Radiator Drag
 

We all know the radiator causes hella drag, right? And we also know that a block is kewl for reducing that drag. However, what I'm wondering is does anyone have any information on how much drag it really is? I'm sure I've seen it somewhere, but I can't recall at all.

Reason I ask is I might be getting a half radiator and I'm wondering if it's worth having my friend fab up some mounts for it.

Eh, do it... then you can get turbo :P

Or just send me the radiator so i can make the turbo-alternator one day :)

I'm pretty sure I could fit a turbo in with the full radiator, but I want the room just for bling factor as well. I'm pretty sure that one day I'll have a budget build crap crx for going to the track with and just pimp this one for FE/EV.

One of the SAE papers that I have is dedicated to cooling-related drag. I'll take a look at it later to see if it offers any relevant info.

Is it something of a linkable nature? I'd want to read the whole thing just to have the thing read, :)

Knowledge is empowering, after all.

Cooling drag is significant enough that Mercedes has an E class with an active grille to match airflow to cooling needs, rather than always pay the price for airflow for worst-case cooling requirements:
https://www.sae.org/automag/globalvehicles/06-2002/

Active grilles are common on aero-aware concept cars.

For some numbers, try here:

https://www.tfd.chalmers.se/~lelo/rva...icles-drag.pdf

(I'm on dial-up at the moment and didn't want to wait for it to open to make sure the numbers are in there, but I think they are.)

I read through some of those papers and haven't found anything particularly pertinent. They focus more on cooling efficiency vs. aerodynamic efficiency, and as such don't say anything like "cooling air requirements account for xx% of aerodynamic drag." I haven't read word-for-word, though. There might be something non-obvious in there that I have yet to find.

It's in there...

I've also seen an excerpt from a paper discussing Volvo aerodynamics claiming cooling drag represents 30% of total drag (but it doesn't say what kind/shape of Volvo...) I suspect for most of our small 4-cyl non-turbo cars, 10% is closer to the mark.

Half radiator here I come!

Ever look at the radiators of large semitrailers? They all have what appears to be a canvas with a V shaped notch covering the radiator. At least in winter. Is reducing radiator drag that simple?

That's true, I'd never really thought of that!

Anyone know a semi driver?

Ninja Edit: Neat read, only casually mentions radiator size though: https://gcep.stanford.edu/pdfs/ChEHeX...0_11_trans.pdf

Edit II: Also, this: https://ffden-2.phys.uaf.edu/645fall2.../solutions.htm

I have only seen this on semi tractors in cold weather, and assume it is to keep from cooling too much. Some have active louvres on the front of the radiator, but not as common.

my thought on it is that any air that enters thru the grill has to exit the engine compartment, and the engine compartment is not aerodinamic, so it's not so much the smoothness of the grill, but the rout the air takes.
I have a half radiator, with all but about 5"x5" hole left open, and when it was 105F out, the temp gauge never budged above half way.

banana's right, SVOman. You still need to block the "excess" holeness in the front of the car.

Though one advantage of using a smaller radiator may be quicker warm-up times since there'll be a smaller coolant volume.

While not totally related to the discussion, I found this. Pretty good read.

I was also thinking about fabbing diy louvres when I start doing aero stuff. I have a couple house vents I picked up for free, and if I can rig a spring on each to keep them closed, I can easily run a cable to the cab to pull them open. I could even block off behind the rad and try to have the air flow down under the car after it goes through the rad, but then I was thinking...
What if the engine block needs some air flow for cooling, so I may need to do some testing too... All in all, too much talk, not enough action! :)

Darin, of course it still needs to be blocked, but if I had a half radiator and left the hole on the other side, :p

Why don't you just block off 1/2 of the radiator, that way it ccostt's a lot less and you cann unblock it if you need it?

According to Road Vehicle Aerodynamics, the drag of the entire cooling system is somewhere between Cd = 0.02 and 0.06, depending on the vehicle.

Ah, good info, got any links? I really need to start working on the link archive! *boo* myself

Gary, having a half-radiator will also reduce weight in the crucial up front portion of the car, look more bling, give more room to work, and lemme run a turbo if I decide to go the LPT route somewhere in the future.

