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Cutting my firewall to improve cooling??


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So I had a thought the other day as I'm driving around in 90+ degree weather watching my temp gauge like a hawk worried it's gonna keep climbing. I want to improve the cooling of the car in stop and go traffic but I don't want to cut the hood or make any visual changes to the exterior of the car if possible. I know that may be crazy but I can hope. I was thinking of cutting vents in the firewall right up into the windshield wiper motor area and let air escape through the vents on the cowl. Am I crazy cuz I think it's a good idea but I've never seen or heard anyone else do this

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1 minute ago, datsun_dom said:

So I had a thought the other day as I'm driving around in 90+ degree weather watching my temp gauge like a hawk worried it's gonna keep climbing. I want to improve the cooling of the car in stop and go traffic but I don't want to cut the hood or make any visual changes to the exterior of the car if possible. I know that may be crazy but I can hope. I was thinking of cutting vents in the firewall right up into the windshield wiper motor area and let air escape through the vents on the cowl. Am I crazy cuz I think it's a good idea but I've never seen or heard anyone else do this

 

Yes and no. Yes you can fabricate a way to allow added engine ventilation through the OEM cowl vents. I did it for my race car (see below link). Keep in mind, there is a lot of debate on whether hot air will escape this way, or high-pressure air at your windshield will be pushed into the engine bay. Either way, its doing something to help cooling. just cutting into the firewall without welding a dedicated duct that has been sealed with seam welds (for structural and sealing purposes both), is not recommended.

 

1) First, you are undermining the job of your firewall, which is to keep an engine fire from cascading into the interior of the car. You have a large open vent from your cowl into your cab at your heater/AC blower ducting.

2) the engine fumes and hot air from the engine bay will work their way into your car because of the same reasons as #1 above. 

3) the firewall/cowl interface acts as a structural "cell" within your larger unibody. Unless you are just cutting a small 3" hole or something similar, a large rectangular cur will undermine the structural stiffness of your firewall at this location. 

 

Coolant is your friend. Air is much less effective at cooling an engine unless it has been engineered to do so (ask Porsche). If you are worried about engine overheating, it can be easily addressed through improvements and overhauling your cooling system. Flush your engine cooling system to get rid of any rust and scale creating restrictions. Consider a larger radiator. Consider either a clutched engine fan, or a dedicated large electric fan. A shroud between the radiator and the engine fan will improve cooling considerably.

 

In general, the Z cooling system is over-sized (design) if everything is working correctly. It is not a car that habitually overheats without something being wrong. If everything is working right, just adding an aftermarket shroud between your radiator and the clutched engine fan will improve cooling at idle by a noticeable amount. 

 

 

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Good advice from @AydinZ71.  I would add one additional thing to consider....if your primary concern is during stop & go traffic, consider popping the hood release and letting the hood ride open a couple inches while relying on the safety catch.  (This assumes that you have a properly-functioning hood safety catch.). Used to do this all the time when I had to drive in a heavily-congested area.  It allows a lot of underhood heat to escape, and doesn’t have the high pressure buildup at windshield base as there is at speed.

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1 hour ago, jhm said:

Good advice from @AydinZ71.  I would add one additional thing to consider....if your primary concern is during stop & go traffic, consider popping the hood release and letting the hood ride open a couple inches while relying on the safety catch.  (This assumes that you have a properly-functioning hood safety catch.). Used to do this all the time when I had to drive in a heavily-congested area.  It allows a lot of underhood heat to escape, and doesn’t have the high pressure buildup at windshield base as there is at speed.

oh yeah, I totally used to do that too... In my case, I literally drove with no fan for years (I was young/dumb) and just left the hood on the catch while in traffic. As soon as the car starts moving, the needle drops. One of the few benefits of our reverse-opening hoods.

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Thanks all for the responses.

I probably should have prefaced this with what I have done to the cooling system. It has an aluminum 2 row radiator from Mishi, two electric pull fans that are thermostatic controlled to kick on at 175° I do have water wetter in it as well. The heater is removed so the heater outlet just circulates back to the head.

So I don't use an OE good latch anymore. I use locking quicklatches for my hood so sadly I can't just crack my hood open. I like how AydinZ71 cut the firewall but I'm hoping to not go that extensive. I was thinking of mounting a pull fan on the inside of the cowl which would pull the heat up in and out the cowl vents. 

 

I live in LA so the traffic is bad and I'd like to drive the car more without worrying about burning down in traffic.

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I live in LA too. The heat this week has been brutal anywhere 10-miles from the coast. I'm really surprised you are having cooling issues with all that hardware! Have you considered the 280-Z style hood vents? You could try the fan you mentioned, but just remember it will be reallllly difficult to get decent flow on a 12v small diameter fan. Any amount will help, but it may fall-short of expectations. Thats why everything 12v is super-sized (like the starter, alternator). Just isn't enough electrical potential. 

 

I also use quik-latches for my FRP hood. 

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Sounds like you have a decent cooling system in place.  I live in the steamy South and run about the same setup on my 3 liter. Have you checked your temp gauge?   Just how hot is it really getting?  Are you pushing coolant out the over flow?  Also, you may have have a bad/worn out water pump. 

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2 hours ago, Mayolives said:

Sounds like you have a decent cooling system in place.  I live in the steamy South and run about the same setup on my 3 liter. Have you checked your temp gauge?   Just how hot is it really getting?  Are you pushing coolant out the over flow?  Also, you may have have a bad/worn out water pump. 

 

In my experience, I have never had the pump fail to spin/push coolant (if the pulley spins) but the bearing DOES wear-out, seize, or leak. Have you seen a case where the pulley spins but the impeller does not? Just curious for my own edification. I'm sure anything is possible under the sun. 

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  • 3 months later...

The Z really only needs a properly ducted 4x28” slit across the front to cool it. Keeping excess air getting in helps stability and aerodynamics.

 

cutting three inch holes under the battery and brake master cylinder has been proven to be extremely effective venting position (low pressure area opposed to high pressure area at cowl)

 

people put thermostatic controlled fans on the exhaust side to force flow through / out in stop and go traffic.

 

no need to go through the upper firewall except to duct inlet air to your intake…

 

you would be surprised what kind of static pressure exists there even at highway speeds…

 

especially compared to behind the wheels in the left and right fender area!

 

vent high pressure to low, and you use/require less open area to accomplish the same exhaust flow…

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