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TL/DR What advice can you share on crate engine interchange? Are the shortblocks interchangeable? Long blocks?
I'm not sure exactly what happened here. I'm pretty sure he got hydrolocked in an Arizona monsoon. Swammi says there is a wayward connecting rod that knocked the starter off. Does that seem likely? Buddy was just sickened and jacked the car back down before poking around in the hole any more... Doesn't seem like the well known starter boss issue is really the culprit here.
Last edited by MACE_Hardware; Sep 22, 2025 at 05:45 PM.
Reason: Update
There's lots of options available, depends on the budget. From short blocks, long blocks iron blocks.... And complete intake to oil pan that will bolt right in. I see the yellow vette in the b.a.t. ad has nitrous. Maybe he blew it up spraying.
There are no Gen III LS1/6 crate motor left in the world. Gen III blocks have cast in cylinder liners that can be sketchy to over bore.
The closest thing you are going to find will to a direct replacement will be a Gen VI motor with Cathedral Port heads. This is a pretty easy swap over with only a couple of sensors that need to move.
Both Thompson Motorsports (talk to Shane) and Golen offer these with proven combinations. Typically these would involve either a 5.3 liter block bored out to 3.898, or an LS2 block with a 4" bore. Either way, I highly recommend staying with an Aluminum block as they are 200# lighter than the iron blocks.
You could do an LS3 swap - but the LS3 crate motors are out of production and the back stock is pretty much gone (I think SD parts has a couple left) . LS3's use square port heads which requires different intake manifolds and is very obvious to anyone who know's what they are doing to spot. If you aren't concerned with such things.. well the LS3 is a damned good combo.
I agree on staying with aluminum blocks, but I don't think the iron blocks are 200lbs heavier. Most actual weight readings I've seen show the aluminum block builds being around 90lbs to 110lbs lighter.....
The only thing I will offer is that if you ever go to sell the car, buyers really trust a GM crate or an LS3 more than other aftermarket sources. At this point it should be a question of it the guy going to keep the car long enough to justify the expense of a fancy new engine, or if he plans to sell the car in the near term then a donor iron block with miles may be the expedient answer.
Buddy does not have the infrastructure to swap engines himself.
His local Corvette specialist says it is minimum $15k to swap in a crate engine - when all is said and done, I can't see it being less than $20k to put in an LS3.
My opinion is that the car is totaled. The car is literally his pride and joy so he does not agree with my opinion.
What I don't like about a LS3 swap is the knock sensors must be moved and tuning is required to adjust their sensitivity for being on the side of the block. Tuners will say they can get it accurate. I went to the Tuning School in Tampa for HP tuners and their answer was you'll never be back to factory accuracy. Something to think about and discuss with who does the swap and tuning. A LS2 swap will be very much like a LS3 swap.
A few friends work on our HPDE cars together and we generally elect to find a used lower miles LS1 or LS6. GTOs and early CTS-Vs can also be used. https://www.car-part.com/ can also be searched for a motor in addition to the usual forums and marketplace.
Having been down this road, he is better off selling the car as is or parting it out and using the over the top BS price quote for swap expense to simply buy another whole C5 and start over. The used market will provide him a fresh LS3 swap with a blower for 20k and he can subtract whatever he gets selling the carcass from that amount. Dead set that's the smart way to go. Dump it and move on. The car doesn't love him. He loves the car. But it's going to gut him emotionally and financially, so put Old Yeller down and get a new dog.
Having been down this road, he is better off selling the car as is or parting it out and using the over the top BS price quote for swap expense to simply buy another whole C5 and start over. The used market will provide him a fresh LS3 swap with a blower for 20k and he can subtract whatever he gets selling the carcass from that amount. Dead set that's the smart way to go. Dump it and move on. The car doesn't love him. He loves the car. But it's going to gut him emotionally and financially, so put Old Yeller down and get a new dog.
Agreed from a numbers perspective and further he can't do the work himself. Given he doesn't have the resources to swap the motor, he likely doesn't have the place to part the car. It'd likely go quick as a roller.
I dunno - for ME to get a car I'd like more than my Z06 is gonna cost $60K minimum.... a $20K engine in-out seems like a bargain in that context. Don't build cars to sell, build cars to own.
I finally looked at the link up top. $15k for a not very upgraded base coupe which we now know was Nitrous nuked likely without a stepper to smooth out the hit or enough fuel tuned in to keep the afr level is what this looks like regardless of miles or cleanliness. That SUCKS.
While it is not the everyday find, I saw an '01 Z06 with 67k miles with $6k in mods go for $17k around the new year. Coupes go for a lot less. $15 could absolutely net your friend a car with a blower and a LOT of good supporting mods already purchased and installed without his expense. For $20k he can get one which is also CLEAN as a whistle with whatever mod combo he likes. It just takes time to stalk them on C5 Modified Buy Sell Trade on FB or on the forum here in the For Sale section. Might be 2 to 4 months to find "the best deal in the US"
Sure, it requires taking a stretch the spend the separate $20k for a new car and then waiting to move the roller chassis... which is very clean.... for maybe $9,000. It is worth more parted out but without the means to do so there is no point. $9k would seem to move it pretty quickly in its mint condition to someone who wanted a project. I would be one of those people who would line up for $9,000. While not highly eager to do the work, someone comfortable doing it for themselves could swap any used engine in and enjoy the car. They could only flip it for profit if they dumped a cheap/free engine in. Still better for him to spend 20k total on another 15k car with this 5k loss than to have spent 15k and then reinvested another 20k on top for a 35k equivalent C5.... of which NONE return that value when sold, not even the 3,000 original mile 2004 Z16 Z06s with the carbon fiber hoods.
