bhvrdr

Hello,

I had been experiencing a lot of transmission lag and a bit of throttle lag and decided to try out the sprint booster to see if it would at least mask the throttle lag problem a little bit. I figured it was a long shot but if at least even masked a bit of the lag i'd have been happy. It didnt. The car did indeed provide noticeably more throttle once it came on but unfortunately it didnt help reduce lag in any appreciable way. I also did not like the reduction in throttle control. A 1/4 throttle input would end up equating to more like 1/2 throttle of pre sprint booster input. Consequently you get transmission kick downs when feathering the throttle and this caused even more lag. Oh well.

To make up for my disappointment I treated myself to some new (used) wheels. I was deciding between AMG split spoke 18s and the C63 wheels. I went this way. I like them a lot. I wrapped them in RE760 rubber for a compromise between longevity and traction.





cheers! mike

c250_2012

rims look great - im also considering purchasing them... got any more pics?

im also dreading the throttle issue that so many people on this forum find irritating..

acr2001

Beautiful wheels.

I'm glad to see your Sprint Booster review (sorry that you wasted your time though). Myself and a large handful of people on these forums have been arguing against the SB for years because we know exactly how it works -- which you've illustrated. Many people seem to be fooled by the SB because that loss of throttle control equates to a better response in their eyes. Based on the engineering of the car and the fact that the SB only alters the gas pedals input to the ECU, it is IMPOSSIBLE for it to reduce the throttle lag that we are all so sick of. If you search the forums for Sprint Booster you'll find a handful of threads with very long arguments about it, and also a very scientific white paper which tested it extensively and proved that it is useless in regards to reducing throttle lag. Good luck with your car, sorry the SB didn't work out. They should refund your money within 30 days I believe.

AdidasC230

Glad to read all this info, I kinda thought the SB was Bull but now I see how it reacts for real and your explanation its a mod I wont be doing.

Invain15

I like the rims. On a 250 I would guess that it wouldn't work properly because it will not help with the spooling of the turbo. I just installed the SB this week and I personally like it on my 300. As far as the initial off the line driving I do find some help with passing cars and to me I believe it is more mental than anything off of the line. Its sort of like when you drive a powerful car the first time. There is something mentally about tapping the accelerator slightly and feeling the torque jolt you forward. Where I really notice the help with the SB is when driving at highway speeds. I put 700-800 miles on my car and I sometimes have to drive like I'm an indy car to weave through this wonderful beltway traffic. No I don't drive like an ******* all the time. Experience this DC nightmare and you will understand. Not to jack your thread but anyone that is considering it should try it. If you live in the area I will let you try mine. For the new 250's I highly doubt that you will notice a substantial difference because your car is engineered differently.

bhvrdr

Hello. A member asked me to update on the lag in acceleration issue I have been having.

After living with the car for a bit and trying some different driving techniques I've found that this lag is most likely coming from the transmission programming and may be exacerbated by how this turbo motor interacts with the tcu.

Let me give examples. First let me also say that on every time I start the vehicle I automatically select the sport shifting button on the transmission. It is part of my daily startup procedure.

When starting from a standstill I notice in manual mode the vehicle will take off well. Anything other tha staionary and the transmission may act confused for a half second or so. In manual mode the car will also not hold revs to redline and will automatically upshift. The workaround would of corse be to just make sure you manually upshift before redline but I have noticed so much lag after a manual gearchange that often the car will automatically upshift before it recognized you input and then it gives a second upshift because of your upshift request. In essence having you go from D1 to D3 when you only requested one upshift.

