In this weather, overheating shouldn't be an issue, unless you are sitting in LA traffic. If you get in traffic keep an eye on the temps and make sure the fan is on if it has a manual switch, if its an auto on just keep an eye on the temps. On the freeway with no traffic, 4th gear and let that small block eat. Your RPM will probably be around 3000 at 65MPH, no going to hurt a thing, except your wallet (fuel costs). Just make sure you have her all tuned up and ready to go, pack a good tool bag with all the basics. If you have prepped the car and done your preventative maintenance, that's about all you can do. Make sure your cell phone is charged and let the trip begin.

Keith

 

what's a good temp / the max I should let it get to? and what do you mean by tuned up, I've done some tuning myself so I know how to change it. other than those 2 questions very clear help thank you

 

Since you really haven't said really what the condition of the engine or the car itself is in, I'm giving you what I would do if it were my car doing the trip.
With 50/50 water/antifreeze and a 15lb radiator cap, I personally wouldn't go over 230*, I would be getting nervous if I saw 220*. What does the car cruise at temp wise running down the freeway? When I say tune up, just make sure your points, condenser, plugs, and wires aren't older than the hills and you have a good fuel filter, check your oil and coolant levels, make sure the tires are not over 6 years old and properly inflated, your belts and hoses look good. General preventative maintenance.

Keith

 

ah, tune wise I'm good I check all that regularly. I actually have never been on the freeway. been rebuilding this car for 3 years working in my garage or highschool autoshop and I just wired the whole car a few months ago. I'll keep an eye on the temps and just pull over for a bit if it gets too high. thanks for the help

 

Good luck!

Keith

 

Been there, done that, many times!
I've had several cars with 3.73 rear gears and a SBC engine, and better plan on staying in the right lane, or taking the coastal 101 route so you can keep speeds to no more than 65mph. Above that for long drives just isn't going to be fun for the setup you have.
As for what to take along. A tool bag with a set of combination end wrenches, and a 3/8 socket set. Also a few various pliers, screwdrivers, some mechanic's wire in a short 10' piece. Maybe a small roll of duct tape too.
Need to take a gallon of water, and a quart or two of oil. And of course your cell phone!
When I finished my '39 Chev build I got 500 miles on the new engine I built and took a 1250 mile round trip road trip. 500 miles going, and 750 miles with a detour coming home. Had all the tools I thought I'd need, plus oil and water in case. One difference is I putt a 700R4 overdrive trans behind my 350, so I could cruise my 3.73 gears at 70 mph and be turning 2100 rpm's. But I've taken trips with my little Austin gasser with 350, TH350, and 3.73 gears also, and I cruise about 55-60 mph to keep my rpm's lower, and not had any issues.

 

I’m guessing this is Oregon or northern Nevada to California. No matter from where east side or west this time of year the weather will be crummy to say the least.

I rather think that if this is a build shake down ride 400 miles from home on a fresh build for any era car is sticking your technical neck out.

As for driving at legal speeds your engine is not turning anywhere near red line in 4th. Up until the 1980’s there wasn’t much use of overdrive ratios. Actually you’re more likely to overheat the transmission especially and possibly the engine because the higher ratio of overdrive slows the engine so it’s not operating as high on its torque and power curves and through the gears it’s loosing gearing multiplication to the torque to where on the tires torque is going down relative to engine RPM so with overdrives operating temps go up because the loading on the engine and trans is higher. Modern vehicles operate substantially at higher temperatures as a normal thing. Hot rods tend to operate higher than factory vehicles especially things like a 240Z with an SBC stuffed in it simply because there isn’t space for an adequate radiator capacity in terms of heat transfer to the atmosphere. Modern fuel injection especially port and direct hide that a little because the fuel is dumped raw into the cylinder thus must perform a phase change from liquid to a true gas which absorbs a lot of heat from the cylinder that now isn’t transferred into the cooling system. The trick here is modern Ricardo chambered heads need to be used that have shapes that foster actions that precipitate this phase change. Older mid 70’s through mid 90’s Chevy heads (and they aren’t alone) don’t do this. The older pre 1973/74 dual quench heads will sorta do this but the big change is the 1995 L31 Vortec head and of course the aftermarket heads with these heart shape chambers that followed.

