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Under hood heat?

Old 09-17-2018, 11:25 PM
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Under hood heat?

Hi guys having some issues with under hood temps,

okay here is some info, I have a 355 sbc, 10.5:1 compression, with headman headers, and the sniper efi system, I had a vacuum leak which was making the car run rich, I noticed that the intake manifold bolts were loose, once I got those guys all tightened down the car sounded and ran nice, I pulled out one of the new spark plugs I put in after solving the running rich issue, and it had what I can describe as white light brownish ash on the end of the plug, so I'm guessing thats good, so basically now the under hood gets so hot that I can't even keep my hand on the hood, everything is hot under the hood even the washer fluid reservoir is hot. The air filter hot, but the temp gauge shows good on both the stock firebird gauge and the coolant temp sensor for the Holley sniper,

is this normal or am I right for being worried something is wrong?

I guess before when it was running rich the excess fuel was keeping things cool,

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Old 01-02-2019, 05:37 PM
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2 Hot 2 Trot (On The Hood)

Originally Posted by theurge
hood gets so hot that I can't even keep my hand on the hood
That doesn’t mean much, in the summer with the sun on the hoods I can’t touch any of my steel hooded cars either, even with the engines cold.

The headers are adding to the hood heat.

If you think you might incur paint damage you can line the inside of the hood with reflective and thermal insulation.

You can wrap the headers with insulation.


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Old 01-02-2019, 07:39 PM
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Re: Under hood heat?

JetHot coat the headers.
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Old 01-02-2019, 08:31 PM
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Re: Under hood heat?

I also had heat problems and have headman shorties. I removed the back weather stripping from the hood which left a 1/2" space along the back of the hood which helped a lot with heat removal from within the engine compartment.
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Old 01-02-2019, 09:54 PM
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Re: Under hood heat?

Ah the aspect of insulation can be confusing in the car world.

You can insulate the engine with coatings, and exhaust wrap. Then add shields and insulating materials on top of that for extra.
I get my shields and insulation from local junkyard.... find cars with the engine removed and usually a couple of 10mm bolts gets you a whole pile of the stuff.
The lady at the counter gives it to me ("whats that?" she says, "just take it..." )

So you pack the stuff in where you can. I pulled the trans and put it in the tunnel for example. Lots of vette owners do that.
Also all down the sides. And over the exhaust system, which is also wrapped. Parts of it coated.

What all this does is keep the heat trapped in the engine and exhaust system. This will do a few things
1. Lower underhood temps (and in car temps, all temps go down outside the engine area obviously)
2. May place additional load on coolers, potentially raises exhaust gas, oil, and coolant temps.
3. Improved heat retention typically means better fuel economy (it might be so slight you won't even notice though)
4. May reduce IAT and improve air density / power output
5. Increased EGT is often associated with improved turbocharger performance, or in the case of headers may favor larger diameter because hotter exhaust gas takes up more volume. Or in the case of small diameter headers a higher EGT will improve low-mid range performance and may choke up top.

It really is a 'recipe' of sorts. For example, Some would want to dial in the exhaust gas temp for maximum velocity in the range where the engine makes the most power (for racing) or in the range where the engine makes the most torque (for... um... pulling I guess) or in the range where the engine achieves max economy (for cruising). This is one excuse to put a cutout on every car now, with a partially open cutout will improve velocity of exhaust gas at low outputs (low RPMS or low throttle position) enough to make mid-range and economy stronger, then open it for max power at a later time, etc...
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