I have been watching the old TV show Highway Patrol in the mornings lately due to alot of down time. Something I have wanted to chat about for a while about hot days and Nailheads. I bought my 66 GS with 80,000 miles on it. I'm in MA and as my car wasn't a show queen and I got to drive it daily in all the seasons. Compression on all the cylinders was maby 12 psi down except for one that was 20 to 30 psi down when the motor was cold or at least not started in 5 or 6 hours. Motor ran very good though, but I remember taking one highway road on several occasions and one day it was really close to 95 - 100 degrees out. I could not get the car faster than 80 mph and it was pretty hard getting to that speed. One cold winter day on the same road I buried the speedo with 4 people in the car.. "yes very stupid and I still cringe 30+ years later. I just have not felt the same weather sensitivity on my 455 cars or even any other cars iv'e owned. I can say the same for 2 other lower mileage GS 401's that I was a passenger in on a hot day that didn't run to strong either and one also being a 4 speed. Back to the TV show Highway Patrol I keep thinking since its based in CA how can the 55 Buick with the 322 keep up on a pursuit on a hot day? Did the the smaller 322 that was the original design not have the same issues in the heat because the smaller 322 was more tailored to the heads limited flow. I see some great times in the 1/4 mile here with 66 GS 401's and swapped in 425's but seeing alot of you have true beauty's that don't see winter i'm wondering just how much better you can run during the winters cold?
i know what your saying but i don't think a nail head gain or loss of power with cold or hot weather is any different then any other engine
Maybe your vehicle had a specific problem with heat, or with the specific day you drove it --vapor lock, detonation, low float level, weak spark, old fuel, plugged air filter, stuck heat riser valve, etc.
c reason I would truly like to think on that one day there was a specific issue, but like I had mentioned I drove this car year round for 8+ years and it was always the same. Even if it cooled down to 70 degree night from a 95 degree day it made a huge difference. This is sad, back in the early 80's when the start of BMW's 3 something series's were getting popular and the Ford Capri's for a while I could barely beat them when again it was really hot, but I would put my 66 GS from a 20 to 30 mph rolling start equal with a stock non ram air 389 or 400 GTO for a 1000 ft. on a good weather day. I had a ride in 2 other 401 GS's back then and the same thing and these where very low mileage motors, they were maby peppy but not fast and I also read a post on another forum that I cannot seem to find about one man mentioning weather sensitivity.. My motor ran great and other than doing a couple wide open throttle runs to clean out the oil from the worn valve seals from time to time you would never think it had reached almost 120,000 miles. Schurkey as far as plugs, wires, fuel filters and fuel all were always changed frequently with good spark and all AC Delco parts. .. Never had a issue of not starting due to vapor lock and the car had full exhaust and I could hear detonation for the "most" part when I would use lower grade octane. A couple things that i'm not sure or don't remember is where the fuel filter was located and if the heat riser valve was working proper but by going what I saw from the exhaust pipes i'm pretty sure it was open. I changed over to a 180* thermostat and never noticed a difference. Only till the day I sold it 10 years later I found out I had been running all that time a Carter AFB 500 instead of a 625. Still though I don't understand why the smaller carb would hurt the low end on a hot day. My air cleaner was the typical aftermarket chrome one but the plastic spacer under the cleaner I used didn't seal on the carb, it kinda just sat on the side bowls off the carb and there was a 3/8 in gap between. I don't think it was a issue with causing extra heat on the carb?? It always felt like it had a asthma in the heat unlike my 455's.. Please not at all to insult members who have beautiful examples of stock or modded but wondering if they are in storage and never have run in favorable weather cold winters day..
My 401 is sensitive to the weather, but only in the range of 2-3 tenths either way. Real hot weather (85+) will slow it down pretty well, but that also happens with my 455's. Real cold weather (40 or lower) makes it run well, but I havent broken any records at that temp, and I have raced it quite a bit when it was so cold I spent the entire time in the car with the heater on..