Cylinder head combustion chamber shape is a huge engineering subject and this also gets into piston crown shape and materials as well as the crunch distance between the chamber step and the piston’s crown. Needless to say, the typical factory round dish piston typical of the SBC is not a good friend to efficient and effective combustion. For these engines a flat top is ideal shape wise where the D-dish is nearly as effective in power output and detonation resistance while allowing for grooming the compression ratio to the needed available fuel octane. But since so much is in play modern chamber shape and certainly when combined with aluminum allows much higher compression ratios for the fuel’s listed octane rating. This in engine design is called mechanical octane, it makes the fuel behave as if it’s 5 or 6 octane higher than its R+M/2 rating on the pump. And that’s with a carburetor or TBI!

The intake manifold though short as things in the plumbing world go cause a lot of mixture mayhem between a carburetor or TBI injection. So it turns out that adding modern Ricardo/Taylor ( GB/US researchers on this subject) to a carbureted or TBI engine with pre 1995 chambers will add 25 to 60 pound feet of torque and about the same horsepowers to these engines depending on the cam used and the original heads. Bigger cams respond with higher gains than smaller cams and pre SMOG closed chamber heads offer smaller gains than SMOG open chamber heads. But the gains are real.

One needs to know that the mid 70’s to mid 80’s open chamber heads were a reaction to lowering NOx emissions as at that time a catalyst to reduce NOx at affordable prices was not available but there were processes of air injection and catalysts that oxidized unburnt hydro carbons. So the answer to getting NOx emissions down was to lower combustion temperatures this accomplished by reducing ignition advance and compression ratio. This was highly inefficient for combustion which jacked the unburnt HC’s way up but with injection air into the exhaust to complete combustion in the exhaust manifolds and early HC oxidizing converters the exhaust was cleaned up of a lot of the SMOG creating crap at the cost of lousy gas mileage.

The 3way converter that reduced NOx, that then freed up oxygen to be used in the next stage of burning excess HC’s that provided the heat to burn CO to CO2 became available around 1986. For Chevy there was an immediate return to the dual quench chambered heads which for the 350 netted the L98 and L05 heads the latter mostly used on trucks as swirl port heads but these two heads share a common chamber shape though different intake ports. In 95 we get the famous L31, Vortec head and that‘s been the standard configuration SBC head since. It makes building a 400 lbs ft, 400 plus horsepower power 350 on a mild cam a no brainer.

So there’s a glance over the history of these engines that occurred before your birth date. There’s more detail but I’ve bored you enough if you got this far.

Bogie

 

That's the reason all modern overdrive automatics incorporated lockup torque converters. Unless it's a heavy rig, or towing a load there's no excess heat with modern lockup converters. Sure wouldn't be with a little 240Z if he had an OD.
Even my pretty heavy 3500 lb. '39 Chev coupe runs in the 200 degree temps. The hottest spot in any transmission is the torque converter where temps run 325 degrees, but I also use a Hayden trans cooler that's isolated from my radiator to help keep temperatures lower than they are with tiny radiator mounted coolers. But even with those the average transmission temps run 175-225 degrees once the fluid leaves the converter and goes through a cooler.

 

Find a governed semi going 60 to 70 MPH in the slow lane. Sit back from it's bumper 100 to 120 feet matching the speed. If it exits find another.

This will let you cruise for most of the trip behind the semi with a good amount of following distance in front of you while keeping the engine happy. Depending on the ride the difference between 65 and 75 may be noticeable.

The soccer moms are going to come up on your butt going 90. But most will get the idea real quick that your taking a long trip. The few that get in between you and the semi will give you like 20 feet before moving in front of you then roughly a second later move back out of that slow lane as they run up on that governed semi's butt. Most people will simply pass you at 90 quickly followed by the semi.

Now when there are no semi's I try to kick it up to 75+ just to avoid the person coming up to you at 90 then sitting along side holding up the others behind them just to check out the ride. At 75+ they can sit behind you and talk/think about "the one they had" before eventually passing or exiting.
Good chance you can find a semi within 10 minutes at 75+ to then sit back behind at 60-70mph.

