Heater delete fan shroud

[landrocket]

Just picked up a 1600dp, guy has plugs where fan shroud fan to heater air goes. Saw a post where there is supposed to be a dime size hole in the plugs, so the fan does not cavitate air, true?

[Marc]

Never heard that one before. Sounds like a myth started by a Chevy guy who knew he needed a restrictor in place of the thermostat if he took it out of his V8.

Until early in the `63 model year no VW had freshair hoses; gas-heater Things and industrial engines didn't either, and none of them needed anything special done to prevent "cavitation".

[sideshow]

I recall when Jake was doing T-1 DTM development he was measuring both open and blocked fresh air hoses. He mentioned "gas heater thing," bay bus, FI beetle shrouds so I can assume it was more than a casual observation.

AFAIKT his opinion was that leaving the factory provided leaks was better for air distribution.

[aussiebug]

VW kept the fan shroud as tightly sealed as it could within the limits of the pressed steel pieces it's made from.

It's supposed to run at about 5psi positive pressure and it NEEDS that to get a good flow of air through the cylinder/head finning, so the fewer leaks the better. Since the bottom of the engine is open to allow the air to escape, there's no chance of cavitation anyway - that could only occur if the main air outlets were covered over, resulting in a huge loss of airflow and increase in back pressure. (Don't try to equate it with a boat propeller cavitating under high revs at low boat speed - water is 800 times more dense than air, so it has a lot more inertia, making cavitation a problem).

Yes, when you turn on the cabin heaters you will loose a little cooling airflow to the heads/cylinders, but that's going to be in winter anyway, when the engine is getting colder air for it's cooling, so a small reduction in cooling airflow is OK.

That other poster might have been thinking about the fact that the heater boxes are designed to "leak" a little air even with the heaters shut off, and trying to match that with "leakage" holes in the block-off plugs for the heater outlets in the shroud. But this has nothing to do with preventing cavitation in the fan - that small airflow through the heater boxes is there to make sure they stay dry (from the hot airflow) all year - otherwise they would rust out from condensation.

So if you are not using the cabin heaters, block off the fan shroud outlets completely.

[TouringBubble]

I just read a lot about this due to getting lots of feedback on my crappy cooling setup. I've got the apparently poor quality slanted shroud ...

Either way, from what I read just today, when Jake Raby did all the testing on shrouds he said that the outlets still needed to flow some air in order to keep the proper airflow through the shroud. This is because the heater outlets were designed to constantly leak some air and the factor shroud was designed for maximum flow with this in mind. Completely blocking off the outlets apparently disrupts the airflow to the cylinders in some way. He was apprently able to back this up with pyrometer data.

I was not able to find anything with his full testing data. This is just what I read ... today. I'm no expert by any means.

[Marc]

I'm with Rob on this.

The heater boxes should ideally have some flow through them at all times (when the heat is "off", some air still passes through them and exits via vents in the control valves). Ideally, if you have no freshair hoses you shouldn't be running heaterboxes.

The fan shroud should not need to "leak" to work properly, if Jake has pyrometer data which indicates otherwise the only explanation which comes to mind is that when blocked completely the freshair outlet "scoops" on a stock FA shroud may cause some bizarre internal turbulence...but that sounds a bit farfetched, it's more likely that his test results failed to account for some other variable.

The best cooling shroud setup I've ever found is the stock L-Jet item with annular ring at the fan inlet. For dual-carb applications where the "hips" of the shroud caused clearance/accessibility problems, I would do some surgery to remove them (and the FA scoops). That was back in the day when the only other options were the "36HP" (actually early NFA 40HP) or centermount shrouds which lacked the internal flow-direction vanes found in the stock DP shrouds. Nowadays you can buy aftermarket "36HP" shrouds which have a fairly faithful approximation of those vanes, I would expect one of those to work acceptably.

And never overlook the importance of the "Hoover Bit" which prevents air spillage at the base of the cooler (the L-Jet shrouds incorporated this function in their shape, but all carb'ed DP shrouds must have one). As a rule, aftermarket shrouds have a gaping hole in this area.

