[GMCnet] Horse power....

[tonka6cuda6--- via Gmclist]

Ok so there is "no replacement for displacement" but i know we are limited. So far it looks like one can move to a Cad 500, twin turbo a la JimK.....
has anyone tried a ProCharger? (Belt driven super charger)

The wife wants to tackle the Rockie Mounts and the Smokey Mountain in the next couple years and has expressed vocally that the coach is a "sled" on
the hills....lol.
--
Rich Mondor,

Brockville, ON

77 Hughes 2600

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[James Hupy via Gmclist]

Change the final drive gearing, sail over the hills, and spend the money
you would have spent on the supercharger to buy us all a round or two next
time we meet.
Jim Hupy
Salem, Oregon

[tonka6cuda6--- via Gmclist]

What is the recommended gearing Jim? And id be happy to buy you folks a round or 2 of Canadian beers....lol.

James Hupy wrote on Tue, 01 October 2019 10:40

[Mike Kelley via Gmclist]

Tonka6:
I am not a mechanic or expert, but I have heard many an expert recommend the 3:70 final drive upgrade as opposed to the 3:55 or 4:10s that are also available.
My buddy Bob Dunahugh tows a 17,000 # race car & trailer behind his 3:70 final drive GMC without a problem - has for years and lots of cross country miles.
When I do my 28’ stretch, I am going w/ the 3:70 final drive from Jim Kanomata.
Just my humble opinion!
Mike/The Corvair a holic

Sent from my iPhone

[tonka6cuda6--- via Gmclist]

Ok thats sounds realistic. I have 4:11 in my car and they are not the best on the highway....lol.

Mike Kelley wrote on Tue, 01 October 2019 11:06

> Tonka6:
> I am not a mechanic or expert, but I have heard many an expert recommend the 3:70 final drive upgrade as opposed to the 3:55 or 4:10s that are
> also available.
> My buddy Bob Dunahugh tows a 17,000 # race car & trailer behind his 3:70 final drive GMC without a problem - has for years and lots of cross
> country miles.
> When I do my 28' stretch, I am going w/ the 3:70 final drive from Jim Kanomata.
> Just my humble opinion!
> Mike/The Corvair a holic
>
> Sent from my iPhone
>

[Keith V via Gmclist]

3.70 is pretty awesome. UNLESS you like to drive >70 on the freeway.
Me I like to take the 2 lane roads and with 3.70 it is a lot happier on the rolling hills.
And yeah, if you step on it, it will go
________________________________
From: Gmclist <gmclist...@list.gmcnet.org> on behalf of tonka6cuda6--- via Gmclist <gmc...@list.gmcnet.org>
Sent: Tuesday, October 1, 2019 10:19 AM
To: gmc...@list.gmcnet.org <gmc...@list.gmcnet.org>
Cc: tonka...@hotmail.com <tonka...@hotmail.com>
Subject: Re: [GMCnet] Horse power....

[tonka6cuda6--- via Gmclist]

Can you just change the gears and chain instead of the final drive? Just seems much easier in theory.....havent actually looked at it.

[James Hupy via Gmclist]

The gearing discussions kinda center around coach size, 23 vs 26, and
towing heavy vs not towing, and finally, 403 vs 455.
It goes something like this:
If you tow heavy, or have a 403 engine in a 26 foot coach, then the 3:70 or
even the 4:10 is what you want.
If you have a light 26 ft or a 23 ft and you do not tow, then a 3:55 will
suffice with a 455.
But, this is not chiseled in stone. And still subject to discussion.
Personally, I have a late 1978 Royale that has a 403, and I sometimes
tow a trailer. So, I have a 3:70 in my coach with Doug Thorley Ceramic
coated headers, a recurved HEI ignition, properly adjusted for the headers
and recurved ignition Quadrajet. It will pull the grapevine coming out of
LA without downshifting.
Coming Northbound over the Siskiyou's on interstate 5, there is one long
uphill that I shift into 2nd for, the other small passes like Wolf Creek I
pull in top gear. So, I can easily run 75 mph anytime I choose. The 403
loves the higher rpms. Never over 3600 rpms except when I downshift.
Jim Hupy
Salem, Oregon

On Tue, Oct 1, 2019, 8:20 AM tonka6cuda6--- via Gmclist <

[tonka6cuda6--- via Gmclist]

Ok....i have a 26' with a 403....i dont plan on towing a trailer at this point in time. So i think the smart choice here will be 3:70 as it seems to
an all around ratio.

