L31 (Vortec 5700) swap

[benjaminearle]

OK, I think I've pretty much decided to swap my very tired, very carbureted LM1 (160HP when new in 1979) for a stock HD L31 from a GMT400-2500 (4-bolt main, 255HP/330Tq) using factory computer and harness. I have a friend of a friend who disassembles these late-model trucks and can give me a good deal on a '99 L31(HD) with a spun main bearing.

I'll keep my TH350/NP203 (twin stick in the future) for now and take the truck up 4" on springs and run 35x12.5s

So, of course I need to do main bearings - would anyone bother to tear it apart and do a $350 Sealed Power rebuild, or just do the $30 bearings and button it up? Any use in re-camming it for DD and very occasional hunting/hauling use?

Secondly, using stock computer and harness will i need to bring anything from the chassis except +12, Gnd, Start and Run? Is the O2 sensor in the manifold or will i need to cut one into my brand new exhaust?

Of course first i need to remove the busted studs from my LM1 exhaust manifolds so i can drive the truck to GET the L31.

Many thanks.

 

[Jims86]

OK, I think I've pretty much decided to swap my very tired, very carbureted LM1 (160HP when new in 1979) for a stock HD L31 from a GMT400-2500 (4-bolt main, 255HP/330Tq) using factory computer and harness. I have a friend of a friend who disassembles these late-model trucks and can give me a good deal on a '99 L31(HD) with a spun main bearing.

I'll keep my TH350/NP203 (twin stick in the future) for now and take the truck up 4" on springs and run 35x12.5s

So, of course I need to do main bearings - would anyone bother to tear it apart and do a $350 Sealed Power rebuild, or just do the $30 bearings and button it up? Any use in re-camming it for DD and very occasional hunting/hauling use?

Secondly, using stock computer and harness will i need to bring anything from the chassis except +12, Gnd, Start and Run? Is the O2 sensor in the manifold or will i need to cut one into my brand new exhaust?

Of course first i need to remove the busted studs from my LM1 exhaust manifolds so i can drive the truck to GET the L31.

Many thanks.

The man to see about this is Oneluckypops. He can guide you through, and even custom taylor your harness for the swap.

 

[89Suburban]

 

[benjaminearle]

The man to see about this is Oneluckypops...

I have a 5 year old so i keep hearing: "The person you need...is Nanny McPhee"

I see a PM in my future.

 

[Jims86]

I have a 5 year old so i keep hearing: "The person you need...is Nanny McPhee"

I see a PM in my future.

Yup, I know what you mean....My kids say we need Momma Odie from princess and the frog.

 

[benjaminearle]

Getting my engine tomorrow

'97 L31 Vortec 5700 already had the intake gaskets done and heads gone through, coming out of suburban that got hit. Good price since I'm going to pull some wrenches to get it out.

Will get a VSS encoder from Dakota and figure out a return-style fuel system.

Here's to hoping that the torque converter mates right up to my TH350 and I don't have to pull the old unit off my broke-ass motor.

This will be fun!

 

[benjaminearle]

Oh boy, got my engine yesterday. Started off a beautiful day. Went to church in the morning and sang next to my wife in the pew. Afterward I forwent lunch to get changed and get a few tools piled together to help extract my pickup's new heart from the cadaver of a '97 suburban - 188k miles but all new top end last year. Turns out the "vendor" needed the Ac compressor so I need one of those now but otherwise the engine is complete and harness complete (we chopped it only at the 4L60E since I'm running the old TH350.

Drove 75 minutes out of town and ended up 1000 yards down a red dirt (later to be mud) road. We towed the 'burb into the shed and started unplugging and unscrewing. The PO needed the AC system intact (had just charged it and wants to save the R134 and the dryer) so he started cutting sheet metal around all the hoses while I undid everything else. I especially wanted to make sure no wires were cut that would make my graft even more difficult. The "convenience" center plug was the worst. I forgot there was a bolt and ended up opening the firewall and pulling it all through.

Then motor mount bolts and bell housing and then we fought with that for a while, breaking the snatch block "rope" and finally putting a tow strap over a beam and pulling with a CUCV. Finally came out and then set it in my truck bed. Did I mention that it's now a monsoon? Nice timing. But, got it strapped down and duct tape over the intake and off I go, drenched, $400 poorer, but very happy. Originally he wanted $500, dropped it to $350 if I'd come help but I felt bad about taking 4 hours of his Sunday so thought another $50 was in order.

