Update:
With the Christmas/semester break, I found about a week and a half to work on the cooling shroud. Unfortunately, I've been suffering from bronchitis/asthma/allergy/something since Thanksgiving, and the persistent coughing led to a broken rib (snapped in half)
, and possibly one more that is presently undiagnosed. This was a painful week.
Also, I'd like to thank local VW enthusiast and racer Scott Sain for providing me the garage space to do the work (as I have no garage). He's definitely one of the coolest folks I've met in the hobby, and is the personification of southern hospitality.
I had two major tasks to accomplish; one was adding the oil drain to the 3/4 head (I used to have this when the car was N/A, and had it welded up when I turbo'd it), the other was to continue development on my Bergmann shroud.
I had a chance to look at the wear patterns on my Pauter lifters. If some of you recall, a few summers ago during the changeover to forced induction, I was not happy with the wear I observed on the ISKY lifters I was originally running. These were a tall pushrod cup lifter; the pushrod cup actually stuck out of the case at full lift. The benefits were running a short pushrod, but we did not consider the increased pushrod angle would reflect enough force into the lifter to cause it to want to "lever" in the bore and cause a diagonal wear pattern. Again, this would probably be fine for a race-only engine that saw limited miles over the course of its short life, especially since the short pushrod would be advantageous; but for a street/daily-driven engine, this isn't what we wanted to see.
Rocky rebushed the lifter bores that summer and we opted to run the Pauter roller lifter. The pushrod cup is recessed into the body of the lifter, closer to the stock pushrod cup location. After 5000 miles on this new set-up, I'm much happier with the wear patterns. There is no more diagonal wear as observed with the ISKY's. The wear pattern on the Pauter lifter is isolated to just the top and bottom of the lifter, indicative of the shear load during both valve opening and valve closing. The wear is consistent across all 8 lifters, on both sides of the engine, suggesting that the oil supply to both banks of lifter bores are also consistent. I've posted a few pics below; excuse the graininess of my cell-phone camera, as I tried to capture the location of the wear patterns just behind the roller wheel on the top and bottom of each lifter (you can kind of see a "dull" patch on the lifter in the 2nd pic; this would be the wear pattern I'm describing). Overall, everything looks good, all roller wheels roll nice and tight, and valve clearances have be consistent over the past year and half. I expect the next 5000 miles will be as trouble-free as the last.
Now, on to the modifications to the Bergmann shroud. One issue I've found with the Bergmann shroud is it's poor fit, gaping holes around the cylinder heads (notably, behind the exhaust port fins). To address this, I made simple deflectors that attached to the heads and interfaced with the inside of the shroud.
The goal was to prevent air from flowing past the cooling fins and simply out of the gaps in the shroud. The deflectors were mounted to the outside of the exhaust port fins, closing a major gap in shroud, and to the head to direct airflow down onto and in between the fins. This is not the most elegant solution, short of reglassing the shroud, but relatively easy.
Another criticism is the lack of airflow around the underside of the cylinders and heads. Several other folks have suggested solutions to aid the control of airflow,
ralf wrote:sumtihg worth considering (no im no guru)
i always had at the back of my head,
911 style fan and shroud, you could try the super cool tins
mod it like sum1 did here in the forums to have the center part form like a pyramid/deflector for the air to move to the front and rear cylinders
should it help? datalogging would judge that,
but from my newbie mind.. it seems ideal seeing that this would make the exit of the air only below each of the 4 cylinders?
modok wrote:
As for bergman's shroud, lemme make an illustration real quick.
ok, see how the airflow is forced into the fins and goes all the way around each cylinder? That's how most aircooled engines are. Does Bernies shroud do that? doesen't look like it
And, of course, if you evaluate the Klaus 911-shroud, controlling airflow around the undersides of the cylinders and heads is one of the unique features that sets their shrouds apart from the rest:
The stock cooling tin, in its complete form, controls airflow down the sides and around the underside of the cylinders and heads. The Bergmann shroud does not; it just dumps air on top and down the sides of the cylinders and heads with no mechanism to direct airflow to the fins underneath, and no mechanism to control plenum pressure. Air isn't simply going to loiter around the underside of the cylinders and heads and cool off like goth kids at the mall.
So, after initially dismissing Ralf's suggestion, I decided to buy a set of Type 3 "cool tins". I should have stuck to my guns because that was a mistake and a waste of money (sorry Ralf); the Type 3 tins simply require too much modification to fit my engine case and interfere with my pushrod tubes. On a type 1 case with standard diameter pushrod tubes, this might be an option. Oh well, lesson learned (again).
So, with a large sheet of aluminum, snips, and some safety wire, I constructed some tin of my own:
fitting the tin around the cylinders:
The tin divides the airflow down the middle. Holes are cut into the underside to provide an exit for the cooling air. If this restricts airflow too much, I can always snip away at the underside to open it up:
And fit into place:
I also extended the tin along the side of the head fins and wrapping around the underside. These fit sung alongisde the head when the shroud is placed on the engine. Hopefully this will direct air across the underside of the head:
After reinstalling the Bergmann shroud with these new tins, I removed the original diverters that I previously installed. I want to start with a new baseline as these new tins and deflectors are going to affect the pressure in the shroud, and likely the air distribution as well. I have only driven the car about 20 minutes since finishing these mods (returning home from Scott's house yesterday). Right off the bat, I noticed that the 1/2 cylinder bank was running warmer than before and the 3/4 cylinder bank was running cooler. This was to be expected; given a fixed supply of air, cooling down one side will result in the other side warming up. Cylinder #3 was the hottest cylinder :-k, but I think the reason for this is that the #3 injector is pissing fuel and running that cylinder rich (this was evident from the top-end tear down). Cylinder #4, which usually is the hottest, was running about 10 degrees warmer than cylinders 1 and 2 around 45 mph or less, and about 15-20 degrees warmer than 1/2 at 65 mph. Cylinder 1 and 2 were within 5 degrees of each other. So far, this appears to be a much better baseline to work with when I go back in to reinstall diverters inside the shroud.
These are just preliminary observations from very little driving, but the results are promising. I need to replace the #3 injector (or just get a new set from RC Engineering...these Siemens injectors are not too impressive) before I do any further development because the #3 CHT is simply not indicative of the tune of the cooling shroud. Once that is fixed, I'll begin concentrating on equalizing air flow between the two cylinder banks.