Future ..will add headers and probably EFI but gotta get the thing safety inspected first which means at least one windshield....got the exhaust leak
fixed so hopefully ill try a glass repair and see if thats good enough.

[John Phillips via Gmclist]

This is kind of off-topic.
I think that if you fix the problem by putting more HP into the system puts
more stress on the transmission and FD. Does going to a lower FD ratio
increase FD transmission reliability?

--

*John Phillips*

[amansfield1104--- via Gmclist]

I was heading to fill up the RV to be ready to pull out to head to Ohio tomorrow for the fall get together. Making a turn on to 4 lane high way it quit. Checked and had fuel pressure and the carb had gas.

Some one stop by and help me get it off the highway.

After getting pulled off the road and getting ready to start to check it out I tried it and it. It had been sitting for a while as I had to go get tow rope. I tried it and it started. Went home. Replacing the HMI coil. What the chance of it being the ignition module?

Art
76 Elangza (sp)

[roy keen via Gmclist]

I made similar modifications as Jim Hupy to my 455. That would be my suggestion especially if you travel in mountain country in flat lands maybe the
3:55 would suffice. Actually the lower gears may yield better fuel mileage as you don't lug the motor as much.
--
Roy Keen
Minden,NV
76 X Glenbrook

[Mark via Gmclist]

As for gearing, I find that the 3.42 gears that my beloved PO installed are perfect for my 26' Royale (heavy) coach, with its mighty 403. Living in
the west, those gears seem to be right at home at any reasonable cruising speed from 60 to 75mph, and from what I can tell don't have a real negative
impact on gas mileage (not sure that would be the case with a much higher numerical gear set). If I was going to tow anything heavy, I'd opt for a
set of 3.70 or similar, no doubt.

The only problems I ever ran into was above 6,000' of altitude (which happens a lot with Flagstaff being just "up the hill" from Mesa, at 7,500' with
lots of 6-7° hills to climb). The carb was fine below that level, but any time I was going up a hill above about 6,000' the motor just ran out of
steam and I'd be mashing my right foot into the carpet, downshifting sometimes to first to generate enough power.

Fast-forward to my last trip to the Grand Canyon, after installing the FiTech fuel injection system. Now it just cruises up the hills - not really
much difference at altitude compared to sea level, which makes it a LOT easier to drive. Sure, I still downshift on the steeper climbs, but can go up
at partial throttle and it sure seems that I'm burning a LOT less gas in the process.

I can't say that the fuel injection system really increases power at sea level, but it sure starts easier and passes emissions with ease (so did my
carb though).
--
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen

[Johnny Bridges via Gmclist]

Once I got the cooling straightened out, my 23' with stock (3.07) gears pulled Cowee Mountain S of Sylva NC both ways with the toad on back without a
problem. Walked over Monteagle, 45 per in S. My 26' has 3.7 gears and with the toad on back and the Jasper motor would spin the wheels on takeoff
although that motor had a lot of cam it didn't need and consequently really chitty mileage until it broke the cranklshaft.

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell

[Matt Colie via Gmclist]

Those that know me know that I was an engine professional in OE land for many years. I also did other things....

Last year I had to "refresh" my engine. I put in the cam by number that Dick Paterson recommended. It is much better than it was, but it is still
cruising below the torque peak at 60 MPH. That is undesirable. It is still actually more comfortable with 70MPH, but both I and fuel rate are less
comfortable. If I had the loose change, I would go to a 3.55 in a heartbeat. But again, this is with a different cam and a VERY LIGHT (9460#) coach.


