Diff between 4speed/automatic dual exhaust
Thread Starter
Safety Car
Joined: Jun 2004
Posts: 4,364
Likes: 221
From: Beecher Illinois
Diff between 4speed/automatic dual exhaust
I have the headers and dual exhaust off my 4speed 79 and am planning on installing it on a friends automatic 78.
I see no interference issues with the front pipes from the headers to the crossmember. Maybe close to the 350 turbo pan but seems doable. At worst a slight ding to the pipe. I'd imagine a 400 turbo would be a problem but not an issue here.
But now, looking through some catalogs. I see even the secondary pipes are different between the 4speed and auto. WHY? What's different back there?
I guess tomorrow I'll do some inspecting under my auto79 to see what if anything looks different before my friend drives down with his 78.
Sure hate to tear his apart and not get the pipes to fit.
I just don't see what a difference there can be from the trans crossmember back???
I see no interference issues with the front pipes from the headers to the crossmember. Maybe close to the 350 turbo pan but seems doable. At worst a slight ding to the pipe. I'd imagine a 400 turbo would be a problem but not an issue here.
But now, looking through some catalogs. I see even the secondary pipes are different between the 4speed and auto. WHY? What's different back there?
I guess tomorrow I'll do some inspecting under my auto79 to see what if anything looks different before my friend drives down with his 78.
Sure hate to tear his apart and not get the pipes to fit.
I just don't see what a difference there can be from the trans crossmember back???
Thread Starter
Safety Car
Joined: Jun 2004
Posts: 4,364
Likes: 221
From: Beecher Illinois
Any thoughts?
I spent 45 minutes under my 79 with auto holding pipes up and eyeballing things. I see no difference from when the pipes exit the trans crossmember between the auto and 4 speed, what could possibly be different about the pipes?
I spent 45 minutes under my 79 with auto holding pipes up and eyeballing things. I see no difference from when the pipes exit the trans crossmember between the auto and 4 speed, what could possibly be different about the pipes?
Race Director
Joined: Feb 1999
Posts: 16,978
Likes: 7
From: In Dreams There Is Truth Ohio
Difference is the automatic frame has a removable crossmember, the 4 speed, the crossmember is welded to the frame but you already know that since you've been under both cars......
Last edited by GDaina; May 21, 2009 at 05:27 PM.
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
On cars with dual exhaust, the hanger bracket (bolted up to the trans mount) which holds the pipes, is straight with the 4-speed cars, and is angled on one side for an automatic. Therefore, the front and back exhaust pipes are different at the junction for an auto vs 4-speed.
I'm not sure of all years of applicability, but that's at least true for many.
I'm not sure of all years of applicability, but that's at least true for many.
Thread Starter
Safety Car
Joined: Jun 2004
Posts: 4,364
Likes: 221
From: Beecher Illinois
I do notice that the single Y pipe exhaust hits the pass side crossmember hole at a slight angle. Both on my 4 speed and automatic. Pretty sure that's the same pipe on both.
The 4 speed dual pipes hit that hole straight through. Hitting the hole straight on doesn't appear to be an issue with the automatic, at least the 350 turbo.
I'm thinking the main concern with the pipe differences is clearing the 400 turbo in the earlier C3s that these pipes were originally designed for.
I plan to use universal hangers at the rear of the crossmember similar to the kit Corvette Central offers. I know the 4 speed hanger won't fit and there's no factory or original hanger for a 350 automatic, just for the 400.
The 4 speed dual pipes hit that hole straight through. Hitting the hole straight on doesn't appear to be an issue with the automatic, at least the 350 turbo.
I'm thinking the main concern with the pipe differences is clearing the 400 turbo in the earlier C3s that these pipes were originally designed for.
I plan to use universal hangers at the rear of the crossmember similar to the kit Corvette Central offers. I know the 4 speed hanger won't fit and there's no factory or original hanger for a 350 automatic, just for the 400.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
First off, let's simplify that whole mess....either get a aftermarket cross support, and if necessary cut the OEM outta there with a sawzall, OR do what I did, but it out about 2-3 inches from the main frame, and splice it back with some 2" angle welded to the cross piece, and run some bolts through the whole mess in the fore/aft mode....
