Educate me: Differences in BB exhaust manifolds for 71-72? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**DeadheadNM** · 10-08-2015, 10:33 PM

I've noticed two styles (borrowed pics below) of exhaust manifolds for 71-72 BB engines. One style has contiguous metal spanning adjacent ports (top pic), the other has no intervening metal between adjacent ports. Were both styles used on pickups? My 72 BB has the "contiguous" style and I believe these are original to the truck.

I'm looking at a spare set that is "discontinuous". The RH has part # 3989310 (looks correct for 402 or 454 passenger car) and the other looks like # 3914619 (couldn't locate application). Would these differing styles be interchangeable in a pickup?

Thanks, Pete

REEDS 72 · 10-09-2015, 12:34 AM

The top pair are the correct ones for for bb what I call the webbing on the bottom pair is gone not right near as I know I have a known original pair on my 72 if you need to know the numbers on them.

**leddzepp** · 10-09-2015, 01:27 AM

My 72 bb is original and has the style in the top picture. The bottom pictured manifold will work, but is not "correct" as far as I know.

**DeadheadNM** · 10-10-2015, 09:46 AM

Thanks guys - I'll consider the set I'm looking at to be from a passenger car.

The exhaust on the C30 has a leak on the LH side that I believe is a bad gasket rather than a manifold crack but haven't had time to dig into it yet.

**70STOVEBOLT** · 10-10-2015, 04:55 PM

My 402 came out of a 71 motor home and has the top ste on the passenger side and the bottom style on the driver side. Must not be original?

volksworld · 10-10-2015, 08:43 PM

nothing runs hotter than a 70's motorhome so the odds of one cracking are very good

Redline novdog · 10-10-2015, 09:37 PM

Interesting! Do you suppose the factory left the webbing for truck engines and chopped it for passenger cars. I did see some casting #'s. are they completely different casting #'s?

**DeadheadNM** · 10-11-2015, 10:51 AM

Quote:

Originally Posted by 70STOVEBOLT

My 402 came out of a 71 motor home and has the top ste on the passenger side and the bottom style on the driver side. Must not be original?

Likely not original but sounds as if these two styles may be interchangeable then.

Quote:

Originally Posted by volksworld

nothing runs hotter than a 70's motorhome so the odds of one cracking are very good

Agree, that's why I'm eyeing a spare set just in case.

Quote:

Originally Posted by Redline novdog

Interesting! Do you suppose the factory left the webbing for truck engines and chopped it for passenger cars. I did see some casting #'s. are they completely different casting #'s?

So far looks as if the webbed examples were used on pickups and the non-webbed examples for passenger vehicles. "Heavy duty" style for pickups maybe?

Redline novdog · 10-11-2015, 07:04 PM

Anybody getting casting #'s. I have a set off of a '79 3/4 ton buried in my shed. If I need to I'll dig'em out. No idea what they look like

Dirt's72 · 10-12-2015, 08:33 PM

Pete I took a look at my 69 396 truck exhaust manifolds today. The lh side was the same part number as the non webbed one you have pictured and the rh side had a different number also non webbed. I'm quite sure they are original to this truck. Not sure exactly when they changed over to webbed. I know the pics of the ones I sent you came off a 71 Sierra grande.

**DeadheadNM** · 10-12-2015, 10:10 PM

Quote:

Originally Posted by Dirt's72

Pete I took a look at my 69 396 truck exhaust manifolds today. The lh side was the same part number as the non webbed one you have pictured and the rh side had a different number also non webbed. I'm quite sure they are original to this truck. Not sure exactly when they changed over to webbed. I know the pics of the ones I sent you came off a 71 Sierra grande.

Thanks bud. I'll give you a holler this weekend. Maybe there was a switch then to the non-webbed at some plants or maybe GMCs?

**71CHEVYSHORTBED402** · 10-13-2015, 12:30 AM

Just went through this though still somewhat a mystery: Per the 1979 parts book:

3994045 LH
333846 RH

with A.I.R. this is the air pump for emission reduction:
343787 LH
353030 RH

I also know at some point 3916178 to 3994046 to 333846.

As for that A.I.R. baloney, forget about it, because the replacement parts can show the same part number for with and without A.I.R. ports. That's the case for at least the 353030, and possibly the 3994045, I can't remember. Fun, right?

Additionally, I can only vouch for the 3994045 and 353030 on my truck that the castings do not match. The RH is like what you show on top of your first picture, the LH is like you show on the bottom of your first picture.

**71CHEVYSHORTBED402** · 10-13-2015, 12:43 AM

Quote:

Originally Posted by REEDS 72

The top pair are the correct ones for for bb what I call the webbing on the bottom pair is gone not right near as I know I have a known original pair on my 72 if you need to know the numbers on them.

