How much boost until detonation? M104. - PeachParts Mercedes-Benz Forum

Turbo E320 · #1 12-15-2008, 07:13 PM

I have around a 9.0:1 compression ratio with my 1.9mm head spacer and I run 92 octane from BP all the time. Currently I run 10-11psi normally on pump gas and have AFR's of 11.8:1 while at WOT. Today I ran 12.5psi really quick racing my buddies dad in his 04 cobra mustang running a AFR of 11.7 to 11.9:1 on 92 pump gas. I ultimately want to run 15psi this thursday on the dyno but I'm not sure when the detonation will begin to occur.

I am NOT making any timing adjustments to this motor under any circumstances unfortunately. The only adjustments will be made by the computer itself with the aid of its two knock sensors and other stuff.

I beat the cobra stang btw.

whipplem104 · #2 12-15-2008, 08:29 PM

Every engine is different. Mercedes runs around 20 degrees total advance depending on what car it is in. The best way to find out is do what you are doing and run it on the dyno. You can also add a led to the knock sensors to see when knock is occurring. A chassis ear will also let you hear the knock and tune for it.
My guess is that with cool weather you may get away with 15 lbs. May need to spray some meth/water for summer heat though.

Turbo E320 · #3 12-15-2008, 08:49 PM

If I fill up with some Citgo 110 would that guarantee a safe 15psi tune? I have the whole fuel table setup based on a very simple algorithm so when I up the boost the car is usually with .1-.4 points of the desired target and minimal tuning is required.

whipplem104 · #4 12-15-2008, 09:01 PM

You should be fine, but again I would put a monitor on of some kind. You can even just put a hose to a bolt on the block and listen. You will know when it starts to knock. It sounds like the whole thing is coming apart.
If you had access to a mercedes scanner, you could just read the computer for knock also.

Turbo E320 · #5 12-15-2008, 09:08 PM

Could I read knock from a live feed OBDII scanner?

whipplem104 · #6 12-15-2008, 10:14 PM

I do not think so on a 97. I do not have a lot of experience on this though.

c280nz · #7 12-16-2008, 12:20 AM

you will be able to both hear and feel it knock on the dyno,
and you can also see the knock on the power curve as a little spike.

im not sure what 110 fuel will do for your standard o2 sensor either, i dont think it will like it much,
if your going to up the boost make it a bit richer to be on the safe side 11-11.5:1 for higher rpm with higher boost,
but be careful,
just tune it on the dyno for what you are going to run on a day to day basis, i would say keep below 12psi,
cars normally run hot on a dyno which doesnt do any favours for detonation,
because the fan they put in front of the car is no were near as cooling or fresh as open air driving, and the load is normally for a longer period of time.

what happened to using ur aem to control ignition timing? did it not work out/

also did phantom grip email you back about if they can produce another clutch pack for my diff?

Turbo E320 · #8 12-16-2008, 01:31 AM

Quote:

Originally Posted by c280nz

you will be able to both hear and feel it knock on the dyno,
and you can also see the knock on the power curve as a little spike.

im not sure what 110 fuel will do for your standard o2 sensor either, i dont think it will like it much,
if your going to up the boost make it a bit richer to be on the safe side 11-11.5:1 for higher rpm with higher boost,
but be careful,
just tune it on the dyno for what you are going to run on a day to day basis, i would say keep below 12psi,
cars normally run hot on a dyno which doesnt do any favours for detonation,
because the fan they put in front of the car is no were near as cooling or fresh as open air driving, and the load is normally for a longer period of time.

what happened to using ur aem to control ignition timing? did it not work out/

also did phantom grip email you back about if they can produce another clutch pack for my diff?

I abandoned the timing control because the mercedes changes it up so frequently the car gets weird power dips and spikes when the car starts to boost while speeding up a entry ramp or accelerating sort of hard off a light.

I think I will just go 12 or 13 psi for now then maybe 15 or even 16 when I get my ageing water/meth kit installed. Seriously I've had my water/meth kit for almost a year now lol I got it last christmas

Phantomgrip is going to need an entire diff unit sent to them as the block for my car was not saved.

JayRash · #9 12-16-2008, 01:51 AM

I say dont over boost your car man, just tune it to a point where u feel the engine dealing with ease with the tune, that way u run it all day at full load with no second thoughts. and plz do go with water/meth injection ur pistons will love u for the cooling
and u can really up the timing with that.

c280nz · #10 12-16-2008, 03:47 AM

i was looking at watemeth but wasnt happy with the simple boost actavated on/off systems, it needs to be computer controlled / flow controlled,
otherwise the car will miss when it first turns on as at low revs when there is too much water and then not enough up top,
aquamist is the only sortof style system id go for

JayRash · #11 12-16-2008, 05:59 AM

you can try this:
http://www.alcoholinjectionsystems.com/p102/Stage-2-Adjust.-Progressive-Trunk-Mount-Water-Methanol-Injection-System/product_info.html

u can prog it to use several inputs.
but ya am at lost tooo
do i go for aquamist or those guys, am still not sure my self,
i like the this kit thou

Turbo E320 · #12 12-16-2008, 07:13 PM

In my experience the water meth will drop the AFR right around 2 points when first activated. I have not seen any missing problems. Computer controlled flow systems are quite new while boost referenced water/meth systems have been employed by makers such as Holley for decades. I could get away with a cheap $200 setup since my turbo lags like a fat kid at a trackmeet.

JayRash · #13 12-17-2008, 01:35 AM

well on my setup and due to the quirks of CIS i need a stage 2 variable controller w/m,
and although am better off with a split second controller and additional injectors at the moment, i am really looking forwardto the cooling effect of the w/m injection. M103 don’t have the oil jets under the pistons :S, i intend to fit them when this 400k km engine gives way, but until then hope it lives as long as possible

.

Joreto · #14 12-17-2008, 04:59 AM

A note of caution , don't know how strong the m104 internals are but be careful if they are factory . My 2.5-16v run fine a long time with boost under 1 bar but when I increased it to 1.3-1.4 a conrod snapped (couldn't take the power :-D ) just after one week of driving (of course most of the driving during that week was at WOT

) . If your bottom end is stock be careful not to over do it ...

JayRash · #15 12-17-2008, 05:44 AM

Quote:

Originally Posted by Joreto

A note of caution , don't know how strong the m104 internals are but be careful if they are factory . My 2.5-16v run fine a long time with boost under 1 bar but when I increased it to 1.3-1.4 a conrod snapped (couldn't take the power :-D ) just after one week of driving (of course most of the driving during that week was at WOT

) . If your bottom end is stock be careful not to over do it ...

was there knocking even the slightest hint of knock?

am not saying that internals are so strong that they can take all the boost u want, but usually its knock that spells the end. i don't know abt the m104 rods, but i do know that 103's are stronger than the 2.5-16 only because the are not built for the high perform as the 2.5 (ironic)

but then again 1.4 on stock internals would break almost every engine bar a mitsu evo
i mean even wrx subs wouldn't take 1.4 for long, nor can any audi tt or golf gti.