I was talking to a guy with an Mercedes W211 E55 that I'd done a TCU tune for. He used his car on the dragstrip and was often having traction issues off the line. He had noticed that when he tried to launch in 2nd gear (by selecting "C" same as our "W" mode), he got better traction but, it wouldn't hold in 2nd and would change up too soon. I'm not a drag racing expert, and I have to roll my car off the line to get a decent time (otherwise there's just no traction). I don't want to buy another set of rear wheels (fitted with drag radials) for occasional use. Would there be any merit in making a drag strip specific TCU tune?

For example, I could replace the existing "W" mode with:

• Start in 2nd gear and move all the WOT changes up to the TCU limiter
• Prevent any kickdown (don't want it going back to 1st)
• Unlock the converter for the 2nd gear start (and leave it unlocked a bit longer) to reduce the effects of the higher gear start.

Any suggestions, or do you think I should just buy some drag radials?

BTW, I'm currently running a 3.27 ratio wavetrac diff. with 285/30 R20 rear tyres. The last time I ran, the best I could do was a flat 12.0s, but with a 125mph ET. I've increased the power significantly since then, so I expect that the traction issues will only be worse.

 

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Andrew, It sounds like a great idea, for someone who competes at drag competitions. IMHO people who creat custome tunes mush have a ROI, and I am not too sure there are enough XF enthusiasts to justfy such a high cost for the manhours needed to creat one. Might be a whole lot cheaper in the long run to buy a few sets of drag radials (when you burn up a set, replace them, if you but a 'lot', say 6 or 8, you'll maybe save more per set).


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Hi GraphiteGhost, thanks for your comments. You're correct about the need for a ROI on the custom tunes, I don't think some people appreciate just how long it can take to develop and test a good TCU tune. In this case I don't think I'd have to do very much, it's just a few tweaks on some existing stuff. The Drag Radials would definitely be the best technical solution, but I don't take my car to the track very often and was thinking that a software change might be best for occasional use, as the ROI on drag radials wouldn't be great either. As I'd use the tune personally, I'm not too concerned about how much time I put into it and the knowledge gained would be applicable to a lot of the other Mercedes TCU tunes I do.

I was mainly wondering if the second gear start stuff with a freed up converter would work or not. The TCU tunes I make these days have 4 modes (Sport(S), Winter(C), Manual, & Agility(A)), with better gear changing and far more options than our original Crossfire's ever had. The tunes run some extra software to be able to access the 4 modes and I think (if the drag mode had merit) I could repurpose the Sport or Winter mode into a Drag (X) mode. The only issue with the TCU software is that it uses the same torque converter lock & unlock settings for all modes, so that wouldn't be great when in one of the other modes that don't want a loose second gear. If the X mode worked OK, I could probably write some extra code into the TCU to swap over the torque converter settings when in X and put them back to normal when in the other modes. That way I could run the same TCU all the time and not have to swap it at the track. The solution would be more suited to the occasional racer.

 

OK, didn't know you were the programmer. Will follow your progress here, Good luck!



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Andrew , have u heard of my car? 10.55 at 132 mph, and i have no traction problem. 3.27 ratio wave trac,,, 10.83 at 127 with open rear (traction control on . this was a few years ago,, sold that car,,2 v8 ran 11.0 at 120 sold that car also now have another srt6, will be installing v8 soon,
now to the street tires i run kumho 275-35/19 ecsta ps91 with wear rating of 260 ( very soft) next ones will be rating of 200, very very soft.
Oh i now am going to be running a 3.90 open rear,, i have a 3.64 with tcu for sale bolts right into our crossfire. ,yes open just like the crossfire without a wavetrac this also fits into a limited , std and or Auto

 

Hi

Thanks for the offer but I drive my car mostly on the Highway so 3.64 is not much use to me and I can make up any EGS52 TCU tune I like. I was just looking to see how far I could go with software changes before I purchased new tyres. I think the 3.27 will work OK (as your original car has shown), but I want to keep my 20" rims. There's very limited options for drag radials in the 20" size, so I think my next step will be some stickier street tyres. I've been looking at some Nankang street slicks. NS2R, 305/30/20 with a ware factor of 180. I'm just not sure if the overall diameter will make them too big to get on and off?

The other thing I've considered is modifying the TCU tune to leave the converter a bit looser (in 1st) and also reduce the torque limiter for 1st gear (as soon as it gets some grip it should be right). Plenty of things to test out, to see what effect they have. Based on your experience, do you have any suggestions on the torque converter control or torque limiting?

 

I do not see a 305/30-20 in my book,, but here are some 295/30-20 is 11.6 wide 3.5 sidewall 27"tall it will fit
305/25-20 is 12"wide 3.0sw and 26"tall ,,255/30-20 is 10 w 3.0sw 26tall 255/35-20 10w 3.5sw 27tall 325/25-20 12.8w 3.2sw 26.4 tall ,,335/25-20 13.2w 3.3sw 26.6 tall and345/25-20, 13.6w 3.4sw 26.8 tall (stock 19" is 255/35-19 10"wide 3.5 sw 26"tall)
any tire with under 260 wear will stick 70 to m80% 200 will stick with a 20" tire about 85 to 90% in this video the tires are close to 100 wear drag radials this was 2013
for street and maybe 2 times a month at the track the stock converter is good

 

Thanks for the info on the tyres. The tyres I have now are: Nankang Noble Sport NS20 285/30-20 (26.8") with treadwear 240 (so not very sticky), NS-20 | Nankang Tyres and I was looking at: Nankang NS2R 305/30-20 (27.4") semi slick with treadwear 120 NS-2R | Nankang Tyres (not sure if 27.4 will fit), but a good 295/30-20 might be a solution (what brand was that?). What tyre pressure do you typically run on the street tyres (at the track)? When you say "stock converter" which converter do you mean, the NA V6 converter, the SRT6/V8 converter, or the M113K converter? They will all fit but have different characteristics. The reason I ask is because, when I had my M113K converter rebuilt, I asked about potentially modifying it's stall speed. They said that the simplest solution would be to use the smaller V6 converter, it would spin up quicker, have a slightly higher stall speed (if I didn't lock it up first with the TCU) and that it had the same clutch inside it as the M113K converter.. Sorry for all the questions.

 

sorry forgot the tranny. i use the V8 transmission converter , the srt6 converter lock up is not strong and will brake down within a matter of time.
as the tranny i use a case sent to me by Rudy and all the parts ,some from the Gt all together the internal new parts are from 4 different Mercedes transmissions, i do have to move my tranny mount about 1" to the rear. once built with all these tranny's stock parts, the transmission is rated for engine HP of around 750 ,,, and after 656 runs on the drag strip and a daily driver for 10 years , the last five of that ran in the 10's sold it ,it now runs in the high 9 second. banned from the track because no roll cage, one is being installed this year
Oh to answer your question stock converter from a SL 55