need exhaust help with engine swap - The 1947 - Present Chevrolet & GMC Truck Message Board Network

1983shorty · 12-11-2005, 03:57 PM

ok. going from straight six in my 83 to 350 engine. i have long tube headers that came with engine but....the exhuast off the headers will run into the crossmember for trans. what do you guys do to run headers? do i need a new crossmember or do i need different headers? i can go to stock exhaust manifolds if i have to but i prefer to run headers. thanks jim

Russell · 12-11-2005, 04:13 PM

Jim, what you need is a transmission crossmember from an early SM465 truck (like 73-78 or so). They have two large humps in them to allow for dual exhaust to travel underneith them on either side of the transmission. Your 83 will have a crossmember that probally has a single downwards dip in it for the factory single exhaust to go overtop of it. Depending on which transmission you are running, you'll likely need to drill a new hole in the crossmember (most of the SM465s I've seen of that era have two bolts holding the tranny down at the back, while many of the newer transmissions only have one in the center, and you'll definitely need to drill new holes in at least the lower plate of the frame.

The crossmember is a 3 peice unit, the big member that goes all the way across, and sits on top of the bottom plate of the frame, with two little supports that go to the top of the frame. Those upper plates are not essential to the strength of anything, so you can choose to omit them if you wish.

BTW -- You have a PM

evan · 12-12-2005, 12:30 AM

I just installed headers on my truck and I started with set of car headers and realized that they weren't going to work because the passenger side one dumped right into that crossmember. I ended up buying some Dynomax truck headers which dump a bit lower. The exhaust shop still had to do a bit of bending to get it to work, but the truck headers eliminated the need for any extreme angles that would restrict flow.

The only issue with going with the full length truck headers is ground clearance. They had to put the passenger side pipe under that crossmember, so that reduces the clearance by 2.5 inches. If you are planning on slamming the truck some time in the future, you should probably get some shorty headers and get the pipe bent tight to the cab. If you do, be sure to get rear (not center) dump shorty's.

7T7 · 12-12-2005, 09:17 AM

I ended up building my own crossmember.
I have a ton of room now.

**N2TRUX** · 12-12-2005, 09:34 AM

Quote:

Originally Posted by 7T7

I ended up building my own crossmember.
I have a ton of room now.

yep, that's what they did on my truck....

1983shorty · 12-12-2005, 04:44 PM

wow ! those members look sweet ! doesnt look too hard to build one either.

1983shorty · 12-13-2005, 05:06 PM

Quote:

Originally Posted by 7T7

I ended up building my own crossmember.
I have a ton of room now.

i am in the process of making one of these crossmembers. using 1 1/2 inch stainless tubing. all the plates will also be stainless. thank god we have a well supplied maint. dept at work !

Prerunner1982 · 12-13-2005, 05:26 PM

my exhaust (off daves old truck) was just routed around the stock member, one pipe went above, other below....

12-11-2005, 03:57 PM	#1
1983shorty Registered User Join Date: Nov 2005 Location: sterling heights , michigan Posts: 208	need exhaust help with engine swap ok. going from straight six in my 83 to 350 engine. i have long tube headers that came with engine but....the exhuast off the headers will run into the crossmember for trans. what do you guys do to run headers? do i need a new crossmember or do i need different headers? i can go to stock exhaust manifolds if i have to but i prefer to run headers. thanks jim

12-11-2005, 04:13 PM	#2
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	Re: need exhaust help with engine swap Jim, what you need is a transmission crossmember from an early SM465 truck (like 73-78 or so). They have two large humps in them to allow for dual exhaust to travel underneith them on either side of the transmission. Your 83 will have a crossmember that probally has a single downwards dip in it for the factory single exhaust to go overtop of it. Depending on which transmission you are running, you'll likely need to drill a new hole in the crossmember (most of the SM465s I've seen of that era have two bolts holding the tranny down at the back, while many of the newer transmissions only have one in the center, and you'll definitely need to drill new holes in at least the lower plate of the frame. The crossmember is a 3 peice unit, the big member that goes all the way across, and sits on top of the bottom plate of the frame, with two little supports that go to the top of the frame. Those upper plates are not essential to the strength of anything, so you can choose to omit them if you wish. BTW -- You have a PM __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap) Last edited by Russell; 12-11-2005 at 04:13 PM.

12-12-2005, 12:30 AM	#3
evan Registered User Join Date: Jul 2005 Location: SK, Canada Posts: 488	Re: need exhaust help with engine swap I just installed headers on my truck and I started with set of car headers and realized that they weren't going to work because the passenger side one dumped right into that crossmember. I ended up buying some Dynomax truck headers which dump a bit lower. The exhaust shop still had to do a bit of bending to get it to work, but the truck headers eliminated the need for any extreme angles that would restrict flow. The only issue with going with the full length truck headers is ground clearance. They had to put the passenger side pipe under that crossmember, so that reduces the clearance by 2.5 inches. If you are planning on slamming the truck some time in the future, you should probably get some shorty headers and get the pipe bent tight to the cab. If you do, be sure to get rear (not center) dump shorty's. __________________ Evan B.

12-12-2005, 09:17 AM	#4
7T7 Regular guy Join Date: Oct 2003 Location: Round Rock TX Posts: 518	Re: need exhaust help with engine swap I ended up building my own crossmember. I have a ton of room now. __________________ 'Frank' 77 Silverado 18 & 20 American CL205s Edelbrock MPFI, 700r4, Baer Brakes 9" F@rd rear, Vintage air, Bags etc etc..

12-12-2005, 04:44 PM	#6
1983shorty Registered User Join Date: Nov 2005 Location: sterling heights , michigan Posts: 208	Re: need exhaust help with engine swap wow ! those members look sweet ! doesnt look too hard to build one either.

12-13-2005, 05:26 PM	#8
Prerunner1982 Registered User Join Date: Oct 2002 Location: Edmond, OK Posts: 5,906	Re: need exhaust help with engine swap my exhaust (off daves old truck) was just routed around the stock member, one pipe went above, other below.... __________________ Jon 1982 Chevy Silverado 350/th350.... RETIRED 1993 Jeep XJ 2 door(Cherokee) 4wd 4.0ltr/AX-15 (5spd)/NP231 .... Oklahoma Roll Call



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