well, i was doing about 12x in 3rd gear, and my car wouldnt go faster. so, how much loss was i suffering because i wasnt going into OD?

 

no ideas?


anyone ever try to dyno in 3rd gear? what was the hp difference between dynoing in 3rd and in OD?

 

dont you always dyno in 3rd gear for an auto, its the 1:1 gear

 

uhm, i thought you were supposed to dyno in OD (i dont have any money to dyno yet, hence my ignorance). since you dont reach your top speed in 3rd, i assumed that it meant that in 3rd, you're not getting the full potential.

 

you wont get an acurate dyno reading in any gear except for whichever one is 1:1 due to torque multiplication.

 

Thats the 2nd post in two days that got eaten by the server, grrrr.

You can dyno in any gear, i'm not sure what you guys mean by 'torque multiplication being a problem', or not being 'at its full potential'. A dynojet calculates the overall gear ratio in terms of RPM/MPH. You can find that ratio on any dyno data sheet like this. That is why you don't have to tell them what rear end gear you have, or what gear you are in. The dyno measures the drum acceleration and the hp it would take to accomplish that.

Here are 4 reasons to dyno in the 1:1 gear.

1) Most importantly, everyone else dynos in 1:1 so it will make your results more accurate to compare with others.

2) There is the least tranny friction in the 1:1 gear, 4th in a manual or 3rd in an auto. On a side note, lower rear end gears, 4.11 vs 3.42s, with a smaller pinion gear could show slightly higher frictional losses but this is minor.

3) The mass of the engine will accellerate slower compered to dynoing in a lower gear which would wind up faster. This makes the inertial losses in the motor smaller compared to the inertia of the drum.

4) It's closer to the optimum rate for data collection. I don't personally 'buy' this reason, but I was told that by a dynojet operater. I don't think that equipment should have any trouble taking accurate measurements on a motor spooling up 2x as fast, but i didn't design it or operate one regularly.

So you could argue that the OD gear would have more friction, but spin up slower which would partially cancel out. ANother consideration is how fast you really want to be spinning that drum

As to why your car didn't shift, i'm not sure. I don't have an A4, but i thought they don't shift into OD when you are WOT and you had to let off a second when you got to that point??? Is 120 mph in 3rd your redline/shiftpoint, or somewhat less than it???



-brent

 

i'm still pulling hard in 4th gear (OD)

it takes a bit more to shift into 4th gear when ure going WOT

 

my car just stops at 120....will not go any faster, and not rev limiter either...just will not shift into 4th, at WOT or maybe 90% throttle.

 

Is it maybe the top speed limiter? If your car didn't come with Z rated tires when it was new, it has or had a top speed limiter on it I believe.

Try taking it to 110 in 3rd, and ease off the throttle so it shifts to 4th, then ease back into it to continue to accelerate in 4th and see if it will pass 120. If it won't then it's just about got to be the top speed limiter.

 

well, almost...it was ~6k rpm. cam redlines at 6.5k

 

Most automatics won't shift into OD at greater than 70% throttle (might be less, I haven't had one in a while). This is to keep you from burning up 4th gear (I have done this, not fun). Partially the same reason the transmission kicks down into third when you nail it. Easier to speed up the car, less chance of breaking the tranny.

 

ahhh wont shift into 4th at WOT? thats great, i thought my tranny was slipping or something.

 

My car will shift into OD at about 125 or so at WOT.

 

The only way I know of to make an auto shift into OD at full throttle is to install a manual valve body. Still, I wouldn't advise doing so. Besides, where can you cruise at any speed greater than 70 and not worry about the cops (autobaugn and deserts excluded)?

 

I believe Montana has no actual posted limits on the Interstate.

However my understanding is that the troopers will stop you for anything over 80 to find out why you're running so fast...

Maybe I'm wrong.

Even so, the only way a car with 3.42s, 3.23s, or 2.73s wouldn't pass 120 is if either the car is WAY down on power all over the place, or it has a top speed limiter.

My car would be running 130 MPH at ~5800 RPM in 3rd.

I have only run that fast in my car twice. The first time was the day I bought it, and the last time was during some Autotap logging for knock retard after my gear install.

Of course, that does not count the dyno pulls where the car was running faster than that.