| [GMCnet] Differences between motorhome and car engines? [message #240873] |
Sat, 22 February 2014 15:29  |
glwgmc
Messages: 1014
Registered: June 2004
Karma:
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Senior Member |
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Hi Darryl,
Based on my experience with them I think all you need to do is tell them it is for a motorhome. They say they do different things internally for motorhome and marine engines plus a different cam for the motorhome application. While there seems to be some differences of opinion on this forum, I found advancing the cam timing four degrees did a good job of lowering the RPMs at which peak torque occurs. Our Royale with the new S&J 455 engine and our Clasco with the stock 455 engine are both geared exactly the same but the Royale seems less labored and more responsive on all kinds of terrane. When asked, S&J supplied a double roller cam gear and chain that could be set at four degrees advanced, zero or four degrees retarded at no additional cost. Most sources I have consulted agree that most traditional engines made after 1971 will benefit from four degrees advance on the cam timing at lower RPMs such as we run in our GMCs because of the need to retard cam timing to meet the
constantly changing emission standards in that era. The racer guys sometimes say retarding the cam timing four degrees will move the peak torque RPM up to the range where they normally run. Some on this forum say it doesn't matter but my experience with the original engine in the Royale (a strong 455 that had been dyno tuned), the stock engine in the Clasco, and this new engine in the Royale suggest it does make a real difference in our application.
Similarly, there seems to be a difference of opinion on this forum about the benefits from the Mondello oil restrictors and/or the Mondello high volume normal pressure oil pump. I asked them to install the oil restrictors (which they did for $125) and I purchased the Mondello oil pump and bolt on pick up tube/screen. They were willing to do a roller cam for $1800 additional as I recall but did not push doing so on these engines. I elected to stay with the flat tappet cam and use GM EOS to make up for any lack of ZDDP in many of the current oils. After lots of research I also elected to stay with a Dick Patterson carb and HEI distributor instead of EFI.
So far, all of these things seem to be working harmoniously together but we won't really know how well for another, oh, say 75,000 to 100,000 miles (grin). Hope this helps.
Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR
Visitors always welcome!
glwork@mac.com
http://jerrywork.com
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Message: 13
Date: Sat, 22 Feb 2014 12:40:32 -0600
From: Darryl Meyers <hospacctg@att.net>
Subject: [GMCnet] Differences between motorhome and car engines?
To: gmclist@temp.gmcnet.org
Message-ID: <3acdc.5308ef1f@gmc.mybirdfeeder.net>
Content-Type: text/plain; charset="ISO-8859-15"
OK, I've pretty much made the decision to replace my engine with a "remanufactured" engine. I'll get on the phone Monday to S&J and maybe Motorworks (Thanks Karen and Jerry for your comments). If anyone has any other rebuilders they have had a good experience with I'd like to hear from you.
What is different about the 403/455 engines we use in the motorhome and the same engines in the Toronado and other automotive applications? I understand the cam is different; what is the difference? Anything else? What do I need to ask for to make sure the engine is set up properly for the motorhome?
--
Darryl Meyers
1978 Eleganza II
El Dorado Hills, CA
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Jerry & Sharon Work
78 Royale
Kerby, OR
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