[GMCnet] Aluminum intake manifold for our 403's

[Bob Dunahugh]

There is a stock Olds aluminum intake that will work for us. The casting number listed in a post before was wrong. The casting number for the large port 1982 to 1985 307 Olds is 22504068. Not ending in 4086. ( Thank you so much to Tom McManus for the correction, and help with my search.) One thing that has come to lite. This is a high demand part in the Olds committee. As it has larger ports then the manifold that came out the last half of the production year of 1985. Edelbrock make two intakes that will work with the heads that our 403's have as far as port alignment. But the carb mounting surface is 1/2 inch higher then our stock cast iron intake. Edelbrock # 3711 has an EGR port at $290. # 2711 doesn't at $320. So I just went out to check the clearance between my carb air cleaner, and the hatch. There is none. ( Body to frame pads are in place ). With the 403 being shorter then the 455. Why is my 403 carb air cleaner against the hatch? So were has the clearance gone that should be there? One thing that I could do. Is mount the manifold in the Bridgeport mill. And lower the carb mounting surface. Put in thicker body pads. Or find an original 307 intake manifold. I'm trying to make sure my EFI will fit after the intake is bolted down.

Bob Dunahugh 78 Royale
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[John R. Lebetski]

Shortening the runner length will sacrifice low torque by shortening runner length. Not sure if a measurable amount without a dyno test but I would
look elsewhere to "cheat". Thinner carb composite gasket of some type or a slightly lower air horn maybe with dual entrant hoses to compensate for
lost height. Thinking out loud.
--
John Lebetski
Woodstock, IL
77 Eleganza II
Source America First

[Gary Kosier]

Bob,

Since I sent you the number on the manifold, I can only apologize for
crossing up the number. Dyslexia can be so annoying. I should
have sent the website www.442.com/oldsfaq/afinm.htp and you can even see a
picture of the manifold. The manifold does not have
the carb sunk down like the 455. That's why the motor is just as tall.
Both motors were designed to fit under the low hoods of a
Toronado and when GMC put them in the motorhomes, they had to cut a hole in
the engine lid and plate over it.
The floorboards in your GMC are 3/4" plywood and the engine lid is 1". You
can get a piece of 1" by 3" aluminum about 33" long and
double up on the rear of the frame around the rear of the hatch and make a
new lid from 3/4" fireproof plywood. This will save some
weight, but won't help on air cleaner clearance. Probably only practical if
you are switching to a carb bonnet and remote cleaner. JWID

Gary Kosier
77PB w/500Cad
Newark, Ohio

--------------------------------------------------
From: "Bob Dunahugh" <yenk...@hotmail.com>
Sent: Saturday, December 31, 2016 1:41 AM
To: <gmc...@list.gmcnet.org>
Subject: [GMCnet] Aluminum intake manifold for our 403's

[Bob Dunahugh]

With my 403 rubbing the hatch now. As did the other 2 - 78 Royales I've had. How would a 455 fit in my 78. Or the other 2 Royales. How much taller is the 455?

Bob Dunahugh


________________________________
From: Bob Dunahugh <yenk...@hotmail.com>
Sent: Saturday, December 31, 2016 12:41 AM
To: gmc...@list.gmcnet.org
Subject: Aluminum intake manifold for our 403's

[Todd Sullivan]

Aren't they the same block?

Sully
77 eleganza 2
Seattle

[James Hupy]

The 403 and 307 and 350 are very similar. The 455 is nearly the same as the
400 big block and the 425 big block. Bore spacing on the 403 uses the
siamese casting method where there are no water jackets between pairs of
cylinders. Bore/stroke relationship is different also. 403 is oversquare,
455 is undersquare. Deck height is different too.
Jim Hupy

[Rob Mueller]

The 455 Toronado has a "sunken" intake manifold and clears the GMC engine
hatch. I have seen some engine hatches with a layer of the plywood "routed"
out so the air cleaner will fit.

AFAIK none of the aftermarket intake manifolds; other than the $860 aluminum
455 manifold designed by Gary Rockwell and sold by Applied will fit under
the OEM engine hatch.

Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808

-----Original Message-----
From: Gmclist [mailto:gmclist...@list.gmcnet.org] On Behalf Of Bob
Dunahugh
Sent: Sunday, January 1, 2017 5:29 AM
To: gmc...@list.gmcnet.org
Subject: Re: [GMCnet] Aluminum intake manifold for our 403's

With my 403 rubbing the hatch now. As did the other 2 - 78 Royales I've had.
How would a 455 fit in my 78. Or the other 2 Royales. How much taller is the
455?

