Re: Under hood temperature while moving
[Re: DGS]
#2512891
06/25/18 07:36 AM
06/25/18 07:36 AM
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Joined: Jan 2003
Posts: 3,575 The Netherlands
BigBlockMopar
master
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master
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Posts: 3,575
The Netherlands
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Cold air intake and underhood airtemp are actually to be seen a bit as different things. You don't change underhood temps by installing a cold air system. Your engine (performance) wants cool air as its more dense and this is what can make more power. During driving, underhood temps will usually drop or stay low, but it's only the 'air' that is being replaced with cooler air. When underhood parts have heated up, they don't cool down as quick. This is when underhood airflow control comes into play. The trick is to properly 'vent' hot air from the engine bay, and not try to cram in more outside air. This is why the front of older cars start to lift and steering gets scary light when driving at high speeds. Air is just 'stacking up' in the engine bay and can't flow out quick enough. The car is almost riding on a cushion of air between the front wheels. If you look at modernday cars, most all of them have heatshields around the exhaustmanifolds. Just look at the 3rd gen 6.xL Hemi's, which have 'shorty' headertubes, enclosed in a sheetmetal covering to retain heat inside. Part of this is maybe for emissions as well as hotter exhaust going into the cat makes it more efficient. Another thing that's very helpful (and just about every car has these days) is some sort of front airdam. This creates a low pressure area behind it which helps 'sucking' out hot air from the engine bay (and lessen air turbulence under the car). I've created a cold air intake on my daily '73 Dart, as well as an front airdam and my engine temps are pretty always about 10-20°F below the thermostat's temp rating. Only when I'm driving/sitting in traffic is when the engine temps gets around or little over the thermostat temp. My cold air entry is just next to the radiator facing forward to the grille. Another thing I noticed with the cold air intake, is the engine doesn't tend to feel 'a bit lazy' anymore after everything is warmed up.
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Re: Under hood temperature while moving
[Re: DGS]
#2512893
06/25/18 07:55 AM
06/25/18 07:55 AM
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Joined: Jul 2005
Posts: 636 Graz, Austria
DGS
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mopar
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OP
mopar
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Posts: 636
Graz, Austria
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Thanks for the reply! Maybe I wasn't clear enough in my first post. I'm strictly talking the intake air temperature. I was comparing a cold air intake (e.g. drawing air from the front or base of the windshield) vs. drawing air from the engine compartment. Obviously the temperature difference decreases with driving speed as the heated air is replaced faster (if the engine compartment is properly vented). Let's say you are driving @60mph - what's the temperature difference between engine bay and outside air? Actually it all boils down to the pressure difference (colder air being denser) - so drawing cold air from a high pressure zone would be the best but is worth the hassle to make all the ducting etc.? I might buy a differential pressure gauge and do some investigating..
Last edited by DGS; 06/25/18 07:56 AM.
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Re: Under hood temperature while moving
[Re: DGS]
#2512907
06/25/18 08:50 AM
06/25/18 08:50 AM
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Joined: Jan 2003
Posts: 3,575 The Netherlands
BigBlockMopar
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The Netherlands
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Hot intake air, when idling (for a trafficlight) is bad too, because when the light turns green you want to have 'performance' again. It doesn't help if your engine then "pings its brains out" because everything is hot and heatsoaked again... I've been thinking about insulating the cold air ducting to the engine, as enginebay heat also warms up the tubing. A double wall tubing should help in keeping the incoming air cooler longer I would think. Also applying a heatreflecting layer on the tubing should be helpful I guess.
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Re: Under hood temperature while moving
[Re: DGS]
#2513109
06/25/18 05:32 PM
06/25/18 05:32 PM
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Joined: Nov 2006
Posts: 2,255 IL
furious70
top fuel
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top fuel
Joined: Nov 2006
Posts: 2,255
IL
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how much of an air dam is needed to create the low psi zone? Wondering if my turbo tubing that hangs below the rad support on my Fury might be giving me some of that benefit?
70 Sport Fury 68 Charger 69 Coronet 72 RR
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Re: Under hood temperature while moving
[Re: DGS]
#2513151
06/25/18 06:48 PM
06/25/18 06:48 PM
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Joined: Nov 2006
Posts: 2,255 IL
furious70
top fuel
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top fuel
Joined: Nov 2006
Posts: 2,255
IL
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makes sense, I wasn't sure if the resistance of having to go over the pipe would be enough to create any pocket.
