'85 K10 LSX/700R4 Swap

[doubeys_nova]

I did an LSX swap with a 4.8L, th350, np208 t-case and 3.08:1 gear sets about 2 years ago. I just roughed it in and worked the kinks and made sure stuff was gonna last before paint and small detail stuff was done

Starting at front and going back I will do my best to list stuff and then tomorrow do a little bit more in depth on each

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. Put the steam port on the heater core supply hose and that pretty much sums up cooling system. A/C I will go into soon on a separate post in this thread.

I am running a 4" CAI with the MAF on the filter end. Followed by a stock truck DBC throttle body with a lokar throttle cable and a bowtieoverdrives.com 700R4 TV cable adapter. Next is a 2005 5.3L stock truck intake with return less fuel rail and 23 lb injectors and that sums up air intake.

Short and sweet I have 862 factory 99 4.8L heads and valvetrain. It is a 4.8 so I don't see any upgrade for that minus maybe a cam unless I get it pro tuned. Stock block and rotating assembly.

Stock truck coils, MSD wires and NGK V-power plugs.

Stock truck headers minus some grinding on pass. side for clearance. No EGR.

Finish this up tomorrow at work.

[truckdude239]

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[doubeys_nova]

I started messing with this truck years ago and recently decided to do a LSX swap. I have the engine in and hooked up. I have the fuel system plumbed in. I am keeping a/c (but due to no a/c lines took a/c stuff off). A couple notches were made to accommodate the passenger side exhaust manifold. Other than that no modification to the vehicle itself was done. I used Dirty Dingo engine mounts (model, year specific) and all stock 99 Chevy engine components. This engine has no emissions from the factory minus the 2 catalytic converters I won’t be using. The engine, tans, transfer case does need moved forward at least one inch but 1 ½” would be better but if I remember right, if I were to switch over to the 4L60E transmission and NP231 transfer case it is around 1 ½” longer. I have a ton of room between the engine and the cooling fan. Most of the swap was just taking my time and making sure everything was done correctly(I did not spend time trying to make it pretty).

I had a stock 99 4.8L with stock 84 drive train and 3.08:1 front and rear diff gears. Now, I have the same 4.8L with an 87 K5 700R4 HD, NP208 and 4.88:1 gear sets. The gear ratio is why I did not go through the trouble of putting the 4L60E in originally but the TH350 didn’t last long with the 35” tires and 3.08:1 gearsets. Once I save up enough money I would like to go with 4.10:1 gears and 35” tires (~69 MPH @ 2000 rpm’s). The final drive rpm to mph is in the same ballpark as the th350 with 3.08:1 diff gears and 33” tires (~64 MPH @ 2000 rpm’s).

Hopefully, if my fuel system works out, I will be running with both tanks. I am trying to keep all the low pressure stuff on the tanks and what not so if it works out I will hook up the other tank. If not, high pressure in-tank pumps and pick-ups will have to be used with a high pressure tank switch. I installed a gauge on the fuel rail supply for easier troubleshooting now and in the future but I am going to pull it off to give the fuel line a little more room for movement. It read 58-60 psi. Soon, I will try to route the fuel line a lot better.

I got the radiator mounting kit from CFR Performance and a universal aluminum radiator which did not work out. I am pulling this set up and putting in a factory diesel radiator with 2 16” fans.

I picked up some 97 Sebring convertible seats at the local yard. I got them to work and they are very sturdy using the factory seat mounting points.

