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  #1  
Old 10-26-2007, 04:25 PM
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Dyno Issues with AWD

I just left the dyno shop. My intention was to show the difference a Level 10 Hydrosystem (Valve Body) has between shifts versus a stock shift setup. Also, I was going to compare a cold air intake setup with the ToMyx intake vs the engine bay setup I previously tested. I don't expect anything hp related to heat going through the air filter since it was tested in the engine bay with the hood open. I wanted to see if the extra length of tubing going into the fenderwell showed any difference than a short tube in the engine with length and/or sound resonance from the throttle bodies. Main purpose though was to look at shifting changes in between gears though.

Anyway, the dyno operator (Andy) was having trouble with the AWD system. The front wheels were moving much faster thant he rear wheels on the rollers. This did not happen with the previous dyno runs I did. With this happening, a dyno run could not be performed. I called TomsSVX inquiring about this while the car was on the dyno. He suggested adjusting the throttle position sensor. It needs to be at .48 - .5 (Help me out here Tom if you read this..) while the car is at idle. This sensor reads info to the TCU to tell it the load on the wheels. I did not do a voltage check there though. Time is money on the dyno. So....we stopped and called it a day.

I will be checking this out this weekend (My voltage). Meanwhile, has anyone else had a problem similar to this? If so, how did you resolve it? I was tempted to put a FWD fuse in and test on the dyno. I have done this on my Outback Sport and XT6 with no problems. Tom highly recommended against it so instead of being stubborn, I had to fight the urge off and let it be.

Anyone else experience rotating wheels at different speed issue? I have only once on one of my XT6s and the tranny was failing. The SVX tranny shifts and operates great right now, even in the pouring down rain (It has been raining hard all day).
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Kevin Thomas
1997 2.2ltr Subaru Impreza Outback Sport Wagon (AWD/Auto) 13.03@100mph
1989 2.7ltr Subaru XT6 (AWD/Auto) 15.912@85.93mph
1996 3.3ltr SVX (AWD/Auto) 15.070@91.38mph
***R.I.P***
2010 RAV4 AWD Sport (13.717 @ 99.19mph )
2015 Honda Fit LX CVT (15.2 @ 90mph)
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  #2  
Old 10-29-2007, 08:43 AM
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Kevin,
I'd suggest checking for codes in both the ECU and TCU. Since both your front and back wheels are turning, you should be able to assume your solenoid C is functioning correctly. I agree with YT to check the TPS voltage. Checking for codes should show if you've got a speed sensor issue. There are two of them (if memory serves me right) and their job is to make sure the front and back wheels are turning at the same speed so the trans doesn't grenade.
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  #3  
Old 10-30-2007, 02:12 PM
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on this note, I have a tranny code for my speed sensor#2 showing, but there is no BIG problem with the shifting. My SVX is a FWD, what do you think the VSS#2 does in the FWD setup??? anyone? I have a weird lag at WOT when the Torque control is enabled.
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  #4  
Old 10-30-2007, 02:37 PM
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Thread moved to appropriate forum.
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  #5  
Old 10-30-2007, 03:24 PM
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Quote:
Originally Posted by Myxalplyx View Post
I just left the dyno shop. My intention was to show the difference a Level 10 Hydrosystem (Valve Body) has between shifts versus a stock shift setup. Also, I was going to compare a cold air intake setup with the ToMyx intake vs the engine bay setup I previously tested. I don't expect anything hp related to heat going through the air filter since it was tested in the engine bay with the hood open. I wanted to see if the extra length of tubing going into the fenderwell showed any difference than a short tube in the engine with length and/or sound resonance from the throttle bodies. Main purpose though was to look at shifting changes in between gears though.

Anyway, the dyno operator (Andy) was having trouble with the AWD system. The front wheels were moving much faster thant he rear wheels on the rollers. This did not happen with the previous dyno runs I did. With this happening, a dyno run could not be performed. I called TomsSVX inquiring about this while the car was on the dyno. He suggested adjusting the throttle position sensor. It needs to be at .48 - .5 (Help me out here Tom if you read this..) while the car is at idle. This sensor reads info to the TCU to tell it the load on the wheels. I did not do a voltage check there though. Time is money on the dyno. So....we stopped and called it a day.

