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Speaking of electrical draw on the Corvette, I'd like to know what alternator you're running? Here's an excerpt from an excellent article on Hot Rod Magazine.
Worth a careful read for sure, because electric fans are a big draw and if you don't already have a heavy duty alternator to supply the juice, your fans may not be getting all the power they need to work at their best.
What most car crafters rarely consider is that the early '60s and '70s vintage alternators rated at 60 to 70 amps were not designed to crank out maximum amperage at idle. Late-model alternators or high-performance alternators rewired by companies such as Powermaster are designed to generate greater amperage at idle. These more efficient alternators are capable of delivering the 40 amps or more required of dual fans running at full boogie along with a big electric fuel pump, lights, and maybe a thumpin' stereo. Add the draw from a pair of headlights and perhaps a defroster or A/C fan, and a load of 50 to 60 amps from the alternator at idle is not unusual. This will also require large 8- or 10-gauge wiring from the alternator to the underhood power source for your fans and multiple solid-ground circuits between the engine and the chassis. A good ground also means the ground wires should be of equal size as the power leads. The biggest electric fan won't run at anywhere near peak efficiency if the ground circuit suffers from resistance. A simple voltage drop test will tell you if the wiring circuit is the culprit.
Yes to both questions, the 78 also has the foam block between radiator and hood.
I have a 78 L82 and am running an open air filter, removing the funky plastic duct over the radiator. That may explain why the temp starting to go up during slow traffic.
Feflicker, here's another angle too. Do you have an idea of how your dual fans are wired up? There are a couple of different ways to do it (in fact a few, if you consider the mounting options for the temp sensor). I've installed three systems so far, including a built up 383 '74 custom pick up and of course, my '74. I did the complete install, including the sensors, fans, wiring, relays and radiator on all of them.
Let's talk temp sensors first. They come in different flavors. Some of them come on at 160 degrees, some at 180 and there are even temp sensors that come on at 200 degrees. You should also have an idea of what sensor or sensors were installed and more importantly, where they're mounted. You can mount them on the intake manifold, the water pump, the cylinder head itself and even the side of the block on the driver's side and that makes a difference too, because those different areas heat up at different rates.
There are different options on how to wire the dual fan set up too. Some people advocate running the first fan off've the temp sensor at 180 degrees and then running the second fan to kick on, when the A/C goes on. Personally, I run two sensors instead, so even with the A/C off on a brutally hot day, the second fan will kick on, regardless of what the A/C is doing. The first one is set up to kick on at 160 degrees and the second sensor is a 200 degree sensor. So when the temp hits 160, the first sensor will put a ground to the relay, energizing it and putting power to the first fan and when the second temp hits 200, the same thing occurs and now you have both fans running until the temp stabilizes (the second temp sensor goes quiet at 185 degrees). Of course, you should have adequate voltage and current to each fan, so they operate at their maximum efficiency, anything less and they won't have the power to operate as they should.
"American Volt" 160'F Grounding Thermostat Fan Switch 3/8" Inch Thread Probe
The fans were wired direct to the back of the starter. The shop told me this spot was a direct throw to the battery and was the best place to wire it. I've heard of people going direct to the alternator, but also read that isn't a good idea either.
I upgraded to a 100amp powermaster 12si alternator prior to installing the fans. There was a 63amp one in previous. I'm not getting dim lights or anything at night, and the car isn't having trouble starting after a night drive with the radio on, so I figured there was enough juice to run the fans.
The SPAL fans put out 2780cfm per dewitts website. The fans are doing great in stop/go traffic, they'll get the car under 200 even if its 105* out. My normal operating temp is about 190* with the a/c on in stop and go. It's only on the freeway at 60+mph, over 100*, and going uphill that I crawl over 200 and start ramping up to 220 (was 240 before the air dam extension).
The SPAL fans come on at 195, off at 175. This is confirmed by the aftermarket water temp gauge I installed. Right on cue they cycle. My sensor probe is installed next to the thermostat for the gauge. For the fans they are in the head, I'm seeing only a few degrees difference between the head reading for the SPAL's and the intake where the gauge probe is.
My fans are BOTH wired to come on at 195, BOTH go off at 175. And are BOTH ALWAYS on when the A/C is on.
My hood does have little vents at the top of it by the windshield, not sure if that is stock or not. But air does appear to come out and go over the windshield (I don't see anything that could block it).
I like the idea for the air/fuel gauge. I already punched a hole for the new water gauge so I could go through the silicon for another gauge easily... I might get it to a shop and have them "confirm" my air/fuel and timing advance just for sanity sake as well...
Getting late! We'll talk tomorrow... Drove the '74 all over today and then put her up with her sister in the shop. The '74 is getting aligned tomorrow and afterwards, I'll take pics of my A/F install as well.
I'm giving this a lot of thinking here, so allow me to quote your experiences so far and I'll put down what I think might help out.
"My normal operating temp is about 190* with the a/c on in stop and go. It's only on the freeway at 60+mph, over 100*, and going uphill that I crawl over 200 and start ramping up to 220 (was 240 before the air dam extension)."
Note that it's only when the engine is under load that it's overheating. There are two possibilities that I thought of. First, is the fuel pressure, because lack of fuel pressure under load (under 5-6 PSI) can cause the engine to run lean. This could be caused by a clogged in-line fuel filter. Often, there are two fuel filters: the big can style, that for example, I have installed by the gas tank and the smaller one between the fuel pump on the engine block and the carb itself. If either one is clogged, that will reduce the fuel available, when the engine needs it most and cause it to run lean.
