Water pump bypass hose?
#2
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I'm sure that the more qualified experts will jump in here, but I always assumed that it was more cooling directed through the Winters high-rise manifold used for the L79/L76 engines to the heads to help with predetonation from the higher compression ratio, due to the domed pistons.
Last edited by Easy Rhino; 10-22-2016 at 06:14 PM.
#3
Melting Slicks
To my knowledge (which is quite limited) '65 didn't have a 350hp motor, they didn't come out 'til '66. That said, all 350hp (L-79) motors have that by pass.
Gary
Gary
#4
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The bypass hose is there to prevent water pump cavitation at high rpm.
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Oddly, that meant you could get six different engines in the '65: 250, 300, 350, 365, 375 HPs, and the big block 396.
It was the last year for the L84 (771 total), the only year for the 396, and I thin the last year for the L76.
Last edited by Easy Rhino; 10-22-2016 at 06:25 PM.
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Mike, I have no idea (I'm just quoting other experts), but the OP's question got me interested, and an internet search says that the real name and purpose of the bypass hose is a closed thermostat bypass hose.
As far as cavitation goes, it is not clear to me (as someone who passed thermodynamics in school) why the L79 would be more prone to cavitation than the 250/300HP versions, as they had the same rpm limits. But I could be missing something, like if the L79 water pump is a larger flow cross-section over the 250/300 version.
Kevin
As far as cavitation goes, it is not clear to me (as someone who passed thermodynamics in school) why the L79 would be more prone to cavitation than the 250/300HP versions, as they had the same rpm limits. But I could be missing something, like if the L79 water pump is a larger flow cross-section over the 250/300 version.
Kevin
Last edited by Easy Rhino; 10-22-2016 at 06:38 PM.
#7
Melting Slicks
Although not what the OP asked about, the L79 was introduced in the 1965 Corvette.
Oddly, that meant you could get six different engines in the '65: 250, 300, 350, 365, 375 HPs, and the big block 396.
It was the last year for the L84 (771 total), the only year for the 396, and I thin the last year for the L76.
Oddly, that meant you could get six different engines in the '65: 250, 300, 350, 365, 375 HPs, and the big block 396.
It was the last year for the L84 (771 total), the only year for the 396, and I thin the last year for the L76.
On topic, I do believe that ALL aluminum manifold motors did have that bypass. Am I wrong again?
Gary
Last edited by Gary's '66; 10-23-2016 at 12:27 AM.
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Hmmm, I was always under the impression that the higher horse powered small blocks were only available in a solid lifter 365hp and up in '65 then, then in '66 horsepower was lowered in when hydraulic lifers were used bringing the horsepower down to 350. Guess I learned something.
On topic, I do believe that ALL aluminum manifold motors did have that bypass. Am I wrong again?
Gary
Gary
On topic, I do believe that ALL aluminum manifold motors did have that bypass. Am I wrong again?
Gary
Gary
Chevrolet's engine choice selection for '65 always seemed odd to me.
Last edited by Easy Rhino; 10-22-2016 at 06:47 PM.
#9
Race Director
From the archives. https://www.corvetteforum.com/forums...-question.html
Mike has always maintained this position throughout the years. Many others have agreed. Probably the right answer.
Larry
Mike has always maintained this position throughout the years. Many others have agreed. Probably the right answer.
Larry
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From the archives. https://www.corvetteforum.com/forums...-question.html
Mike has always maintained this position throughout the years. Many others have agreed. Probably the right answer.
Larry
Mike has always maintained this position throughout the years. Many others have agreed. Probably the right answer.
Larry
FWIW, I'm not disagreeing with Mike - he's taught me a lot here. Just trying to keep learning.
#11
Melting Slicks
Although not what the OP asked about, the L79 was introduced in the 1965 Corvette.
Oddly, that meant you could get six different engines in the '65: 250, 300, 350, 365, 375 HPs, and the big block 396.
It was the last year for the L84 (771 total), the only year for the 396, and I thin the last year for the L76.
Oddly, that meant you could get six different engines in the '65: 250, 300, 350, 365, 375 HPs, and the big block 396.
It was the last year for the L84 (771 total), the only year for the 396, and I thin the last year for the L76.
