I'm guessing it's been tried, but is there a downside to forcing fresh oncoming air into the engine compartment? I've read that removing the rain tray does not help cooling which tells me the 2 engine compartment side vents are more than adequate to feed the centrifugal cooling fan; so perhaps increasing engine compartment air pressure and reducing relative air temperature would help.

So don't laugh too hard at the pictures It's a first pass attempt.

I did a couple of runs on my normal joy ride and am qualitatively seeing about a 5 to 10 degree head temp reduction and quicker cooling to normal temps after an uphill grade. Also cruising at 65mph in 5th I'm seeing about a 10 degree reduction in steady state temperature. I have a big hole in the back due to a 3D print problem and my duct tape keeps on flying loose so not getting full duct air. I just have a VDO head temp gauge on #3 plug. As many of you know the VDO has 50 degree hash marks; so not real accurate reads.

So is it correct that head temps are not affected by outside air temp, that's an oil temp thing?

Has anyone tried this? The stock grating is still in place. Can I be doing any harm?

Click to view attachmentClick to view attachment

I’ve been trying to think of ways to bring more air to the motor but was looking at coming from the underside….Paul

Kinda reminds me of the old swamp coolers.....only for your engine.


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Years ago I played around with a data logger and a fairly sensitive air pressure sensor - would be interesting to see if the air pressure in the engine compartment is affected by removing the lid completely.

I think he’s on to something here. The area is a lower pressure, so simply removing the lid would change airflow, but forced air from the edges would really add movement in areas that should benefit from it.

The rain tray is not a tight fit so plenty of air flows thru that section too.

The MR2 aftermarket has a nice looking air duct.

It is a general consensus of opinion that the area over the engine lid has slightly lower pressure.

I think Jake R said removing the rain tray made no difference to engine temps, so I doubt removing the lid would improve fresh airflow through the fan.

I'm just guessing here but my assumption is the airflow over the engine fresh air intake area does not provide an efficient supply for the engine compartment. By forcing air into one intake port, I'm hoping to provide a flow of fresh air to constantly evacuate the engine compartment (through the opposite port and seam leaks) and provide positive pressure to the fan intake.

I do need to redesign the intake for better fit, mounting and printability. Still learning the capabilities and limits of the 3D printer.

Didn't want to reinvent the wheel if someone has already tried this and has results. Also wanted to get opinions if I could cause harm to my car of which are not obvious to me

I would use a temperature compensated thermocouple setup on your #3 spark plug instead of your VDO gauge.

The VDO gauge, although good looking, has the connections between the K-Type TC and the voltage leads in the engine bay which will basically give you the temperature delta between your engine bay temperature and your head temperature, which is not accurate.

Using a new ring type TC with longer thermocouple wires would allow you to make that connection in the cabin which would be cooler and closer to room temperature (temperature at which the gauge is factory calibrated) but still hotter in the summer time than room temperature.

Having a temperature compensated gauge will ensure your head temperature measurement is accurate no matter what your surrounding temperature is.

In your current setup, changing the ambient air temperature in the engine bay may affect your reading independently of the head temperature.

The results of your investigations are only as good as the quality of your measuring setup. Good luck with your project!

Although I have no scientific evidence, My personal experience differs.

One day my engine was overheating sitting in stop and go, to mostly stopped traffic on a local interstate highway. I had pulled over to let the engine cool, and opened the engine lid to facilitate that.

When pulling back into traffic I neglected to close the engine lid and being on the highway I just continued driving with the lid up. I was surprised how much cooler the engine ran with the lid up. ( I did have a rain tray installed)

Since then I installed one of Sergio's GT lids and have noticed that my head temps stay much cooler in the hot summer weather.

In the winter, I reinstall the regular lid with rain tray.

Perhaps Im dense. What are you trying to accomplish? Reducing head temps by adding/forcing cool air to the top of the engine (presumably to feed the impeller fan)?

Here's a much more accurate thermocouple set-up.

