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| [GMCnet] 455 vs 403?? [message #294487] |
Tue, 26 January 2016 16:24  |
Tony
Messages: 59
Registered: January 2016
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Is there a significant difference between these two engines? Enough that I
should avoid a 403? Most of the GMC's I find have the 455, but a few have
403cid motors. The only thing I was thinking is a bit less punch, parts
availability but wondered if the motor/trans were different (good or
bad??).
Loving this group. Everyone is incredibly generous with knowledge and
polite.
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--Tony
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| Re: [GMCnet] 455 vs 403?? [message #294505 is a reply to message #294487] |
Tue, 26 January 2016 19:57  |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
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The most likely numbers I've seen show the 403 gives up only about 10 horsepower and 10 foot/pounds of torque to its big brother. Being lighter is an advantage (though small), and it's not quite as tall so you have a little more flexibility in air cleaners with a 403. I'm very (!) happy with my 403, and know it's quicker than any of the 455 GMCs I've driven, though it also has a Holley carb, Thorley headers, a 3" exhaust and 3.42 gearing. But either way, you're going to have more than enough power to pull the coach, and will get 9-10mpg.
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] 455 vs 403?? [message #294506 is a reply to message #294505] |
Tue, 26 January 2016 20:19 |
Hal StClair
Messages: 971
Registered: March 2013
Location: Rio Rancho NM
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I 'had' a 403 in our 1977 Royale and have a 455 in another 1977 Royale. The 403 had a 3.55 and a set of headers, the 455 has a 3.23 and stock exhaust. The 403 would get about 2 mpg better milage and out pulled the 455. Just my observation.
BTW, the 6.5 TD seems to get 35% better economy and out pulls the 403 quite dramatically.
Hal
"I enjoy talking to you. Your mind appeals to me. It resembles my own mind, except you happen to be insane."
1977 Royale 101348,
1977 Royale 101586, Diesel powered,
1974 Eagle Bus 45',w/slideout,
Rio Rancho, NM
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| Re: [GMCnet] 455 vs 403?? [message #294507 is a reply to message #294506] |
Tue, 26 January 2016 20:29 |
Mr ERFisher
Messages: 7117
Registered: August 2005
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Read here
http://gmcmotorhome.info/engine.html#403_VS_455
On Tuesday, January 26, 2016, Hal StClair
wrote:
> I 'had' a 403 in our 1977 Royale and have a 455 in another 1977 Royale.
> The 403 had a 3.55 and a set of headers, the 455 has a 3.23 and stock
> exhaust.
> The 403 would get about 2 mpg better milage and out pulled the 455. Just
> my observation.
> BTW, the 6.5 TD seems to get 35% better economy and out pulls the 403
> quite dramatically.
> Hal
> --
> 1977 Royale 101348,
>
> 1977 Royale 101586,
>
> 1974 Eagle Bus 45',w/slideout
>
> _______________________________________________
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Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
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Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: [GMCnet] 455 vs 403?? [message #294509 is a reply to message #294487] |
Tue, 26 January 2016 20:56 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
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Tony wrote on Tue, 26 January 2016 15:24Is there a significant difference between these two engines? Enough that I
should avoid a 403? Most of the GMC's I find have the 455, but a few have
403cid motors. The only thing I was thinking is a bit less punch, parts
availability but wondered if the motor/trans were different (good or
bad??).
Loving this group. Everyone is incredibly generous with knowledge and
polite.
--
--Tony
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Unsubscribe or Change List Options:
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I've driven both and I think the variations between coaches is bigger than just the engine itself. The 403 does feel happier at higher RPM's and I think after all the years, the 403's are a bit more trouble free.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] 455 vs 403?? [message #294516 is a reply to message #294509] |
Tue, 26 January 2016 22:46 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
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We know that the 403 pulls better milage than the 455.
I know Miguel at MGM-GMC runs the 3.70 gears and headers and feels it stays
up with the 455 in majority of the cases.
On Tue, Jan 26, 2016 at 6:56 PM, Bob de Kruyff wrote:
> Tony wrote on Tue, 26 January 2016 15:24
>> Is there a significant difference between these two engines? Enough
> that I
>> should avoid a 403? Most of the GMC's I find have the 455, but a few
> have
>> 403cid motors. The only thing I was thinking is a bit less punch, parts
>> availability but wondered if the motor/trans were different (good or
>> bad??).