This is basically how I drive most of my classic rides or any of my square bodies on the highway. It is more relaxing and safer then being "in the pack" of people going 90 while others are holding them up(in the fast lane) at 70 who soon get cut off(as they should be if the slow lane is completely open). The ones that go 70 in the fast lane are to scared or stupid to know how people should merge into that slow lane.

I drove semi for 7 years with a governed semi in the slow lane. Very few exceptions where I felt it was needed to move over for a 4 wheeler that could not go faster or slower to merge how they should.
When driving in general and especially when pulling a trailer I am in that slow lane going a constant speed. They figure it out after a few seconds and often get in front of me before going 5-15mph faster or drop back before going 5-15mph faster.
When driving a classic do the same thing. Just hold your ground and stay out of that fast lane.

I like to use an app called Waze when driving. It lets me know of things like vehicles on the shoulder(those I move over if possible), police ahead(move over also), object in roadway(tires or roadkill), and railroad tracks ahead(to save your rims/tires/oil pan/ground effects). I been using this thing for years and while it can be inaccurate in the final location of residences at times it is based on a community that gives live updates in real time. It's like Telsla's current network of all there cars(and robots) talking to each other without the them telling on that one person in the group that wants to go 50mph over the speed limit briefly.
If that guy going 50mph over the speed limit causes a crash then I will have fellow waze'ers ahead of me telling me "item in roadway" "lane is blocked" along with "traffic reported ahead" possibly "police ahead" and if it is far enough ahead the route can be recalculated around the mess. If not I can give more following distance to avoid the 1/2 bumper in the right lane. If by the time I come up on it the stuff has been cleared then fellow wazer's will update that also.

As far as a tool kit(keep this in the ride at all time (cheap tools only)
-Cheap socket kit with a 5.5, 7, 8, 10, 11, 12, 13, 1/2, 9/16, 14 sockets and a ratchet of course with two 3" extensions.
-Wrenches with the above measurements with a adjustable and a pair of pliers.
-Wrap 10 feet of 16 gauge wire in a ziplock. Wrap of 10 feet of 10 gauge wire in a ziplock.
-Wire cutter/strippers and circuit tester with a lightbulb not LED.
-Cheap universal screwdriver kit that has flathead, philips, and torqx bits
Sure you can add to this

-Spare rotor
-Spare blade fuses and relays
-Hand warmers and a blanket(the blanket can keep you warm while also be used for laying/kneeling down on without being covered in mud etc).
-A gallon of Distilled water filled 3/4 the way up. For adding to coolant or if need be drinking while waiting on a tow truck. At 3/4 it has room to freeze and not burst the container.
-Can of fix a flat(as a last resort)
Sure you can add to this

Before taking a long trip pull the tires off the car. Using the in car tire kit. This does a few things. It lets you know the kit actually still works and lets you see if you have a lug nut that is impossible to remove kind of deal. Better to find out in the garage where you have more powerful tools and time for pentrating fluid to work then when your on the side of the road with cars flying past at 70+ in heavy rain.

I perfer to upgrade those scissor jacks with a bottle jack(if it will fit under) or a cheap 1.5-2 ton mini floor jack(fits under anything). I still use the scissior jack as a 2nd safety measure. But its alot easier to lift things with hydraulics.
Having two gives you reduncy and doing this before hand lets you see that you actually have that lug wrench in the car and that the spare is not flat.
Of course I still carry a dedicated thing of fix a flat and throw a 12 volt tire inflater/jump starter in the ride just in case that spare turns out to be flat(I never forget to check things before hand).

Oh and after checking that everything works by pulling the tires off and then back on then retightening the lugs after a short 10 mile drive make sure to put that tire changing kit back into the car. Has never happened to me more then twice. Thats where the can of fix of flat comes in or the stuff for waiting on a tow truck.

As far as a tune up. Before doing these I like to wipe down the side of the block and transmission(i often paint these silver) and then take a few short drives to see if I find any runs. Wiping down the block keeps you cleaner when working on it while letting you see that a leak is coming from the valve cover and not the rear main etc.

