[GMCnet] Differences between 403 and 455

[Dominik Hertle]

Hello all,

Can anyone sum up the differences between both available engines ?
As I know during the model 1976 model year they changed from the 455 to the 403 engine.
What is the difference in power, economy, reliability, maintenance ?
Should I choose my GMC by the engine in it, or are they about equal in general ?

Thank you all,
Dominik
--
- The good the bad and the ugly and its all me -
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[Hal StClair]

Ouch, you are looking for some heat here.
Both were fine power plants although the 455 was probably a stronger unit. The 403 seems to be a more fuel efficient platform mileage wise and there
are a lot of high mile units with this engine out there. If you are planning to tow with one, the higher torque of the 455 would probably be
advantageous although either will work with the right gearing.
I think the later (1977-78) units with improved a/c might be worth looking at and the 77 came with either engine depending on date of build so you
have a choice of either.
I have two 1977 Royales, one with the 455 and the other HAD a 403. The 403 with 3.55's and headers without running the a/c averaged about 10 mpg, the
455 with 3.21's closer to 8.
JMHO, Hal
--
1977 Royale 101348,

1977 Royale 101586,

1974 Eagle Bus 45',w/slideout

[Robert Mueller]

Domink,

Google is your friend:

http://en.wikipedia.org/wiki/Oldsmobile_V8_engine

http://www.442.com/oldsfaq/ofe403.htm

http://www.442.com/oldsfaq/ofe455.htm

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426

-----Original Message-----
From: Gmclist [mailto:gmclist...@temp.gmcnet.org] On Behalf Of Dominik Hertle
Sent: Friday, June 05, 2015 7:21 AM
To: gmc...@temp.gmcnet.org
Subject: [GMCnet] Differences between 403 and 455

Hello all,

Can anyone sum up the differences between both available engines ?
As I know during the model 1976 model year they changed from the 455 to the 403 engine.
What is the difference in power, economy, reliability, maintenance ?
Should I choose my GMC by the engine in it, or are they about equal in general ?

Thank you all,
Dominik

[gene Fisher]

Read here
http://gmcmotorhome.info/engine.html#403_VS_455

--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html

[Chris Choffat]

--
-Chr$: Perpetual SmartAss
Scottsdale, AZ
77 Ex-Kingsley 455 SOLD!
2010 Nomad 24 Ft TT 390W PV W/MPPT, EV4010 and custom cargo door.

Photosite: Chrisc GMC:"It has Begun" TT: "The Other Woman"

[George Beckman]

USAussie wrote on Thu, 04 June 2015 16:08

> Domink,
>
> Google is your friend:
>
> http://en.wikipedia.org/wiki/Oldsmobile_V8_engine
>
> http://www.442.com/oldsfaq/ofe403.htm
>
> http://www.442.com/oldsfaq/ofe455.htm
>
> Regards,
> Rob M.
> The Pedantic Mechanic
> Sydney, Australia
> AUS '75 Avion - The Blue Streak TZE365V100428
> USA '75 Avion - Double Trouble TZE365V100426
>
>
> -----Original Message-----
> From: Gmclist [mailto:gmclist...@temp.gmcnet.org] On Behalf Of Dominik Hertle
> Sent: Friday, June 05, 2015 7:21 AM
> To: gmc...@temp.gmcnet.org
> Subject: [GMCnet] Differences between 403 and 455
>
> Hello all,
>
> Can anyone sum up the differences between both available engines ?
> As I know during the model 1976 model year they changed from the 455 to the 403 engine.
> What is the difference in power, economy, reliability, maintenance ?
> Should I choose my GMC by the engine in it, or are they about equal in general ?
>
> Thank you all,
> Dominik

The links provide all the details and statistics. I have some gut feeling comments.

