Guys,

2005 Z51 MN6 cammed - supercharged

I'm starting to get a real launch from my car when downshifting into 4th and 3rd gears. When I say launch I mean the whole front of the car jumps and the thing is ready to launch. Now if I wanted to go go go its great but this is happening when I'm downshifting and coming to a light. I also get "Engine Drag Control Enabled" in my DIC.

Any reason for this, I read other posts on this message and I'm sure my tires are not slipping. However, I have new Vossen Wheels 19 fronts and 20's on the rear, would that cause issue with the computer??

Thanks,
Bonez

 

Launch? you mean lurch forward? and how recent after the wheels did this start, like right away? I think it could be the wheels/tires combo.

 

It's immediate as soon as the car goes into gear and I let off the clutch.

 

Do you just pop the clutch out? Have you tried brining the RPMs up on the engine before you release the clutch?

 

Also check out Page 3-59 of the Owners manual

ENGINE DRAG CONTROL ACTIVE
This message displays when engine drag control is
active. When driving in a lower gear in rainy, snowy,
or icy conditions and then letting up on the accelerator
or downshifting, the rear wheels may begin to slip and
this message displays. This message stays on for
a few seconds following the engine drag control event.

 

I'm in FL and its been nice all the time, no rain or anything on the roads and I wasn't even going all that fast, like 30-40mph.

 

No, usually RPM's are low and then I downshift but I do not rev the RPM's up beforehand. Never did and never had that happen.

Talked to my shop, might be something needed in the tune / computer.

 

Do you have the stock sized tires on the car?

Drag control is normally activated when the car thinks that the rear tires are rotating too slowly in relation to the fronts - it thinks that you have managed to get the rears sliding or losing traction (ice, snow, rain) as a result of your downshift. If you have larger diameter rears (or smaller fronts) the the car can get the wrong idea. There is nothing wrong with this. btw. It's the car doing a normal thing (unless yours is screwed up somehow.) The message is just to let you know that the low level surging you'll feel is the car doing its thing. It's an informative message and not a "get this fixed" message.

Z//

 

Thanks for the above, appreciate it. However, the issue that bothers me is the "lurching" or "surging" forward because it could be dangerous if the car jets forward and someone is near me in front, that is my concern.

The tires I have are bigger than stock, stock on a C6 is 18 fronts 19 rears, my wheels are 19s front and 20s rears. However, this just started happening a week or so ago. I've had the tires on for like a month+.

 

The car isn't going to "jet forward". What's happening is that the car is feeding a tiny bit of throttle into the system to try and get the rear tires to quit sliding. What you're feeling isn't acceleration. It's less deceleration. There is a difference. If you're following someone closely enough for this to cause you to hit them then I suggest that you're following them waaaaaay too closely

But this may be the first time that you have created the situation that caused the car to bring drag control into play. The wheel size is not the issue; it's the mathematical relationship between the front and rear tire diameters. That's the starting point for the computer's calculations.

Your choices are:

- get the front and rear tire relationship back in sync.
- drive the car with the traction control system off (or at least comp mode)
- get used to it

Experiment/practice with the car to learn when it happens so you know what to expect. If you learn how to make it happen at will you'll quickly realize that it's not really a big deal. Any brake or throttle input will cancel the drag control, btw.

My car has bigger rears and I get the drag control event every now and then - usually at higher rpm & speed. I can make it happen just be letting off the gas - no downshifts required. I just accept it as part of the car. Other folks have gone to a size bigger rears -and- a size bigger fronts which preserves the front/rear ratio.

Z//

 

If your not matching revs accurately on downshifts, that's a major problem. If you fail to do it in a corner you could lock the rears and crash the car. I would make sure you are matching accurately so that the momentum of the car is never being used to drag the rpm up after you go to the lower gear. You can do it with the clutch in, or ouble clutch and do it in neutral. If under braking, this involves heel-toe technique...

 

What are the tire sizes of your front and rear tires?

 

Not rev matching on the downshift? That's performance driving 101.

 

the above is very interesting, and could the be the cause. and it could be the overall relationship of diameters is slightly different (or more than slightly) from stock and the computer is reading it occasionally under certain circumstances.

 

Can be risky if you don't!

We need to know the tire sizes?

 

Unless there is actually something wrong with his car (which is probably not that case - but it could be) then it's probably the tire sizes. Faling to rev match could/would also bring it on. If I had to guess I'd say that tire size changes have brought the car closer to the threshold where drag control will activate and then the failure to rev match brings things over the threshhold - even at relatively low rpms and speeds.

There have been quite a few threads on this in the C6 Z06 forum. A search on "drag control" should present lots of good information on the topic.

Z//

 

thanks for the info! I don't recall reading about drag control activating in any other thread on C6 General.

 

Bill

 

Guys, thank you so much for this input, I'm going to review this with my shop guys and I'll probably deal with it, never happens at high speeds but your right I probably will have to pay attention to the car closely and see if I can recreate when I want, which I have been doing.

My Tires are Pirelli P Nero Zero
275/30/19
305/30/20

 

The Pirelli's you have are not that far off from the OE diameters but slightly increase the likelihood of getting drag control.
Pirelli=== GY
F 25.6 === 25.7
R 27.2 === 26.9

Just try to keep the rev's up while downshifting.

Bill