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I have searched this forum and several others and have not really found to much info on using an L8T crank in an LS block to build a stroker motor. I am doing this now so I figured I'd start a build thread to share the overall experience and details that go into it. The motor is a gen IV L92 that I purchased from a salvage yard. It came out of a 2007 Yukon Denali (was running with approx 165k miles).
I have torn the motor down and cleaned and inspected everything and I am satisfied that it is a good motor to build. This will be going into a 1967 Camaro. I am going the pro-touring / restomod route. This will be primarily a street car (weekend toy) and may see and occasional trip to the drag strip or a HPDE day every once in a while. Good street manners and dependability are very important for this build. Mainly looking for good mid range torque and a redline in the 6500rpm ballpark.
I will be using a rotating assembly from Mast Motorsports that uses a L8T crank and rods, which they do some additional machining to. My understanding is they grind and polish the crank (0.010" undersize) to get tighter clearance tolerances than what comes from GM. I believe they also resize the small end journal on the rods to use a standard LS piston pin diameter and bushings (I will have to confirm this part about the rods). The rotating assembly uses custom Wiseco 2618 forged pistons setup for this application, I know it requires a custom compression height piston to accomodate the L8T crank's 3.858" stroke.
There are a few reasons why I chose this route. I wanted to build a N/A stroker, The price point was very attractive to me. I actually like that fact that it uses a new GM forged crank. I also like the 3.858" stroke and keeping an "over square motor". This will easily meet my power goals, and in all honesty it's just something a little different from the norm.
I will be using stock 823 heads un-ported. I will have new LS3 intake and exhaust valves installed, so a valve job and resurfacing / milling will be part of the job. I will be using a stock LS3 intake manifold. I am going to plan on 10.5 - 11:1 static compression ratio. I will be running 1 7/8" long tunes headers w/ 3" collectors (X pipe, no cats, 3" SS exhaust). The car is going to be running all C5 corvette drivetrain (T56 transaxle wit3.42:1 rear gear). Rear tire size is 295/40R18 (approx 27" dia). Car is expected to weigh in around 3200lbs. Should be a blast to drive on the street!
Right now I am purchasing parts needed to bring the block and heads to the machine shop. I will be doing the assembly myself once I get everything back. So far here is what I have:
L92 stock block - will get .005" oversize hone, align hone, and whatever else it needs
stock 823 heads (bare castings getting the treatment mentioned above)
ARP main studs and head bolts
Monster S-Twin disc clutch and flywheel. Note, the L8T crank requires an 8 bolt flywheel. I spoke with the folks at Monster and they were able to get me a clutch package that will fit the C5 corvette torque tube and use an 8 bolt flywheel.
Summit Racing C5 corvette harmonic balancer (standard dia, no underdrive) w/ ARP balancer bolt
Cam Motion 0.670" lift double spring kit (most likely will go with steel retainers for the street, not sure yet)
Johnson 2116 LSR tie bar lifters
Holley Terminator X EFI
That's about where I am at the moment. The rotating assembly is getting delivered next week and I will be getting the order with Cam Motion placed on Monday. I have spoken with a few local machine shops (Space Coast FL area). I am expecting it will be late Feb / early March by the time I get the block and heads back (also will be getting the rotating assembly balanced). In the meantime I will be planning out the rest of the build (rockers, timing chain assembly, oil pump, etc.)
I will post updates as things progress. I am open to input / feedback.
Make sure the piston kit or whoever knows you are doing this with a sleeve length of 5.50 inches (L92) or you can check the length by measuring your block yourself. Sometimes these guys assume you are using a longer sleeve (like ls7 block 5.85 inches) and the piston taper is different. Sounds like from your description they do but check. The stock crank for this motor is 3.62 inches you are .230 longer thus the piston will come out the bore more. They fix this with a shorter piston and a different taper to the piston. Also spend money on a good set of rings.
Make sure the piston kit or whoever knows you are doing this with a sleeve length of 5.50 inches or you can check the length by measuring your block yourself. Sometime these guys assume you are using a longer sleeve (like ls7 block) and the piston taper is different. The stock crank for this motor is 3.62 inches you are .250 longer thus the piston will come out the bore more. They fix this with a shorter piston and a different taper to the piston. Also spend money on a good set of rings.
Yeah man you touched on a couple of really good points there. I had a few conversations with the folks at Mast Motorsports tech line. They were great to work with. I did discuss the build and what block I was using. They did tell me this assembly is set up for a stock deck heat LS block with stock sleeves. They have Wiseco make the pistons specifically for this application. I really like the fact that the stroke on the L8T crank is under 4". It should not pull the piston "out of the hole" at BDC nearly as much.
Your piston will be out of the hole it is simple math. Stroke is 3.85, sleeve 5.50, total piston height probably 2.2 inches (the piston height is usually inch more than the compression height). So 5.5 - 3.85 = 1.65 inches your piston is 2.2 inches so you pop out about .550 inches. However, many LS motors the piston does pop out the bottom even on the stock L92 you just have to build for it. I just finished my 455 LS motor and I stick out about .385 inches (5.80 sleeve, 4.125 stroke and 2.05 piston height - 1.05 compression height).
