| [GMCnet] Differences between motorhome and car engines? [message #240873] |
Sat, 22 February 2014 15:29  |
glwgmc
Messages: 1014
Registered: June 2004
Karma: 10
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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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| Re: [GMCnet] Differences between motorhome and car engines? [message #240906 is a reply to message #240873] |
Sat, 22 February 2014 19:50  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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| glwgmc wrote on Sat, 22 February 2014 16:29 |
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.
<snip>
Jerry Work
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Jerry et al,
It was my experience that the peak torque, which always occurs at the crankshaft speed for peak volumetric efficiency, does not change or move with the change of camshaft timing. This is all the same mapped engine and cam we are talking about. The real difference here is I am talking about real numbers and you are thinking about perceived driveability. The two are related but not identical. On the V10, we ran some what we called "thick data". A typical dyno power curve is done at 400 RPM steps. We did the development stuff at 100 and around the torque peak at steps of 50. Only automated controls can do that in a day because it also included spark and fuel loops.
My advice is to talk to the people that ground the cam. They will tell you where to set it. If you have to get keys ground, then do that. (Ground keys are offset to allow more precise cam timing.)
Matt - I still am not used to this keyboard, but we are better.
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Differences between motorhome and car engines? [message #240999 is a reply to message #240873] |
Sun, 23 February 2014 13:47 |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
Karma: 7
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Senior Member |
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I have to disagree with you on that if you are speaking of cam LSA or duration, which most certainly DOES effect peak torque RPM points.
However if you mean advancing/retarding the cam [IE the intake lobe center angle]I agree to a point. Sometimes it does make a big difference in drivability. Advancing usually boosts the responsiveness particularly in low compression smog engines or engines that are a little over cammed. The torque peak may not change all that much but it does seem to move the shape around. Advancing the cam usually raises cranking compression
One thing to check is what LCA the cam is specced at. Some manufacturers build in a certain amount of advance
76 Glenbrook
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