Nope, no links, just the book itself. I can post more if you're interested (I need to work on my typing speed). What specifically do you need?

No no, don't worry yourself, I was just thinking to put a link to it in the archives, :)

That book is referred to so often. I just ordered my copy.

One of the Chalmers articles that I printed out says that engine cooling contributes 5% to 9% of total vehicle drag. My Civic has only a 4" x 4" opening in the front of the grill block and so far I have have no overheating problems even in 100F temps and when climbing up the NC mountains in 85F heat. I have complete underbody panelling so I exhaust the cooling air out through my front wheel wells and a small amount exhausts out through my exhaust pipe tunnel to keep it and the cat converter cool.

Found another reference to a concept car with an active grille - Ford's Prodigy PNGV concept, 0.199 Cd:

The "front breather" reference is a comparison to the GM precept car which had a rear engine layout that permitted even more streamlined front end design (no grille) as well as venting cooling airflow into the vehicle's wake.

source: https://www.findarticles.com/p/articl...59035635/print

It seems the grill block is the time-honored solution to reduce radiator air drag. Most radiators are apparently oversized enough to prevent overheating even when the grill is blocked off. If this is true, then why shrink the radiator? It might raise the risk of a boilover. If anything, I'd be tempted to make it bigger in order to enable me to reduce airflow even more (additional weight not withstanding).

I've been incubating the idea of an active grill for a few months and I think there may be a simple solution to minimize the grill air flow w/o risking an overheat.

As for the speed of warmup, isn't that what the thermostat is for?

I mainly want to reduce its size because most people I talk with that've seen my wire tuck give me hell about how big my radiator is. It's really really really too big!

Anyway, you're right about warmup, Iono what I was smoking when I thought that.

ah, now I see. Someone else suggested diy movable louvers. That would certainly work.

I was thinking about an even simpler mechanism: a sliding shutter in the grill block. It could either be moved manually when the car is stopped or even linked by cable for real-time adjustment. I should get some of that cloroplast stuff. What kind of glue works? Is it made of PVC? 'jes wunderin'

The formula one boys are the ones to ask how much radiator is needed.
F1 cars have radiators only just big enough to prevent boiling at their average speed.
That is often why when they have a too long pit stop that about 5 laps later they often have an engine blow up.
To cut drag the radiators are too small and they cant bing the temp down if it climbs too high - Kar-Boom

"Gaping maw". :D Laughing.

I was going to use that exact same phrase to describe the gi-normous combined grille opening area on my car.

https://www.lubedev.com/smartgas/quickies.htm

"Imagine a 50-percent reduction in the use of automotive fuel in the U.S. THIS IS INDEED POSSIBLE and it could be implemented very quickly. In our own cars we have exceeded 50-percent reductions. Neon went from 26 to 62 MPG. Mazda went from 13 to 44 MPG. Olds went from 12 to 30 MPG."

This is with NO aero mods and NO driving techniques. Straight highway mileage.

... that's the second time I've heard that term used
this week. :)

I'm partial to Hu-normous. :D

Yes, but that's also bull****. 35% reduction in fuel use by switching to 20w40, sure. If anyone comes on here trying to pitch that I'll fall over laughing.

I have to agree - whenever I follow a new link to read something at that site, I find more material that reduces the author's credibility even further. There are just too many "technical" statements and explanations that are beyond nonsense. I could list examples, but it's been done before, and it's OT in this thread anyway.

Yeah running heavy oil in the engine when cold will bypass the filter and pump unfiltered oil through the bearings - not good - not to mention the extra load on the oil pump usually driven by the cam shaft.

Ignorance is generally its own reward?

If you are standing on railroad tracks and watching a train coming...but deny that it is...you get rewarded?: :confused:

If some really hot babe says lets get it on and you run the other way...you don't get your reward? :rolleyes:

I'm not going to have discussions in bold with people who insult my intelligence or openmindedness.

I have yet to find myself on the tracks watching the train hit, mehbe the next time I'm in a drug induced stupor I will have such beliefs, but until then I'm not listening to this old man's proofless, theoryless ramblings.

End of story.