Fuel enrichment: How much fuel is too much fuel... discuss - General - VWDiesel.net The IDI, TDI, and mTDI source.

• Fuel enrichment: How much fuel is too much fuel... discuss by Staley on 28 Jul, 2004 21:38
• There are alot of informative posts on this forum about adjusting and modifying injection pumps..
  I am going to take apart one of my old NA pumps for my first experience with exploratory surgery on it.
  
  Over the last month I have been slowly adjusting the fuel adjustment on the back of the pump..
  and finally reached the factory installed stop.
  After reading here.. I removed the stop and gave it a whirl.. The diesel now smokes a good bit more
  during acceleration and little too none with normal cruise. Where do you stop..
  the Rabbit becomes more fun with every 1/4 turn!
  
  I was talking with my frined Mike at Overland today and told him about
  my special "fuel" adjustment modification and he told me to be careful.. that it can damage
  the engine from excessive heat.. (melt a piston)
  
  I have noticed lately that with more turns of the adjustment under high load ex: hard 3d-4th gear
  acceleration (50mph - 85mph) the coolant temperature guage will climb from
  center to almost 3/4 of the way to hot. (with a/c on)
  It IS obvious that the engine is making alot more heat..
  
  So my question is.. where do you stop..
  
  I saw the picture of fspGTD's Rabbit PUKING some SERIOUS smoke from the tailpipe..
  now that IS some excess fuel! LOL
  
  Later,
  Mike
• #1 by QuickTD on 28 Jul, 2004 22:57
• Increasing fueling beyond the point of smoking heavily will not really increase the power much more. Mike is correct, the more fuel you add the greater the heat produced, and the greater the risk of burning a piston or an exhaust valve. This is especially true when you add more fuel to an already smoking engine. A pyrometer is a useful tool for evaluating how much further you can go. Sustained exhaust gas temps above 1200-1300º are risky. Short spurts to 1400º are tolerable. A pyrometer is a fairly expensive instrument but you can always use it on your next diesel.
• #2 by fspGTD on 29 Jul, 2004 15:07
• I advise to be safe and prevent a piston from melting, always keep exhaust gas temperatures at or below the stock thermal limits.  If you just take a stock engine and start cranking up the fuel quantity, beware, because at high altitudes and wide open throttle, you will surely be able to exceed the factory thermal limits and will be running the risk of melting a piston.  It CAN happen.  So be safe and if in doubt about increasing your fuel quantity, watch your EGTs.
  
  Things I've found that have a drastic effect on reducing EGTs are: installation of a large-diameter, free-flowing exhaust system, and installation of an intercooler.
  
  Also, based on my experimentation and contrary to what other people may believe... there IS a significant of more power to be had by increasing the fuel quantity above the smoke limit.  Even with my "overly rich" fuel setting, is is noticeable that the power drops off as the fuel temperature heats up, this is because the fuel is getting less dense and so the fueling level drops as the fuel temperature increases.  Relocating the fuel filter into the passenger fender-well does help to delay somewhat the heating of the fuel, however.
  
  The power loss was even more severe when the exhaust system broke and hot exhaust was blowing right at the non-heat shielded fuel tank, which must have heated up the fuel quite a bit.  Although it was smoking less than normal, it was still quite a bit (and in fact, most of the pictures up here of my car Taken from '03 Nationals are with the broken exhaust, blowing at the fuel tank, and less fuel quantity than normal...), and it was quite a bit noticeably down on power.
  
