2008 Suburban HD - 8.1L swap (frankenburban 2.0)

[fidelity101]

Okay great. I'm sure you've probably been through this but I ordered a book from Larry Hofer on 8.1 build stuff and it talks about if you are using that kit with 8.1 that he cut a piece of moon shaped aluminum to fill the groove in the bottom of the cover and JB welded in and them ground it smooth so there was a smooth surface for o- rings style pan gasket to seal against otherwise it would leak. I don't know if that helps you or not.

I have not read the book - hopefully the new cover does not have these old issues. its a different design - I had spoke to him about this swap and we went back and forth on some ideas but ultimately he wen't a different route - I had asked him about how he handled the 58x conversion and he had mentioned its in the book...

I double checked the balancer and I had taken off 3.-4mm last time, I just dropped off a new balancer to be machined 2.5mm and go from there, it seemed a bit much and was given some bad belt angle possibly related to why it wants to toss the belt at any throttle over a puddle.

next up is exhaust leaks and hydroboost leaks and a another re-calibration. Some general spring time maintenance

 

[Drtrider82]

Shiny parts! like Christmas! The book is very vague on the swap. It has some good info in there but I would honestly send it back if i could based on how I was treated on the phone. Called to find out if they sold .020 over forged pistons and he just belittled me for asking questions. needless to say I did not order the rockers and cam from him that I was considering. I hope that gets you all taken care of. Do you have 90k on the swap now? How is transmission tuning? That is my biggest worry at this point. I don't want it to be all janky and weird and smoke a transmission. I am planning on taking this accross country next year with a 30 ft toy-hauler. I got a ways to go still.. I am still looking at the pistons! Thanks for posting all this, has helped me a lot.

 

[fidelity101]

no the truck has 90k on it, the swap has ~36k on it, motor is somewhere around 150K miles now - you definitely need someone who can do a trans tune to do as the 6L90 is torque sensitive shifting, and with the extra 2 gears it makes it a little more challenging than a 4L80 where you just change a few shift points and bump up the pressure.

around town cruising its shifting at around 2000 rpm and quietly picks up speed, its very comfortable.

 

[Drtrider82]

Alright so i was looking at piecing together the trans adapter kit using a 3/8 bell housing spacer, shims, bolts, dowels etc. It then occurred to me that the 6l90 is cast 360 degrees around instead of the traditional dust cover/ inspection cover. Did you use the tin cover in the kit or am I missing something. I haven't dug in yet, I'm just trying to think through as much as I can before I tear this down. If I have to order the Chevrolet performance kit as you did I will, just didn't want to spend the money just to toss the flexplate.

 

[fidelity101]

The inpsection cover does not fit and yes the flexplate is wasted, save it for a swap meet sometime.

 

[fidelity101]

Okay so quick update and to elaborate on a few things. The trigger kit is more focused on hot rod swaps (454s) than big trucks that came factory with EFI (496s) so there are some issues.

1. the new cover design to not support truck accessory drive water pump, (not sure about van/ single serp belt/big truck style, they may use the same waterpump)

so you must grind part of the CAM sensor boss away for the top bolt location so unfortunately this is a wasted feature.



2. Because of the new casting mold, the sensor won't leak oil past the o-ring.

3. You need a few bolts to switch to allen style because there are some recessed bosses so you for hot rod swaps you get better clearance on aftermarket harmonic balancers.

4. The lower section of the timing cover that meets the pan has a gap in it which causes the oil pan gasket to not seal properly, Larry mentions this in the 8.1 performance manual but its a bit vague:

"The front oil pan seal radius on the timing cover needs to be modified. The gen 5 and Gen 6 timing cover has a groove for a lip seal to mate to the oil pan - but this doesn't work with the 8.1L oil pan (gen 7)"

this small variation within big block generation's timing cover/oil pan gasket makes the front lower part of the sealing issue a challenge, in the performance manual they mention how they fixed it with some JB weld and allowing the gasket to seal properly but there is no diagram. Does anyone have a 454 cover they can send me so I can line up and make some clarity for everyone on this swap? I already shelled out the 30 bucks for this book to help out too lol.


