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2008 Suburban HD - 8.1L swap (frankenburban 2.0)

When I got my 04' suburban, I drove the 6.0 and the 8.1.......the 8.1 was much more fun to drive! The 6.0 was OK but nothing to write home about. I had to look a long time but found an 8.1 and never regret that decision!

Although my boat is not a monster (20.5' long), the suburban tows it very well!
 
8.1 all the way. Cool build. If an 8.1 can pull a 24,000 pound gvw class a motorhome down the road and pass diesel pushers climbing grades it will tow like a monster in a burb.

Gm was dumb to ever stop building them. But every one that they sold was one less dirtymax on the road. They couldn't have that so they killed it. Now wait till some of the 8.8l variations coming from psi hit the street. Booyah!
 
Chevy305 said:
Nice work so far.

About the injectors, the 8.1 injectors are bigger than the LY6 injectors. I've even heard of people swapping in the 8.1 injectors onto a hotrodded 6.0 to support added horsepower. So dropping down to 6.0 injectors will probably max them out. I don't have exact figures nor have I messed with them before but this is what I've read.
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Just to touch on this...yes some guys put 8.1 injectors on early generation 6.0's. My brother has a 2000 3/4 ton burb with a 6.0 that he ended up throwing a cam, heads, intake and a pretty healthy tune on. He ran that for a bit with stock 6.0 injectors and ended up swapping over to 8.1 injectors and it made a pretty big difference. But once again, that was an early generation 6.0. I believe the later generation 6.0 injectors (like what was in the burb in this thread) were rated for lots more than the earlier generations. So in the case of this build, the OP will probably be fine to run his stock injectors from the pulled 6.0

ZooMad75 said:
8.1 all the way. Cool build. If an 8.1 can pull a 24,000 pound gvw class a motorhome down the road and pass diesel pushers climbing grades it will tow like a monster in a burb.

Gm was dumb to ever stop building them. But every one that they sold was one less dirtymax on the road. They couldn't have that so they killed it. Now wait till some of the 8.8l variations coming from psi hit the street. Booyah!
Click to expand...

Still makes me mad that GM took away the BBC market. I get that all the new LS's make great power, but they only do it at such high RPM's that when it comes to towing, its more of an annoyance. So if you want to buy something to tow well, you are stuck with dmax's. With the costs of diesels getting so outrageous these days (even in the used market), I honestly believe there is a market for the weekend tow guy for a BBC again. They could take the PSI 8.8l platform and just throw an LS style injection on it and slap them in 3/4 and 1 ton trucks again, and I bet they would sell a bunch...but what the heck to I know...All I do know is if GM does ever bring back a BBC platform in their consumer truck market, I'm buying one brand new (with a manual behind it)...and that's saying a lot since I've never purchased a brand new vehicle in my life and never have planned to


This is a cool build. I do like me some 8.1 action. I have a 1989 V3500 crew cab square body with an 8.1/NV4500 swapped into it...problem is I haven't finished it yet cause the last year I moved from CO to ID and sold/purchased homes. And I think my 8.1 I purchased off craigslist very well may be junk as I knew it came from a wrecked truck and sat for a while. But this winter I plan to probably just purchase another pulled 8.1 (one I can hear run first) and swap it in sense mine is completely setup for an 8.1 (all the way down to exhaust being done). Can't wait to drive it!!

Keep up the good work!
 
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They stopped offering the suburban in 3/4 ton in 2013 - since then its been half ton trucks only fort his body style, then since Chrysler and Ford don't have any big blocks anymore, this is literally the last of the big blocks :O

/que madmax music

anyways...


I managed to get some work done this weekend. I painted the frame and while I let it dry I was able to get a few things sorted out to prep the engine for re-install. Swap the fuel injectors over and re-install the rail and drop the oil pan to clean it a bit, some sludge at the bottom but nothing crazy. And foremost was to tackle the robustness of the reluctor wheel install.

