Ali SC3

iTrader: (10)

going to have to agree with Gerrb on all points there. the extra pressure never hurts if you have a proper setup so you don't blow seals, but some people blow seals and wonder why... crank case ventilation needs to be stepped up also. also the drain line on the turbo needs to be of sufficient size with the increased pressure, generally most people run at least a -10 an drain and it works out fine on that side.
Also to note most na-t are going single turbo, you are going to stock twins which is double the oil flow so it will probably drop some of that extra pressure compared to using it on a single turbo, bringing you back to a normal zone. you could also get away with the vvti pump though but if you are pushing big power later you might as well go gte since you are on twins with more oil demand.

If its not overheating right now, I don't think you need to get the head resurfaced, I would just pull it off, scrape the old gasket off, straight edge check to verify (it'll be straight), and then reinstall. Stock you are even allowed a hair of warpage but you have to seriously overheat the head to cause that, like have it hot and still beat on it for a couple laps. it does not sound like you did that at all. If they have to grind the head down then yes they will have to dissasemble it, hot tank it, and clean it, and reassmeble. when I got mine done it was around $300 for that work (There are 24 valves and they charge per valve).

When I did the GTE headgasket, I just took it off and put it back on, never went to a shop. still boosting hard to this day.

Have you taken a look at your overflow bottle lately? is it bone dry?
often on toyota's when it starts to get a small coolant leak the overflow will go dry, and if you top it off it will overheat the motor until it goes dry again. something to do with the pressures involved in the 2 systems. keep an eye on the overflow.

Also the storage idea is not a bad idea, especially if you have to use your car. that swap is so involved it will take weeks (you will inevitably be missing parts or bolts etc..), so if you need your car your best bet is to do it on a spare motor and drop that in, even then dropping it in might take someone the whole weekend the first time around, then you can just run your current motor as it is and bandaid it along with oil changes and whatnot.

Also check out the next oil analysis, there is always that possiblity that there is nothing wrong with your engine at all, and that there was coolant residue left in the pan you drained the oil into or something silly like that.

scblackout

iTrader: (2)

Thank You! It's decided, I'll look for a modified tt pump. Missed a great deal on sf PHR, ($125) hoping another shows up else gotta bite the bullet and go new.

I'm using 3an feed, 10an drain for turbo (6766), and catch can should be ok as it's greddy dual 10an, dual filter + drain from LesJet a few months back.

KahnBB6

iTrader: (5)

Thanks again guys! Busy last few days.

Thank you Gerry. That's a very welcome possibility. I'd love to have no head gasket issue after all. Somehow some coolant got in there and that just seems like the most likely culprit given the mileage on the unopened engine. I've just wanted to be informed and fully prepared if it does... and also try to preserve the original rod bearing life if there is ample warning ahead of time.

A new Koyo TT radiator was installed in 2013. Water pump was last replaced just before 190K miles with the last timing belt change (it has about 51,000 miles on it). Someone mentioned a long while back that they thought it was leaking through the weep hole. I inspected the pump several times and found no such leak-- even recently.

I have planned to install another new water pump when the timing belt is required 9,000 miles from the current odometer reading (with a new accessory belt tensioner, t-belt tensioner and cam seals). I have all of those parts with the exception of the GE accessory belt tensioner. I do have a new GTE M/T belt tensioner set aside for the swap.

The main thing has just been waiting to see what the newest oil report details are. That'll be tomorrow. They're finally analyzing the sample today.

(Lesson learned: only use UPS or Fedex to express ship these samples out for analysis. The US Postal Service will not even allow you to pay for expedited shipping if you declare you are sending engine oil even if you offer to throw money at them )


If I have to do it that would be amazing. Assuming the bottom end is okay and I don't bother to have the oil pump changed out it would keep the cost down considerably on an engine I do not wish to pour more money into. $300 or so was what my mechanic said his cylinder head shop would charge to cut the head and check it over... which made me very skeptical to hear. But you're quoting the same ballpark even with disassembly and reassembly.

