fruitsalt

Hi guys,
I was wondering as to when do you upgrade the stock injectors.

The car has the following mods:
- Euro charged mid length headers, with no cats so straight piped.
- 77mm super charger pulley
- Large heat exchanger
- Johnson heat exchanger pump ( changing to Bosch 010 soon)
- 1 step colder spark plugs
- K&N drop in filters

herpderp

Do you know your current injector duty cycle? anything past 80-85% at WOT and I'd be looking at larger injectors.

Also, if you ever plan on running full e85, or ethanol blends, you'll want larger injectors for that too, possibly with a upgraded fuel pump.

87geeinn

You upgrade injectors when: You start upping the ante with significant power adders (e.g., aftermarket supercharger, cams, heads, etc) and/or different fueling (e.g., E85)... basically anything that demands a significant increase in fuel delivery beyond what the stock injectors can handle. As mentioned by @herpderp above, you cannot answer this question unless you know the duty cycle of your injectors at WOT. Only part I would disagree on is, as long as you aren't at 100% DC, you're fine. At 80-85% you still have some injector left on the table.

With your mods, you're nowhere close to maxing out the stock injectors. And as a side note, I would advise against "one step colder plugs." MB decided on a specific heat range for a reason. Very, very few of us have M113k-powered cars modified to a degree which warrant a cooler plug. Cooler plugs are used to reduce the propensity for detonation when running things much harder. Colder plugs on a stock engine or one with mild modifications is just asking for fouling plugs because of deposits that collect on the plug which won't burn off as part of the normal combustion cycle. Now if you throw a Weistec charger with a small pulley, full exhaust, aggressive tune, and other supporting mods then that may warrant a colder plug.

Don't just throw things on the car that take you a step backward because it's popular or a vendor offers it.

Do you even have a tune?

fruitsalt

Thank you for the info. Yes I do have a eurocharged tune on the vehicle currently.
When I got the tune I did tell them I had 1 step colder spark plugs.
These were installed by the previous owner, the previous owner had it tuned from eurocharged as well, I had to get a new tune with rear o2's on for emission, now am back on the tune that the previous owner got.
Would you recommend removing these and going back to factory spark plugs.

also I am planning a coolant system refresh this weekend, since the radiator is over 15 years old and not sure when the rest of the parts were changed. The car runs around 96-97 C in the city ( ambient in mid 90 F), do you think that is normal or is that high ?

Thank you for the information, I am new to MB and learning as I go.
Will look into the duty cycle this weekend when I can get my hands on a snapon scanner.
I do not believe that I need bigger injectors with the current mods, and I am not planning on modding it further other then switching to coilovers, just wanted to be sure that its not something that I should be looking into.

87geeinn

As far as plugs go: If it were my car, I would switch them over to a normal range plug. You'll be fine as it is now but I would suspect the colder plugs will eventually start to get deposits on them and need more frequent changing vs if you had normal heat range plugs in there which can easily go 100k miles. If you do decide to swap them out, change the wires as well if you don't know when they've last been changed. BTW, the heat range of your plugs are not a factor in the tune.

Coolant temps: Factory thermostat is 190F/87F so I would expect temps around that. Sounds like you may be running a tad hot but I'm not sure. Again, Google is your friend.

Try some Google dorking. Yes, that's actually what it's called. For example, plug "site:mbworld.org E55 coolant temperature" (without quotations) in the search bar on Google. This will limit your results to this site and give you plenty of reading material on the subject.

Exotic-metal55

Duty cycle is best way to go but can be a challenge for the average person to get the info. Age and wear of parts can effect injector flow but in general you can bolt on a 77mm /83mm , cooling mods , air intake with fresh tuned up car and good fuel system. Any weakness in fuel pumps or injectors will hurt flow a lot. Once you add the above mods and throw on headers, then most cars exceed injector capacity, especially when the density altitude drops in cold weather.

fruitsalt

Thank you, I've tried googling and seem to get conflicting answers. Going by what I know from my BMWS, I will assume running 7-8 C over thermostat temp to be considered normal for coolant temp.

Thank you, I will try to get the duty cycle for the injectors, haven't been able to borrow a snap on scanner to see if it would be capable of doing so. Last time I did connect it to the car, it seemed pretty limited in what it could do on the Mercedes platform