Hercules86

had three different tuners tune the car within the past 2 years the last tune being lets dyno tune which i taugh would be the best option since it was dyno tuned!!


im still extremely unhappy with results. my a/f ratio is at 11.2 isnt this suppose to be the ratio for a supercharged car. i know na vechiles are suppose to run from a 12.3 up to 13.1 a/f ratio.

the car is actually slower then before and i dont pull out of the hole like i used too. according to dynolicious pre and post tune im actually almost 1.5 seconds slower from 0-60 and my hp#'s are down more then 30hp??


let has great service and very nice respectful staff....any advice on what to do here? should i get me old file back and wait for another dyno tune?

Quadcammer

there is a lot of info missing.

1. what model 220 do you have?
2. what other modifications do you have?
3. Have you datalogged to determine timing, as well as a/f through the powerband (and yes 11.2 is way rich).


My opinion is that you should leave an MB tune stock unless you have so many mods that the tune just doesn't work.

c131frdave

A leaner car can make more power, however things have to be perfect. A top fuel dragster runs lean (which is why they blow up in a massive fireball sometimes when they are too lean...). If your fuel isn't high enough octane, you're engine will knock, and the computer will retard the ignition severely limiting power (to keep your pretty Mercedes from making a big fireball ). I'm betting that is why you are seeing a slow start.

If your tuner was told to make maximum power, all he cares about is what the car is making at higher rpm. If you had an area of low pressure going through the day he tuned the car, and now you have an area of high pressure, (assuming you aren't turbo/supercharged) leaning out the car that much could make a huge difference with the change in weather (the MAF/MAP sensors will compensate during normal driving, but under WOT, the engine is open loop and goes strictly off the fuel map).

I'd have the guy tune it back to 13:1 or so. If you are hell bent on wanting a quick car, put nitrous on it and get the power when you want it instead of playing with the fuel injection. A lean engine is a hot engine (heat is power), and with detonation, high temperature, and heat expansion of aluminum components, you are taking 2000 miles of wear from the engine every 500 miles of actual driving. (ok, that's a guess, but lean engines are short lived)

Quadcammer

while there is a lot of correct info in your post, there is also a lot of questionable stuff.

Unless there was a tornado nearby, an area of low pressure is gonna have practically no impact on the a/f. There are sufficient fuel/timing tables to get close enough that you shouldn't have more than a few basis point change in a/f.

Also, you make the point about open loop, but then make the point that a lean engine has a shorter life. Since the commanded a/f of 13.1 (I like about 12.8 personally) is only at WOT, the engine will 98% of the time be run in closed loop with the feedback sensors attempting to keep the a/f stoich. Therefore its not lean for the vast majority of its life and its life expectancy should not be meaningfully shortened. Not to mention, we aren't talking about a hugely powerful engine (3XX from a 5.0 3v engine is nothing worth talking about), nor is 13.1 THAT lean.

Vadim @ FD

Hercules:

Can you post a dyno graph?

What engine do you have?

Hercules86

Vadim i will pm you all info. Im gonna redyno the car this week and get you a new graph

c131frdave

With your air to fuel ratio that low (11.2, not 13.1), it will have a tremendous effect on power. I agree with you that the effect wouldn't be tremendous in a carberated car, but this car has a knock sensor in it. If the car was tuned as lean as possible for the current weather conditions, as soon as those conditions change, your car will likely start pinging at wide open throttle. The computer is what will greatly retard the performance of the car, not the weather directly.

A lean engine definately has a shorter life. I'm assuming the poster is in WOT all the time. Why tune the car if you aren't going to use the power. During normal driving, the car will rarely see over 80 bhp or so. Only under WOT will it see 3XX, and when it does, it will be using the fuel map- and I believe the poster said 11.2:1. That IS lean. Very lean. Lean enough to burn pistons.

During normal driving, the external sensors monitor a/f ratio and adjust the fuel to best conditions. When you jam the throttle to the floor, those inputs are ignored and the computer looks at a graph. It constantly looks at the throttle position sensor. When it sees it going past 95% (presumably- not sure where Merc decided WOT begins, but 95% is pretty standard), it looks at engine rpm and throttle postion and where it intesects the fuel curve on the graph, that's how much fuel it puts into the engine. Any tune is a tune to that graph. If the car is supercharged or turbocharged, the tune will be to the waste gate control or whatever also, but principally it is to the fuel curve.

Irregardless, 11.2 is way too low.

Quadcammer

I agree that 11.2 is way too rich. The rest of your post is inconsequential. I'm aware of how EFI cars are tuned. I have spent an obscene amount of time tuning my supercharged mustang.

That said, 13.1 is not that lean.

Finally, there is a difference between using the power and being at WOT all the time.

It seems like you are trying to prove your knowledge on the subject, but it doesn't seem like you have much actual experience here.

c131frdave

Just 22 years...

Hercules86

isnt 11.2 mean its running rich not lean??


13.1 mean its about normal not too lean as oliverk said

Hercules86

i just wanna know whats at which a/f the cars makes more horsepower and torque.


does it make more power at 11.2 or 13.1??


and with 55k camshafts, 55 spring and retainer installed this week shoiuld i leave it at 11.2 or get my orginal 13.1 file back??


thanks

Quadcammer

Yes, 11.2 is very rich for an NA car. My 700rwhp cobra with 20psi of boost only runs an 11.3 at its 7500rpm redline. Not all of this fuel is burned, and the unburned fuel is used to cool the cylinder.

Although I still don't know your current mods, I tune with a commanded a/f of between 12.8 and 13.1 is fine. Any tuner worth his salt will datalog the car with a wideband, read the plugs after pulls, and make sure the knock sensors are not active.

Once you install the cams, you will need to have the car tuned or at least have the tune checked. Cams can cause cars to act a bit funny, and can certainly alter fueling needs, especially at lower rpms.

Now Dave, the number of years doesn't mean much. What has your involvement been in efi tuning for the past 22 years? How many vehicles have you tuned?