I have planned to buy new OEM valve stem seals from DM to have on hand.

I also don't see why the head wouldn't be straight since the engine has not overheated.


Just as you say, I've heard of other people having done exactly the same thing so long as they had no blown head gasket and overheating of the head and block.

Completely dismantling the GE head just to fix this issue just didn't seem to be necessary if so many people do exactly what you have described for NA-T conversions.

Good point. I have checked occasionally because I have had to refill some coolant in the radiator here and there (due to having broken open the coolant system so many times in the previous year: leaking HCV repairs, opening the throttle body, replacing the ECU coolant temp sensor, etc.)

I have not noticed it to be bone dry, no. Currently the level has been fine.

And I have also not noticed contaminated or milky/brown coolant in the radiator at all.

The wait is over... finally. Blackstone confirmed to me that today they are analyzing the most recent oil sample from the last day the car was driven nearly two weeks ago. I'll be in touch with them tomorrow to hear the results and their interpretation.

Next time I will send through UPS or Fedex to get it there faster.

That is amazing to hear from you Gerry! It has been exhausting to compile all of those things in the list and organize them. That is what I meant when I mentioned that if I had chosen to sell everything off... I would never try this same USDM GTE swap ever again. Since I have all those parts already I feel confident I can finish it.

I really have wanted a GTE engine fairly close to "stock", just BPU'd to 400 crank horsepower. 450 crank tops in the future.

It's very sound advice what you suggest to just find a $500 2JZ-GE engine to build off of. That would make the most sense because I am sure paying a shop to install every little hose, clamp and screw would not make much financial sense. I wouldn't want to do it that way in the first place but I was considering that as a future Plan C due to my trouble with workspace constraints.

Guys, yes it is possible. I think. I know of several storage facilities I could look into. The last time I casually got a quote for a small unit at one of them I think they wanted $150/month though. Even in Los Angeles I feel that's rather ridiculous on top of apartment rent so I'd try to get something for at least half that figure.

The two biggest concerns of mine would be: since they would be paid handsomely for the unit will I be left alone to work inside it at any time during their open hours? And more than that, how to find one of those storage places one can trust as to an internal theft? I have heard more than once that storage unit theft can sometimes be an inside job... which frankly makes me wary.

The other factors are the sections of the GTE swap that I can still do without acquiring a GE block to put into a storage unit: 6-speed wiring harness conversion, GTE head rebuild, twin turbo rebuild, intake manifold section cleaning (including the EGR port and valve scrubbing) and minor repair to the inside vacuum port threading (I'll show and explain that later).

Much of the rest is just drilling an oil pan for the turbo drain and a lot of assembly.

Another possibility is that I could buy a GE engine or a GTE shortblock and a 1000lb engine stand in Florida where I do have work space and the help of a family member who is no stranger to engine assembly and bring the GTE parts back there bit by bit to complete everything. There is also a shop in town that specializes in GTE swaps. But this would be a considerable bit of trouble to transport or ship all of those things and drive the car there and back to California under time constraints to return at a specific time. Especially since as you have both wisely mentioned there could be residual bugs or missing pieces right after the engine is installed. Driving almost 3,000 miles cross country only days after swapping in an engine might not be the smartest thing... even if most of the wearable parts being used would be brand new.

....

On the oil pump subject:



Wow. I had not realized how popular the modified GTE pumps are outside of application with GTE blocks. Better oil pressure is always good, yes. It's all the posts of front main seal or cam seal blowout that has concerned me.

So you're both saying that the fact I am using USDM twins also contributes to better using that extra oil pressure, since it's two identically sized turbochargers asking for more oil than a common NA-T setup would?

Since I will be keeping a very stock top end this will also pull more valve cover and crank case pressure back into the intake system?

Ali, I already have all the factory USDM TT oil pan turbo drain parts including the stock elbow. Are you suggesting that I shouldn't use these parts if I went with a PHR TT oil pump?