Know why the castings under the ports don't match LH vs RH?

68Gold/white · 10-13-2015, 09:51 AM

Quote:

Originally Posted by Dirt's72

Pete I took a look at my 69 396 truck exhaust manifolds today. The lh side was the same part number as the non webbed one you have pictured and the rh side had a different number also non webbed. I'm quite sure they are original to this truck. Not sure exactly when they changed over to webbed. I know the pics of the ones I sent you came off a 71 Sierra grande.

Picture looks like my 68 396's also...non webbed...of course.

**71CHEVYSHORTBED402** · 10-13-2015, 11:52 AM

Where/what is this "webbing" you guys are referring to?

**DeadheadNM** · 10-13-2015, 08:48 PM

Quote:

Originally Posted by 71CHEVYSHORTBED402

Where/what is this "webbing" you guys are referring to?

The iron that bridges the bolt hole flanges between adjacent ports - pics illustrate the differences between "webbed" vs. "no-web"

**71CHEVYSHORTBED402** · 10-14-2015, 02:18 PM

Quote:

Originally Posted by DeadheadNM

The iron that bridges the bolt hole flanges between adjacent ports - pics illustrate the differences between "webbed" vs. "no-web"

Oh, now I see it thank you. "Damn my eyes".

Anyone know why the castings under the ports don't match LH vs RH? I believe this is consistent for many BBC vehicles, if not SBC as well.

10-08-2015, 10:33 PM	#1
DeadheadNM Carpe manana Join Date: Dec 2010 Location: Eau Claire, WI Posts: 12,443	Educate me: Differences in BB exhaust manifolds for 71-72? I've noticed two styles (borrowed pics below) of exhaust manifolds for 71-72 BB engines. One style has contiguous metal spanning adjacent ports (top pic), the other has no intervening metal between adjacent ports. Were both styles used on pickups? My 72 BB has the "contiguous" style and I believe these are original to the truck. I'm looking at a spare set that is "discontinuous". The RH has part # 3989310 (looks correct for 402 or 454 passenger car) and the other looks like # 3914619 (couldn't locate application). Would these differing styles be interchangeable in a pickup? Thanks, Pete Attached Images __________________ 1972 K5 CST Highlander Blazer: http://67-72chevytrucks.com/vboard/s...d.php?t=708547 1972 K20 Cheyenne Super: http://67-72chevytrucks.com/vboard/s...d.php?t=528308 Members met: ORANGBLAZ, 2003 silverado, MikeCofield, BB72CHEVKT, Duncan&Son, Sameyrasmea72, THENEWMEXICAN, HotRod C/10, brianthelion02, Sport/Truck, ryanroo, michael bustamante, Dirt's72, Already Gone, WestButteTruck, 57taskforce, Moreyel, painterljp, AASmedic, SoCoC10, Lumaestas, carbuff382, Chevyland Last edited by DeadheadNM; 10-08-2015 at 10:35 PM. Reason: Clarified point

10-09-2015, 12:34 AM	#2
REEDS 72 Registered User Join Date: Apr 2011 Location: AMERICAN FORK, UTAH Posts: 535	Re: Educate me: Differences in BB exhaust manifolds for 71-72? The top pair are the correct ones for for bb what I call the webbing on the bottom pair is gone not right near as I know I have a known original pair on my 72 if you need to know the numbers on them.

10-09-2015, 01:27 AM	#3
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 20,031	Re: Educate me: Differences in BB exhaust manifolds for 71-72? My 72 bb is original and has the style in the top picture. The bottom pictured manifold will work, but is not "correct" as far as I know. __________________ 1972 C/10 Cheyenne Super SWB. Restored, loaded, slammed. 1968 C/10 50th Anniversary LWB. Unrestored, stock, daily driver/work truck. RIP ElJay RIP 67ChevyRedneck RIP Grumpy Old Man RIP FleetsidePaul

10-10-2015, 09:46 AM	#4
DeadheadNM Carpe manana Join Date: Dec 2010 Location: Eau Claire, WI Posts: 12,443	Re: Educate me: Differences in BB exhaust manifolds for 71-72? Thanks guys - I'll consider the set I'm looking at to be from a passenger car. The exhaust on the C30 has a leak on the LH side that I believe is a bad gasket rather than a manifold crack but haven't had time to dig into it yet. __________________ 1972 K5 CST Highlander Blazer: http://67-72chevytrucks.com/vboard/s...d.php?t=708547 1972 K20 Cheyenne Super: http://67-72chevytrucks.com/vboard/s...d.php?t=528308 Members met: ORANGBLAZ, 2003 silverado, MikeCofield, BB72CHEVKT, Duncan&Son, Sameyrasmea72, THENEWMEXICAN, HotRod C/10, brianthelion02, Sport/Truck, ryanroo, michael bustamante, Dirt's72, Already Gone, WestButteTruck, 57taskforce, Moreyel, painterljp, AASmedic, SoCoC10, Lumaestas, carbuff382, Chevyland

