Quote:
Originally Posted by turbo8765
I'm very familiar with dyno'ing BMWs and the associated issues. I'm not new to this game by any stretch. I remember when the e46 M3 was labelled as un-dynoable. I'm sure you remember as well. Bear in mind the issues related to dyno'ing BMWs are related to getting a successful run. The cars limit revs and/or power when there is a significant delta between front and rear wheel speeds. Once you've overcome that hurdle and completed a successful run, they're the same as any other high output car.
Do they cut timing due to higher temps given reduced airflow relative to a moving vehicle? Of course they do, as you know all cars do so. As you know there is a general trend whereby cars with increasing power, compression, timing, and/or boost are more susceptible to this effect. Obviously this is also a function of cooling capacity as well. The E and M in this test face exactly the same challenge with respect to reduced airflow.
Your point is that putting the power down more effectively at beginning of a run = faster ET AND higher trap. And that all else being equal the AWD car puts the power down more effectively therefore traps higher... all else being equal.
You've clearly spent a lot of time at the dragstrip right? You clearly have a vast and varied exposure to all things related to drag racing. Then I'm sure you've seen a powerful RWD car switch from streets to slicks and ET improves but trap speeds fall. Given the amount of exposure you've had and your knowledge base I'm sure you're familiar with this phenomenon... so how do you explain it?
BTW.... a little quick to throw "ignorant" out eh.
|
It can be explained by a couple of things. Most people run drag radials that are using a wheel/tire combo that are not stock...usually lowering the overall tire height. This changes the effective gear ratio and might actually improve acceleration down low but could cause an extra shift during a quarter mile run. The extra shift..especially during the final 66' feet of the run (where the trap speed timing lights are) can negatively impact trap speed. Also, stickier and wider rubber are great for getting off the line...but as speeds build...especially with cars that are travelling 120+mph through the traps... the additional rolling resistance becomes a liability. This is especially true of drag radials that are aired down to 15 to 20 psi. Like I said...great for getting out of the hole...but they become a liabilty further down the quarter mile run when traction is no longer an issue and aerodynamic and frictional drag become the enemy.
Sorry if you didn't like the "ignorant" comment.... I only responded in-kind to the inference that my lack of knowledge led me to believe something was wrong with the dyno run..