190E 3.0-12v Turbo - Page 29 - PeachParts Mercedes-Benz Forum

whipplem104 · #**421** 11-17-2012, 06:28 PM

That is not horrible but could definitely be better. Was this peak at what rpm?

Joreto · #**422** 11-18-2012, 01:39 AM

Interesting thing is that it peaked between 5000-5500 (could not see exactly as I was watching mostly the boost gauge) and the held the same value to the rev limiter. I think it's a lot since I found a formula that calculates it to pressure before the turbo and a rough calculation gave me around 2.76:1 back pressure, which is a lot more than the recommended (if my calculations are correct) . I'll have to make an adapter for the EGT bung and measure the pressure before the turbo.

Here is a quote from http://www.tercelreference.com

Quote:

Say you have a turbo operating at a turbine pressure ratio (aka expansion ratio) of 1.8:1. You have a small turboback exhaust that contributes, say, 10 psig backpressure at the turbine discharge at redline. The total backpressure seen by the engine (upstream of the turbine) in this case is:

(14.5 +10)*1.8 = 44.1 psia = 29.6 psig total backpressure

o here, the turbine contributed 19.6 psig of backpressure to the total.

Now you slap on a proper low-backpressure, big turboback exhaust. Same turbo, same boost, etc. You measure 3 psig backpressure at the turbine discharge. In this case the engine sees just 17 psig total backpressure! And the turbine's contribution to the total backpressure is reduced to 14 psig (note: this is 5.6 psig lower than its contribution in the "small turboback" case).

So in the end, the engine saw a reduction in backpressure of 12.6 psig when you swapped turbobacks in this example. This reduction in backpressure is where all the engine's VE gains come from.

whipplem104 · #**423** 11-18-2012, 09:19 AM

Wow, I did not know that. So in that case the back pressure is pretty significant. That explains why so many turbo cars respond so well to a down pipe.

Joreto · #**424** 11-25-2012, 03:37 AM

Fixed the fuel issue by modifying the stock setup from 2 pumps in series to two pumps parallel. After that I had to retune part of the fuel table where the injectors were maxing out. The injector duty cycle dropped from 110% (reported by megasquirt) to 75% which gives me enough fuel to increase the boost pressure later on. We also measured the fuel flow of the stock pumps i.e. off the car, no pressure regulator, just tied to a battery. The stock 911 pumps flowed ~180 - 183 l/h (per pump,so two in parallel should be good for ~360 l/h free flow), also tested a walbro 255 pump which flowed exactly ~255 l/h on the same test bench.
A word of caution about the 044 pumps, it turns out there are two 044 pumps :

0 580 254 044 -this is the one you want to get if your considering swapping to a 044

0 580 464 044 - this one has a much smaller flow, similar to the 911 pump ...

About the back pressure issue. I went to an exhaust specialist who looked over the exhaust system and came to the conclusion that the back pressure is not caused by the down pipe but by the rear muffler, so this week the rear muffler will be changed.

Lastly, last Saturday I went to an airfield where I did over 20 runs 0 to ~ 240 km/h, the car performed great with no problems. With the colder weather and the retuned maps it was also a bit quicker than before.

Joreto · #**425** 12-22-2012, 10:54 AM

Dynoed the car today, the result is 298.9 hp/427.5 nm at the wheels at 0.7 bar (10.15 psi) ... I'm happy

. One thing that I noticed is that the car was rich according to the dyno WB. My WB showed AFR ~12:1 when the dyno WB reported ~11:1, so my WB may need changing.

Here is the dyno graph.

Next year, when I fix the back pressure problem I'll get the car back on the dyno and this time tune it.

yzn · #**426** 12-22-2012, 11:37 AM

what wideband are you using? maybe it needs calibration

whipplem104 · #**427** 12-22-2012, 12:34 PM

That is a pretty solid power curve. Like yzn said maybe recalibrate the sensor and also adjusting the voltage scale.

Joreto · #**428** 12-22-2012, 01:56 PM

I'm using the old (non linear) zeitronix WB, it doesn't have calibration.

Joreto · #**429** 12-23-2012, 02:04 PM

Dyno video
http://www.youtube.com/watch?v=0RMCxefdOzA

Joreto · #**430** 01-28-2013, 10:20 AM

Last weekend I changed the exhaust system from this (1x76mm)

to this (2x63mm)

Right away the car felt faster (same boost level), so this weekend I decided to do a few runs to compare the results with runs done before.

Here are the results (I've tested the g-tech on a drag strip and it show ~0.2 slower times)

Bad news is that after the second run the gear box started to whine on all gear except 5-th and revers. This coming weekend I'm going to drain the oil to see in what condition it is, mean while I'll be looking into a new gear box. Any recommendations on a strong manual mercedes box apart from another getrag unit ?

whipplem104 · #**431** 01-28-2013, 10:46 AM

That is really quick. That is 118mph and with a awful 60' time.

Joreto · #**432** 01-29-2013, 03:55 AM

Thanks, MPH is good, 60' times are bad since I launch at ~2500 rpm because of wheel hop. Hopefully I'll sort out the back end sometime this year (gotta have a little free time

) and try to eliminate the hop . Main problem now is to decide what gearbox to use . Read the thread on the 722.6 , it would be nice if it could be made to shift manually .

RBYCC · #**433** 01-29-2013, 08:02 AM

Great numbers

The lower back pressure exhaust always unleashes the pent up turbo power !
It's logical...faster you move the gas out the better the turbo makes power

Joreto · #**434** 01-30-2013, 03:02 AM

Thanks Ed, the car is finally beginning to feel like a fast car :-D . I'm planning to modify the down pipe which in my opinion should lower the back pressure even more, but that'll come after the gearbox is rebuilt. Plan is to have the car in top condition for the open drag day in May, aim is to get into the mid 12 secs at the strip in street trim

.

whipplem104 · #**435** 01-30-2013, 09:16 AM

Quote:

Originally Posted by Joreto

Thanks, MPH is good, 60' times are bad since I launch at ~2500 rpm because of wheel hop. Hopefully I'll sort out the back end sometime this year (gotta have a little free time

) and try to eliminate the hop . Main problem now is to decide what gearbox to use . Read the thread on the 722.6 , it would be nice if it could be made to shift manually .

You can absolutely shift the 722.6 manually. I use the cruise control stalk in my old wagon. You can use pretty much any input that is digital to shift. For drag racing you want to use the wot settings though and it will shift at a preset rpm.

For wheel hop the biggest thing is stiffening up the engine mounts. The next is solid differential mounts and subframe mounts. The issue is all the flex and unload on the drivetrain. If you can stand it solid engine mounts also. But it is pretty rough. I want to make an engine shock system that holds the engine in the correct spot but does not effect the vibrations. I was thinking one mostly up and down for torque and one mostly side to side. Also want the extra bolt down locations.