I have run 3 455s. (2 coaches and the current on its second engine. (I dump oil in it every 300 miles.) My friend Randy, who got me started in this
madness, has the 403. He tows and I usually don't. He has a 3.70 final drive. I have a 3.21. Even with him towing, I have never had to wait for him.
We both have converted to fuel injection. He is a sharp tuner but I am not a total slouch. He consistently gets better mileage than I do. I have a
hard time getting the same mileage when he is towing and I am not towing. When he doesn't tow he gets way up into the 10.n.

We live at 2400 feet and there are a couple of fair grades to get here. I rode up once in Randy's coach and that thing came up the hills like a champ.
He never shifted and it never hesitated. We were flying. I come up in my coach often, obviously. I don't shift down every time... it is one of those
do I, don't I things. I am pushing taller gears but the 403 doesn't mind RPMs because of the shorter stroke. It seems like a tidy, tight engine but
small blocks are like that.

Last fall when they were in CA we had to pull a head off the 403. Sure was nice having more room to work in the hatch.

One oddity about the 403 is that it has siamese cylinders, meaning there are no water jackets between 2&4, and 6&8. (other side as well) Apparently
this is not a problem. I forget the mileage he has on the coach... I am guessing 78K or something like that. We could feel no ridge at the top of the
cylinders. Cylinders looked perfect.

If I ran on to a nice 403, I might just consider swapping. (hate to think about finding all the brackets.)

--
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George

[lenze middelberg]

Dominik

This one for sale in the Netherlands
http://www.marktplaats.nl/a/caravans-en-kamperen/campers/m927614617-gmc-motorhome-motorhome-bj-1978.html?c=a2384ef0ece270f44503df9f8598c624&previousPage=lr

12 meters and handshift? Stil not looking bad
--
Appie
eleganza 76 "Olga" ( pictures at http://www.gmcmhphotos.com/photos/g6489-olga.html
Fulltiming in Europe since july 1 2014
Denmark

[Randy Van Winkle]

George Beckman wrote on Fri, 05 June 2015 00:27

> One oddity about the 403 is that it has siamese cylinders, meaning there are no water jackets between 2&4, and 6&8. (other side as well)
> Apparently this is not a problem. I forget the mileage he has on the coach... I am guessing 78K or something like that. We could feel no ridge at
> the top of the cylinders. Cylinders looked perfect.
>
> If I ran on to a nice 403, I might just consider swapping. (hate to think about finding all the brackets.)

What George said! I have a little over 100K miles. It has been a good running engine. As George said, we pulled the head last winter because of a
Tuliped intake valve. The cause is a little uncertain, but I believe it was caused by a failed spark plug. It appeared the electrode on the plug
came loose and welded itself to the ground lug. Replaced valve and all seems to be good after around 5,000 miles.

I love the 403 when mated to a 3.70 final drive. I would not let the type of engine be a deciding factor in making a coach decision.
--
Randy & Margie
'77 Eleganza II '403'
Battlefield, MO

[James Hupy]

I have a heavy 78 Royale with a 403. One of the first things I did to it
was to change the final drive gear ratio from a 3:07 to a 3:70. Monday on
the way home from a rally in Washington state, we ran into a headwind down
the Columbia Gorge that I estimate was 50 to 70 mph. I could easily run
over 65 miles per hour against that wind, but prudently slowed down to 55
to save fuel. I made up for it on the way south from Portland. I saw 80 on
the speedometer a couple of times. My 403 has over 120,000 miles on the
clock. It runs as well now as it did when I bought it with 80,000 miles. It
will run with the 455 very well, with the exception being at the bottom of
a hill when I let the RPM's fall below 2000. In the 1800 to 2200 rpm range,
the 455 will out torque the 403. But not above 2800 - 4000 rpm. No prudent
person will drive a GMC above 4000 rpms on highways with traffic anyway.
Either way, both engines are reliable as an anvil if you maintain them
well. If I stay out of the 4 barrel, I consistently get over 10 miles per
gallon.
Jim Hupy
Salem, OR
78 GMC Royale 403