Bob Dunahugh

[Bob Dunahugh]

Got some great info on getting air to the TB. Need to go back and review the e-mails. This is my basic thought's on what I THINK I want. Open for input on this thought. Like to use the fiberglass scoop in the grill that I have from Applied. Then a hose to an air filter assembly. Next a hose to a plenum that's mounted on the TB. I've seem were guys mount an open K&N filter just behind the grill for cooler air. I use K&N filters in my road racing Yenkos. Lots of air flow with minimum turbulence to my velocity stacks on the 4 carbs. Great at 6 to 8,000 RPM. But there not conducive for my GMC. With an air filter plan together. Then I'll know if milling the intake manifold TB mounting surface will be required. Or working another angle to the GMC.
Bob Dunahugh


Well. I must confess. I'd forgotten how far the 455 intake drops into the valley. Right pass me. Thanks. for bringing me back on that. So my next issue is what part do I get to get filtered air into my 454 TB? Even with all that I've do to this GMC. Witch has been EVERYTHING. There's just no end. But I like that.

Bob Dunahugh


________________________________

With my 403 rubbing the hatch now. As did the other 2 - 78 Royales I've had. How would a 455 fit in my 78. Or the other 2 Royales. How much taller is the 455?

Bob Dunahugh

There is a stock Olds aluminum intake that will work for us. The casting number listed in a post before was wrong. The casting number for the large port 1982 to 1985 307 Olds is 22504068. Not ending in 4086. ( Thank you so much to Tom McManus for the correction, and help with my search.) One thing that has come to lite. This is a high demand part in the Olds committee. As it has larger ports then the manifold that came out the last half of the production year of 1985. Edelbrock make two intakes that will work with the heads that our 403's have as far as port alignment. But the carb mounting surface is 1/2 inch higher then our stock cast iron intake. Edelbrock # 3711 has an EGR port at $290. # 2711 doesn't at $320. So I just went out to check the clearance between my carb air cleaner, and the hatch. There is none. ( Body to frame pads are in place ). With the 403 being shorter then the 455. Why is my 403 carb air cleaner against the hatch? So were has the clearance gone that should be there? One thing that I could do. Is mount the manifold in the Bridgeport mill. And lower the carb mounting surface. Put in thicker body pads. Or find an original 307 intake manifold. I'm trying to make sure my EFI will fit after the intake is bolted down.

Bob Dunahugh 78 Royale

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[Pete Smith]

What's the standard intake manifold height on the motorhome 403?
--
Cary, NC

No Coach yet but trending towards mid kitchen Rolaled, 77 or 78, 403, hopefully with good original Imron paint.

[James Hupy]

To be precise, manifold height should have some parameters. If you are
referring to the carb mounting flange, you probably should measure from a
point that normally does not get machined as a result of engine overhaul.
Such a place might be the end walls of the lifter valley where the end
seals reside when the manifold is mounted to the engine. From that point,
the vertical distance to the carb base flange can be determined. I
personally have seen several intake manifolds on 403's that differed a good
bit in height, so, I don't know which one was "factory correct" for a GMC
MOTOR HOME, and which one was transplanted from another Olds model. I have
also seen Edelbrock "Performer" aluminum intakes with stock Quadra jet
carbs, as well as square bore AFB'S and Holley 4 barrels bolted down, using
a variety of air intakes. 40 years is a very long time for anything
automotive to remain stock, especially, pot metal carbs. I have done a
couple of Howell efi conversions on 403 engines, I use a Turbonetic right
angle snorkel combined with 3" stainless steel exhaust tubing combined with
an "air hog" air cleaner. Jim K has all the pieces in his catalog including
a really snazzy red convoluted silicone rubber hose and a machined aluminum
adapter that can be mounted to the floor of the coach. I took pictures,
but, god only knows where they are today.
Jim Hupy
Salem, Or

[Chris Tyler]

[quote title=JohnL455 wrote on Sat, 31 December 2016 09:13]Shortening the runner length will sacrifice low torque by shortening runner length. Not

sure if a measurable amount without a dyno test but I would look elsewhere to "cheat".

Actually if you mill the manifold you decrease the plenum volume, the runner length remains the same.Conversly, Adding plenum volume [spacers] helps
top end power rather than low end

I spoke with Edelbrock tech aboiut this when I was looking into putting a Performer manifold on my 455. They said it could be milled 1/2 with no
problems, perhaps more but risked cracking

They mentioned the older edelbrock manifolds [C4B? I forget #] were lower

They also said they really had no data on torque under 2500, but felt there would be a small gain on the low end due to higher velocity.

I ended up not installing it as it would still require hatch mods. If I ever need to pull the manifold [stock iron] maybe I will
--
76 Glenbrook

[Bruce Hislop]

Bob,
I posted some photos of how I did my air intake to the TBI. Like others I used the snorkel from a Jeep, but I found it did not run well. I surmised
that the air was not making the 90 degree turn into the TB evenly between the two barrels. A local plumber let me rummage through his discard pile
and I found a piece of plastic pipe that fit the TB and snorkel. Since I could not seem to cut it perfectly square, I sealed the pipe at the snorkel
and onto the existing 1" riser on the TB using some Scotch 33 tape and a couple ty-wraps.

