T4 Engine tin: thermal design Options

[914_teener]

Jake and others use an exothermic coating on the cylinders themselves while masking the fins. I've written a couple of threads on this coating.

Absolutely agree that the airflow is NOT laminar and the the principals are quite simple.

Now....it may actually help to plug all the holes. Racing headers and engines increased performance ( via scavanging) by insulating the headers to increase air flow. So kevlar tins may actually help scavange.

I would submit that the stock heat exchangers actually might aid in air scavaging across the cylinders (which are creating most of the heat) with the cooling air as it is directed downwards. The German engineers with the materials they had availble...what they were doing. If something worked better then...they would have done it.

External oil coolers also help although I never ran one and ran my car many many times in stock config in 120 Degrees plus ambient.

My two bits...and from experience.

[Superhawk996]

You could use the Fan that is already in the Eng bay for additional flow? (IMG:style_emoticons/default/rolleyes.gif)

Might not be quite that simple.

You need to be conscious that pressure differential dictates direction of airflow.

Example: if the auxiliary fan isn’t running - the engine fan will blow air out of the auxiliary fan - decreasing airflow available to the engine.

Similarly if the auxiliary fan was able to overpower the engine fan you could end up with degraded cooling. Not likely but something that should be considered. Probably would want a one way flapper on the aux fan to prevent that sort of reverse airflow - similar to the little flaps down on the heat exchangers.

What complicates this is that the engine fan is operating at variable speed while the auxiliary electric fan will operate at fixed speed. Might be hard to ensure the balance never results in airflow being pumped in the wrong direction.

[Geezer914]

Biral cylinders?

[VaccaRabite]

Does an oil cooler do anything for head temps? During normal driving My oil is so cold it concerns me. My head temps are fine and change quickly based on load. It's early in the season of course and my 2.0 is stock besides the exhaust and kn filter.

Not really. Oil temps and head temps tend to move independently of one another. I tend not to think highly of using oil temps as "the" indicator of engine temp. Like you, I also monitor head temps. Keeping the oil cool is good in that it keeps the oil from premature breakdown - which was more of a problem in the past then it is these days. But head temps is what's going to determine if you are going to loose a valve seat and munch a cylinder. Oil provides some cooling of the heads, but only some.

I would suspect a remote oil cooler in a normal engine would just result in oil that is too cool for far too long.

This is not my experience, but it really depends on how the cooler is set up. In my 2056, the oil cooler is shut until the oil hits about 180 degrees, and then flow is opened to the cooler. At 205 the fans turn on. My oil temps stay around 215 on long drives with a heavily loaded 914. For my new engine I'm going to try the cooler without the fan pack first and see how that does for temps. I'd like to eliminate the electrical draw of the fan pack if possible.

Ideally an aux cooler is not always on, but has some sort of thermostat control to allow the engine to warm up. Shoving cold oil through your cooler isn't good for anyone.

Zach

[914werke]

(IMG:style_emoticons/default/sunglasses.gif)

[DRPHIL914]

You could use the Fan that is already in the Eng bay for additional flow? (IMG:style_emoticons/default/rolleyes.gif)

Might not be quite that simple.

You need to be conscious that pressure differential dictates direction of airflow.

Example: if the auxiliary fan isn’t running - the engine fan will blow air out of the auxiliary fan - decreasing airflow available to the engine.

Similarly if the auxiliary fan was able to overpower the engine fan you could end up with degraded cooling. Not likely but something that should be considered. Probably would want a one way flapper on the aux fan to prevent that sort of reverse airflow - similar to the little flaps down on the heat exchangers.

What complicates this is that the engine fan is operating at variable speed while the auxiliary electric fan will operate at fixed speed. Might be hard to ensure the balance never results in airflow being pumped in the wrong direction.

@Superhawk
@914werke
-simple thoughts from a simple mind) (IMG:style_emoticons/default/idea.gif) (IMG:style_emoticons/default/rolleyes.gif)
i probably need to go back and absorb better some of what you posted i just skimmed it, but thinking about the different things here just a couple thoughts and questions,
and i am not an engineer nor did i stay in a holiday inn express last night, although i might tonight so i might have better thoughts on this tomorrow, (IMG:style_emoticons/default/lol-2.gif)
but for now,
my first question is about the air flow and pressure pulling/pushing air over the cylinders. It seems that the back side of the motor is a dead end, and so as mentioned before by others turbulence ensues, flow is disrupted , reduced heat exchange and extraction, if its + above and - below, can an additional fan below pulling air from above, or creating negative pressure how ever you want to say it, could this help? just like our pulling fan on the aux oil cooler? I mean a 50 degree reduction in head temp from acouple of 3/8" holes?? might not got hru the trouble of other approaches if its really that simple, but would a fan under pulling air from thetop down over and out help? seems it might.-
- thought #2: regarding the air from from the front impeller and the use of heat exchangers- is it possible that any air flow being directed out the bottom to the j-tubes and thru the heat exchanger(especially in warm weather when its not needed), if the little flapper is open and letting air go out below instead of all the air being directed over the top of the motor, this would in the heat of the summer hurt the effectiveness of cooling the top of the motor, less air flowing thru the top.