70 Sport Fury 68 Charger 69 Coronet 72 RR
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Re: Under hood temperature while moving
[Re: DGS]
#2513437
06/26/18 12:43 PM
06/26/18 12:43 PM
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Joined: Dec 2003
Posts: 22,696 Bitopia
jcc
If you can't dazzle em with diamonds..
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If you can't dazzle em with diamonds..
Joined: Dec 2003
Posts: 22,696
Bitopia
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Good to know! That confirms my suspicion that cold air intakes don't make any difference in the air temperature the engine sees at highway speeds. I disagree with your conclusion. My thinking, cold air does make a difference, even though it may vary, and the pressure differential advantage at our highway legal speeds would likely be negligible, if even measurable.
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: Under hood temperature while moving
[Re: DGS]
#2513456
06/26/18 01:10 PM
06/26/18 01:10 PM
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Joined: Aug 2011
Posts: 2,859 Pattison Texas
CSK
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master
Joined: Aug 2011
Posts: 2,859
Pattison Texas
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My car is a different car with cold air intake,sitting in traffic or running down the freeway runs better, had to retune the carb.
1968 Charger COLD A/C Hilborn EFI 512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim 2020 T/A 392 Stock 11.79 @ 114.5
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Re: Under hood temperature while moving
[Re: DGS]
#2513622
06/26/18 07:03 PM
06/26/18 07:03 PM
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Joined: Jan 2003
Posts: 3,575 The Netherlands
BigBlockMopar
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The Netherlands
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Here's a screenshot from MegalogViewer of my car running a short trip on the highway. (Right-click the image to show its larger/original size).It's showing engine RPM (White trace) and MAP (=Engine load or 'reversed vacuum') as the Red trace in the top row. The lower part shows Engine Coolant temp in Green and Intake air temp in Yellow. The car had been driven before this day, but you can see the engine temp rising from the start, while the intake air temp rising very slowly until after the highway part (center section) and the car encounters slower stop&go traffic.
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Re: Under hood temperature while moving
[Re: DGS]
#2514693
06/28/18 11:19 PM
06/28/18 11:19 PM
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Joined: Jul 2006
Posts: 4,319 Puyallup, WA
StealthWedge67
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Puyallup, WA
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General rule of thumb: Heat issues in slow traffic = airflow issues Heat issues at highway speeds = coolant flow issues.
LemonWedge - Street heavy / Strip ready - 11.07 @ 120
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Re: Under hood temperature while moving
[Re: DGS]
#2516636
07/02/18 10:59 PM
07/02/18 10:59 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
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New York
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Chrysler (and the others) got it right 50 years ago. The air cleaner snout has a diaphragm (vacuum-operated) flap with 2 positions: 1. is open to a duct leading to the radiator support, and allows ambient only. 2. is below the snout, selected by the flap closing, and admits pre-heated air passing over/through a shroud over the driver's side exhaust manifold. 3. what temperature the can's interior sees is determined by a thermal vacuum switch inside the can. When the engine and underhood temperature is low (cold day, cold start) it admits only pre-heated air until the can interior temperature is 150 degrees (?). Above this, it blends cold air to keep the temperature nearly constant for best mileage and accurate mixture. 4. in addition, low engine vacuum (WOT) opens the flap and admits only cold air for max power regardless of can temperature.
Other than a larger snout, this idea still works perfectly with very few components.
Boffin Emeritus
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Re: Under hood temperature while moving
[Re: kwikblownhemi]
#2516642
07/02/18 11:06 PM
07/02/18 11:06 PM
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Joined: Jan 2007
Posts: 7,664 IN
ahy
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IN
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I am running MS controlled MPEFI on a 480ci Hemi '69 B-body. Edelbrock intake with 2x1000 cfm throttle bodies, with the IAT sensor originally in the air cleaner base between the throttle bodies.
I had the Ramcharger ductwork off the hood for a while. The IAT ran 60 degrees or so above ambient.
With the ductwork on and a good seal to the air cleaner, on the road IAT went to about 10 degrees above ambient.
Air temps 11 degrees cooler offer a potential HP gain of about 1% -assuming the mixture is corrected for the temp change.
As a sidenote, getting meaningful IAT is not easy. I dealt with sensor heatsoak issues on hot restarts. Moving the IAT sensor into the ductwork and modifying the sensor transfer function table cleared it up. My experience is roughly the same... ambient + 50-60 degrees F in summer with open element air cleaner and EFI measuring intake temps. Colder denser intake air helps power.
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