L18 8.1L swap resource thread

[efituned]

What are y'alls thought about plugging the rear oil pressure sending unit location and using the port next to the oil filter? Is that port in the same plumbing of the sensor port on the back of the block. Is the oem sending unit needed by the PCM? I would like to run a mechanical gauge that is feed from a more accessible port.

 

[Larry]

I’ve never done it that way but it should work. No, the PCM does not need to see oil pressure input but that also depends on how your tuner has the ECM set up. Neither of my transplanted 8.1L’s have any oil pressure input to the ECM.

 

[Russell]

As Larry said, you'll get a DTC set without it hooked up unless it is disabled in the tune.

 

[-stew-]

Does anybody have any links to other swap threads? I'm soon to be gathering parts for a spring swap and would like to to some reading up. On the electrics side of things, how close is this to an LS swap? Like for gauges, mainly.

 

[Larry]

Does anybody have any links to other swap threads? I'm soon to be gathering parts for a spring swap and would like to to some reading up. On the electrics side of things, how close is this to an LS swap? Like for gauges, mainly.

There are lots of swaps going on at the “8.1L Swap Classifieds” group on Facebook with links to various builds.

As far as the wiring side of the 8.1L it is pretty much the same as the Gen III “LS” engines up through about 2007 outside of some minor circuits being wired a tad different such as the crank sensor. There are some other differences where the 8.1L had electronic throttle for all years whereas the “LS” engines got it in 2003 or 4. That is not to say you must run electronic throttle though. I don’t! Again, its back to tuning…..

As far as gauges, you can be like a lot of people and throw money away at Dakota Digital stuff and pull sensor data from the ECM or be like me and just run the factory gauges just like they were designed to run on the old carbureted engines. My oil pressure, temp gauge, A/C and alternator all operate just like they did on the original 350 engine harnesses directly to the sensors themselves on the engine….just like the old days. A lot of it depends on how you order your harness, ECM tune and come up with the right sensors. Actually, you can screw in an old sending unit into the 8.1L oil pressure port or you can change the pig tail on the truck harness to plug into the stock 8.1L oil pressure sensor. Either way, the gauge will work fine. As far as a temp gauge, just screw in an older 454 temp sensor in the driver’s side head coolant port (same spot BBC’s have always had pipe plugs) and plug your original truck temp gauge wire to that. The actual coolant temp sensor the ECM reads from is on the passenger’s side head. That one will plug into the harness for the ECM.

Long story short…..you don’t HAVE to run all the aftermarket gauge junk to run a 8.1L or an early “LS” engine although many people do it for some odd reason. Each to their own…..I like leaving my cluster bone stock and saving a $1000 on aftermarket crap. The 5.3L I’m putting together for my buddy’s ’91 K5 will be the same way. The gauges will run on the engine just like they did on the TBI 5.7L before it and totally independent of the ECM.

Think about it…..your gauges don’t know if the engine is a 250 6 popper, TBI 350 or a torque machine 8.1L and it is none of the gauges damn business what is under the hood

 

[-stew-]

Thanks Larry! I posted on the CK5 bookface page and tagged you requesting a link to that group. I can't find it.

 

[-stew-]

Found it! Man is the search function on bookface TERRIBLE!

 

[efituned]

Well got the engine & transmission in yesterday...


Things left to do:
- Headers ( I wish I could have used the stock manifolds)
- Fuel System
- Wiring Harness
- Oil & Transmission Coolers
- Modify Transmission Gear Selector Linkage & Transfer Case
- Decide whether to go DBW or mechanical throttle

Any recommendations on headers, not really looking for performance gains, just looking for something that's an easy fit..?

 

[Larry]

Looks right at home in there! Stabbing the engine in there is the easy part. The next steps will take forever! LOL

As far as headers, I wouldn’t use them. I would just find some 73-87 BBC manifolds and run with them. If you really feel the need to spend money on headers my recommendation would be the Sanderson 67-87 BBC shorty headers. I have those on my Burb but would not buy them again. Already tired of fixing header leaks in under a 1000 miles. I have not had ONE single exhaust leak on the K10’s 8.1L in almost 8 years and 35K miles running mid-80's manifolds.

