Underhood temps...

phils89sc

Registered User
What can be done to reduce underhood temps on our cars? Does anyone make an air extractor type hood that doesn't look seriously Fast and Furious?
 
First make sure the factory devices are intact and working.

Check:
  • side baffles are in place along the front of the intake area before the condenser?
  • foam baffles from the condenser to the radiator in place?
  • insert from the lower area behind the radiator back to the cross support still there?
  • chin spoiler still there?
  • radiator fan(s) working properly?
These can be especially critical on cars that have been significantly lowered.

Do the basics: clear debris from front of condenser; use a fin comb to straighten fins on all coolers; confirm the overflow tank line is clear; pressure check the radiator cap; check coolant concentration; clean the engine to remove built up grime; check for dragging brakes/bearings; unload the trunk.
 
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My guess is the op may be asking about just general under hood temps. I.e. you will see some race cars with heat extractor inserts in the hood positioned somewhere just behind the radiator such that hot air from the radiator will come out through the inserts and flow over the top of the hood.
Otherwise a cowl hood with the rear open with vents can help.

Like this:
PA060760.jpg

PA060757.jpg
 
My guess is the op may be asking about just general under hood temps.


In that case, it sounds like someone asking permission to just cut holes in the hood :)

No one needs permission for that - go for it!

And yes, I agree with the cowl hood option.
 
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Otherwise a cowl hood with the rear open with vents can help.

Mike, that is not a good suggestion as far as I see it. A cowl induction hood is just that, an induction hood. The vents in the back are designed to allow air into the engine compartment and can cause an air flow issue through the radiator. If you look at the factory cowl hoods on the old muscle cars you'll see that they have the whole underside of the raised portion closed off except for where the factory air cleaner butts up to it to allow cool air from the cowl to enter the engine.

This is the only vented hood on the market for our cars but it cost nearly $700 before shipping and is only available for 89-93:

http://www.usbody.com/__Photo-Product-Views/A-Hood-Specs/T-Hoods/thunderbird_gt-41.htm
 
Mike, that is not a good suggestion as far as I see it. A cowl induction hood is just that, an induction hood. The vents in the back are designed to allow air into the engine compartment and can cause an air flow issue through the radiator.

Old muscle cars used cowl hoods to leverage the low pressure area created near the base of the windshield. They increased this low pressure area by having the air cleaner isolated there causing fresh air to be drawn in.

In the case of our cars, This low pressure area has a high pressure area under the hood, thus the high pressure area from under the hood will be drawn to fill in the low pressure area at the windshield causing a flow of high pressure air out the top of the hood and low pressure air filling from beneath the car and/or through the radiator.

that's the theory at least. It would be easy to test with a few pieces of yarn and tape along the trailing edge of a cowl hood. See if the yarn is pulled into the cowl, or stays above it.
 
I gotta admit...for $700.00..That looks realy ghetto!!

Mike, that is not a good suggestion as far as I see it. A cowl induction hood is just that, an induction hood. The vents in the back are designed to allow air into the engine compartment and can cause an air flow issue through the radiator. If you look at the factory cowl hoods on the old muscle cars you'll see that they have the whole underside of the raised portion closed off except for where the factory air cleaner butts up to it to allow cool air from the cowl to enter the engine.

This is the only vented hood on the market for our cars but it cost nearly $700 before shipping and is only available for 89-93:

http://www.usbody.com/__Photo-Product-Views/A-Hood-Specs/T-Hoods/thunderbird_gt-41.htm

I think that hood looks horrible! That is definetly 2 fast 2 furious!!
 
Holes 'n hoods

This one's for sale...
m7648.jpg
~
work.2169526.4.flat,550x550,075,f.not-built-for-gas-mileage-1636.jpg
This one gets lousy gas mileage...
 
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Old muscle cars used cowl hoods to leverage the low pressure area created near the base of the windshield. They increased this low pressure area by having the air cleaner isolated there causing fresh air to be drawn in.

In the case of our cars, This low pressure area has a high pressure area under the hood, thus the high pressure area from under the hood will be drawn to fill in the low pressure area at the windshield causing a flow of high pressure air out the top of the hood and low pressure air filling from beneath the car and/or through the radiator.

that's the theory at least. It would be easy to test with a few pieces of yarn and tape along the trailing edge of a cowl hood. See if the yarn is pulled into the cowl, or stays above it.

The area in front of the windshield is a high pressure area. I have a cowl hood and did test it. I attached ribbons at the cowl area and they very quickly went into the cowl when I drove down the road.

Mike
 
The area in front of the windshield is a high pressure area. I have a cowl hood and did test it. I attached ribbons at the cowl area and they very quickly went into the cowl when I drove down the road.

Mike

One problem with that then.... You have to have a low pressure zone under the hood so the air is drawn in through the radiator etc. If you change the hood so air can get drawn in from there, you are raising the air pressure under the hood behind the rad therefore the less air that is going through the rad to cool it.

Our cars rely VERY heavily on pressure differential to flow air through the rad to cool it since we don't have a big frontal area to capture air. The location of shrouds etc needs to be very carefully done to actually lower the pressure in the engine bay, not raise it. Under the car air flow dynamics also come into play as well.

I've seen SC's with nice hoods and opened ducts that get way too hot too fast because the openings are in the wrong spot.

Fraser

Fraser
 
One problem with that then.... You have to have a low pressure zone under the hood so the air is drawn in through the radiator etc. If you change the hood so air can get drawn in from there, you are raising the air pressure under the hood behind the rad therefore the less air that is going through the rad to cool it.

Our cars rely VERY heavily on pressure differential to flow air through the rad to cool it since we don't have a big frontal area to capture air. The location of shrouds etc needs to be very carefully done to actually lower the pressure in the engine bay, not raise it. Under the car air flow dynamics also come into play as well.

I've seen SC's with nice hoods and opened ducts that get way too hot too fast because the openings are in the wrong spot.

Fraser



Fraser

I concur with what you say here. I currently have the cowl open and the coolant temps run 180 deg F with little effort. I do have a block off plate that I can install if needed; but it hasn't been an issue to date.

Mike
 
Hood Vent

Six years ago I restored my 35th, and wanted to do something different with the hood. I looked at all the fiberglass stuff out there and didn't like any of it. I like the flat hood and none offered a hood to vent air out, so I made my own from the stock steel hood. I lowered the center 1 1/4" just in front of the rad. It took about two days of very careful cutting and welding to rough it out. Not much can be done with the stock hoods simply because of how they are designed in regards to the under side framing and the SC is an issue of clearance with raised tops and that. If I were to do one for a customer it would be expensive. I have a few good ideas for these hoods but cost and calling for them are not practical.
 
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