OldDave said:your flex plate shows no signs of any weights welded on it and all the info I can find says the 8.1L is internally balanced.
any be careful if you buy a cam, the 8.1L has a different firing order that the old BBC.
That was my assumption as well and due to recent findings the cam is currently out of question right now due to flexplate situation.
From what I've read you can easily switch to BBC firing order by repinning the injector harness and moving the plug wires to match. Makes sense.
In reply to 2002maniac :
in this application the firing order doesn't matter and they do a pretty good job of outlining the 8.1 BB compatible cams.
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.
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)
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.
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?
Some good news, is that the valve covers cleaned up real well and I sprayed them with a high temp clear:
I would call one of the big race converter shops and see if they offer a flex plate that would solve your dilemma. maybe B&M, or TCI. or maybe they can add 3 more lugs to the converter and move all 6 out to the correct circumference.
and as far as shimming the TC away from the flex plate, we used to do it all the time, just make sure the converter can spin freely when pushed as far into the trans as it will go and that there is more than enough room so that you have to pull it at least.125" forward when adding shims. that way it won't be bottomed out against the pump drive, but has the deepest engagement with the pump.
OldDave said:I would call one of the big race converter shops and see if they offer a flex plate that would solve your dilemma. maybe B&M, or TCI. or maybe they can add 3 more lugs to the converter and move all 6 out to the correct circumference.
and as far as shimming the TC away from the flex plate, we used to do it all the time, just make sure the converter can spin freely when pushed as far into the trans as it will go and that there is more than enough room so that you have to pull it at least.125" forward when adding shims. that way it won't be bottomed out against the pump drive, but has the deepest engagement with the pump.
I called up B&M/TCI/BTE/PTC all of them had no flexplate option.
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 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...
Not a lot of feedback from the custom torque converter shops... but pursuing my parallel path of OEM parts, GM may have a solution for me it turns out...
Chevrolet Performance Transmission Adapter Kits 19154766:
Couple key comments -
Can I use the newer LS 4L60 Family electronic transmissions behind the older Small Blocks and Big Blocks?
As noted above, the bell housing pattern is essentially the same, but you will have the opposite converter nose to crankshaft pilot issue. (compared to LS engine to old style trans) The torque converter pilot on any LS style 4L60 family transmissions will bottom out in the crankshaft before the bell housing touches the block. In this case you need adapter kit p/n 19154766 to space the bell housing back approximately 9.6mm to gain the proper clearance between the converter and crankshaft when using the newer LS style 4L60 family transmission behind a traditional small block.
Torque Converter to Flexplate Bolt Circle Diameter (BCD)
There are basically 3 different torque converter to flexplate bolt circle diameters (BCD) used by GM over the years.
The 4L80 family and TH400 use an 11.5” (292.1mm) BCD.
The early 4L60 (pre-LS engine), TH350, 700R4, 2004R, P/G, etc, use a 10.75” (273.05mm) BCD
Later “LS” style 4L60 family transmissions use an 11.062” (281.0mm) BCD. (6L80 is also 281mm)
Rear Crankshaft Flange Bolt Patterns
All early Chevrolet Small and Big Block with two piece rear main oil seals used the same 3.580” diameter 6-bolt flange pattern for attaching the flywheel or flexplate to the crankshaft. The Big Block has kept the same 3.580” 6-Bolt pattern regardless of the seal design (one piece or two piece) throughout its history.
In the mid 1980s the small block changed the rear main oil seal to a one piece design using a 3.000”
All Gen III and Gen IV LS design small blocks use a 3.110” (79 mm)
The BB and early SBC have a 9.6mm longer crank compared to the LS style engine.
So it sounds like if I go with this kit and I re-drill my existing flexplate to match to the torque converter pattern and then this will work but the engine will sit 10mm forward in the truck so I may need to get a little creative in my engine mounts/mount brackets or move the trans brace backwards and take up some yoke slack.
It also sounds like if you have an LS you need dished flexplate to make up for the offset because of the shorter crank to maintain the bellhousing flange to crank flange gap. If you have an older style engine or BB with the long crank you need the flat flexplate to maintain that gap. Again this supports my theory that the the new LS engine family is just an SBC built with a computer instead of a drafting pad.
So meanwhile with the downtime, I went ahead and started assembling what I could and get done what I needed to. I am a huge fan of chasing threads with a tap so everything bolts together nicely and without a fus. So I replaced the exhaust studs that were missing and chassed the remainders with a die, mostly because I couldn’t get them out.