  I did some G-tech runs as a matter of fact when I got to Topeka with the broken exhaust (it feel off somewhere during the road from from Seattle to kansas) and the G-tech confirmed power was down vs where it "should" have been, by quite a bit.  I think that was due primarily to the hot fuel reducing the fuel density and therefore fuel quantity being lower.
• #3 by Staley on 29 Jul, 2004 21:35
• Thanks for the advise.
  I think I will play it safe and back up some..
  I have not installed a turbo yet.. but that is in the near future.
  Later
  Thanks
  Mike
• #4 by QuickTD on 29 Jul, 2004 22:34
• While I don't doubt that there is more power to be had by going past the point of heavy smoke, it certainly doesn't do much for diesels public image, nor does it do the motor any favours. I will admit, I try to discourage it whenever I can. It's real easy (and real tempting) to just crank the screws in until it smokes like a tire fire. You can then be sure you're using ALL the air... :roll:  It is far more challenging to carefully tweak the settings for nearly the same power without the huge clouds of smoke. I wan't to see all those neat diesels from europe brought here eventually. Doubtful that it will ever happen if the legislators and do-gooder types see nothing but billowing clouds of noxious black smoke from every diesel they encounter. Those that run their cars at spectated events, directly in the public eye, please take note...  :wink:      
  
   Another factor in the hot fuel=low power equation is the effect of fuel viscosity on timing advance. As the fuel thins the pump housing pressure tends to drop due to increased leakage though the return orifice and past the timing piston and transfer pump vanes. This can have significant effect on timing advance and therefore power. I've often wondered if a fuel cooler might be a good addition. I know in the A3 cars the fuel is picked up from the same baffled "well" in the tank that the return fuel is dumped into. This is of great advantage in the winter but not so much in hot weather. I wonder if a small trans cooler in the feed line after the filter would help. If the line from the cooler were insulated all the way from the cooler to the pump it should be possible to keep the fuel near ambient. The automatic trans rotary pump TDI's use a fuel cooler in the return line to the tank. The new PD engines use a liquid cooled fuel cooler. It uses engine coolant that is directed through an isolated section of the radiator and cooled to near ambient to cool the fuel via a fuel/coolant heat exchanger. Seems like a lot of trouble to go through, maybe they're on to something?
• #5 by BlackTieTD on 30 Jul, 2004 11:00
• Quote from: "QuickTD"

  Those that run their cars at spectated events, directly in the public eye, please take note...  :wink:  

  
  
  
   :lol: *cough*brysonjake*cough* oh excuse me..
• #6 by fspGTD on 30 Jul, 2004 14:25
• Hey now, I can appreciate your concern, but rest assured, I think the smoking (and the fact that I am seriously racing a diesel, and actually doing well!) actually gives the opposite effect from what you describe, I mean yeah the smoking does get people's attention, but the funny thing is that so many other race car engines (keep in mind NO ONE in the non-stock prepared classes have emissions devices, IE: catalytic converters... racing is primarily about going fastest and winning, not being courteous to green-peacers!) the car is going so fast, people usually don't even realize it's a diesel until someone else tells them.  This even happens to announcers!
  
  It was funny, at '03 nationals, when I was running, the announcer was making these comments like "somebody needs to tune their carburator!" and then someone told me, there was simultaneous yelling of a bunch of people who knew that I raced a diesel from the audience: "IT'S A DIESEL!!!"  And that I think, is making a very positive impression - IE: the fact that a mid-80's diesel can be so competitive, people don't even know it's a diesel because the common belief that ONLY a gas car could be made competitive, is so prevalent in our society.
  
  Question: would you rather have me turn down my smoke level and forfeit any chance of success at the most competitive national-level events, or keep my smoking and maybe have a shot at making the first diesel to take a national championship in a serious racing competition against ALL OTHERS driving gas-powered vehicles?
  
  You should be informed that a lot of other racecars give off WAY much nastier exhaust fumes and smoking than the harmless particulate matter emissions coming out of my richly-tuned Diesel.  I'm talking about tired engines that give off lots of blue-grey oil smoke, headache-inducing stuff good to be clear of - high in carbon monoxide content and other really nasty fumes.  This kind of smoke is the worst and by far more environmentally polluting than even thick diesel PM emissions, IMO!  It is not even really fair to compare them.  I kinda even like the smell.    It's totally tolerable.  The blue-grey smoke is much worse.  But maybe that's just my opinion.  And there are a lot of other non-cat, "richly" tuned gas motors out there that are racing too!  Then there are the class of cars running extreme-high octane "race" gas, their exhast also has a very "sweet" distinctive odor... I myself am not too thrilled about the smell of it and prefer the smell of my diesel, but I know a lot of other racers who love that smell.
  