If I had any 26' anything, I would put a 3.70 in it at the earliest convenience.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

[Will via Gmclist]

If there is someone out there in the rare situation that they have a 3.7,
but wish they had a 3.5... I have a 3.5 that i have not yet installed into
my 26'. I would swap if it helps. 3.5, 3.7... both are better than the
3.07! Its a win for me no matter which one goes in.

-Will

[tonka6cuda6--- via Gmclist]

So did everyone do a crown gear and pinion swap or did they change the gears and chain?

[John R. Lebetski via Gmclist]

Don't use 4.10 in a muscle car with shorter 14-15" wheels and 60 series tires for comparison. We have usually 16" with 75 series tires.
Also the chain sprocket swap multiplies torque before the transmission clutches and hard parts. The final drive swap lightens the torque load on the
trans.
I'm happy with my USA 3.42 gears overall. Above 6% grade the 3.70 would be better but then not as good at 70 and above.
--
John Lebetski
Woodstock, IL
77 Eleganza II

[John R. Lebetski via Gmclist]

If "it's a sled" on the hills something is wrong. Even with 3.07 you can just grab S or L though sooner than with higher number final. Throttle cable
not pulling fulling is almost a given. Stuck advance if never serviced is another given. Secondary lockout stuck due to gum or choke malfunction also
a possibility

--
John Lebetski
Woodstock, IL
77 Eleganza II

[John R. Lebetski via Gmclist]

Boosted induction is a good way to make (restore) power at altitude. You have to be careful with heat though. Boost in cars is usually used for short
blasts, passing, merging etc. A long grade for 15 mins is a different story. You need a systems approach not just an add-on.

--
John Lebetski
Woodstock, IL
77 Eleganza II

[tonka6cuda6--- via Gmclist]

I guess thats not a fair statement as the purchase trip home from out East the kick down didnt work and i never downshifted it manually....i guess i
could have and gained a few RPM. I still need to check the carb but SWMBO wants yo drive this as well and manual downshifting isnt going to
fly....trust me.


JohnL455 wrote on Tue, 01 October 2019 17:49

> If "it's a sled" on the hills something is wrong. Even with 3.07 you can just grab S or L though sooner than with higher number final. Throttle
> cable not pulling fulling is almost a given. Stuck advance if never serviced is another given. Secondary lockout stuck due to gum or choke
> malfunction also a possibility


--

Rich Mondor,

Brockville, ON

77 Hughes 2600

[Mike via Gmclist]

This is a great discussion. I've got a 78 Royale with the 403. Already planning on FI once I get all the bugs worked out and want to pull my jeep.
I'm thinking 3.7 gears (which doesn't seem all that low to me, since my jeep is 4.10 and I want 4.88's!). How do these engine respond to headers and
a Cold air style intake? Probably need a cam to really fix the late 70's engine management for economy.
--
Mike and Jessica
West Michigan (Just north of Grand Rapids)
1978 Royale Twin bed, Dry Bath

[Chris Tyler via Gmclist]

Regarding the original question: While I dont have a procharger in my gmc, I have a good bit of experience with turbos and roots style positive
displacement superchargers and some seconary experiance with centrifugal blowers like the pro charger.

First, I think mounting one in a GMC would be an absolute bear as well as making service difficult. Second, Centris work better as RPM increases. PD
blowers work as soon as you crack the throttle, and turbos take load and a bit of time to spool up. I dont think a pro charger is the way to go for
our application.

A PD blower would be nice, but comes at he cost of hatch mods, higher intake air temps and high cost.

To go with boost I think a low boost turbo is the way to go. I will get around to it eventually as I have the parts already. Not a priority in the
flatlands of FL.

Agree with gears being your best bet right now. Years ago, when I lived near Don Garlits in Sefner and my buddy was friends with his daughter he told
me the best and fastest route to performence was without a doubt gears and a cam. Holds true for our GMCs too, I think.
--
76 Glenbrook

[Richard Denney via Gmclist]

No, everyone buys a final drive as a complete unit.

Another option is the well-regarded planetary final drive used by Cadillac,
with a 3.21 ratio. I have one, but my coach is even lighter than Matt’s. It
climbs well enough but it is not geared for drag racing.