Also, since I need to keep the top of the engine very stock I am not sure if I can add the -10AN PCV and oil catch can additions you're both suggesting. That probably falls into the category of "the BAR interprets that as tampering with the sealed engine system and since it differs from stock and has no CARB E.O. number we can fail you. We don't care if it does not affect emissions whatsoever." I could be wrong but I'd have to check on that.

Right now I have a brand new 2JZ-GE VVT-i oil pump and all new seals, a new crank sensor (with the little bolt), etc. all ready to go into whatever GE engine block I choose to install it into.

...

I will be in touch with Blackstone tomorrow afternoon and I will have a new PDF report from them that I will post here.

Depending on what they say about the bearings I'll determine how I want to go about addressing this issue... if it really is an ongoing issue.

KahnBB6

iTrader: (5)

I am tempted to try one of these kits before dropping $2500+ on my engine.

Gerry, Ali... have either of you tried one of these before? Is this kind of test reliable?

The one used in this video is a U-View Hydro Carbon Radiator Leak Cooling System Tester (P/N 560000). It's $57 on Amazon.

Ali SC3

iTrader: (10)

you can probably get away with the stock pcv on one side and just making the hose on the passenger side larger to a can or even like stock. you may get some blow by but with the twins I think the extra oil pressure should go down a hair. I would just go stock tt pump or even GE pump just to be safe on yours since you need stock looking top end.

its funny in that video its a 1fz landcruiser notorious for BHG's. I have never used that test before, but it is interesting. might be worth a try or even a compression test. I would think if that much coolant is in the report, it would be missing from the overflow or radiator at some point, so mark it and keep an eye on it.

KahnBB6

iTrader: (5)

I will probably go with the GE VVT-i pump if I stay with a 2JZ-GE block. I am not planning for big power numbers with this swap. GE pumps seem to work well with NA-T conversions anyway.

I didn't realize the engine was a 1FZ-FE or that those engines are known for BHG issues like the 7M.

I'm going to order one of those test kits today. Can't hurt and apparently they do not lie.

Finally got to speak to a Blacksone technician on the latest sample. Within 348 miles of use they did see the wear numbers reduced and possibly less coolant in the oil. He said this could also be due to the residual oil left in the system mixing with the new oil. However there is definitely continued contamination going on. To note, the car still hasn't been driven more than 1 mile on the very last oil change. They'll be publishing the report very soon and I'll post it here for comparison as soon as I get it.

It's looking like I will be getting the head gasket serviced no matter what.

Edit: Here's the latest.

KahnBB6

iTrader: (5)

All right. I am going to go ahead and repair the 2JZ-GE configuration as is.

I was going to order one of those test kits but... I really don't think I need any more confirmation that it's the head gasket.

Parts-wise I already have:

--New OEM cam seals
--New OEM front main seal
--New 2JZ-GE accessory belt
--New OEM timing belt
--New timing belt tensioner
--New Aisin 2JZ-GE water pump (and new OEM gaskets for it)
--New OEM harmonic balancer to replace the 241K original

Need:

--New OEM 2JZ-GE accessory belt tensioner (original has probably never ben replaced)
--New OEM head bolts OR ARP studs (I know everyone loves ARP studs but to have a normal shop do this job would OEM head bolts be a better choice?)
--New OEM GE head gasket
--New GE valve cover gaskets + tube of FIPG
--New OEM valve stem seals (in case they are needed for the cylinder head)

Additionally I am wondering if it is a good idea to have the 2JZ-GE VVT-i oil pump installed at this time... whether or not I use this block with turbos in the future. Is there any benefit to having a fresh pump in there after 241K miles and after some compromised engine oil has been run through it?

Also, for the oil pan turbo drain blank area I think I will pick up a standard -10AN oil drain fitting and a cap to seal it. It may never be used but if the oil pan does need to come off for any reason I want to have it drilled, tapped and cleaned out of any shavings. Or maybe this is not a good thing to have done at a common repair shop.

