High rpm guys: anybody playing with cam timing?

[Patrick]

I've been reading through a lot of back posts. My experience with heavy truck engines in the past leads me to believe that diesels will handle a lot more fuel/boost/heat at higher rpms because of the larger quantities of air helping to cool the whole thing. One of the limiting factors for efficiency then becomes flame times. In the older big cummins engines, the only way to change injection timing was to change cam timing, because the injectors were fired by a push rod off the cam just like the valves. Same cam. Varying the cam  timing would move the peak torque up or down. In theory, you could do the same with the stock cam in a 1.6 or 1.9 to help. Get the valves open a little sooner at higher rpm . Would hurt at low revs, help at high revs. Don't think anyone builds a degree wheel for a diesel volkswagen though!

[lord_verminaard]

I've thought about this a bit as well.  It gets to the point with fueling and boost where you can only go so far before the gains are minimal.  I would think that the cam would be a limiting factor, although the compression ratio and resulting piston-to-valve clearance limits what the cam can do.  TDIRs has come up with different cams for TDI's, and I think there are a few companies out there with TDI cams.  But I think the TDI has a little more clearance than the IDI's do.  I would think that playing with cam timing a little on a high-rpm engine would be bound to produce some results either way.  I'm pretty sure any adjustable timing gear for an 8-valve engine would fit the IDI diesel.  

Brendan
84 Scirocco 8v
00 Camaro L36 M49

[Spike_TDI]

 I'm pretty sure any adjustable timing gear for an 8-valve engine would fit the IDI diesel.  

Brendan
84 Scirocco 8v
00 Camaro L36 M49

Nope,
 1) Belts wider on the diesel.  
 2) ID bore and taper are different

[Patrick]

Adjusting would be easy with no key on the cam. Question is, how do you know where you put it? Would have to build something that measures directly of the cam.

[VWRacer]

Patrick, for some background material, read this post from our old forum. Tdrs and others discuss using a GTI cam in a TDI, but the same philosophy may be applicable to an IDI engine for getting more air into the engine at higher RPMs. OTOH, advancing the cam may turn out to be dicey due to the already very tight valve-to-piston clearance, so going to slightly higher lift and duration, as with the GTI cam, may be the only realistic option.

That having been said, there may be more room than I think, so when I get home this weekend I'll post some digi-pics of the adjustable cam on the GTI motor in my CSR. You guys will all instantly recognise the cleverness of this approach, and I can just see it now...bent valves everywhere!

[VWRacer]

It turns out that I have the pics on my laptop, so have started a new thread on the DIY adjustable cam pulley in the FAQ section. Have fun!

[Patrick]

Neat idea, but more work than we need on a pulley that's not keyed to the cam. If someone really wanted to make it easy, all they need is an adjustable camstop to set the timing, right? trick is doing the work the hard way (measure TDC and opening of the intake valve on#1) and move the cam, do the measurement again, figure out how many degrees you moved it,(eg 3degrees advance) make a jig to fit, and you have a new camlocking plate for 3 degrees advance. Could be a lot of messing around the first few times (say 4 jigs at 1,2,3,and 4 degrees) but would make the engine much more tunable.Could be easier though. If the timing is set factory, and you move the belt 1 tooth on the cam, where do you wind up? (360 degrees divided by the # of teeth on the gear).

[caddy]

i will post some picture of my special puley to fit a gti came shaft on a tdi head.

[Dr. Diesel]

back in the dark ages, I bent a full set of exhaust valves advancing the cam what looked like just a little bit on a 1.6.  Right now, I'm running my 1.9's cam advanced just a hair. That is to say, with the cam locking plate installed, there's a little bit of slop. with the plate installed, I moved the cam forward (adv) to take up this slop.  The engine has good tug down low, and flattens out a bit after 3500 rpm. Admittedly, this could just be the nature of the (1.9) beast, or a pump tuning factor. The engine's still not broken in yet, and I haven't played with tuning yet. To really qualify this, i'll have to do back to back comparisons with the current setup followed by taking up the locking plate slop in the opposite direction.  Will post more later.

please re-read my first sentence and beware!