Manny sells a kit that used to be a Caspro product, as I dimly recall. It’s
called power-drive, I think, and it uses a smaller engine sprocket on the
chain drive, with a shortened chain. By itself, it is the equivalent of a
3.5:1 final drive, when used with the stock 3.07 differential. When coupled
with the 3.21, you get the equivalent of a 3.67:1 ratio.

Rick “who doesn’t tow but who does drive up and down lots of hills” Denney

--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com

[Jim Kanomata via Gmclist]

I’ll put it this way,
I was few years behind when the lower gears emerged in 1988.
3.42 was not sufficient and even our 3:55 was not there.
Marvin Peck GearMaster convinced me to develope a 3.70.
Since he was lot more experienced than any ratio .
If you know about the engine torque and why the gear ratio is instrumental
to gain advantage.
Even the trans ratio of 3.50 and a 3,21 final to produce 3.67
Also a good mechanical distributor advance is very important. This can make
a big difference when climbing.
We get tremendous amount of feed back from 3,000 owners of 3.70
Miguel of MGM GMC is a big proponent of 3.70 and 403.
Several are running the 4.10 with 403 and know 4.10 on a car wheel differs
than the coach.
Thinking one can install a turbo system is dreaming.
I did it back in 1991 and learned much during the first two years.
I still use that coach, but I need to rebuild the Cad with the new Turbos
, oh I use the 3.70 LSD final drive.
Again knowing the torque courve of the Cad 540 , 3.70 does best.

--
Jim Kanomata
Applied/GMC, Newark,CA
ji...@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502

[tonka6cuda6--- via Gmclist]

Im now convinced that a 3:70 gear ratio would be a bonus....now how to get there will be the key.

As far as forced induction....well i have built many high performance vehicles over the years for myself and customers....as much as some may see it
as difficult all one needs to do is look at the engine bay with the 403 in it and visualize all that open space on the left side....lol....winter
project i guess.

[John Wright via Gmclist]

We got our first coach in late 1998 and it was a bone stock 403 with a 3.07 final drive. In the flat lands is was just OK, but needed some help with any hills. Added a 3.55 final and it really woke up the engine. It was lugging along at 2250-2300 at 65 mph and had no punch. The 403 is a big bore /short stroke motor and likes RPM. With the 3.55 I could climb most grades in super and keep it right at 50/55 mph and stay with most 455 units. The sweet spot was right about 2850/2900 RPM. You guys with the 3.07 final drive the motor doesn’t get up on the cam till about 75 MPH and then it really likes the RPM.

When we got the Buskirk stretch in 2011 is was set up with a 3.21 final and a 3.50 chain drive making it a 3.67 final drive ratio. The coach is heavier than a 26’, when we travel for the winter the coach weights close to 18000# and that includes 14300# for the coach and almost 4000# for the towed that also is a trailer, but it pulls most of the mountains grades out west without problems. The longest grade that we typically did was the grade out of White Sands over the hill into Las Cruces, NM on US70 and it does drag us down to 35 mph on the last part near the top of the grade. If we were to do a lot of mountain driving all the time I would consider the 3.55 or 3.70 final drives, with the 3.55 final drive and the 3.50 chain the effective drive ratio is just a smig over 4.11. With the 3.70 final drive and 3.50 chain the effective ratio is 4.47. I also do use the stock 225/75R/16 size tire. If you have installed a lower final drive ration (3.55 or higher) you lose more than 4% of the drive ratio each tire size you go larger than stock sizes. You are defeating the purpose of adding the final drive in the first place. The engine in the stretch is a 461CI Jasper BB Olds (Built when Jasper was building great RV motors), with MPFI, custom ignition, headers and a 3” exhaust system, 2.5” before the mufflers and transition to 3” just after the SS Flowmaster mufflers. Except for the 3” long pipe going down the side of the coach it is all SS including the tail piece.

My personal experience, yours may differ.

J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 29.5’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan

[powerjon via Gmclist]

Mike,
The 3.7 gear with the 403 motor is a good choice. It will give you plenty of pep and allow you to haul around that Jeep. How heavy is your Jeep?
Headers are a plus, as would be going to a 3" system when using the headers. Gearing for us is somewhat different for us as compared to a standard
vehicle. We use the gearing to get the motor up in its sweet spot. Did you see my post from earlier in the day, look for powerjon!

