# Quattro on a FWD Dyno?



## Atomic Ed (Mar 19, 2009)

Did a little research and couldn't come up with a definitive answer. It's my impression that to dyno a 225 on a FWD dyno, all you need to do is pull the #31 fuse. My builder insists that you disconnect the shaft and/or the Haldex. 

What is everyone else doing for single axle dyno runs?


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## hunTTsvegas (Aug 27, 2012)

Atomic Ed said:


> Did a little research and couldn't come up with a definitive answer. It's my impression that to dyno a 225 on a FWD dyno, all you need to do is pull the #31 fuse. My builder insists that you disconnect the shaft and/or the Haldex.
> 
> What is everyone else doing for single axle dyno runs?


I've only heard of folks pulling the fuse as well. Would be a lot of work to disconnect all of that for some dyno runs.


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## 20v master (May 7, 2009)

Your builder is wrong. Also pulling the ebrake up also disables Haldex.


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## [email protected] (Jul 1, 2009)

I'd say that your builder has a fair argument. The issue is that the driveshaft will still be spinning inside the Haldex.











For some time now, I've looked at this as a potential drag on the drivetrain which might be robbing the Quattro TT of power on the 2wd dyno. But I've never been able to find any documentation to support that notion. Instead, I've come across this document posted on Waks:

http://www.wak-tt.com/haldex/haldexfuse.htm


It sounds like running that Haldex coupling with the fuse disconnected is a reasonable concern. Nevertheless, I have done it on our test car multiple times.


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## 01ttgt28 (Jun 23, 2009)

Dyno my tt at force feed (also where the franken turbo car gets dyno seen it their) and they unplugged my
Haldex and pulled the fuse


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## Atomic Ed (Mar 19, 2009)

[email protected] said:


> I'd say that your builder has a fair argument. The issue is that the driveshaft will still be spinning inside the Haldex.
> 
> 
> 
> ...


This has been the crux of the discussion between my builder and me. He's conservative on things like this and I’m willing to take a little chance. The above was the same points he was making. But like the most of you say, it’s been done many times before with just the 31 fuse pulled.

He wants to take the TT up to an AWD dyno 2 hours away and I’m willing to go with a local FWD dyno. But I can’t deny he knows his stuff when it comes to Audis/VWs, so I guess I will yield to his knowledge and experience and make the drive.


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## [email protected] (Jul 1, 2009)

Atomic Ed said:


> I will yield to his knowledge and experience and make the drive.


I recommend you do a good bit of road logging before troubling with that trek to a dyno. Since you're running Maestro, you can deduce a great deal about the performance from the logs.


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## Atomic Ed (Mar 19, 2009)

[email protected] said:


> I recommend you do a good bit of road logging before troubling with that trek to a dyno. Since you're running Maestro, you can deduce a great deal about the performance from the logs.


We're in the middle of this now. We're hitting an IAT spike that's pulling timing at the moment. Builder has some ideas on how optimize the setup to reduce the spike. We want to get the tuning dialed in without WMI before we move on to the next phase. 

Looks like we're booked for Jan. 2 and/or 3 for the dyno run.


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## [email protected] (Jul 1, 2009)

If you've got logs I'd love to see them. 2.1L of motor ought to be a lot of fun.


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## Atomic Ed (Mar 19, 2009)

[email protected] said:


> If you've got logs I'd love to see them. 2.1L of motor ought to be a lot of fun.


The car and all of the logs are at the shop right now. I'll post them up as soon as I can after the dyno run is completed.


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## M this 2! (Feb 8, 2012)

It's WAY easier. under the back, just unplug the Haldex. It's the plug on the back side of the Haldex and next to the exhaust heatshield. VF does this daily.


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## Marcus_Aurelius (Mar 1, 2012)

The problem with this is that you'll still spin the bevel box, drive shaft, all the way to the input shaft! As mentioned in the Wak document, the mechanical pump will provide some fluid pressure and spin some of the clutches. This is unwanted stress that anyone should avoid if they can (burnt clutches is the concern with this practice). I've done it once in my car and don't think it's something I'll risk very often. You'll sometime hear that haldex cars dynoed in 2WD layout with the fuse pulled (or haldex unplugged), yield similar numbers when on a 4WD dyno. It's because you're still spinning and suffering from most of the 4WD drivetrain parasitic loss (even with the haldex without power). Not recommended!

