"Josh Holder when asked the question on Corvette Today Podcast this week said there is absolutely no benefit to them unless you have a European c8 with the particulate filter."

Josh's statement is technically reckless by using absolutely. There are proven benefits and concerns that have been expressed: more dirt and contamination getting into the engine bay, reduced ground clearance, etc.

 

a very helpful thread

 

I agree. The single biggest heat producer in that engine bay are those high-mounted Cat Converters! Deleting or modifying those will surely lighten your wallet with the associated reflash of the computer, Dyno calibration, etc.

 

So, if engine bay temps can be lowered, that should also reduce heat soak into the trunk. And if that's true, by also adding some heat reflective material to the back side of the trunk, you would think you could get a sizable reduction in temps in the trunk. Yes?

 

Yes, I did that. I took out the carpet liner and put some Hood insulation in-between it and the fiberglass body.
I used the sticky-backed stuff that you put under carpets on the backside of the air filter "door".
It made a big difference to the "pizza oven".

 

I bought and installed itsonlyairandfuel's air deflectors two years ago. They are well made, solid in construction and have very good fit and finish. For the most part, I drive my Z06 early Sunday mornings typically for 60 to 80+ miles in warm weather at 90+ mph and well above. Oftentimes sustained speeds well into the triple digits.

I never looked at the engine compartment temp sensor readings, but it was quite apparent to me when pulling into my garage, parking the car and lifting the engine hatch (I have a coup), much less heat was coming out of the engine compartment. This was very noticeable. I have also found the engine compartment fans hardly ever come on anymore compared to when I did not have the deflectors. I have not seen a difference in my coolant and oil temps, although, I never intentionally tested specifically for this. But, insofar as the engine compartment temps are concerned, there is a big difference. Just today, in fact, I drove roughly one hour at highway speeds at 80 degrees ambient and found the contents in my trunk which I had to retrieve were cool.

All in all, while increasing air flow into the engine compartment thereby lowering engine compartment temps might not make sense in engineering terms, I like the results and will keep the deflectors. Reducing all the components in the engine bay to less heat exposure should help to increase the service life of things like hoses and tubing.

If you look at this logically, increasing airflow in the engine compartment with these deflectors should increase the relative air pressure on the engine side of the auxiliary cooling radiators which, in turn, should reduce the pressure drop across them, thereby reducing their effectiveness. I have found no discernible difference in any of my oil or coolant temps though.

 

Yep herd Josh Holders very detailed statement as WHY where there are REQUIRED with European particle filters. They direct air at the Particle Filters that gets very hot. He clearly said they do not help the US cars. Said IF they did they would have added. Perhaps he has seen Forum Speculation and "measurements" and felt he needed to use Absolutely? I would not call his statement reckless!

The dude is a graduate Mechanical Engineer, Linkedin says he graduated top in his class. He has been a straight shooter providing a lot of info. PLUS he has real carefully instrumented GM accurate engine compartment temp data. The antidotal random temp measures on a Forum are fun to read BUT are no way definitive.

I recall when these European C8 air scoops were 1st discovered. Forum Speculation said must be for the Autobahn and sustained high speeds. Sounded logical. But then racing would cause similar issues and they are not added to even the Z06 with 07 Track option OR the ZR1 and ZR1X!! Hmm!

Since in a US Car the extra air is not directed at a hot Particle Filter how do we know that adding them doesn't change the air flow pattern from where GM has tests and controls the engine compartment air to deal with most critical elements? NOT SAYING they will cause issues BUT just adding because it sounds good in not smart IMO! Now IF he is asked if they can do any harm and he elects to answer would be of interest.

SIDEBAR
HERE IS WHAT THE PARTICLE FILTERS are all about fro Google AI:
To meet strict European emissions regulations, European-spec C8 Corvettes require Gasoline Particulate Filters (GPFs), also known as Petrol Particulate Filters (PPFs). These exhaust components physically trap and remove microscopic soot and particulate matter produced by the direct-injection engine.

Why They Are Required
The European Union's emissions mandates dictate severe limitations on particulate emissions (Euro 6 standards). Direct-injection engines naturally produce more microscopic particulates than older port-injection engines, necessitating these filters for street-legal operation in the EU.

Impact on the European C8
The addition of the GPF significantly changes the car's behavior and layout compared to U.S. models:

• Power Loss: The restrictive nature of the filters causes a drop in engine output. For example, European Stingray models drop to roughly 475 horsepower (down from the U.S. 495 HP). Similarly, European Z06 models drop from 670 HP to 636 HP.
• Exhaust & Sound: The filters physically alter the exhaust system, reducing overall exhaust sound output to stay within European noise limits.
• Thermal Management: Because the filters trap soot and get extremely hot, European C8 models—such as the Z06—require additional underbody cooling deflectors to help duct air up and away from the engine bay.
• Not Present in the US: U.S.-market C8 Corvettes do not feature GPFs because American emissions standards focus more on different chemical pollutants like NOx rather than ultrafine particulate matter.