[Matt Colie]

appie wrote on Fri, 05 June 2015 02:45

> Dominik
>
> This one for sale in the Netherlands
> http://www.marktplaats.nl/a/caravans-en-kamperen/campers/m927614617-gmc-motorhome-motorhome-bj-1978.html?c=a2384ef0ece270f44503df9f8598c624&previo
> usPage=lr
> 12 meters and handshift? Stil not looking bad

I never spoke Dutch. Even my German has gone unused for decades, but I read the posting myself.
No, I don't think it is 12 meter long, I think it is 7,9.
I really want to see a coach like this with a manual transmission. None were built. The parts to make one never existed. So, if true, you should buy
it as a collector's item.

Matt
--
Matt & Mary Colie - Members GMCMI, GMCES
'73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

[Ken Burton]

Every time that I see this topic pop up, I want to say 52.


--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

[Chris Choffat]

you mean forty two...


now where is my towel?

--
-Chr$: Perpetual SmartAss
Scottsdale, AZ
77 Ex-Kingsley 455 SOLD!
2010 Nomad 24 Ft TT 390W PV W/MPPT, EV4010 and custom cargo door.

Photosite: Chrisc GMC:"It has Begun" TT: "The Other Woman"

[George Beckman]

James Hupy wrote on Fri, 05 June 2015 08:58
> <snip>

>
> It will run with the 455 very well, with the exception being at the bottom of
> a hill when I let the RPM's fall below 2000. In the 1800 to 2200 rpm range,
> the 455 will out torque the 403. But not above 2800 - 4000 rpm. No prudent
> person will drive a GMC above 4000 rpms on highways with traffic anyway.
>

> Jim Hupy
> Salem, OR
> 78 GMC Royale 403

Yes and those with an stock torque converter shouldn't be lugging down below 2200 as it is below the stall. Heat can build pretty fast.

I have a Switch Pitch which when not in switch it has a stall that must be around 1700. On a hill my 455 is as poopy as the next at 2000 RPMs. We are
tugging a lot of weight. 2400-3000 makes it much happier.

Good point about 4000 RPMs. Lost my governor and it wouldn't come out so I drove home in low on country roads at 3800-4000 and while you get used to
it, things sound they they are going up and down pretty fast in there.

--
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George

[Bob Dunahugh]

The 403 has the same stroke as a 350 Chevy. And due to it's large bore. It has no water jacket between the cylinders. And that feature is the same as a 400 Chevy. And because of that bore to stroke ratio. The 403 gets vary happy above 3000 RPM. When I get out West in the Rockies on long, steep grades with the 24 ft enclosed trailer. I shift down to second. Run the RPM's up to the 4 to 4,500 RPM range. This helps to keep the trans fluid temp in a reasonable range.
Bob Dunahugh78 Royale

[Bob de Kruyff]

George Beckman wrote on Sat, 06 June 2015 18:51

> James Hupy wrote on Fri, 05 June 2015 08:58
> > <snip>
> >
> > It will run with the 455 very well, with the exception being at the bottom of
> > a hill when I let the RPM's fall below 2000. In the 1800 to 2200 rpm range,
> > the 455 will out torque the 403. But not above 2800 - 4000 rpm. No prudent
> > person will drive a GMC above 4000 rpms on highways with traffic anyway.
> >
> > Jim Hupy
> > Salem, OR
> > 78 GMC Royale 403
>
>
> Yes and those with an stock torque converter shouldn't be lugging down below 2200 as it is below the stall. Heat can build pretty fast.
>
> I have a Switch Pitch which when not in switch it has a stall that must be around 1700. On a hill my 455 is as poopy as the next at 2000 RPMs. We
> are tugging a lot of weight. 2400-3000 makes it much happier.
>
> Good point about 4000 RPMs. Lost my governor and it wouldn't come out so I drove home in low on country roads at 3800-4000 and while you get used
> to it, things sound they they are going up and down pretty fast in there.