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Components: J type TC with 14mm spark plug ring & 10' extension, Cold junction compensated digital readout all very inexpensive, look on E-Bay

That's good to know. Thanks for the information.

I know the VDO gauge is not that accurate, but at least for the year + I've been using it it has been consistent. My understanding is that higher engine compartment temperatures would cause the VDO to read low. I can't imagine forcing fresh air in would lead to higher ambient, so at least my gauge will error "conservatively".

As to what I'm trying to accomplish: Just trying to find another way of improving our cars. I actually don't have an engine temperature problem, but lower head temps is always better. I guess the bottom line is I'm just playing and thought I'd share

Are you running a pair of these?

https://914rubber.com/floor-pan-air-deflector-for-914

Rather than addressing the low pressure on the top of the engine, these are supposed to make the pressure lower under the engine to help pull the air through.

If I recall its been tested and having these in place does make a difference.

+1 on Sharing cooling ideas.
+1 on bringing air from below.
+1 on having the air deflectors.

Highland,

Interesting approach to forcing more air into the engine bay with your 3D printed scoops. I would think that well shaped scoops would help as it has been stated before that the area behind the 914 roof and targa bar is in a low pressure area. I am surprised the original 914 design did not include some form of ram air intakes for the engine compartment. The scoops you have made remind me of a more extreme idea, that Joe Sharp 914 Ranch has been developing in his build thread. Check out his scoop design beginning on page 16 of his build thread.

http://www.914world.com/bbs2/index.php?sho...5484&st=300

biggest problem a 14 has got is getting rid of the hot air out from underneath it when it is sitting running in stop start traffic in hot conditions? man it builds up under there in aus on a hot day. turns into a bubble of hot air under there all the way to the tops of the rear guards. engine tin seal rubber needs to be in very good condition to keep it under the car and out of upper engine bay where the fan can suck it straight back in - would be a bad feedback loop.

ok on the move with the air deflectors doing their job mentioned above.
almost like you need an extractor fan underneath some days in australia?

no getting around that the car was designed for european and north american climate.

standard vws with rear engines could start running notably hotter down here on extreme days - and they could discharge exhausted cooling air straight out the back and not trap it underneath. always used to back off in my old bug and squareback, drive it at 50 out on the highways in high summer super hot days. thats when they all blew up.

i avoid driving in high summer here. UV/southern hemisphere ozone depletion will get you anyway, so no fun. australia. if the spiders and the snakes don't get you the sunburn will.

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wondering if anyone in the USA has ever had that experience of sitting at the lights, on a warm day, and puff of wind blows and then a bubble of hot air dumps into the cabin if you have the roof off. just having been blown out from under the car. if you weren't sweating allready...........

Read these 914 aerodynamics papers:

Not a good idea. The air on the street is 20F hotter.

I've been thinking about this too for my track car. Maybe placing a deflector on the aft end of the roof. Something maybe 18 inches or so wide that sticks up about 4" above the roof line and spaced 3-4 inches behind. Not a scoop, but just brings air into the engine area

There is a flaw in that paper. It is physically impossible for a significant amount of air to flow upward on a stock car.

good stuff mr. b. you have some good gear/research you have accumulated.

air flow along flanks of 914 confirms vw thinking on the old type 3.
the long louvre vents on rear guard flanks of those were into plenums that then fully seal ducted cooling air and induction air into the engine. they never had any tin-ware separating lower engine from upper engine. just a separated ducted cooling intake.

you want to keep your cooling air intake as far from your heated air exhaust as possible in everyday conditions of stop start go slow traffic. i reckon porsche got it right for the 914 as an everyday car (except when it comes to something like death valley/and or/australia). fortunately you don't get caught in traffic jams in death valley?



as an aside, 917s just had a dirty big hole in the top and the fan sucked it straight in.
and they were going at 230mph. no ram tube etc for cooling. they might have been trying to ram induction air in later on.

What about these on a quarter with GT flares
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I'm interested. We could thermoform some ducts that could be easily installed and removed without damage to the body. As noted in the aerodynamic studies there is a backward flow of air on the deck. Ducting to the sides would allow for cool air to displace stagnated air at a much faster rate. This should help with cooler Temp air supplied to the intake and fan housing. Resulting in a higher air density and cooler air over the head and cylinder fins.