We started the process with two 10’ pieces of 1½” angle 3/16” thick. We measured across the truck and decided we should just cut 2 5’ pieces of angle and center them in the truck (they did get shortened about ¼”-½” total). He then took a piece of cardboard and mocked it up to fit the floor. We then took that and made one side to fit and mirrored it for the other side. Overall widths and lengths are determined by the seats/ center console desired. For the 97 Sebring Convertible seats it was 12 ½” centers. We tacked the two long pieces to the two short pieces and test fit. It fit really well. Used ½” holes for the four factory 3/8” seat mounting holes in the floor provided us with a little room for adjustment.
Next, we bolted it in and set the seat on the frame to see where the seat needs to be, to be centered on the steering wheel. After marking that we welded another piece of angle in on the outside ends to adapt the holes requiring tabs to mount to. We extended this additional angle off the back of the frame to catch the back hole. We used 3/8” holes for all the 5/16” bolts used for mounting the seat track to the frame. The holes in the seat track were pretty large so we took two, 6” long, ¼” nipples from the hardware store and cut them to provide a bushing to fill some of the space. I believe mine were 3/16” long. Notes: you want the piece of pipe to be short enough that the seat will tighten against the angle iron not the bushing. All holes lined up center on the angle iron except were the tab is at. Even they lined up center on the vertical portion of the angle though. Measure all holes for yourself before drilling them. I mounted the seatbelt control box behind the transmission tunnel on the floor.

The wiring harness I ordered came with a fuse block and a programmed computer. The fuse block has four relays already installed. One for each, the computer, fuel pump, low fan, high fan. I was going to use an 03’ish S10/Blazer style computer holder set up. It mounts to the top of the coolant reservoir. I hooked up the plugs (pretty self explanatory) and then began soldering wires together. You need a constant 12v, a key hot 12v (has to be hot when engine is turning over also), 2 grounds (one in the harness and one in the fuse block) and that is all to get it to start. I ran approximately the same size wire (same size or larger) to lengthen any wires needing extended. For example, the fuel pump wire, the key hot, and a few others. When hooking up the fan, hook up the low fan wire to your primary fan and your high fan wire to your secondary fan. Since I only have one fan I just tucked the high fan control wire under the fuse block. From there I hooked up the OBDII port. It requires a ground, a key hot and the signal wire. And then hooked up the check engine light I purchased from a local parts store. I need to lengthen the crank sensor wires a couple inches but other than that the wiring was pretty well done.

For sending units and gauges, I ordered Autometer Sport Comp, electric, short sweep oil pressure and water temp gauges. They came with 1/8” NPT sending units. I used a 12.5x1.0 adapter for the water temp and a 16.5x1.5 adapter for the oil pressure. The stock sending unit is utilized by the computer so a second sending unit was placed behind the passenger side exhaust manifold. There is an 8mm allen head bolt in the head that I removed to install the adapter fitting and sending unit. With this you can either buy a shallow sending unit or drill out the adapter fitting. I chose to drill out the adapter fitting (so the sending unit node would slide through) to save $15 on the new shallow sending unit. I used a 21/64” drill bit and drill press to drill it out. I then unhooked my intake and removed the stock oil pressure sending unit(not used by the computer) and installed the electric sending unit with the 16.5x1.5mm adapter. I connected the wire to the sending unit before reinstalling the intake. Next, I ran the wires through the firewall into the cabin to connect to the gauges. I pulled the guts off of the back of my small gauges and installed the guts from Autometer short sweep gauges so the sending units are correct for the gauges. Haven’t seen how it is going to work so I will come back to that later.

I ran the harness through the firewall at a factory grommet just above the back of the engine. I am a little fuzzy on where I am going to mount the computer and fuse block now but will come back to it as soon as I get more info.
I pulled the heater box completely apart and cleaned/replaced parts and will hopefully have a fully functional heater/A/C system when done.

This has some specific info in it that I typed up awhile back and skimmed through to change anything that I did differently. I cannot get pictures to load but if I figure it out I will post as many pictures as I can of stuff

[NastyBuzzard]

Does the 4.8 feel weak in the truck? Reason I ask is bc I have a 87 gmc v1500 4x4 longbed single cab i am thinking about putting a 4.8 in bc I can get a whole truck for such a good deal!

[doubeys_nova]

If i ever get around to changing to 4.10 gears it might feel a little more sluggish but still with 4.10 gear sets it shouldnt take much engine to pull the truck around.

With the 4.88 gear sets I have had it loaded heavy and pulled car trailers with cars on them with ease.