 

[-stew-]

Looks right at home in there! Stabbing the engine in there is the easy part. The next steps will take forever! LOL

As far as headers, I wouldn’t use them. I would just find some 73-87 BBC manifolds and run with them. If you really feel the need to spend money on headers my recommendation would be the Sanderson 67-87 BBC shorty headers. I have those on my Burb but would not buy them again. Already tired of fixing header leaks in under a 1000 miles. I have not had ONE single exhaust leak on the K10’s 8.1L in almost 8 years and 35K miles running mid-80's manifolds.

Do you thing you're leaving power on the table running manifolds? What are you doing for exhaust otherwise? Currently i just have a generic flowmaster hanging off the (shot) factory y-pipe and nothing else.

 

[Larry]

Do you thing you're leaving power on the table running manifolds? What are you doing for exhaust otherwise? Currently i just have a generic flowmaster hanging off the (shot) factory y-pipe and nothing else.

Dunno, don’t care . I suppose if you trying to squeak every ounce of power out of an engine headers sure wouldn’t hurt any but if you want to bolt something together that will reliably stay together exhaust manifolds are the way to go.

The K10 has 80’s 454 manifolds with true dual 2.5” pipe with a cross pipe behind the cab and dual Thrush mufflers. The Suburban is similar but with Sanderson shorty headers with the pipes ran down the driver’s side into a dual inlet/dual outlet Magnaflow xmuffler. Not real thrilled with the way it sounds. There are pictures of the Suburban exhaust in the Polar Bear thread. The K10 sounds much better IMHO.

 

[efituned]

On the 73-87 swap trucks, what are y'all using for lower radiator hose and the heater hose that would normally factory T into the lower radiator hose?

 

[Larry]

On the 73-87 swap trucks, what are y'all using for lower radiator hose and the heater hose that would normally factory T into the lower radiator hose?

The lower hose depends on which 8.1L water pump you are using.

I run the Medium Duty/G-van/Workhorse water pump and accessory brackets and use the typical square body BBC lower hose. This water pump will accept the typical ole BBC square body lower hose

The Silverado/Sierra water pump had a different outlet. Not sure what people are using for a lower hose

The heater hose return goes to the port in the radiator tank. I haven’t seen any 4 core radiators without the return port in the tank. If you don’t have a big radiator you’ll probably want to get one.

 

[Kay86K5]

I have a couple question regarding this swap. On the MAF sensor if you decide to swap over to the L29 throttle body. First of all, where is the MAF located on the stock L18? On most of the LS based motors they are right next to the throttle body. So just thinking about it if you swap to a different throttle body to keep mech throttle, how does this affect the MAF sensor? I saw Larry's post on the first page that shows his aftermarket air intake set up that looks like he adapted the stock MAF sensor into this, but what is everyone doing if you are swapping to the L29 throttle body?

Also, what is the final consensus on the VSS? I know it was discussed a couple pages back, but are you saying the L18 pcm does not need any type of VSS/speed signal to run correctly? Just seems weird to me, but that could be because I know with TBI it's almost necessary (as I just did a TBI swap in my K5 not too long ago). Anymore input from you guys on this would be great.

Lastly, has there been anyone who has successfully set up dual sattle tanks to work with this now? I saw the discussion about not being able to find the correct size return line, but has anyone found a good success to simply have the dual tanks work well with this?

I just purchased a 1989 v3500 crew cab with a TBI 350 in it that I want to swap an 8.1 liter into. It would be freaking sick!!!

 

[Larry]

I have a couple question regarding this swap. On the MAF sensor if you decide to swap over to the L29 throttle body. First of all, where is the MAF located on the stock L18? On most of the LS based motors they are right next to the throttle body. So just thinking about it if you swap to a different throttle body to keep mech throttle, how does this affect the MAF sensor? I saw Larry's post on the first page that shows his aftermarket air intake set up that looks like he adapted the stock MAF sensor into this, but what is everyone doing if you are swapping to the L29 throttle body?