A second and more troubling transmission lag problem is in the downshifting. When attempting to downshift by depressing the throttle 3/4 to full throttle there is significant delay. Although mixture control in the ecu could be partially blamed I am doubting it plays much of a role. It doesn't matter much if using 3/4 throttle or full throttle the tcu seems easily confused and delays gear change. Unfortunately using manual mode will not allow very tight control of downshifting either. Consequently both downshifting in preparation for cornering as well as when powering out of corners there is a significant lack of throttle/transmission control. Take the case of going into a corner and wanting to make sure you have downshifted before starting to add steering angle (while you are still in the braking zone). Well the auto tranny in sport mode will not automatically blip the throttle and downshift. Many others will. So in this case you are forced to use manual mode. The problem again is that manual mode is very slow to respond to downshift requests. You really need to plan a head or you'd be part way through the turn before the downshift occcurs and of couse bye bye rear end traction if that occurs. The same issue could be said for powering out of a turn. Since the car doesn't automatically downshift into turns you lose a lot of time coming out of a turn because if you add throttle to quickly you'll get a downshift while still having steering angle applied and not yet through the turn whereas if you were able to stay in the correct lower gear you could be progressively feeding throttle out of the turn and even using the throttle to rotate the car slightly if needed.

The two issues above I don't think are exacerbated much by the turbo but one area that is probably would be part throttle acceleration at cruising speeds. This is situations on the street where you are passing or speeding up a bit from an already cruising speeds. Here I think load variables from the turbo spooling probably come into play. An example would be cruising at 2500rpm and adding only 1/4 throttle input. In an NA motor this would likely not cause a downshift but would cause smooth and mild acceleration in that gear. In the turbo car the turbo gets spooled fully by the light throttle input at that rpm and the increase in load has the transmission downshifting for pretty light throttle application. Not totally unexpected in a turbo car though.

Hope that clarifies some experiences I've had. I'm still in love with the car but on the top of my wishlist is a TCU performance flash

Cheers! Mike

wnunez89

wheels like nice

jctevere

Sorry to hear about your gripes. The Sprint Booster does not reduce lag as others have suggested. However, it doesn't mean it is particularly useless. What it can help do is help establish a more "aggressive" driving profile so that it eliminates indecisiveness in the TCU where instead of a single downshift, it will perform a double downshift (skipping a gear - unique to the 7-gtronic) which provides great power and response. Also, the TCU may learn to hold gears longer.

However, I believe I have found the best solution to this problem. When you click the shifter to the left and it goes into manual mode, it displays a 6. Unlike other transmissions, this is not a real manual mode, it just means that the transmission will utilize the first 6 gears however it sees fit (regular D uses all 7) and you can even reduce this to 5, 4, 3, 2, or 1. But I like to just leave it in 6 and drive around town. I find that when used in conjunction with "S" mode, it holds gears longer, has GREAT response, and improves the ride quite a bit. Would definitely recommend you try it out!

QwikSilverA4

bro its not like our B5s man. you and i both came from AZ.com and our DBWs were slow unless we chipped. sprint booster is like adding the sport button to our cars... unfortunately on these c250s its not an improvement.

jimmythegreek

Im sure there will be remapping soon for 250 ECU's to help w early spooling of the turbos, and Id bet there will be aftermarket turbos really soon. Id like to see a big honkin turbo w a ECU tune on one of your guys 250 soon

Glyn M Ruck

Nice wheels look great!

Thanks for the honest SB feedback!

acr2001

This is an interesting idea! I wonder if it really makes a difference or if it's in your head? I'll certainly have to give it a try, thanks!

Glyn M Ruck

BTW - I would keep an eye on the European tuners. They have done quite a lot to improve lag & flat spots on the 250 diesel. I'm sure they will improve the Turbo M271 Evo map.

Glyn M Ruck

The SLK 250 has just been road tested by our local "Car" magazine. Their observations are identical to yours for 722.9 transmissions with the new "Economy" flash on Blue Efficiency models. This slightly erratic behaviour is greatly ameliorated with the higher torque V6 & above engines. I suspect we will go through another round of software updates to improve driveability.

That said they were extremely complimentary as to fuel economy the car achieved driven enthusiastically.

bhvrdr

Thanks very much for all of your feedback.

Yes, I'm enthusiastically awaiting any performance tunes or OEM updates.

I tried running in D6 and D5 and although there was an initial placebo from the luck of getting a couple relatively quick shifts, I found overall back to back driving using regular S mode and the D6 and D5 mode yielded similar results. Oh well.