Empty, the truck gets it. If you compare the power on a stock truck 4.8L to even a stock truck 454 of the 80's the 4.8 is going to kill it. the engine management on these newer engines is by far superior to old carb/distributor set ups. These little guys sit around the 300 mark hp and lb/ft with a tuned power curve.

When using the 4.8L, adapt a gear set the will put you at a little higher rpm than if you run a 5.3/6.0. i would run 3.73's in 33 and down tire size and 4.10 in 35 and up tire sizes but i have overdrive too. 35's without overdrive either mean really high highway rpm's or a toasted transmission. i had a TH350/3.08 gear set combo initially with my 35's and that trans lasted a whole 6 months/10k miles before all forward gears were gone. i switched to 4.88's and a K case 700R4 and drove it for over a year(and i dont baby it) with out a slip or bad shift still.

[NastyBuzzard]

Originally Posted by doubeys_nova

If i ever get around to changing to 4.10 gears it might feel a little more sluggish but still with 4.10 gear sets it shouldnt take much engine to pull the truck around.

With the 4.88 gear sets I have had it loaded heavy and pulled car trailers with cars on them with ease.

Empty, the truck gets it. If you compare the power on a stock truck 4.8L to even a stock truck 454 of the 80's the 4.8 is going to kill it. the engine management on these newer engines is by far superior to old carb/distributor set ups. These little guys sit around the 300 mark hp and lb/ft with a tuned power curve.

When using the 4.8L, adapt a gear set the will put you at a little higher rpm than if you run a 5.3/6.0. i would run 3.73's in 33 and down tire size and 4.10 in 35 and up tire sizes but i have overdrive too. 35's without overdrive either mean really high highway rpm's or a toasted transmission. i had a TH350/3.08 gear set combo initially with my 35's and that trans lasted a whole 6 months/10k miles before all forward gears were gone. i switched to 4.88's and a K case 700R4 and drove it for over a year(and i dont baby it) with out a slip or bad shift still.

Thing is, I am about to buy a 01 4x4 150k mile ext cab silverado. Come to find out it has a 4.8 instead of 5.3 like advertised. I checked vin, owner took a while to convince. Anyways I am getting the whole truck minus doors, front & rear seats, bed, front fenders, and hood for $900.

My current set up is a 1987 v1500 4x4 long bed single cab w/ 3.42s 32" tire 350 tbi/700r4 241 tcase(out of 91 k5 blazer), instrument cluster out of 91 as well. My tbi has less than 10k but I can't get it to run like I want with the flat top pistons bored .030 over w/ vortec roller cam. So I am tired of dumping $ into it and I want to go ls.

I have heard I can swap the 3.73 locker rear out of the 01 silverado onto my truck though. I was just thinking of staying with 3.42s b/c I will never lift over 4" or go up as far as 35" tires. Back in the day with stock engine and 3.08s I ran 36s for a long time with no real issues. But thats when that truck had all the bottom end torque of the stock cams powerband, with the vortec cams powerband being 1500-4800 my bottom end is barely there now.

[doubeys_nova]

Swapping the carriers i doubt will work since everything is metric anymore. swapping the entire axle should work and give you disc brakes in the rear. 16" rim minimum though.

3.42 vs. 3.73 isnt worth the extra cash IMO. i have all 87 Blazer stuff minus front and rear axles(D44/Truck 12 bolt).

You are a step ahead having the 91 trans/t-case though. the electronic output is exactly what you need for the computer.

Purchase the crankshaft extension/adapter piece(like 10-20 bucks) and take the 4.8L flexplate and extend the holes to bolt to the 700R4 torque converter or drill new holes. dont waste your money on adapter flexplates.

With a 4.8L in that you will be very happy with the investment.

If you like deep aggressive sounding exhaust have a shop custom make 2.5" true dual exhaust with typical flowmaster 40 series. most people will not believe me when i tell them it is a 4.8L and it is no louder than the road noise in cabin.

That t-case should mate to the 4L60E in the truck. that would also be another great approach. 4L60's are getting easier to find than 700R4's around here.

