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New 8/4/05. 8/06/05
We've got a mini hot streak here with the temps getting into the upper 80's and lower 90's so I've been investigating under hood temps and the old resistor on the IAT mod in reverse.
First I fastened my IAT sender to the PCV hose on the front valve cover. This was to see if the timing is significantly affected by extreme high temps. Today driving home I saw 165F under the runners and at the IAT with the timing at one time down to 6 degrees advanced from the usual high twenties (not at WOT either). So half way home I put the IAT back in and the timing came back to the lower and mid twenties. It was still over 165F under the intake as measured by a remote t-couple and 100F for the IAT.
So I popped the hood to the safety latch to scoop in some more air. The temp within a mile was less that 10F over ambient under the runners and the IAT temp dropped to within 3F of ambient. Outside temp was 88F by way of the climate control readout. IAT was read through AutoTap and the remote t-couple was to a digital thermometer.
Need one of the hoods like the '72 GTOs had. Something like this but the opening wider and not as high and defined.
Tonight I took out the bottom part of the cowl on the drivers side (something I wanted to do at Putman and forgot). I put the grill part back and will do some more data gathering tomorrow.
Paul
Today we had the same weather conditions a bit more headwind but still upper 80Fs lower 90Fs depending on terrain.
I took off the lower passenger side cowl, the part that is inside the engine compartment. The area under the runners was 160F+ yesterday. Today with just that part removed the temps were 125F or so. A nice drop of 30F+ degrees. So I took off the upper part too and left it wide open on the passenger side. Under 60 mph the temps rose about 10F to 135F or so. At speed over 70 mph the temps went back down to ~120F, interesting.
Tonight I took off the drivers side cowl bottom but have put both cowl top parts back on. PITA because of the windshield wiper motor. I'll see what this does if the ambient temps hold out and are similar to what I've had the last two days.
I also felt the runners when I got home. The surge tank and upper runners attached to it were ambient temp or so but the lower runners attached to the IRM were too hot to touch. As was the TB even though there is no water going through it. The 90 that the TB is bolted to is bolted directly to the front lower runner, this and the support straps conduct heat directly into the TB and into the surge tank. Took the straps off and removed the two studs that hold the 90 to the front lower runner. Then inserted an 1/8" thick piece of rubber sheeting under the it to keep the 90 from making contact with the front lower runner . I have already insulated the rear and bottom of the surge tank.
Paul
Hey Paul, if you can make it out to Lapeer in the fall we should get an infrared thermometer (or do you call them thermofeet down there?) and check the temps of various cars. I know last year my intake was hot when I compared it to Larry's. I think that the coating might be great for the summer but will hurt me in the fall and spring.
Ian
I don't run the EGR either. if you have the EGR hooked up, then all the intake cooling attempts are hopeless.
Paul
What about something like the plenum spacers? (I don't remember what they are called.) I've seen them for my little truck, don't remember what they were made from, they were about 1/2" thick, looked like plastic, went between the lower intake and motor, insulated the intake from the engine heat. Has anyone tried something like this?
k mier
Making some phenolic spacers for the lower intake or even the lower runners would cause clearance and fitting issues to most SHO motors. The EGR tube, DPFE hoses and support straps would all have to be finessed.
On the other hand if you didn't have any of that stuff....
Paul
Questions:
1. Would the Gen III cowl hood provide more air circulation?
2. Would removing the little rubber strip between the bumper cover and hood be worth the effort, or would things hit each other?
3. What about getting after-market turn signals and putting them below, while removing the the OEM turn signals. Would that provide more air circulation?
Michael Hurd
1. Yes, the cowl hood would definitely benefit TREMENDOUSLY in alleviating underhood temps.
2. Don't know.
3. You'd need to actually duct the air so it circumvents the radiator. Otherwise, you are still pre-heating it w/ the rad. before it gets to the engine compartment.
I like the idea of running some air ducting to get fresh air from the air dam or fenders up into the engine compartment. As it stands now, all air pretty much has to come through the radiator or up around the exhaust manifolds before it can get to the top of the engine.
I thought about cutting two 3" holes in the lower cowl and ducting some of the air from there down to the surge tank area. The upper cowl cover should baffle rainwater pretty well while allowing air in.
Dan Carman
What I saw today is if too much opening is there then the exhaust heat tends to get pull up and out while cruising and actually adding heat to the area under the runners.
Today I took both lower cowlings out and had both tops on. This actually raised the temp about 15-20F over what I had the other day with just the passenger side lower cowling removed.
So I put the passenger side one back in because it is easier and will leave the drives side out for now. I also put in some insulation at the end in the middle of the passenger side lower cowl to keep the engine air from entering the cowl.
For the record....
~88F average ambient temp
~5-10 mph head wind
50-60 vehicle speed
A/C on
Rear rubber gasket removed from hood
140F under the runners in the middle.
Passenger side lower cowl removed ~120F-125F
Passenger side lower and top cowl removed ~135F-145F
Passenger and drivers side lower cowl removed, both top pieces on. ~135F to 145F
The cowl area at the base of the windshield is actually a high pressure area when moving but I was surprised to see the temps higher with more area removed to provide better air flow.
Paul
8/06/05
Correction = *******
For the record....
~88F average ambient temp
~5-10 mph head wind
50-60 vehicle speed
A/C on
Rear rubber gasket removed from hood
*******160F-175F under the runners in the middle.*******
Passenger side lower cowl removed ~120F-125F
Passenger side lower and top cowl removed ~135F-145F
Passenger and drivers side lower cowl removed, both top pieces on. ~135F to 145F
Paul N