Camshafts

[DVST8R]

Well here is a topic that I am sure there will be some debate. I for one no very little about camshaft design so this is for me and others like me to learn from. It has been expressed a many times, and a few times recently that the stock cam, isn't good for high rpm application, nor is it even good for making max power in the non modified rpm band.

With this being said I am sure that it wont be long till I blow the HG or get my twin fab finished, at which time I am either going to port the 1.6 head, or find a 1.9 head and port it, while the head is off I will oring the head and possibly the block, and goto either the 1.9 metal HG or a custom copper one, as well as studs. I will also look into porting the precombustion chambers and have some piston work done to drop the CR the "right" way. To bring this back on topic since the head will be off I want to have the cam either re-ground to the best that it can be, or replaced. So please discuss, and help enlighten the cam challanged    

The few things that I know are lift determines how far the valve opens, duration is how long it is open for, overlap is the time that both valves are open, or if its negitive how long there both closed.

I have heard that more overlap will produce more power and help the turbo spool quicker, but I don't "know" this, but fuel economy will be the price which for me is fine, but some will care.

[vwmike]

Ok, I guess I'll go since I was the nay sayer in the other thread.

I haven't been able to find the diesel cam specs but I've heard duration was in the negative. From everything I know about camshaft profiles it seems virtually impossible to make a camshaft that flows well on the top end and is free from overlap.

First I'll start out by taking a look at the stock vw gas camshafts.

Solid lifter

Stock 1.6 - .406 lift 230* duration 10* overlap 110 lobe center

Stock 1.8 (JH) - .369 lift 212 duration 110 lobe center

G grind - .423 lift 235* intake duration, 234* exhaust duration - 16.5* overlap 109 lobe center

Schrick 272 .432 lift 272* duration 52* overlap 110 lobe center

The stock 1.6 cam is ok, but nothing amazing. As you can see they dumbed down the 1.8 cam for emissions. As a result that engine falls flat at about 5500 rpm. I know this from great experience. I had one of those in stock form once upon a time. Power specs - 90hp@5500 rpm

The G-grind is the european Heron 1.6 cam and is a popular upgrade. It allows the gas engine to make power up a little over 6k (btw, the Heron 1.6 had bigger valves than the regular 1.6). If you move up to something like the Schrick 272 you start running into the issue of port size. The stock 1.8 ports are too small and flow will become the limiting factor before you run out of camshaft. In a ported head the 272 should make power up to around your 7k rpm goal.

Hydraulic lifter

1985 GTI - .401/.402 lift 221* intake duration, 224* exhaust duration 2.75* overlap 109 lobe center

Schrick 272 .449 lift 272* intake duration 268* exhaust duration 50* overlap 111 lobe center

Stock G60 - unknown lift 220* duration 0* overlap 110 lobe center

The 85 GTI was no speed demon. It's stock power output was 100hp@5500 rpm. Once again, the 272 would probably make it to about 7k rpm. Notice the stock G-60 cam has zero overlap. For any of you who are not familiar with forced induction, this is common. When you have overlap you'll find that boost pressure will push right through the intake valves and out the exhaust valves which is bad for cylinder filling and at the very least increases the boost threshold.

Now, what does that mean? Well, if the 85 GTI had .2 liters more displacement and a more aggressive camshaft but made peak power at 5500, what does that mean for the 1.6? I can draw the following conclusions:

-The 1.6 diesel camshaft is of significantly less duration. This means that there is no time for proper cylinder filling at high rpm.

- The 1.6 diesel ports are smaller. Airflow will thus be hindered at a lower rpm if all else remains equal

- The 1.6 diesel valves are smaller. This will also hinder flow at high rpm.

Some other notes on custom camshafts: I would raise the question whether or not you can actually increase the duration of the camshaft. Tolerances in diesel engines are so close that I'm not sure there is a long enough "window" for the valves to be open for duration to be increased without possible piston to valve contact. I'm not saying it can't happen, but this is something that concerns me. Even so, you may stand to gain a couple hundred rpm worth of useable power before the bottleneck in the system moves elsewhere (ports, valves). Some of you (Jake) may find this useful as to be as competetive as possible within your racing class. Otherwise, I can't see this being a worthy investment.

For me, I'll stick with improving upon what the diesel does best - make torque and get good mileage.

