I was recently involved in a techno-debate with cleatus12r and he knows a lot more about diesels than I ever will, but the question of tuning and boost has been pestering me. My red line to the wastegate is removed and I have a low-mileage stock turbo in "Stinky". I have the Ford AIS intake with 60eM and 80e tunes (among others), but I have stock exhaust. Stock tune boost creeps up to 20 PSI, where the 60eM and the 80e both lurch to 20 PSI and climb to 27.

What gives?


My goal has always been to keep Stinky stock-ish (no real performance mods like injectors or bigger turbo) and to chase the elusive 20 MPG highway. I've reached 19.5 (calculated) on a long highway run, so I can taste the dust of my quarry. I will be purchasing a 4" exhaust very soon, but I want to get the AE first. I can do both in one hit, but I would rather get the AE to find out if there be demons lurking about under the hood before I plunk down for the exhaust. This also gives me the opportunity to learn what the truck does before and after the exhaust mod.


Thoughts?

 

I am not sure what you are asking? Apologies for that.

Are you asking about how quickly the turbo spools due to the increased combustion?

Or are you asking what gains besides EGT's and airflow for your diesel air pump an exhaust will net you?

 

Fuel/Heat.. Other than that I have no idea..

 

If your getting 19.5mpg now I don;t think I'd play with it if you want it to be stock. Some have lost mpg with bigger exhaust rather then gain. You got air intake, I didn't notice on muffler or cat but it running good. 20 boost on stock tune is right, or even couple pounds high, 27 with load is all about what your going to get, I'm supprized it don't defuel. If you want less egt, go 1.0 exhaust housing, thats what banks dose. Not meant for arguement.

Chet

 

With tuning you will see the boost shoot up pretty quickly with a stock turbo. I found that after I installed a ported compressor housing the boost builds much smoother and the engine pulls better in the mid to higher rpm range.

You can get similar results with a 1.0 AR turbine housing too.

 

With mileage like that -19.5 -I don't think you're gonna find too many demons but it is nice to be able to check the numbers, with ae-

 

19.5? i dream of getting 15 one day...

 

More fuel, equals more exaust, which builds boost. Tunes add fuel!

 

I've heard rumors of losing MPG with the 4" as well, that's why I've held off this long. I can't wrap my head around as to why - maybe somebody knows the dynamics behind this. Defuel - I've read posts on this happening, but I don't know what that feels like... or maybe I do but I don't recognize that I've lost something.

As for EGTs, I'm all good. The highest I have ever seen was 1200 on the manifold (for about a second) and that's when I'm on a steep grade while passing, then OD kicks and the problem disappears. Under normal conditions in the mountains, I see anywhere from 500 on the flat to 1000 on a climb. I still have to learn what the EGTs do when I tow the boat and try out my tow tunes.

With good EGTs and boost, the 4" would then just be for sound effects?

I get a black puff when I stomp on it, but it disappears when the boost catches up. If I slow the spoolup, wouldn't I risk more coal? When I removed the red line, I took off this little bleeder tube and I was peaking at 25 PSI boost. The mechanic that had this before me put the bleeder tube on there for some kind of aid with boost, but I don't know what it's about. I bought this from a dealer, but I learn more every day about how the previous owner really loved on that engine.





That was my theory, but I didn't know if the stock tune did something to the EBV or something else to mute the boost.


Everybody's responses are exactly what I was hoping to get here. Everything I've done to the truck before was black and white, but now I'm in that zone where things are much better than they were and I'm sneaking up on diminished returns. As I understand this, I might have hit the sweet spot and any mods from here on just add power at the expense of MPG.

Once I get that AE, I will be sharing data from my truck and I will be looking into data recording.

 

A puff of black smoke on initial hard throttle is normal. Black smoke is essentially unburnt fuel that is being expelled. The reason you get this at first is there is not enough air. As boost builds, you get the required air for your fuel mixture and it burns more efficient. If you are looking for the most power, you want to have more than enough fuel for the air you are pumping through. Blowing coal is a waste of fuel. If you are looking for MPG's you don't want lots of black smoke. If you are racing you want a decent amount, but really it is a balance of air/fuel ratio.

The tube removed from the turbo wastegate line is a trick to not open the wastegate when the wastegate solenoid is asking for the actuator to open. Disconnecting the red line is the same thing as having that there. Really the only time you would get the solenoid to open is on really heavy throttle or when letting off the throttle after heavy acceleration. The idea of the wastegate is to dump the turbine side pressure when it is not needed to save the turbo.

Here is the Wikipedia answer:
A wastegate is a valve that diverts exhaust gases away from the turbine wheel in a turbocharged engine system. Diversion of exhaust gases regulates the turbine speed, which in turn regulates the rotating speed of the compressor. The primary function of the wastegate is to regulate the maximum boost pressure in turbocharger systems, to protect the engine and the turbocharger. One advantage of installing a remote mount wastegate to a free-float (or non-WG) turbo includes allowance for a smaller A/R turbine housing, resulting in less lag time before the turbo begins to spool and create boost.[1]

 

Tuned exhaust can be an important asset to an internal combustion engine. The dynamics of expanding exhaust gasses that rapidly cool as it is channeled down a tube is a bit over my head though...
I once attended a seminar on the subject and from what I gathered, the general principal is that some sort of balance is desired when any system is designed or modified. It is generally agreed that some savaging effect should be present since it actually helps maintain the flow of exhaust gases towards their exit point. What you don't want is the exhaust pulse to stall in the pipe if it can be avoided. As the exhaust travels down the pipe, the gasses begin to cool rapidly and the speed of flow actually slows down. With too large of a pipe, the gasses could stall and all scavenging effect would be lost.