Most of my camping around here is in the mountains and my 403 is routinely in the 4000rpm range in 2cnd gear. It seems to be relatively happy there. I
still have my 3.07 final drive and as long as I have a suitable ratio spread, it's going to stay that way.
--
Bob de Kruyff
78 Eleganza
Chandler, AZ

[Dominik Hertle]

Thank you all for your contribution.
I think my question may sound a bit silly to you who drive GMC on every occasion.
Maybe one can only tell the real difference after having driven both engines.
What I hear is that both engines are good when taken care of.
This is like almost any other car. There are no bad cars out there.
Only badly maintained ones.

But something I really hate is a screaming engine, like when you have 3000 - 4000 rpm
at highway speeds. I am used to have a humming V6 running 2200rpm at 120kph.
My mums' 4 cylinder FIAT does 4000rpm at roughly 130kph - This drives me mad.

So while good fuel economy is important to me, I think quietness is number one.

Maybe I should drive a 455 and a 403 GMC first, so I can decide what to look out for.

And just for your information - I am looking for a coach in the USA or Canada, not Europe.

All the best,

[Ken Burton]

I own a 455 and have driven several 403's on extended distances (cross country trip of several thousand miles.) I would not let the engine size enter
into a decision of what to by. In most cases I would have to look under the engine cover to tell what engine is in them because they drive the same
on flat land or in the mountains.

--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana

[Johnny Bridges]

Get hold of one of the Fiat 850 Spyders (one of the best looking cars ever built) or one of the 850 Coupes (faster than the Spyder but seriously
yougly) and hit 70 per and lookit the tach. Nicest sounding high revving engine - Mike Hailwood lapping Talladega on the 6 cyl Honda GP. According
to one of the guys on the team, it made best power at 17 - 19K. Dunno if that's accurate, but it sounded like cloth ripping down the back straight.

https://www.youtube.com/watch?v=4YW7rnDy0x4

--johnny

--
'76 23' transmode Norris upfit
Braselton, Ga.

"Sometimes I wonder what tomorrow's gonna bring when I think about my dirty life and times" --Warren Zevon

[Robert Mueller]

Dominik,

You answered your own question: "Maybe I should drive a 455 and a 403 GMC first, so I can decide what to look out for."

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426


-----Original Message-----
From: Gmclist [mailto:gmclist...@temp.gmcnet.org] On Behalf Of Dominik Hertle

Sent: Monday, June 08, 2015 6:33 AM
To: gmc...@temp.gmcnet.org
Subject: Re: [GMCnet] Differences between 403 and 455

Thank you all for your contribution.
I think my question may sound a bit silly to you who drive GMC on every occasion.
Maybe one can only tell the real difference after having driven both engines.
What I hear is that both engines are good when taken care of.
This is like almost any other car. There are no bad cars out there.
Only badly maintained ones.

But something I really hate is a screaming engine, like when you have 3000 - 4000 rpm
at highway speeds. I am used to have a humming V6 running 2200rpm at 120kph.
My mums' 4 cylinder FIAT does 4000rpm at roughly 130kph - This drives me mad.

So while good fuel economy is important to me, I think quietness is number one.

Maybe I should drive a 455 and a 403 GMC first, so I can decide what to look out for.

And just for your information - I am looking for a coach in the USA or Canada, not Europe.

All the best,
Dominik

[Chris Choffat]

Dominik wrote on Sun, 07 June 2015 13:32
> ...
> But something I really hate is a screaming engine...
> Dominik

Then you won't want a Ford V8 or V10 (overhead cam). I routinely run 4500+ RPM up hills with my 4.6.
I wouldn't sustain that RPM on a GMC. The Ford will do it all day long.

--
-Chr$: Perpetual SmartAss
Scottsdale, AZ
77 Ex-Kingsley 455 SOLD!
2010 Nomad 24 Ft TT 390W PV W/MPPT, EV4010 and custom cargo door.

Photosite: Chrisc GMC:"It has Begun" TT: "The Other Woman"