Get it back to my temporary garage space and onto a stand where now she waits for a thorough cleaning and removal of the harness entirely so I can actually get to things. I'll try and post some pictures soon.

 

[foamypirate]

Awesome! Looking forward to progress. I've been kind of tempted to swap a Vortec 350 into my 84' if my TBI 305 ever dies...

Of course, I've been tempted to put a big block, a hot small block, an Atlast I6, and an LSx in, so that may not mean much!

 

[benjaminearle]

Awesome! Looking forward to progress. I've been kind of tempted to swap a Vortec 350 into my 84' if my TBI 305 ever dies...

Of course, I've been tempted to put a big block, a hot small block, an Atlast I6, and an LSx in, so that may not mean much!

Well, budget for 4+ hours to get the L31 out if you are working on the floor of a civil war era barn with a bag (yes, bag) of tools. Or spend the money and get a dressed engine that's already cut out.

I just didn't trust anyone to get me the WHOLE harness. Hard to type today with my beat up hands. They look like I lost a fight with a propeller.

I thought about BBC, LSx, an I6 (turbo-ed) and even just a decent carb'd engine (though I HATE carbs - except correctly adjusted factory carbs or uber-sexy Webers). Oh and briefly a Toyota 4.0 V8 (1UZFE). The L31 seems to have the fewest things to work out and get a "turn the key and go" install.

 

[benjaminearle]

Today's update - looks like I'll have to get a little deeper in my pockets than anticipated just to really get going.

Some exhaust reading has informed me that the Vortec manifolds will hit the Square's frame, so i'll be keeping my old manifolds. Well, they (of course) don't have provision for EGR, so I'll need that programmed out.

Also, since my PCM is a black box from a '97 I will have to get a signal converter to take the Dakota Digital VSS from 8,000 pulses/mile to 4,000.

Still looking for a pinout for the Convenience Center plug and the *** of wires above it.

 

[Jims86]

unless you need EGR for state inspection, use your old manifolds.

 

[benjaminearle]

no inspection on anything this old in GA. I'll plug the EGR port and have it tuned out. If i get the tune done for 89, 91 or 93 octane fuel will I lose much by not having EGR?

Also, anyone know the pinout for the bulkhead connectors from a 97 Suburban? I need to know what to splice to where on the '79 bulkhead connector.

 

[Jims86]

woops....was thinking you were going carb for some reason. you can actually drill and tap the older manifold to provide EGR, but yes, It can be shut off, but I would have some further tuning of fuel and spark tables done per the fuel you will run in the absence of EGR.

 

[benjaminearle]

woops....was thinking you were going carb for some reason. you can actually drill and tap the older manifold to provide EGR, but yes, It can be shut off, but I would have some further tuning of fuel and spark tables done per the fuel you will run in the absence of EGR.

Hmmm, interesting idea to have the manifolds drilled and tapped. Could most any machine shop do that or does someone special need to be contacted?

Anyone care to weigh in on the pros and cons of maintaining or deleting the EGR system?

I'm taking today to clean up the old engine lots of degreaser later it looks pretty nice. I wish there was a easy way to run the old chrome air filter assembly and maintain the MAF. Anyone relocated it just above the throttle or does that just not provide enough straight pipe? Not to mention nothing to secure the round filter to.

 

[benjaminearle]

woops....was thinking you were going carb for some reason. you can actually drill and tap the older manifold to provide EGR, but yes, It can be shut off, but I would have some further tuning of fuel and spark tables done per the fuel you will run in the absence of EGR.

Hmmm, interesting idea to have the manifolds drilled and tapped. Could most any machine shop do that or does someone special need to be contacted?

Anyone care to weigh in on the pros and cons of maintaining or deleting the EGR system?

I'm taking today to clean up the old engine lots of degreaser later it looks pretty nice. I wish there was a easy way to run the old chrome air filter assembly and maintain the MAF. Anyone relocated it just above the throttle or does that just not provide enough straight pipe? Not to mention nothing to secure the round filter to.