Would it be prudent to have the oil pickup removed and cleaned? Or replaced?

Lastly and without question I want to have the main bolt at the oil filter area replaced with the IS300 Union bolt I have. I'll pick up another one as a spare later. With this I want to hook up an oil pressure sender to hook up to either a VDO gauge or my LXCC display screen. After this experience I think it's a good idea to install an oil pressure gauge in the car.

The only variables in this amount of work will be whether or not I should replace the oil pump and tap the oil pan should it also need to be removed. No oil pump replacement would mean no oil pan removal.

The cylinder head... I do hope is in good shape and won't need any work.

What do you guys think?

gerrb

iTrader: (34)

Use the ARP head studs .. just tell them to the amount of torque if they are not familiar with those studs.

If there were bearing wears .. use new oil pump . You don't want any of that dirt lingering within your oiling system.

CatManD3W

iTrader: (18)

TT headgasket and ARP studs....while you have it apart do valve stem seals.....new waterpump, oil pump, etc...

Best to do it when engine is out of car


But im confused I thought you were doing a complete engine swap not just using GE block and GTE head.

Ali SC3

iTrader: (10)

I wouldn't bother with valve stem seals if going with ta gte head later... if its not blowing blue smoke on startup its probably fine. now if they do dismantle all the valves to surface the head then yeah go ahead and do it.

Do the waterpump for sure.
ARP's are a no brainer cause they are reusable, and you will need them for the gte head.
i would also do the oil pump and get it out of the way, throw the crank trigger in there so you have it done for later. normally they don't go bad but since you are uprading later anyways while you are paying for labor on the headgasket you can these little things knocked out now for not that much extra.
oil pan comes off to do the oil pump generally, so have it drilled for the return line then and you will get one of the most annoying na-t items out of the way for later.

IS300 union bolt can be done later but would be easier to access when the head is off. you can use a tee off of it, so you can have the pressure sensor and the oil line for the turbo's. the thread on it is BPST but t can be retapped or if you use thread sealant you can even stick an npt fitting in there even though its not ideal. I might have the bpst "tee" that has an AN fitting on it and a spot for the pressure sensor, Ill see if I can find it for you I dont use it I just run the oil line right off the union bolt.

Yup that is a 1FZ, the 2jz's big brother. on the inside it looks so similar to a 2jz but its 4.5L but they didn't use the newer style metal headgaskets on them and the nature of such a long cylinder head results in BHG's every 150k or so unless you get the work done to upgrade the headgasket. You can slap a turbo on them also just like na-t, I wanted to build one but now that I have a 2uz truckI am pretty happy with the v8 just as is.

KahnBB6

iTrader: (5)

Thanks Gerry! Ok. I'll use ARP head studs and the new VVT-i oil pump. I will have the oil pan turbo drain drilled and capped off as well regardless of whether it gets used on this block or not.

Do you think a new oil pan pickup is also a good idea or is that overkill?

I don't have workspace available here unfortunately. And I have looked into the local storage unit as an engine workspace idea. Not as workable in this area so far as I've been able to tell so far.

I'll be using ARP head studs, a new Aisin 2JZ-GE water pump and I will have new cylinder head valve stem seals set aside on standby in case they are needed. Although I'd prefer Ali SC3 be right in that the head probably needs no work. I'm okay with around $300 give or take for the GE head prep if I must but no more than that.

A full timing belt job with new belt, tensioners (both) and harmonic balancer replacement will also be a part of this. I had already acquired most of those things a while back to set aside for the next t-belt job.

You heard right. The original plan was to have everything in place to set up this original GE block to bolt the GTE head, intake, turbo system, oil feed and electronics on top in case I needed to or wished to. Building up another GE or GTE block was always "Plan B" or "If Feasible" or "Preferable".