[Rat407]

One question, remember I'm no mechanic. There isn't any overlap in the 1.6 diesel is there? If there was wouldn't it help in the area of producing vacuum?  Remember I'm no mechanic but due to the nature of the this diesel that is why we have to run a vacuum pump, right? I agree on the part of no over lap due to valve to piston clearence. In my mind and experience, (valve to piston contact with minimal timing slip) there really isn't much room at all, zip nadda nill!!!

[racer_x]

Overlap isn't particularly good for turbos, not even on the gassers. On the diesels, it's nearly impossible to get overlap. With stock pistons and head gasket, it is impossible to get overlap.

Overlap also relies on a tuned header to create some scavenging vacuum at the exhaust port and in the cylinder to start drawing intake charge in. So wituot a tuned header, it's pretty useless. And you would need a header tuned to 4000 RPM's or so to use any overlap on a nomally asthmatic diesel to any advantage. That would mean that you would be making your own header from tubing from scratch, because none of the headers available for these engines will be tuned to that low an RPM range. Also, with only 18cc of volume above the piston, there's not much chance of "storing" vacuum from the header tuning even with no overlap or negative overlap.

With the turbo, the benefits of overlap pretty much go away. First, you don't have the tuned header scavenging effects, because there's a turbo on a standard manifold. And you also have boost in the intake which will blow through the exhaust valve and that wastes any benefit from the overlap.

With lift and duration, there are some very rigid limits in the diesel as well. The intake valve opening profile and the exhaust valve closing profile have to be pretty close to the stock cam. You can add duration on the closing of the intake valve and the opening of the intake valve (by widening the lobe center angle), but there's some limits to that as well. Also, more duration gives you a higher optimunm RPM range, and you can get beyond what the diesel engines can reach if you go crazy on duration.

One thing you might consider is machining the piston crowns for enough clearance for the "J grind" (049J markings) cam from a 1.7L or JH 1.8L solid lifter engine. That cam has about half the negative overlap of the diesel cams, and it has more duration than the stock diesel cam. FWIW, the last time I changed the timing belt, I actually tried to put a J cam in. It clunked when the valve(s) hit the piston(s) after maybe 10 to 15 degrees of crank rotation.

If you want to have something custom ground, more lift in the center of the cam lobe will definitely help, but the whole piston/valve geometry limits you in the first half of the opening profile on the intake and the last half of the closing profile on the exhaust. A cam that makes the valves go "CRUNCH!" won't make much power.

Finally, porting and polishing the port passages in the head is a great idea. The stock ports aren't the best for flow. And with a diesel, polishing the entire intake runner in the manifold and the port in the head to a mirror finish is a good idea. Matching the head and manifold at the intake manifold gasket also helps out a lot. You don't need any turbulence in the intake air in the diesel to mix the fuel mixture. It's not like a gasser in that respect. Polishing everything is good. On the normally asthmatic engines, you want to be careful about going too big on the ports and reducing the velocity and momentum of the airflow. But on a turbo, I would think that bigger would be better.


Bigger valves would also help. I haven't looked at the whole geometry of the diesel heads. I'm not sure if you could fit the 40mm/33mm combination from the JH head in there. If those valves can fit, that would help too.

I wouldn't do any porting in the pre-combustion chamber unless you really know what you are doing or you have a large pile of diesel heads to experiment with. I'm pretty sure there's not much to be gained there, and a whole lot to lose.

And you don't want to lower compression much. If you add even 3cc's of volume above the piston, you'll be lowering the compression below 20:1, and starts will get very difficult, especially in cold weather. You're starting out on the really steep part of the volume/compression curve, so a little more volume drops compression a whole lot at first.

Here's a "chart" of volume above the piston vs. compression ratio:

cc above piston | compression ratio
18 | 23:1   
*********************************************************************
18.5 | 22.4054054054054:1
*******************************************************************
19 | 21.8421052631579:1
*****************************************************************
19.5 | 21.3076923076923:1
***************************************************************
20 | 20.8:1
**************************************************************
20.5 | 20.3170731707317:1
************************************************************
21 | 19.8571428571429:1
***********************************************************
21.5 | 19.4186046511628:1   
**********************************************************
22 | 19:1
*********************************************************
22.5 | 18.6:1   
*******************************************************
23 | 18.2173913043478:1
******************************************************
23.5 | 17.8510638297872:1   
*****************************************************
24 | 17.5:1
****************************************************
24.5 | 17.1632653061224:1
***************************************************
25 | 16.84:1
**************************************************
25.5 | 16.5294117647059:1
*************************************************
26 | 16.2307692307692:1
************************************************
26.5 | 15.9433962264151:1   
***********************************************
27 | 15.6666666666667:1
***********************************************
27.5 | 15.4:1
**********************************************
28 | 15.1428571428571:1
*********************************************
28.5 | 14.8947368421053:1   
********************************************
29 | 14.6551724137931:1
*******************************************
29.5 | 14.4237288135593:1   
*******************************************
30 | 14.2:1
******************************************