Also, if you wanted to use the inspection cover you need to install it when the engine is not attached to the transmission because of the bellhousing spacer, it makes this complicated in vehicle/attached.

I'm currently working on my spare intake manifold with this free time with this quarantine time we got too, give it the same treatment

 

[fidelity101]

images aren't working: let me try here

 

[Drtrider82]

Ok so I grabbed a couple photos of the gen 6 big block oil pan and gasket. The cover I have that came on the 8.0 is the same that you have. I am not smart enough to post photos here I suppose. Im pretty sure the covers you have are just gen 6 big block covers with cam sensor provisions. I think Larry is talking about filling the groove in the new cover matching the outside radius so the oring from 8.1 pan can seat to it. If you lookup a 99 k2500 suburban with 7.4 you can see how pan gasket sits in the groove on cover. An o ring would not be seated to anything and would probably leak pretty severly.

 

[fidelity101]

Ok so I grabbed a couple photos of the gen 6 big block oil pan and gasket. The cover I have that came on the 8.0 is the same that you have. I am not smart enough to post photos here I suppose. Im pretty sure the covers you have are just gen 6 big block covers with cam sensor provisions. I think Larry is talking about filling the groove in the new cover matching the outside radius so the oring from 8.1 pan can seat to it. If you lookup a 99 k2500 suburban with 7.4 you can see how pan gasket sits in the groove on cover. An o ring would not be seated to anything and would probably leak pretty severly.

your timing kit has the double cam sensor bolt holes, or just 1 attachment point?


but yeah and none of this is outlined in the GM trigger kit either... but I think you're right - this is focused on the gen 6 BB but just so happens to "fit" the 8.1 but needs some modifications.

email the photos to me and I can post them : [email protected]

 

[Drtrider82]

Mine just has the single mounting position and I am running all 8.1 accessories, brakets and water pump so wouldn't work for me either. I shoot the photos over now, the oil pan is just a rounded edge, picture isnt very clear.

 

[Blue85]

Been reading through your thread as I'm doing a 6L-->8.1L in my GMT800 burb.

Funny thing is this is the same part number for AC compressor as the 6L, but I can't seem to find a photo where they bolt up this 4th hole in any photo...

so I made a bracket just in case.

I went through the same thought process and ended up just leaving the 4th hole floating. When I got the 8.1 there was no bolt there and in the few pictures I've found there was nothing there.

Because of this size you need to throw away the plastic spacer that the LY6 radiator uses to mount the rubber isolators of the radiator into the core support locator holes. The 8.1 radiator takes up this space so there is no need for this plastic component. Also these rubber isolators/locators are in different lengths center to center, the Ly6 is about 36 inches or so apart, whereas the 8.1 is 41 inches apart, a quick hole saw does the trick and you basically make a hole right next to where the core support gets bolted to the frame at the body mount location.

The core support is NOT the same between the two engines, however you can tell it was built on the same manufacturing assembly line as the both but they have unique part numbers so it is close enough.

Here you can see where there is a hole on the core support but no threads, a quick weld nut there and this lines up perfectly. The radiator sits in its new holes on the bottom and bolts right up to the top. And appears to bolt into the “factory” location.

On mine, there was no set of holes for the 8.1L radiator. I ended up sourcing the a core support from a Duramax since in GMT800 BB and D-Max use the same parts here. Not sure if that holds true on GMT900. I put pictures and measurements in my build thread: https://ck5.com/forums/threads/quadrasteer-suburban-tow-rig.339146/page-6

So it turns out you need to put weld nuts or rivet nuts in all of the unused locations on the core support because the fan shroud is different between the small/big block so you need to use those to attach the upper half of the fan shroud.

What did you end up placing in these holes? The picture looks like you can see through, while the GMT800 bars are sealed, so all those mounting holes are blind.

