Refresh my BBC396 or Swap to LS

[J_T]

Looking for a little guidance on what to do with my BBC 396.

I Bought a running 1972 GMC Jimmy. Needs some body work but everything else is functional and usable so I haven’t had much motivation to disable it to start fixing it up. I figured I can start working on the drive train and do it in pieces so I can keep using it.

BUT someone swapped in a Big Block, numbers read GM 1967 396 with Th350. The swap appears out of a Similar aged Pickup using stock parts as nothing appears custom and if BBC was an option in the Jimmy It’d appear factory (but plate reads SBC350). It has the Standard 12Bolt rear end (don’t know ratio yet it but I assume it hasn’t been touched.)

Since its already not a numbers matching I’m not as motivated to keep everything stock. What I want is whats best for long term reliability and some fun factor to use with my family without going high dollar as its not going to be a show vehicle. I’ve read about 6.2L LS swap with 4l60E but the price is considerable to obtain and then rebuild and also adding electronic control but that’s the reliability I’d like for this vehicle.

The 396 runs fine with some oil burn and standard chevy leaks. I’d like to go with a Holley Sniper- or similar type fuel system, something self contained, instead of the current weber. I do occasionally pull ATV/motorcycle trailers or boat with my other vehicles so want to keep that option. It would be nice to have the overdrive so maybe 700R may be better if I keep the 396. But I could make the 396 look like a stock Chevy under the hood.

Questions:

• need guidance to decide if I should go through LS swap or should I have the 396 refreshed (and heads and cam) and maybe see if more can be massaged out of it without spending an arm and a leg.
  
• What performance comparison can I expect between the LS 6.2L and a rebuilt 396 with cam, heads and throttle body fuel injection. I'm coming off a 12V cummins so no racer but i'd like something that can stand up to the exhaust rumble that it'll have. I know this will be tough as 50+ year old technology but I've seen amazing things with BBC but never owned one so don't know what it'd take to liven it up.
  
• Which would cost more to get the comparable results compared to the other? (comparing stock 6.2L LS, 4L60E, electronic control etc and conversion parts, vs to rebuilt 396 and maybe 700R, and fuel injection)
  
• Can the 12bolt rear and Dana 44 front handle anything a sensibly built 396 give it? (My first big block trying to decide between rebuilding them or ¾ ton axle swap are in the future. (my past fun vehicles have been ¾ ton diesels so I liked the robustness and bullet proof factor and simplicity but they were pickups and not family fun vehicles)

[Thealien]

Tough question and I am not sure it will be easily answered.

What are your planned use of the vehicle? Local? Trips on the highway? Plan on keeping the vehicle forever or selling it?

I swapped a 5.3 LS into a 72 Jimmy about 10 years ago. I went from 10 miles per gallon too close to 20 miles per gallon. I would need to drive about 1,000,000 miles to recoup the cost of the LS swap though.

One of the advantages to me of the LS swap is drivability and easy starts. I could leave that vehicle for six months turn the key and it would fire right up. Adding the Holley fuel injection to the 396 could make that as efficient and as dependable but I have no first-hand experience. I have someone doing an installation on my 1970 to 2 Wheel Dr. Blazer and he loves the Holley fuel injection systems.
I could leave that vehicle for six months turn the key and it would fire right up. Adding the Holley fuel injection to the 396 could make that as efficient and as dependable but I have no first-hand experience. I have someone doing an installation on my 1970 22 Wheel Dr. Blazer and he loves the Holley fuel injection systems.

I am interested to hear some of the other replies.

[hemi43]

Scrap the big block.
Numbers matching on these trucks makes no difference on value. You wont regret installing a 5.3 with a 4L60E. If you go the 6.2 route, I would probably want the 4L80E.
If you're handy, the swap is not expensive at all. Best thing to do is find a fairly low mileage 2002 Chev/GMC truck in running condition.
The day I bought my Blazer project, I also bought a rotted 2003 GMC with around 160k miles on it for $500. All I did was pull the rocker cover off to make sure the engine wasn't full of crap, and replaced all the gaskets. These engines when properly maintained should be good for 400+K miles. The transmission will have to be rebuilt anyways because you will need to install the Advanced Adapters output shaft.
If you do the work yourself, it shouldn't cost anymore than around 3K for the swap.
I mentioned trying to find a 2002, and that's because its the last year of drive by cable.
You will however need to change the gearing in the diffs which is an added cost, but again, fairly reasonable if you do it yourself.
IMHO, any engine more than 25 years old should be at the end of a chain to be used as a boat anchor.
I did my swap 4-5 years ago, have put over 20K miles on it, and get well over 20 MPG. It always start, tons of power, and doesn't stink going down the road. My only regret is using a 2003 with drive by wire. Works great, but has a lousy pedal feel which can't be tuned out on a factory computer. If I was to do the swap again, I would definitely use an aftermarket computer to control both the engine and transmission.

[70cst]

Originally Posted by hemi43

Scrap the big block.
Numbers matching on these trucks makes no difference on value. You wont regret installing a 5.3 with a 4L60E. If you go the 6.2 route, I would probably want the 4L80E.
If you're handy, the swap is not expensive at all. Best thing to do is find a fairly low mileage 2002 Chev/GMC truck in running condition.
The day I bought my Blazer project, I also bought a rotted 2003 GMC with around 160k miles on it for $500. All I did was pull the rocker cover off to make sure the engine wasn't full of crap, and replaced all the gaskets. These engines when properly maintained should be good for 400+K miles. The transmission will have to be rebuilt anyways because you will need to install the Advanced Adapters output shaft.
If you do the work yourself, it shouldn't cost anymore than around 3K for the swap.
I mentioned trying to find a 2002, and that's because its the last year of drive by cable.
You will however need to change the gearing in the diffs which is an added cost, but again, fairly reasonable if you do it yourself.
IMHO, any engine more than 25 years old should be at the end of a chain to be used as a boat anchor.
I did my swap 4-5 years ago, have put over 20K miles on it, and get well over 20 MPG. It always start, tons of power, and doesn't stink going down the road. My only regret is using a 2003 with drive by wire. Works great, but has a lousy pedal feel which can't be tuned out on a factory computer. If I was to do the swap again, I would definitely use an aftermarket computer to control both the engine and transmission.

For some folks number matching does but ... J_T - you need to do what you want to do.