  I would however, consider for the big events, switching back to biodiesel.  That really changes the smell of the exhaust (like french fries or some other kind of yummy cooking!), and I think then, most spectators might ask for me to smoke more for them!    :lol:  But I'm still developing the car really, had some problems once with a bad batch of biodiesel that plugged up my fuel filter and it really was something I didn't want to have to worry about so I switched back to conventional diesel.  BioDiesel is just not high on my priority for the smaller local/practice events.  I have also been keeping somewhat of a low profile that my car is a diesel.  I don't want to be so public about it until I am doing really, really well.  I want people's views of a racing diesel to be that it is a fast, nationals trophy-winner.  So, I am thus far laying pretty low in the PR department.
  
  Now let me make clear, I'm not advocating running an extra-rich setup for a street driver.  My car is a dedicated autocross racer.  For a street setup, I would try and be courteous to the other drivers and tune the fueling level just up to the smoke limit, where I agree you can probably get about 85-90% - or most - of the overall power that is available.  Whenever I drive cross-country, it's not like I'm smoking along the interstates... I'm just puttering around at low loads.  It only smokes when I've got my foot deep into it.
  
  I guess we can have different opinons about how is best to further diesel public appreciation... but IMO, the biggest way I can further the diesel cause is to win a trophy at SCCA nationals in my car, which is also the first diesel to have ever raced at the SCCA nationals level of competition.  Imagine that - the first and only diesel to race takes a trophy - how good that would make diesels look in a magazine feature, etc.  I think people understand that it's racing, and my class allowes removal of emissions control devices, and that so there is nothing wrong with some smoke coming out of the tailpipe for the total time of, probably near only 30-60 seconds per weekend of racing that my car is doing WOT full acceleration.
• #7 by fspGTD on 30 Jul, 2004 14:39
• Quote from: "QuickTD"

  Another factor in the hot fuel=low power equation is the effect of fuel viscosity on timing advance. As the fuel thins the pump housing pressure tends to drop due to increased leakage though the return orifice and past the timing piston and transfer pump vanes. This can have significant effect on timing advance and therefore power. I've often wondered if a fuel cooler might be a good addition. I know in the A3 cars the fuel is picked up from the same baffled "well" in the tank that the return fuel is dumped into. This is of great advantage in the winter but not so much in hot weather. I wonder if a small trans cooler in the feed line after the filter would help. If the line from the cooler were insulated all the way from the cooler to the pump it should be possible to keep the fuel near ambient. The automatic trans rotary pump TDI's use a fuel cooler in the return line to the tank. The new PD engines use a liquid cooled fuel cooler. It uses engine coolant that is directed through an isolated section of the radiator and cooled to near ambient to cool the fuel via a fuel/coolant heat exchanger. Seems like a lot of trouble to go through, maybe they're on to something?

  
  
  That is a good point on the timing possibly is varied with fuel pressure, or perhaps dispersion of the spray into the combustion chamber.  If fuel coolers were allowed in my racing class, I probably would be adapting an Automatic-TDI fuel cooler to my car, to increase consistency.
  
