When you think hoodscoop, you probably think Subaru WRX STI, Dodge Challenger Hellcat, maybe Corvette ZR1 or Ford Mustang GT500. All of these cars use scoops for the same reasons: either to assist with cooling some kind of fluid (i.e. they send air to a heat exchanger filled with intake air, coolant, or oil, or these scoops can actually be vents that exhaust air to improve cooling/aero) or they’re part of the engine’s air intake. That’s what hood scoops are for: They help the engine breathe or they help the engine keep its fluids cool. But there is one hoodscoop that does something totally different, and I’m still having a hard time wrapping my head around how ridiculous it is.
My mind is being blown right now. As you may have read in James Gilboy’s piece today about the mid-90’s Toyota Celica GT4 (a WRC Rally homologation car not sold in the U.S.), the vehicle featured a tiny hoodscoop to cool the freaking timing belt.
When I first read it, I did not believe it. But then I found a February, 1994 press release by Toyota titled “Toyota Introduces Newly-Remodeled Celica GT-Four Limited Edition WRC Model Also Available,” and here’s what’s in it:
Design
With its diagonal mesh grids and large central “power” bulge, the new all-aluminum engine hood emphasizes the GT-Four7s potent, sporty looks.
-
Use of aluminum reduces hood weight by about 8kg
-
Center-right air-inlet maintains highly efficient cooling of the timing belt in severe running conditions
-
The large right and left air outlets improve cooling efficiency inside the engine compartment
What the hell? How? Why?!
The hood scoop in question is this tiny one on the ST205-generation Toyota Celica GT-Four.
Here’s a closer look thanks to YouTube channel “furiousdriving” (check out their review here):
But how exactly does this hole flow air to the timing belt? This photo from a Cars & Bids auction shows a square-shaped outlet under the hood:
That square opening meets up with this square-shaped seal at the top of a duct on the turbocharged 2.0-liter 3SGTE engine:
But does that duct actually feed air into the timing belt? It loos like it’s a few inches away from the cover. This eBay listing for a 3SGTE engine gives us a good look at the duct:
You can see in the image that the duct appears to reach over the valve cover and down, toward the back of the engine. Here you can see that the duct appears to mount between that valve cover and the engine oil fill location:
If you look at how these 3SGET motors are set up, that’s all one piece — the valve cover includes the oil fill:
As you can see in the image above, there is no hole in that valley in front of the oil fill other than the spark plug hole, and obviously Toyota isn’t feeding air into a spark plug hole, which means this duct must be sending air outboard toward the timing cover. And indeed, in this photo, you can clearly see that there’s some kind of flat black piece between the base of the duct and the timing cover – presumably it’s a plastic extension that connects the two, allow air to feed into timing belt area:
I found a video of someone doing a timing belt job on their GT-Four, and I don’t see exactly where that duct feeds the timing belt; here you can see the timing cover off, but no clear hole for the air from the hoodscoop:
But then I found this old listing for a GT-Four timing duct itself:
If you look at those two mounting holes, they line up with the two elevated ones on the valve cover, just above that spark plug. It’s clear that, though we can’t see it in the screenshot above with the timing cover off, there must be a hole where the end of this duct enters the timing cover area from above to cool the belt.
Why did Toyota feel the need to cool a timing belt? I have absolutely no idea; obviously it was what thermal engineers refer to as a “time at temperature” problem (i.e. the time to failure at what the manufacturer considered a not-unusual underhood component (i.e. timing belt) temperature was too short). I’ve never heard of anything like this, which makes this without question the craziest hoodscoop of all time.
The timing belt vent originated on the ST185 RC/CS Celica, the homologation version of the ST185 WRC rally car (5000 produced). The plastic duct feeds a recess between the timing cover and the cam wheel cover backing plate.
From memory, the vent was to cool the timing belt. And there is also the water pump and oil pump further down the block under the covers.
As I previously owned a RC and restored it, I took the engine out a couple of times and cleaned the engine so am familiar with the vent/duct in question. Needed to fix the steering rack mount, paint the engine bay, etc. I also have a gen3 3SGTE engine in my ST185 widebody with the duct in question.
Anyway, the cam belt vent is bolted to the cam cover by a couple of M6 bolts. It sits between the backing plate and the water to air intercooler. The cam wheel cover backing is a standard part and is not specific to the vent from memory. There is a gap between the backing plate and cam cover already and the vent just feeds into the gap. Note, this is for the gen 2 3SGTE. Will need to check my gen 3 3SGTE to check if the gap is still the same (should be).
While this is a functional component, the anti-lag system on the Gen3 3SGTE engine from the WRC homologation version is non-functional, though i know someone who made the system work. Heat exchanger water sprayers are cool and feed water from the windscreen washer reservoir. Blah blah Celica nerd blah blah.
Anyway, bonnet vent and duct are functional. Homologation papers for the Celica’s are available via the FIA WRC archive for free if you want to see more WRC related cool things.
If you need photos let me know and ill pop out to the garage or find them on the NAS.
