What to Know When Doing an LT1 Swap

oldsmobile joe

Royal Smart Person
Nov 12, 2015
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So, if you've done a successful LT1 swap in you're G-Body, I have a few questions.
as stated earlier, i've done 2 lt1 swaps into g-bodies. both are running and driving. my gmc caballero i've been driving for two summers. will drive it anywhere. 3-4 hour trips one way with no problems. the G wagon i completed last fall and have over a 1000 miles on it. my son has it down at school, two hours away. so if anything goes wrong, i'll be road tripping to help fix it. i'll start by answering your questions and then add some tips from there.

First, what was the biggest issue during the swap? Was there something you may have done differently?
wiring, lots of wiring. i have the 95 and 96 gm service manuals for guidance. i started with a complete engine, dash and body harness (all the way back to the tail lights) wiring harness and start stripping out what i don't want or need. i like having the factory harness to pick from, i get to chose what features i get to keep and i don't have to buy any extra wiring. i kept the pcm out in the left front corner under the factory air cleaner box. i utilized any much of the original engine bay wiring as possible. anything extra that needs to go inside the car, goes thru the old cruise control hole in the firewall.

Did you keep the AC? Was there issues with that?
the a/c compressor will fit without any mods to the frame. but, there is no clearance to when the engine moves under throttle torque and not enough room to get the drive belt on or off. i massaged the area on the right frame rail just behind the idler arm mount with a little heat from a yellow map gas torch and a 10lb sledge. i used the sledge more for the size than for the weight. it need to be massaged about 1/8" to 1/4". with this done, the compressor won't touch the frame and it provides room for the factory b-body p/s lines to be used. here are some pics. fyi, compressor will need to be attached to the accessory drive bracket before mounting of accessory bracket to engine. now with all that said, i have not finished the a/c install. but plan to this summer. b-body compressor lines will be used. just need to make it all fit.
gmc lt1 4.jpg gmc lt1 3.jpg gmc lt1 6.jpg gmc lt1 5.jpg
How did you do the fuel system?
i have not done this on a coupe or sedan yet. i was able to use the factory nylon fuel lines. mount the fuel filter on the left frame rail like the b-bodies do it and be sure to cover the fuel line with plastic convolute like the factory does to prevent chaffing. on my G wagon i used a fuel pump and sender from an astro van inside the factory wagon tank. on the caballero i used a fuel tank from a 91-96 b-body wagon. for a coupe or sedan, i would try a tank from a fuel inj monte. use the f.i. sender with an upgraded fuel pump. i would modify the hard lines on the sender to match the nylon fuel hose snap fit connections. i would strip the fuel pump wiring from the factory b-body harness to be used for this.

And finally, is there something important I should know/ do before I dive into the swap myself?
patience. keep asking questions. i'll help as much as i can. and i know others here on the forum will to.
 

oldsmobile joe

Royal Smart Person
Nov 12, 2015
1,649
113
mpls
here is follow up on this subject. i build my cars for cruising and fun. i don't drag them. i'm too afraid of breaking them. my most recent lt1 swap is on my G wagon. i started with buying a none running 95 caprice with an lt1 for $600. a little putzing around and found the opti-spark that was replaced at the dealer 2 years earlier was junk. replaced that with a junk yard sourced one with new cap and rotor and the engine started and ran. drove the car around the block and confirmed trans shifted through all gears and reverse. i then stripped the engine, trans, and the wiring all the way back to the fuel tank. i even kept the cruise control. the only wiring i left in the car was for the doors and front lights.
the G wagon was equipped with a tired 305 chevy motor. using the motor mounts and shells from that engine i placed the lt1 and trans in the wagon. i utilized the engine driven cooling fan behind the wagon 305 radiator using modified f-body radiator hoses. using the f-body radiator hoses allows getting rid of the b-body pressurized coolant jug. pcm and b-body air box are mounted in the left front corner. factory exhaust manifolds fit just fine. i've tried using aftermarket f-body shorty headers, but found they do not fit. the collectors hit the frame on both sides.
factory wagon shift linkage fits just fine. i used the factory wagon trans crossmember, it was necessary to extend the slot for the trans mount and only placed the crossmember on the frame so only one bolt on each side were attached. i did this knowing i was going to use a single mandrel bent exhaust pipe of 2.5" exiting out the right side behind the tire. i don't like having exhaust exiting on the same side as the gas filler door.
p/s hoses are factory b-body. some b-bodies have variable assist p/s pumps to adjust for road feel. do not this pump. the lines will interfere with everything else going on on the right side of the engine. the b-body p/s hoses are a little long, but can be tucked up out of the way. see last pic in post #11.
i used the b-body water pump so the heater hoses can be routed to the heater core easier.
i didn't feel like having my pcm programmed, so i kept all the factory stuff like air pump and canister. i mounted the charcoal canister in the right front corner under the radiator support, attached to the frame. like b-bodies do. i also change to rear gear to be equal to the donor car rear gear and tire size.
other than not having a cat conv, my swap is full emission and can be scanned like a factory car.
here are some pics.
 