I keep saying all this because if you seek out my build thread you'll see where a simple 19k purchase snowballed to multiple times that value and I have yet to finish the project. He is absolutely better off removing his emotions from it and moving on unless he has a friend who can do an engine swap one weekend for 2 or 3 grand labor and a donor engine - of which there are many out there but it takes some hunting.
Coincidentally... if he sells the car.... I might be interested in the painted roof panel.
BTW, buddy has never filled the N2O tank and I'm pretty sure it was just for show with the PO.
He took his bore scope and he says he can see the piston in the hole but the connecting rod is AWOL. Seems like what you get when you hydro-lock the engine in an Arizona Monsoon.
I've been dragging my feet on putting a lift in the shop at my new house, but sooner is better than later.
I will be in AZ end of January and told buddy that if he gets a trailer I'll haul him and his car up here and we'll put in a "used" engine ourselves. Then he gets to shake it down with a 1200 mile winter drive home. What could go wrong?
BTW, buddy has never filled the N2O tank and I'm pretty sure it was just for show with the PO.
He took his bore scope and he says he can see the piston in the hole but the connecting rod is AWOL. Seems like what you get when you hydro-lock the engine in an Arizona Monsoon.
I've been dragging my feet on putting a lift in the shop at my new house, but sooner is better than later.
I will be in AZ end of January and told buddy that if he gets a trailer I'll haul him and his car up here and we'll put in a "used" engine ourselves. Then he gets to shake it down with a 1200 mile winter drive home. What could go wrong?
That's about all I can do...
C6-LS2-MN6 will be removing and selling the LS1 out of his 2003 C5, with only 7,800 miles, and will replacing it with a built LS7. Send him a pm.
I keep saying all this because if you seek out my build thread you'll see where a simple 19k purchase snowballed to multiple times that value and I have yet to finish the project. He is absolutely better off removing his emotions from it and moving on unless he has a friend who can do an engine swap one weekend for 2 or 3 grand labor and a donor engine - of which there are many out there but it takes some hunting.
Just to piggyback off of this:
I bought my 1999 FRC in August of 2007 for $23k. In January of 2010, it lost oil pressure.
I still own that car. A couple grand for a used twin turbo kit. A few grand new turbos. A few grand for a used, forged LS2. A few grand for a used TR-6060 and C6Z diff. Ten grand to build the trans and diff. A few grand on the fuel system. A couple grand here and there for things like brakes, wheels, suspension, body work, seats, cage.......The car doesn't run yet. It has been 15 and a half years.
Having the money to repair the vehicle, the self-control to not upgrade the vehicle, and the time to do it yourself is hard to come by.
I bought a 2004 Z06 in January of 2024 because I missed driving a C5. It was more cost effective and logical to buy a 2004 Z06 than to try and get the 1999 FRC running.
One day, the FRC will run again. Maybe. Hopefully.
The way I see it is that your friend has three options:
1) Get a junkyard engine, throw it in and drive the car until the wheels fall off.
2) Sell it as a rolling chassis. Put that money toward the purchase of a car that runs.
3) Get on some Factory Five Racing / kit car forums, buy a GTM Supercar kit and use his C5 as a donor car. This is a stupid option. Do not do this. It is exactly what I would do, and I am stupid.
Share the definition of a "sunk cost fallacy" with your friend. It is the phenomenon whereby a person is reluctant to abandon a strategy or course of action because they have invested heavily in it, even when it is clear that abandonment would be more beneficial.
I bought my 1999 FRC in August of 2007 for $23k. In January of 2010, it lost oil pressure.
I still own that car. A couple grand for a used twin turbo kit. A few grand new turbos. A few grand for a used, forged LS2. A few grand for a used TR-6060 and C6Z diff. Ten grand to build the trans and diff. A few grand on the fuel system. A couple grand here and there for things like brakes, wheels, suspension, body work, seats, cage.......The car doesn't run yet. It has been 15 and a half years.
Having the money to repair the vehicle, the self-control to not upgrade the vehicle, and the time to do it yourself is hard to come by.
I bought a 2004 Z06 in January of 2024 because I missed driving a C5. It was more cost effective and logical to buy a 2004 Z06 than to try and get the 1999 FRC running.
One day, the FRC will run again. Maybe. Hopefully.
The way I see it is that your friend has three options:
1) Get a junkyard engine, throw it in and drive the car until the wheels fall off.
2) Sell it as a rolling chassis. Put that money toward the purchase of a car that runs.
3) Get on some Factory Five Racing / kit car forums, buy a GTM Supercar kit and use his C5 as a donor car. This is a stupid option. Do not do this. It is exactly what I would do, and I am stupid.
Share the definition of a "sunk cost fallacy" with your friend. It is the phenomenon whereby a person is reluctant to abandon a strategy or course of action because they have invested heavily in it, even when it is clear that abandonment would be more beneficial.
Wow, a 15 year build, what we’re or are you thinking. Sell everything, get a low mile C6z06, heads, cam, intake, tune, and your at 575wheel, and you can drive it across the country or track it if you want. Good Luck.
I'd probably go with an LS2, since it has all the same mounting points as the LS1/6, uses cathedral port heads, and has a 24 tooth reluctor wheel. As far as I know it's a direct drop-in, and very affordable.
I'd probably go with an LS2, since it has all the same mounting points as the LS1/6, uses cathedral port heads, and has a 24 tooth reluctor wheel. As far as I know it's a direct drop-in, and very affordable.
Early Ls2s were 24 tooth but not all. My post above has a link to the LPE conversion box and their instructions contains a list of motors by year and platform listing the sensors used.
LS2s do not have provisions to use LS1/6 knock sensors, they must be relocated which comes with mixed results.
Need New Engine - Crate Engines (?) - 2001 Base
