Need a little advice from some experienced tuners

[StinkyDog]

I removed the muffler from my 5" Magnaflow turbo-back exhaust. This is because the muffler shrinks to a 3.5 inch inlet and seems counterproductive to opening up the exhaust. Anyway, with the reduction in exhaust velocity, the truck gets slightly worse mileage which I assume is due to the reduction in torque due to the loss of scavenging ability with the open exhaust. I know that with pressurized engines (turbo) that exhaust velocity is not a huge factor and they benefit from a wide open exhaust.

I know it's flowing more air because it smokes MUCH less when trounced on.

Now the question....

I am sure this can be tuned, but I'm not sure where to go with it. Obviously it has more air available, so it wold seem logical to add more fuel. Is it worthwhile to add boost to help increase exhaust velocity and return to that "sweet spot?"

I am not asking you to share your specific tunes, just a point in the right direction.

Thanks!

[LB72004]

is your mpg loss all highway, in town or both?

removing restriction in the exhaust will cause the exhaust gasses to exit the engine faster. high pressure to low pressure, the higher the difference the faster the flow.the faster the exhaust gasses flow the faster the turbo will spin, creating more boost. additional boost where not needed is energy wasted turning the turbo, making heat, etc.

try adjusting the turbo vains in the cruise areas so as to make less boost. this will help increase the efficiency of the engine some.

just a thought

[StinkyDog]

Thanks for the response!

It seems to be only highway mileage. I am getting about 15-16 in town, but only about 19 on the highway. I was getting 20 - 22 pretty regularly. Of course, ambient conditions affect any tune, but the ambient conditions haven't changed all that much.

I was thinking along the lines of reducing boost in cruise as well. I will be modifying my tune shortly to reflect that.

Don't know how much further I can go with the timing. Right now it sits around 6.5 running at 75MPH. THis equates to roughly 90% (stock is 85%) with light load on the engine. Oddly enough, I have run the timing up considerably (as high as 13 degrees) and the truck gets QUIETER! I can't seem to wrap my brain around that one. Of course that drops the EGT considerably... but the cylinder pressure and temp must be much higher.

Any thoughts on maximum timing?

Thanks again for the response!

[Wheelz]

Just a note, you can drop the target vain (sp?) position, but if you don't reduce target boost they will still run mostly closed.

[andrewjamesbond1]

Just a note, you can drop the target vain (sp?) position, but if you don't reduce target boost they will still run mostly closed.

^^^ He has a point. You need to look at your Enable Fuel and Disable Fuel control in your Boost Folder. That will let you command whether or not you or the computer is controlling the vanes. If I were you, I would just drop your cruising boost down to 2-4 psi and let the computer sort out the vanes for you. This will let your truck open the vanes and let the exhaust flow more freely.. You might sacrifice some spool up when going WOT, but your butt isn't going to feel it. As for you running high vane position during cruise, when you increase your timing, you are putting more heat into the heads and pistons, just like you mentioned. That also reduces your EGT's, which reduces the amount of "power" your exhaust gasses have to drive the turbo. So to compensate, the ECM closes the vanes more to try to maintain your commanded boost. This is probably why you are running higher vane positions than stock in cruising areas.

[Wheelz]

Also, since you are really messing with timing, not enough stress is put into fine tuning the pilot event. The pilots timing and amount is just as critical and dependent on main injection timing. At idle the pilot is mainly used to control noise, but under load it is used to control ignition delay and burn rate, which is what your trying to compensate for by advancing the timing. There are some good technical papers out there free for the reading if you search "pilot injection timing"

I'm in the middle of evaluating a tune with pilot timing maps that in no way resemble the stock maps, and with no extra fueling, the truck pulls considerably harder than stock when you step on it, and it's quiet enough you cannot hear the motor running above 45 mph as long as your cruising. I am hoping to run it on a dyno once I feel I've tweaked it as much as I could. I'll have some good mpg results in a month or so.

[StinkyDog]

Thanks so much!! There's lots of food for thought here. I have just barely begun to mess with the pilot timing. I am definitely going to do some deep research on pilot timing.

I had not thought about thought about advanced timing causing reduced flow and hence reduced "power" from the turbo.

I dropped the vane position 10% and reduced the cruising boost by 2psi. I will be installing the tune in my truck tonight. I'll post here with the results.

Again, I can't thank you guys enough for the information!

[LB72004]

hey, Weelz!

do you have any tricks on pilot timing? i have done a lot of googling and reading on the pilot timing and there is not much on where to put the pilot event, just that it is before the main. i have adjusted some of me tunes (DSP5) to see if i can tell the differences and the only thing i can tell is a mild change in the tone of the engine. not much in anything else. so for i haven't run it long enough to see MPG gains. for the most part i have always left them stock but lately i have had a renewed interest in optimum pilot timing.

i was just hoping for some pointer that would speed up my tuning to i dot have to reinvent the wheel.

Thanks Jason

[Wheelz]

http://archcomb.itc.pw.edu.pl/downloads/46_2010.pdf

This one helped me out the most and seems to be pretty accurate.

I've read of people on here decreasing their pilot timing to .9mm3 but I've had better success increasing the amount. What you are trying to do is adjust the pilot amount so that it aids in complete combustion. Also the dwell time helps fine tune the ignition delay and how fast it burns.

I know it matters because I tested a tune that had less timing than stock at 1500 and 1600 rpms, but I had advanced the pilot out to 20* (I forget what ms that was off hand) and got about 2 mpgs better than stock. That tune on the highway was as quiet as a gas engine.

[StinkyDog]

Thanks Wheelz! I'm going to spend some effort and time on pilot tuning. I added the post injection back in and gained HUGE power. This is no doubt due to more complete combustion.