V8 heat confusion

[Pyro]

81's seem like a lot of jet. I use 70's on my 750 vaccum secondary (3310) with a 244/244 at 0.050" cam. runs mid 11's at 120 and mid 10's at 135 with n20.

 

Your ignition timing is low. And low timing will make it over heat. Try another 5 or 6 degrees.

[bjhines]

The swirl tank is pressurized with a radiator cap on top. It serves as a high pressure reservior.

 

The differential pressure for flow(purging) comes from the water pump.

 

The constant-bleed points are located at high/hot spots on the HOT SIDE OF THE THERMOSTAT(in the waterjacket).

 

The drainback is plumbed to the water pump inlet(as close to the impeller as possible). This provides differential pressure for a small amount of bypass flow.

 

There is one additional purge port. It functions slightly differently. The cold side of the thermostat housing OR the radiator fill neck may also trap air. It is also plumbed to the swirl tank and will flow intermittantly.

[stangracr]

Hey Dennis Im new here but noticed you are in KC Mo. I also am from KC and am building a ford powered Z car. I have some pictures on the Ford v8 side. I am at KCIR quite often. I would love to see your car. Hope to have mine completed by next spring or earlier.

[sstallings]

This thread has covered everything I would have recommended and more, except for one small point. Before I start, you should know that I am not yet a Z V8 expert, I'm a novice just getting started, but I've used, modified and maintained V8s in all of my other hotrods for 30+ years. The only point in this thread not yet covered is your timing curve. Since you're running a carb, and I assune, a conventional distributor, your centrifigal advance springs may be too strong, bringing your total timing in late. That would be easy to miss if it idles well on initial timing and vacuum advance, and runs well under load and at WOT with total timing, but only gets hot at part throttle. Lighter springs and earlier timing advance might buy you some reduction in temps. That being said, as someone else already pointed out, 210-220 is not really hot under the conditions you described. At 235-240 I'd start worrying more about a major fix, but with a 20 lb. cap and a sound system, you can safely run higher temps. 180-190 is old school and not very effivient anymore.

Steve

[bjhines]

A google search has been relatively fruitless. But here is a guy with some similar ideas http://www.vaportrailracing.com/ . He has made his system far too complex and expensive though. This can be accomplished with minimal investment using the stock thermostat and radiator cap.

 

Here is an aftermarket improvement to the factory GenIII RX7's AST coolant purge system. Keep in mind that the main source of air in the gen3-RX7 coolant system is due to boost leakage into the cooling system. The factory swirl tanks are notorious for bursting. This is an overpriced aluminum version of the tank.

http://www.tripointengineering.com/product_info.php?cPath=388_396_425&products_id=1588&osCsid=2448b04e3a091ab2cb9752c1d40767bc

 

...

[ferreido]

I have the same problem with my 280ZX. No problem on open road, but stop, go and the needle starts climbing. I have two electric push fans and a solid engine driven suction fan, shrouded sealed around the radiator, tried different thermostats, tried different electric fans, played with the timing curve (Pro-Flo EFI) and nothig works. No air pocket problems as filling point is the highest. (See pic's in member gallery)

 

I am in the process of getting a custom copper radiator made up as the allunimum one does not seem to do the work (Cost of $750 - thats how fed up I am with this problem) . Will have it fitted by this weekend and give feedback.

[bjhines]

ouch... 750$$$ for a custom 1920s tractor radiator.

 

You should get some temp readings from the aluminum radiator to make sure it is getting as hot as the cylinder head temps before you go with some kind of strange custom radiator. The heat transfer properties of the different metal alone is not going to solve your problem. Copper vs aluminum ain't that different. The radiator ain't yer problem bo.

[heavy85]

Copper vs aluminum ain't that different.

 

I dont know what the problem is here but yes copper is a much better conductor than aluminum (almost twice) and you will get better performance out of copper for a similar size radiator. Copper is heavy and expensive which is why aluminum is used more for racing.

 

Cameron

[dr_hunt]

I dont know what the problem is here but yes copper is a much better conductor than aluminum (almost twice) and you will get better performance out of copper for a similar size radiator. Copper is heavy and expensive which is why aluminum is used more for racing.

 

Cameron

 

Not exactly, the aluminum radiators have larger tube size then the copper/brass ones do, which slows the velocity of the water down for more residence time in the rad for more heat transfer and provides larger surface area for heat transfer. Copper/brass radiator cores are not available with large tube size as far as I know, instead they use smaller tube size which inhibits airflow throught the radiator, which is one of the advantages to the aluminum rads. At least that is the school of thought anyway.

[heavy85]

Not exactly, the aluminum radiators have larger tube size then the copper/brass ones do, which slows the velocity of the water down for more residence time in the rad for more heat transfer and provides larger surface area for heat transfer. Copper/brass radiator cores are not available with large tube size as far as I know, instead they use smaller tube size which inhibits airflow throught the radiator, which is one of the advantages to the aluminum rads. At least that is the school of thought anyway.