Cheers David 🙂
Yes. Without a doubt the craziest reason for a hood scoop. But maybe because the cars I’ve had that I knew have had them have timing belts inside of a sealed environment. I replaced two timing belts on a VW TDI, and I am about 35K away on doing it on a Honda V6.
My first car, a Datsun 510, which had an OHC, I had no freaking idea how all that stuff worked. My second car, a Peugeot 504, probably didn’t have a timing belt. If it did, I didn’t know that either.
Either way, they got totaled in accidents before I could outlive them. Neither one of the accidents were my fault, by the way… Both made it way past 150K miles.
Anyway, I’m paying attention now.
Does it have some sort of screen or filter on it? I can just imagine some large moth getting sucked in there and making a mess in the timing belt area.
No, no filter or screen. Fully open from factory, so crap could go all the way through to the cam belt.
I wonder if they tried to induce flow at all (specially shaped pulley, entrained air from belt movement?) or if it was just supposed to be ram air. Would need a more detailed teardown to see what happens where that duct meets the belt.
If the design case is indeed drifting as American Locomotive suggests, that would be high throttle low forward speed so I doubt there’d be much ram air at all.
yeah twist those pulley spokes and you have a mini turbo.. One would think even though the temp delta from ambient is higher, you would make it up on flow off the spinning pulley
Ram air. Cambelt, cam wheels, pulleys are standard items. Nothing special with those components.
Man, it’s not every day I learn something new about cars, but today is one of those days. Obscure AF.
I’ll pay it forward by giving you one back. The C4 (92-97) had heated door locks. Yeah. DOOR LOCKS. You activated them by holding the driver’s side door handle upwards for 5 seconds, and if the temp sensor indicated it was below freezing, it would heat up the driver’s door lock so your key would slide in.
The car also came with heated mirrors and windshield sprayers. 🙂
At the advice of my chemistry professor, I used to carry a bottle of isopropyl and a syringe in my backpack so I could de-ice the locks on my Fiero. Maybe GM learned something from us “up north.”
Good thing you didn’t get caught with the syringe. Some places that might have been drug paraphernalia. I don’t know how there’s a second r in there, but several web sites said, that yep that’s how you spell it.
My experience was probably around 1996. It was a big plastic syringe; not something you jam into your body.
The second half of your response is suspect. Are you a human?
Captcha says I am a human. Other websites say my spelling is correct.
I love days like this on this site. And yes, sometimes it is as obscure AF. And why I am happy to pay. Dusting off some old neurons is worth the money.
A C4? Is that a Citroen? I kind of remember them. And if it’s what I am remembering, I thought they looked pretty cool.
I loved my Peugeot 504 and the 307 I rented many years later.
And a diesel Fiat Croma Estate 5M I rented years after that. That thing was awesome.
I would love to live in Europe, or maybe LATAM where I could buy something Chinese.
But here in the US I have a Honda Accord with only 65K miles on it and it will likely outlive me.
C4 Audi.
E30 BMWs also had heated door locks as part of the cold weather package.
Not much can beat the ram air scoops on a 4th gen trans am. Apparently, i havent tested this yet, at a certain speed, the air being forced into the ram air scoops can actually result in positive pressure in the manifold at full throttle.
“They’re speed holes, they make the car go faster”
So, this is Toyota’s answer to David’s gripe about timing belts?
This is amazing.
Seems functional to me?
Love it!
I still say the AMC Scrambler hood scoop was the wildest. And the AMC Rebel Machine scoop was the coolest, simply because the Tach was included in the design.
Alternatively it can act as the muzzle for the 7.62 mm multi barrel minigun. (Carmageddon Edition only)
I love that game so much. It was free on iOS a few years ago. It’s my go to on long flights, every time.
You should ask the guys at Bad Obsession Motorsports who made Project Binky!!
I’m sure they would know.
I don’t know if you’ve ever driven on a back road with the possibility of dears jumping on the road ahead of you before. They luvs them some headlights. This looks like a hoity toity high falooting JC Whitney Gold Club Member stick on dear whistler to me. Gaaarrwanteed to keep those bucks off that 2 lane back road on them there northern highways!!!
Does Project Binky have one?
Don’t say that! They’ll start again with a complete re-design to include it!
“While Nik welds the timing belt vent bracket, the timing belt vent scoop bracket, the timing belt vent scoop cover bracket, and the timing cover bracket, I’m gonna get the funk out”
No Binky doesn’t have the vent. The engine on Binky is a standard gen2 3SGTE, not the RC/CS version of the engine with the homologation parts including the water to air intercooler, cambelt vent, etc. This is because on the early episodes, the celica has bonnet with a scoop, not a vent like the RC/CS. Nik did add and build a water to air cooler as we know, but no timing belt vent.
We best not recommend Nik to build a vent, otherwise he’ll redesign the whole front end again! Haha
“I think we overestimated the need of cooling for engine bay area” – Probably some Toyota designer when reviewing GT4 to help designing GR Corolla
That’s got a much taller hood and a timing chain, the 80s-90s were obsessed with low hood clearance and small/hidden front grilles, compare the frontal cooling area of a current base Corolla to the Celica, and it becomes clear why the Celica needed the extra airflow.