Once your sure you have no leaks(or at least know where they are) you can do basic inspections.
Plug wire inspection, spark plug inspection, cap/rotor inspection, points inspection, hoses inspection, belts inspection, air cleaner inspection, fluid level check, lights check, wipers/washer check, heater check, and most importantly radio check. If anything looks questionable or bad then fix it.

On the coolant front I do this check and top off fluids including filling the overflow to the cold level.

Get in the cold ride and without warming it up head down a country road(no one around) getting up to 80mph as fast as you can driving a bit mean while getting there and hold it there for about 10 seconds before cruising down to 70 for about 5 seconds and then pull over and sit with the thing idling for 30 seconds. The thing should have gotten to full operating temp by now and it should be sitting somewhere around 190-205F(with a 195F thermostat). After idling for 30 seconds drive mean once again back up to 80mph before dropping to 55 and cruise back to where you had the thing parked.
Shut it off and let it sit for 5 minutes. Lisen for any bubbling sounds. After 5 minutes start the thing and it should start somewhat easily. Now with your foot on the brake and the thing in drive sit in the thing for 15 minutes just idling watching that temp gauge. After 15 minutes if it has not went over 210 your good. Shut the thing off and slide some cardboard under the radiatior leaving that there till it cools off then check the level once cold.

What you simulated is having a sit down lunch then getting back onto the highway before coming across a traffic jam. You also simulated pulling into a gas station and after filling up you were able to easily start the thing.
Now that you tested these in a somewhat controlled situation when you encounter them you will know your cooling system will be up to the task.
Your coolant should swing between 190 and 210 during these test. If it is below 190 then you have a lower thermostat or none at all and it should be replaced with a 195F thermostat. Hotter coolant temps produce more power and the fluids are designed to work with coolant around 200F.



This is long enough. Stop reading and get to work.

 

If the car was built right, it will turn 4500 RPM all day long in 100 degree heat

 

1972 240z had 2 ratios, one for manual cars 3.36:1, one for automatic cars 3.56:1 IIRC

So the SBC won't be turning that many RPMs at highway speed

 

Considering the likely small diameter tires a 240Z will have, his current 3.70 rear gears with what is likely a 24" tire will be over 3600 rpm's at just 70 mph.
The SBC has no issues turning that, but having been there it's no fun hearing that little 350 screaming constantly at 3600+ for hour after hour. And the idea of taking it up to 90 MPH puts the engine at nearly 5000 rpm's, and it wont do that very long before something decides to let go.
I've got big old 29" rear tires and not fond of watching my tach spinning 3000 rpm's constantly on long drives at 70 MPH. So I take my '39 with OD if I'm driving more than maybe 90 minutes.

 

wow numbers like that make me wonder how people raced back in the day with a top speed of 90. either way now days every other highschooler has a bmw that would dust my car lol

 

Technology keeps moving on. A lot is working out the cost so it’s affordable. Until that point is reached these technologies are in some corporate or university back shop being reviewed, updated, played with till some breakthrough is made in some combination of materials, processes, coatings, machining and many other affectors.

Here’s a great story of how long and hard and expensive what appears to be simple to solve problems typical of how long the development cycles can be and how people fight over the financial rewards and how outsiders benefit with nothing else than jobs that didn’t previously exist.

https://en.wikipedia.org/wiki/Shuji_Nakamura

The problem I see with the internet and cell phones is it makes it appear that things happen nearly instantly when in fact they don’t.

When I was in college (58-62) my electronics class was mostly teaching tube technology but the transistor was already in full replacement swing though it netted about one chapter in my Fundamentals of Electronics textbook. Ten years further on the transistor and discrete parts of inductors, resistors, capacitors were miniaturized onto the first then low density integrated circuits. In another ten years we were getting the first high density integrated circuits and that ball just keeps rolling to where today.


Your generation is at the minimum going to have to deal with Hybrots and Cyborgs.

Bogie

 

These engines were designed to run all day long at the then-70 MPH interstate speed limit. 3000-3500 RPM for an extended period of time is nothing. I run my older cars at 70-80 MPH all the time with zero issues and no OD transmissions.

 

Yep, my 350 in my S15 is into 400,000 miles it is just now starting to show a decline in oil pressure, still doesn’t burn oil.