With a help of a friend we cut down the stock harmonic balancer using a lathe, you have to have a chamfer on it so the reluctor wheel fits properly. Its about 1mm of a step, the OEM hub has a gradual step as well but likely to just not cut the front seal upon install. However the reluctor wheel has this opposite feature to accommodate it so it must be retained or clearance appropriately.
Then I got the flexplate back from the machine shop with the new pattern.
After that it was time to get moving so I started to get the engine together and install the harmonic balancer/oil pan/timing cover/water pump.
Now its wiring time, the original wiring has a plastic sleeve that was all but brittle and collapsing so on a decent build you are ordering new hardware it helps to spend the extra 25 bucks and get some nice loom to protect everything so I wrapped the harness worth about 25’ worth and only have maybe 1-2 feet of wire uncovered. I didn’t bother to remove most of the plastic protection except where it was clearly deteriorating into pieces. This is a wrap around kind so I just tape it to keep it shut that way you are not fishing wire through the loom.
The wiring job for getting the gen III engine on Gen IV is pretty easy.
1. Passenger side knock sensor is the easiest but the wiring is a bit tight, not sure if I will need to extend this or not but the red hole is where the existing one was located (LQ4 have these in the valley of the V for some stupid reason so good luck with that). The thread boss nearby (circled orange) is already tapped for m8x25 so I just hit it with the surface disc and chased the threads for a good contact. Existing knock sensor threads are a larger pipe thread, not sure about running a plug in there then drilling/tapping it but this seemed easier and maybe the knock sensor will perform more normal, just an assumption.
2. Driver side knock sensor is a little “harder” but same concept of moving it to the other boss however the boss is drilled and tapped for an m6 bolt so you need to get a 7mm drill or 17/64” and then re-tap it to m8x1.25 thread pattern (circled orange) here there is a lot more wire length as well and clears behind the installed engine mount easily.
3. Electrically the CLT are the same but the ½” NPT is a bit hard to find adapters for so I just cut the connector and did my own 2 pin weatherpack. Since the ECU reads resistance like a DVOM the wires won’t matter which way you connect them. What is not shown is the harness lengthened, I think it needs a few more inches for routing purposes and not melting it with the exhaust manifold.
4. These are the easiest, two 2 pin connectors need about 4-6” length increase.
5. The cam sensor is the same connector but because my LY6 had VVT they have a 5 pin connector, you don’t need this anymore so I cut the wires and hid them in the loom. The wires are too long with this setup too so I cut the extra wire length and omitted the connector (circled in green). If you want to keep this harness section intact you can just junkyard a new pigtail or order one online.
6. Here is the “hardest” wiring job, the crank connector is totally different and in a different location, you need to shorten the wires and then hookup the correct wires to the new connector, luckily they are the same orientation (lock mechanism upward when connector facing you) so wiring is pretty easy
Here is the new connector, you can find this in the junkyard off of a 4.3L from an S10 or blazer etc actually, colors may be the same – not sure on that part but I got this pigtail online for about 20 bucks.
(LY6 connector to new58x connector)
· Pin A to Pin 3 (white wire with black trace)
· Pin B to Pin 2 (grey wire with black trace) (ground)
· Pin C to Pin 1 (purple wire with white trace)
They are both wired the same and electrically the same with the same wire colors just the connector naming is reversed…
So with that all done it was time to install the spacer kit, it came with longer dowels and a bellhousing flange.
I was afraid that spacing the engine 10mm forward would mess up the engine mount alignment but I undid the trans mount that allows some forward/aft movement and was able to eat up this gap with that slotted tolerance in the crossmember and push the transmission backwards in vehicle a touch. A bit of wiggling later and careful guidance and the engine was mounted in without having to modify the stock mounts in any way shape or form. It is currently bolted down.
Now I just need to verify if the spacers provided are enough because I do not want to grenade a transmission or tqcv. I want to double/triple check this area before I go further with installing everything else just in case I need to remove the engine again.
Awesome! I guess this is one reason parts bin cars are nice.
Link to that loom?
In reply to java230 :
yup!
https://www.mcmaster.com/#catalog/123/857/=19n1x6y
makes it look real expensive build but its actually quite reasonable.
Nice work! You're on track for a factory quality install.
I've been enjoying this thread a lot - you do beautiful work!
You make me want to re-loom my truck. I hate that the plastic loom is starting to crumble.
when I first saw the comment about moving the engine ahead 3/8", my first thought was there should be enough wiggle room in the trans mount to absorb it. good to see it worked out that way.
yeah, pre two seal era swapping chevy engines was a piece of cake, from four cylinders to 454's they all had the same bellhousing, flywheel, and starter patterns. (mostly)
2002maniac said:Nice work! You're on track for a factory quality install.
