How does lower compression affect performance? - page 1 - IDI Engine - VWDiesel.net The IDI, TDI, and mTDI source.

• How does lower compression affect performance? by dave friday on 21 Jul, 2012 08:17
• Afternoon all,as above,the compression figers came out at 370psi[on all 4 cylinders].
  Any comments?
  Ta.
• #1 by libbydiesel on 21 Jul, 2012 11:00
• Your compression is only slightly below spec for your elevation (1400 ft).  There could also be inaccuracy caused by your gauge or adapter.  You should not have any operational issues provided everything else with the engine is in good repair.  With 370 psi on all all cylinders it should be able to start easily down to the single digits in degrees F and should run well and get decent fuel economy.   
• #2 by dave friday on 21 Jul, 2012 11:46
• Thanks Libbydiesel,it starts instantly! we are about 300ft above Albox, the 370 is compensated for that altitude, i'll check the the injection pump timing,what would you recomend?
  Ta.
• #3 by R.O.R-2.0 on 21 Jul, 2012 13:24
• Quote from: dave friday on 21 Jul, 2012 11:46

  Thanks Libbydiesel,it starts instantly! we are about 300ft above Albox, the 370 is compensated for that altitude, i'll check the the injection pump timing,what would you recomend?
  Ta.
  

  
  ignition timing wont change your compression.. if it starts good and runs good, leave it alone.
• #4 by ORCoaster on 21 Jul, 2012 23:54
• R.O.R.  His question is about performance.  Since he has established the fact that compression is good enough and not a problem he is now asking for IP changes. For Performance.  Trouble I have with this is does he want good fuel economy or good speed?  He didn't qualify "performance"
  
  So what way do you want to go Dave Friday?  Lots of Kms to the Liter or Kms to the hour? 
• #5 by dave friday on 22 Jul, 2012 02:21
• Hi ORCoaster,yes your right I want to get a bit more power/speed,Spain has a lot of long hills and very often the van is down to below 40 mph!.
  The engine was reboared,new head,oil pump etc 40000miles ago and a recon turbo 2000 ago.
  The injection pump drive spindle has a bit of play!
  So any ideas?
  Ta.
• #6 by R.O.R-2.0 on 22 Jul, 2012 15:04
• Quote from: dave friday on 22 Jul, 2012 02:21

  Hi ORCoaster,yes your right I want to get a bit more power/speed,Spain has a lot of long hills and very often the van is down to below 40 mph!.
  The engine was reboared,new head,oil pump etc 40000miles ago and a recon turbo 2000 ago.
  The injection pump drive spindle has a bit of play!
  So any ideas?
  Ta.
  

  
  ideas? get the pump rebuild. do the gov mod. turn up the fueling a bit..
  
  INSTALL AN EGT GAUGE!!
  
  time it to ~1mm for performance..
• #7 by ORCoaster on 22 Jul, 2012 15:06
• Dave,  Before we go changing things one way or the other we need to know where are, for reference.  So, first question do you have a dial gauge or can you borrow one?  The idea here is to determine where you are with the timing.  What engine are we talking about?  1.6 or 1.9 L?   My 1.6 seems to run well with more advance rather than less or at least it did.  I have a new head on it so that may change.  But the range of the 1.6 is from .88 to 1.05mm for timing.  I am not sure on the 1.9.  
  
  After doing the head work I put mine right back to .93 mm where it was so I can adjust accordingly.  That is my baseline.
  
  So, if you don't have the tools we shift to a less accurate but no less functional method to improve performance.  I trust you, assume you, know that there are marks on the IP pulley and the the top of the IP bracket.   Find the marks on both.  Set it to TDC on the flywheel and pointer for the #1 cylinder and clean them up good and maybe even paint them white.  Or Green or Red.  Have I lost you yet?
  
  If both marks are directly across from one another then you only have to note that.  IF the IP pulley mark is toward the engine or towards the front of the car you will need to scribe a thin line across the top of the IP bracket so you know what you initial setting was.  
  
  Now do you know how to loosen the four nuts on the pump and the nuts on the back of the pump holding the delivery lines?  17 mm wrench on the line nuts, 13 mm on the four nuts and bolts on the pump.  Loosen the line nuts just a bit to make them slack and relieve the binding force on them.  I generally then go for the nut on the timing belt side, then the lower one behind the head of the pump with a socket wrench.  Then I shift to a box end wrench an loosen the engine one a bit and then ever so slowly release the front one.  Why slowly?  Cause I watch that scribe line to see if I am moving the pump in the process.  
  