>>
>> Loving this group. Everyone is incredibly generous with knowledge and
>> polite.
>>
>> --
>> --Tony
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
> I've driven both and I think the variations between coaches is bigger than
> just the engine itself. The 403 does feel happier at higher RPM's and I
> think after all the years, the 403's are a bit more trouble free.
> --
> Bob de Kruyff
> 78 Eleganza
> Chandler, AZ
>
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Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] 455 vs 403?? [message #294588 is a reply to message #294525] |
Thu, 28 January 2016 01:55 |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
Karma: 11
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markbb1. As to your question about the trans power drive. And my remark below on that topic. Back before Jim K at Applied GMC. came out with his 3:55, 3:70, and 4:10. We didn't have much for options with final drive ratios. So the power drive offered an option to help reduce luging of the engines. Both the 403, and 455. Plus the power drive is cheap to install. The power drive increases the engine speed but not the trans. Thus you're able to produce more torque to the trans. This extra load,that you can apply to the trans. This increase will produce extra heat in the trans. But the trans oil pump isn't turning any faster. Thus not pumping more oil to the trans cooler. ( I could go into relief valves, and bypases. But that's another discussion. ) Changing the final drive will reduce the torque load on the trans, and engine together. My 78 Royale, 403, with a 3:70 final drive is among the few GMC's out there that pull heavy loads constantly. I'm talking from 17,000 to 21,000lbs GVW loads. The drivetrain is pure stock except for the 3:70 final drive. No headers, 3inch exhaust, side vents, extra coolers, and I only use 87 octane ethanol. When I put the 3:70 in. My engine, trans, and final drive temps went down. The mileage went up. My milage at the 17,000lbs level is generally at the 10.2 MPG. Went thru the Eisenhower tunnel West of Denver ( 19,000lbs at 11,000 feet above sea level. No problem.) Then down to Death Valley, and Lake Havasu City. This was all in Aug of 2007. Ask anyone that goes to the GMCMI Rallies. They can vouch to this. As to Manny, Dick Paterson, and Jim K at Applied. The same tune will be played by all. Bottom line on the power drive. Better than nothing, it's cheap, but I wouldn't do it. I Forgot. Trans fluid life. Heat is death to the fluid. Mileage isn't as much of an issue. I change mine every 9 to 12,000 miles. As to the average GMC. 25,000 mile is a good limit without towing. Trans fluid is CHEAP. A trans rebuild isn't.
Bob Dunahugh.78 Royale
From: yenko108@hotmail.com
To: gmclist@list.gmcnet.org
Subject: RE: 455 vs 403??
Date: Wed, 27 Jan 2016 01:33:19 -0600
I've had both. Pull an enclosed car hauler with a GVW of 21,000 lbs with my 403 - 78 Royale. Or with Linda's 5,000 lbs lift van behind. We're at 17,000 GVW. Last 3700 mile trip. Averaged 10.2 MPG's. Pure stock except for Jim K's 3:70 final drive. As to the power drive conversion in the transmission. I would never consider putting one in for any reason. As they don't reduce the torque load on the trans. The thing is that the 77, and 78's are the better GMC's. Because they're the one's with all of the latest updates that GM had developed at that time. Plus GM was using Inron paint in those years. Extremely durable. The 78 that I just bought. I washed it. And I can see details in the reflection.Bob Dunahugh.2-78 Royale's1- 73 GMC
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| Re: [GMCnet] 455 vs 403?? [message #294592 is a reply to message #294588] |
Thu, 28 January 2016 03:55 |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Bob,
HUH?
http://www.mannystransmission.biz/tranny/
Scroll down to the bottom.
Regards,
Rob M.