The Intake Air Temperature sensor is mounted into the side of this riser pipe.

The air filter is a K&N look alike mounted upfront.

The PO had cut out the hatch cover where it was routed for the air cleaner. Then he added a piece of plywood and a piece of sheet aluminum. As you
can see in the photo, its hardly noticeable.

Someday I hope to make some improvements and make it all look pretty.

Link to pics:
http://www.gmcmhphotos.com/photos/g7008-efi.html



--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
Hubler 1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

[Todd Sullivan]

Bob, I hand built a duct out of aluminum to feed the TB on my 77 royale 455
and routed it to a K&N conical filter. The biggest filter I could find
which was the same size as the one sold for my 7.3 liter powerstroke. The
biggest challenge was getting a duct of sufficient volume off the top of
the engine between the valve covers and the aluminum floor framing of the
cockpit. New body pads made a big difference in engine to hatch framing
clearance. The duct was a rectangular tube leading off the top of the TB
toward the front of the engine. I put a turn in the duct at a point where I
had the best shot out of the engine bay exiting the drivers side of the
engine and angled downward at about a 45 ^ to a transition to a 4" straight
aluminum pipe via a 90^ rubber elbow. The leading edge of the round pipe
held the k&n which terminates behind the left headlamp bucket. Fender
liners were not present when I bought the coach and I never added them
back. I never ran the TB with any other setup so I do not have any
performance data as far as how well /poorly my air intake impacted
performance. I do know that I could light the front tires with a stab of
the throttle on dry pavement( 355 lim slip diff). Mileage depended upon
pace. I seemed to get around 10mpg cruising at 65 mph or less. One real
negative of the k&n filter was that the unmuffled exposed air filter
generates a lot of intake noise when under load which made it hard to
converse while driving in that condition. If I were to do it all again I
would build an enclosure for the filter or a resonator box seen on most
modern engines to reduce engine decibels.

Sully
77 eleganza 2
Seattle

[Gary Kosier]

Bruce,

When I put the Cadillac in, I used a collection of by Spectre that I got
from Jegs. I made a new engine lid, eliminating the original cutout
for the air cleaner. I made a raised area over the snorkel only and our
waste basket goes right on top of that, making it inconspicuous.

Gary Kosier
77PB w/500Cad
Newark, Ohio

--------------------------------------------------

From: "Bruce Hislop" <br...@perthcomm.com>
Sent: Sunday, January 01, 2017 12:02 PM

To: <gmc...@list.gmcnet.org>
Subject: Re: [GMCnet] Aluminum intake manifold for our 403's

[Bob Dunahugh]

The stock iron 403 intake carb base surface is 2.75 inch's above the front block horizontal surface. My concern is that the Edelbrock 2711 alum intake is 3.2 inch's. But the Mondeo shop says that the 2711 manifold will work in a GMC.

Bob Dunahugh 78 Royale

--

---

[Pete Smith]

I can machine one if anyone is interested in trying it out.....if anyone is willing to risk spending the money to get one.

Hard to tell from the pictures of the 2711 but 0.5" might be more than it can be reasonably machined.
Might also cause other clearance issues with cables and hoses.....

Pete

--
Cary, NC

No Coach yet but trending towards mid kitchen Rolaled, 77 or 78, 403, hopefully with good original Imron paint.

[Gary Kosier]

Bob,

The aftermarket has drop center air cleaners that will allow you to get
everything under the engine cover as long as the carb is not butted
solidly up against the lid. HOWEVER, what this does to air flow is another
story, as you well know.

Gary Kosier
77PB w/500Cad
Newark, Ohio

--------------------------------------------------

From: "Bob Dunahugh" <yenk...@hotmail.com>
Sent: Monday, January 02, 2017 2:05 AM
To: <gmc...@list.gmcnet.org>
Subject: Re: [GMCnet] Aluminum intake manifold for our 403's

[Bob Dunahugh]

The stock iron 403 intake carb base surface is 2.75 inch's above the front block horizontal surface. My concern is that the Edelbrock 2711 alum intake is 3.2 inch's. But the Mondeo shop says that the 2711, and 3711 manifolds will work in a GMC.


Bob Dunahugh 78 Royale

[Bob Dunahugh]

The stock iron 403 intake carb base surface that we have is 2.5 inch's above the front block horizontal surface. The 307 stock Olds aluminum intake has the carb deck height at 2.5 inch's also. The Edelbrock 2711 alum intake is 3.2 inch's. But the Mondeo shop says that the 2711, and 3711 manifolds will work in a GMC. Tonight while removing my original iron intake. I found a difference as to the 307 aluminum intake. The 307 intake manifold doesn't have the bolt boss for the alternator support bracket. But that's not going to be difficult to modify that bracket.

[David H. Jarvis]

http://www.jegs.com/photos/350AB.jpg

Lay a straight edge across the carb base.
Measure the front height, measure the back height, add the two together.
Then divide by two. That's where you get your 3.20" from.