[aussiebug]

And another thing Landrocket...

Do you have the movable thermostat flaps in place or not (even if the thermostat is missing)?

If not - that could be part of the poor cooling problem.

Those flaps have TWO functions.

1. They work with the thermostat to provide a fast and even warm-up of the engine.

2. But if you have no thermostat (you should - even if you live in a hot climate), they still have a second function - when open, the outer movable flap touches the inner edge of the head finning, resulting in a separate air path inside the shroud for the heads and the cylinders. Since the air is driven outwards from the fan around the edges of the shroud a little more than through the middle of the shroud, those flaps result in a larger proportion of air going to the heads, and a smaller proportion going to the cylinder finning. Since the heads run hotter than the cylinders, this balances the cooling better. Without those movable flaps (held open if no thermostat is fitted), the cylinders get slightly overcooled and the heads get slightly undercooled.

[neil68]

I tried the "dime-size holes" in the plugs and it didn't affect the temps much at all (in fact, they actually increased slightly, so I went back to the fully plugged outlets).

I also asked on another forum for details/proof of any supposed "data" that might exist, and none was forthcoming. I think it was just speculation about duplicating the bleeder hole air flow, and the theory was just too much of a reach. The bleeder hole is for cooling the pipes, and doesn't appreciably affect the air flow inside the shroud (physics).

My current 2332 cc has had the FI doghouse outlets fully plugged for several years and the temps are very good...similar to a stock engine with heater boxes. I strongly agree with the previous comment that you need to seal all potential leak areas and that includes the unused stock heater outlets

[Piledriver]

I can verify Jakes observations re: T4 fan housings.

Closing off the HX air feeds completely made cylinder/cylinder diffs ~30F worse vs. wide open and with a 3/4" hole.
(I saw ~no delta wide open vs 3/4" restrictor)

OTOH, a Vanagon T4 shroud (designed without the feeds) was significantly better than any of the above T4 setups, and everything ended up ~30-50F cooler.(same fan)


OTOH, T4s use forward curve fans (like AC squirrel cage units, tech wise, if not appearance wise)
...which are ~infinitely pickier about the shrouding design than the backward curve on a T1.

[helowrench]

Alrighty then, long post eaten by the hampsters.

I remember the testing, and some of the results.
IIRC the results showed a more even cooling, with a lower temp spread between the cylinders with a dimeish size hole.

There should be posts on this, with Jake discussing it.

[Marc]

I'd expect more from the man who believes there's a measureable performance gain from balancing the camshaft. Why was no data taken with an equalizer tube between the FA outlets, or perhaps with various sizes of plenum chambers or damping chambers installed? Jake may know more about the Type IV than most people on the planet, but when it comes to the Type I he'll never be a primary information source IMO.

[landrocket]

Okay guys, I just had a couple of "pops" and reading through all this stuff is great, but in all honesty lets not belittle other vw people and keep to the subject at hand. Mr. Moderator please advise. This forum is the best out there, I have been on more than several. So hear is what I am going to do, wire everything wide open, run fully synthetic oil and hold my foot to the floor, rebuild everything at 3000 miles, repeat. You guys are so funny!!!!!!

[helowrench]

But if you drill the dime size hole, it will last until 3275.8 miles.
Your decision..

[neil68]

I think Marc hit it right on...Type 4 information often does not transfer well to Type 1 engines. No one is belittling others' information, but it is certainly helpful to challenge it (in a respectful way) when you've observed otherwise.

I've just found that much of what that Type 4 shop has stated over the years on the Type 1 forums just does not happen in my experience over the past 35+ years. Interesting that the same company gave up building Type 1 engines years ago...they just couldn't get their theories to work. I have no doubt that by all accounts they build a reliable Type 4 engine, so that's great for the hobby...however, this is "The Type 1 Forum".

[Piledriver]

Probably not a matter of theories working or not...

There's just no point trying to sell $10-15K T1 motors.
The market is too small to consider.