After much debate I went with a roll 1/8” roll pin, however I had made a very small woodruff key from another key to help locate the wheel correctly on the gear so I could drill the hole for the pin in the right location.

uc


The gear was deep enough that I didn’t need to drill all the way through but a standard size hardware store roll pin would work fine:

uc


Here is it completed, all that’s left is to re-install the cover and install the crank pulley and oil pan.

uc


I haven't done that part yet because I need to shorten the harmonic balancer by 3.5mm because of the added thickness of the reluctor wheel (2mm) and the thicker crank gear (1.5mm) so that the belt drive is aligned, otherwise it will be 1 to 1.5 ribs off and that will want to toss a belt. Need to do a machine shop run and have that turned around quickly before I can proceed. You CAN PROBABLY do this part yourself with a grinding disc or file but I'm gonna opt to have this done with higher accuracy and be confident that its flat and straight.
 
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Not much I can do now, just waiting on parts to arrive (and come back from the machine shop) – I might have clicked a few wrong clicks so it’s taking a few days longer than anticipated to continue the progress. So until brown santa arrives I managed to paint the frame.

uc
 
Here is the woodruff key I made that would make it flush with the reluctor wheel installed on the crank gear. I then glued this piece to the wheel so I could secure its location while I drilled the hole to lineup/spot my rollpin hole on the gear itself.

uc


Some parts showed up today so I got to work in completing the throttle-body swap, needed to get longer bolts to mate the throttle-body to the tb adapter because the casting was too tall on the tb for the hardware provided - but that was an easy fix.

Proceeded to then add my PCV system ports to the valve covers, those are now done and will be taken into work tomorrow for some sandblasting and eventually painting.

After this I ran out of things to do again… so I started tearing into what I could do with the time I did have, so I took the tq converter off of the LY6 to check it out.



PROBLEM! AKA fun fact, the 6l90E on the Ly6 has 3 bolts for the tq converter to flexplate, the BB has 6:

uc


And they don’t line up at all…

uc


And the big block may have a unique flexplate that is not shared with the Duramax.



The 6.6 got the Allison during the GMT900 but there was no big block for GMT900 so the current parts bin method may not work for this. Maybe I need a custom flexplate? Or the other option (purely assuming things here with parts bin rationale) that the 4l80/85E tq converter will work since it is the same bolt style (6 pad 11.5” spacing) and was offered in the big block… they both have the same pilot diameter (1.7”/43.22mm) but all other dimensions are currently unknown to me at this time.



transpurple100.png


Does anyone know how different the tq converters would be between the hydromatic 4 speed HD and the hydromatic 6 speed HD? Yet there is nothing wrong with my current tq converter (mechanically/condition speaking)

The wildest option is weld tabs onto the tq converter to use the 6 holes but I think this is most prone to error and might cost more in the end.

So this then that sent me down the rabbit hole, until I found this…

http://www.floridatorqueconverters.com/transmissions-chevrolet-6L80E-6L90E.html

looks like there is a 6 bolt 11.5 bolt circle for the 6l90E so then this should bolt up to my current flexplate. The tq converter has the same pilot and hub dimensions but the price says call… so that can’t be cheap and not to mention hurricane.

Per rock auto here are the 6l90E TQ converter dimensions:

uc


Chevrolet Performance has 2 different big block flexplates. The image on the one looks to be a 3 bolt but different google searches show 6 bolt…

And I do not know if the 8.1 flexplate is internal or externally balanced.
 
The 8.1 is internally balanced. Love the build.
 
Thanks! I just want to drive my truck again - itching to get this done.

I assumed as well, I didn't see any weights attached to the flexplate - which makes a custom flexplate idea a bit easier.

I'm really curious to see if the 4l85E tq converter works or is compatible with the 6l90E.
 
Okay so time to poke a bit further into this. I confirmed that the 4l8X series tq converter will not work on the 6l90 trans, totally different animal so that idea is out.

uc


So the pattern isn’t quite totally off, the spread is the same on the 3 pad vs 6 pad but about a .5” inboard however that doesn’t fix the body of the torque converter hitting the flexplate issue. Which is resolved by 1/8” shim (aka 3 fender washers) but my understanding is that you can’t shim a tq converter that way because it will break the transmission (which I am hoping to avoid)

uc


These flywheels both use the 168 count ring gear and same diameter (here you can seem them mesh together like a big gear) and again have a similar spacing but like any LS to BB comparison everything is larger. The center bore is 10mm larger and because of this the crank bolts are 10mm farther apart as well.

uc


Here you can see the BB overlaid on the LY6 flexplate. The ly6 is concave to accommodate the weird housing of the torque converter. Possible idea is drill out center bore, then clock it 30* roughly and then re-drill for big block crank footprint.