  On the PD motors... they have a very demanding application.  The fuel actually travels through galleys drilled in the head to reach to injectors... sort of like oil galleys.  There must be some heat conducted from the aluminum head.  Part of the development of that motor was to try and make the heat conduction to the fuel in the head even between all cylinders.
• #8 by andy2 on 30 Jul, 2004 18:25
• unless I,m pissed off a someone behind me I,am always constantly doing my best to make the least particulate matter by making boost before I get on the fuel.I Always use the rear view mirror to monitor my smoke,I agree It impresses people more when you can go quick without smoke but then again they do need to know that its diesel and not a gaser.In Ontario here I know I would fail the 35% opacity limit set for the 1991and up heavyduty diesels(snap test), along with most other IDI's out there, but my car can pass with flying colours on the Light duty test whitch involves viewing the exhaust at idle for any colour of smoke coming out. its stupid that I have to fail trucks that smoke during a quick acceleration test that would not smoke at all when going down the road with boost, then have my beast passing the idle test and be capeable of producing piles of smoke If I were to do the same quick acceleration test. stupid money grab test that is :x however it is one other advantage to owning a diesel here beacuse the test is almost impossible to fail umless the engine was really sick,unlike the gasers which are dynoed and monitored hardcore for any small breach in limits.I just had to get it out of my system :lol:
• #9 by QuickTD on 30 Jul, 2004 18:40
• Just yanking your chain Jake.  . Please don't feel that you have to explain yourself.
  
   First off, kudo's for racing a diesel! Naturally, I would prefer you succeed without blowing too much smoke. But with the restrictions on boost modification in your class I'll have to agree, there isn't much you can do. It's is hard to make good clean power on 9 psi of boost, I've tried. Biodiesel may reduce the smoke, but the reduction will come at the expense of power. The energy density of biodiesel is at least 10% lower than that of petrodiesel.
  
  I don't doubt that there are some foul smelling gassers out there. I'll wholeheartedly agree that their exhaust is nasty, headache inducing stuff. However, they will always have an advantage in the court of public opinion because their exhaust, though more toxic, is less visible. People are stupid, what can you do...        
  
  
  

  Quote

  cough*brysonjake*cough* oh excuse me..

  
  
  $hit disturber...
• #10 by QuickTD on 31 Jul, 2004 00:40
• Seems I can offend everybody today...
  
   Wasn't taking a shot at biodiesel, just repeating what the biodiesel people state concerning BTU content. I really thought it was just a commonly accepted figure. I have no real world experience.
  
   Just talking out of my ass I guess, no offence intended to those with asses, or who can talk or, anyone else?...
• #11 by lord_verminaard on 31 Jul, 2004 10:05
• Good point- I think I remember a few dyno runs on the TDI club where people actually gained power and economy by switching to a bio-blend.  It makes sense to me, the difference in BTU's per unit are nil compared to the benefits to an internal combustion engine.
  
  Remember, the Rally TDI uses soy bio fuel, and they just set a new world record at Pikes Peak for diesel vehicles.  
  
  Go diesel, go!  
  
  Brendan
  84 Scirocco 8v
  00 Camaro L36 M49
• #12 by fspGTD on 31 Jul, 2004 13:50
• Based on my experiences with running B100 in the 1.6lTD, the B100 gave better power output and reduced smoke levels vs petro diesel, however a GOOD tank of petro diesel with stanadyne performance formula additive I feel is comparable to B100.
  
  Basically the thing that turned me off at the time on the bio was I think, crappy storage or refinement...  I got some batch that had these globular mucous-like junk in it that completely clogged my fuel filter so bad, to the point that the engine wouldn't start.  I later found that this junk was likely the byproduct of algae in the fuel, which means that it wasn't stored very well at some point in it's distribution.  I have never seen such a problem with petro-diesel.
• #13 by Centurion on 03 Aug, 2004 13:03
• That muccus stuff is called "mosquito spray" - Trust me! - I ran into this when my grandfather 30 years ago was brewing something in gas cans we used to fuel the cars/dune buggy / tractor.
  
  Mind you - it took me days to drain and clean that stuff out!
  
  One comment about Bio - is that up in oour neck of the woods - our - minus 40deg winters would probaly freeze that stuff solid!
  
  I know the mosquito spray didn't move at that temp!
  
  Centurion