J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 29.5' Stretch
75 GMC Avion (Under Reconstruction)
Michigan

[Mike via Gmclist]

powerjon wrote on Wed, 02 October 2019 11:32

> Mike,
> The 3.7 gear with the 403 motor is a good choice. It will give you plenty of pep and allow you to haul around that Jeep. How heavy is your Jeep?
> Headers are a plus, as would be going to a 3" system when using the headers. Gearing for us is somewhat different for us as compared to a standard
> vehicle. We use the gearing to get the motor up in its sweet spot. Did you see my post from earlier in the day, look for powerjon!
>
> J.R. Wright
> GMC Great Laker MHC
> GMCGL Tech Editor
> GMC Eastern States Charter Member
> GMCMI
> 78 GMC Buskirk 29.5' Stretch
> 75 GMC Avion (Under Reconstruction)
> Michigan

Thanks John! I did see your post. Sounds like you have a pretty sweet set-up in that Buskirk. To answer your question, my jeep is 4000 lbs, give or
take. I haven't driven it across the scales yet. It is an 04, with the inline 6 and running 33" tires. I'm familiar with gearing up to get the revs
up, its the same for that old 4.0L tractor engine that Jeep used for a bazillion years. Its not terrible with 4.10 gears, but when I start pulling
some of the bigger hills in N Michigan, she definitely benefits from a downshift...the 4.0L is in its sweet spot around 3000 RPM. Here is the Jeep...I
like showing her off too!



Back to the coach, FI, Gears and some tubes will go on the list. Nice thing is that stuff will still work when I have to do the eventual rebuild.
Its not eminent, but I know that sometime in the next few years, my engine will need a rebuild.

--
Mike and Jessica
West Michigan (Just north of Grand Rapids)
1978 Royale Twin bed, Dry Bath

[Ken Henderson via Gmclist]

I installed the 3.50 chain drive in my 23' in '98. After 30k-40k miles I
moved that 455 & 3.50 to the 26'my son now has. After 82+k miles there's
never been ANY problem. And it's quieter than any higher ratio final drive.

No question the chain mod imposes more torque on the tranny. But the 425
has stood up extremely well to far more than any 455 will ever put out,
much less a 403.

But a final drive is MUCH easier to install unless the engine's out anyway,
as mine was.

Ken H.

[KC via Gmclist]

Browsing only phone so maybe I missed it but I don't see anybody talking price....how much does it cost to have somebody swap out to the 3.70 gears
for you? Ballpark.

Afraid that maybe beyond my capabilities.
--
Kevin Carter
1977 Kingsley
Centennial CO

[Jerry Burt via Gmclist]

Kevin,
This will give you an idea of what a new one will cost. You might get lucky and find a used one but don't hold your breath.
It may be worth picking it up from Applied and save shipping, core charge, and crate.

https://www.gmcrvparts.com/product-p/gm1-1.001.1.htm

COMPLETELY ASSEMBLED UNIT WITHOUT OUTPUT SHAFT.SPEEDOMETER REDUCER REQUIRED **_HIGHLY RECOMMEND LIMITED SLIP DIFFERENTIAL **.
CORE NEEDS TO BE RETURNED IN 45 DAYS TO GET THE FULL REFUND ON THE CORE.

Final*:
3.07 [Add $1,259.95]
3.21 [Add $1,095.00]
3.55 [Add $1,605.00]
3.70 [Add $1,698.80]
4.10 [Add $1,948.40]
Core Charge*:
$350 Core Charge -Rebuildible Core Required For Refund, 45 Day Limit [Add $350.00]
Core Shipping Crate*:
Core Shipping Crate $100 [Add $100.00]

Installation labor would be additional.
--
Patti & Jerry Burt Fresno, CA.
73 Gmc 26' Canyon Lands
77 Palm Beach - Parts Coach
Members: FMCA - GMCMI - GMCWS
A truly happy person is one who can enjoy the scenery on a detour.