But it is a built engine on a very low mile 880 block that was cleaned and inspected but not rehoned. Pistons are D-Dish 4032 forgings with moly rings. Original bearings reused, LT4HOT roller cam installed, double row roller timing chain, coolant modified for conventional flow 1994 LT1 aluminum heads using stock diameter valves with mild porting using 7/16th rocker studs and aluminum roller rockers, compression ratio is 10.7 squish/quench is .053 inch, GMPP LT1/LT4 carb intake with an Edelbrock AVS-1 carb, modified Speedmaster 7000 distributor and E core coil. This with dyno room headers pulled 412 horses at 6100 RPM and 423 pound feet of torque at 2700 RPM. This essentially is late 1990’s early 2000 technology applied to the classic Gen I SBC.

As a comparison going back to late 1960’s very early 70’s the same block with the then Camel Hump heads with mechanical fuel injection and a cam that almost didn’t close the valves it had so much duration with compression approaching 12 to 1 struggled to produce 375 horses. Today you almost can’t avoid getting that kind of power with a much milder cam, Vortec or aftermarket heads and a carburetor and doing it with 9.5:1 compression. A lot of it is heads and pistons.

The modern heart shape chamber and pistons using a D dish to manage compression instead of the factory round dish and cams that use less total duration but more crammed into the .050 to .050 period with more lift combined with induction and exhaust that breath better at higher lifts make much more power. To a great extent this is using the lessons learned on WW-2 aircraft engines.

You also see this on the newer aluminum engines. The factories played with aluminum blocks back in the late 50’s and into the 60’s but basically they tried to cast an aluminum block in the same likeness of a cast iron block. This structurally didn’t work as aluminum just isn’t as strong or stiff as iron. The OEM’s in the 1990’s finally started to advantage aircraft engine knowledge arriving at the need to beef up the bottom end through design rather than added mass and the acceptance that you just can’t run the rubbing wear of pistons and their rings on aluminum walls. So government regulation on emissions and fuel burn forced the changes we enjoy today.

Without this external pressure there shouldn’t be any doubt that the auto manufacturers would simply kept making bigger cast iron engines and bigger cars to hold them because that’s the less costly way to go.

The amazing thing to me as an aerospace engineer was how long and how painful the automotive OEMs made of employing these technology changes. We got what is known as the “Malaise” years through the 70’s into the early 90’s where factory performance was dead. This is what you get when finance guys run things. We lived through this seeing the death of GE under Jack Walsh then the salting of American corporations with these GE people that then destroyed Toys-R-Us, McDonnell Douglas and now is in the process of destroying Boeing, Chrysler, Ford, Harley Davidson.

Bogie

 

One of the improvements made in engines was when most car makers went to roller camshafts! The old flat tappet cam and lifters wore faster than rollers do, so that extremely fine metallic particles got flushed throughout the engine's oiling system, and only larger particles got caught in the oil filter.
When Chevy went to the one piece rear main seal roller motors suddenly lifespan between overhauls went way up! The same flat tappet engines that were wore out at around 100,000 miles were then going double that.
When you had to wear in a flat tappet engine for 20 minutes at 2500-3000 rpm's you know that cam and lifters were wearing themselves immediately so they fit together better. And that wear didn't stop after the 20 minute breakin period!

 

Turning higher rpm is all good if things are designed for it. But the difference in mileage between 60 and 90 is noticable.
I have had several squarbodies with 4.56 to 5.71 gearing without overdrive. They will cruise at 80 all the way from Michigan to Florida. But I will take 150 gallons to do so. Following a semi 15 miles slower I can save around 15 gallons and tons of stress on me and the powertrain.

I am oldschool where when the gauge hits 1/4 I fill up. Both from a standpoint I don't trust the gauge and knowing it may be 20 miles till the next pump in some states.

Part of a roadtrip is enjoying the drive. If it takes a bit longer then it does.

