1983 C10 305 to 454 Swap

Wojo21212 · Jul 14, 2024

I am in the process of installing a 454 & TH400 out of a 1979 C2500 LWB GMC truck into my 1983 C10 SWB that had a 305 with a TH350 (Motor & Trans were gone when I bought the truck). After installing the motor & transmission the transmission crossmember doesn't line up. I do know the TH400 is 2 3/4" longer than the TH350's (I think). The original transmission mount is like 7"-8" too far forward. Is this normal? I am going to buy an aftermarket transmission crossmember for dual exhaust & mount it to the frame. Also what is the best long tube headers for this set up that has good frame clearance & won't burn up any spark plug boots? I am running aluminum heads on this motor. Thanks!

Mr Clean · Jul 14, 2024

bucket · Jul 14, 2024

Howdy from Ohio!

There's a lot of variables here and there's also several ways to skin that cat.

But in short... the original th350 should have been a long tail. Your th400 from your donor truck should be a short tail with a bolt-on yoke (shorter overall length than the long th350). If so, you can remove the bolt-on yoke and get a slip yoke from an 80's K10 truck, Suburban or K5. Using the K10 slip yoke, the original driveshaft will be close enough in length to work.

There should be a second set of holes in the frame to use your original crossmember.

Headers meant for a '68+ Nova fit well.

ali_c20 · Jul 15, 2024

Welcome from Austria. Pics please.

legopnuematic · Jul 15, 2024

Welcome from Missouri.

WFO · Jul 15, 2024

Welcome from the Texas Panhandle.

Catbox · Jul 15, 2024

Second the Nova headers.
I got these from a buddy as he had new ones for his Nova.
They bolted right up and fit great.

You must be registered for see images attach

We have a manual transmission and they clear everything with out any issues.

You must be registered for see images attach

Looking under the truck the Nova headers tuck up real nice like...

You must be registered for see images attach

Putting my head and phone on the ground, you can then see the collector and that they are higher up than the front crossmember...

You must be registered for see images attach

dabranco12 · Jul 27, 2024

Second on the slip yoke, also I have a spare slip yokes 1 bolt on 1 slip style, and an extra universal cross member for dua vs l exhaust on a 2wd. I am in the same process as well just on an 84 suburban. Overall driveshaft length is different due to transmissions being different. You also need to set up a system to operate the passing gear for the th400. My next question is how is the 454 built? Also hooker 2454hkr headers if you going new

bucket · Jul 27, 2024

dabranco12 said:
Second on the slip yoke, also I have a spare slip yokes 1 bolt on 1 slip style, and an extra universal cross member for dua vs l exhaust on a 2wd. I am in the same process as well just on an 84 suburban. Overall driveshaft length is different due to transmissions being different. You also need to set up a system to operate the passing gear for the th400. My next question is how is the 454 built? Also hooker 2454hkr headers if you going new

That's why I mentioned the slip yoke from a K10. It is 32 spline, but longer than the typical 2wd yoke. When going from a long tail th350 to a short tail th400 that originally had a bolt-on yoke, the K10 yoke makes the shaft long enough to work ok. It could stand to be 1/4-1/2" shorter, but it works fine.

1983 C10 305 to 454 Swap

Wojo21212

Junior Member

Mr Clean

Super Moderator

bucket

Super Moderator

ali_c20

Full Access Member

legopnuematic

Licensed Junk Dealer

WFO

Full Access Member

Catbox

Full Access Member

dabranco12

Junior Member

bucket

Super Moderator

Similar threads

Latest posts

Forum statistics