All in all, I know you would be very impressed with the outcome by switching to the LSX. If you ever want to go to a bigger engine just drop in bigger and have it tuned again. i am about to put heads on a 6.0 and swap the 4.8 to help sell mine. 6.0's are known to hit over 400-450hp with cam and heads. anything beyond that your not looking for a reliable driver.

[NastyBuzzard]

The truck I am getting has the 4L60E and all in it and it seemed to be in good shape so I am swapping in the 4L60E, I have heard too many horror stories about the tv cable adapted to ls motors and all. Plus Id like to be able to plug in a tuner and adjust shift points if I feel like it.

The 700r4 I have is rebuilt with transgo shift kit and corvette servos, both it and the 350tbi have less than 10k so I am hoping to sell that combo for some decent coin.

I have heard that my 4lo wont work with the 4l60e though if I dont have some kind of switch.

I am really considering swapping the newer rearend for the disc brakes and the 3.73's, just eventually will need to do the front, plus if I use the 3.73s I wont have to adjust for the 3.42s but will probably have to anyways for the 32"s, I am also trying to consider mpgs as well. I would prefer 16" or taller tires, plus in my opinion on the stock rear it sits inside the wheel well a little far so it looks offset to the inside, the 2" wider rear may help with that too I think.

This is all so awesome, I am so excited about doing the swap and appreciate every ounce of advice I can get. The most worrisome thing for me is the wiring!!!

Also the truck I am buying already has true duals on it as well!! Except I dont remember it having an xpipe or hpipe. I am hoping I can find a way to swap that on there, although I know the tcase is on the opposite side of mine...

I am wondering about headers if they are worth it, I don't really care about high HP #s, more so the bottom end torque and the power being where I normally drive the truck.

Also wish there was a way to get the gas tank to go on my truck. I am tired of fighting with the saddle bag tanks to be honest. Id prefer one simple tank, I thought about the blazer tank swap but I'd like my fuel door to stay in stock place to be honest, I don't want to have it routed to the rear of the bed. '

Thanks!

[doubeys_nova]

I am thinking yours has a HI/LO switch to tell the TBI computer. if not it is probably just a 12v switch that sends a signal to the computer when in 4LO.

for the tv cable, I bought the bowtie overdrives stuff and everything works great. fabbing up my own brackets/cables/spring was not feasible. i will leave that to the pro's.

15" tires and rims are fading out anyways. i would recommend 18" rims since just about everything is that way anyways. you would have 7" sidewalls still on 32" tires.

Our trucks run 2 different tracks factory. the rear end is narrower than the front end or it is just that way on everything i have ever looked at.

I wasnt aware those trucks could have true dual exhaust because of the gas tank. most people y pipe it after the cat. either way the exhaust shouldnt fit inside the frame rails. factory truck manifolds dump inside the rails. the guy that did my exhaust told me that was the hardest part getting the exhaust out of the frame rail and bent towards the back. i cut the pipe off just behind the O2 sensors so i could work out the kinks and drive it to the exhaust shop. stock manifolds vs. headers on a 4.8 is pointless IMO. no cats, no a/c pump and no smog pump will free that little engine up quite a bit.

I am running an inline walbro 255 with corvette style regulator filter and all braided line. if you go this route prep yourself for investing some money into fittings. the quick connect AN fittings are expensive but worth every penny. you could try to mock up the tank under the truck and see but i am sure i wouldve seen something about it when i was doing research if it was possible.

Wiring...I bought my harness from SSP wiring. make sure you can solder and have everything to solder with. i spent hours extending wires that were a bit short. the base tune they gave me is not a bad one but is not great by any means.

FOR GOD SAKES PLEASE clearance your crossmember for the oil pan or you will have to pull your intake on and off all the time to do anything on the backside of the engine. It doesnt take much but i really screwed myself but not doing it. when i jpull the engine this year i am gonig to knock it out. get that engine as far forward as you can. you will have nearly a foot of room in the front so dont sweat that. I wish i wouldve done a dual fan set up from the get go with a diesel radiator. wheeling it does tend to get hot after long periods.

