more air but the same x amount of fuel, therefore you run lean. I am obviously wrong somewhere because tunes on the dyno work on the street. So where am I wrong or what information am I missing?

SStolen

iTrader: (22)

My understanding of this is flawed even further because you would be under a different load in every gear.

oange ss

iTrader: (50)

unless you're a load bearing dyno, like Mustang, but even then you'll have no moving air flow into the motor, depending on type of intake, may or may not effect the tune

jimmyblue

iTrader: (11)

Backwards on the MAF, it's all the PCM uses
above 4000RPM and steady MAP conditions.
The dyno is seldom used for part throttle
tuning and transitional throttle tuning, which
is where you spend 99+% of your time on the
street. A car that hauls *** at the track but
coughs and stumbles all the way to work (like
an automotive hangover) is no fun.

This is why you want your own tools instead
of calling the plumber for every hairball.

white2001s10

iTrader: (4)

Yes it is very different. It's also different in each gear and also changes with speed due to wind drag. A dyno does a terrible job of simulating dynamic load changes.
The piston speed changes with loading, and I don't mean average piston speeds. The piston speed at 4000 RPM in first gear is NOT the same as piston speed at 4000 RPM in fourth gear, even though a calculated average would show them equal.

In a high load situation like spooling at low RPM in high gear, there is a large amount of mass moving through the engine, but a relatively low piston speed. This allows boost to build and increases exhaust volume per engine revolution.

I'm not a big fan of the MAF so I won't even get into that.

SlickVert

iTrader: (5)

On my NA cam only car, if I set my AFR on dyno to 13.1 it will richen to around 12.7 on the street. I use the dyno to only get numbers and see what it like as far as timing.