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From SBC to BBC mount question 78 k20

cyclone

cyclone

1/2 ton status
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Did a qic search, no luck.
If we swap our 350/465 with a 454/400, do we need to move/change the motor mounts, move crossmember? Any help would be appreciated. Thanks
 
i have no idea what so ever but my guess would be if they were from the same style and 2 or 4 bolt main then it'd be fine but you'd have to move the trans mount.

again im wrong, this is my guess, i want someone to correct me so i learn!
 
my stepside was originally a 305 and the PO dropped a 454 in and had to move the motor mounts (and did a poor job of it) im going to redo them when i put the FI 454 in and go with the performance motor mounts from DIY4X
 
The 454 will drop right in place the only thing you may have to redrill/move is trans/t-case crossmember.
 
I'm in agreement with previos answer. I replaced a SBC 350 to a BBC 402 in a 78 p/u and did not have to change any motor mounts. I stayed with a 465 so don't know about tranny mount changes.
 
86454K30 said:
The 454 will drop right in place the only thing you may have to redrill/move is trans/t-case crossmember.
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This has been my experience also. The BBc is a drop in. You have to move the trans crossmember because the T-400 is aprox 4" longer than a T-350.
 
The SBC and BBC share the exact same motor mount location from the bellhousing forward. The problem with "some" engine swaps from SBC to BBC are from oil pan clearance issues in which case there are taller mounts and or different shaped oil pans. This was generally a car issue though and not a truck issue.
 
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I know when I was thinking of doing this on my 71 k5 there were issues with firewall clearance on the valve covers. I even had to put shorter valve covers on my small block because the tall ones touched the firewall. Not sure on the second gen though. Also I noticed that if I wanted I could move the front crossmember forward a few inches to clear the firewall. You might be able to do this also and that would bring the tranny forward if its longer. If you could move it forward enough you can keep your drivelines. Its my knowledge from the first gen so hopefully it works for the second gen.
 
I'm in close to the same process now but I'm just swapping the motor. I had installed ORD's SBC crossmember and am going to have to swap it out due to oil pan clearance issues, but for a factory crossmember, it shouldn't have to be modified. I've had a lot of luck using Moroso's engine mounts and I really like ORD's. If you need Clamshekks for the big block I have them ....PM me for the info.
 
I'm looking into the SBC to BBC swap as well and I have two additional questions related to doing it.

First. How well does the SM465 and NP208 handle a more or less stock TBI 454? I'm keeping most everything stock and will be towing a trailer (6-7K pounds) with my K20. Will I want to upgrade either the tranny or the t-case?

Second. What do people do about running exhaust? Are there bolt in kits anywhere or am I going to have to custom fab up a solution?
 
During the research I've done, the 465 will hold up to mild BBC's but the trans shops I've talked to recommend switching to the 12 in clutch as opposed to the 11 in that comes with a smallblock. The bellhousing will accept both but you have to check the flywheel for the 12 in bolt pattern.
 
As far as exhaust, Headers with air tubes (if your rig has A.I.R. system) kinda have to be used ....pending legality of Tx. The stock manifolds will work but the rest of the exhaust will most likely have to be made up from bolt in parts from a 3/4 ton truck.
 
I went from a 350 to 454. I had heard of people having issues with old rubber mounts and the extra weight of a 454 causing the oil pan to hit the crossmember. Because of this I used ORD's semi solid mounts and have plenty of oil pan to crossmember clearance. It can be a simple bolt in, depending on quality of existing motor mounts and oil pan configuration. As others stated, since you are using a different transmission you may have to drill new holes for the crossmember (some trucks had multiple holes for different setups, so you may get lucky).
 
Just be sure you don't use solid motor mounts and a solid tranny mount. $hit WILL break. As long as one has a rubber/poly mount to allow some flex, you'll be fine.
 
Busted Knuckles said:
Just be sure you don't use solid motor mounts and a solid tranny mount. $hit WILL break. As long as one has a rubber/poly mount to allow some flex, you'll be fine.
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Depends. I had brand new stock rubber motor mounts and t-case mounts. I noticed the transfer case lever would tip quite a bit under power so I put Energy Suspension Polyurethane t-case mounts in (keeping the stock rubber motor mounts). What that amounted to was a broken TH350/NP205 adapter ($$$) as the rubber mounts allowed the motor to flex, but the ES t-case mount did not allow the flex and caused the adapter to give.

Basically you don't want to mix rubber with poly or vice versa. I run semi-ORD mounts now due to truck pulling with 500HP. Some guys here with healthy motors run solid and have no issues other than vibration.
 
I can guarantee that if you use SOLID mounts - no bushing, rubber, polyurethane, whatver cushioning material you choose, just metal-to-metal mounts - you will break stuff. Drag racers figured this out a long time ago and I'd imagine it's at least as bad or worse with 4WD stuff with all the flexing that they do.
 
Busted Knuckles said:
I can guarantee that if you use SOLID mounts - no bushing, rubber, polyurethane, whatver cushioning material you choose, just metal-to-metal mounts - you will break stuff. Drag racers figured this out a long time ago and I'd imagine it's at least as bad or worse with 4WD stuff with all the flexing that they do.
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I'll post some pics this week. Several motors over 500CID and well over 500HP with big wide pulling tires.
I've only seen one break and that was due to poor craftsmanship :crazy:
Granted I wouldn't want it for a daily driver, but a purpose built vehicle it will work.....
 
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