C3-Over the winter I purchased a 1974 Corvette Convertible. Thought it had a really good heater, car was nice and warm. Now in the dead of summer, the car is Extremely hot. With the windows and top down, the heat gets sucked into the car, comes in through the vents at my feet, runs up my legs and slaps me in the face on the way out the back. The center console gets hot to the touch. The automatic shifter gets very hot and even the car keys feel as if they could burn you. The car get so hot that after you cut it off and get back in about 15-20 minutes later it won't start, as if the ignition switch is disconnected. Totally dead. Once it has cooled back down, starts right up, no problem. Everyone has told me that corvettes are just hot running cars, but this heat, to me, seems very excessive. The vents for heat and AC open and close as they should. I have even tried bypassing the heater coil. Any suggestions on where to begin on solving this problem? Thanks
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Re: 1974 engine heat
The car runs hot because the ignition map is set up for emission control to keep the EGT at over 1000 degrees F all the time, including idle. You can mitigate this by remapping the ignition to the antecedent non-emission controlled engine from the mid sixties including converting to full time vacuum advance, installing a suitable VAC, and reworking the centrifugal as required.
If all the various seals in the HVAC system are original, they are likely deteriorated and leaking.
Install a manual shut off valve in the heater core inlet hose, and keep it closed except when you actually need heat.
Duke -
Re: 1974 engine heat
Thanks Duke. I will try out your suggestions. I have never heard of an ignition map (I'm not much of a mechanic), but I know people woh know people and can figure it out. I am prety sure all the HVAC seals and equipment are original too and will check them out. Thanks again, LouComment
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Re: 1974 engine heat
There are two primary variables that determine the optimum spark timing for a given set of the virtually infinite number of engine operating conditions - manifold vacuum and engine revs.
This is why vintage engines have what's called "centrifugal advance" and "vacuum advance". If you plot the spark advance requirement against these two variables on a X-Y-Z plot you get a surface. Thus the term "map".
Modern engines use the same basic parameters, but also use engine air inlet temperature and coolant temperature to select from various maps in order to ward off detonation, shorten warmup time, and optimize fuel economy, all while meeting emission standards.
In my experience, VERY, VERY, VERY few people including most "mechanics" understand the ignition map requirement for the entire operating range from idle through the myriad part load and cruise conditions and on to WOT.
Good luck.
DukeComment
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Re: 1974 engine heat
Duke-----
Not on a 1974. The emission systems on 1974's are very problematic. If one tries to change ANY of the specs or components, one will often find that it "screws everything up". With everything set right at factory spec and with the emissions system as originally installed, one can often just barely achieve driveability. Change anything and it usually ends up with a LOSS of driveability.In Appreciation of John HinckleyComment
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Re: 1974 engine heat
On a '74 it will also probably require some carb recalibration, including the choke system. The problem is finding anyone who understands these issues and knows how to properly recalibrate both the ignition map and carburetor.
Of course, all of the above will likely increase emissions, so if the car still requires emission testing, the best bet is to have everything to OE spec and just live with the heat, poor driveability, poor performance, and poor fuel economy.
Ignition maps on 1975 and later models are not so retarded and fuel calibration is not so lean because the catalyst aftertreatment allowed higher engine out emissions, which allowed fuel and ignition maps to be recalibrated for better driveability and fuel economy, but any power improvement was more than absorbed by the substantial exhaust backpressure increase that the single catalytic converter added, which is why 1975 was the horsepower nadir.
DukeComment
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Re: 1974 engine heat
Hi Lou, what engine and transmission combo do you have, and does the motor still have the stock A-I-R system, or has it been tampered with.
Ken.Comment
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Re: 1974 engine heat
Ken, the car has a 350, L-48 engine with a TH400 Automatic transmission. i think the previous owner liked to tinker with things, so I don't know everything he had adjusted, replaced, or taken off and put back on. I'm not much of a mechanic, know just enough to be dangerous, kinda like the previous owner. But I get help from well qualified mechanic friends or just have them do what needs to be done. I have'nt had to do much to the car since I got it. Bascally, it just needed a new radiator and tires. Other than that it runs really well. I have enjoyed driving the car for the past 8 months and hope to drive it for the next 20 years, or as long as i can get in and out of it, whichever comes later. But the excessive heat has got to go. 100 degree summer temps are hot enough. Thanks for any ideas you may have, LouComment
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Re: 1974 engine heat
Hey Lou,
So it's a standard engine, and I've seen this before. Someone wants to get the motor to perform really well, so what do they do?, they advance the timing so far to get maximum vaccum and quick response. But at the same time the engine gets very hot, and quickly, and can lead to other problems. I've seen exhaust, and headers get red hot in no time, and I mean RED hot. Also the carburator being set way too lean can also cause this, but I doubt that the later was done.
Ken.Comment
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