I will be checking this out this weekend (My voltage). Meanwhile, has anyone else had a problem similar to this? If so, how did you resolve it? I was tempted to put a FWD fuse in and test on the dyno. I have done this on my Outback Sport and XT6 with no problems. Tom highly recommended against it so instead of being stubborn, I had to fight the urge off and let it be.

Anyone else experience rotating wheels at different speed issue? I have only once on one of my XT6s and the tranny was failing. The SVX tranny shifts and operates great right now, even in the pouring down rain (It has been raining hard all day).
The TCU has nothing to do with the distribution of torque front to rear. The TCU varies the split on the basis of sensed wheel speed front/rear.

This whole scenario demonstrates just how unreliable are dyno readings. I gather than in this instance power was being read from only one axle, with the other running free, and it was going too be a matter of judgement when deciding if both axles were turning at the same speed. If this was the method used in respect of previous testing of the intake, the figures are certainly very suspect, as is the dyno operator.

It has been stated that, the US cars were equipped with a centre clutch as a means of enabling two wheel dyno systems to be used in respect of anticipated smog laws. Any dyno which simply provides a means of allowing the one set of wheels to freely rotate, can not in any shape or form provide reliable measurements, but can be used for simple smog testing.

Unless a dyno is highly sophisticated and measures total power delivered by both axles, measurements must be taken with the front drive fuse in place, so that all power is delivered by the front wheels. This fact can not be disputed.
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Old 10-31-2007, 07:38 PM
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Quote:
Originally Posted by Trevor View Post
The TCU has nothing to do with the distribution of torque front to rear. The TCU varies the split on the basis of sensed wheel speed front/rear.

This whole scenario demonstrates just how unreliable are dyno readings. I gather than in this instance power was being read from only one axle, with the other running free, and it was going too be a matter of judgement when deciding if both axles were turning at the same speed. If this was the method used in respect of previous testing of the intake, the figures are certainly very suspect, as is the dyno operator.

It has been stated that, the US cars were equipped with a centre clutch as a means of enabling two wheel dyno systems to be used in respect of anticipated smog laws. Any dyno which simply provides a means of allowing the one set of wheels to freely rotate, can not in any shape or form provide reliable measurements, but can be used for simple smog testing.

Unless a dyno is highly sophisticated and measures total power delivered by both axles, measurements must be taken with the front drive fuse in place, so that all power is delivered by the front wheels. This fact can not be disputed.
Trev, I posted what I believe the problem to be. It is a bad transfer valve solenoid assy according to a 'Torque Steer' thread. I now have torque steer under heavy acceleration. I will be looking into getting this fix (If it is in fact the problem).

Oh yeah, I never tried to convince you of the dyno readings because I already knew of your stance on dyno tests. I encourage any and everyone to test these things by their own means. I respect your opinions and facts on these matters. Everything is suspect!

Even still, I have not read anything from Subaru that states the intake was engineered specifically for the car. I am talking about the throttle body to maf sensor to resonator box in the wheel well. I have the whole Road and Track 'Birth of the SVX' on my computer and have read the article a couple of times. Nothing on the intake (throttle body to maf sensor to intake resonator in wheel well) itself. Only past the throttle body is where the engineering seem to began. I could have missed something though. Could you point out where and why the stock intake would be considered a 'best fit' for the SVX? We can take this off line if you like.

The stock intake looked like a rush fit to me and it seems they simply put a box around the throttle body because it was the easiest thing to do and possibly help reduce intake volume [As in sound volume]. There is not a lot of space between the throttle bodies and the fire wall. The intake box certainly does not seem to support air flow though. Again, everyone is encouraged to test their intake design and fabrications though.

