Here's what I did. This may not be the 100% correct or best way, but it's worked so far. I was in the same boat, '92 Speed density TPI / T5 to LT1 / T5. I used a '97 LT1 (from a T56 car), and was told to stay away from the '93 ones. '94-95 are OBDI and 96-97 are OBDII, pick your poison.
The block (305 TPI/350 LT1) is essentially the same. The LT1 block does has an additional mounting hole for the 4th gen engine mounts.
TPI block = ' . '
LT1 block = . ' . ' but it only uses the first three. You'll use the engine mounts from the TPI block or really any V8 third gen mounts and the latter three holes in the block.
The allowed Canton pan for the TPI will bolt right up to the LT1 block. I did have to remove the windage tray from the LT1. *** I found out the following the hard way. With the LT1 dipstick and the third gen pan, the reading will be different. I added 6 qts upon installing since that's what the pan takes. A while later, I actually checked the dipstick and it read Add, so I did, something around a quart (it's been a while, my memory is failing). This becase kinda frequent during racing and I was sorta worried I was burning so much oil. I finally realized what was going on and that I was overfilling it quite a bit. It now reads right at the bottom mark, at the Add when it has ~6 qts.
Since we have to use the LT1 exhaust manifolds, you MUST also get a LT1 y-pipe. All normal people who put a LT1 into a third gen will use headers. Nobody in their right mind would use the LT1 manifolds. There are no y-pipes that will fit a third gen with LT1 manifolds, so I cut off the first 3-4" off the LT1 y-pipe (since the flanges of the manifolds are funky) and had one made.
Since the opti is driven off the cam, you'll have to use the LT1 water pump, which means the TPI accessory brackets won't fit. I ended up using all the LT1 brackets, alternator, power steering pump etc. I had to buy another A/C delete pulley. Spend the extra and get the one from GM.
P/S pump was sent off to PSC like a lot of 4th gen guys do. I wanted as little custom parts, so I used a '95 Impala power steering line (with some slight massaging) to the steering box. One disadvantage of this is it runs thru the serp belt. To change the belt, the p/s line needs to be disconnected. I may change this later for some -AN lines. I made a hokey bracket for the resevoir, and some 3/8" low pressure hose to get it basically where the third gen overflow tank was, which inturn made me buy a different and smaller overflow tank.
I'm still using a WC T5. Rebuilt it with the upgraded cluster support plate. I don't do drag race launches and try not to abuse it. Axle hop will kill the T5 faster than an extra 30hp/10ft*lbs IMHO. I had the TPI flywheel balance matched to the LT1 flywheel at a machine shop since there is some uncertaintly if the imbalances are the same. TPI flywheel and clutch, T5 bellhousing, slave, all bolts right up. Of course the electical plugs won't work, so no speedo or reverse lights.
To go the T56 route, you need to either modify the trans crossmember or get one from Spoon or Hawks Third Gen. I think you'll also have to notch the shift hole in the chassis a bit since the T56 shifter is more rearward I believe. Not sure how the slave comes into play with this route. I think the torque arm will slip right in, but cannot confirm that.
Driveshafts are the same length no matter which way you go, third and 4th gens are the same length.
I think either starter should work. I put in the LT1 starter since it's much smaller and the wiring fit up a bit nicer.
TPI fuel pump is sufficent for the LT1 pressures. On the LT1 engine, I was told an adjustable f/p regulator isn't worth it.
I've never made -AN lines, so for the fuel lines I got some from
http://www.purechoicemotorsports.com/ They have a kit just for this swap. You'll need to tell them what fittings you have on the hard lines on the car. They were very helpful on the phone. I did however, add some 90* fittings for where it goes into the LT1 fuel rail.
Conflicting reports, but I think the LT1 radiator is smaller than the third gen. I had a b4c radiator (and spares), so I stuck with that. There are a few ports that are different, but it's all workable. I think it was a
'92 Corvette lower hose, and a '97 Camaro upper hose (which ever year has the T). I'll have to look, but I can't remember if I bypassed the TB and just used it for the steam line to the back of the heads.
I kept most of the "Y" air intake from the TPI, in theory anyways. I bought another setup from a mass air third gen car. The mass air "Y" has a hole for the air temp sensor (wires had to be lengthened a few inches). It also has a shorter rubber boot since there is now a MAF between in inlet and the throttle body. I took that whole mess to The Home Depot and found a rubber hose in the plumbing section to go from the "Y" to the MAF, and used the mass air third gen rubber boot from the MAF to the throttle body. The LT1 stuff is slightly bigger, but I kinda forced it on. Lots of people don't use the "Y" and go with a 90* elbow and a cone filter. Some say the "Y" restricts the power too much. I still made over 270hp with it.
The check engine light will stay on unfortuantely. A few things will cause this, but only one is unsolvable (at this time). The speedo (VSS) can be solved by using a T5 tailshaft from a V6 4th gen and reluctor ring and stuff. The rear O2 can be bypassed with use of O2 sims. The fans check can be made to work the same as the LT1. The EGR can be left intact since it doesn't really affect anything, weighs next to nothing, and it one more place for a block off plate to leak. The AIR system check is the killer. I removed the AIR pump and plugged the manifolds with IIRC 3/4" oil pan drain plugs.
http://www.dormanproducts.com/p-21570-090-008.aspx Since there's no way around the check (no reprogramming allowed), the CEL will stay on (unless you keep the AIR setup, I wouldn't), which makes doing any of the rest of the tricks pointless.
For VATS, get this if Nick's car doesn't already have it.
http://www.bakerelectronix.com/products_vats/
It is possible to get the PCM inside the cabin using the stock LT1 harness, tho not quite in the stock third gen spot. It involved deconstructing the plastic shells on the connectors to the PCM. I have a temporary mount for my PCM in the passenger footwell til I come up with something better.
The wiring was the trickiest for me. The LT1 engine harness doesn't need a whole lot of outside input other than a few grounds, a few constant power and a few ignition power, a few for the OBD port. I made a new fuse block for all of this. The fan(s) is another area that will need addressed if you still want them controlled by the pcm. I'm not 100% sure, but I think the fans will come on anytime the CEL is on. May be a moot point if your fans are on a completely separaty circuit already. I can't remember, but I think there is something about using a resistor inlne with the alternator field wire in place a bulb.
This site was very helpful for LT1 info and wiring.
http://shbox.com/1/4th_gen_tech1.html
Thirdgen.org is a wealth on info if you havn't found it already. They have a section just for LT1 swaps.
*edit* The LT1 I dropped in had 101k+ miles. I put in new valve springs, valve seals, v/c gaskets, (can't remember if I did a rear main seal or not) oil pan gasket, and oil pump & Canton pan, plugs and wires. Unrestricted it was 272/315 on the dyno.
Hope this helps.
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