Forcing Air into the Engine Compartment, Engine Cooling ??? Options

[Highland]

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 (IMG:style_emoticons/default/av-943.gif) 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?

[JmuRiz]

...

And worked well on the Ferrari BB (IMG:http://www.914world.com/bbs2/uploads_offsite/d39a3h63xew422.cloudfront.net-50-1629131747.1.jpg)

[johnhora]

Another pic of the engine lid airflow...



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)

[Superhawk996]

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.



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.



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



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.



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.

[Maltese Falcon]

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.

[wonkipop]

@Superhawk996

great set of figures, good explanation. (IMG:style_emoticons/default/beerchug.gif)

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).



@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.

[stownsen914]

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 ...

[Literati914]

Another pic of the engine lid airflow...

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.


.

[914sgofast2]

Another pic of the engine lid airflow...

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.


.

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.

[arbitrary]

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?

[brant]

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.

[PCH]

Maybe the hell hole is just the poor over heated car trying to cool itself.

[PCH]

Superhawk996 is right on. The most important thing is that engine tin is well sealed and there is no pressure loss from the high pressure area which is the area between the cylinders and the engine tin. Air leaks can occur around the spark plugs and through the holes that are present for the spark plug cable holders and any other holes or joints. These unsealed holes will rob the cylinders of the high pressure cooling air that the fan has forced in.

[wonkipop]

right on @PCH
and @Superhawk996

there is a fan in there...........
and it doesn't want to be sucking in anything hot, or blowing anything hot where its not supposed to be, because....... its a pretty good fan. and its supposed to be a ducted cooling system, there is nothing passive about it.

[KSCarrera]

At the last hillclimb event 10 days ago, it rained (well, it is the UK). I had a pair of GoPros fitted, one facing to the rear, allowing me to watch the way the water droplets moved as the car picked up speed. Those on the decklid were drawn forward towards the grill but those on the panel ahead of the grill remained pretty well static except when cornering. Max speed on the hill around 70mph.

https://youtu.be/shsi-iYdO-8

[Highland]

Even though my scoop experiments to date have been yielded poor results, I felt like I should give an update; mostly cause all the input I received was useful in trying to improve what already is adequate cooling.

Based on your input I put thermocouples at the fan inlet and between the tin and engine where the stock CHT is.

Today the ambient temperature was about 75F. I ran with and without the scoop. My fan inlet temperature was about 100F and the CHT ran between 110 to 120F depending upon rpm.

With the engine off and parked in my garage the temperature started to climb. I didn't watch it till the temperature rise reversed, but the fan probe (basically engine compartment) got to 135 F and the probe by the CHT got to about 270F. I took a mini leaf blower and blew into my scoop getting my fan probe to drop about 15F (to about 120F); and yes, it did rise back to 135F after I removed the leaf blower.

The scoop I used was resigned for better flow and directed air to the fan, but I think it still lacks efficiency and capacity to make a difference. Those side vents are awfully small for 914's fan compacity and based on some of the comments it seems the air flow from the vents to the fan are poor.

Oh well, back to the drawing board. (IMG:style_emoticons/default/confused24.gif)

[bbrock]

Even though my scoop experiments to date have been yielded poor results,

I disagree. I would call these excellent results. Okay, so the result wasn't what we hoped, but you had an idea and tested it with actual data! How rare is that?!! My hat is off to you for providing useful data to build on. Thank you. (IMG:style_emoticons/default/smilie_pokal.gif) (IMG:style_emoticons/default/pray.gif)

[r_towle]

The fan will only move a fixed amount of air, or CFM
Adding air won’t change what the fan can push.

Adding flaps underneath, like the factory did, creates more suction which helps the fan work better.

This is an oil cooled car, air assisted.
If you live in a hot climate, I would focus on oil cooling.

Consider the newer Boxster and 911 with split coolers up front underneath each headlight,
Look at the real estate you can get under those areas with a two row or three row cooler, then add “finned” tubing to route the oil up and back, and best the tubing inside the outer rocker cover.

You would be amazed how adding oil cooling, and like Mark said, adding the additional oil capacity, will dramatically help cool the motor.

[Superhawk996]

Even though my scoop experiments to date have been yielded poor results,

I disagree. I would call these excellent results. Okay, so the result wasn't what we hoped, but you had an idea and tested it with actual data! How rare is that?!! My hat is off to you for providing useful data to build on. Thank you. (IMG:style_emoticons/default/smilie_pokal.gif) (IMG:style_emoticons/default/pray.gif)

(IMG:style_emoticons/default/agree.gif)

(IMG:style_emoticons/default/wub.gif) the fact that you're gathering and analyzing the data!

[brant]

The fan will only move a fixed amount of air, or CFM
Adding air won’t change what the fan can push.

Adding flaps underneath, like the factory did, creates more suction which helps the fan work better.

This is an oil cooled car, air assisted.
If you live in a hot climate, I would focus on oil cooling.

Consider the newer Boxster and 911 with split coolers up front underneath each headlight,
Look at the real estate you can get under those areas with a two row or three row cooler, then add “finned” tubing to route the oil up and back, and best the tubing inside the outer rocker cover.

You would be amazed how adding oil cooling, and like Mark said, adding the additional oil capacity, will dramatically help cool the motor.

(IMG:style_emoticons/default/agree.gif)

[Dave_Darling]

One point that some seem to be forgetting is that the air in the engine bay is usually pretty hot. Getting cool fresh air in there can only help.

Demick did some tests and found that air at the side of the engine bay was significantly cooler than air in the middle of the bay. He was able to drop his intake air temps by 10F or 20F by building a different intake snorkel, and he said he could get most of that benefit just by turning the stock air cleaner half around so the snorkel pointed off to the side of the bay.

Anecdotally, we have seen improvements in some cases. John Rogers (see some of his Tech Articles over on Pelican) put a deflector across the back of his roof panel, and saw cooler engine temperatures on his race car.

Charlie Davis looked into different cooling setups in terms of oil temp, and documented his attempts and findings here: https://members.rennlist.com/chuxter/TempTests.htm

--DD