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1963 Ford F350 with Detroit 453 conversion spotless MUST SEE!!!

Posted By LargeCar3406 Sunday, June 27, 2010 7:57 AM
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1963 Ford F350 with Detroit 453 conversion spotless MUST SEE!!!

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Geoff Weeks
 Posted Thursday, July 01, 2010 3:06 PM
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The 6-71 and 6-110 (roots type) share the same size blower... the -110 turns it faster then the -71, The -110 has bigger bearings and gears on it but the same lobes and case size.
Bill White
 Posted Thursday, July 01, 2010 2:58 AM
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Positive-displacement superchargers are usually rated by their capacity per revolution. In the case of the Roots blower, the GMC rating pattern is typical. The GMC types are rated according to how many two-stroke cylinders, and the size of those cylinders, it is designed to scavenge. GMC has made 2-71, 3-71, 4-71, and the famed 6-71 blowers. For example, a 6-71 blower is designed to scavenge six cylinders of 71 cubic inches each and would be used on a two-stroke diesel of 426 cubic inches, which is designated a 6-71; the blower takes this same designation. However, because 6-71 is actually the engine's designation, the actual displacement is less than the simple multiplication would suggest. A 6-71 actually pumps 339 cubic inches per revolution.

Aftermarket derivatives continue the trend with 8-71 to current 14-71 blowers. From this, one can see that a 6-71 is roughly twice the size of a 3-71. GMC also made -53-cubic-inch series in 2-, 3-, 4-, 6-, and 8-53 sizes, as well as a “V71” series for use on engines using a V configuration.



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Geoff Weeks
 Posted Thursday, July 01, 2010 2:14 AM
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Detroits use a "scavange pump" of the Roots design, not a supercharger. The Roots blower can, if fitted on an engine  that allows the cyl to be filled above atmosphereic pressure become a supercharger. Some of the biggest stationary engines use scavange pumps, some not even connected to the engine directly, but with an external power source. I saw a documentry about a large, double acting stationary engine somewhere in Calif that used external pumps. it fired on both sides of the piston (like double acting steam engines). It had water cooled pistons IIRC and large cross-heads below to connect it to the connecting rod outside the lower cyl chamber. IIRC the rotateing mass of this engine was measured in tons! Again, going from memory it had external scavange and coolant pumps that were driven independant of the engine itself.
Geoff Weeks
 Posted Thursday, July 01, 2010 1:49 AM
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I don't have the timeing "map" for the newer engines. I believe they raise the ports a bit (keeps the intake open longer) and can modife the exhaust timeing a bit. With the higher air box pressure, the scavangeing is better. Most of the power gained on the turbo engines is due to the bypass blower, the bypass opens and unloads the blower which draws considrable hp from the engine. The real problem is: it is hard to get all the scavangeing done in the short time the piston is near the bottom of the cyl. If you keep the exh open longer you cut down on the compression (ratio), if you close sooner you trap burned gasses. Same goes with raiseing the (intake) ports, the sooner the ports open (and later they close as this is a funtion of how high in the liner they are) the less piston travel that can produce power or compression.

   The blower is a fixed displacement pump, and contrary to what some believe, if you add a turbo (and increase the air into the blower) you do not relieve the load on the blower, but increase it. To ease the load on the blower, you must releive the pressure across it. It doesn't have to be a large opening, as most of the air will pass right thru the lobes of the blower, but large enough to keep it from biulding pressure across it. Turbo engines also slow the blower speed (different drive gear ratio) compared to non turbos, which helps reduce the power draw on the engine. The blower can provide enough air for starting and low speed, and is supplamented at higher speed and fuel settings by the turbo.

  I once pulled one airbox cover on a 6-71 and started it. It will run with one cover off, which shows how much air the blower does move. I'm not saying it had enough air to run down the road, but enough to run in the shop.

  An intresting sidde note: The 6-71 and 6-110 share the same blower (although the 110's use larger bearings and gears)... the way that is possable is the 110 turns the blower faster (and being a fixed displacement pump) and it moves more air to meet the 110s needs.
Thursday, July 01, 2010 1:55 AM by Geoff Weeks
Wolfcreek_Steve
 Posted Wednesday, June 30, 2010 6:32 PM
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Geoff Weeks (6/30/2010)
On a Detroit the airbox is above atmosphere, but the cyl isn't due the the port and valve timeing. The intake timeing is fixed by the port placement, the exh by the cam. In most cases the intake ports close before the exhaust valves so the cyl will not be above atmospheric pressure. so by definaition, it is not supercharged as the cyl isn't above outside pressure.


This what I thought. When a turbo is added, do they change the valve timing, move the ports to get more air into the cylinder?


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Steve Peterson
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Geoff Weeks
 Posted Wednesday, June 30, 2010 4:51 PM
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  • They ( small, crankcase scavanged 2 strokes)use the crankcase area under the piston to pump the mixture into the cyl... when the piston goes up the area under the piston gets larger,drawing in a fresh charge to the crankcase, when the piston goes down, the crankcase is pressureized by the decrease in volume, when the rings pass the intake ports the mixture can move into the cyl, force the remaining spent gases out the exh port.
On a Detroit the airbox is above atmosphere, but the cyl isn't due the the port and valve timeing. The intake timeing is fixed by the port placement, the exh by the cam. In most cases the intake ports close before the exhaust valves so the cyl will not be above atmospheric pressure. so by definaition, it is not supercharged as the cyl isn't above outside pressure.
Bill White
 Posted Wednesday, June 30, 2010 4:49 PM
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Big diff. in a gas mtcy engine and DD Richard, That information was from a DD site. Take care....Bill


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Richard
 Posted Wednesday, June 30, 2010 4:17 PM
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If a two stroke engine cannot naturally aspirate, how did all those 2 stoke motorcyles work that I rode in the 1970's  without a blower?

Life  is like a roll of toilet paper the closer  you get to the end, the faster it goes!  Enjoy each day.
Bill White
 Posted Wednesday, June 30, 2010 10:39 AM
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Junkmandan,

 

Here is how a dd 2 stroke works.

All 71 series engines utilize uniflow scavenging, where a gear-driven Roots type blower mounted to the exterior of the engine provides intake air through cored passages in the engine block and ports in the cylinder walls at slightly greater than atmospheric pressure.  The engine exhausts through push-rod operated poppet valves in the cylinder head(s), with either two or four valves per cylinder.  Unit fuel injection is employed, one injector per cylinder, with no high fuel pressure outside of the injector body.  The injectors are cycled from the same camshaft responsible for opening the exhaust valves.
a two stroke Diesel engine cannot naturally aspirate (draw in) intake air, a blower is necessary to provide sufficient air to scavenge exhaust gasses from the cylinders and support combustion.


Bill



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Wolfcreek_Steve
 Posted Wednesday, June 30, 2010 6:53 AM
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Think of it as an exhaust scavenging pump, that is its actual use on a Detroit. IMO

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Steve Peterson
Central Wisconsin

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