I am waiting to see your numbers Ed! opcorn:


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## [email protected] (Jul 1, 2009)

Marcus_Aurelius said:


> You'll sometime hear that haldex cars dynoed in 2WD layout with the fuse pulled (or haldex unplugged), yield similar numbers when on a 4WD dyno. It's because you're still spinning and suffering from most of the 4WD drivetrain parasitic loss (even with the haldex without power). Not recommended!


I had an experience consistent with that theory when dynoing the FrankenTT on a 4wd DynoJet. When we pulled the fuse and ran only the front wheels, the power reading was unchanged. I'd assumed the anomaly was with the dyno system. Interesting. Too bad nobody's ever investigated this question (and reported on it). For a while I've been curious to try a simple test: pull fuse #31, put the car on a lift, and run the car in gear. Do the rear wheels spin at all?


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## hunTTsvegas (Aug 27, 2012)

[email protected] said:


> I had an experience consistent with that theory when dynoing the FrankenTT on a 4wd DynoJet. When we pulled the fuse and ran only the front wheels, the power reading was unchanged. I'd assumed the anomaly was with the dyno system. Interesting. Too bad nobody's ever investigated this question (and reported on it). For a while I've been curious to try a simple test: pull fuse #31, put the car on a lift, and run the car in gear. Do the rear wheels spin at all?


I recall seeing a video in which someone did this. The wheels did still spin but were easily stopped by simply placing a hand on them. Can't seem to find it right now though.


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## Atomic Ed (Mar 19, 2009)

Marcus_Aurelius said:


> I am waiting to see your numbers Ed! opcorn:


Soon my friend, soon.


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## Atomic Ed (Mar 19, 2009)

[email protected] said:


> I had an experience consistent with that theory when dynoing the FrankenTT on a 4wd DynoJet. When we pulled the fuse and ran only the front wheels, the power reading was unchanged. I'd assumed the anomaly was with the dyno system. Interesting. Too bad nobody's ever investigated this question (and reported on it). For a while I've been curious to try a simple test: pull fuse #31, put the car on a lift, and run the car in gear. Do the rear wheels spin at all?


Some speculation on my part. 

First, if you are using a standard haldex controller, the same dyno numbers would be consistent with how the haldex expected to operate in this condition, i.e., fwd with no unbalanced load to engage the rear drive. So I would expect the numbers to be the same.

If you have a blue haldex controller or better, it would depend on if there is a torque request to engage the back drive. (This would be dependent on the type of dyno.) Like you said Doug, it would be interesting test. Maybe a better test would be to put the TT on the front dyno rollers with the back wheels off the ground and load the front wheels, if anybody has the guts to try this. :screwy:

I think this is why some dynos have a tough time with dynoing a TT due to the on again/off again haldex engagement.


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## Atomic Ed (Mar 19, 2009)

hunTTsvegas said:


> I recall seeing a video in which someone did this. The wheels did still spin but were easily stopped by simply placing a hand on them. Can't seem to find it right now though.


I would expect this at low speed and no torque on the front. Should be a different story at WOT and loaded on a dyno.


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## Marcus_Aurelius (Mar 1, 2012)

[email protected] said:


> I had an experience consistent with that theory when dynoing the FrankenTT on a 4wd DynoJet. When we pulled the fuse and ran only the front wheels, the power reading was unchanged. I'd assumed the anomaly was with the dyno system. Interesting. Too bad nobody's ever investigated this question (and reported on it). For a while I've been curious to try a simple test: pull fuse #31, put the car on a lift, and run the car in gear. Do the rear wheels spin at all?





Atomic Ed said:


> Some speculation on my part.
> 
> First, if you are using a standard haldex controller, the same dyno numbers would be consistent with how the haldex expected to operate in this condition, i.e., fwd with no unbalanced load to engage the rear drive. So I would expect the numbers to be the same.
> 
> ...


With the haldex turned "off" you'll have a rear wheel still spinning with the car on the lift. The hydraulic pressure engaging the clutches is low but still enough to create engagement. The spinning rear wheels can be overcomed by a small force, but what that does is spin the the clutches internally (not good for their life). 