Also, what is the final consensus on the VSS? I know it was discussed a couple pages back, but are you saying the L18 pcm does not need any type of VSS/speed signal to run correctly? Just seems weird to me, but that could be because I know with TBI it's almost necessary (as I just did a TBI swap in my K5 not too long ago). Anymore input from you guys on this would be great.

Lastly, has there been anyone who has successfully set up dual sattle tanks to work with this now? I saw the discussion about not being able to find the correct size return line, but has anyone found a good success to simply have the dual tanks work well with this?

I just purchased a 1989 v3500 crew cab with a TBI 350 in it that I want to swap an 8.1 liter into. It would be freaking sick!!!

The throttle body itself doesn’t care where the MAF is located. The MAF sends the inlet air temperature and air inlet grams signal to the ECM, not the throttle body. A mechanical TB or electronic TB has no bearing on MAF in anyway but the ECM needs to be tuned for electronic throttle or mechanical. Almost all Workhorse RV and commercial stepvan’s had the MAF over 2 feet away from the TB on 4.8, 6.0 and 8.1L engines.

My experience with VSS consensus is it is not needed on a stock engine with a manual transmission. However, if you use a 4L80E VSS is required. That is straight from Howell Engine Development and other tuners I have spoken with. Keep in mind, TBI is entirely different in that it is a speed density system but then again, I’ve successfully done TBI conversions without using VSS as well. I’ve also learned on my Polar Bear Suburban’s 8.1L with a RayLar 202 cam that the combination of VSS and electronic throttle would help a tuner mask the bad habits of the large cam. I’m not interested in adding either of those to my Suburban so the RayLar cam is coming out and a new stock cam is going back in this December (The RayLar cam is sold).

As far as the dual tank set up, no…. I have not actually read where anybody has successfully gotten the dual tank switch valve to work properly behind an 8.1L. There are forum stories where people were successful with them on LS engines which run the same fuel pressure so I am not sure what that is about. All I know for certain, is mine absolutely would not work with several different Pollak (OEM switch valve) valves as it drove the head pressure well up over 100 psi. Once the switch valve was removed from the return side, head pressure came back down to normal (62 psi). I feel the 5/16 return port on the Pollak switch valve is just too restrictive. I tried a carbureted switch valve, a junkyard '87 TBI switch valve and a brand new '87 TBI switch valve. I scoured every corner of the internet for a different switch valve to use other than a Pollak with no luck. In the end, I just use the RH tank to push fuel into the LH tank. Works great as long as you remember to turn off the damn transfer pump switch. If anybody comes up with a solution to the dual tank switch valve I would love to hear about it.

 

[bigblock72]

I have a couple question regarding this swap. On the MAF sensor if you decide to swap over to the L29 throttle body. First of all, where is the MAF located on the stock L18? On most of the LS based motors they are right next to the throttle body. So just thinking about it if you swap to a different throttle body to keep mech throttle, how does this affect the MAF sensor? I saw Larry's post on the first page that shows his aftermarket air intake set up that looks like he adapted the stock MAF sensor into this, but what is everyone doing if you are swapping to the L29 throttle body?

Also, what is the final consensus on the VSS? I know it was discussed a couple pages back, but are you saying the L18 pcm does not need any type of VSS/speed signal to run correctly? Just seems weird to me, but that could be because I know with TBI it's almost necessary (as I just did a TBI swap in my K5 not too long ago). Anymore input from you guys on this would be great.

Lastly, has there been anyone who has successfully set up dual sattle tanks to work with this now? I saw the discussion about not being able to find the correct size return line, but has anyone found a good success to simply have the dual tanks work well with this?

I just purchased a 1989 v3500 crew cab with a TBI 350 in it that I want to swap an 8.1 liter into. It would be freaking sick!!!

The MAF usually goes next to the air filter, the throttle body will have no effect on the MAF. Just need the right software to make the IAC work and eliminate throttle body codes.