What's happened right now is that I got an early warning of an impending head gasket failure which has already shown some accelerated bearing wear-- though probably not too much bearing wear YET. As a result I haven't been driving the car since earlier this month until I have it taken in to replace the head gasket.

Since it's at this point a bit prematurely I am going ahead to fix the problem with the GE setup left as is but with a couple of future proof or insurance policy additions such as a new oil pump with the crank sensor provision, an oil pressure gauge and tapping the oil pan turbo drain (out of the car) and capping it off.

I have 93% of the USDM GTE parts to begin the conversion. It's just that some things such as the wiring harness (not yet converted), ECU (not yet rebuilt with new capacitors), twin turbos (not yet rebuilt) and GTE cylinder head (fully dismantled and in need of a basic rebuild) aren't ready to just drop onto a prepped block right away.

Right now I am double checking that I have all the gaskets and small things needed for the repair.


I agree and I'd prefer that be the case. I have no blue smoke on startup. Nothing abnormal from the exhaust after having overhauled much of the GE fuel system and GE ECUs.

New waterpump, brand new ARP head bolts and new oil pump will all go in at Gerry's, CatMan's and your unanimous suggestions. And the oil pan turbo drain.

When the repair to stable GE spec alone gets this involved and you all feel even a fresh oil pump will help since I have a brand new one sitting around already then it just doesn't make sense to me not to do these things anyway.

I'm trying to keep the total repair for this at about $3K. I'm leaving some additional cash buffer room in case it's a few hundred more than that but that's my expense goal as it stands right now. Less than that with little to no GE head work would be fine with me.

Though I don't plan to act on it I am keeping an eye the projected expense notes on doing the same work with a (hypothetically) prepped GTE head.

...And right now I do have a brand new GTE water pump also. That and all the little metal parts and gaskets that make it bolt up correctly to the GTE head. And the sensors that go into that area. I could just as easily have the engine bolted back together that way with the 2.4mm Cometic head gasket for the same money It wouldn't run yet but I'd technically have a GTE engine

^^ This is also what I have been thinking would be wise. I already have a new IS300 union bolt in my GTE parts. I figured now would be the best time for it.

I don't want to re-tap the bolt. I'd like to find the correct BPST fitting that goes to whatever fitting will allow for one oil pressure sensor and (in future) one oil feed line that will go around the back of the block and connect to the USDM turbos. Actually I need to make sure the USDM turbo oil feed flange will work with an aftermarket line. I've looked at the one feed line that Driftmotion sells for their NA-T conversions.

Ali if you can tell me what part it is that you have that goes from BPST to a "Y" I'd love to know! Thank you!

I also have the entire TT oil cooler system including the U-shaped pipe the goes around the block. that probably would not be very hard to swap over as well at this point especially if that central bolt comes off. There is one metal piece I have not been able to find or identify yet that looks like it insulates the water pipe from the heat of cylinder #6. I think I do need one of them:





Yeah, I have always liked those 1FZ Land Cruisers. The inferior stock head gasket is news to me but I've also been informed about their insanely bad fuel economy: about 13mpg city AND highway. Should be expected I guess. Just as with the 2JZ cars fuel was very cheap when those were brand new. They are otherwise as durable as it gets.

I think you probably have the advantage with your 2UZ vehicle honestly.

Why Toyota never bothered to sell any 1HZ or 1HD-T diesel Land Cruiser 80's in this country is beyond me.

That said... look at what the ones we did get can do off road. I miss real Toyota off-roaders like those.

....

Thank you Gerry, Ali and CatMan. I'll be starting on this process very soon. With this level of involvement and cost I have not wanted to rush into it without thinking it through carefully beforehand and future proofing the work that is done. I might as well do a bit extra to prep the bottom end for turbo at this point.

On the note of building a second engine block later on I'd still like to do this and I will most likely acquire one in Florida where I have ample workspace available for it to sit as long as is needed on an engine stand and have help.

