| Re: 455 or 403 in my coach? [message #361982 is a reply to message #361978] |
Tue, 26 January 2021 09:20   |
C Boyd
Messages: 2629
Registered: April 2006
Karma:
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Senior Member |
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Mr. Wood, the 403s I am familiar with belonged to friends that I was helping on. The 403 has larger pistons and a shorter stroke than the 455 and calls for 12* initial timing and a carb with different idle circuits. It doesn’t want to idle like the longer stroke 455 engines at 650 rpm. The idle circuit is the extra stuff we are talking about. I did try to figure out what it does and why but I still am not sure. If engine conditions are at the right temp and all the different components are working correctly it controls the idle speed dashpot when the transmission is in Drive. I also believe it has something to do with controlling the EGR valve which the motorhome does not have. I believe when you stop and transmission is in drive the engine is held at a faster idle and when you put it in park it idles down so you can shut the engine off without dieseling. I know the parts are not easy to test and bout impossible to find. If the only reason is to stop dieseling when you shut engine off I believe you can accomplish that by using the electric dashpot to be active and control idle while running and closing the butterflies completely when turned off as in other GM model cars. I have also used the dashpot to activate with the A/C to increase idle speed with A/C on. As for advise on to keep and use or take it off? Everybody I asked said take it off and turn the engine off while still in drive if dieseling is an issue. In my case the owner wanted it to work so I did the best I could.. if you do decide to take it off, post the parts on the swap meet as I know of a few people that are looking for parts to get theirs working. I’m sorry I’m not much help.
[quote title=JRWood wrote on Mon, 25 January 2021 09:11]
Mr. Boyd, that is an excellent description of all the vacuum operated controls on my 403. It is very original looking. It is a recent purchase but I have worked on a Royale also with a 403. My question; I would like to eliminate all of those devices that are unnecessary ie, thermal vacuum tree, solenoids, hoses, etc. and just have the vacuum advance on the carb ported vacuum and appropriate port for trans modulator. In your opinion, are those factory devices worth retaining? Would they likely even function properly at this age? Is it ok to eliminate them?
C Boyd wrote on Sun, 10 January 2021 12:14Sir, if it is factory OEM.... the steel fuel line from fuel pump to carburetor is routed to the left of the top radiator hose on a 403 and is routed to the right of the radiator hose on a 455. A 403 will have an idle solenoid stop on the carburetor shaft and an extra vacuum tree on drivers side to control the electric solenoid on the front of the drivers side head which is fed from a solenoid bolted on the front of the passenger head.. A 403 and a455 have the same number of detents for valve cover bolts but 403s are only tapped and drilled in every other one. On a 403 it is cast on the side of the block in big numbers. A 455 is a big block and will have a sunk down intake to clear the floor. A 403 is a small block and does not need the lower intake. A 403 has a more noticeable dog leg in the pass exhaust manifold to clear the oil filter and cooler adapter.
C. Boyd
76 Crestmont
East Tennessee
[Updated on: Tue, 26 January 2021 09:23] Report message to a moderator |
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