[doubeys_nova]

i will gather some wish i would've's over the weekend and post them up on here. that will be much more beneficial than how to's. if you are stumped by anything go straight to google and dont look back. all the information is laid out much better than i could do by multiple people out there. this is a very simple set up and you will over think just about everything or atleast i did. now it is super simple.

[NastyBuzzard]

Thanks for the advice!! Great information!

If I can't get away from using the stock saddle bag gas tanks I plan to have to dump a lot of $$ into fittings and high pressure fuel line/rubber.

I got my electric fans off a 08 impala, fit great on my stock radiator, all i had to do was trim some plastic with my shears. Wasn't anything to it. I got a thermostatic controller from advanced and wired it all up, it was a lot easier than I thought. However, this 4.8 comes with a mechanical fan and I want to keep my electric fans so I got to figure out a way to wire them into the factory harness. I think it can be done!

[doubeys_nova]

aftermarket harnesses can have a HI/LOW ooptional fan relay controlled by the computer added. one plus to have a professionally built harness but they sit at about $750 w/ computer and base tune for what you have. then it is just a couple hours on a dyno getting it fine tuned. a fine tuned 4.8L should be a very efficient, powerful machine. if i wasnt switching to a 6.0 i was going to get mine done.

[NastyBuzzard]

Honestly though, I'd like to build my own harness for the experience of it. I have set a budget for this and paying for wiring is something I am having trouble justifying, especially since I will have every bit of wiring from the truck including the fuse block and all.

[doubeys_nova]

a lot of reasearch will get you where you need to be on the harness. you shouldnt have electric fan trigger wires or the programming to run them on the computer but that can be programmed by whoever you have do the tuning.

Dirty dingo engine mounts specific for the truck worked great for me. i shouldve put new lower mounts in when i had the chance but didnt.

Trans should just need new holes drilled in the frame for the existing trans cross member. 700r4, 4L60 and 4L60E are pretty much the same trans. your t-case should bolt right to the 4L60E.

Exhaust, you might be able to get it to fit with some pie cuts and stuff. that all depends on your fab skills.

for your air intake you either need to relocate the battery to the drivers side and run stock/aftermarket breathers for the donor truck or custom build one for the drivers side.

guages, you can get sending units that match the factory guages or do autometer. i put autometer guts on my factory guages to keep the stock dash. not cheap but it works

radiator hoses are just factory hoses from the donor truck with a steam port tee'ed in to the heater hoses. dont try to block off the steam port. i did and it failed epicly had sprayed coolant everywhere.

Vacuum, there is a vacuum port on, i think, the back of the intake manifold. that will need to be used for your interior and brake booster.

solder, solder, solder. these sensors are sensitive so you want the least amount of resistance you can get.

are you running A/C?

[NastyBuzzard]

A/C is not real a high priority, but one day, yes I would love to have it. It does get muggy hot down here in South Carolina.

What I have decided is to take the gauge cluster, steering column and hopefully the fuel tank out of the 2001 silverado to be put into my truck. I will also be using the rearend out of the 2001 for the 3.73s/posi, wider rear end, and disc brakes.

My plan so far is to completely take all of the wiring out of the 2001 and integrate it into my 87. I'd really like to make everything run off of the 2001 fuse panel/box.

So far dirty dingo is looking like my best bet, unless anyone took some measurements so I can make my own.

I want to try and get everything to work, even the key fob!! I won't really worry about airbag or abs. But I would like to integrate my electric fans into the ecms and off of the thermostatic controller.

I plan to relocate battery to ds. I need to look into that.

I really want to get rid of saddle bags and mount the gas tank from the 01 and all that goes with it to where the ds saddle tank is now. Also be able to use stock filler neck location.

Life would be easier if I could just set my 1987 body onto the 2001 frame!

[doubeys_nova]

for A/C:

Early 90's blazer/jimmy a/c bracket with the bottom leg cut off and a 94-95 R134A pancake style pump from a truck or car. then all you need is custom lines and a support bar from the exhaust manifold to the back of the bracket.

There is a great write up on, i think a monte carlo, with pictures and stuff out there.