Cam-Shift...Power-Shift & Minimum Spool-up rpm

[Mark(The Miser)UK]

:?: Anyone have to hand the limits of cam advance/retard before clobbering the piston? Is it as far as 1 cam tooth? :?:

  Also how much shift in peak power or efficiency is there?

 :!: Finally whats the lowest rpm that a IDI turbo will spool up? :!:
(A poster on another site has a 1.5 N/A and a 1.6TD which he wishes to use as a cogenerator.) He's looking at an 18kw alt and needs to run at 1800rpm. He doesnt feel a turbo'd system is effective at this low speed.
I feel my turbo is spooling up from 1500rpm

Thanks for all replies...

[Patrick]

The Garrett  on my 1.6 comes on a lot stronger at 2500. The little one on my 1.9 spools a lot sooner. Might have to go with a smaller turbo......

The other possibility is gear reduction.

[Mark(The Miser)UK]

The other possibility is gear reduction.

 :lol: Ah now that's an idea :lol:

[fspGTD]

In my Rabbit racer, accelerating wide open in 3rd or 4th gear on a flat road, the full 9-10psi boost pressure doesn't happen until the engine gets to 3500RPM.  But it is a very light under 1800 lb car, not to mention lightened flywheel and close-ratio GTI transmission.  So what happens is the vehicle accelerates so quickly that the turbo doesn't have much time to spool!  (The turbo is the stock "big" 1.6lTD Garrett, or the TA0304B.)

When loaded wide open in a steady state condition, (I have one hill I usually test on in 4th gear at a constant 2000RPM... applying brake as needed to maintain that RPM with wide open throttle), mine will now develop full boost pressure.  However, when it was stock but with the only change being a 2" exhaust after the stock downpipe, it would barely make any boost pressure in the same test (boost would only rise to around the 0-2 psi range.)

Changes that I found put more energy into the turbo were: enlarged exhaust system, increased fuel quantity, intercooler, ceramic coatings to exhaust manifold and downpipe, and thermal-insulation wrapped turbine housing.

[Mark(The Miser)UK]

As this chap is running his engine on a platform ?Outside? Large exhaust would be no problem. Heck if he went for the turbo'd engine no exhaust wouldnt be too loud; or just a downpipe maybe.

If he's looking at 18 kw or a third of basic rating I wonder what sort of loading that equates to? (Is it enough to trip the turbo?)

If the turbo does boost at this level; does it need to go beyond say 2psi to maximise efficiency?

Crikey Jake  you vehicle is light at 18001b  my 'Q' is a little under 2400lb net or 3 adults hidden in the back extra (

[racer_x]

:?: Anyone have to hand the limits of cam advance/retard before clobbering the piston? Is it as far as 1 cam tooth? :?:

Nowhere close to one cam tooth. More like about a quarter of a cam tooth if I had to guess. I've never tried to run any retard or advance on the cam. With the cam exactly at TDC, there's about 0.5mm (0.020") of clearance between the valves and the pistons. Moving the cam more than a degree or two would be a really bad idea.

[Mark(The Miser)UK]

:?: Anyone have to hand the limits of cam advance/retard before clobbering the piston? Is it as far as 1 cam tooth? :?:

Nowhere close to one cam tooth. More like about a quarter of a cam tooth if I had to guess. I've never tried to run any retard or advance on the cam. With the cam exactly at TDC, there's about 0.5mm (0.020") of clearance between the valves and the pistons. Moving the cam more than a degree or two would be a really bad idea.

 :evil: Seems extremely fine; so those who aspire to have one of those adjustable gasser cam sprockets can 'kiss the baby' if they overdo  the adjustment... :evil:

[racer_x]

:evil: Seems extremely fine; so those who aspire to have one of those adjustable gasser cam sprockets can 'kiss the baby' if they overdo  the adjustment... :evil:

Actually, I understated the clearance issue. The intake valve gets as close as 0.2mm (0.008") to the piston with the stock cam timed to stock specs.