Thanks for the compliments on the wheels too. I love the new look.

cheers! Mike

LandSeaAir

I think that is a great explanation as to why the SB works, it makes a lot of sense. I did the TCU reset with the pedal only half down (a method recommended to temporary simulate an SB) and the only benefit I found was the quicker downshift, I didn't realize that it double shifts, but that make sense)

Do you think the lag is a result of the turbo? I know many people don't like the lag on the C300s, but that's not a turbo issue, more a ecu or tcu issue. Wondering if the turbos are really laggy or its just Benz wire-be-throttle up to its old tricks.

kevink2

I think you are correct. I have owned & modified several turboed cars with manual trans's. A few years back, I test drove a VW 1.8T auto, and was dissappointed in the gear modulation. The root of the problem is taking a 7spd trans that works great with a NA engine, and then try to add another system that is conrolling a somewhat undersized turbo that wants to rapidly speed up above 300,000 rpm's to destruction.

When stopped in manual or auto mode, have you tried a little throttle-with-brake to help spool the turbo?

For oem turbos, the hp curve falls more dramatically than for a na engine. So optimum shifts may well be below redline. The shifts in manual mode (ie M6) may well be close to optimum.

-- Anyone have a link to the oem hp/torque curves? --

I think the "others" would be the Audi DSG twin clutch/input shaft, and the similar BMW SMG expensive manual based automatic tranz's ... apples and oranges. You still basically have an automatic trans with torque converter, clutch bands, and planetary gear sets.


You may need to be in lower gears approaching the corner with the final downshift while braking ... you could experiment with adding throttle when you want that last dnshift to occur.

Again, you have 7 speeds, so if you can get used to working at higher rpms (lower gears), you have a better chance of staying in a gear in manual mode through and exiting the corner.

Is there a boost gage that shows full boost for your example?

The engine's max torque level of 229 Ft-Lbs @ 2,200-4,300 rpm includes your 2,500 rpm example. Although you may have been at 20" of manifold vacuum while cruising, steady state, most modern boost control systems would have you at about 4-5 psi exit the turbo. This pressurizes the intake up to the TB, so little TB opening is needed for a big power increase. It sound like a design flaw in the TCU if it allows downshifts when all that torque is available.

One thing not mentioned is the option of using an approved XW-30 oil, vs the XW-40 you use. If you look at the 229.5 approved list, at least 1/3 of the oils are XW-30's. Lighter oils with floating seal based turbos result in more rapid boost build, especially when starting with a cold engine. High anti-wear additive packages, usually needed for aggressive cam profiles, are not needed with turbo profiles.

Note that I based my answers regarding track like driving, on many years of driving HPDE events, even before the HPDE term was not used. Since I was qualified for solo driving for years, I was invited to be an instructer. I declined.

.

kevink2

In his case, the SB was mostly a problem related to excessive downshifting, partly due to the turbo.

The White Paper showed in Fig-1 that it increased pedal response, and really proved nothing about the ecu lag you implied.

Data-logging would be an excellent way to show any ECU (or TCU) lag, by simply plotting pedal and TB motion, along with fuel injector duty cycle. The following MB log, if true, shows the ECU can overrule the pedal request for TB opening, as you have suggested.

Data Logger for MB

This was a beta unit at the time, but I'm sure there are other universal data loggers that could work with a lap top.

.

Glyn M Ruck

MBSA have told me that processing latency is inherent in the ECU for FBW throttle & there is programmed lag by design that could be changed.

kevink2

Latency could be exacerbated by also having to manage a turbo. With datalogging, which seems unusually scarce for an MB forum, would show whether we are talking milliseconds or large fractions of a second.

.

Glyn M Ruck

Indeed Kevin!

bhvrdr

I've got a HEX CAN datalogger I can hook up. I just figured it's TCU related. I'll need to mess arround and see what channels are what on this ECU.

cheers! Mike

kevink2

Please do it! There is a despeate need for hard dater about ecu lag.

----------------------------------------------------------

Note dater is Massachusetts slang for data.

The Massachusetts final er and a rule for word pronunciation:

If the word ends in a, banana, you drop the a and add er, bananer. But, in general, if the word ends in er, super, drop the er and add an a, supa! )

.

Glyn M Ruck

Please I would do it myself but I don't have the capability.