Hi, I haven't noticed alot of differences during spring and summer months, but in late fall it does seem to come alive a bit more, much easier to bark them in second and every once in a while third. (4 speed) I can say after a full day of driving on a hot day late July early August, both me and the car feel tired but no AC is my excuse and could just be my perception at the time. Regards, Jim
So wish to have a time machine right now, more for nailhead the heat issue than finding the lotterys winning numbers. Seriously though I can't think the one cylinder that was down 20 or 30 pounds would make a difference and I was running those generic mufflers that the early store that became Auto Zone later on. Just reaching for straws here but remember by just adding new tail pipes I went from spinning these sticky recaps for 20 ft. to maby 5 ft. That just showed just how strained the nailheads exhaust was when hot out but.... the ground also got hotter and stickier also.. Never tried ice under the intake nor the heat blocker intake gasket.
Exhaust restriction could account for hot weather performance drop off. If the systems are all tuned properly (carb/engine/ignition), on a hot day more air needs to flow through to get the same amount of fuel vapor. If the exhaust isn't allowing that flow, you would see poor performance. Just a thought, but that could explain it.
I have been dwelling on the hot air less dense gas issue you mentioned but why so much on the low end. I can see it starving for fuel as the rpm's go up but on the start the carb has to be full of gas in the bowls. This weather sensative issue also made it hard to tune somewhat. At which temp and point do you start to tune? I played a bit with the timing and swaped and changed advance springs a weights back and forth and also had a AFB carb kit with jets and needles but which like I said found out later the carb was a 500 cfm but jetted it at times with the 625 specs. I ended up always going back to the original setup. I was 99.99% sure the guy I bought it from never played with the distributor.. Tried a Q-jet and manifold that I had but that carb needed a rebuilt and saw no difference. The 425 I bought from a 66 Riv had the MOST!!! carbon buildup I have ever seen in a motor when I took it apart. Just a note, the car had a 3:23 posi out back from a 66 GTO. I only mention the GTO because I know in 66 the GS wasn't available with 3:23's and didn't want any confusion..
It's not a question of the fuel in the bowl, it a question of moving the fuel through the engine. Although you make a good point that at low RPM's the exhaust restriction shouldn't be an issue... Afraid this may remain a mystery...
Very true...... At the same time the thin hot air gutless air is easier to push though.... Thick powerful air is harder to push through.... Boils down to it all NA motors are subject to air density... Turbo motors are subject to it all so... but thats more like pushing the thick vs thin air...
I truly understand that all engines love cold air, that I do. But after the years I just came to believe these low breathing motors were what they were in the hot days. I drove in 2 other GS's and seemed the same, one was a Auto and 2:93's and 4 speed with 3:36's. Now I did stupidly crack the block on my dads old 66 Wildcat with only 49,000 miles in 1978 so I never got to know that motor well. The motor showed no symptom's of a stuck heat riser valve or vapor lock. Tranny didn't slip and the switch pitch worked. No vacuum leaks and no gasket leaks. Sitting with friends back then and when we brought up hypothetical races with other friends cars and we always mentioned " you never know which car would show up" meaning mine. lol! Someday maby we will get this..
Do not forget carburetor jetting; if the If the jets are too large the fuel/air mixture will be too rich, This will definitely hurt hot weather performance and depending on the temperature difference may help cold weather get up and go. Perhaps a good carburetor person (or you if you know carburetors) can find a set of jets and rods that will work better. Another way-out-there possibility is that at the time your car was built there were low and high-altitude carburetors. A normally-aspirated carburetor-equipped engine that runs well in Boston or San Francisco will definitely not run well in Denver or Albuquerque. I did not look to see where you live, but in the very unlikely event that you have a high-altitude car in a low-altitude area or especially the opposite, it will run poorly without a carb swap or re-jetting. Bonehead alert! I reread the OP and see that you live in Massachusetts. So did I for many years and hot weather performance was never an issue. There is no reason for a properly set up Nailhead to be more affected by temperature then any other normally-aspirated engine.
