Decided to LS swap

[open_road_toad]

I’m running that size up front and 315/35r20 rear(exact same height) and it’s gutless with a 3.27 rear gear. I would recommend a 3.42 at the least, unless you end up with 6l80-90 then the 2.73 would be fine off the line but 6th might useless most the time. It would be 1500rpm at 70mph.

I will definitely look into this. I’m going with the 4L80.

 

[KansasOBS]

I appreciate the input. Only thing I’ve purchased so far is the engine and radiator. I bought the radiator earlier in the summer bc I was having some overheating issues while running the AC in the middle of the summer. I wanted to switch to electric fans so I pulled the fans off a 2006 2500 in the salvage yard. I bought a new radiator for that truck from NAPA. It’s up in the rafters in the garage still in the box.

I’m not 100% on using that setup.

No problem, glad to see you didn't take what I said the wrong way, and considering other options. The 4L80E is a good all around transmission, and pretty durable for GM automatics, as far as the electronic stuff.

Went to the same type fans on mine. I will warn you that if you watched any videos or whatever with people doing the swap, most of them are no good. That fan setup originally sits on a straight lip across the core support, the core supports on our trucks have an indention in the center, and its offset. Only one of the three lower mounting feet actually lands on anything decent. I sectioned out the center of another OBS core support, and welded it in on mine, so it was straight. Person could use a piece of angle also.

I do not recall if the 88-91 supports are different there or not, but this may be something you run into. You can run the fans without the side tabs, but I would really recommend a solid base.

You may end up with your own good plans using things differently, just figured it worth mentioning just in case it might save you any time.

 

[open_road_toad]

No problem, glad to see you didn't take what I said the wrong way, and considering other options. The 4L80E is a good all around transmission, and pretty durable for GM automatics, as far as the electronic stuff.

Went to the same type fans on mine. I will warn you that if you watched any videos or whatever with people doing the swap, most of them are no good. That fan setup originally sits on a straight lip across the core support, the core supports on our trucks have an indention in the center, and its offset. Only one of the three lower mounting feet actually lands on anything decent. I sectioned out the center of another OBS core support, and welded it in on mine, so it was straight. Person could use a piece of angle also.

I do not recall if the 88-91 supports are different there or not, but this may be something you run into. You can run the fans without the side tabs, but I would really recommend a solid base.

You may end up with your own good plans using things differently, just figured it worth mentioning just in case it might save you any time

No problem, glad to see you didn't take what I said the wrong way, and considering other options. The 4L80E is a good all around transmission, and pretty durable for GM automatics, as far as the electronic stuff.

Went to the same type fans on mine. I will warn you that if you watched any videos or whatever with people doing the swap, most of them are no good. That fan setup originally sits on a straight lip across the core support, the core supports on our trucks have an indention in the center, and its offset. Only one of the three lower mounting feet actually lands on anything decent. I sectioned out the center of another OBS core support, and welded it in on mine, so it was straight. Person could use a piece of angle also.

I do not recall if the 88-91 supports are different there or not, but this may be something you run into. You can run the fans without the side tabs, but I would really recommend a solid base.

You may end up with your own good plans using things differently, just figured it worth mentioning just in case it might save you any time.

This is exactly why I’m here so no worries at all. I appreciate the feedback and opinions. I willl most likely pick up a 4L80 core this week.

I’m not liking the way the upper rad hose is run across the front of the engine on these swaps. I’ve found some swap specific radiators that have the inlet and outlet on the passenger side. I might just go that route. I should be able to return the radiator I bought.

I’ll update on the progress for sure.
Thanks.

 

[open_road_toad]

I’m running that size up front and 315/35r20 rear(exact same height) and it’s gutless with a 3.27 rear gear. I would recommend a 3.42 at the least, unless you end up with 6l80-90 then the 2.73 would be fine off the line but 6th might useless most the time. It would be 1500rpm at 70mph.

So the 4L80 has a 4th gear ratio of .750 I used a gear calculator online and in order to run at as close to 2000rpm at 70mph I have to change the rear end gears to either a 3.42 (like you suggested) which puts me at 2088rpm~70mph or a 3.08 which will be 1878rpm~70mph. I’ll confirm this with the transmission shop but what would you suggest? I do use this truck daily and I’ve taken multiple out of state trips with it.

 

[Alteca]

So the 4L80 has a 4th gear ratio of .750 I used a gear calculator online and in order to run at as close to 2000rpm at 70mph I have to change the rear end gears to either a 3.42 (like you suggested) which puts me at 2088rpm~70mph or a 3.08 which will be 1878rpm~70mph. I’ll confirm this with the transmission shop but what would you suggest? I do use this truck daily and I’ve taken multiple out of state trips with it.

I have a 4l60 currently. The first gear is 3.06 and that combined with the 3.27 just does not get it off the line very well unless you’re making a solid amount of torque. The 4l80 has a 2.48 first gear so the problem would be amplified by almost 20% hence y I recommend at least a 3.42. Around 2100 rpm for 70mph is perfectly fine IMO. I ran my truck on the interstate at 2500rpm for over an hour straight with zero issues, it seemed happy there.

 

[open_road_toad]

I have a 4l60 currently. The first gear is 3.06 and that combined with the 3.27 just does not get it off the line very well unless you’re making a solid amount of torque. The 4l80 has a 2.48 first gear so the problem would be amplified by almost 20% hence y I recommend at least a 3.42. Around 2100 rpm for 70mph is perfectly fine IMO. I ran my truck on the interstate at 2500rpm for over an hour straight with zero issues, it seemed happy there.

Perfect. Thanks.
I just picked up a 4L80e out of a 2003. I’ll be dropping it off at the transmission shop later this week.