I have searched this forum and several others and have not really found to much info on using an L8T crank in an LS block to build a stroker motor. I am doing this now so I figured I'd start a build thread to share the overall experience and details that go into it. The motor is a gen IV L92 that I purchased from a salvage yard. It came out of a 2007 Yukon Denali (was running with approx 165k miles).
I have torn the motor down and cleaned and inspected everything and I am satisfied that it is a good motor to build. This will be going into a 1967 Camaro. I am going the pro-touring / restomod route. This will be primarily a street car (weekend toy) and may see and occasional trip to the drag strip or a HPDE day every once in a while. Good street manners and dependability are very important for this build. Mainly looking for good mid range torque and a redline in the 6500rpm ballpark.
I will be using a rotating assembly from Mast Motorsports that uses a L8T crank and rods, which they do some additional machining to. My understanding is they grind and polish the crank (0.010" undersize) to get tighter clearance tolerances than what comes from GM. I believe they also resize the small end journal on the rods to use a standard LS piston pin diameter and bushings (I will have to confirm this part about the rods). The rotating assembly uses custom Wiseco 2618 forged pistons setup for this application, I know it requires a custom compression height piston to accomodate the L8T crank's 3.858" stroke.
There are a few reasons why I chose this route. I wanted to build a N/A stroker, The price point was very attractive to me. I actually like that fact that it uses a new GM forged crank. I also like the 3.858" stroke and keeping an "over square motor". This will easily meet my power goals, and in all honesty it's just something a little different from the norm.
I will be using stock 823 heads un-ported. I will have new LS3 intake and exhaust valves installed, so a valve job and resurfacing / milling will be part of the job. I will be using a stock LS3 intake manifold. I am going to plan on 10.5 - 11:1 static compression ratio. I will be running 1 7/8" long tunes headers w/ 3" collectors (X pipe, no cats, 3" SS exhaust). The car is going to be running all C5 corvette drivetrain (T56 transaxle wit3.42:1 rear gear). Rear tire size is 295/40R18 (approx 27" dia). Car is expected to weigh in around 3200lbs. Should be a blast to drive on the street!
Right now I am purchasing parts needed to bring the block and heads to the machine shop. I will be doing the assembly myself once I get everything back. So far here is what I have:
L92 stock block - will get .005" oversize hone, align hone, and whatever else it needs
stock 823 heads (bare castings getting the treatment mentioned above)
ARP main studs and head bolts
Monster S-Twin disc clutch and flywheel. Note, the L8T crank requires an 8 bolt flywheel. I spoke with the folks at Monster and they were able to get me a clutch package that will fit the C5 corvette torque tube and use an 8 bolt flywheel.
Summit Racing C5 corvette harmonic balancer (standard dia, no underdrive) w/ ARP balancer bolt
Cam Motion 0.670" lift double spring kit (most likely will go with steel retainers for the street, not sure yet)
Johnson 2116 LSR tie bar lifters
Holley Terminator X EFI
That's about where I am at the moment. The rotating assembly is getting delivered next week and I will be getting the order with Cam Motion placed on Monday. I have spoken with a few local machine shops (Space Coast FL area). I am expecting it will be late Feb / early March by the time I get the block and heads back (also will be getting the rotating assembly balanced). In the meantime I will be planning out the rest of the build (rockers, timing chain assembly, oil pump, etc.)
I will post updates as things progress. I am open to input / feedback.
Are you open to tire size suggestions? I'm curious as to why you're going with a 27" tall (40 series) tire? Why not go with the C5Z 295/35/18 tires? Maybe availability? Anyway, I don't know what width limits you have. Not apples to apples, but I ran 315-30-18 Michelins on the rear. Damn things are about $1k/pair!!! They may nor clear your setup, but thought I'd throw this out there. The C5 drivetrain w/T56 has been known to scatter the diff with high rpm clutch drops and sticky tires. That's why I avoided a tall rear tire, because it increases the load on the diff, and everything else. My 315s were 25.6" diameter. Also, have you considered running a 17" setup in the rear? A bit more sidewall will improve traction at the strip, and wont kill cornering for HPDEs, though 18s would be better for cornering. Sounds like a great build. My car weighs 3250, and it is a lot of fun. I've got a cammed LS7 in it-617hp@crank. 2 years ago at Thanksgiving, an Audi R8 V10 wanted to race me. My car looks stock, with a cammed idle. He probably thought he was going to hand me my ***. Instead, I passed out heaping helpings of R8 ***. Havent seen him since......
I am considering something similar but their 389 set up for my 4.00" bore LY6 long block with a TKO600 behind it. I have a LS3 manifold and have zero'd in on Cammotion's Titan 3 as my likely cam choice with Hooker's 1 7/8" swap headers.