Oh, and vwmikes cam specs leave out the lift spec where duration was measure. And the measurements he gave are different on different cams. For example, the numbers he gave for the 1.6L gas cam and the "G grind" are total duration, where the duration he specified for the JH cam is at 0.050". The JH cam is about 10 degrees shorter in duration than the 1.6L gas cam, and about 15 degrees shorter than the G grind if you compare duration at the same lift on all the cams. IE, if you go at 0.050" on all of them, they would be somewhere around 212 degrees for the J, 222 degrees for the 1.6L cam and 227 degrees for the G grind.

[Mark(The Miser)UK]

19.5 | 21.3076923076923:1
***************************************************************
20 | 20.8:1
**************************************************************
20.5 | 20.3170731707317:1
************************************************************
21 | 19.8571428571429:1
***********************************************************
21.5 | 19.4186046511628:1   
**********************************************************
.

  :mrgreen:  Ah but have you got any numbers to back this up? :mrgreen:

[vwmike]

Oh, and vwmikes cam specs leave out the lift spec where duration was measure. And the measurements he gave are different on different cams. For example, the numbers he gave for the 1.6L gas cam and the "G grind" are total duration, where the duration he specified for the JH cam is at 0.050". The JH cam is about 10 degrees shorter in duration than the 1.6L gas cam, and about 15 degrees shorter than the G grind if you compare duration at the same lift on all the cams. IE, if you go at 0.050" on all of them, they would be somewhere around 212 degrees for the J, 222 degrees for the 1.6L cam and 227 degrees for the G grind.

Sorry, look how late last night that was posted

Even so, I thought it still proved my point about peak power vx camshaft profile.

Take a look at this cam chart if you want more numbers.
http://www.techtonicstuning.com/cams.asp

[chrissev]

In my mind and experience, (valve to piston contact with minimal timing slip) there really isn't much room at all, zip nadda nill!!!

you are right there.  Almost nothing at all.  Worse on the 1.6 than on the 1.9.  If the timing belt on the 1.6 is on a tooth off, you need a new cylinder head.

[VWRacer]

Most interesting info and a great discussion...thanks!

Mike, I missed your "naysayer" post on the other thread, but I don't understand why you think cams can't help the performance of a diesel, or is that not what you meant?

On the old forum there is a thread where a guy from the UK talks about fitting a solid lifter (83-84 JH?) GTI cam to his 1.6TD. He was so impressed with the increased performance that he had Piper Cams grind him a custom version that is even better. Looking at the table on the link I am guessing that there is little or no overlap with a solid GTI cam, but with its greater duration and (maybe) lift it can flow more air at higher RPMs. I can't access that forum from work, but will try to find it later if someone doesn't beat me to it.  :mrgreen:

[vwmike]

Most interesting info and a great discussion...thanks!

Mike, I missed your "naysayer" post on the other thread, but I don't understand why you think cams can't help the performance of a diesel, or is that not what you meant?

On the old forum there is a thread where a guy from the UK talks about fitting a solid lifter (83-84 JH?) GTI cam to his 1.6TD. He was so impressed with the increased performance that he had Piper Cams grind him a custom version that is even better. Looking at the table on the link I am guessing that there is little or no overlap with a solid GTI cam, but with its greater duration and (maybe) lift it can flow more air at higher RPMs. I can't access that forum from work, but will try to find it later if someone doesn't beat me to it.  :mrgreen:

I wasn't saying a cam wouldn't help the diesel. I was saying that the stock cam is not very well suited for high rpm power and due to the closer tolerances it seems less than likely that a huge change in camshaft profile would be possible. I don't doubt there would be gains but I would be willing to bet the gains would be from about 4500-5500 rpm. peak power at 7k still seems unrealistic to me.