Mathematical calculations show that a 3.5" diameter exhaust pipe can just barely support the maximum flow of exhaust gases discharged from a pair of 2' up-pipes when a factor is applied to account for the reduction in exhaust gas temperature as the material travels down the pipe. So, in theory, a stock exhaust system should not be restricting HP readings on an unmodified engine and could even provide just the perfect amount of savaging effect to help evacuate the exhaust gases in the most efficient manner, thus maximizing MPG at a certain RPM range.

The exhaust system on my F450 is 3 1/2" in diameter and has an exhaust back pressure gauge that takes it's reading between the turbo and exhaust brake. Under normal driving, that gauge never moves....not even the tiniest bit. I may have seen it flutter at WOT, under heavy load but only when engine is in the 3100 RPM range. Under those conditions, the needle on the gauge might be showing 1 psi or less of back pressure. So, based on that data, the stock size exhaust system is not restricting flow by any measurable amount.

When my PHP chip arrives, I'll try out the hottest setting and see if I can get that gauge to move. It stands to reason that more fuel would create more gasses which should make more exhaust pressure downstream of the turbo....so it would be interesting to see what changes I might witness with the different calibrations. However, even though I'll likely be making more power, I still think the stock size system will be up to the task. Changing things like injector size and turbos would likely require an associated exhaust diameter change since it appears the OEM system might have been sized specifically for stock components. However, this is just a guess on my part...

This would be a good question for Cody since I am also curious if there really is anything in the stock (or custom) calibrations that could result in 'de-fueling' under certain conditions.

I can say that I've owned my '99 F250 for quite a while and I didn't get any aftermarket gauges until mid-2006. At that time I only added two gauges (trans temp and boost). I didn't add EGT or Fuel Pressure until June of 2010 just prior to our annual camping trip to the forest. Total weight of truck and trailer is 24,800 lbs and I was curious to see what my EGTs really were since I had made that very same trip a dozen times before. When it came time to make the big climbs, I put my foot to the floor and looked over at the EGT gauge where it climbed right up to 1400 degrees or so. My first impulse was to lift off the throttle since I had learned that temp was too high but then I talked myself into staying in it since that is what I would have done prior to having a gauge.

At that moment, I had plenty of power to pull the hill and was holding a steady speed in 3rd gear. After about 20-30 seconds, it felt like the engine power was decreasing and I began to loose speed while my EGTs were dropping at the same time. If 'de-fueling' actually exists, then perhaps that is what it might feel like.

Now-a-days, to climb that very same hill, I simply pull down to 2nd gear and apply just enough throttle to keep the RPMs in the 2500-2600 range. The truck will want to go faster, but I just let off the throttle and manage my speed so it's in the 43-45 mph range and EGTs haven't been a concern since. I feel like having an EGT gauge has helped me become a more sensible driver and learn what my engine likes and doesn't like. One of the things that it doesn't like is to be lugged down in a higher gear at lower rpms...

Looks like a product called "boost tube" that was supposed to bleed off some of the pressure signal used to open the wastegate.
Boost Tube
I am not sure how effective this tube would be unless one also adjusted the pre-load on the arm to increase the amount of drive pressure required to open the valve.
Seems like disconnecting the red line would be a more effective method to increase boost and thus more power...
With the red line connected, the wastegate diaphram could begin receiving a signal when boost reaches 6-8 psi under some conditions. Disconnecting the red line effectively disables the PCMs ability to regulate boost which may not be a bad thing for maximum power but it seems logical that it could possibly have a negative effect on MPG under some circumstances. Were you able to get 19 1/2 mph with the red line disconnected?


If you are so inclined, it would be an interesting experiment to use AE to measure exhaust back pressure with your 3 1/2" diameter exhaust and then compare to readings you get when the 4" system is installed. You might want to log two separate runs, one for stock and the other in one of your higher hp calibrations. Then do the same thing once the new exhaust is in place and compare the readings.

Data points might be RPM, MPH, EBP and Volume Fuel Desired.
I am assuming these would be WOT runs with EOT at least 140 degrees.

 

I just have a sec to reply, but I've read everything and I will be back in the morning with more comments and questions. This is getting good!

 

The PCM will defuel via a signal from the MAP sensor at approximately 23 PSI of boost. I have experienced this and is why I installed the Riffraff OCR. Does this ring a bell?

 

Is this needed with tuning? I would think the tunes could override the defuling.

 

Fueling. There is much more low boost fuel on hotter tunes. That is the cause of the puff of black smoke when you nail the throttle. Fuel is the biggest controller of boost. The wastegate does very little. I didn't notice any real difference on mine hooked up or not. I don't think the vans even had a wastegate.