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Old 06-29-2019, 02:01 PM   #1
RV-8iator
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New L31 crate motor and new tranny to replace 89 4x4 5.7 tbi L05

New L31 crate motor and new tranny to replace 89 standard cab HD chassis 4x4 5.7 tbi L05. 4.10 rear axel. Which specific L31 and which specific tranny? Current trannny is THM400 (MX1 3 speed). Recommendations and degree of difficulty? I found the thread with the "New L31 crate motor to replace 5.7 tbi" but nothing on tranny. Carb or keep tbi? Long or short block? All help appreciated! Mechanically/electonically skilled but never did engine swap before!
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Old 06-30-2019, 02:07 PM   #2
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Re: New L31 crate motor and new tranny to replace 89 4x4 5.7 tbi L05

Think you're in for a world of hurt.

1) Crate motors don't come with intake system or ignition. Have to find that. You will also need the PCM specific for an early Vortec.

2) Early vortec uses 66lb fuel system. Not sure a TBI fuel system is capable of that. Probably have to change the sending unit.

3) fuel system hookup is only Vortec which no other engine ever used. You would have to convert that (at least near the engine).

4)L31 used a 4L60E and others that are PCM controlled so you would need a trans controller if you don't find the PCM for a Vortec.

5)Once you get the ignition system in and running, you need a pretty sophisticated scanner (Snap-on Solus) for example to do the cam position retard.

You have too much work for me. I wouldn't do it. I would consider a true PFI and go with a system like FAST or better yet a system like Holley has that can do the trans also.
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Old 07-01-2019, 10:27 AM   #3
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Re: New L31 crate motor and new tranny to replace 89 4x4 5.7 tbi L05

Thanks, Speedy! I think you are correct, way too much work with a new crate engine. How about new vortec heads and intake manifold for my old L01 motor with 100k miles, running well, except for the usual somoke on startup (valve guides?) and keeping the TBI? My old tranny TH400 works, just does not want to move initially on startup (drainback from front pump problem?) if the truck sits for a few days.
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Old 07-01-2019, 12:19 PM   #4
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Vortec and TBI don't mix

The vortec heads won't accept the bolt pattern of your L05 manifold.

Maybe this would be more your speed.
https://www.gmperformancemotor.com/parts/12681430.html

While you have the engine out, it would be a good time to overhaul the tranny. TH's are no big deal. You can get a video on how to do it and stop and start the video for each section. If you do it yourself, it will not be expensive. It is best to deal with every issue at one time (unless you are under a time constraint like a DD for a job) then to have to deal with each worsening problem later.
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Last edited by speedygonzales; 07-01-2019 at 12:26 PM.
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Old 07-01-2019, 01:05 PM   #5
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Re: New L31 crate motor and new tranny to replace 89 4x4 5.7 tbi L05

In the first post, the OP was looking to put an L31 into his truck and not use the newer fuel injection.

GM makes a manifold, its salty but it does everything you need it to.

You can run your current TBI on a vortec motor(or your LO5 with vortec heads).

You will need a 96+ left exhaust manifold if you need to keep EGR.

https://www.summitracing.com/parts/nal-12496821


The L31 has a roller cam installed. The LO5 does not.
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Old 07-01-2019, 01:48 PM   #6
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Re: New L31 crate motor and new tranny to replace 89 4x4 5.7 tbi L05

Quote:
Originally Posted by 95 S_Trucker View Post
In the first post, the OP was looking to put an L31 into his truck and not use the newer fuel injection.

GM makes a manifold, its salty but it does everything you need it to.

You can run your current TBI on a vortec motor(or your LO5 with vortec heads).

You will need a 96+ left exhaust manifold if you need to keep EGR.

https://www.summitracing.com/parts/nal-12496821
Excellent info here.
As for trans, you need a heavy duty trans, so either keep the th400 or you'll need a 4L80, but that requires a stand alone computer to control it for $500+.
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Old 07-02-2019, 08:48 PM   #7
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Re: New L31 crate motor and new tranny to replace 89 4x4 5.7 tbi L05

I did the L31 swap into a 95 with the TBI system intact. I have a parts list and whatnot if you decide to do the swap. It was well worth it for extra power as well as slightly better fuel economy believe it or not. It's not that bad of a swap if you leave the TBI in place and get a chip.
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Old 07-04-2019, 06:41 AM   #8
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Re: New L31 crate motor and new tranny to replace 89 4x4 5.7 tbi L05

I have done this swap its easy straight foward the engine block has the same mounting points as the engine you have so there is no problem there , nothing wrong with mating to the th400 ,I would leave that in and see how you like before spending the extra money on the 4l80 or 60 . if you are going to tbi FI I would look in to fitech or one of tthe other companys mentioned . I run fitech FI with no issues ,but if you are on a budget go with a carb , you will still have to do a electric fuel pump because the L31 block casting is not made to except a mechanical fuel pump . what you need to do is compile a list on what parts you will need for this swap and see the actual cost vs just bying a flat tappet GM crate motor and switch your parts. if you are staying away from the original TBI install , you will need you can use your distibutor just reolace the gear with a melonized gear you need that for a roller cam, you will also need to plug the cam sensor in the timing cover and replace your fly wheel and of cporse you will need a vortec style intake , also you will want to convert to a single serpintine belt system found on the 96 and up vortec ,you can get the entire setup at your local junk yard cheep. just make sure you get everything off that particular engine. I am sure I am forgetting a few this but these are the most expensive parts on the list when doing this coversion.
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Old 07-04-2019, 08:00 AM   #9
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Re: New L31 crate motor and new tranny to replace 89 4x4 5.7 tbi L05

The 88-95 serpentine system will boot to the L31. No need to change it unless you want to. The 89 already has an electric fuel pump in the tank. The LO5 flex plate will bolt the the L31. Both are 1 piece rms engines. Good call on the distributor gear.
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Old 07-04-2019, 08:44 PM   #10
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Re: New L31 crate motor and new tranny to replace 89 4x4 5.7 tbi L05

Quote:
Originally Posted by 95 S_Trucker View Post
The 88-95 serpentine system will boot to the L31. No need to change it unless you want to. The 89 already has an electric fuel pump in the tank. The LO5 flex plate will bolt the the L31. Both are 1 piece rms engines. Good call on the distributor gear.

You are rite Sir thanks for the correction, but I do think the L31 has 2 diffrent flex plates that can be used depending on the L31 crate engine used 2 bolt or 4 bolt main , if a 2 bolt L31 is used I think you are correct but the L31 Hd 4 bolt version uses a differant flex plate
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Old 07-05-2019, 04:05 PM   #11
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Re: New L31 crate motor and new tranny to replace 89 4x4 5.7 tbi L05

-The mains for the crank have nothing to do with the flexplate at the end of the crank.
-Some vortec blocks have the mechanical pump pad cast but the hole for the pump pushrod will not be drilled and the cam does not have a lobe to operate the rod either.
-Yes, you need a factory melonized distributer gear. They are cheap.
-Don't know TBI but the factory vortec timing cover has a spot for a sensor that needs to be plugged or a normal timing cover swapped on instead if you aren't using that hole. There is also a cam reluctor plate that can be removed if not using the sensor.

The only really special part for a vortec motor is the intake manifold and distributor gear, everything else is standard small block stuff.
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