[Dr. Diesel]

and to throw a monkey wrench into everything...
 last summer, I had a stock internal'd 1.6 hydraulic engine turning 6400, and a modded internal'd 1.6l turning 7000+ all with stock vw diesel cams.  the 6400 engine (i'm sure it could have gone further, and probably did on more than one occasion when i was autocrossing not watching the tach) was still pulling hard at that point, but generally was put in the next gear for the simple reason of not particularly wanting to grenade my daily driver. (which happened for other reasons anyway    :roll: )
the modded engine ended up with 17.5:1 compression and generally sucked at any rpm, though it approached ok-ness  (another one of my new words) over 25 psi and 3500 rpm. Anyway, that engine was generally a disappointment but proved to me that a diesel was perfectly capable and very willing to rev to unheard-of levels.
If the current 1.9L project engine 'puts out' for me the way i'm hoping, then I'm not going to bother with another super high rpm 1.6L, as I love the low end grunt of the 1.9L.  If not, then I'll try again with a 1.6 revver engine that has a decent compression ratio.

Incidentally, after 600km of 35psi there was evidence of combustion gas leakage between cyls 1&2 and 3&4. This was with raceware studs, and a fibre-type 1.6L head gasket. Not sure if a 1.9L steel gasket would have made any difference.

[vwmike]

Do you have any dyno charts? I'd really like to see how the power curve was shaping up.

Does the 1.9 gasket fit well on the 1.6? I would imagine the larger bore of the gasket would drop compression slightly.

[VWRacer]

Actually, I'm not surprised at all!

Most of what we "know" is what we've learned from fuel-governed diesel engines and normally aspirated engines - particularly gas engines.  But a diesel is not only unthrottled, which permits a full gulp of air to much higher RPMs than the same cam would permit on a gasser, but is TD'd as well. Compressed air is quite eager to enter the cylinder when the valve does open - just pull the valve out of a tire at 15 or 20 psi if you need to be reminded how eager cpmpressed air is to escape...

From then on it's just a matter of adding fuel to reach higher RPMs. No magic cam is really needed.  

[Dr. Diesel]

Do you have any dyno charts? I'd really like to see how the power curve was shaping up.

sadly, no. I heaved that engine due to it's low compression ratio. I was looking at G's for handling purposes at that time though, and didn't see any rapid fall-off of acceleration at any point up to were i shifted.
the other thing is the chassis dyno around here needs a tach signal to operate. working on a solution for that too.

[racer_x]

Most interesting info and a great discussion...thanks!

Mike, I missed your "naysayer" post on the other thread, but I don't understand why you think cams can't help the performance of a diesel, or is that not what you meant?

On the old forum there is a thread where a guy from the UK talks about fitting a solid lifter (83-84 JH?) GTI cam to his 1.6TD. He was so impressed with the increased performance that he had Piper Cams grind him a custom version that is even better. Looking at the table on the link I am guessing that there is little or no overlap with a solid GTI cam, but with its greater duration and (maybe) lift it can flow more air at higher RPMs. I can't access that forum from work, but will try to find it later if someone doesn't beat me to it.  :mrgreen:

Sorry, I'm not believing it. I tried a J cam (solid lifter from a JH engine) in my diesel head once. Valves hit pistons when I turned the crank by hand. Unless this guy machined something for more clearance, there's no way he actually ran the engine with a 049J cam installed.

IIRC, The J cam (vw part number 049 109 101J) has about 7 degrees with both valves closed. The diesel cam has around 11 degees with both valves closed. The J cam has 0.369" of lift (both intake and exhaust), and the diesel has 0.315" of lift on the intake valves and 0.354" of lift on the exhaust valves. Intake valve clearance is the big limiting factor. On the diesel with the stock cam, the valves come within 0.2mm to 0.3mm (0.008"-0.012") of the piston.

You might be able to grind the diesel intake opening profile and exhaust closing profile onto the J cam and get something that works and delivers better performance than the stock diesel cam. You might also be able to cut some valve relief into the pistons for valve clearance, but again, you would have to be careful not to remove any moer than necessary for valve clearance, and that might lower compression more than you want (see chart above).

The J cam does have enough duration to run optimum volumetric efficiency somewhere around 4500-5000 RPM's. For duration, it's just about right for the diesel engines. The problem is valve to piston clearance with that cam installed.

[QuickTD]

On the old forum there is a thread where a guy from the UK talks about fitting a solid lifter (83-84 JH?) GTI cam to his 1.6TD. He was so impressed with the increased performance that he had Piper Cams grind him a custom version that is even better.

You're thinking of Simon Cooper, TDIRS. He was using a gas cam in his TDI but it required clearancing of the head so the cam lobes didn't interfere and cutouts in the piston tops for valve/piston clearance.

 Anybody know for sure if the 1.5/1.6 NA solid or hydraulic cams are any different than the turbo cams?