 

I stand by my reckless label of Josh’s statement. A better statement would have been – the air deflectors are not needed on the US version for the intended purpose on the European C8. However, the air deflectors provide more air into engine compartment which reduces temperature, and considering that about 60 – 70% of engine heat is removed through convection, the air deflectors can help bring down engine peak temperatures faster.

The attached picture shows the location of the air deflectors in relation to the GPFs. The air deflectors are actually bent forward which seems to direct air forward slightly. I’d like to see the CFD results that show the scoops direct air to the GPFs. I agree the scoops increase the air into the engine compartment. I also think this air helps the keep the exhaust manifold cooler based on location and direction of the deflectors.

“Power Loss: The restrictive nature of the filters causes a drop in engine output. For example, European Stingray models drop to roughly 475 horsepower (down from the U.S. 495 HP). Similarly, European Z06 models drop from 670 HP to 636 HP.”

Yes, the GPFs add extra head loss that results in lower HP and higher exhaust pressure and temperature. Also, the potential for operating at prolonged high speeds (high engine HP) amplifies the issue for the European version.

“Thermal Management: Because the filters trap soot and get extremely hot, European C8 models—such as the Z06—require additional underbody cooling deflectors to help duct air up and away from the engine bay.”

“Air up and away from engine bay.” Not directed at GPFs. Does it help reduce the GPF temps – yes. If it reduces the GPF temperature, why wouldn’t it help reduce the trunk temperature which is in the same location and is consistent with my measurements and others here?

 

This is a very interesting statement. It suggests that the additional airflow provided by the deflectors actually reduces the pressure drop across (and therefor air flow through) the radiator. The radiator of course heats the air entering the engine compartment, while air from the deflectors does not get "heated". Those side scoops are enormous and very likely produce significant positive air pressure in the engine compartment. Those little deflectors are pushing against that. Obviously they seem to make a difference in measured engine bay temp, at least at the points where it is being measured.

 

The engineers are concerned about engine compartment peak temperatures and the time duration at those temperatures. Reducing temperatures that are already significantly lower than peak temperatures to begin with will likely have negligible effect on component life when components are designed to meet the peak temperatures at the specified durations.

We don't have access to all the data that the GM engineers have nor the specifications for the components. Aerodynamic flow is tricky. It could be the engineers compromised optimal cooling when they installed the deflectors to to avoid exceeding peak allowable temperatures when the GPF filters were installed. The less than optimal cooling may be considered acceptable in a country like Germany with lower average high ambient temperatures but would be unacceptable in areas with higher summer temperatures. The fact that the OEM deflectors are not mirror images suggests there is more to them than meets the eye. Without access to the data we don't know, it is all guessing. It is quite possible Josh Holder's statement is accurate.

 

Yep can't make a statement about what these bottom deflectors do without what GM has, actual comprehensive engine compartment cooling data in critical areas. GM no doubt spent a lot of effort in defining size, shape of rear fender scoops and passages AND Exit Air Vents. As all ME cars must.

SIDEBAR
I was involved in engine/generator cooling for large engine driven welders. We acquired a business that had recently started to sell engine driven welders as part of their offering. They were using an Italian built generator and US engine. Turned out the US engine company would NOT warranty the engine unless they did the cooling tests on the combined engine generator enclosure at OUR expense. Generator cooling was also an issue and that was coming from the overseas supplier. Got out of that situation by stopped selling and fortunately they had only sold few.

One of my former Business Managers and friend, left and took over the business selling small engine driven welders and engine driven air compressors mostly to rental agencies. He was expanding the line to higher capacity welders and wanted us to handle the product since we had none. I was very hesitant. But had thought of a product that the industry had missed. At the time I had a pick-up truck that I added an aluminum tool box across the front of the bed. Seeing many contractors had engine driven air compressors in their truck bed and some also had engine driven welders thought a combo in a locked tool box would be a great product as theft was an issue. Mentioned the key was cooling. He had the company supplying the combo engine/welding generator and engine drive air compressors conduct the cooling tests. Turned out placing inlet air and exhaust vents where needed to cool critical areas was not trivial. He applied for a patent. Recall at our next Industry annual exhibition he had a large pick-up truck in his booth welding and operating air driven nail guns from the Truck Box!

 

The good news is we are in no way overthinking this