[Patrick]

Well, part of the reason I asked is because I put my 1.6TD together without a locking plate, and I noticed after everything was tightened up that it was advanced a little (groove not dead level across). Never having messed with a volks diesel before, I didn't realize the sprocket wasn't keyed to the cam. I figured you just got what you got. Then I started reading here. Steep learning curve!  Anyhow, the engine is a little on the lazy side on the low end, you can hear the turbo spooling up pretty good at about 2400 or so, and things really start to happen bigtime at about 3000. The pump (to the best of my knowledge) is completely untouched, and I think the timing on the pump may be a little retarded, but it's real close. (running about 750-800 km on 45l of winter fuel.) This is in a 4 door 92 jetta with air and power steering, over 500,000 on the chassis.

[Dr. Diesel]

if anything, advanced cam timing should improve bottom end at the expense of top end. if you're getting sluggish engine performance, checking pump timing with a dial indicator and tuning it's settings may well be in order, especially after having the belt off.

[Patrick]

Okay, maybe I said it wrong.What I should have said is that the pully is advanced on the cam, hence the cam is retarded, and yes, I need to put a dial indicator in the pump, just haven't got around to it yet! :oops: I can't be very far off though, the car starts and runs well, and the mileage is about as good as I expected this time of year. THis is a 1.6TD I took out of an 84 Jetta, 138,000 km. Bought the car as parts for an 84 gasser, was told the engine was junk. Story went like this. The owner got the car from his mother, put an oil pressure guage in, and thoughtthe pressure was too low. He rolled in a set of bearings and put in another oil pump (turns out from a junk gasser!).When he fired it up, it went from low to nothing. When I got the car home, I figured I'd check. I put a new oil filter on , filled the crank with oil, screwed a guage in the head. Engine fired easily, but I got no oil pressure reading.  I pulled the pan and found that the oil pump had a loose screen, and had picked up a washer off a pan bolt that he had lost, and broke the pump. Promptly gave up on putting this in my 84!
Jump ahead a year, purchased a high mileage 92, already ringed once. Not having any experience with volks diesels, when the car ran okay after a pull start, no noises, but was hard to start, I figured glow plugs, maybe injection system. since I had a parts motor, I bought the car. When I started reading about these things and discovered bad compression as a likely cause, I bought a compression tester and got 260 lbs on #4, went bacj to the other motor. Pulled it out of the parts car, pulled all the main caps and rod caps, and decided that the other guy must have had all his problems in the drive and shut the car off in a hurry, No damage to the crank!!! I put a set of bearings and the right oil pump in the engine ,new water pump, and crank seals (just because it looked like it was a lot easier out of the car) checked the glow plugs (since I had the pump off to change from A1 to A2 mounts and change the air conditioning bracket to one with power steering)and put it in the car. Just lined everything up and put the belt on. I know the cam is retarded a little (should fix it) and am guessing from the way it runs that the pump could use a little advance too. Didn't want to play with anything until this motor that sat for several years has run for a few months.   It started out using about a litre of oil in 1500 km for two or three litres, seems to have quit. I suspected crankase vents or turbo, because the rings are tight enough that it started at -22c on a windy day , not plugged in. Still working out a few bugs, but the car runs good! BTW the turbo is a Garret.

I like th pulley design. Reminds me of one I saw off the fuel pump of an older  Cat truck motor. They have variable timing on the fly though. Timing changes with engine speed. counterweights and springs! ( and a lot more money!)

[lord_verminaard]

I like th pulley design. Reminds me of one I saw off the fuel pump of an older Cat truck motor. They have variable timing on the fly though. Timing changes with engine speed. counterweights and springs! ( and a lot more money!)

I think someone on here posted a link for a pulley like that for gasser VW's.  I know at one point someone made one, but it was expensive and I dont think it sold very well.  Neat idea though, almost like VTEC or Vanos or something for 8v's.  

Brendan
84 Scirocco 8v
00 Camaro L36 M49

[Mark(The Miser)UK]

Hi forgive me for my ignorance; but what is the purpose of your adjustable sprocket?
It looks like it has a keyed parallel hole whilst the diesel has a tapered boss and although also  keyholed its just pretend  :wink:
If cam advance needed just slacken off nut an advance CS and pump. Then retighten.
At a loss as to where you are? then mark bolt head on cam; as this always tightens to same position relative to cam.(Using same torque...MAYBE) :?:

One gasser variable not available is ignition timing...Unless perhaps the laborious gasket shimming is undertaken...or...maybe a homemade design of a sparkplug in a glowplug body  :twisted:

Mark(The Miser)UK
'87 TD Quantum

[Mark(The Miser)UK]

What you really need is three studs with rack and pinions behind to move along your mm scale.
Mark(THe Miser)UK