The Pedantic Mechanic
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Bob Dunahugh
Sent: Thursday, January 28, 2016 6:55 PM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] 455 vs 403??
markbb1. As to your question about the trans power drive. And my remark below on that topic. Back before Jim K at Applied GMC. came
out with his 3:55, 3:70, and 4:10. We didn't have much for options with final drive ratios. So the power drive offered an option to
help reduce luging of the engines. Both the 403, and 455. Plus the power drive is cheap to install. The power drive increases the
engine speed but not the trans. Thus you're able to produce more torque to the trans. This extra load,that you can apply to the
trans. This increase will produce extra heat in the trans. But the trans oil pump isn't turning any faster. Thus not pumping more
oil to the trans cooler. ( I could go into relief valves, and bypases. But that's another discussion. ) Changing the final drive
will reduce the torque load on the trans, and engine together. My 78 Royale, 403, with a 3:70 final drive is among the few GMC's
out there that pull heavy loads constantly. I'm talking from 17,000 to 21
,000lbs GVW loads. The drivetrain is pure stock except for the 3:70 final drive. No headers, 3inch exhaust, side vents, extra
coolers, and I only use 87 octane ethanol. When I put the 3:70 in. My engine, trans, and final drive temps went down. The mileage
went up. My milage at the 17,000lbs level is generally at the 10.2 MPG. Went thru the Eisenhower tunnel West of Denver (
19,000lbs at 11,000 feet above sea level. No problem.) Then down to Death Valley, and Lake Havasu City. This was all in Aug of 2007.
Ask anyone that goes to the GMCMI Rallies. They can vouch to this. As to Manny, Dick Paterson, and Jim K at Applied. The same tune
will be played by all. Bottom line on the power drive. Better than nothing, it's cheap, but I wouldn't do it. I Forgot. Trans fluid
life. Heat is death to the fluid. Mileage isn't as much of an issue. I change mine every 9 to 12,000 miles. As to the average GMC.
25,000 mile is a good limit without towing. Trans fluid is CHEAP. A trans
rebuild isn't.
Bob Dunahugh.78 Royale
From: yenko108@hotmail.com
To: gmclist@list.gmcnet.org
Subject: RE: 455 vs 403??
Date: Wed, 27 Jan 2016 01:33:19 -0600
I've had both. Pull an enclosed car hauler with a GVW of 21,000 lbs with my 403 - 78 Royale. Or with Linda's 5,000 lbs lift van
behind. We're at 17,000 GVW. Last 3700 mile trip. Averaged 10.2 MPG's. Pure stock except for Jim K's 3:70 final drive. As to the
power drive conversion in the transmission. I would never consider putting one in for any reason. As they don't reduce the torque
load on the trans. The thing is that the 77, and 78's are the better GMC's. Because they're the one's with all of the latest
updates that GM had developed at that time. Plus GM was using Inron paint in those years. Extremely durable. The 78 that I just
bought. I washed it. And I can see details in the reflection.Bob Dunahugh.2-78 Royale's1- 73 GMC
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] 455 vs 403?? [message #294620 is a reply to message #294592] |
Thu, 28 January 2016 11:37 |
powwerjon
Messages: 849
Registered: March 2013
Karma: -2
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Senior Member |
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I also run a 3.21 final and a Manny power drive in my transmission for a 3.67 final. Works great for us and the trans temp very rarely gets above 160 going down the road and the coach and toad weight just over 18.5K pounds going down the road fully loaded. The trans temp will rise a little on long grades such as Hwy 70 over the hill into Las Cruses, NM from the east. It might rise to about 175 to 180. I typically have down shifted into 2nd gear and my speed is right at 50 mph at just over 3000 rpm and I am not lugging the motor at any time. I have 2 coolers on the transmission side, the one in the radiator and a large plate style after the radiator cooler. I have a 3.42 final drive in the shop that I am considering installing this coming summer to lower my final ratio to a 3.90 (3.8988). The engine in our coach is 461 cu. in. Jasper RV Olds, back when Jasper was hand building the RV engines in the late 90’s. It has an Accel Gen 6 MPFI system. I have owned both a 403 and a 455 engined coach. The 403 is a big bore short engine which really likes RPM. It was a real dog with the 3.07 gear and would never run well until it reached 75 to 80 MPH which got the engine up into the 2750+ rpm and on the cam. When I install the 3.55 final it would run with any 455 and was ready to rock and roll when you need to pass and I have always run at 64 to 66 MPH on the road. I have got 10+MPG only once in the last 18 years as a GMC owner. It was on my first trip in our new GMC to a club rally in 1998 and it was 10.2 in fairly flat roads no towing, 403 and 3.07 final. I will never get close to 10 MPG as I tow and my GVW is alot more than most of you out there. In flat country with the cruise on at 65 I average probably near 7.5+ MPG. and it is worst in the mountains. I don’t really care about MPG, because it is our home for 4+months out of the year until we bought a home here in Tucson. We put more than 10K miles on our coach year traveling this wonderful country seeing all the things that it has to offer.