10-10-2015, 04:55 PM	#5
70STOVEBOLT Senior Member Join Date: Jun 2005 Location: Winona Lake, IN Posts: 6,414	Re: Educate me: Differences in BB exhaust manifolds for 71-72? My 402 came out of a 71 motor home and has the top ste on the passenger side and the bottom style on the driver side. Must not be original? __________________ 70 C/10 SWB 402/TH400/3.73 "The Needy Beast" 200,000 Mile Club Disc Brake Club Owner installed options: Front Sway Bar Power Steering Power Brakes Cigar Lighter Courtesy Lights Deluxe Side Markers Wiper Delay Sliding Rear Window Power Windows Power Locks Sniper EFI 2015 Silverado 1500 LS 4.3/6L80/3.23 lowered 2" front & rear

10-10-2015, 08:43 PM	#6
volksworld Registered User Join Date: Apr 2011 Location: formerly NY currentlyNC Posts: 390	Re: Educate me: Differences in BB exhaust manifolds for 71-72? nothing runs hotter than a 70's motorhome so the odds of one cracking are very good __________________ 1970 short step c10 leaf spring 454

10-10-2015, 09:37 PM	#7
Redline novdog Registered User Join Date: Jan 2012 Location: Washington,Il Posts: 632	Re: Educate me: Differences in BB exhaust manifolds for 71-72? Interesting! Do you suppose the factory left the webbing for truck engines and chopped it for passenger cars. I did see some casting #'s. are they completely different casting #'s? __________________ It builds on my intelligence when I make a mistake, Boy am I building on it! '67 C-10,'70 Nova SS

10-11-2015, 07:04 PM	#9
Redline novdog Registered User Join Date: Jan 2012 Location: Washington,Il Posts: 632	Re: Educate me: Differences in BB exhaust manifolds for 71-72? Anybody getting casting #'s. I have a set off of a '79 3/4 ton buried in my shed. If I need to I'll dig'em out. No idea what they look like __________________ It builds on my intelligence when I make a mistake, Boy am I building on it! '67 C-10,'70 Nova SS

10-12-2015, 08:33 PM	#10
Dirt's72 Registered User Join Date: May 2013 Location: Albuquerque, NM Posts: 1,106	Re: Educate me: Differences in BB exhaust manifolds for 71-72? Pete I took a look at my 69 396 truck exhaust manifolds today. The lh side was the same part number as the non webbed one you have pictured and the rh side had a different number also non webbed. I'm quite sure they are original to this truck. Not sure exactly when they changed over to webbed. I know the pics of the ones I sent you came off a 71 Sierra grande.

10-13-2015, 12:30 AM	#12
71CHEVYSHORTBED402 Senior Member Join Date: Feb 2009 Location: Northern Nevada Posts: 7,320	Re: Educate me: Differences in BB exhaust manifolds for 71-72? Just went through this though still somewhat a mystery: Per the 1979 parts book: 3994045 LH 333846 RH with A.I.R. this is the air pump for emission reduction: 343787 LH 353030 RH I also know at some point 3916178 to 3994046 to 333846. As for that A.I.R. baloney, forget about it, because the replacement parts can show the same part number for with and without A.I.R. ports. That's the case for at least the 353030, and possibly the 3994045, I can't remember. Fun, right? Additionally, I can only vouch for the 3994045 and 353030 on my truck that the castings do not match. The RH is like what you show on top of your first picture, the LH is like you show on the bottom of your first picture. __________________ Tony 71 Custom Deluxe, SWB, 2WD, 402, A/C. I developed an assembly kit for restoring the (a) truck from the ground up. My build thread, and more on the assembly kit https://67-72chevytrucks.com/vboard/...d.php?t=730025 Last edited by 71CHEVYSHORTBED402; 10-13-2015 at 01:21 AM.

10-13-2015, 11:52 AM	#15
71CHEVYSHORTBED402 Senior Member Join Date: Feb 2009 Location: Northern Nevada Posts: 7,320	Re: Educate me: Differences in BB exhaust manifolds for 71-72? Where/what is this "webbing" you guys are referring to? __________________ Tony 71 Custom Deluxe, SWB, 2WD, 402, A/C. I developed an assembly kit for restoring the (a) truck from the ground up. My build thread, and more on the assembly kit https://67-72chevytrucks.com/vboard/...d.php?t=730025



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.