The second possibility is the fuel pressure regulator itself. Many people run the cheap-ee Holley unit that runs for $29. I've personally seen three of these fail (including mine) and I now run a far more expensive (but trouble free) Aeromotive unit like this one for $99:
I also purchased the Aeromotive Fuel Pressure Gauge as well, because I wanted not only a nice looking, liquid cooled gauge, but an accurate one as well $29.
The third possibility is the jetting of your carb under load. This is going to be hard to ascertain with the car sitting in the shop on an exhaust gas tester, versus going up the hill at 60 mph+, with the AC on and pulling hard. That's why I'm glad you're getting the Air/Fuel Ratio gauge and I think everyone, with a vintage carb setup like we have, should have one.
The last and most difficult aspect of this, may be the aerodynamics of the C3 itself. We discussed this extensively in the 'Interior Heat' thread and it is a tough problem, because basically, you have a Chevy SB or BB, sitting in a sealed box, with only the underside exposed to any kind of airflow at speed.
True, the radiator is the front of the box, but that's not exactly conducive to free flow out of the box either. With your 76, I suspect the vents at the back of the hood, only vent the wiper area and not the engine. In fact, there's a rubber seal all the way around! And it's a pretty small box too, not like a Nova, Impala, Chevelle, etc.
When I get my '74 back this afternoon, I will take pictures of my A/F Ratio Install and how I routed the wiring and mounted the A/F gauge itself.
One more thing, came to mind. I have my first fan, kicking on at 180 degrees. That's 15 degrees earlier, than what you have your fans kicking on at. Just my opinion, but at 195, your fans might be playing 'catchup', especially when your engine is already under load. I'm running the BMW dual sensor setup, but in the other installs, I've been installing the 160 degree sensor, because I'd rather have it kick in early then late.
PS: I like the BMW dual sensor setup, as it has BOTH Low and High temp sensors in a single unit, but the biggest pain, is trying to find a metric to standard fitting and it was a unicorn chase! It was only available from ONE machine shop in West Virginia and they cost $27 each.
I don't even know if there is a fuel pressure regulator anywhere on the car, will have to look for it. I know we did a new fuel pump and also pressure tested the lines when we replaced the rubber lines by the fuel tank. Being a new motor, the fuel filter is also new, it is the little metal can style and it's right by the carb.
Maybe I'll get a diff temp sender to get the fans to kick on earlier, but this time of year the A/C is turned on right away anyway so the fans are always on.
I think I'm going to need somewhere new to mount gauges if I'm going to try and find all the gauges you have
I don't even know if there is a fuel pressure regulator anywhere on the car, will have to look for it. I know we did a new fuel pump and also pressure tested the lines when we replaced the rubber lines by the fuel tank. Being a new motor, the fuel filter is also new, it is the little metal can style and it's right by the carb.
Maybe I'll get a diff temp sender to get the fans to kick on earlier, but this time of year the A/C is turned on right away anyway so the fans are always on.
I think I'm going to need somewhere new to mount gauges if I'm going to try and find all the gauges you have
The fuel pressure gauge mounts in the engine compartment, so no problem there, I'll provide pics or my setup. The A/F gauge easily mounts on my steering column, with a large hose clamp. You can get the hose clamp in black, so that it looks a little bit better. I have a tilt telescoping column, so that was not a hindrance either, though it was a tight fit. I will update with pics later this afternoon, probably 5 PM, PST.
Here is my AEM A/F ratio setup. First, there are others on the market, but to the best of my knowledge, only the AEM doesn't need recalibration and it uses a Bosch 02 Sensor for real accuracy.
Steering Column mount. It doesn't really get in the way of anything and it looks good and is readily readable, right there in front of your nose.
Engine off, ACC on, but it still gives you a reading of the of the exhaust gases that are still inside! Note the yellow arrow on the sweep gauge. It goes from Green (Rich) to Red (Lean), with yellow in between. Helpful, because you'd be surprised at how much it bounces within a certain range. And that's because the carb is not as accurate as an EFI system and runs independent (for the most part, late C3's got computer controlled carbs, starting in 1978).
02 Sensor Mounting and heat shields.
Route the wire harness straight back to the firewall and secure it to the other wires running along the back and then up and into the fender wire harness on the drivers side. AEM gives you a ten foot loop! This is because it's universal.
Take the excess wire and put it to the side after you route it to the 02 Sensor. After it's connected and secured to the firewall from the 02 Sensor, take the extra slack and create a tight loop. Zip Tie it with a few zip ties to make it secure and then stash it on the top of the fender, basically hiding it.
BTW, if you're running a GM Serpentine Belt Drive ('87 to '91 Caprice), it bolts right up, beautiful castings, BUT you must run a Reverse Flow water pump! Not sure if you even have one, but if you do, make sure you get the correct pump. What direction it runs, depends on the belt routing. Note the front of the Intake, and you can see the BMW dual temp sensor, with the 2 yellow wires and the Ground.
Caveat: Here are the hood vents I designed and had installed. I used 3M body adhesive tape and believe me, you can't pry it off. Not everyone's cup of tea, but this is an old street racer with a lot of patina. Sure lets out a lot of heat when it's standing still!
Hood open and you can see how much open area there are in the vents. Every little bit helps and personally, I like how they look.
05-15-2016, 09:35 PM
