65kodey

Hello all,

Need to get the car smoged but worried about the two wheel dyno test on the all wheel drive system. Any advice on this topic?

cairo94507

My local smog shop said all wheel drives were exempt from the roller test. Take that with a grain of salt as I was in the M5 and not the 4S getting a smog.

Macster

I've had my 03 996 Turbo smogged a couple of times and it doesn't go on any rollers at all. The tech does the test with the car parked on the drive at the entrance of the test bay.

camsoccer

Took my wife's AWD BMW in for a smog a few months ago and the tech told me that they can't smog AWD vehicles on the roller. Instead the tech will take the smog test while your car is at idle and then to simulate the car being on a roller the tech will conduct a second smog test with your vehicle in neutral at 1500 RPM's... It's pretty straight forward and unless you have your cats by-passed you shouldn't have any issues passing.

65kodey

Thanks All for the replies. So they did not put it on the two wheel Dyno! I have read in other sites that if the car was on the two wheel dyno it would not hurt the awd system, that its not the same as 4wd. Can this be true?

Andrew Ward

How would a gundo hack impact the test?
Thanks

JohnnyBahamas

Depends on the shop and the tech... and if they can/do see it during visual.

Some shops see ANY modification in the engine compartment, no matter how tangentially the mod is related to emissions, and they just stop there telling you to go away out of fear of the shop getting a fine, or worse, I suppose.

Emission wise, I would think that there would be no effect... other than the test sounding better.

Macster

Not likely.

I'd not try this to find out what would happen, but my WAG is the DME would detect the rotating rear wheels with the stationary front wheels as rear wheel spin and engage the power to the front diff. The car would jump off the rollers and into whatever was at the front of the car.

Even if the car was placed on 4 independent rollers my info is this will damage the coupling, the center differential, that transfers power to the front diff.

The only 4 wheel dyno or roller setup Porsche sanctions is one in which the rear rollers drive the front rollers at the same speed so the car's DME thinks the car is on the "road". Porsche specifies somewhere in the factory manual (at least for the 996 Turbo) what type of or brand of dyno is Turbo AWD compatible/safe.

Andrew Ward

Ok thanks

Ynot

I took my C4S to get emissions and they don't put it on rollers even though they have 4 rollers for 4 wheel and AWD cars.

65kodey

Thanks Macster for your insight.

What I had read "somewhere" was that the DME detects that the rear wheels are spinning and not the front so it disables the front diff from getting power. That the power to the front wheels is only applied when the wheels are already spinning.

zcasper

I just got C2S my smog checked in Mountain View. The computer told him the dyno wasn't needed at all. But he did say that all all wheel drive cars are exempted as long as there's not a way to disable it.

Macster

News to me but the newer cars with the DME controlled clutch pack might have this level of control. I said "might".

But -- and this is important -- I'd have to have something from Porsche clearly stating just what kind of smog test dyno, power testing dyno, any kind of dyno, was ok to use before I put my AWD Porsche on one.

Even then I'd be reluctant unless it was clearly needed.