Wow John sorry as I just happened to see this post as I thought it had died out. Silly question or better put stupid question, your not saying that a GM Plant in MA or Detroit will put a leaner or richer jetted carb on CA plant built car?
like Codman said,,,, the factory jetted the carbs according to the region the car was to be delivered to..... altitude will affect the jetting ratio... and also the temp.... combine the two and you get the ol double whammy ..... my best nailhead car would be affected by extreme heat only after 3 back to back hard charging runs.... but only just enough that I could tell it... other people wouldnt notice..... But the way you really make a nailhead perform is open up the intake flow, open up the exhaust flow.... not neccessarily headers,,,, put some real stiff gear behind it like 3;90 or more and take advantage of the torque and quick rev ability.... Doc
I was 17 in the late 79 when I got my 66 GS and had some nailhead experience with my fathers old 66 Wildcat that he gave me. Didn't learn or know much about them as I thought in the 8 or 9 years I drove my Skylark GS till I joined this forum 35 years later. I knew motors but not all of the specifics of a nailhead Yes a I read some old car magazines and even wired in the switch for the high and low stall. It was till I got Jefferson Bryants book plus getting a laptop at 52 for my first ever computer and finding this forum that I learned more in 1 month than all the 9 years of driving it. I did not know just how rugged nailhead blocks are and having forged rods and cranks. I only found out about the "reverse" valve train setup when a friend told me it needed a valve job because it was blowing blue smoke in the morning at times and I took the heads off and brought them to a machine shop that was there for ages and figured he knew these motors...............He told me the heads and valve seating were in great shape and amazed because it had by now 90,000+ miles. He charged me $40 and I took the heads back and put them back on. He never told about the intake valve seals though, did he not see them, I don't know?? I just punched the throttle wide open a few times on occasion and it cleared it out fine but didn't know about the use of intake seal's till I came here. I tried a variety of intakes, a Q- jet on a Q- jet manifold from a 66 Riv, a Offy dual quad "yes I know now about them" and a set of brand new AFB's that came with them, I tried a factory dual quad with the carbs from the offy kit an even the carb that had the choke from the dual kit on the factory 4 barrel intake. Never "felt" a difference plus the Q- jet came of the 425 engine that I bought from a Junk Yard. That 425 had so so so much carbon build up, pistons, rods, top and bottom of the bores and heads, so much you almost couldn't see the valves.. Since swapping intake manifolds on nailheads is relatively easy I gave it a shot but I knew the Q - jet needed a rebuild. It's just you never knew where to start with the weather sensitivity issue as far as tuning and wish so bad a I had a time machine so members could give advice and I could put what I have learned to a test.. I would of loved to put some 3:90's in it but when my sister used the family car and my father would need to drive somewhere on occasion and i'm sure he would of hated those steep gears. I had the ST400 out of the 66 Riv but in all honesty the cars frame went from beginning stages of frame rust to bad really quick
Let’s get our minds focused and armed with the right knowledge to make logical conclusions on this type of thing/ issue! 1) The only reason we need fuel in the cylinder of a internal combustion engine it to heat the air. When whatever amount of air that a cylinder gets inducted into it is heated , it then expands to push on the piston . The fuel is only there to burn and thus heat the air. The more air we get into the cylinder and heat up the more power is made. Fully remove from your mind / brain that it is any form of explosion that is pushing on the piston , just forget that wrong line of thinking that may be looming in your mind for however many decades! Look at the process this way. We do away with any type of fuel and we then replace the spark plug with a 5/16” thick 1” long section of solid copper wire. Next we get the cylinder filled to a nice 100% VE, we close the valve and we have the piston at TDC. We then we run 1000 amps at 12 volts thru that solid copper and vaporize it. The result of doing that will be to heat the air just like having fuel to burn in the cylinder.