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Last edited:

oldsmobile joe

Royal Smart Person
Nov 12, 2015
1,649
113
mpls
as with the G wagon, the caballero is simliar with the exception of the fuel tank outlined earlier and the cooling system.
here i'm running an lt1 camaro radiator, modified radiator top plate and dual cooling fans.
 

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LT1B-Body

Greasemonkey
Thread starter
Feb 25, 2021
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Maricopa Arizona
I see you used the factory manifolds, how'd you make that work the exhaust system?
 

oldsmobile joe

Royal Smart Person
Nov 12, 2015
1,649
113
mpls
I see you used the factory manifolds, how'd you make that work the exhaust system?
on the G wagon, i used f-body cast iron manifolds with factory f-body y pipe. fit perfectly. on the caballero i used factory b-body manifolds with a y pipe from a 305 chevy v8. i used about 2inches of pipe from each b-body cat conv and bugger welded them to the y pipe. i did it this way because i knew i was going with single exhaust.
if i was doing a coupe or sedan, i would go with duals.
if your not using the egr valve system, you could go with g-body shorty or full length headers. unfortunately, no one makes an lt1 header with egr port to fit a g-body.
 

oldsmobile joe

Royal Smart Person
Nov 12, 2015
1,649
113
mpls
one item i forgot to mention was speedometer. on the caballero i modified the speed o meter by swapping the face on to an electronic speed o meter from a '90 suburban. then hooked up to the vss signal from the ecm. now i have to program the pcm to make it accurate.
on the G wagon, i used the speed o meter drive box from dakota digital. it works great and it now interfaces with blue tooth to your phone for programming. i placed it on the left fender well, in front of the washer bottle and next to the b-body cruise box.
 
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LT1B-Body

Greasemonkey
Thread starter
Feb 25, 2021
123
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Maricopa Arizona
using the f-body radiator hoses allows getting rid of the b-body pressurized coolant jug.
Can you go into a bit more detail?
I think the steam pipe needs to exit into a pressurized reservoir, but I'm curious what you did.
 

Ribbedroof

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Jan 4, 2009
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Can you go into a bit more detail?
I think the steam pipe needs to exit into a pressurized reservoir, but I'm curious what you did.
I have seen mention of people running it into the radiator tank. Given that nearly every aftermarket "replacement" radiator has that infernal extra port with the sketchy rubber cap, works out well.

Following along, as I THINK i'm about ready to attempt this on my wagon, after too many years of distractions (kids, house, coupe...you know..life)
 

oldsmobile joe

Royal Smart Person
Nov 12, 2015
1,649
113
mpls
f-body lt1s don't run a pressurized reservoir. the steam line is plumbed into the upper radiator hose. this pic is from my gmc caballero which is running an f-body radiator and dual cooling fans. for my wagon, i modified this same hose for use with a g-body radiator.
gmc lt1 12.jpg

this next pic is of the lower hose, again from an f-body. for the wagon, i used a caprice lower hose that was modified to fit a g-body radiator.
gmc lt1 11.jpg

for the heater hoses, i like using the b-body water pump and heater hoses. they wrap around and are anchored at the accessory bracket.
 

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