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Old 09-12-2008, 07:02 PM
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bypass tube

On the new edelbrock performer rpm intake manifold it has a coolent passage hole to go to the water pump. On our original intake manifold on the 400ci did not and the water pump hole for the bypass was pluged off. now that we have the hole on the intake manifold should i run the bypass tube? what are the advantages or disadvantages of using the bypass?

Thanks,

Mike

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Old 09-12-2008, 07:15 PM
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Even so I`m not sure, it would seem as if this would be if your not running hoses to the heater core, just as a race engine would do. In the old days we used to rig up stuff from the intake to the water pump since there were no provisions for doing a bypass and making it look neat. But thats how it works for racers on a budget. The SBC has it`s own bypass, and in race conditions it`s blocked off and a couple of small holes are drilled in the thermostat to act as a air bleeder and bypass, this is especially true on the later Vortec blocks being they came without a bypass.
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Old 09-12-2008, 08:23 PM
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Quote:
Originally Posted by SBCfan04
On the new edelbrock performer rpm intake manifold it has a coolent passage hole to go to the water pump. On our original intake manifold on the 400ci did not and the water pump hole for the bypass was pluged off. now that we have the hole on the intake manifold should i run the bypass tube? what are the advantages or disadvantages of using the bypass?

Thanks,

Mike

The bypass is intended to keep coolant circulating when the thermostat is closed to prevent steam pocket formation and to heat the engine up more quickly than would occur if coolant was circulated thru the radiator.

The advantage and disadvantage to plugging it and putting holes in the thermostat are:

Advantage; holes let trapped gasses out, certainly making filling the cooling system a lot simpler and they provide the bypass flow necessary to prevent steam pocket formation before the thermostat opens and major flow starts if no other bypass is present.

Disadvantage; the holes allow a flow thru the radiator which adds warm up time. On my truck, which still has the heater hose and factory internal pump bypass, I also put a couple 1/8 holes in the thermostat to aid filling the radiator. In the cool wet Seattle winter this added 3 miles to the time it takes to get to 180 degrees. The surprise is that a couple 1/8th holes would have that much effect. I put them in the thermostat back when I first built Franken-mouse and was having a hard time cooling it. So I was constantly draining and refilling and I just got tired of the time and effort it took to burp the system. So a couple vent holes went a long way toward gittin' the job done.

Bogie
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Old 09-12-2008, 10:00 PM
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thanks a ton for the info.
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Old 09-15-2008, 05:00 PM
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Disadvantage; the holes allow a flow thru the radiator which adds warm up time. On my truck, which still has the heater hose and factory internal pump bypass, I also put a couple 1/8 holes in the thermostat to aid filling the radiator. In the cool wet Seattle winter this added 3 miles to the time it takes to get to 180 degrees. The surprise is that a couple 1/8th holes would have that much effect. I put them in the thermostat back when I first built Franken-mouse and was having a hard time cooling it. So I was constantly draining and refilling and I just got tired of the time and effort it took to burp the system. So a couple vent holes went a long way toward gittin' the job done.

Bogie[/QUOTE]

Now I know why I can NOT get any heat in the engine in the winter when on the hiway. I end up stopping and ideling for a few min. to let the heater catch up!!!! Lucky it dosent get to cold down here in the desert, or for very long!
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Old 10-03-2008, 01:29 PM
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would there be any bad effects if i didnt run the bypass tube and didnt drill holes in the thermostat? or would i be ok?
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Old 10-03-2008, 08:55 PM
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In the mid to late 70s
on a manual transmission pick-up the heater hoses were routed from the intake>>>to the heater core>>>>and back to the water pump.

On an AT equipped truck----the return hose did not go to the water pump, but directly to the radiator.

Since these trucks had full flow thru the heater at all times (non AC) there was your bypass.

There is a bypass built into the block and water pump on a SBC and it should be sufficient all by itself.

My 454 79 takes FOREVER to warm up and actually never gets all that warm.

