Hi guys. We got off topic and were talking about underhood temps in my thread about the intake elbow. I thought I'd do a little research into this topic and post what I found.

I have a cheapo indoor/outdoor thermometer with a wired probe. I put the probe behind the driver's side headlight where my car takes in air (stock airbox is removed; it's how the car came). I drove around town both in the morning (about 63*f) and during mid day (83*f).

What I found is that when stopped the underhood intake temps increase quickly. In the morning the temps would get to above 120 after a long stop light. During the mid day, temps would exceed 140 (max on the unit). Upon driving, temps would quickly drop to within 10* of ambient within 1/4 mile of driving.

I also was on the freeway today with temps about 70* and noticed that at about 25* temps would remain even and above that at 30mph, the underhood temps would start to drop. Anything above 35 and the temps would drop pretty quickly.

A few things to note, the thermometer didn't show real time temp changes, so it could have been slow going up and slow coming back down.

Basically beyond 30mph, even with my "hot air intake" setup, the engine is breathing near ambient air temps.

I will try to measure with a infared heat guy later and see what temps the various pieces of the intake tract are. I have one but need to find it. I'll update the thread once I find it.

So, to the people that say that an exposed cone filter is the end of the world... it obviously isn't. it's not ideal, but it's not going to kill your performance once you're moving.

 

Do you still have the hood insulation still on?

 

is that the cover over the blower/intercoolers, ect? If so, no, it's off the car now.

 

I was thinking the material that is on the bottom side of the hood. I was wondering if that kept the heat in the engine compartment at all.

 

I haven't taken that part off. It remains stock

 

Ok, I was just curious if it decreased the temps at all (or increased them).

 

The underhood insulation is for sound attenuation, not heat.

 

But it is insulation, which would hold in heat...

I was curious if there is a difference when it is in place vs removed.

 

Junk the hood blanket, its like a 20 Tog duvet for your engine!!! i'd also paint the underside of the hood matt black (absorbs heat)........also will be good for cooking eggs on the hood if you ever take the jag for a pic nic

Totally correct though the hood blanket in main will be to keep noise levels down in the cabin and to a certain extent stop the hood paint on the top surface getting scorched if/when the engine gets too toastie.

 

Not so fast (no pun intended). I think, but all of us are only guessing here, the short length of the intake tube probably isn't that much of an issue from getting heated up on the outside. But with the cone filter sitting right in the bath of temperatures you describe means you're sucking all of that hot air into the engine when you're not moving. That pre-heats the entire intake tract that much more and the aluminum tube WILL warm up more quickly than an insulated (inside and out) would. Not so sure I agree with your conclusions. I think the filter is the bigger issue though.

My race/track car has a similar set of issues only twice as much as there are dual air filter/intake tracts because it's twin turbo. Some people have gone to the cone style filter sitting behind the headlamps but I stayed with the stock box because it has a snorkel like intake that extends under the headlamps and directly into clean air. Once I'm out on the track it probably isn't much different because of the huge air flow track speeds. It's not a drag car.