NOW, before aftermarket was out...I cut the bottom of my cross supports where the exhaust loops passed through....opening it up entirely...then triangulated and welded in support for the support, so to speak....over the top, so the pipes are in fact maybe a inch lower than stock at this point....trick being, I can pull that support outta there in a heartbeat, drop the whole exhaust outta there, and have done with it....
no pipe cutting, no careful routing/bending/fiddling with systems that don't quite fit, no use of silly hangers in that tailshaft mount area.....
in other words...through use of a sawzall, and a cutter and a welding buddy MY stuff is the way GM should have done it OEM style....
NOW, before aftermarket was out...I cut the bottom of my cross supports where the exhaust loops passed through....opening it up entirely...then triangulated and welded in support for the support, so to speak....over the top, so the pipes are in fact maybe a inch lower than stock at this point....trick being, I can pull that support outta there in a heartbeat, drop the whole exhaust outta there, and have done with it....
no pipe cutting, no careful routing/bending/fiddling with systems that don't quite fit, no use of silly hangers in that tailshaft mount area.....
in other words...through use of a sawzall, and a cutter and a welding buddy MY stuff is the way GM should have done it OEM style....
Thread Starter
Safety Car
Joined: Jun 2004
Posts: 4,364
Likes: 221
From: Beecher Illinois
Whoa! I'm not trying to remanufacture everything. I'm simply wondering why the 4speed and automatic exhausts are different.
I see no reason the front pipe won't hit the crossmember hole straight on and also clear the 350 turbo oil pan. Like I've said a couple of times and I guess I'm looking for confirmation on, the bigger 400 turbo WOULD present clearance problems.
This was just an opportunity by me and my friend to use a like new existing exhaust system without a lot of hassle. Cutting the pipes up is not an option.
I see no reason the front pipe won't hit the crossmember hole straight on and also clear the 350 turbo oil pan. Like I've said a couple of times and I guess I'm looking for confirmation on, the bigger 400 turbo WOULD present clearance problems.
This was just an opportunity by me and my friend to use a like new existing exhaust system without a lot of hassle. Cutting the pipes up is not an option.
Last edited by KapsSA; May 21, 2009 at 10:19 PM.
Safety Car
Joined: Apr 2000
Posts: 3,802
Likes: 61
From: Wichita KS
Best thing to do is get his car up in the air and lay your pipes up there and eyeball it to see what's what. Look for differences between yours and his and determine if those differences are show stoppers or just in need of some tweaking.
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Thread Starter
Safety Car
Joined: Jun 2004
Posts: 4,364
Likes: 221
From: Beecher Illinois
I've been doing that with my other Vette. I'm convinced it's a go, but I'm just getting nervous.
I would really, really hate to have his old exhaust in a pile on my floor and find a problem fitting the duals
I would really, really hate to have his old exhaust in a pile on my floor and find a problem fitting the duals
Thread Starter
Safety Car
Joined: Jun 2004
Posts: 4,364
Likes: 221
From: Beecher Illinois
Well, got the exhaust installed in the other guy's 78 automatic. No big issues. Had to ding a header pipe to clear his recently installed Steeroids and the pass side head pipe came close to the front corner of the trans pan. Another small dent with the ole ball pean!
Be a pain to drop the trans pan for a fluid change cause one bolt is going to be hard to reach but doable.
Pipes crossmember rearward were perfect. Everything's so sturdy we didn't even need to put hangers at the trans crossmember.
He's happy and I'm happy
Next week we install my big oil pan on his 78
and the pass side head pipe came close to the front corner of the trans pan. Another small dent with the ole ball pean! Be a pain to drop the trans pan for a fluid change cause one bolt is going to be hard to reach but doable.
Pipes crossmember rearward were perfect. Everything's so sturdy we didn't even need to put hangers at the trans crossmember.
He's happy and I'm happy
Next week we install my big oil pan on his 78