 

Sorry good Doctor but I've never really bought 'resident time' theory. It is a fact that copper transfers heat almost twice as good as aluminum does. So for the exact same shape, tube size, fins, etc you are going to get much better performance out of copper but it is relatively very expensive and very heavy. I dont get the whole large tube / slow flow thought process. Kind of like the orifice in the water pump - I think it's to prevent pump cavitation another side benefit other than allowing the water more time to go through the radiator, although it may be used to reduce water pump power draw. Think about it - if by having slower flow you have more time to cool off in the radiator it also means you have more time to heat-up in the engine which means you just have a higher temperature rise across your engine. If the gauge is at the outlet of the radiator you may think the engine is running cooler but if you look at the water coming back into the radiator it's not really. Anyway I'm digressing and theorizing so take it for what it's worth. Back on topic ... you actually want turbulent flow both on the water and air side to get the best heat transfer - slow flow does not get you this. Very efficient coolers often use turbulators on the water or oil side (oil cooler) to get the best heat transfer out of them. These are often like little offset fins inside the tubes to mix up the flow. Trying to slow the flow seems to be just a bandaide to a low cost, inefficient design or a way to get a 'one size fit's all' approach that is not too restrictive and is good enough for most applications.

 

Sorry for the long post here ...

 

Cameron

[pparaska]

Conductive heat transfer (through metals, other solids) is inversely proportional to the tube wall thickness also:

http://www.engineeringtoolbox.com/conductive-heat-transfer-d_428.html

So before you can really make a comparison, that equation alone needs to be fully filled out for each radiator tube. Then you have to consider the area the tube wall presents to the coolant and the air, in the directions those fluids are flowing over the wall to understand the convection heat transfer to and from the sides of the tube wall.

 

Note that radiators are made from brass, not copper and brass, and brass actually has a lower conductive coefficient of heat transfer than aluminum:

http://www.copper.org/applications/automotive/radiators/no_flux.html

[bjhines]

And before you do all that theoretical math you can get a temp probe and meter from HomeDepot and figure out if your radiator even gets enough hot water through it in the first place.

[Pop N Wood]

The radiator ain't yer problem bo.

 

I agree with that. Concentrate on that statement and forget the copper vs. whatever.

 

Copper is massively better at conducting heat. I worked in a power plant one summer, and they had to replace a copper steam condensor cause the copper ions were causing problems else where in the plant. You would not believe how much larger the stainless steel condensor had to yield the same cooling capacity. what was even more interesting is how they replaced the condensor. They had basically built the plant around the original condensor, so replacing it was a piece of engineering art.

 

But like Pete said radiators are brass, which is only marginally better at conducting heat than aluminum.

[dr_hunt]

Well we could go into the math, relatively simple, but aluminum rads are more efficient.

 

This may be the same link but the new radiators are copper/brass.

 

http://www.copper.org/applications/images/header_applications_05.jpg

 

Supposed to have lower air pressure drop than aluminum but are still heavier than aluminum and are not claiming to be more efficient than aluminum.

 

I read an SAE paper on aluminum radiators and according to that paper they are more efficient than copper or copper/brass. It can be purchased here if you really want to get to the nitty gritty of the why and how.

 

http://www.sae.org/technical/papers/770830

[ferreido]

Sorry, should have mentioned that my current Alum Rad has a 1 and 9/16 core size almost max for our local standard cores. The copper Rad will be 3 and 9/16 as it is custom made.

Might be a bit of an over kill, but I do not want any more overheating.

Will collect it tomorrow.

[Pop N Wood]

Brass is copper alloy, so not sure what is meant by copper/brass.

 

The thermal conductivity of copper is significantly better than aluminum. But radiators are not made out of copper, they are made out of brass. And the thermal conductivity of brass is a good bit less than aluminum.

[sstallings]

Hey guys,

 

I'm not the expert here on radiators, but I just finished reading a three part series on cooling systems over the last few months in Street Rodder Magazine (probably not a big source for Z owners). However, I can end the copper/brass vs. aluminum debate. The good news is: YOU'RE BOTH RIGHT! Copper/brass is much more efficient than alluminum, BUT, aluminum radiators exchange more heat than copper/brass ones. Why, you ask? Because the lead in the solder in copper/brass radiators lowers the efficiency of the base metals to less than that of aluminum, which has no lead solder joints. Aluminum cores are welded aluminum to aluminum, so there is no loss over the base metal.

 

Also, modern aluminum cores are more efficient at heat transfer because they flow more air per square inch with less restriction than multi-core copper/brass radiators. There is also an expensive alternative called the "heat sponge" copper radiator that is supposed to be four times more efficient than a traditional design. The guy that makes them will build any size, shape, tank configuration you want, but he ain't cheap. I've seen them advertised for big blocks in '30s street rods because those radiators are physically smaller than needed to cool that much engine.

 

I'd agree with the writer who suggested that this problem might not be your radiator at all. The only way to find out would be an additional water temp sensor or two at the inlet and /or outlet to be sure. I really want you to solve this problem before I run into it. Good luck.

Steve

[ferreido]

I have fitted the new 3" core copper rad and my problem is solved. Open road temp 190 and the max stop go temp 198.

[bjhines]

well... There ya go... Could we get a pic of this fancy radiator.

[ferreido]

I'm not so sure about fancy, but defenitely heavy. 14Kg compared to the 4kg of the old one.