studman

A few weeks ago, I was dyno tuning my car. Once the car was tuned, I humored myself and ran pulls in each gear from 2 to 5. Upon returning home, I put all the runs into the RunViewer software and noticed the following:


2nd gear is consistently 10 HP/TQ below 3rd, 4th, and 5th gear.

Anyone else ever noticed this? Also, if you are gonna dyno soon, can you pull a run in 2nd gear to see if it's just my car, or if they are all like this.

Also, the pull in 5th gear reached 157.10 MPH. And it still had one more gear to go. However, my tires were already heated up from all the other tuning pulls, so we shut it down before they reached their top rated speed of 168 MPH. Please remember that this is on a dyno, not in a real-world environment, where it would be drag limited.

Progress

iTrader: (26)

Isn't the top speed of most cars recorded in the top gear, not the overdrive gear? In your case, 5th would be the highest speed. Am I right?

itdood

I think it might have to do with the way the dyno calculates based on the gear ratio. It probably used the wrong ratio for that particualr gear.

The reason I say that is because I thought dynos are most accurate when you do a pull where the motor and trans are as close to 1:1 as possible. That's why they say for a MT, the most accurate pull is 4th gear.

If the wrong ratio were applied to the calculation you'd see less area under the curve at all points which you do here.

The only other explanation I can think of would be more friction in the drivetrain for 2nd, but that would make no sense since 2nd is riding on the same shaft as some of the other gears, so you would have seen the friction problem there too.

One last thing, I've never heard of anyone doing pulls in any other gears other than 4th for a MT, since it's the closest to 1:1 gearing.

IceY2K1

iTrader: (3)

You mean 6spds?

Because, many 4th/5th gen 5spds dyno in 3rd even though 4th is closer to 1:1, since it's easier on the car and really doesn't matter in the end unless you're trying to compare your car against non-Maximas.

itdood

Actually I wasn't sure what gear in the Max's are best, that's just my experience with other cars.

IceY2K1

iTrader: (3)

IIRC...4th/5th gen is 4th and 5.5 gen is 5th for closest to 1:1.

However, I'm still waiting for SteVTECs alarm to go off and him to reply, but it really doesn't make a difference as long as you can adequately load the engine and collect enough data in the length of time for a complete pull. If you do a pull in 1st/2nd, you're going to get too quick of a run to collect consistent/adequate data and top gear will be too long and cause the engine to heat soak/lose power.

SteVTEC will explain this a lot better then I can.

SteVTEC

2nd gear has you accelerating a lot quicker. So a higher portion of the engine's power is being used to pay for the inertial parasitics. As in, it takes energy to actually accelerate the engine itself, the tranny, diff, shafts, and your wheels - they don't just spin up to speed freely. At WOT and steady state (you can do this on an active load biased dyno) the engine is at full throttle but there's zero acceleration. None of the engine's energy is being used to actually accelerate the drivetrain, so inertial parasitics from acceleration are zero and you'll see pretty much the engine's full power at the wheels.

SR20DEN

iTrader: (7)

SteVTEC is correct. Because of the boat anchor 46 pound flywheel/clutch combo that these cars have. This is a major drawback to using an inertia style dyno, however I believe they're more real world than a brake style dyno. If you get a much lighter flywheel it will show up on a dynojet.
I have always felt that my car showed a more accurate representation of its actual power in 3rd than 2nd.