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>At full power, the XR-7755 generated a tremendous amount of heat. Speaking as a full time engine mechanic for a small chain of midwestern repair stores, this

>At full power, the XR-7755 generated a tremendous amount of heat. Speaking as a full time engine mechanic for a small chain of midwestern repair stores, this is the death-knell of every heavily customized car. Heck, 3/4ths of the engineering for a Dodge Hellcat or Mustang cobra is just to keep the thing cool enough that the driver isnt chased out of the cockpit. You cant idle them the same way you idle a Toyota...they'll burn up. the Dodge Viper is another perfect example of engine displacement gone wild. The intercooler and radiator are massive, but the additional cylinders and their size means the V-10 motor has 10 cylinders firing onto a 90-degree crankshaft, which means it has an uneven firing interval for two of the ten cylinders. it makes the idle rougher than a garbage truck, and very prone to overheat with a 220 degree camshaft.

dsfyu404ed 8y ago
I'm not seeing how crank and cam specs significantly affect cooling at idle all else being equal. Any cooling system that can work under load will be fine at idle. Edit: For something like a race-car that's trying to minimize weight/power loss by running the minimum radiator/fan necessary and depending on airflow from movement (or rely on the fact that you're only running 1/4mi at a time) I can understand. Still, that's a cooling system sizing issue, not a cam or crank issue. A street going vehicle isn't going to have a cooling system that's sized within a hair of inadequate like that. Power output (and heat generated) at/near idle should be fairly constant regardless of cam and if it's not the higher power output cam profiles will probably have lower power output at/near idle (this depends a lot on the engine, some engines force you to choose where you want your power, some are hard to throw "too much cam" at). No matter how you cut it only so much air can get passed a closed throttle and that amount of air only corresponds to a certain amount of fuel, that puts an upper bound on heat generated at idle. I can see how adding forced induction could significantly affect heat generated at idle but even then, if everything is sized properly it shouldn't be much of an issue. This place is really turning into Reddit where you get down-voted for questioning anyone who sounds knowledgeable.
- maxxxxx 8y ago
  Cars depend on air moving through the cooling system under load which means it's at speed. Cooling at idle can be a big problem for high performance cars. Going to the extreme, F1 cars have to be super careful not to overheat when stopped.
  - justin66 8y ago
    > Cooling at idle can be a big problem for high performance cars. Or any air cooled car ever made. But the reality is that in a lot of designs, idling will test the effectiveness of the cooling system more than driving the car at speed. (Adding power only exacerbates such a problem. The OP completely fails to understand this) It's much less of a problem than it used to be, with lots of cars including electric fans to help out the radiator, but it used to be standard to see a warning in the owner's manual about temperatures increasing in slow traffic or at idle.
    - maxxxxx 8y ago
      "Or any air cooled car ever made." Are there still any being built? I thought the 911 was the last holdout until they also switched to water cooling. "with lots of cars including electric fans to help out the radiator," I had that fan breaking once in my Miata and temperatures went into the red really quickly in LA rush hour.
      - justin66 8y ago
        They switched the 911 over to water-cooled in the late nineties, yes. Prior to that, Porsche got the idle temp problem somewhat under control using powerful electric fans positioned in front of some of the oil coolers, but there's essentially no reliable way to cool four-valve cylinder heads with a purely air-cooled engine (the 959 used separate water cooling just for the heads), so they decided the whole thing was a performance dead end. The air-cooled 911 Turbo did get up above 400hp with two-valve heads before the change, though. > I had that fan breaking once in my Miata and temperatures went into the red really quickly in LA rush hour. No doubt. Once you train yourself to hear that fan, you realize how much the car depends on it.
fhood 8y ago
Take the hood off, bring a cooler of ice water, don't get stuck in traffic, stop every 10-15 minutes to cool off. Problem solved.
- maxxxxx 8y ago
  I had to do this with my first car which had a leaky cooler :-). Always had a bottle of water with me.
eecc 8y ago
Used to have an Alfa Romeo 180 boxer engine. Made a weird ratchety noise but it was quite fun to ride. Besides the obvious overhead of multiple cam shafts, synchronization and so on, what do you think of this engine?

dsfyu404ed 8y ago

I'm not seeing how crank and cam specs significantly affect cooling at idle all else being equal. Any cooling system that can work under load will be fine at idle. Edit: For something like a race-car that's trying to minimize weight/power loss by running the minimum radiator/fan necessary and depending on airflow from movement (or rely on the fact that you're only running 1/4mi at a time) I can understand. Still, that's a cooling system sizing issue, not a cam or crank issue. A street going vehicle isn't going to have a cooling system that's sized within a hair of inadequate like that. Power output (and heat generated) at/near idle should be fairly constant regardless of cam and if it's not the higher power output cam profiles will probably have lower power output at/near idle (this depends a lot on the engine, some engines force you to choose where you want your power, some are hard to throw "too much cam" at). No matter how you cut it only so much air can get passed a closed throttle and that amount of air only corresponds to a certain amount of fuel, that puts an upper bound on heat generated at idle. I can see how adding forced induction could significantly affect heat generated at idle but even then, if everything is sized properly it shouldn't be much of an issue. This place is really turning into Reddit where you get down-voted for questioning anyone who sounds knowledgeable.

maxxxxx 8y ago
Cars depend on air moving through the cooling system under load which means it's at speed. Cooling at idle can be a big problem for high performance cars. Going to the extreme, F1 cars have to be super careful not to overheat when stopped.
- justin66 8y ago
  > Cooling at idle can be a big problem for high performance cars. Or any air cooled car ever made. But the reality is that in a lot of designs, idling will test the effectiveness of the cooling system more than driving the car at speed. (Adding power only exacerbates such a problem. The OP completely fails to understand this) It's much less of a problem than it used to be, with lots of cars including electric fans to help out the radiator, but it used to be standard to see a warning in the owner's manual about temperatures increasing in slow traffic or at idle.
  - maxxxxx 8y ago
    "Or any air cooled car ever made." Are there still any being built? I thought the 911 was the last holdout until they also switched to water cooling. "with lots of cars including electric fans to help out the radiator," I had that fan breaking once in my Miata and temperatures went into the red really quickly in LA rush hour.
    - justin66 8y ago
      They switched the 911 over to water-cooled in the late nineties, yes. Prior to that, Porsche got the idle temp problem somewhat under control using powerful electric fans positioned in front of some of the oil coolers, but there's essentially no reliable way to cool four-valve cylinder heads with a purely air-cooled engine (the 959 used separate water cooling just for the heads), so they decided the whole thing was a performance dead end. The air-cooled 911 Turbo did get up above 400hp with two-valve heads before the change, though. > I had that fan breaking once in my Miata and temperatures went into the red really quickly in LA rush hour. No doubt. Once you train yourself to hear that fan, you realize how much the car depends on it.

fhood 8y ago

Take the hood off, bring a cooler of ice water, don't get stuck in traffic, stop every 10-15 minutes to cool off. Problem solved.

maxxxxx 8y ago
I had to do this with my first car which had a leaky cooler :-). Always had a bottle of water with me.

eecc 8y ago

Used to have an Alfa Romeo 180 boxer engine. Made a weird ratchety noise but it was quite fun to ride. Besides the obvious overhead of multiple cam shafts, synchronization and so on, what do you think of this engine?