engine swap??

[lawdog49]

OK, bought the 91 Burb beast (350tbi/700R4) with 300K on the clock.  truck is really well taken care of, with lots of documentation- but I think the engine is original.  Runs decent, but after changing intake gaskets I still have significant oil leak from rear main.  I want to make this truck very reliable, so I'm just kinda unsure about the longevity/reliability of this engine at this point and I don't want to pour a ton of money into it.  A few options I've considered

1.  Go all out and drop a BB in, as heavy as this truck is- I would think a BB would help to get it moving, without seeing a terrible drop in MPG.  Would my injectors work, or do BB TBI trucks have bigger injectors?  I know the 700r4 would need to go in favor of something stronger (4l80e??  how hard is this swap?)

2.  383, great for torque, less complicated swap than the BB- but still an expensive motor (gonna prob buy a crate motor from somewhere-unless I can find a deal on something to have built locally)

3.  crate 350- can get an LM1 for about $1300, would be very cost effective- but is it powerful enough for this heavy truck without mods?  don't wanna void a warranty on a new engine with internal mods..

don't do alot of towing, occasionally a 5000 lb camper.  want to keep the truck awhile, and eventually lift a little- so the BB is appealing for really making a true beast out of it, but expensive to do and I'm unsure what MPG will wind up being..

[Captkaos]

Mine has 345K on it.  I know the motor is orginal, I don't think twice about driving it (well, maybe now at $4 a gal), but I drove it last week, so...

454 has different injectors and a different chip, it will kill your mileage say from normal 15-17 to a static 12.  You would need a 7060 ECM to controll the TBI and the 4L80E

you have to be conservative on how radical the 383 will be so the Existing ECM will controll it.

If I was going crate motor I would get one for a cop car, but definitely a 1 piece main replacement.  Factory the motor was rated at 190/210hp. and 300lb/ft.

The burb should tow fine with a SBC.

[Lt.Del]

Are you sure you have the 700r4 in a 91?
My 91 Sub has the 5.7L and 4L80e (or is it 60 e?) electronically controlled trans.

I have 195k on it and she runs like a top.  Definately not underpowered. I have a 7k lb camper trailer that I haul to the mountains often.  On flat terrain, I ususally have her runnin 75mph pulling that 30' trailer.

The engine/tranny are original.   The only time i put oil in it is when I change the oil.--every 4k miles.
 

 

[Captkaos]

Andy, you have the 4L80E in yours since it is a 3/4T, 1/2T got the 700R4 (or 4L60).  The electronic 4L60E didn't come out until 1993.

[Lt.Del]

Ah, thanks Chris for the clarification on the tranny.
Those '91 engines are bulletproof in my opinion.

[DnStClr]

75?! 
anybody seen a cop?
Hey,seriously-make sure your trailer tires are fully inflated at recommended pressures for those speeds guys.
I agree that the 350 should give you all you need to tow as long as the rear end and cooling systems are up to snuff, since you only tow occasionally. I would have  a 3.73 differential installed.   

[Lt.Del]

75?! 
anybody seen a cop?
Hey,seriously-make sure your trailer tires are fully inflated at recommended pressures for those speeds guys.
I agree that the 350 should give you all you need to tow as long as the rear end and cooling systems are up to snuff, since you only tow occasionally. I would have  a 3.73 differential installed.   

Where's a cop    Did I say 75, I meant 55    Cops break no rules

Speaking of the tires, I blew two out last August.  Of course it was hot as heck outside, blew one going to North Carolina.  Camped 7 days, got the tire fixed in town there, came back and blew another.  Thank goodness I got the tire fixed down there so I had a spare.

As for a cooling system, definately have an aftermarket tranny cooler.  I have one rated at 35,000 lbs.  I also have an oil cooler hooked to the filter.  And, I have a 3.73 rear. 

[Skunksmash]

Which 700R4 aftermarkey cooler would yall recommend? I heard they like to die due to heat.

[Lt.Del]

Heat is what kills trannys.  I don't know about the manufacturer of coolers, but, a good store chain will have good coolers.  Just keep in mind when installing one you run the fluid through the cooler first, then route it through the radiator. In otherwords, the flow of fluid goes to cooler first, then radiator then back to transmission. I took the grill off my truck and installed the cooler in front of radiator.

[ccz145a]

the flow of fluid goes to cooler first, then radiator then back to transmission

I always thought you would put the cooler downstream of the radiator. Get it as close to water temp as posible, then get as close to ambient temp as posible. Please let me know if this is right or wrong.

[Skunksmash]

Well i have seen people who have them mounted near the transmission itself. Just kinda angled to catch the air that just naturally flows by. This was probly a 10"x16" little radiator looking thing.

[Lt.Del]

the theory about putting the cooler before the radiator cooler is that the fluid works more efficiently when it is at operating temp, hence, running it through the radiator cooler last. 

[Skunksmash]

Yeah but i bet it is much easier to just mount it near the transmission. Though i don't know what effect this would have vs putting it up by the radiator.

[lowbucktruck]

You could just rebuild the 350TBI motor that you have, that would be cost-effective.  I have an old '73 C20 3/4 ton longbed with a GM Goodwrench 350 (carbed) and Turbo 350 tranny that I use for towing and heavy work, she tows big loads just fine.
If you are considering a motor swap, could just go to the junkyard and find an LS motor, but then you have to deal with changing ECU, and probably the wiring harness.  For the cost, an LS swap might be cheaper than a big-block swap (and better gas mileage than a BBC).  Ask everyone on here, some of these guys have done an LS 6.0 engine swap. 

[lawdog49]

kinda looked at doing a new motor swap, but i don't know if i want to go the route of all the associated headaches of completely changing to something like that.  anybody know if my 91 350 should be 2 or 4 bolt mains?  i have tossed around the idea of just building the 350 in it, maybe with a 383 kit and put some good heads on it.  i can deal with the down time for this if i have to, but obviously would prefer to just swap in a crate engine.  383 crate motors aren't in my budget though, and i think in reality the BB isn't either.  anybody know what heads will work well with a TBI motor and intake- i don't know the ins/outs of swapping vortec style heads.  been searching for a good TBI specific site with a company that has a proven set of components for a strong TBI motor.