There's no need for the adjustable cam sprocket on the diesel. If you want to advance it one or two degrees, or retard it one or two degrees, you can just change the position of the cam holding fixture by one or two degrees when you set the cam sprocket on the cam. Diesels don't have a key on the camshaft sprocket, and adjusting the cam timing is part of the normal timing belt change procedure. You position the cam with the cam positioning fixture (or a home made substitue), loosen the bolt on the cam sprocket and tap it a few times with a rubber mallet to work any tension out and get the sprocket exactly centered. Then tighten the bolt back to spec.

If you use a hunk of angle stock for the cam locating fixture, you could use feeler guages between one end of your "fixture" and the top surface of the head to set a measured amount of advance or retard. But be careful and if you alter cam timing from stock, make sure you turn the engine a few times by hand with a wrench on the crank bolt to make sure nothing hits.

Oh, and don't use the cam locating fixture to hold the cam when you loosen the nut, it can crack the camshaft.

[fspGTD]

No problem here running the camshaft 2 crank-degrees retarded (except that it might have contributed to hard starting.)

[steve]

I read a book called Performance Tuning by A. Graham Bell. It's a very informative book and describes the effects and benefits of camshaft and exhaust tuning. So I tried advancing my cam 3 degrees on my 84 1.6 TD with excellent results! The power curve shifted to a lower rpm and made the car respond much better in stop & go traffic.

I initially used the feeler gage under the cam tool method.  But came up with a far easier and more reliable method.  Position everything like you normally would when setting up the timing belt - but prior to tightening the cam sprocket bolt, just rotate the crankshaft off of TDC in the direction you want to go by counting flywheel teeth.  To advance the camshaft, rotate the crank backwards compared to the normal operating direction.  

Note that camshaft advance is measured in crankshaft degrees.  If you use the "feelergage under the cam alignment tool" method then you need to double the number of degrees of adjustment since it turns half as fast as the crankshaft.  ie: 3 degrees of camshaft advance = 3 degrees measured at the crank = 6 degrees measured at the cam.

Of course it helps to know how many flywheel teeth there are and figure out how many degrees per tooth.  Someone once counted theirs for me and found 132 teeth which would be 2.9 degrees per tooth.  Someone else had 128 teeth.  So, yours may be different.

Here's an excerpt from the book:
"Basically, advancing the cam will improve bottom end and mid-range power... around 2 degrees will have very little effect, but from 4 to 8 degrees it will show a marked improvement in midrange power, with some decreasing maximum power... Generally I prefer to run all road & rally engines with the cam 6 to 7 degrees advanced."

Now keep in mind that this is a racing book and they expect you to do your homework on valve to piston clearances and camshaft selection. I'm very leary of doing more untill I do the appropriate valve clearance tests. It seems to me that the only danger is that the intake valve could open too early and hit the piston. The other "events" either don't matter (exhaust opening is with piston near BDC) or happen sooner providing more clearance (intake closing sooner & exhaust closing sooner)

While rotating the engine prior to starting will help identify a catastrophic interferance situation, the valve & piston should have positive clearance and this is the unknown.

I did all that prior to replacing my cyl head which was just plain worn out.  After installing a new head, I put it back at the stock setting and I haven't played with it since then because the power was good.  Proceede with caution...

[caddy]

:?: Anyone have to hand the limits of cam advance/retard before clobbering the piston? Is it as far as 1 cam tooth? :?:

  Also how much shift in peak power or efficiency is there?

 :!: Finally whats the lowest rpm that a IDI turbo will spool up? :!:
(A poster on another site has a 1.5 N/A and a 1.6TD which he wishes to use as a cogenerator.) He's looking at an 18kw alt and needs to run at 1800rpm. He doesnt feel a turbo'd system is effective at this low speed.
I feel my turbo is spooling up from 1500rpm

Thanks for all replies...

for a low rpm range you can use a "small" turbo , who can spool at 1500tr, but not efficient after 2500. :wink:

[fspGTD]

Steve - great info!  Thanks for posting these results.