I have emailed back and forth with Mast and they have told me (relative to the 389 at least) their assembly uses 4032 Wiseco pistons, comes with the rings and is balanced by Mast. My block will require some work to clear the center counterweight of the L8T crank. I have an email out to them about the compression height and volume of the pistons but other than that, their rotating assembly is viable for my application.
I wanted to keep a 40 series tire for street driving. I wanted something with a little more side wall as the suspension will be on the stiff side as I am using C5 Z06 springs. I have had cars with 30 and 35 series rear tires before. It was fun in the twisties but got old when cruising around town. If I actually start doing any track day stuff I would most likely wind up getting a second set of wheels and tires accordingly. While the block and heads are at the machine shop I am going to be doing some upgrade on the rear diff to beef it up a bit.
That is interesting about the 4032 pistons. I had specifically asked them if they had that available as an option for the 402cu kit and the tech line told me they only had the pistons made in the 2618 alloy. For what its worth I was always a Pontiac guy as my first car was a 69 LeMans. A 389cu LS motor would be super cool!
Here is a cut and paste of the email I got back from Mast in response to my questions. I can't speak for the accuracy beyond this is what Mast told me:Subject: RE: Questions: LS - Gen III/IV Rotating Assembly Kit - 389 Cubic Inch- Wet Sump
Is the L8T crank drilled a sufficient depth to accommodate a traditional pilot shaft? "Yes it will take a traditional pilot bushing".
I see that I would need an 8 bolt flywheel, but to adapt a TKO transmission, I would need a flywheel that is .400 thicker. Do you know of a source for a conversion flywheel? "The 8 bolt pattern is common to the LSA engines as well , we do not deal a whole lot with flywheels , but I would look to McCleod or Center Force for a flywheel"
Looks like the assembly uses the factory L8T connecting rods. Do you have a recommended RPM limit for this rotating assembly as I think the recommendation for the L8T is only 6200 rpm? "Rpm, would try to stay under 7000, most cams for a build like this will probably make peak power around 6800."
Is the assembly balanced? "Assembles are balanced"
What material is used by Wiseco for the pistons and do you know what the recommended piston to bore clearance is? "These pistons are 4032 aluminum. We generally hone the blocks to the pistons and the clearance can vary by application and intended usage." "As a side note , the iron block require clearancing around the center main web because of these are center counterweighted cranks".
I did follow up with McCleod and confirmed that they do have a 8 bolt flywheel that is .400 thicker so one can use a TKO/TKX or traditional GM 4 speed behind either an LS with an LT crank or an LT engine. Here is the email from McCleod: "Thank You for your interest in McLeod Racing. We make what you’re looking for. Part Number 460548."
Also Mast got back to me and confirmed the compression height is 1.2010 for this assembly. According to my calculations that puts this piston about -.012 in the hole so some deck work or somewhat pricey Cometic head gaskets are likely necessary for my rec port application to maintain compression ratio.
I received everything from MAST a few weeks back. The pistons are 2618 forged Wiseco's. MAST must have them do some private label branding. Here is the spec sheet that came with the pistons.
My kit came with MAHLE file fit ring packs and ACL Race Series rod and main bearings. Overall I am happy with the components that came with the rotating assembly kit.
The L8T rods look pretty much identical to gen 5 rods and are beefier than the gen 4 rods that came out of the L92. Also confirmed that they came with ARP rod bolts installed.
I have everything at the machine shop now. I am hoping they will get to it this week or next. This brings up two questions for a sanity check.
Compression ratio: Everything I have seen suggests that for a LS street motor running 93 octane that you want to be no higher than 8.5:1 dynamic compression. I have received the camshaft from Cam Motion and using a few of the online calculators it is looking like I will have to set the static compression ratio at 10.5:1 to achieve the desired dynamic number. Here is the cam spec sheet with the valve events. Let me know what you guys think. Am I on the right path setting this up for a 8.5:1 dynamic compressions ratio? Note, I am planning to run a new set of GM OEM MLS head gaskets with 0.051" compressed thickness.
Second question, Squish Clearance: Everything that I have read suggest that for a LS motor in a NA application with 2618 pistons that you want to run nothing tighter than 0.040 - 0.45" clearance. I've also heard that 0.040 is pushing it. Would you agree with 0.040-0.045" squish clearance being a good target? I will talk with the machine shop about this as well and get their take.
I am very eager to see what they say about decking the block. When I do the math I believe I came up with the pistons being about 0.012" in the hole using a nominal stock deck height 9.240". It wouldn't surprise me that the pistons would have a compression height to allow the block to be decked to clean things up. I will go over everything with the machinist and see what he has to say about decking the block and milling the heads to achieve both compression ratio and squish clearance. Worst case I can always swap out the head gaskets to fine tune things if needed.
I’d think that a 165k mi block may need some type of deck cleanup from stock (9.24) so your .012 may shrink a little. Really looking forward to this as I have the same crank but considering a 6.200 rod build a d 4.065 or less bore.
01-14-2023, 10:44 AM
L92 402cu stroker build (L8T Crank + rods) 