 

I take the approach of "just go." Don't stress. Familiarize yourself with the radiator cap pressure rating, the thermostat temp, and drive. Here's the thing about coolant temp. It has nothing to do with the temperature, it has to do with when it starts to boil. If you drive it all day and it gets to 220 degrees and stays there without boiling, keep going. What you need to be aware of is if it shows a trend of rising temps on hills or in slow traffic. That means that more heat is going INTO the coolant than the radiator can remove. If it boils over, stop immediately and shut it down.

Engine damage from overheating happens because the water against the iron becomes steam. Steam is a terrible heatsink, so what you get is areas of super-heated iron next to areas of iron that still have water. Iron melts at something like 2700 degrees, and combustion temps are about the same ballpark. It's not the temperature that gets you, it's the heat. As long as you're not boiling, the engin doesn't care if it's 160 degrees or 300 degrees. Boiling is your indicator that you need to stop immediately. When you shut the engine off, you're no longer putting combustion heat into the coolant and preventing those super-heated areas from warping, cracking, or seizing.

 

If it boils over, stop immediately and shut it down

maybe a bit of a dumb question but how would I know if it is boiling while I am driving? is there a visual indicator?

 

4.56 gears, even with a tall 29" truck tire would be over 4200 rpm's at 80 mph. I sure wouldn't think of driving that fast with most stock SBC engines myself.
And those 5.71 gears would be 5300 rpm's! Not sure how long a stock engine would hold up, but doubt it would be much of a road trip.

 

You get you some balanced tires and a good radio you wont mind a 4500-5500 drone.


The 5.71's had several 3 hour trips at 70-75 with nothing but a 355 on a very mild build. Shock loading, clutch drops, and sucking air instead of oil made that a long list of cheap junkyard SBC that made it under the hoods of my projects. Most engines were swapped when the bone stock cheap clutches were at 10k.

Most stock sbc are good with 5500 with nothing more then a cam and rockers. Blow up one long block and swap stuff over to the new one to make it live at 5500. You can do a basic vortec head swap and other goodies but its not needed with most heads.

SBC were getting harder to find (under $400) by 2010.
I would not swap one into anything today.

The very last SBC I killed I was in a C30 pushing roughly 5k and lost a rear main. No warning it just died when it seized. Walked 2 miles to a truck stop grabbed 2 gallons of 15w-40 and poured it in. Yea I had a rod knock and the oil soaked clutched slipped a bit for a few miles. I drove it home taking backroads. Then I drove it another 20 miles before parting that truck out because I had another project and no room. I have video of that old girl unlike most of my rides that were simply photographed with the things being stored on a imac, photobucket, and kodak cd's.

Now I just play with 5.3's which also will laugh at 5500. When those get hard to find maybe electric motor swaps will have become cheap enough to justify.

The first time I drove a rotary I freaked out a bit at the rpm. But that quickly faded after a few corners.

Having to stop every few couple hundred miles does get old with the higher rpm though. But thats easily fixed by simply swapping out axles (or 3rds) for a diffrent ratio.
Something like a 3.42 ratio with car tires tends to love cruising at 70mph without overdrive. Of course a higher ratio is good for more torque. But life is full of comprimises. If the OP want to build the ride for smoking tires then a ratio in the mid 4's will make even a smog 305 feel fun. If they want to build it for cruising in style then 3.42 or 3.08 and something like 350-380hp will still be fun going down the highway without overdrive. All about what you want to do with the ride.

For a simple road trip I would not worry about rpm to much. The cruising 100 feet behind a semi thing is more a stress reliever then anything. If your in that left lane I expect you to be going at least 10 over to make a clean pass around whom ever is going slower. Commuting to work etc I will cruise at 72 and then kick it up to 80 to make a clean pass around a semi before dropping back to 72 once I am 100 feet in front of them (or I see someone coming up at 90). Its tons more relaxing then driving 90 in the left lane just to save a percentage of drive time.

To many camera's and such out today for me to justify speeding more then needed to make a clean pass on a road trip where I will probally spend a extra 10 minutes at a sit down restraunt anyway.

If you just sit 100 feet behind that semi good chance you can follow it for hours before it gets off or you will need to get fuel. Just give it a try your next time to work etc where you have a extra 10 minutes and can cruise 100 feet behind a semi at 65-70. Tons less stress and also generally safer.