 

[fidelity101]

The 4th hole looks to be floating on the 8.1 anyways so no biggie there.

Maybe the GMT800s had unique tooling for the core support but drilling a few holes and rivnut or weld nut was an easy solution.

I went with weld nuts on the blank holes.

 

[Drtrider82]

To the radiator comments, I installed the 8.1 radiator today and was pretty straight forward. I drilled the bottom mounts and it dropped right in lining up with blank holes. My radiator upper mounts have probably at least and inch of side to side adjustment. I just moved them inward a little past the empty holes, drilled and tapped the support. ‍ probably not as good as a weld nut, but I didnt have any. Rivnuts are great until they are not and spin in the holes. Ill keep an eye on it, but I suspect it will work well. Just options.

 

[fidelity101]

just as I finished my air compressor install

and clean up the PCV system - this happens:

lots of recent quarantine maintenance down the drain - I hope to get the engine out by next week and asses my options.

 

[centexk5]

Oh that sucks.

 

[Blue85]

Glitter? That sucks bad. What do you think let go?

 

[fidelity101]

sounds like it flattened a cam lobe. I hope it get it out next week and see what I got to work with. May try a 544 route or a 511 or stick with the 496. depends on what needs to be replaced ideally and how much I want to spend on transmission updates.

could just be a bearing? (best situation) Lots of copper but there are some non copper debris as well...

 

[fidelity101]

in other news of "I'm a dumbass"

I believe some of my issues is my PCV routing setup and probably had an impact on the tune/caused some lean issues. I need to throw these valve covers away and start over, anyone need these fancy baffles?



This is how I had it.

but this mimics the 6L setup which I thought was okay, but its not...

Realizing I need to get air intake suction from the crankcase I neglected completely this orifice:

there is a NPT port here plugged that is for the medium duty vehicles - they use this port for an oil drain on the air compressor that is attached to the accsesory drive, it runs on the oil from the big block. So effectively I need to do this:

and tune it properly instead of driving it around all the time and mucking with orifice sizes/etc...

but one still the question remains, what size tubing should this be? Its a 1/4" NPT port in the front and a 3/8 NPT in the back, the stock PCV was only a few millimetre port in the throttle body and bottom side of intake manifold. The inlet and outlet of the catch can is also 3/8s"

 

[bigblock72]

in other news of "I'm a dumbass"

I believe some of my issues is my PCV routing setup and probably had an impact on the tune/caused some lean issues. I need to throw these valve covers away and start over, anyone need these fancy baffles?



This is how I had it.

but this mimics the 6L setup which I thought was okay, but its not...

Realizing I need to get air intake suction from the crankcase I neglected completely this orifice:

there is a NPT port here plugged that is for the medium duty vehicles - they use this port for an oil drain on the air compressor that is attached to the accsesory drive, it runs on the oil from the big block. So effectively I need to do this:

and tune it properly instead of driving it around all the time and mucking with orifice sizes/etc...

but one still the question remains, what size tubing should this be? Its a 1/4" NPT port in the front and a 3/8 NPT in the back, the stock PCV was only a few millimetre port in the throttle body and bottom side of intake manifold. The inlet and outlet of the catch can is also 3/8s"

3/8" hose/tubing will work fine.

Will the catch can will have vacuum?

What are you using for an orifice/pcv valve?

Where will the fresh air be drawn in?

 

[fidelity101]

3/8" hose/tubing will work fine.

Will the catch can will have vacuum?

What are you using for an orifice/pcv valve?

Where will the fresh air be drawn in?

Will the catch can will have vacuum?
Yes

What are you using for an orifice/pcv valve?
TBD at the moment, I was thinking of using a one way check valve inline with the tubing to the catch can but stock setup does not run one.

Where will the fresh air be drawn in?
from the back of the plenum that has already been filtered and drawn past the throttlebody into the intake?

this is my assumption at the moment.