Ed, I don't think the programming plays any role in this, especially when it's all switched "off". What we are experiencing on a dyno with fuse pulled is all mechanical and a result of having a mechanically coupled fluid pump. Stock, blue, or competition/orange controllers are identical once the software is out of the loop.


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## [email protected] (Jul 1, 2009)

Marcus_Aurelius said:


> Ed, I don't think the programming plays any role in this, especially when it's all switched "off". What we are experiencing on a dyno with fuse pulled is all mechanical and a result of having a mechanically coupled fluid pump. Stock, blue, or competition/orange controllers are identical once the software is out of the loop.


I'm reminded of a butter churn. Those things are not easy to work. Wait, how old am I again?


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## Atomic Ed (Mar 19, 2009)

Marcus_Aurelius said:


> With the haldex turned "off" you'll have a rear wheel still spinning with the car on the lift. The hydraulic pressure engaging the clutches is low but still enough to create engagement. The spinning rear wheels can be overcomed by a small force, but what that does is spin the the clutches internally (not good for their life).
> 
> Ed, I don't think the programming plays any role in this, especially when it's all switched "off". What we are experiencing on a dyno with fuse pulled is all mechanical and a result of having a mechanically coupled fluid pump. Stock, blue, or competition/orange controllers are identical once the software is out of the loop.


Doh! :banghead: I was thinking of Doug's runs when I wrote this, AWD-FWD. You're right Max, shouldn't make any difference on the dyno and the fuse pulled.

So the summary is; to be really safe (and maybe more accurate), drop the shaft. But running with the shaft in place seems to be a low risk due to the experience of the group.


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## Atomic Ed (Mar 19, 2009)

[email protected] said:


> I'm reminded of a butter churn. Those things are not easy to work. Wait, how old am I again?


Still younger than me!


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## [email protected] (Jul 1, 2009)

Atomic Ed said:


> So the summary is; to be really safe (and maybe more accurate), drop the shaft.


That's a test I can easily do at FFE. But the transfer case will still be engaged unfortunately. Here I think is an interesting insight. Our FrankenTT dynos at ~310 to the wheels, while a Mk4 driven by a FrankenFriend named spartiati shows a good 25whp more on the same dyno, same day. Yet look at how the cars compare on the street:











Ignoring the hapless wheel spin of his fwd car, it's pretty clear that the Haldex car is very competitive with the Mk4. Yet the dyno will show the fwd car with equivalent low-end torque and more horsepower.


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## [email protected] (May 14, 2009)

hunTTsvegas said:


> I recall seeing a video in which someone did this. The wheels did still spin but were easily stopped by simply placing a hand on them. Can't seem to find it right now though.



Same thing happens to front wheel drive cars with the car out of gear, you still have very small amounts of power being transferred to the wheels. You can stop it by putting your hand on the wheel. 


As for the running the TT in FWD, I still believe running on a true load bearing 4wd dyno is the only true way. When it comes to it I want to see real numbers, not FWD numbers then the hypothetical AWD numbers. 


I put down 299AWTQ last time I dyno'd the TT on 93 octane. 


:thumbup:


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## 01ttgt28 (Jun 23, 2009)

My question is who has awd dyno ? I went to ffe for my tt and had to unplug my haldex and fuse 
Just need to know for my next dyno .i dont want to start pushing 450 500 hp and damage the system or my blue controller.And I'm still waiting on my dyno sheet after i called a couple times still nothing :facepalm:


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## [email protected] (May 14, 2009)

01ttgt28 said:


> My question is who has awd dyno ? I went to ffe for my tt and had to unplug my haldex and fuse
> Just need to know for my next dyno .i dont want to start pushing 450 500 hp and damage the system or my blue controller.And I'm still waiting on my dyno sheet after i called a couple times still nothing :facepalm:


EPL, The Shop CT, KTR, ESP all have AWD dyno's


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## [email protected] (May 14, 2009)

01ttgt28 said:


> My question is who has awd dyno ? I went to ffe for my tt and had to unplug my haldex and fuse
> Just need to know for my next dyno .i dont want to start pushing 450 500 hp and damage the system or my blue controller.And I'm still waiting on my dyno sheet after i called a couple times still nothing :facepalm:


EPL, The Shop CT, KTR, ESP all have AWD dyno's


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