Exhaust Question

Kilian

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Might be dumb questions, but when I complete my project I will have the cab and front sheet metal from an 83 GMC on a 1975 3/4 ton 4WD frame. 350 V8, stock manifolds, TH400, NP208. I've been looking at what Heartthrob Exhaust sells and they have sets for 1973-1980 4WD 3/4 tons and wondering if that would be the correct setup, or if would need something for 81-87? Or some form of a hybrid to go from the 80s manifolds to the 70s frame?
 

AuroraGirl

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Might be dumb questions, but when I complete my project I will have the cab and front sheet metal from an 83 GMC on a 1975 3/4 ton 4WD frame. 350 V8, stock manifolds, TH400, NP208. I've been looking at what Heartthrob Exhaust sells and they have sets for 1973-1980 4WD 3/4 tons and wondering if that would be the correct setup, or if would need something for 81-87? Or some form of a hybrid to go from the 80s manifolds to the 70s frame?
what crossmember do you have?
Those older 4wd trucks had a flat crossmember and the exhaust would have to make a bend upward to clear that while the np208 one possibly has clearance for under or over depending on what oen
 

75gmck25

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5.7
This is a picture of the duals on my ‘75 K25 with an NP203 (during installation, so all pipes are not yet tightened), which may be the same chassis as your truck. Not sure about your cross member design.

Look at all the pipe clearance next to the transfer case on the driver’s side, and then look how tight it is on the passenger side. It was challenging to get that pipe centered and not have it rest against the transfer case, or bang on the crossmember over bumps.
 

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AuroraGirl

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that is true, an np203 for sure leaves little room. I cant wait to see what his setup looks like
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Kilian

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Thanks for the replies. The '75 frame currently has the flat crossmember as is shown in the posted photos; it came with TH350 and NP203. I have the newer crossmember for the NP208 and was going to use that with the TH400/NP208 combo. Does that mean a newer exhaust setup would work front to back?
 

AuroraGirl

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which one./
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AuroraGirl

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if it helps visualize at all what the np203 setup with dual exhaust looked like from factory on the 78 k10 pics I showed, here is the diagram of the OEM setup
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Im guessing the manifold was log type and had a pretty much straight back dump that the long straight pipe hooked too and rode closeby but not into the t case and shifter for it
the exhaust hangers are both right at the back of cab where I assume was shortly before or maybe after the mufflers (first ones)
 

Kilian

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Sorry for delay in responding...busy around the farm. Here's the crossmember that I'm planning on using. Looks to be like the second photo that was posted.

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