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Old 12-10-2017, 02:57 PM   #2
robertsjm711
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Join Date: Jul 2017
Location: Lebanon, Oregon
Posts: 241
Re: 5.3 to 91 gmc 5 spd

I assume you meant "91 GMC 5.7 5 speed", and if so... I have this from another similar post on another forum.

I have a 5.3 and am planning on using a Muncie M20, I think the principle is the same. The devil is in the details.

From what I have read you need:

-Fly wheel from a 4.8 or 6.0
https://www.summitracing.com/parts/luk-lfw387

-Clutch kit for your trans (I need a 10 spline, yours may be different)
https://www.summitracing.com/parts/luk-04-049

-Something to do the clutching (I am using hydraulic but I cant imagine mechanical being bad)
https://www.summitracing.com/parts/hre-82870

-Pilot bearing for LS
https://www.summitracing.com/parts/ADO-CT1082

-Shifter (obvious, I know, but mine was a pain- Thanks Hurst)

-Bell housing: This may be tricky - or not. I am using a 6263756 truck housing. The distance from the older trans are .4"(?) further from the engine that the LS - something about the crank shaft flange. It depends on which crank you have will determine if you need to make adjustments. They make flywheels that are thicker, but they are $$$ (for me, at least).
I also had to use an adapter ring to mate the trans to the housing (http://dennymac.com/muncie-bell-housing-adapter-ring)

- cross member mount: I made one

- VSS for the 5.3 computer
https://www.summitracing.com/parts/rpc-250-4153

Resources I use:

https://ls1tech.com/forums/conversio...-ls-motor.html

https://www.youtube.com/watch?v=RCGl5HbrUeE

I am using a Walbro external pump - not sure if the TBI has enough flow/pressure. I bet there are aftermarket kits - or maybe a stock one from a LS vehicle. There are returnless and two line fuel rails on the 5.3s

Radiator should be fine

I made my own motor mounts, but your application may have more options for pre-made

Use harness & computer from the 5.3, I used https://www.facebook.com/pg/LT1-Swap...70183759682543 as a guide. I will also use them for my computer reflash until I can get it to a dyno shop.

Can't say about the pan. There are different ones depending on your 5.3, I have the truck one and it is wicked deep in the rear.

I bet the fan will work, I don't think the 5.3 will make more heat than the 5.3.

There are the gauges that may need researched - not sure if they will line up. And OBD2 port, but those are cheap.

EDIT: To be clear, I am still in the installation & parts finding phase and have not tested all of this.
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