Gary
Last edited by Gary's '66; 10-22-2016 at 09:12 PM.
#12
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Oh, that's okay. I am not correct The 250HP engine was NOT available in '65. My turn under the chair.
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From the archives. https://www.corvetteforum.com/forums...-question.html
Mike has always maintained this position throughout the years. Many others have agreed. Probably the right answer.
Larry
Mike has always maintained this position throughout the years. Many others have agreed. Probably the right answer.
Larry
Quoted from Hot Rod Magazine's Pit Stop with Marlan Davis:
"Theoretically, a water pump bypass hose serves two functions: it promotes quicker warm-up on cold-start, and helps prevent water pump impellor cavitation. Although most small-block Chevys have internal water pump bypass passages, the big-blocks do not, so in theory an external bypass hose is required. However, there are two workarounds that should let you slide by without connecting the bypass hose. First, if coolant always circulates through the heater core whether the heater is on or off (this is the case if there is no shutoff or vacuum-actuated valve mounted in-line on the heater transfer hoses or screwed into the intake manifold), the constant circulation pathway should be sufficient to accomplish the bypass function as well. Alternatively, you can experiment by drilling several small 1/8-inch holes in the thermostat's mounting flange underneath the water outlet housing.
Says to promote quicker warm up and help prevent pump cavitation which is what I indicated in the link you posted from several years ago. What wasn't stated in that quote was that the OEM SB's that had the by-pass fitting in the water pump also had the by-pass in the leg of the pump plugged to prevent it from flowing coolant.
#17
Safety Car
The bypass hose is there to prevent water pump cavitation at high rpm.
In addition to this, there is the internal bypass on the pump leg into the block. I can't say for sure if an engine originally equipped with external bypass had the internal bypass plugged, but I can say that mine did not. Why would Chevrolet plug the internal bypass on engines equipped with external bypass. It would be defeating a redundant safety control for no good reason.
Last edited by 65tripleblack; 10-23-2016 at 12:33 PM.
#18
Safety Car
Since everyone seems to have their own opinion, let me insert one engineering fact. We're talking about a centrifugal pump. Cavitation happens on centrifugal pumps when the suction flow is insufficient. Bubbles "explode" on the low pressure side of the impeller causing metal removal. If you throttle the discharge, cavitation does not occur. At extremely low flows vs high impeller rpm, you may get "surging" from instability, that isn't the issue here.
I can't accept cavitation as an issue on these engines.
What does make sense is controlled warm up with different metal expansion rates. The ability to flow more coolant with a given standard pump to add heat to the runners to evaporate an increasing fuel air mixture with high rpm usage. More uniform intake temperature control to prevent exhaust passage burn through as aluminum will melt at a lower temperature than cast iron. More accurate intake temperature control to aid in controlling F/A ratio to promote better controlled combustion at higher CRs.
Aluminum is used simply to reduce weight. Modifications from standard CI configuration are simply to make it last longer under heavy use. You get the same performance with CI intakes and do not need the modifications, but you loose the weight reduction.
I can't accept cavitation as an issue on these engines.
What does make sense is controlled warm up with different metal expansion rates. The ability to flow more coolant with a given standard pump to add heat to the runners to evaporate an increasing fuel air mixture with high rpm usage. More uniform intake temperature control to prevent exhaust passage burn through as aluminum will melt at a lower temperature than cast iron. More accurate intake temperature control to aid in controlling F/A ratio to promote better controlled combustion at higher CRs.
Aluminum is used simply to reduce weight. Modifications from standard CI configuration are simply to make it last longer under heavy use. You get the same performance with CI intakes and do not need the modifications, but you loose the weight reduction.
Last edited by pop23235; 10-23-2016 at 01:52 PM.
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#20
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Cavitation happens on centrifugal pumps when the suction flow is insufficient. Bubbles "explode" on the low pressure side of the impeller causing metal removal. If you throttle the discharge, cavitation does not occur. At extremely low flows vs high impeller rpm, you may get "surging" from instability, that isn't the issue here.
I can't accept cavitation as an issue on these engines.
What does make sense is controlled warm up with different metal expansion rates. T