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Old 09-17-2001, 02:23 PM   #1
Jim Lewandowski
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Default Misc. WRX 2.0 Turbo engine/tran/mech. questions

Is the turbo in the 2.0 watercooled?

Has anyone used synthetic in the trans/diffs?

Easy to change your own oil?

Anyone come up with anything to prevent the little dimples that occur on the intercooler surface (I believe I saw this on projectwrx.com). I was thinking of some screen that could be put inside the hood scoop which wouldn't restrict airflow but would keep the larger debris out.

It looks like shifing to 6000 RPM in first gear is optimal based on the dyno curve I saw on projectwrx.com. IOW, 1-2 is a 45% RPM drop. The RPM drop lessens with the higher gears which is optimal from an accel. standpoint. Thus, it might be optimal for a 5500-5700 RPM shift in other gears (I haven't completely worked out the numbers).

JL
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Old 09-17-2001, 02:41 PM   #2
jmott
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yes its watercooled.

yes its easy to change your own oil.
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Old 09-17-2001, 02:46 PM   #3
Zahnster
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Because of the transmission gearing, this is the optimal shift points as determined on a dyno in an earlier test.

For near stock power levels:
1-2: Redline
2-3: 6500
3-4: 6500
4-5: 6400

It's not about the curve dropping, it's about where the torque curves cross. 1st and 2nd never cross, so holding 1st till redline is still faster than shifting to second earlier.

It think once you make some mods that hold boost better at high rpm, shifting at redline in each gear is best. Don't quite remember that part of the test.
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Old 09-17-2001, 03:35 PM   #4
Jim Lewandowski
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Quote:
Originally posted by Zahnster
Because of the transmission gearing, this is the optimal shift points as determined on a dyno in an earlier test.

For near stock power levels:
1-2: Redline
2-3: 6500
3-4: 6500
4-5: 6400

It's not about the curve dropping, it's about where the torque curves cross. 1st and 2nd never cross, so holding 1st till redline is still faster than shifting to second earlier.

It think once you make some mods that hold boost better at high rpm, shifting at redline in each gear is best. Don't quite remember that part of the test.
***
I may certainly be wrong, but a stock dyno chart shows only 125 lb. ft. @ 7000 RPM. Thus, if you delayed shifting until redline, you'd be making less torque for the final portion of 1st gear than if you shifted @ 6000 RPM. IOW, if one shifts at 6000 RPM and is making 175 lb. ft. and when entering the next gear, were making MORE lb. ft. than if shifting was delayed, 6000 RPM would be better than delaying the shift.

I always thought one's optimum shift points were an issues of making the MOST torque for the longest time (IOW, the AREA under the torque curve for each gear would dictate the RPM shift points). For example, it's easy to see that any shift that drops the RPMs below 3500 would not be optimum.

Can you explain what you mean by torque curves crossing (I thought there was only one for an engine)?

JL
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Old 09-17-2001, 03:39 PM   #5
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maximize the area under the POWER curve.

power = work/time.

you want to maximize that.
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Old 09-17-2001, 03:51 PM   #6
Jim Lewandowski
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Which power curve? Torque or HP?

Torque is the answer as HP is a mathematical calc. BASED on torque (which is why the curves always cross @ 5252 RPM).

So, in the above, if one were to shift from 2nd to 3rd @ 7000 RPM, the RPM would be PAST the peak torque RPM when entering 3rd gear. That's not ideal.

JL
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Old 09-17-2001, 04:02 PM   #7
TurboRex
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Jim, I agree that people may be shifting this car at too high of an rpm. However, I think my tach is off and maybe they all are. It would be nice to know if the dyno rpm is actually the tach rpm in our car. This could help considerably. I shift at 6500 according to my tach but feel the real rpm is 6000. Anyone know the accuracy of these tachs?

Thanks,

Greg
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Old 09-17-2001, 04:27 PM   #8
Jim Lewandowski
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I would think the tach is quite accurate. I checked mine @ 60 RPM based on Car and Driver's numbers (25 MPH for every 1000 RPM = 2400 @ 60). It was right on. Turns out the automatic is also 2400 RPM @ 60 MPH.

Point being, shifting too late is usually never optimal from an accel. standpoint based on the average engine's torque curve. IOW, an RSX may have a much later-developing torque curve than our turbo cars.

JL
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Old 09-17-2001, 05:09 PM   #9
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My speedometer is off about 4%. I was on cruise and ran through one of these speed checks. My speedometer said 74 while the radar said 71.

I have also found out that my fuel cut off is at about 7300 rpm (ran nearly that high on my last test run in third gear). However, if you look at the dyno run by turboxs you notice that fuel cutoff is around 6700 rpm on the dyno.

My feeling is that the tach is off about 500 rpm on the top side. If this is true, then the best shift points (on a stock wrx) would be at (per the tach) 6500 in first, and then 6000 thereafter. If Jim is right, then we should be shifting into 2nd at 6000, and then at 5500 thereafter (for drag racing anyway). I will have to test this some time. Has anyone ever tested this as to which is best?

I have heard people saying that 7000 to 2nd is best with 6500 thereafter. However, I am not sure if anyone tested shifting lower.

Greg
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Old 09-17-2001, 05:34 PM   #10
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I forget where the thread is but one of the other things to consider is torque at the wheels. This is where it becomes interesting. You are determing the power through the transmission with the mechanical advantage of reduction gearing....
I forgot who it was but they mathematically found that the 1-2 shift occurs at redline, and the others should occur at 6800 rpm with a stock WRX....
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Old 09-17-2001, 07:24 PM   #11
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Like Akirasoft said, the chart that with the multiple torque curves was one that showed wheel torque, not motor torque. Someone ran 5 runs on the dyno, one per gear and set the graph up to show straight torque at the wheels.

Torque is the twisting force that makes the car accelerate (not trying to start a HP vs. TQ:which one is more important debate here). So where the car is putting down more torque, it will pull harder.

The reason that you don't want to shift before that point, even though the motor might produce more torque at lower revs, The tranny is putting you at a mechancal disadvantage because of higher gear, thus reducing wheel torque more than the motor is at the high revs. hth's
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Old 09-17-2001, 07:54 PM   #12
Jim Lewandowski
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Quote:
Originally posted by Wave
Like Akirasoft said, the chart that with the multiple torque curves was one that showed wheel torque, not motor torque. Someone ran 5 runs on the dyno, one per gear and set the graph up to show straight torque at the wheels.

Torque is the twisting force that makes the car accelerate (not trying to start a HP vs. TQ:which one is more important debate here). So where the car is putting down more torque, it will pull harder.

The reason that you don't want to shift before that point, even though the motor might produce more torque at lower revs, The tranny is putting you at a mechancal disadvantage because of higher gear, thus reducing wheel torque more than the motor is at the high revs. hth's
***
So, someone got actual wheel torque for each gear to help decide shift points (I'd guess overkill, but maybe not!).

Can you explain this last part? I thought the pure fact that the motor is producing more torque at X RPM was better than less torque at Y RPM regardless of anything else. Are you saying that the mechanical losses (% HP/torque loss thru drivetrain) is different for each gear to the point that shift points aren't as simple as looking at a generic torque graph?

JL
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Old 09-17-2001, 08:44 PM   #13
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I present the post I reference for my information:

http://i-club.com/forums/showthread....ht=shift+point

Make sure to look at the graph and discussion about half way through the first page as well as the part in the first post.
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