Start a build thread so we can follow along. Any weird or new swap 8.1 issues we can add here.
CK5
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L18 8.1L swap resource thread
- Thread starter Larry
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Right, there hasn’t been much said about adding an oil cooler because its very straight forward. Get a pair of ½ pipe thread AN fittings for the block then mount a cooler and run lines to it. Pretty simple. If I could find the real estate under my rigs, I wouldn’t mind having one too.
Seriously, is there really any other clutch worth using besides a 12”??
.......Of course, a 12” clutch fits. The 8.1 isn’t a little LS engina that requires oddball spacers and clutches 
And no, the 8.1 uses its own unique flywheel 12582964. It is only shared with the 8.1L, GMPP crate 572 and PSI 8.8L. Right now that flywheel is $211 on Summit Racing
Centerforce Part numbers:
DF024909 - Dual Friction, Clutch Pressure Plate and Disc Set
This is basically the typical 10 spline GM 12” clutch used from the beginning of time up until around 1995 or so when GM moved to the integrated release/slave. This set is what is in my K10 with the external slave and same clutch part number I used when it had a 465 and mechanical clutch. The dowl pins on the 12582964 need to be removed and 2 or 3 holes in the pressure plate opened up to accommodate the larger metric bolts
When I first installed the 8.1 in my K10 in 2009, I reused the same exact 12” DF024909 that was on 454 that I pulled out. The black crap smeared all over the PP is what’s left of an old clutch fork boot that fell inside on a snow run one time
DF097310 - Dual Friction, Clutch Pressure Plate and Disc Set.
This is also a 10 spline 12” clutch but the disk and pressure plate are unique to integrated slave/release bearing. Same as above where, the dowl pins on the 12582964 need to be removed and 2 or 3 holes in the pressure plate opened up to accommodate the larger metric bolts. This is basically an L29 454 clutch and what Rob has in his K5 and what is in my Suburban.
CF does list another part number for a GMT400 3500-HD with an 8.1L/NV4500 and yet a different one for a GMT800 8.1L/ZF 6 speed. I never had a chance to get my hands on those to see what the differences are. I suspect the GMT400 version is mainly the PP has provisions for the dowl pins and a larger holes for the metric PP to Flywheel bolts and the GMT800 is different yet because the ZF S6-650 has a very funky release bearing/slave unit that is much different than a NV4500 version where the PP fingers look different in Centeforce’s pictures. Neither of those CF part numbers existed when I started doing 8.1 swaps so I've stuck with what I know works instead of trying the other two part numbers...plus they cost more, probably due to low volumes
This is a DF097310 mounted in Rob's K5
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So it is said, so it shall be.........Right, there hasn’t been much said about adding an oil cooler because its very straight forward. Get a pair of ½ pipe thread AN fittings for the block then mount a cooler and run lines to it. Pretty simple. If I could find the real estate under my rigs, I wouldn’t mind having one too.
Seriously, is there really any other clutch worth using besides a 12”??
And no, the 8.1 uses its own unique flywheel 12582964. It is only shared with the 8.1L, GMPP crate 572 and PSI 8.8L. Right now that flywheel is $211 on Summit Racing
Centerforce Part numbers:
DF024909 - Dual Friction, Clutch Pressure Plate and Disc Set
This is basically the typical 10 spline GM 12” clutch used from the beginning of time up until around 1995 or so when GM moved to the integrated release/slave. This set is what is in my K10 with the external slave and same clutch part number I used when it had a 465 and mechanical clutch. The dowl pins on the 12582964 need to be removed and 2 or 3 holes in the pressure plate opened up to accommodate the larger metric bolts
When I first installed the 8.1 in my K10 in 2009, I reused the same exact 12” DF024909 that was on 454 that I pulled out. The black crap smeared all over the PP is what’s left of an old clutch fork boot that fell inside on a snow run one time
DF097310 - Dual Friction, Clutch Pressure Plate and Disc Set.
This is also a 10 spline 12” clutch but the disk and pressure plate are unique to integrated slave/release bearing. Same as above where, the dowl pins on the 12582964 need to be removed and 2 or 3 holes in the pressure plate opened up to accommodate the larger metric bolts. This is basically an L29 454 clutch and what Rob has in his K5 and what is in my Suburban.
