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.
Topic: Thoughts on AHU TDI camshaft in a 1.6NA Hydro (Read 3610 times)