  Now with pump loose push on the top to move your IP pulley mark about a pencil line width towards the engine and cinch down the front bolt so it stays.  Tighten all the rest.  Pull any rag you might have put under the head to catch diesel drips.  Now go take it for a drive.  Any better?  
  
  How would I know?  Well again back to baselines.  Find a section of road you can have to yourself and find a mark along the side.  Stop, accelerate in what ever manner you normally drive and time how long it takes you to get to another marker on the side of the road.  Up through third should do.  Try again with the timing pump changes.  Any faster?  Remember drive it like you tried to do the first time.  Hard to do but can be done.
  
  If you are better off for the change try a bit more until you get to a point of no return.  In that the change you made is not giving better performance.  You may find this to be the case on the first shot and might need to pull the pump to the other side of your index marks to check it.  
  
  If timing changes don't do the trick there are other pump screws and such to play with but verifying the timing would be my starting point rather than just dumping more fuel to it.  That is what the next step would be.  
  
  But I stop here and let you go tweak on the timing now.  Let us know if you have any luck on this.  
  
  DAS
• #8 by dave friday on 22 Jul, 2012 17:58
• Thanks ever so much everyone,
  I rebuilt the engine so know all about the timming  point on the clutch cover [v]
  I set the pump timing with my dial gauge [to .85]
  The engine is a 1.6td [jx] with solid lifters of course
  I have a hill that i use to check the performance
  I will report back
  Thanks again.
• #9 by libbydiesel on 22 Jul, 2012 19:18
• 0.85 is very retarded for the JX.  Go for 1.05.
• #10 by ORCoaster on 23 Jul, 2012 00:31
• I agree.  .85 is way low.  Might need to adjust the idle once you bump it. 
• #11 by dave friday on 23 Jul, 2012 11:55
• Ok i must of reset the pump to around .95mm when did the head gasket[2 years ago],
  I reset it to 1.00,it seems a bit better but when starting from cold it still seems to miss a bit [cured by pulling the cold start lever out] and this at 26deg c !!
  One thing its allways done is to do a puff of smoke every 2 or 3 seconds [under load] not huge but i can see it in the mirror.
  What happens if i set the pump to more than 1.05mm?
  Ttfn.
• #12 by ORCoaster on 23 Jul, 2012 15:00
• Depending on wear on the pump it might help it out.  That is the danger of just using the numbers on our diesels.  The numbers were developed before the oil industry decided to start playing with the basic fuel we use.  ULSD is much different than what Bosch thought we would be running in it.  For a real change dissolve about 4 ounces of parrifin wax into a gallon of diesel and pour that into the rest of a tankfull of diesel.  I not only thickens the fuel but adds cetane to the mix.  I also add about 2 oz of ATF to keep the injectors cleaner but not sure that was enough after last weeks pull and clean on them.
  
  As the pump wears, and I am thinking with PSI of 370 measured you have wear of parts, the setting by the numbers becomes meaningless.  That is why you just keep bumping the timing and testing for performance.  Your best place might be 1.2 and if I try that it runs like crap because my sweet spot is .95 or something to that effect.
  
  So tweak away, and for giggles do the wax you are going to flip on it.  Just listen to how quiet it gets on slick fuel.
• #13 by dave friday on 23 Jul, 2012 18:06
• Thanks ORCoaster,I'll try setting the pump the way you said,Im dont know if i can find parrifin wax here.
  And I'll change the little plastic thermostat on the fuel filter.
  Thanks.
• #14 by ORCoaster on 23 Jul, 2012 21:36
• Anyone you know do any canning of fruit or jelly.  That is the wax I use.  Buy it right next to the canning jars.  About 3 dollars a box.  Does me 8 tanks or 80 gallons, cause I only use 2 oz at a tank but for demo purposes I suggest 4 to see what it really can do if you care to add that all the time.  Just be careful as your temps are on the flip flop of us.  So cold is not good as it will get solid in the tank, or worse filter.  Nothing hot water couldn't fix if in the filter.  Or a heat gun.