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Thread: Poor Performance When Hot

  1. #11
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55 Tony View Post
    It's more like when hot, it runs like it did when I had a c/r of about 7:1 (1978 smog motor) and a smaller cam, instead of now close to 10.5:1 with a larger roller cam (not counting when it's not too hot) Maybe even more of a difference.
    Without some data on performance, it's pure speculation as to how much power you're losing. The hotter and less dense the air is, the less power you'll get.

    I don't know about the hotter the engine the better, that's great for efficiency, but not for HP.
    So for a given amount of fuel, and a given engine, you don't think higher efficiency gives you more power? Really? Increased compression ratio increases efficiency with the same amount of air and fuel. Does it increase power?

    "In general terms, the larger the difference in temperature between the hot source and the cold sink, the larger is the potential thermal efficiency of the cycle. On Earth, the cold side of any heat engine is limited to being close to the ambient temperature of the environment, or not much lower than 300 kelvins, so most efforts to improve the thermodynamic efficiencies of various heat engines focus on increasing the temperature of the source, within material limits. The maximum theoretical efficiency of a heat engine (which no engine ever attains) is equal to the temperature difference between the hot and cold ends divided by the temperature at the hot end, all expressed as absolute temperatures (in kelvins)."
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  2. #12
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    Of course there are many practical reasons not to run the engine as hot as possible. First thing, engines aren't built to do this, they are built to run correctly at the temperatures we normally see.

    The guys that run Pro Stock and similar naturally aspirated classes at the drag strip typically use a chiller to circulate 40°F. water through the cooling system between runs. The engine typically finishes a run at 160° or so. Running the engine this cool lets them run a bit harder (maybe use a little more timing etc.) without detonation.

    But the biggest thing is just the weather. Power level varies proportionally with intake air density - barometric pressure, temperature, and humidity. Usually the air density for a given location varies about 10% or so from winter to summer.


    The difference between a very low compression BBC and a high compression BBC is far more than 10% - meaning there is something else going on.

  3. #13
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    I remember seeing a guy pull a quick connect on his 6.90 1/8 mile Q-jet 350 dumping 220 degree water on the ground and pouring cool water in between passes. A lot of effort but that's what it took to run the numbers he did. Forecast here for weekend are for temps around the century mark with humidity, was planning on a race weekend myself but I think I pass.

  4. #14
    Registered Member chasracer's Avatar
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    Well, looking at your pic I see a few things. One is that we are stuffing a BBC in where a mouse used to live. The engine compartment on these cars while looking like a huge tin can is actually pretty bad about air flow over and around the engine. A BBC on average is simply going to make more hp per cubic inch as the heads are certainly more efficient than those of a mouse motor. And in turn you are going to develop more heat. Open that hood just as soon as you get back to the pit area. And if you can make some concessions to getting air through the engine compartment it wouldn't hurt. Next is the trans cooler attached to the front of the radiator. Nothing in particular is wrong with putting it there except if performance is the game then the additional heat from the trans transmitting to the coolant is not helpful. If you can move it somewhere else that would be good. I know your ride is a street/strip vehicle but I can tell you right now that most of us that race do not want to see water temps above 150-155 at the starting line. And while it's not too common anymore as most of us now run alcohol, dumping coolant between runs and refilling was a normal routine. I couldn't see what kind of cooling fan you had but if you have an electric one that can be controlled with an on/off switch that would be good and in between runs, use a garden sprayer to spray water on the radiator to remove temperature. Back when I ran my Chevelle on race gas, making sure the garden sprayer was full and spraying the radiator was one of the race jobs my kids used to be tasked with during an event. Just remember that each run stacks temperature and once the engine is up there on temp (not just coolant temp) it gets harder to dissipate that heat. Try to stay on top of it and see if that doesn't help the performance some.
    Last edited by chasracer; 06-13-2018 at 01:47 PM.
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    I don't know if or how much it helped, but I've heard from more than one person how they used to put bags of ice on the intake manifold for as long as possible before the race or next race. And I don't know if they help any, but they still sell fuel chillers at Summit. A container with a coil that the fuel goes through and filled with ice/ice water. These days I think it's more of a retro thing.

    Another note on efficiency, 14.7:1 a/f ratio is the goal for efficiency without detonation, but down between 10:1 and 11:1 for the most power.

    Bottom line: Efficiency does not = power
    Last edited by 55 Tony; 06-13-2018 at 02:00 PM.
    Tony

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  6. #16
    Registered Member chevynut's Avatar
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    Quote Originally Posted by chasracer View Post
    Well, looking at your pic I see a few things. One is that we are stuffing a BBC in where a mouse used to live. The engine compartment on these cars while looking like a huge tin can is actually pretty bad about air flow over and around the engine. A BBC on average is simply going to make more hp per cubic inch as the heads are certainly more efficient than those of a mouse motor. And in turn you are going to develop more heat. Open that hood just as soon as you get back to the pit area. And if you can make some concessions to getting air through the engine compartment it wouldn't hurt.
    A hot engine compartment has nothing to do with it. He has a cold air intake. The engine temp is staying at a reasonable level and there's no reason a high under-hood temp is going to cause any problems unless it heats up the air in the cold air intake. The engine sees coolant temperature, not engine compartment temperature.