- also i watch my head temps and oil temps and you do see that when the oil finally gets full circulation as the aux cooler thermostat open and the extra oil flows the head temps decrease, ( in answer to another persons question about oil effecting head temps, yes it does)
-i have a 2.1 motor - i run 20/50 oil( high zppd valvoline dino oil )and higher compression etc so having the auxcooler is a must, even in 80 degree weather down in Amelia Fl a few weeks ago, my fan was not turning on so those oil temps went up a good bit idling in traffic, no air flow over the Aux cooler, i think it was around 230, but next stop i fixed the wiring to it and got it working and after that even sitting in traffic, and also under harder driving, it never went over 210, and head temps btw in this situation also were reduced.
I have new tin and alll new tin with new seals, spark plug hole seals in place etc. so just keeping it to the air flow issue, seems that allowing air to go out the lower side hurts flow to thetop, and maybe a fan under sucking air from the top could help? other wise any way to get air to flow better over theback side of the motor from top down should help - id like to see a picutre of where those 2 3/8" holes were placed as well.


Phil

[ClayPerrine]

If you want to improve the engine cooling, you need to realize that the designers of the 914 didn't realize that the air intake for the engine compartment is in a low pressure area. The air moving over the top onto the rear decklid creates a suction at the engine compartment.

So the engine runs hotter than designed. But there is something that can be done for it. Upgrade the Floor Pan Air Deflectors.

(IMG:http://www.914world.com/bbs2/uploads_offsite/www.mecatechnic.com-1143-1680185732.1.jpg)

These were added to improve the engine cooling by creating a low pressure area under the car to pull out the hot air. They were a step in the right direction, but they can be improved.

Go to your local big box home improvement store and buy some rubber garden edging that is taller than the factory air deflectors. About twice the height works. Then attach it to the front edge of the engine compartment, running the whole width of the car.

It's rubber, so it won't hurt it if it drags a little on speedbumps, and if it is too low, just shorten it up a little. The extra width and length will cause a low pressure area under the car when moving, and that will draw air through the engine.

It helps to have all of the holes blocked and all the engine compartment seals intact and functioning. An external oil cooler will also help.

Living in Texas, anything we can do to lower engine temps is a good thing. And this is a cheap and easy thing to do.


Hope that helps.

[914werke]

If you want to improve the engine cooling, you need to realize that the designers of the 914 didn't realize that the air intake for the engine compartment is in a low pressure area. The air moving over the top onto the rear decklid creates a suction at the engine compartment.

So if stock, the areas that are used to "feed" unheated fresh air for engine intake ...are limited to the open side grills. (IMG:style_emoticons/default/wacko.gif)
It seems sealing those areas (to prevent that air from being sucked) & (semi) pressurizing the top of the engine with outside cool air would improve engine cooling? Except .. when not moving (IMG:style_emoticons/default/sad.gif)

[yeahmag]

What am I looking at here?

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[technicalninja]

That's the early pre-heater thing for additional heat to the air filter housing referenced a few posts back.
That one is perfect!

[914werke]

That's the early pre-heater thing for additional heat to the air filter housing referenced a few posts back. That one is perfect!

yup 4 parts. The top tin with the specific cutout, the R tin piece with specific cutout, the metal duct & the plastic tube.

[r_towle]

These are oil cooled engines using air.
Complete and proper tin, with every piece sealed properly along with sealing off all air passages from top to bottom , that seems to be all we need except really hot areas of the world, or when you raise the HP up over 150 ish

[searunner]

These are oil cooled engines using air.
Complete and proper tin, with every piece sealed properly along with sealing off all air passages from top to bottom , that seems to be all we need except really hot areas of the world, or when you raise the HP up over 150 ish

My experience.
Some years ago I have one 911 S2.4 1972 around 190 HP it have 13 LITER oil circulation a big Oil tank and a big OIL cooler that in the RIGHT front wing
NO electric FAN cool the radiator
OBVIOUS the cooling of the engine was the OIL- helped in part by the AIR and ENGINE FAN
the 914 engine have less power and in theory can have les cooling necessity BUT
the cooling system of the 914 is less efficient than the 911 so if the use is in warm land (as ITALY or TEXAS) cooling the OIL can be a big help to engine- the advantages was the better OIL low temperature and oil viscosity

[emerygt350]

You don't want low oil temperature though. Optimal oil temp is at least 210. Lower than that you can end up with all kinds of impurities and end up weakening the oil and damaging the engine. I see lots of water cooled engines that people put low temp thermostats in which never allow the engine to reach even 180 degrees. Not a good plan.

