I've been doing some research on why the Z seems to decrease performance as you complete more laps in a session. Conventional wisdom points to heat soak, but I'm trying to dig a little deeper into what about heat is causing the issue. From what I've read, heat soak occurs two way, conductive (parts touching) and radiant (heat traveling through the air).

My OBD2 data indicates that Intake Air temps are much cooler when at speed than when standing still, so it doesn't really point to radiant heat on intake air temps. In my case, it's an HR with stock intakes. The issue is that temp is read at the MAF, so that air still has to travel through the MAF hose to the plenum so therefore this may be a potential cause point when intake heat is heated by radiant heat in the post-MAF hose or conductive (plenum connected to cylinder head).

I know they make a plenum thermal gasket to help reduce conductive heat soak into the plenum and from what I've read a silicone hose is less conductive than the stock rubber post-MAF hose but wanted to see if people saw better, quantifiable performance with these mods. However, it just doesn't seem to add up to the consistent loss of performance the Z seems to have after a few laps, but that is just my subjective opinion.

I'm also curious to any other potential heat-soak remedies that people have some decent quantifiable data on (e.g. vented hood) that are also worth looking at to improve lap after lap performance.

BTW I do have a oil cooler so oil and water temps are generally acceptable (<270F Oil, <212F Water) so I don't think that is strong cause of performance drop.

 

Air from the MAF to the valves may increase temp by only a degree or two, you high oil temp can cause a little bit of HP loss. My bets are that your slower lap times are more caused by tire heat.


Ops , just looked that you have an HR, it's your oil temp. The ECU retards timing with high oil temps. Usually starts around 240 degrees

 

an easy mod to aid in big time cooling is to buy a set of billet alum hood spacers that raises the rear of the hood up an inch.. far more effective than a CF goofy hood IMO. The Iso thermal gasket is great as well. The intake hose part as Novak states is probably not an issue but might as well change it anyways..
all these things can assist you in keep ing your oil temp down.. id naca duct your oil cooiler as well if the cooler isnt functioning to its fullest extent.
I have a cooler too and will be watching this measurement as well. They say just having a cooler at all helps regardless of heavy airflow, but i have the option to directly vent it as well...I felt it was important and put the gauge right on my column.
Sounds like this may end up a REAL thread lol.. ill stay subd.

 

Thanks Terrasmak, that makes a lot of sense. I didn't think intake temp alone could take many tenths or a second off lap times. I'm running Time Trials so I'll have to do some research on how best to cool the car down mid-session.

Unfortunately the hood spacer is just a myth, at least when the car is moving. My understanding is the the base of the windshield is high pressure and the engine bay is low pressure when moving so basically it would suck air in, not out, and stay behind the engine. Standing still though, it would allow heat out because now the lower pressure is outside the engine bay.

 

Interesting thought.. You made me run off and read a bit.. Im going to test this on our car when i get mine back.. Appears theres convroversy and it also appears it because every car acts a bit doifferently w this..

I assumed it would be great for stop n go traffic in town.. But ill just try the yarn trick to see if theres hp or lp behind the hood when im at fwy speeds..

 

On most cars the engine compartment pressure is high relative to atmosphere but its lower then the air pressure at the cowl. Newer cars may have aero aids to reduce the under hood air pressures through undercar or wheel well venting. If you prop up the back of the hood you destroy that.