It has a lot to do with fashion, in the 90s aerodynamics were the big thing, everyone wanted to make slick cars with rounded noses to cut through the air, and since cooling induces drag, they tended to end up with exactly as much frontal opening as necessary and no more. Of course, when they introduced bigger, more powerful engines, they had to get creative with cooling.
Nowadays, big grilles are in fashion, more grill = more power and people want to sell that. Just look at BMW for an egregious example. So base cars are designed with way more grille than necessary, and when they bump up the power, all they have to do is take some of the decorative, blocked-off grille and un-block it. Of course, they’re never satisfied with that, so they add even more blocked-off decorative grille around the already excessive cooling area, for styling.
Pedestrian impact regulations, too.
That is wierd.
Us spec legacy turbo had no intercooler so it’s all turbo cooling. Jdm legacy turbo of the same time was water/air so I assume turbo cooling was also the goal of the hoodscoop.
Please note cooling issues existed because a head was wrapped in exhaust pipes and hot oil was dumped into the head from the turbo.
Its official Japanese name is グローリーホール
did he just say a cuss word in Japanese?
Glory Hole
They have one in Osaka
What is a glory hole?
You will have to look it up in the Urban Dictionary. We can’t really get into the definition here, for decency’s sake.
Merriam-Webster lists the vulgar definition behind four other innocent uses, and 1 I have heard used many times.
https://www.merriam-webster.com/dictionary/glory%20hole
Whatever it is, let’s just be sure to keep Roy Wort at a safe distance.
I suck at reading katakana, but it looks like “glory hole” (gurorihoru, transliterated).
Only thing I can think of is that is that in actual rally conditions, where there may be lots of high-throttle, low-speed drifting, that the under hood temperatures got pretty high. That coupled with sustained high-RPM operation possibly led to the timing belt getting excessively hot, requiring some kind of cooling solution, which then carried over to the production car.
Good point. I don’t know where the line was exactly with how much the street cars needed to share with the race versions, but that might be it.
10lbs of crap in a 5lb sack was one of the default problems of that era celica. I expect 300+ hp just made it worse. Imagine the thermal issues on any 90s car having 50% more power.
I have to say though, the 90s insistence on small cooling passages to minimize drag set us up to make some pretty sick body kits.
Imma go out on a limb and say the actual rally car version’s cooling & vents setup was so different from the road-going version, nothing about these vents would match or directly compare.
timing belts suck
So big gear wheels are better?
From my extremely limited knowledge – it’s seldom the belts or chains that go wrong themselves due to stretching.
It’s the tensioners and guides that break, allowing stretched chains and belts to jump.
Tensioners and guides go wrong due to heat/cold cycling – making them brittle and prone to breaking.
I can’t tell – but my bet is that the vent is pointed at the belt tensioner.
That’s my best guess.
The tensioner would be smack dab in the middle of the timing belt route, not on the top.
Also timing chains have guides that break, mechanical/spring-loaded belt tensioners usually last longer than the belts themselves.
So what happens when Mr. & Mrs. chipmunk decide that looks exactly like a good place to raise Alvin, Theodore, and that other one that they keep forgetting the name of? Or perhaps store some walnuts in the timing belt cover?
Speaking of weird hood scoops, I bet hardly anyone notices the hood scoop on the Mercedes-Benz W123. The guys at the car wash were certainly surprised when it sucked up a towel.
Its not a normal timing belt, its a cool timing belt.
“Welcome to cool side of the timing belt”
– Billy Dee Williams
was that solely a Family Guy thing or did he also have a penchant for cool pillows in real life
He’s just cool.
timing belts are inherently not cool lol
Assuming Toyota wouldn’t do this unless there was a problem, please follow the recommended maintenance schedule for the timing belt on your GT-Four.
Since it’s a mid-90s Toyota, I’m assuming the maintenance interval of NEVER will be just fine?
Car Nerd: “Wow, cool, they’re cooling the timing belt – that must mean it’ll last a long time!”
Engineer: “Huh, they’re cooling the timing belt – that must mean it’s under a lot of thermal pressure and won’t last very long.”
Nobody is designing and building that scoop / duct setup unless there’s a reason for it. There’s even cost in just assigning the part numbers. This thing’s even going to need a different timing cover.
Right before I bought a house, I was Car Nerd, except it was about the intricate drainage system in the backyard. Right after the first rainstorm, I became Engineer.
I’ve found that perspective (“It’s like that because it has to be and this is the cheapest solution”) very helpful.
*When it comes to home repairs, etc the sentence ends with “…and they needed to spend 20% more than they did.”
The previous owner of my house worked in concrete. Concrete was his hammer, and he thought every house problem was a nail.
A friend of mine who owned an GT-Four Celica and he described it as one of the best looking cars he’s ever seen on a flatbed tow truck, because that’s where it normally was.
Wait, I thought the MR2 was the baby Ferrari?
Wow, my grammar here is horrible.
There is no grammar here.