As another member noted the aerodynamic quiet spot just past the firewall needs to be broken up. The air deflectors do this quite well. We added tip vortex generators to maximize the efficiency.

These are a pretty simple add to any car.
https://914rubber.com/floor-pan-air-deflector-for-914

We include the hardware too.

The LE spoilers also help.

The papers are very cool - thanks to @jeffbowlsby for sharing them. I have not run across these before.

With respect to which way air flows, that is a limitation of the modeling. No effort appears to have been made to account for the flow into engine compartment induced by the crankshaft fan and I don’t think I saw sufficient model detail to account for actual underbody geometry and the underbody air deflectors on OEM. Focus of the paper real was on determination of Coefficient of drag. I may have glossed it too quicky and will re read later.

Overall I guess I’m still confused by the OP purpose of wanting more air flow on a strrret car. If it is in trying to make an air-cooled engine run at the same oil or head temps as a water pumper, then it’s just tilting at windmills. Air cooled engines simply run hotter due to the cooling dynamics involved.

If his car has some sort of overheating problem, it would be wise to find root cause of that rather than trying to re-engineer the air flow. But I applaud the experiments!

Mikey, just installed your air deflectors on my 6 GT Tribute, very nice product and easy install. Also having good engine tin and rubber seals to body keeping lower engine heat out and all top cool air coming in going over cylinder/heads. Best, Mark

Seems to me that the main heat issues (on a street driven 914) is when stopped at lights, traffic jams, stop-go traffic - ON HOT DAYS. As was mentioned, that heat really builds up under there. So the scoops to me wouldn’t be as important. Getting heat out from the underside of the tin might be nice though… what about some small fan arrangements under there that help to expel some of that heat? Maybe programmed to run off the oil temp sensor? And/or some modern type of heat shielding between the exchangers and engine? Just my thoughts on the subject, ymmv.


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Did y’all miss the above statement? Nothing wrong with trying to improve the situation right?


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Anyone tried gluing strips of yard to the top and sides of targa area where the low pressure spots are located so a scoop or spoiler could be used to direct air into the engine grill?

Next question? Thse are al found on my 914 Classic site under Vintage Photos.

Wow..never seen these before. Just goes to show you that they knew what they were doing when they originally designed the body in white car.

When I first read the title of this thread...I don't think you want "higher pressures" in front of the fan. Like Mark said...you want lower pressure as this is a forward curved scroll fan. If turbulence is created around those tips, the fan becomes less efficient at doing this. Thiink of an airplane wing here. You might get cooler air but I seriously doubt you will get cooler engine temperatures by doing that as fan efficiency will be sacraficed. This is why the deflectors are there at the end of the body pan.

I had a side project where I was going to use exothermic paint on the cylinder bores and heads where the tips and exposed surfaces of the fins were not. I was also going to insulate the HE's exteriors and use exothermic on the tubes. My thought was to gain the difference in the exhaust and make the HE's more efficient and gain heat at the same time. Sold everything to Rob -Beat Navy and I think he went a different route with his car.

I think as designed the car does pretty well disapating heat. I used to drive mine over 100 degress often and never had any issues. I did run without the rain tray though during the Summer becuase of idling in traffic.

Hey Rob!

I put an external ceramic coating on those HE's and have been meaning to put them on my ride. I don't know whether the welding repairs or ceramic coating cause a fitment issue, but I could never get them to seat on my heads. Just wouldn't go over the head studs, so rather than fighting it I just kept using my SS HE's.

Just before I recently dropped my engine (to fix a failing oil pump ) I gave them another test fit. I aggressively ran a rat tail file thought the ears, and I think I finally have them so they'll work. I'm excited to see how they work and if the ceramic coating reduces heat transfer directly under the car in any appreciable way. Should get them on this week.