Plug the ports in the manifold and water pump, and if your temps do not spike up and down too drastically for the first 15 minutes, you should be okay.

If the temp gage goes all over the place while warming up and takes forever to settle in to operating temps-----install the bypass between the intake and water pump
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Old 10-05-2008, 01:47 AM
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thanks, the truck is actually a 78 gmc jimmy so thats cool.

Thanks for the info,


Mike
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Old 10-06-2008, 11:59 AM
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Quote:
Originally Posted by SBCfan04
would there be any bad effects if i didnt run the bypass tube and didnt drill holes in the thermostat? or would i be ok?
The pump will cavitate as its dead headed. That's to say there is no circulation of coolant into the pump and pressure being held against the cooling passages with no flow. So the impeller is thrashing what coolant is trapped in the pump to froth. Froth will eventually mix with the coolant when the thermostat opens and starts a flow, but now there is a lot of entrapped gasses which reduces the coolant's ability to carry heat. Not to mention the physical beating the impeller, it's shaft and bearings take.

Perhaps more importantly, there is no coolant flow inside the engine while the thermostat is closed and there is no by-pass. The problems form this are that coolant doesn't heat evenly inside the engine there are cool places and super hot places. Within the head there are several of these super hot places around the spark plug, exhaust valve and port that become extremely hot even though the engine is cold This causes the coolant adjacent to these areas to boil. The steam formed, while very hot, does not carry heat from the metal as liquid coolant does, the metal in this area then becomes critically hot. This can and does result in cracking, as the immediate area that is overheated presses against the cooler metal surrounding it which prevents further outward movement, so a crack forms to relieve the strain.

The by-pass whether in the pump as with Chevy, or as a separate circuit, which often flows thru the heater core, provides a coolant circulation within the engine while the thermostat is closed. This prevents the pump from cavitating and frothing the coolant, but more importantly keeps coolant moving over the super heated areas of the head around the spark plug and exhaust valve seat and port preventing the formation of steam pockets that lead to local overheating with resultant cracking of the casting.

The by-pass can be eliminated and the thermostat retained by drilling several holes into the thermostat that will allow coolant to circulate past the thermostat when it is closed. This solves the problem of cavitation with in the pump and provides circulation to prevent the formation of steam pockets, but it adds a new problem. The situation now is that the engine will take considerably longer to warm up as there is cold coolant flowing thru the radiator. Extended warm up means the engine will be on cold start mixture enrichment (choke) longer which puts a great deal of liquid gasoline into the cylinders. This is bad for fuel mileage and emissions, which most hot rodders look upon as abstract problems they're not concerned about, but there are real problems this causes that they are concerned about; these stem from fuel dilution of the oil because the excess liquid fuel being is forced around the piston and the related loss of top end lubrication from the oil being wiped off the walls by this excess fuel, leading to wear of the cylinder-wall, rings, and piston thrust surface. These effects will show up in short and long term consequences, some of which are that the oil will form varnish and sludge from the acids that come from chemical reactions between fuel and oil. The oil starved rings will loose their seal from accelerated wear resulting in lost power and shortened engine life.

Bogie

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Old 10-07-2008, 12:37 AM
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Steam Pockets