Thank you, that's the plan! When someone pops the hood they won't see anything different, no special instructions to operate it either - just work like an OEM vehicle. I'm just picky when it comes to certain things now. I used to just give everything a few ugga duggas and call it guten tight. I haven't decided If I will put the 8.1 cover on yet or not. It would hide a lot of wiring and look a bit more OEM too.
Got a few things buttoned up last night, hopefully getting it fully assembled this weekend then call a few friends for HP tuners help.
fidelity101 said: I haven't decided If I will put the 8.1 cover on yet or not. It would hide a lot of wiring and look a bit more OEM too.
Do it! Besides making it nice and tidy, it will be pretty subtle hint that something awesome has been done.
This build and the stuff that Cousin_Eddie rolls out is awesome ....keepin' it stock appearing is really an art form. I kinda get that your up against it , but 1.7's would be an easy afternoon. Great work!!!
Now the moment of truth, the tqcv spacers provided are 7mm whereas the bellhousing spacer is 9.6mm, this should give proper tqcv clearance, and it did! We have a 6mm gap with the tqcv full seated which is good enough to pull it forward without it disengaging the pump drive and breaking a transmission/tqcv.
The rest is just assembly for the most part, re-assemble everything but once that occurs I need to worry about the tune, kinda curious just to start it up and see if it will idle, I don’t see why not but I am not familiar with HP tuners. I have a few resources available but has anyone tried to overwrite a tune? I mean I would unlock the VIN/ECU for the truck but then can I just download/upload the stock L18 tune to the PCM? Or am I better off manually inputting these values. IE since the TCM is separate on the gen III LS stuff I wonder if it will get all wonky. The other thing is the torque messaging for torque managing the clutch to clutch shifts and shift points etc, this will need to be adjusted independently. Long story short, I don’t know anything about HP tuners other than everyone uses it.
Some progress however, I do need to take the harmonic balancer off again though to get the rust off of the shaft where the seal rides, (now that I’ve shortened it) I neglected to clean this up enough and I don’t want to do a front main seal job after the front clip is assembled and etc. I really hate using the harmonic balancer install tool. ..
Making progress during the re-assembly should be fully put back together this weekend then ready for a tune.
PRO TIP #1: Install trans dipstick BEFORE putting the engine in while the trans is lowered, it is much easier. No wait - its physically impossible to do it if you don't. I cut the bracket off where it attached to the back of cyl head so I can install it while the engine is in the vehicle. real big PITA.
PRO TIP #2: connect the oil pressure sensor before you put it in the engine bay, or at least before you connect the driver side cat/exhaust. not impossible but unnecessarily difficult.
Trying to assemble everything from the rear forward, but I wanted to get this low hanging fruit out of the way: A/C compressor.
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.
When I redid the AC on my 8.1 Burban this summer, the compressor only used 3 mounting bolts just like yours.
On hptuners there is a function to select all different tables and paste them into your tune
More progress assembling everything, the core support is back on and a lot of the little other tid bits, wiring is hooked up. There is one hang up on the cooling system though. I did opt for the 8.1 radiator/cooling system entirely but it was not as plug and play as I thought.
PRO TIP #3: when using the AC delco radiator it needs the AC delco lower radiator hose, on the radiator end it uses a large quick disconnect fitting like the oil/trans cooler lines use. This radiator is cheaper than the other aftermarket radiator but the other radiators use a traditional lower radiator hose. So keep this in mind when ordering parts, in the end you will spend the same amount of money because the AC delco radiator is cheaper but the hose is more expensive, the other brand radiator is more expensive but the hose is cheaper.
Here is the 6.0 radiator in front of the 8.1 radiator, it is actually quite a bit larger in each dimension overall.
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.
Almost done with the swap, The only thing left is wait for the correct radiator hose to come in the mail then install the cooling fan/shroud, add fluids and put the fascia and lamps on then its ready for a tune and good to go!
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.
Need to hook up the heater core lines and then add fluids and we are ready to test fire later today. Not sure how well the truck will run without the maf hooked up, waiting on the intake kit to come in the mail and that should be the last thing before getting a tune done.
Happy belated friday the 13th! got some fluids in and with everything hooked up, it started and runs and idles! no scary story here :)
The stock intake (LY6) has too many resonators on the piping they collide with virtually everything, otherwise it should fit but with the 8.1 TB kind of clocked upward a bit I am worried about hood clearance. I will try and junkyard a solution meanwhile I wait for my flowmaster unit.
All that's left to do:
Nice work!
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