I agree with Literati914. My car's head temps are great, even when not moving. But my car's oil temps really spike without significant air movement under the car on hot days. I feel like the oil "cooler" is just cooking the oil over the HE's.

It does. I did the same thing some 10 or more yrs ago with a NEW set of SSi's. It both reduced the the under car temps...some, & noise associated with the thinner construction SSI's but also DRAMATICALLY increased cabin heat production to the point even with the best sealing I could muster Id get some radiant bleed through the tubes into the cabin when off/closed.

Sweet, good stuff Rich. Except the part about putting heat in the cabin when you don’t want it!

I’ll follow up with my observations at some point.

Hey Rob:

Hopefully not a thread de-rail....but good to know you are still doing it and hope to collect on that beer...hopefully Springtime. I'll send ya a PM if I and when I make an East Coast tour. Love to see you new engine set up.

The idea was to exothermicaly coat the inside and outisde of the exhaust tube and insulate (ceramic coat) the outside of the stock HE's shells. Like insulating your house you would get better thermal scavaging in the cylinders and while at the same time getting less heating in the engine bay during hot weather....and maybe better heating from the stock set up. Don't know but that was the thought.

a detail i used to notice about vw type 3s was the difference between air grille intakes on a notch versus a fastback. the fastback had them on the flanks and shared its rear guards with the squareback. it would have made mass production economic sense to also share the rear guard set up for the notch but they didn't.
it must not have been aerodynamically good for the inflow into air intakes on the flanks.

the 914 is similar to the notch in a way. its a blunter rear to the cabin turret.

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there was no difference in the rear profile rake of a 4 door 411/412 or a 2 door fastback.
somehow that rake must have better suited intake vents on the rear deck lid.
it is interesting where they position those vents on the various cars dependent on rear profile.

having said that, a 911 is a fastback shape and has the intakes on the lid, so the type 3 fastback is a bit of a mystery to me.

they didn't have any choice with the squarebacks, no other place but the flanks.

I have contemplated the same thing for my T4 powered Notchback. Low pressure zone behind the rear window is the location for the air inlets. Think 70's F1 for inspiration

Seems to have good air flow on the rocker and they come in fiberglass. Could pick up some cool air with a scoop and think brake cooling ducts. That size from each side would bring in some air with out over pressurizing the engine bay. (someone mentioned fan issues) Maybe like this: Red is exposed, blue is inside with start collar and orange is the flex tube to a small collar added to let air into the engine bay.

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Works well on a Cayman!

Honestly,
The best cooling is probably obtained by increasing oil quantity. The 72 I bought out of Reno used to carry a canoe on top and drive up to Tahoe. It has an external oil cooler mounted behind the trans axle. Good for 2 more quarts of oil+ cooling.

And worked well on the Ferrari BB

Another pic of the engine lid airflow...

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the quick and easy is to:

add 914 Rubber's air deflectors (what factory did for 914-4)

add one of Sergio's GT engine lids (what factory did for 914-6 GT)

and if it's still a problem.. the as mentioned oil cooler which also adds capacity (what the factory did for 914-6 GT)

There really is no need for guessing what is possible.

Spent a few minutes online to help frame the scope of what could hope to be accomplished.

Here is the defining equation for convective heat transfer (air cooling) and the associated cooling coefficients for air vs. water.

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Now let's look at how much the heat transfer would increase if you could get a 50 40 degree decrease in inlet temperature vs. what you currently have. Assumed a head temperature of 300F and ambient air of 110F as baseline.

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Now let's look at what the increase would be if you could go from 110F right into a refrigerated box at 30F.

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And most importantly - lets look at what happens if you have poor engine sealing and start recirculating hot air from under the engine back to the fan intake.

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The end game should be obvious. More to be gained by ensuring the engine is properly sealed vs. trying to bring in cooler air.

Likewise, the switch from air cooling to oil cooling (or water) is a 30 times more efficient solution as far as heat transfer goes.

Still applaud the experiments and agree some improvement is bettering than none. Just wanted to put some numbers and percentages to what is feasible rather than speculating.