Bogie, there's a good article in Dec. 08 CarCraft about the GenI heads from a retired GM engineer, Don Webb. He was in on the ground floor of the GenIII engine design. He explains how GenI heads have 13 steam pocket areas that trap coolant long enough to create bubbles, which causes many different types of cooling problems. When one drop of coolant vaporizes it expands approximately 500 times it's original size, so it's not hard to understand why steam bubbles cause havoc in any cooling system. #1,The 13 steam pockets on the GenI head were a result of attempts to lighten the casting and were caused by different bolt patterns on the ends & on manifold faces. #2,The siamesed exhaust valves created a hot spot on the bridge between the valves. #3,The siamesed intake ports were limited in cross-sectional area by the pushrod and the head bolt between them.
The GenIII head design cured the problem by going from 5 to 4 bolts per cylinder, saved money & created much more space for the free flowing ports. Eliminating the distributor and moving the water crossover to the pump cleaned up the valley and made room for the superior composite inlet manifolds. If you were to cut a GenIII head horizontally to reveal the surface of the water jacket, a perfectly flat surface would be observed. This flat surface allows coolant to flow easily to the ends of the heads and helps eliminate steam bubbles, which vastly improves rapid cooling. This revolutionary yet simple, flat surface helped eliminate pump cavitation and helped allow much-higher-powered engines without having to add cooling capacity. (Mostly quoted from Don Webb's article.)
This Info came from someone asking why GM went from 5 bolts to 4.
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Old 10-07-2008, 03:31 AM
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The bypass is just that, a bypass. You MUST keep the t-stat in if you keep the bypass open. If you don't, the coolant will go to the bypass circuit and not the radiator. The bypass is just a loop of coolant that does not go to the radiator. If you decide to take out the t-stat, then you must plug the bypass circuit.
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Old 10-07-2008, 11:20 AM
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Quote:
Originally Posted by SSedan64
Bogie, there's a good article in Dec. 08 CarCraft about the GenI heads from a retired GM engineer, Don Webb. He was in on the ground floor of the GenIII engine design. He explains how GenI heads have 13 steam pocket areas that trap coolant long enough to create bubbles, which causes many different types of cooling problems. When one drop of coolant vaporizes it expands approximately 500 times it's original size, so it's not hard to understand why steam bubbles cause havoc in any cooling system. #1,The 13 steam pockets on the GenI head were a result of attempts to lighten the casting and were caused by different bolt patterns on the ends & on manifold faces. #2,The siamesed exhaust valves created a hot spot on the bridge between the valves. #3,The siamesed intake ports were limited in cross-sectional area by the pushrod and the head bolt between them.
The GenIII head design cured the problem by going from 5 to 4 bolts per cylinder, saved money & created much more space for the free flowing ports. Eliminating the distributor and moving the water crossover to the pump cleaned up the valley and made room for the superior composite inlet manifolds. If you were to cut a GenIII head horizontally to reveal the surface of the water jacket, a perfectly flat surface would be observed. This flat surface allows coolant to flow easily to the ends of the heads and helps eliminate steam bubbles, which vastly improves rapid cooling. This revolutionary yet simple, flat surface helped eliminate pump cavitation and helped allow much-higher-powered engines without having to add cooling capacity. (Mostly quoted from Don Webb's article.)
This Info came from someone asking why GM went from 5 bolts to 4.
Hey thanks, I hadn't seen that article, so I'll hunt that down. Yeah the Gen I and II engine is very difficult to cool properly and often doesn't take kindly to closing off the bypass even when not operated with a thermostat. Certainly a lot of what I've seen leads back to the problem that you sight from the article. For endurance racing this has been a long standing problem with the SBC to which just about every trick know to man has been tried. But as more and more power was extracted coming into the early 1990s the hand writing was on the wall that the top end cooling problems could no longer be solved with patches and tricks. The SB2 and SB2B heads really did it, the power you can produce with these things simply couldn't be properly cooled. There was no place left to turn but a redesign, and the times were ready to integrate the design for better strength, lower emissions, and higher output with better fuel economy, so we have the new LS family.

Interesting thing I've noted over the years as how Ford and Chevy took different approaches to engine development. The small block Chevy quietly went thru a great number of variations, but these were largely confined to the back room, a few racing teams, and select ,allbeit mostly high end, customers. So when the LS was finally released to production it was pretty close to an optimized design for the imposed constraints. Ford's approach to the Modular V8 was done using production as a beta test lab, the result is for many years there were all sorts of variations put into different models, and the engine's teething problems became a public display of what should have been back room R&D in my opinion. I'm not saying one way is better than the other, but from an expense standpoint it does seem to me that using production as a test facility is rather expensive not only in real dollars, but also in the risk of alienating customers saddled with a problematic purchase. In the end it worked out for Ford but in-between there are some real gems, LOL, of this engine.

Bogie
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