CF does list another part number for a GMT400 3500-HD with an 8.1L/NV4500 and yet a different one for a GMT800 8.1L/ZF 6 speed. I never had a chance to get my hands on those to see what the differences are. I suspect the GMT400 version is mainly the PP has provisions for the dowl pins and a larger holes for the metric PP to Flywheel bolts and the GMT800 is different yet because the ZF S6-650 has a very funky release bearing/slave unit that is much different than a NV4500 version where the PP fingers look different in Centeforce’s pictures. Neither of those CF part numbers existed when I started doing 8.1 swaps so I've stuck with what I know works instead of trying the other two part numbers...plus they cost more, probably due to low volumes
This is a DF097310 mounted in Rob's K5
Nice art workRight, there hasn’t been much said about adding an oil cooler because its very straight forward. Get a pair of ½ pipe thread AN fittings for the block then mount a cooler and run lines to it. Pretty simple. If I could find the real estate under my rigs, I wouldn’t mind having one too.
Seriously, is there really any other clutch worth using besides a 12”??
And no, the 8.1 uses its own unique flywheel 12582964. It is only shared with the 8.1L, GMPP crate 572 and PSI 8.8L. Right now that flywheel is $211 on Summit Racing
Centerforce Part numbers:
DF024909 - Dual Friction, Clutch Pressure Plate and Disc Set
This is basically the typical 10 spline GM 12” clutch used from the beginning of time up until around 1995 or so when GM moved to the integrated release/slave. This set is what is in my K10 with the external slave and same clutch part number I used when it had a 465 and mechanical clutch. The dowl pins on the 12582964 need to be removed and 2 or 3 holes in the pressure plate opened up to accommodate the larger metric bolts
When I first installed the 8.1 in my K10 in 2009, I reused the same exact 12” DF024909 that was on 454 that I pulled out. The black crap smeared all over the PP is what’s left of an old clutch fork boot that fell inside on a snow run one time
DF097310 - Dual Friction, Clutch Pressure Plate and Disc Set.
This is also a 10 spline 12” clutch but the disk and pressure plate are unique to integrated slave/release bearing. Same as above where, the dowl pins on the 12582964 need to be removed and 2 or 3 holes in the pressure plate opened up to accommodate the larger metric bolts. This is basically an L29 454 clutch and what Rob has in his K5 and what is in my Suburban.
CF does list another part number for a GMT400 3500-HD with an 8.1L/NV4500 and yet a different one for a GMT800 8.1L/ZF 6 speed. I never had a chance to get my hands on those to see what the differences are. I suspect the GMT400 version is mainly the PP has provisions for the dowl pins and a larger holes for the metric PP to Flywheel bolts and the GMT800 is different yet because the ZF S6-650 has a very funky release bearing/slave unit that is much different than a NV4500 version where the PP fingers look different in Centeforce’s pictures. Neither of those CF part numbers existed when I started doing 8.1 swaps so I've stuck with what I know works instead of trying the other two part numbers...plus they cost more, probably due to low volumes
This is a DF097310 mounted in Rob's K5
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Muchos gracious
Hey all.
This thread is an awesome resource! Thanks to all that have contributed.
I am in need of some clutch help. I have a new 8.1 flywheel. When I had my NV4500 built, the builder said he had a larger input shaft that he would install. Mine is 1.23" ish in diameter and 10 spline. Didn't realize at the time that a clutch would be so hard to locate. I have spoken with Centerforce and they said they used to make one but discontinued it.
Anyone have a part # for a disc and pressure plate for this setup with an internal slave? Or would it be better to just swap back to an 1 1/8" input shaft?
Here is my Project Rig (1965 IH Panel) that is getting a full GM swap! 8.1, NV4500, NP203/205 Doubler, 14 bolt FF rear, 10 Bolt front.
This thread is an awesome resource! Thanks to all that have contributed.
I am in need of some clutch help. I have a new 8.1 flywheel. When I had my NV4500 built, the builder said he had a larger input shaft that he would install. Mine is 1.23" ish in diameter and 10 spline. Didn't realize at the time that a clutch would be so hard to locate. I have spoken with Centerforce and they said they used to make one but discontinued it.
Anyone have a part # for a disc and pressure plate for this setup with an internal slave? Or would it be better to just swap back to an 1 1/8" input shaft?
Here is my Project Rig (1965 IH Panel) that is getting a full GM swap! 8.1, NV4500, NP203/205 Doubler, 14 bolt FF rear, 10 Bolt front.
Pretty sure that input was only in 2001 and 2002 3500HD’s.
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Yup, There it is! I've been searching 2500's. Didn't think to look at 3500's. Thanks a bunch!!
