Thoughts on AHU TDI camshaft in a 1.6NA Hydro - IDI Engine - VWDiesel.net The IDI, TDI, and mTDI source.

• Thoughts on AHU TDI camshaft in a 1.6NA Hydro by Quantum TD on 12 Feb, 2011 22:47
• So, I've been running an AHU 1.9TDI camshaft in my Rabbit Pickup for the past 2.5-3 years. I went with it, because at the time, I couldn't find a correct 1.6NA/TD hydro camshaft (my engine's out of a 1987 Golf). I had broken mine in the process of removing the the sprocket. Someone had hammered that thing on there, and when I hammered it off, the nose fell off with the sprocket.
  
  The bottom line is, I miced the lobes on a stock 1.6 hydro camshaft and the 1.9TDI camshaft. Here's what I discovered:
  
  1) The 1.6 has higher intake lift and duration as compared to the 1.9TDI intake lobes
  2) The 1.6 has lower exhaust lift, but longer duration as compared to the 1.9TDI exhaust lobes.
  
  My thoughts as to the differences are as follows. With more intake air being forced into the motor, perhaps the intake duration and lift needs to be less on the TDI, and/or the valves are bigger to allow more air. On the NA, since air is simply being drawn in, the lift and duration needs to be longer. And/or, the valves are smaller.
  
  I am currently running a stock 1.6NA hydro camshaft at the moment, and I must say that the butt dyno says that it has more low end power. The problem is, I can't scientifically isolate this new-found low end power with the camshaft specifically, since I changed the injection pump at the same time I replaced the camshaft. Overall power feels the same, but with the old camshaft/pump, it seemed to still pull fairly well at higher RPMs and breath better. But again, it could be the pump I put on (rebuilt, unmodded: see below).
  
  I have been told that there is a difference in the diameters of the cam bearing journals on Mechanical lifter cams. So, if you were thinking of going this route, you'd need to have a hydro engine.
  
  
  
  
  The back story on the pump:
  
  Anyways, the economy on my truck has always sucked. I never got over 40MPG, despite good rolling bearings, suspension and small, balanced tires, great compression (over 420 on each cylinder), rebuilt injectors, resealed pump, etc.  The best I ever got was 38 MPG in the summer in mixed driving. The worst until this week was 32 MPG in the winter with the same snow tires I'm running now. I had always chalked up the low MPG to the pump.
  
  Well, the pump started acting up this winter. I'd try to start it, and would have to jamb the pedal to the floor to get enough fuel to flow to the injectors to fire off. Glow plugs are fine, and I assume compression is still good (need to check that again next). It turns out, the pump would lose fuel overnite. There were no bubbles in the feed line, and I just replaced all the return lines, including the main one back to the tank. I thought that perhaps the pump was leaking out of the input shaft. I could see an oily residue on the timing cover, and I thought it smelled like diesel.  Anyways, I pulled the cover, and the pump was not leaking. So where's the air coming from? I may never know since I swapped out the pump today, with one I had completely cleaned internally and reassembled with new seals about 2-3 years ago and stored it filled with ATF.
  
  I took it out for it's maiden voyage with the new pump today, and it seems fine. I'll check the fluid level tomorrow and figure out if I need to replace some more hoses to prevent the pump from sucking air overnite. But I figured I'd swap the pump anyways to try to improve MPG (the last tank was an abysmal 29 MPG with un-balanced snow tires).
  
  So, tomorrow, a few more checks. I'll check compression again and see what it says (it almost felt like it was low on two cylinders when I was cranking by hand today). Hopefully, this pump will get me back up there. But I really do need to check the internal pressure. I still need to get a timing light with tach.
• #1 by RabbitJockey on 13 Feb, 2011 07:05
• this is all interesting, i've been curious about tdi cams for a while
• #2 by dieselherb1 on 13 Feb, 2011 09:27
• Couple of things to think about. I have a pump in my truck that would not pull fuel from the tank, so I mounted a lift pump, works now. But now the front seal leaks so going to replace it maybe the pump will pull again. Also about your lack of MPG. What trans. do you have in the truck? Several ratios out there best ones 7A,FF,FN.
• #3 by Quantum TD on 13 Feb, 2011 10:29
• Quote from: dieselherb1 on 13 Feb, 2011 09:27

  Couple of things to think about. I have a pump in my truck that would not pull fuel from the tank, so I mounted a lift pump, works now. But now the front seal leaks so going to replace it maybe the pump will pull again. Also about your lack of MPG. What trans. do you have in the truck? Several ratios out there best ones 7A,FF,FN.
  

  
  Good point. I've got an FN out of a 1982 Jetta. So, 3.89 R&P and .71 5th gear. It's about the best you can go for MPG. I don't think that's my problem.
  
  I should also note that just about all the brake and suspension parts have been replaced over the past 3 years, without any notable improvement in MPG. The bearings are all good and spin freely without noises.
  
  The snow tires do have some effect I'm sure. I was running them last year until about May, when the switch back to summer diesel had occurred and MPG was notably less (about 1-3 MPG). When I installed new summer tires (175-70/R13), the ride got a lot smoother and MPGs went up. That was my best tank (39 MPG). Even so, the worst I ever got in the winter was about 32-33 MPG.
  
  I'm really hoping the home-rebuilt pump makes the difference. It seems to run fine, but it sounds like I've got a few ticking lifters. Maybe they need to build up pressure. I'm hoping a long, hot run will free them up.
• #4 by R.O.R-2.0 on 13 Feb, 2011 10:31
• wouldnt a 3.67 gearset be the only way to get better economy? tranny wise i mean..
• #5 by Quantum TD on 13 Feb, 2011 15:36
• Quote from: R.O.R-2.0 on 13 Feb, 2011 10:31

  wouldnt a 3.67 gearset be the only way to get better economy? tranny wise i mean..
  

  
  Yeah, but not in a gutless 1.6NA. I've tried one before, and it's way too tall. It makes acceleration a real PITA. 1st and reverse are basically worthless.
  
  If you've got a turbo, then it might be a different story.
• #6 by R.O.R-2.0 on 13 Feb, 2011 18:40
• oh, yea, i wouldnt run 3.67's on a n/a unless it was a built up n/a, or a gasser..
  
  my TD rabbit used to love the 3.67 gears i had in it..
• #7 by Dakotakid on 14 Feb, 2011 19:19
• Not sure this will help, but....
  My first VW pickup was purchased brand new in late '81. It was a 1.7 CIS gas with the standard 4-speed (not some sort of 3+E version). This pickup had NO topper. I never achieved more than 24 mpg. Never.
  
  Then, I acquired a mint '81 diesel with 0.71 5 speed trans in it. It had the top-of-the-line Glasstite topper (was about 3 inches taller than the cab). Drove it all over the western half of USA from Dallas to St. Mary in Montana and everything in-between. I don't think I ever did better than 40 mpg in it. Didn't really care (for the most part) as I was buying diesel for 45 cents in Missouri and 38 cents in Texas at that time! Wow.....
  
  I am sure others will disagree, but, I don't think your mileage is all that abnormal for n/a, toilet bowl, little exhaust, etc.
  To tell you the truth....I HATED windy days in that pickup. It always meant that I would be jamming gears like a redneck trucker on whites!
• #8 by Quantum TD on 14 Feb, 2011 21:49
• Nah, I hear you. Windy days for this slug mean POOR MPG. I know that always. I drove from CT to TN in early January, and I think I had it in fifth gear about 15% of the time. Headwind+loaded truck = 4the gear non-stop.