J.R. Wright
GMC GreatLaker
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 Buskirk 30' Stretch
1975 Avion (Under Reconstruction)
Michigan, On Location in Tucson
> On Jan 28, 2016, at 2:55 AM, Robert Mueller wrote:
>
> Bob,
>
> HUH?
>
> http://www.mannystransmission.biz/tranny/
>
> Scroll down to the bottom.
>
> Regards,
> Rob M.
> The Pedantic Mechanic
>
>
> -----Original Message-----
> From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Bob Dunahugh
> Sent: Thursday, January 28, 2016 6:55 PM
> To: gmclist@list.gmcnet.org
> Subject: Re: [GMCnet] 455 vs 403??
>
> markbb1. As to your question about the trans power drive. And my remark below on that topic. Back before Jim K at Applied GMC. came
> out with his 3:55, 3:70, and 4:10. We didn't have much for options with final drive ratios. So the power drive offered an option to
> help reduce luging of the engines. Both the 403, and 455. Plus the power drive is cheap to install. The power drive increases the
> engine speed but not the trans. Thus you're able to produce more torque to the trans. This extra load,that you can apply to the
> trans. This increase will produce extra heat in the trans. But the trans oil pump isn't turning any faster. Thus not pumping more
> oil to the trans cooler. ( I could go into relief valves, and bypases. But that's another discussion. ) Changing the final drive
> will reduce the torque load on the trans, and engine together. My 78 Royale, 403, with a 3:70 final drive is among the few GMC's
> out there that pull heavy loads constantly. I'm talking from 17,000 to 21
> ,000lbs GVW loads. The drivetrain is pure stock except for the 3:70 final drive. No headers, 3inch exhaust, side vents, extra
> coolers, and I only use 87 octane ethanol. When I put the 3:70 in. My engine, trans, and final drive temps went down. The mileage
> went up. My milage at the 17,000lbs level is generally at the 10.2 MPG. Went thru the Eisenhower tunnel West of Denver (
> 19,000lbs at 11,000 feet above sea level. No problem.) Then down to Death Valley, and Lake Havasu City. This was all in Aug of 2007.
> Ask anyone that goes to the GMCMI Rallies. They can vouch to this. As to Manny, Dick Paterson, and Jim K at Applied. The same tune
> will be played by all. Bottom line on the power drive. Better than nothing, it's cheap, but I wouldn't do it. I Forgot. Trans fluid
> life. Heat is death to the fluid. Mileage isn't as much of an issue. I change mine every 9 to 12,000 miles. As to the average GMC.
> 25,000 mile is a good limit without towing. Trans fluid is CHEAP. A trans
> rebuild isn't.
> Bob Dunahugh.78 Royale
> From: yenko108@hotmail.com
> To: gmclist@list.gmcnet.org
> Subject: RE: 455 vs 403??
> Date: Wed, 27 Jan 2016 01:33:19 -0600
>
>
>
>
> I've had both. Pull an enclosed car hauler with a GVW of 21,000 lbs with my 403 - 78 Royale. Or with Linda's 5,000 lbs lift van
> behind. We're at 17,000 GVW. Last 3700 mile trip. Averaged 10.2 MPG's. Pure stock except for Jim K's 3:70 final drive. As to the
> power drive conversion in the transmission. I would never consider putting one in for any reason. As they don't reduce the torque
> load on the trans. The thing is that the 77, and 78's are the better GMC's. Because they're the one's with all of the latest
> updates that GM had developed at that time. Plus GM was using Inron paint in those years. Extremely durable. The 78 that I just
> bought. I washed it. And I can see details in the reflection.Bob Dunahugh.2-78 Royale's1- 73 GMC
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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