VSS is not necessary when running a manual trans or old style automatic (th350, 400 etc) there can be a small difference in drivability on some manual trans applications with the right manual trans tunes but only the most anal types will notice. If you use a 4l80e trans then VSS is necessary.

Dual tanks are a little finicky, but I have done them on different EFI swaps (not an 8.1l specificly) with some success. Use an elctric pump in each tank with a switch to select the pumps and senders. Tee the pressure lines together (no need to put valves or selectors or anything) the non running pump will act as a check valve so all pressure from the running pump goes to the engine. The return line can be run through a normal 3 port selector valve or simply Teed back to the tanks.

 

[Kay86K5]

Thanks for the reply guys. That's good to know on the MAF sensor. That is what I was thinking, especially after I saw Larry's photo of his air intake setup, just wanted to make sure.

I have not found motor or tranny yet, so everything will depend on what I find there. If I find a donor truck with a newer tranny, then I will swap it and deal with VSS then. But if I find a real good deal on just a motor, I am not opposed to bolting it up to the th400 in the truck now as it shifts really good (has anyone run an 8.1 on here with a th400 behind it? Did you regret not putting an overdrive tranny behind it? Any and all advise on that would be great. I plan to use this crew cab as a tow rig mainly).

I will have to look at all the options of the dual tanks. Would love to carry that much fuel, but defiantly not a deal breaker as far as the decision to swap an 8.1. These things are a freaking awesome motor!

 

[efituned]

So I've started on my wiring harness...if running a DBW throttle is there a necessary TAC module that controls theTB or connects the pedal to the TB?

I was going run DBW TB to save from buying a mechanical TB, but if I have to buy a TAC I might as well buy a mechanical TB and cable. My electronic TB connector is busted anyways, so I am not sure it will even work.

Back to the wiring, everything seems straight forward, just eliminating some of the wires I don't need like A/C, EGR, rear O2, etc. The harness I have had a Allison behind the 8.1, so I'll have to repin(add pins) to the where the 4l80E should be. The swap is almost complete, dropped of the rear driveshaft today to get cut. I have to buy 3 coils that were missing from the engine, MAF, program the ECU, and figure out the transmission linkage.

 

[Larry]

But if I find a real good deal on just a motor, I am not opposed to bolting it up to the th400 in the truck now as it shifts really good (has anyone run an 8.1 on here with a th400 behind it? Did you regret not putting an overdrive tranny behind it? Any and all advise on that would be great. I plan to use this crew cab as a tow rig mainly).

There are a few 8.1L swaps running around with TH400’s but I don’t think anybody ever regrets swapping in an OD trans. While not an automatic, I ran a SM465 behind my K10’s 8.1L for the first 1.5 to 2 years. With 4:56 gears the lack of OD was a killer for highway driving.

So I've started on my wiring harness...if running a DBW throttle is there a necessary TAC module that controls theTB or connects the pedal to the TB?

I was going run DBW TB to save from buying a mechanical TB, but if I have to buy a TAC I might as well buy a mechanical TB and cable. My electronic TB connector is busted anyways, so I am not sure it will even work

Yes, for 8.1Ls if you plan to run DBW you most definitely need a TAC module. I consider myself above average when it comes to wiring and rewiring but personally, I wouldn’t ever waste time reworking a harness from a donor truck. The best $600 you can invest into a late model engine swap is to start with a brand new stand-alone harness.

 

[efituned]

Yes, for 8.1Ls if you plan to run DBW you most definitely need a TAC module. I consider myself above average when it comes to wiring and rewiring but personally, I wouldn’t ever waste time reworking a harness from a donor truck. The best $600 you can invest into a late model engine swap is to start with a brand new stand-alone harness.

The wiring doesn't scare me at all, I've done plenty of custom engine harnesses on bmw, honda, and mercedes. Sometimes can be time consuming, but it gives something to do. I plan on posting some pictures when I am done with the harness along with the rest of the swap.