I tried this simple air scoop attached to the right side targa sail panel in the early '80s; it worked well enough to feed cold air into an intercooler mounted near the battery tray.
After the (undersized) intercooler blew its hats, I just mounted the largest available Spearco/Blackstone intercooler, popping through the rear trunk. At speed that brought an intercooler temp differential of over -100°f between inlet and outlet of the cooler.
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@Superhawk996

great set of figures, good explanation.

tells partly why VW kept moving the inlet vents on kombis higher.
sitting around in stop go traffic you don't want to be sucking exhausted hot air straight back in the fan, even from outside the car. feed back loop is possible.
(though there is some aero stuff going on too, the early louvres would not have been so great at speed, not that speed was something kombis could achieve).

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@JmuRiz
the sexy ferrari flank vents aren't necessarily there for cooling. might be for induction air? or brakes. don't know enough. but the main cooling stuff is up the front as per even model Ts. same goes for the boxster.cayman. different problem from air cooled car where a lot more air volume is being moved in and exhausted out from a not so great location in the car - about half way down the sides.

re suggestions for rocker intake vents for cooling 914s.
ok on the move. but would be not so good in stop and go traffic.
perfectly for exhausted cooling air blown out underneath to get sucked back in via feedback loop at ground level when stationary. just like having leaky engine tin?

an oil cooler a long way from the engine with maybe a fan assist is more effective than anything else after good engine tin seal. my old german vw mechanic back in the 80s used to say, zis is not an air-kueled kar, zis is an oel kueled car. he was kind of right. he offered that as an explanation for why type 3s always blew up more than beetles in australia. the oil cooler was very compromised where it was positioned in the type 3 engine. its not compromised in a type 4, they actually thought about it properly by then.

EDIT - i've remembered there was a fad for fitting aftermarket fibreglass/plastic scoops on type 3s in australia in the late 70s/early 80s. you put them on over the long flank vents on the fastbacks and squarebacks. turned out they were a not so good idea in city traffic aus hot summer driving. word was they inhibited air flow intake in stationary conditions. wasn't like the propellor fan on a type 3 was a work of genius either trying to draw air through a smaller cross section opening.
might have been ok on the highway as a ram intake. probably forced cooled harder than the dumb fan.
thats not to criticize the side grill vents suggested in this thread, they are not reducing the cross sectional area of the intake.

Aircooled engines need all the cooling help they can get. 914s are a bit more compromised than 911s due to the engine placement and not getting great airflow there. Aircooled engines depend a lot on oil cooling, including for the heads. Granted they are essentially "splash cooled" by oil, but keeping the oil cool prevents the convective head transfer to the cylinders and heads that would otherwise occur, and type 4s run pretty hot.

But air does help too. On the racecar (mine has a 6), I put a NACA duct in the front hood and ran a 7" diameter duct through the cockpit, and I get noticeably lower cylinder head temps. This is a common mod on raced 914s. Not practical for a street car, I realize ...

I wonder to what degree this effect is diminished, if at all, when running with the top off. I understand that these cars don’t run hot with the roof off but it’d be interesting to see what the yarn does. Maybe no difference but you’d have to think that the long roof run helps with the low pressure swirl of air.


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Seeing that picture, I am wondering if a small lip spoiler mounted to the rear of the roof would encourage more air to flow onto the engine compartment.

Apologies if I’m missing something but isn’t low pressure over the engine lid of limited use? Wouldn’t low pressure there tend to reduce the air pressure in the engine compartment which is counter productive to cooling and engine air supply?

2 cents from my experiments with added air.

We used the air feed to run to a cooler

version 1 was a scoop below the firewall
version 2 was this scoop out the passenger side window

Version 3 was an electric fan


all 3 were measured with a temp gauge on the cooler, run on the track, multiple weekends...


the electric fan out performed both ram air scoops

I'm just saying... add an electric fan if you want to on the engine lid
but these are not likely to make a big difference on your head temps
I think the ram air from the front (big 6inch pipe through the length of the car) would be the only one that would show a significant improvement.