    Next is the trans cooler attached to the front of the radiator. Nothing in particular is wrong with putting it there except if performance is the game then the additional heat from the trans transmitting to the coolant is not helpful.
    Again, it does no harm unless the engine is overheating, which it isn't.


    I know your ride is a street/strip vehicle but I can tell you right now that most of us that race do not want to see water temps above 150-155 at the starting line.
    So why is that? It's because you're generating so much power and 75% of it is lost to the coolant and exhaust. That can cause the coolant to get too hot at the end of the run if the cooling system can't handle it. If the engine could stay at 180-190 all the way, you don't need to worry about engine temp. A hotter engine is more efficient.

    And while it's not too common anymore as most of us now run alcohol, dumping coolant between runs and refilling was a normal routine.
    The engine is creating just as much heat with alcohol as it did with gasoline. So why isn't it common to dump the coolant now? Because it wasn't necessary back in the day either.

    Underhood temperatures have little or nothing to do with engine performance as long as the engine is getting cool air and the coolant temp remains where it should be.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  7. #17
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55 Tony View Post
    I don't know if or how much it helped, but I've heard from more than one person how they used to put bags of ice on the intake manifold for as long as possible before the race or next race. And I don't know if they help any, but they still sell fuel chillers at Summit. A container with a coil that the fuel goes through and filled with ice/ice water. These days I think it's more of a retro thing.
    Think about it...what does a gasoline cooler do? It makes the gas more dense if it makes it to the engine without heating up. All that does is make the charge richer, which you can do with a larger jet size or longer EFI pulse. That cold-can stuff was and still is bogus.

    Another note on efficiency, 14.7:1 a/f ratio is the goal for efficiency without detonation, but down between 10:1 and 11:1 for the most power.

    Bottom line: Efficiency does not = power
    For a given engine making X amount of power, as you increase efficiency it makes more power. Simple mathematical fact. Higher compression makes an engine more efficient, therefore it increases power. A turbocharger utilizes otherwise wasted exhaust heat to force more air into the engine, thereby increasing it's efficiency and making more power. Don't know why that's so hard to understand. You're confusing fuel consumption with efficiency. Efficiency is how well the engine uses the fuel that's delivered to it. Higher efficiency for a given amount of fuel means more power.
    Last edited by chevynut; 06-13-2018 at 02:56 PM.
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

  8. #18
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    Well will someone tell me if my cold air intake is nice, looks dumb but works, or other opinions. It started out as I think a Cadillac housing with a tiny little snout. I made it much much larger. I could use a repainting, it's been through a lot. The titainium alloy flex part is actually very hard to bend, oh and it's 4" diameter. And check out that wing nut on top, surely someone knows what that was at one time.
    Tony

    1955 Bel Air Sport Coupe

  9. #19
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    Quote Originally Posted by chevynut View Post
    Think about it...what does a gasoline cooler do? It makes the gas more dense if it makes it to the engine without heating up. All that does is make the charge richer, which you can do with a larger jet size or longer EFI pulse. That cold-can stuff was and still is bogus.
    Another note on efficiency, 14.7:1 a/f ratio is the goal for efficiency without detonation, but down between 10:1 and 11:1 for the most power.

    Bottom line: Efficiency does not = power[/QUOTE]

    For a given engine making X amount of power, as you increase efficiency it makes more power. Simple mathematical fact. Higher compression makes an engine more efficient, therefore it increases power. A turbocharger utilizes otherwise wasted exhaust heat to force more air into the engine, thereby increasing it's efficiency and making more power. Don't know why that's so hard to understand. You're confusing fuel consumption with efficiency. Efficiency is how well the engine uses the fuel that's delivered to it. Higher efficiency for a given amount of fuel means more power.[/QUOTE]

    You evidently do not understand what I wrote about air/fuel ratio. Also, a turbo does not use exhaust heat to force more air, it uses the flow of the exhaust top power itself. Don't some have intercoolers? That's because heat is bad. If the turbo runs cooler it works better.
    Tony

    1955 Bel Air Sport Coupe

  10. #20
    Registered Member chevynut's Avatar
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    Quote Originally Posted by 55 Tony View Post
    Well will someone tell me if my cold air intake is nice, looks dumb but works, or other opinions..... The titainium alloy flex part is actually very hard to bend, oh and it's 4" diameter.

    Personally I think it looks fine, but I would have used regular tubing instead of that corrugated stuff for the actual hose. Are you sure that's titanium? Why would it need to be?
    56 Nomad, Ramjet 502, Viper 6-speed T56, C4 Corvette front and rear suspension


    Other vehicles:

    56 Chevy 2-door BelAir sedan
    56 Chevy 210 4-door sedan
    57 Chevy 210 4-door sedan
    1962 327/340HP Corvette
    1961 Willys CJ3B Jeep
    2001 Porsche Boxster S
    2003 Chevy Silverado 2500 HD Duramax
    2019 GMC Sierra Denali Duramax

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