How much boost until detonation? M104. - Page 2 - PeachParts Mercedes-Benz Forum

wbain5280 · #16 12-17-2008, 06:00 AM

Any boost over 14.7 psi will cause detonation causing conn rods to snap. Your engine needs a knock sensor for sure. Here is a link to the late Gus Mahon, FWD turbo drag racer.

Main page: http://www.gusmahon.org/index_main.htm

Tech page: http://www.gusmahon.org/html/tech%20diagrams.htm

RIP Gus M.

RBYCC · #17 12-17-2008, 07:53 AM

Quote:

Originally Posted by Turbo E320

I could get away with a cheap $200 setup since my turbo lags like a fat kid at a trackmeet.

Is it possible that your single turbo is too large?

Turbo E320 · #18 12-17-2008, 09:01 AM

No its my manifold, there is a restriction I have yet to remove because I am lazy

Also wbain, how are my rods going to snap at just 15psi? They are just like the m103 rods correct? Pumpish is ran 20+ psi on a stock engine m103.

wbain5280 · #19 12-17-2008, 09:37 AM

Under higher boost, 15 and over, you need to add extra fuel otherwise there is detonation. The easiest way is to add a cold start valve with a pressure switch set to 14 .5 and dump fuel. See Gus's site to see how he did it. He drag raced turbo 4cyl Chrysler and Dodge cars. The Manual boost valve works great too, what he calls the Grainger valve.

Joreto · #20 12-17-2008, 09:56 AM

Quote:

Originally Posted by JayRash

was there knocking even the slightest hint of knock?

no there was no knock at all

, car fuel wise was in the low 11-s (4x630cc injectors, ignition and fueling controlled by megasquirt, I run a permenently mounted wideband and EGT sensor)

Joreto · #21 12-17-2008, 10:03 AM

Quote:

Originally Posted by Turbo E320

No its my manifold, there is a restriction I have yet to remove because I am lazy

Also wbain, how are my rods going to snap at just 15psi? They are just like the m103 rods correct? Pumpish is ran 20+ psi on a stock engine m103.

I think that actually it's not the boost but the HP/TQ that snaps rods, so its actually up to how much HP your making ....

Turbo E320 · #22 12-17-2008, 10:04 AM

Quote:

Originally Posted by wbain5280

Under higher boost, 15 and over, you need to add extra fuel otherwise there is detonation. The easiest way is to add a cold start valve with a pressure switch set to 14 .5 and dump fuel. See Gus's site to see how he did it. He drag raced turbo 4cyl Chrysler and Dodge cars. The Manual boost valve works great too, what he calls the Grainger valve.

I use a computer. An AEM Fuel/Ignition Controller. If I didnt have that my AFR's would be in the 14's

I can add the extra fuel and knock the AFR's into the lower 11's if needed, If i really felt like it I could drown the motor with AFR's in the 9's. Currently I run 11.8:1 AFR at 10-11psi but as I said I could easily richen it even further.

Joreto · #23 12-17-2008, 10:10 AM

Dumping fuel to avoid detonation works up to a given point, from there on it can't help you and either you start retarding the ignition timing or you use water/methanol injection. In your case I guess the ECU helps by pulling timing if detonation is sensed, question is how much can it pull ?

whipplem104 · #24 12-17-2008, 10:31 AM

Even if the ecu is sensing knock and pulling timing, you do not want to do this.
I think it can pull 30 degrees if I remember. There is actually a code for maximum. But the motor should not be tuned for the computer to pull timing as it will be adding timing back when knock goes away and then knock will come back and so on. Mercedes is also only looking for large amounts of knock. On a motor being pushed hard it could and probably will blow up.
Also as far as how much the motor can take, ignition accuracy is a big factor.
The pre 60-2 teeth motors only have 4 teeth on the flywheel and ignition resolution becomes a factor. I do not think that total boost or horsepower at 15psi is going to blow the motor tomorrow if done properly. I have seem m104 motors hydro-lock and not break or bend rods. But it will not take it forever.
The rods are the same as the stock 2.3 rods and m103 rods also. The pistons are not. I would say that the m103 pistons are definitely more robust.
Also Roman's m103 has 9.2:1 compression stock and he is using e85 which is 110 octane. I think that the head will lift without studs before it blows up if it has a good tune.

Joreto · #25 12-17-2008, 10:39 AM

Quote:

Originally Posted by whipplem104

I think that the head will lift without studs before it blows up if it has a good tune.

Yep, forgot to mention the 16v used ARP head studs :-D. What I wanted to say in the beginning is go slow and be sure what your doing, as they say - "better safe then sorry" ..... As to the tuning whipplem104 is right, tune for no detonation on the fuel you run very day

Turbo E320 · #26 12-17-2008, 12:24 PM

Quote:

Originally Posted by whipplem104

Even if the ecu is sensing knock and pulling timing, you do not want to do this.
I think it can pull 30 degrees if I remember. There is actually a code for maximum. But the motor should not be tuned for the computer to pull timing as it will be adding timing back when knock goes away and then knock will come back and so on. Mercedes is also only looking for large amounts of knock. On a motor being pushed hard it could and probably will blow up.
Also as far as how much the motor can take, ignition accuracy is a big factor.
The pre 60-2 teeth motors only have 4 teeth on the flywheel and ignition resolution becomes a factor. I do not think that total boost or horsepower at 15psi is going to blow the motor tomorrow if done properly. I have seem m104 motors hydro-lock and not break or bend rods. But it will not take it forever.
The rods are the same as the stock 2.3 rods and m103 rods also. The pistons are not. I would say that the m103 pistons are definitely more robust.
Also Roman's m103 has 9.2:1 compression stock and he is using e85 which is 110 octane. I think that the head will lift without studs before it blows up if it has a good tune.

Thats the kind of response I was looking for

Looks like after my transmission is done, I will be investing in some head studs.