However I was discussed this idea with a trans shop they were suggesting that the BB crank will be too long and you would need to shorten the crank because its too tall, I am not sure if he was just trying to sell me a custom torque converter or not.

Running out of options anyone got ideas or validity to his concern? If the crank is too tall couldn’t I just make a spacer for the bellhousing to engine then to make up for this?

Some good news, is that the valve covers cleaned up real well and I sprayed them with a high temp clear:


uc



Back to the googleboard…
 
Have you completely ruled out the converter?

I just ask because that could be your best bet. The 8.1 never came behind the 6L90E so it may be an opportunity to get a perfect stall for the new trans.
 
454Sub said:
Have you completely ruled out the converter?

I just ask because that could be your best bet. The 8.1 never came behind the 6L90E so it may be an opportunity to get a perfect stall for the new trans.
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I'm down to custom flexplate or custom converter but I think it may come down to converter. I don't know what kind of stall I would need for my new trans. stock seemed fine to me - I just do towing with the truck between 6k-10klbs

Tony Vickers said:
There is no replacement for cubic inches.
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Amen, really looking forward to having peak LY6 torque at basically 1500rpm for the bb.
 
I would go with the converter.

Since the 90E never had a 8.1 and only came with the 6.0s the stall wouldn't jive with the 8.1.

Probably pick up some nice performance out of the converter vs nothing gained from the flexplate other than money savings.
 
454Sub said:
I would go with the converter.

Since the 90E never had a 8.1 and only came with the 6.0s the stall wouldn't jive with the 8.1.

Probably pick up some nice performance out of the converter vs nothing gained from the flexplate other than money savings.
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Yeah money savings would be ideal because this was an unplanned expense, I had ASSUMED that this would bolt up and had I known that it didn't I may have just rebuilt the 6.0 with a cam/tune/headers call it good but too late for that big block is sitting infront of me and an 8.1 liter radiator/hose setup should arrive from UPS today...
 
I called up B&M/TCI/BTE/PTC all of them had no flexplate option for this swap.

So I have spent the past few days calling around and some shops don't even deal with the 6 speeds, they only do 4 speed stuff when it comes to tq converters. It looks like a custom flexplate is out due to the spacing of the crank, there is no crank spacer on the big block like there is on the LS engines. Each way points me back towards custom torque converter and the shops that typically do 6l80/90 stuff have it in cars primarily and their lowest stall available is 2800 rpm which is way too high for this application. I'm not looking to run a bunch of spacers and adapters, would rather this just work. Ideally I should have just overhauled the 6L with a cam and some other bolt ons and called it good - can't go back now though!

Pro-torque seems capable of making what I need - started some discussions with them this morning and hopefully have something begun to built this week, Something something billet cover and multi disk something something. They do some diesel stuff so they are aware of the application and needs hopefully this works out well. I would like to have this installed in the truck early October because I only have a 90 day warranty on the junkyard engine. Its been 32 days so far and a long way to go...
 
2800 isn't to high on a mild big block. A friend of mine has a built 8.1 and runs a 2500 in his. 4 speed but same concept. Pulls a trailer just fine and also has burned 2k in BFGs in 7 months.
 
454Sub said:
2800 isn't to high on a mild big block. A friend of mine has a built 8.1 and runs a 2500 in his. 4 speed but same concept. Pulls a trailer just fine and also has burned 2k in BFGs in 7 months.
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I can't seem to find a good resource for the stock stall speed the best I see is about 1800-2000. This will be a stock big block I don't think I will be doing much of power adders. the race car is getting jealous that all the work and attention is going to the tow vehicle. Almost forgot I use the tow vehicle for another purpose lol.

are you suggesting he has burned through a set or two of BFGs? yikes.
 
You don't want a 2800 stall with peak torque well below that. It will feel soggy down low. I think you are on the right path to get a custom converter built to suit the engine torque specs.
 
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