[Superhawk996]

You don't want low oil temperature though. Optimal oil temp is at least 210. Lower than that you can end up with all kinds of impurities and end up weakening the oil and damaging the engine. I see lots of water cooled engines that people put low temp thermostats in which never allow the engine to reach even 180 degrees. Not a good plan.

Sacrilege - just look at all the folks shooting for 190F oil or getting completely freaky when oil hits 230F (IMG:style_emoticons/default/wacko.gif)

But. . . Interwebz mythology won’t die (IMG:style_emoticons/default/dead horse.gif)

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[wonkipop]

These are oil cooled engines using air.
Complete and proper tin, with every piece sealed properly along with sealing off all air passages from top to bottom , that seems to be all we need except really hot areas of the world, or when you raise the HP up over 150 ish

even works in real hot areas of world.
beetles were legendary in outback australia.
back when water cooled cars regularly overheated.
beetles just kept going no problem.

the only ones that suffered a bit were the type 3 with the suitcase motor.
you had to back off in summer out on the open road.
hold them at 55 mph cruise. then they were happy.
the horizontal oil cooler laid over cylinder 3 was a flaw.

the type 4 probably has the best designed cooling system of them all.
perhaps in a hi po version with increased capacity it gets dicey, but not in stock form.
they sorted out the oil cooler location and ducting.

interesting conversation here, but for my two bobs worth i think engine tin material is kind of a marginal gain if anything. a bigger fan and more air flow is probably the answer. ducting to the fan? the type 4 sedan and wagons all had a dedicated sealed boot and duct to the cooling fan and could draw the air in from optimal surfaces on the external body work.

[914werke]

Now almost 50 yrs on I see fewer & fewer "STOCK" engine configurations which you can guess usually means more heat to deal with.

perhaps in a hi-po version with increased capacity it gets dicey, but not in stock form.

(IMG:style_emoticons/default/rolleyes.gif)

[r_towle]

I found that it takes a lot of detailing to properly seal off the top of the engine.

Spark plug seal, heater tubes or covers for those
Cleaning out all the junk in the fins of the cylinders.
Getting the outer gasket properly sealed to the lip on the tin ( gun cleaning wire brushes, on a cordless drill, just sayin)
The two little air diverters on the bottom of the firewall.

I echo the VW beetle and VW Bud are both long living vehicles in super hot climates.

[wonkipop]

Now almost 50 yrs on I see fewer & fewer "STOCK" engine configurations which you can guess usually means more heat to deal with.

perhaps in a hi-po version with increased capacity it gets dicey, but not in stock form.

(IMG:style_emoticons/default/rolleyes.gif)

i guess if you think tinware material is contributing to the problem or could improve cooling you would roll your eyes. (IMG:style_emoticons/default/biggrin.gif)

for me, like i said - an interesting conversation going down in this topic.

of relevance is something i have always noticed, which is the tinware and the magnesium fan casting are actually reasonably cool to the touch when the engine is running.
particularly the fan casting which does not seem to get hot at all. probably not surprising given the amount of air moving through it.

they certainly get very hot after shut down. particularly the fan casting.

i've always thought the mid engined application of the standard VW engine ran a bit against the grain of the air path in the rear engine cars. particularly the way the tin curves back around at the opposite end to the fan in the rear engined cars. its a real full seal that sends the air back along the underside of the engine so it can be drawn out of the car at the low pressure point at the underside of the tail. the 914 has a bit of a problem in that respect as its trying to send air flow in a counter direction.
sure there are underside air guides and plastic deflectors to assist but its a kind of an inbuilt problem with turning the engine around. i'm not sure VW or porsche got it entirely correct. its probably the only way they could do it without a major redesign of the engine tin but that would have defeated the purpose of using as many standard components as they could to keep it economically viable.

i suspect a lot of the heat shedding issues with higher performance engines might be along the underside of the cylinders and heads rather than the upper surfaces that are in the initial air flow?

it would be interesting to know if the same engine in the 912E ran slightly cooler.

PS
of interest in this regard was some special tin that was developed for the type 3 engine for hot climates (like australia). all the early engines did not have it. and overheated.
its a piece of tinware that wraps around the cylinders on the underside and is similar in some ways to the small deflectors in the type 4 that are up between the cylinders.
its more extensive a deflector in the type 3 hot climate spec engines. the problem was definitely on the underside of the cylinders with these particular cars. the beetles here did not have that deflector. ran cool enough without them. the twin carbies also helped the engine run that tiny bit cooler.

[emerygt350]

The 912 comparison would be very interesting.