For now I'm doing what I need to on this coast.

scblackout

iTrader: (2)

If you have the opportunity, could you create a breakdown list of the parts that you are going to be using? I was shocked when you figured 3k for the rebuild portion as that is higher than I expected, but if that is what it takes then so be it. Not going to do this job 1/2 way to only regret being cheap later on.

Like yourself I have been collecting parts for my NA-T rebuild and it sounds like we are on similar paths. I am hoping to have every single piece in place before I take the engine out as paying for a storage garage to work in is rather expensive and paying to wait on parts would be a downer. I'm finding that it's not the 'big' parts that everyone knows about, but the little things that add up and can take some time to order. It's what I don't know I need that concerns me.

KahnBB6

iTrader: (5)

scblackout, I certainly can but do you mean for the overall GTE swap or this current repair situation? Those are two different lists although instead of being clear cut it's now become a bit of a mixed repair and upgrade at the same time. The nearly eight month long smog repair situation diverted from my swap and now this situation with a failing head gasket and coolant in my engine oil has become a further diversion from just focusing on my GTE swap. Now I wish I'd known about the head gasket issue well before overhauling the rest of my stock engine.

Are you also going to go the route of a GTE cylinder head conversion or are you going to do a more conventional NA-T conversion? The way I am doing my GTE swap plan is not like a normal NA-T and many things will be different. It's better thought of as a recreation of a 100% stock (other than the block) USDM 2JZGTE Supra 6-speed engine. This is almost entirely due to CA smog rules.

You are very correct. The "major" parts for any build are just the easiest things to identify. I've spent many hours and days going through online microfiche style EPC's to find all manner of hoses, gaskets, bolts, nuts and many other tiny things that are taken for granted. This is probably harder when trying to recreate a stock engine than it is to do a custom setup where the aftermarket support is very widespread.

...

Now my $3,000 budget estimate to get my engine fixed as it is right now in the stock configuration is a padded estimate based on quotes I've had from my mechanic. And I have not really included many of the parts I will need to provide. I am not doing the bare minimum. It's still possible I could take the car to FSR Motorsports within their schedule timeframe since they did not quote me much more... other than for the cylinder head. But I will probably stick with my local mechanic for this.

Rough breakdown as was quoted to me if I provide all the parts:

--Remove 2JZ cylinder head and replace with new head gasket
--full timing belt replacement
--water pump and thermostat replacement
--new coolant

14 hours labor:
about $1500.00

Add on replacing the oil pump (I'll provide the new one):
5-6 additional hours labor

I will pre-tap the oil pan drain stud holes before taking the car in but have the shop bore out the drain area when the pan is off. Not sure what that will add.

Finally, if the cylinder head isn't straight I'll spend about $300 getting it machined and reassembled. I'll provide new valve stem seals just in case they are needed. I can see some sludged oil in one of the valve covers when I take the cap off that was not there before and that will have to be cleaned out but it does not look to be in the way of the cams themselves. Inspection will tell all. Not wishing to spend $1000+ to fully rebuild the GE head. I will only spend that amount on the USDM GTE head and its original valvetrain that I already have in a crate.

Altogether I am guessing this all can easily hit $3K spent to repair everything to running condition in non-turbo form.

If I added service to the block with new Clevite crank bearings, rod bearings and new ARP rod bolts and nuts I am sure it would get even more expensive. This is why I am hoping the Blackstone reports I have read so far indicate that the compromised oil has not affected the rotating assembly very much in only 4,000 miles or so.

.....

As soon as I get my own order list completed tomorrow I will post it here with part numbers and prices to give you an idea, scblackout.

As for the main swap list I have it partially posted on the first couple of thread pages but I do need to update everything to what is current. I have been trickling in random GTE parts all along since 2013.

...

Another thing that occurred to me this weekend is the clutch. Since I have a factory 7MGTE clutch and pressure plate that was just recently put in I do not think that spec will hold up to the roughly 300whp of the stock 2JZGTE for very long unless I drive very, very moderately. Works fine for the NA engine's 180whp.