We can argue about the results all day long. I only question the stock intake setup. It has bothered me for years and I'm glad to be done with it. Let's start a new thread on it. Don't forget though that my dyno runs were all pretty much in the 165whp-169whp range for the STi air filter/cut resonator combo. I think if there was a problem with the dyno or turning of the wheels on the rollers, the variance would be much greater than 4whp over a years time, even though the dyno was moved to a new location.

Let's focus on intake design and why the stock one (from throttle body to resonator) is considered best or better than what anyone on the site can make.
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1997 2.2ltr Subaru Impreza Outback Sport Wagon (AWD/Auto) 13.03@100mph
1989 2.7ltr Subaru XT6 (AWD/Auto) 15.912@85.93mph
1996 3.3ltr SVX (AWD/Auto) 15.070@91.38mph
***R.I.P***
2010 RAV4 AWD Sport (13.717 @ 99.19mph )
2015 Honda Fit LX CVT (15.2 @ 90mph)

Last edited by Myxalplyx; 10-31-2007 at 07:41 PM.
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  #7  
Old 11-01-2007, 12:32 AM
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Kevin,

Unfortunately I made a Typo and I apologise. My opening sentences should have read:-

“The TPS (Not the TCU) has nothing to do with the distribution of torque front to rear. The TCU varies the split on the basis of sensed wheel speed front/rear.”

The TPS does not operate as you suggested, viz. “This sensor reads info to the TCU to tell it the load on the wheels.”


I do not agree with you in respect of the SVX intake, I am confident that all has been carefully engineered, regardless of any Road and Track article.

The designers would not have invoked extra production costs involving complicated tooling to produce a plenum at the entrance to the throttle bodies, if this was not desirable. At first sight the plenum may appear as an obstruction in an otherwise smooth passage, and as a result you state:-

“The stock intake looked like a rush fit to me and it seems they simply put a box around the throttle body because it was the easiest thing to do and possibly help reduce intake volume [As in sound volume]. There is not a lot of space between the throttle bodies and the fire wall. The intake box certainly does not seem to support air flow though.”

As I have pointed the plenum is intended to provide a means of commencing a “tuned” system at that point and the plenum is part and parcel of the design. The resulting system is carefully designed/engineered, to provide optimum engine performance in line with the intended design parameters covering the car as a whole. Only in the event that it is intended to alter these parameters should modification be attempted.

Currently it would appear that the object is to raise the power band upwards in RPM. It is possible that alterations to the inlet may assist in this direction. However in this respect, to date nothing has in fact been proven.

As mentioned previously, I contend that the first modification/experiment to be tried, is to clear and free up the passage between the two main plenums, leaving the remainder of the inlet tract as standard.

N.B> In all of this, IT IS COMPLETELY STUPID TO CARRY OUT MORE THAN ONE MODIFICATION AT A TIME BEFORE MEASURING A RESULT. If this procedure is not strictly adhered to all analysis is futile, wrong and useless.
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Old 11-01-2007, 02:01 PM
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Quote:
Originally Posted by Trevor View Post
As I have pointed the plenum is intended to provide a means of commencing a “tuned” system at that point and the plenum is part and parcel of the design. The resulting system is carefully designed/engineered, to provide optimum engine performance in line with the intended design parameters covering the car as a whole. Only in the event that it is intended to alter these parameters should modification be attempted.
We agree on this part! Seems like all is well then. Actually, I think this applies to just about any make/model car that has any iota of engineering applied to it. How much attention to detail and engineering of the intake and other parts are up to the manufacturer, their engineering team and how much R&D $$ they wish to apply to various parts of the car. So...I agree!
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Kevin Thomas
1997 2.2ltr Subaru Impreza Outback Sport Wagon (AWD/Auto) 13.03@100mph
1989 2.7ltr Subaru XT6 (AWD/Auto) 15.912@85.93mph
1996 3.3ltr SVX (AWD/Auto) 15.070@91.38mph
***R.I.P***
2010 RAV4 AWD Sport (13.717 @ 99.19mph )
2015 Honda Fit LX CVT (15.2 @ 90mph)
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