 

Like I mentioned earlier with a 50/50 mix of water and antifreeze and a 15lb cap, you should be good for 235* before boiling.

Keith

 

I thought the rear end was a 3.70 where did this 5.70 come from?

3.70 gearing while a bit stiff was not uncommon of production vehicles of the 1950’s. As engines were getting bigger and automatics more common in the late 50’s and 60’s we see this move to less ratio like 3.00. In the mid 70’s into the 80’s with the national speed limit being 55, and Sammy Hagar wrote and performed “I just can’t drive 55”, then these axle ratios of 2.700 or thereabouts became common. They pretty much remained the same as fuel injection cam to be even after the 55 limit was trashed. But really 3.7 at interstate speeds is just fine.

As for cooling after all you don’t need to drive 70 plus if that’s a problem to cool but this is winter so I don’t see that a problem even in the desert. You should run 50/50 to minimize freezing risk and minimize internal cooling system corrosion. Aside from that the important things are keeping air out of the cooling system and keeping things wetted in there. Keeping air out and preserving coolant from loss is a job of tge radiator cap among others and a recovey puke tank. This lets the system vent the expanding hot coolant to be drawn back in from the puke tank as the system cools off after shutdown, this also kerps air out which in the cooling system greatly accelerates consumption of neutralizer's in the coolant that protect from corrosion and their loss along with engine heat and the mix of different metals in contact with the coolant increases the rate of corrosion. So keeping the coolant clean and fresh and the system burped of air are important things to keeping the engine alive. The pressure cap is used to raise the boiling point of the coolant to help insure it keeps surfaces wetted. When there is local nucleate boiling these hot surfaces get dry and that starts a destructive sequence that cracks castings. For the SBC this is commonly seen between the adjacent exhaust valve seats which often blows the head gasket between cylinders 2 and 4 or 3 and 5. Another common crack is between the hot exhaust seat and the cooler intake seat or to the spark plug and either or both seats. Chevy typically puts the temp sender on the left side head between cylinders 1 and 3. This is done because coolant pump rotation naturally favors pumping more coolant to the right bank than the left, so the left head should show an overheat sooner than anywhere else. whether this is enough advance warning to save the day, I less than convinced. But I understand engineers in the lab, been there, done that. Sometimes you get lost on unsless tangents and this seems one of those tangents.

I will say that I don’t think people give the cooling system the respect and love it deserves.

Bogie

 

cerial mentioned cruising at high speed with 5.71 gears.

And turning up the radio wont save your engine cerial. It will just make you unable to hear it until it blows up.

 

Yeah I did see that! Another product of my indoor speed reading.

I‘ve tended not to use my racers for daily drivers. Probably the stiffest rear gears I drove on the street was my 56 Lincoln powered 53 Merc, rag top that used 3.89 final with an overdrive B&W, T85, 3 speed stick. Built in my senior year of high school it was my college ride it did San Louis Obispo to San Diego and back on a pretty regular basis on the 101 which was mostly 2 lane road back then.

Hot rodding was still young and surfing in its infancy. Lots of Ford flat heads, Chrysler hemi’s and Caddy or Olds powered Fords on the street. Now and then a Buick nail head. The SBC still something of a rarity in rod builds. At the beach surfing was wood, long boards that are pretty heavy and very expensive. Carved balsa covered with poly-resined fiber glass were gaining a foothold these being lighter, smaller and cheaper with foam cores being the new but rather rare thing. PVC plumbing just coming on, I remember they built a new shop building at my high school that used PVC plumbing, you couldn’t drink the water from the drinking fountain as the taste of plastic was so strong.

Bogie

 

So my answer may come a bit late, but here are my 2cents:
If your car is in regular working order, I mean daily-driver style/ turn the key and go on a daily basis, then there is no reason to worry about anything. 3.70 rear end is not that bad, but since you are not sure, maybe get a tach to keep an eye on the engine RPM, to give you an idea. And sure, you may not be able to cruise with new car traffic at 90mph all day, but so what? Your car is way cooler than pretty much any car passing you!
My main advice after that would be a AAA membership, for the roadside assistance; if anything, it works great for peace of mind. And once you have peace of mind, you can just enjoy the trip, at whatever speed!