It was installed because the clutch wore out prematurely due to a failing clutch master cylinder and resources were being diverted to repair the GE engine for smog already.

The more I think about it, everything that happened with the SC since late last year was directly pointing to buckling down and pushing forward with the GTE swap even with the necessary downtime. Didn't seem that way at the time but it sure does in hindsight.

This is why if I have to do involved unexpected repair work and I don't have workspace to pull the engine I want to cover what bases I can, within reason. For now.

scblackout

iTrader: (2)

I'm doing a standard mid level NA-T build, but other than part numbers I am assuming that most components will be the same in concept at least. The best example I can give is that most threads just say throw on a tt head gasket and arp studs and your good to go. Of course forgetting that while doing that you should change water pump, idler, welded sprocket for higher hp, valve stems, etc.. Hardest part is knowing where to stop and yet making sure I don't skimp out on anything I will regret later.

KahnBB6

iTrader: (5)

Honestly Gerry and Ali SC3 are the gurus on the NA-T subject

If you have a 1992-1997 SC300 you need some combination of the following:

--OEM TT (1.3mm) head gasket (yes, this is what will work for the approach you are using)
--ARP head studs + OEM head washers (avoid the ARP washers)
--Upgraded fuel pump (OEM TT or other)
--12V Fuel Mod with a relay (to keep it safe)
--Oil pan tapped for a -10AN turbo drain (Driftmotion; it's best to remove the pan off the car to do this)
--turbo manifold of your choice and turbocharger of your choice (DM and Boostlogic sell kits or individual parts)
--Intercooler, pipes and couplings of your choice (DM and Boostlogic also sell piping kits for SC's)
--I think you will need upgraded injectors over the 330cc factory NA ones. Not sure what is cheapest
--Spark plugs... I know there are recommendations and gap ranges for NA-T's but I don't know that info offhand
--JDM Aristo 2JZ-GTE ECU: buy one used. Have it capacitor serviced at DM or Tanin. Follow Ali SC3's TT ECU Mod thread to make use of this on your NA engine. This is the least expensive and best engine management solution for NA-T setups
--cats, downpipes, etc. is really up to how you want to do that
--EGR? You can remove it or follow Ali SC3's recent thread posts on how he kept his functional on his NA-T engine
--Rear end ratio. If you are on the 4.272:1 factory rear end (automatic) you may want a 3.916 (3.92) from an SC400 to swap in.
--An LSD is pricey but great for ANY SC with or without a turbo or V8

I also know that the stock SC300 Automatics are not as strong as the A340's found in Aristo 2JZGTE's, Soarer 1JZGTE's and all Supra MKIV TT Automatics. Better to have one of those behind any JZ turbo engine. Even with a W58 5-speed you can keep those below their breaking threshold and make them last but it's all in how you drive them. An R154, AR-5, CD009 or T56 would be much better manual gearbox choices.

I know there is more to this and it's absolutely not a small parts list. I often use https://partsouq.com to find STOCK configuration parts from old microfiche transfers of all the Toyota models. Then I order parts most often from dealers with Trademotion sites like Carson or Pembroke Pines if I am not buying aftermarket parts.

It is not as easy as people make it sound to go NA-T but there is a lot of documentation and help after all this time. I've heard it argued that in the past it was easier to swap in a genuine early Soarer 1JZGTE complete motor set since most of it bolts in and the harness more or less plugs in without much modification after you extend the wires about 18 inches. But those days of cheaper-than-NA-T may be over due to the current availability of those engine sets. That and I still think 1JZ-GTE VVT-i engines (non-DBW) are much better.

And then there is my type of swap which is just about the most tedious and questionable one anyone should attempt. Really, your mild NA-T build will give you the same potential I am planning to plateau at for quote a lot invested just to have a "CA legal" turbo engine (300whp stock and 350-380whp slightly modified). I'm okay with that but it's not the right choice for most.