My original NV4500 I used in mine came from a 1998 3500hd, but it had the normal input shaft diameter.
I’d stick with the more common input shaft if you can’t source a clutch for the bigger one.
Centerforce does make a clutch for the internal save 4500 with the 1 1/8” input. That’s what I have in my truck.
I’d stick with the more common input shaft if you can’t source a clutch for the bigger one.
Centerforce does make a clutch for the internal save 4500 with the 1 1/8” input. That’s what I have in my truck.
Yes they do. I would prefer to go with a Centerforce but then would have the added cost of another shaft. I plan to use this rig in the mountains so maybe stock would be better/less bite on the trails. Think I may just go with a stock organic setup for now. Can always swap it in a few years if it don't do what I ask it to.
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I love the Travelall! I remember seeing it around the socials before
It would be much better to go back to a 1 1/8 for many reasons. As stated above that input was only used in the NV4500 behind the 2001-2002 GMT400 3500-HD with an 8.1L, which is a two year unicorn and that truck used the integrated slave/release bearing which leaves you with pretty much only one decent clutch option which is the LUK 04203, but again….that beast required the internal slave and it sounds like you want to run an external slave.
I suppose going to the bigger trans input adds beef (although I never heard of 4500’s behind anything habitually breaking inputs) it leaves you with less than sterling clutch options. LUK is okay, but its certainly no Centerforce.
Centerforce did make a Dual Friction clutch kit for that big 4500 input for a while as I mentioned above and I had forgotten it was in the input diameter that was different. They make one for the ZF 6 speed/8.1 as well which has an even bigger input of 1 3/8 like in my Silverado HD ZF/8.1.
Tell him thanks but no thanks….
Right, but yours came from behind an L29 which was still 1 1/8. The 4500’s in the GMT400 8.1L 3500-HD were their own beast.
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Thanks
So I am confused about intake bolts for these engines. The Raylar folks say throw the silver bolts away and use the 70mm black ones. The TBS on page 1 say use 12561518 which when I google it is listed as silver bolt 65mm. ARP doesn't support this engine any more I have had a hell of time finding intake bolts. I am thinking just ordering 6x70mm flange head bolts, anyone know the pitch 1.00 or 1.25 ?
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The intake bolts do get confusing. What the deal is the earlier 8.1L intake bolt holes in the cylinder heads where open down into the intake valley. Somewhere along the line in the early days, GM thought the open holes allowed oil to crawl up the intake bolts and let to the oil consumption, which was never really the case….its their lack of PCV that leads to oil consumption. They also added dowl pins to the gaskets that was supposed to help with alignment and somehow with oil consumption as well.
Anyway, as a fix they came up with longer bolts to help stop the oil from climbing up the bolt (not sure the thinking behind that) and to be compatible with the different intake gaskets, but changing the bolts never changed anything on early engines. They still used oil like all of them. My 2001 Silverado had that done when it was still in warranty and it drank 1 qt every 1200 miles like clock-work before and after the new bolts and gaskets.
The biggie is to match the bolts to the gasket part number and know if your intake bolt holes in the cylinder heads are blind or open, as you don’t want to stick a long bolt into a blind hole and snap it off when torquing it down like I did on my Suburban’s 2009 8.1L. Or, if you know the year of the engine, and if its before 2004, use the longer ones and gaskets that match. If 2004 or later, use the shorter ones with the gaskets that match. In fact, I think there is only one gasket part number now anyway if I remember right.
I’m pretty sure the bolts are 1.25 pitch. .25 and .50 are the most common on GM stuff
well I found some 6x70mm arp bolts package 660-1011 they 1.0 pitch. I guess I better pull one and check, since the info I used to find these is from Farce book 8.1 page. Not sure 6mm ever came in anything larger than 1.25 pitch. Thanks Larry
Confirmed the silver bolts in my 01 8.1 are 6mm by 65mm 1.0 pitch
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Dang, I wouldn't have guessed .0 pitch. Regardless of length, they all have the same thread pitch anyway.
So now you know they're 65 MM, order new ones and the matching gaskets and you'll be set. Becareful torquing them, they break really easy!
So now you know they're 65 MM, order new ones and the matching gaskets and you'll be set. Becareful torquing them, they break really easy!
Yep 40+ years wrenching my torque elbow is finely tuned.Will use 1/4 drive for sure
Will use 1/4 drive for sure
"Calibrated elbow, Calibrated eyeball..."