 

[OutlawDrifter]

LS's love RPM. Don't be afraid of more gear.

I would do a 3.73 at a minimum, especially if you're considering 20" wheels. That's a lot of added rotational mass. 3.73 @ 2180rpm is 67mph. Around town doing the DD stuff, it'll drive better with the deeper gear.

I run a 3.73 with a 295/50r15(26.8") on my '49 GMC that is 6.0L/4L80E swapped.

My Z28 has 3.92s and a 25.7" tire(it's got a T56, so not really the same with the .5 6th gear, but I still use 5th way more than 6th on 2 lanes)

 

[Moofus02]

So the 4L80 has a 4th gear ratio of .750 I used a gear calculator online and in order to run at as close to 2000rpm at 70mph I have to change the rear end gears to either a 3.42 (like you suggested) which puts me at 2088rpm~70mph or a 3.08 which will be 1878rpm~70mph. I’ll confirm this with the transmission shop but what would you suggest? I do use this truck daily and I’ve taken multiple out of state trips with it.

I've got a tbi and vortec 5.7 with 342 gears. C1500 tbi sub and 95 k1500 ecsb really wanted a little more gear but were bearable compared to me 273 geared scsb. Everything else has 373 gears. Except my 95 k2500sclb. That has 410. The 373 geared are 00 5.7 Tahoe, 99 5.7 sub, 02 k2500 8.1 sub and 04 6.0 Escalade ext. I run 85 to 90 on freeway. At 70 the 373 trucks are around 2k but I normally run at 2400 to 2600 rpm at high speed. The sbc,454 vortec and 8.1 have the torque to pull tall gears but will run all day at my normal speed just fine. The 6.0 is gutless down low. A good efficient large diameter converter that multiplies torque well like l31maxexpress runs would be on my list. My Escalade had a junk 3500 converter that just made heat. My 8.1 has a converter that flashes to about 2800, acts like a cvt at light throttle but hooks up good. If it unlocks at speed I pick up about 200 rpm. The 3500 I have jumps 1000rpm when it unlocks at 90. Had the radio cranking and didn't notice. Made 340° trans temp and lost front seal and smoked the trans. In a 2wd toy driver i would get a good converter that would let the 6.0 launch and multiply the torque to get you moving. A cheep converter will give you the stall speed but waste the rpm by building heat instead of moving you forward. As happy as the ls motors are about rpmi would go with a good converter and skip the 342 gears and go 373 min. In a toy/ driver 410, in a toy I would go 456 and still not be afraid to run to work at 90. Don't get me wrong I like the 6.0 I have but on the street a sbc or bbc has more useful torque and can get away with taller gears. The ls motors don't get happy until they are over 3000 rpm. I would shoot for a road rpm of no less than 2400 and I wouldn't be afraid of 2800. Yes at 70 with 373 my 6.0 was just above 2000 and was ok but it wasn't happy there and would unlock the converter on hills. Pick up the speed so I was at 24 to 2800 and it would hold overdrive and lockup. Didn't seem to hurt milage at all running 20mph faster. I think the engine is more efficient at higher rpm. My brother's truck has 410 gears and he gets 2mpg better at 90 than 70.
Good converter and plenty of gear is my rec.

 

[open_road_toad]

I've got a tbi and vortec 5.7 with 342 gears. C1500 tbi sub and 95 k1500 ecsb really wanted a little more gear but were bearable compared to me 273 geared scsb. Everything else has 373 gears. Except my 95 k2500sclb. That has 410. The 373 geared are 00 5.7 Tahoe, 99 5.7 sub, 02 k2500 8.1 sub and 04 6.0 Escalade ext. I run 85 to 90 on freeway. At 70 the 373 trucks are around 2k but I normally run at 2400 to 2600 rpm at high speed. The sbc,454 vortec and 8.1 have the torque to pull tall gears but will run all day at my normal speed just fine. The 6.0 is gutless down low. A good efficient large diameter converter that multiplies torque well like l31maxexpress runs would be on my list. My Escalade had a junk 3500 converter that just made heat. My 8.1 has a converter that flashes to about 2800, acts like a cvt at light throttle but hooks up good. If it unlocks at speed I pick up about 200 rpm. The 3500 I have jumps 1000rpm when it unlocks at 90. Had the radio cranking and didn't notice. Made 340° trans temp and lost front seal and smoked the trans. In a 2wd toy driver i would get a good converter that would let the 6.0 launch and multiply the torque to get you moving. A cheep converter will give you the stall speed but waste the rpm by building heat instead of moving you forward. As happy as the ls motors are about rpmi would go with a good converter and skip the 342 gears and go 373 min. In a toy/ driver 410, in a toy I would go 456 and still not be afraid to run to work at 90. Don't get me wrong I like the 6.0 I have but on the street a sbc or bbc has more useful torque and can get away with taller gears. The ls motors don't get happy until they are over 3000 rpm. I would shoot for a road rpm of no less than 2400 and I wouldn't be afraid of 2800. Yes at 70 with 373 my 6.0 was just above 2000 and was ok but it wasn't happy there and would unlock the converter on hills. Pick up the speed so I was at 24 to 2800 and it would hold overdrive and lockup. Didn't seem to hurt milage at all running 20mph faster. I think the engine is more efficient at higher rpm. My brother's truck has 410 gears and he gets 2mpg better at 90 than 70.
Good converter and plenty of gear is my rec.

Thanks for that. I’ll talk to my transmission guy about a proper converter.

 

[RDF1]

I use CircleD converters in all the trucks and cars I build.
You will need to be set on your tire size and gear ratio before ordering a converter.