• Protip: Profile posts are public! Use Conversations to message other members privately. Everyone can see the content of a profile post.

Resurrecting a 91 w/32,000 miles on thats been in storage for 15 years.

6 March 2024
San Francisco
Hello all,

I'm resurrecting a 1991 5-speed that has 32,000 miles on it. It's been sitting since sometime around 2008. It's been started occasionally and driven about 1000 miles in that time. The car is owned by a good friend of mine. He's an older Japanese man , bought the car new in 1991 and is still today very much into Japanese car culture. He has every service record and I'll read through them as soon as I get them. He's asked me to bring the car current for services, do anything safety related and any mods that may make the overall experience better, like upgrading the audio head unit. He plans to drive it on a regular basis, some back roads and drives with friends but no trackdays.

So I've been tasked to go through the car completely, top to bottom, front to back. Deal with all service, age and safety related issues. And if possible since find street tires (<200 Tread Wear) in the original 15"/16" sizes. As he's into Japanese car culture, he's stated that I can modify the car in anyway that I see fit as long as it's tasteful, keeping with the right look and adds to the overall experience. He I are on the same page when it comes wheels/ride height, etc. If I cannot find tires for the original 15"/16" I'll probably do a 17"/18" staggered setup with high quality Japanese wheels and replace the suspension to bring the car to a nice but useable ride height.

Which brings me to the next problem. He purchased a house years ago but the driveway is not compatible with the stock NSX front overhang, hence the storage this whole time. I want to lower the car slightly to get the right look but ride quality and usability is paramount. I've had great luck with the Ohlins DFV Road & Track kits from Ohlins Japan on R32/R33/R34 Skyline GT-Rs and JZA80 Supras. However, I need to be able to raise the front (and possibly the rear) in order to get the car in the garage at home. It would be nice if it's GPS based, I've seen systems like iLift but I wanted to get your advice.

I'm considering things like a 6-speed conversion with a LSD. I'm not sure I'll do anything to the engine besides exhaust. Again your input is appreciated.

Thank you and I appreciate your time.
There are options for the factory 15/16 wheels for 200 TW tires when I looked a few months ago such as Dunlop Direzzas, Falken RT-615s and 660s, and Potenza RE-71RS to name a few. Suspension wise, sounds like either Ohlins or KWs outfitted with a cup kit to raise the car when necessary would work. For a 91, I'd recommend changing out the factory cast headers to an aftermarket set as well if you're changing up the exhaust.
Welcome to NSX Prime and great story. NSXs that sit for a long time have different issues than ones that have been used heavily. Here are some things to consider:

Internal corrosion: The coolant should be changed every 3 years (and no more than 5) because the anti-corrosion additives break down and the water in the coolant starts to corrode the engine internals and all steel hose fittings like the ones on the main water jacket. My 92 covered only about 2,000 miles between 2012 and 2018 and during that time the corrosion completely ruined a brand new water pump installed in 2012- the bearing sounded like sandpaper. So, you'll want to remove all 23 coolant hoses and inspect the pipe fittings. The car will definitely need a new water pump as well. Plus a new set of hoses, obviously. The standard timing belt/WP service will apply here too.

Rubber seals: While the engine is out for the TB/WP service, you should replace all of the rubber seals and O-rings on the engine since the 33-year old ones are completely hardened and cracking at this point. Failure to do so will set you on a never ending path of chasing small oil leaks on the engine. You can reference my build thread for the full discussion of a proper NSX engine refresh. I can send you the parts list if you want.

Brakes: When the NSX sits for years, the water in the brake fluid rots out the pistons. You should disassemble the brake calipers and inspect the pistons. Any pitting or corrosion on the machined sliding surface means the piston must be replaced. Do the seals too. This is a safety issue.

Window regulators: The original moly grease in the window tracks tends to harden into a crust that makes the windows go very slowly and puts a lot of strain on the regulator. Also, the rubber guide feet on the track tend to fall off and land at the bottom of the door interior. These need to be addressed before they cause the regulator to fail, which can result in a stuck window at best or dropped glass at worst. Sitting for years without use accelerates the hardening of the grease.

Capacitors: The early cars (91-94) are stating to age out in the liquid-filled capacitors used in various systems. The caps are swelling and leaking acid onto the PCB, causing damage to the circuits. The climate control is the most notorious and annoying. The most dangerous is the gauge cluster. It can and has caused fires that result in the loss of the car. I'd pull the cluster, CCU, stereo, speaker amps and other modules and have them inspected and repaired by BrianK or a shop like T3TEC.

Fuel Injectors: When the NSX sits for years, the wax and varnish in the gasoline hardens and can cause issues in the injectors. I would send the injectors out to RC Engineering in Torrance for service, drain the gas tank and replace the fuel filter.

I'd also look at the motor mounts and HVAC system.

I'd address the above before moving on to mods. It's probably $5,000 to $10,000. Complete 6-speed transmissions are no longer produced or sold by Honda/Acura, so you have to find a used one. They are extremely rare. T3TEC in Japan can build you a new one, but the wait is more than 6 months and cost is approaching $20,000. I'd keep the 5-speed. With 32,000 miles, it's still got a ton of life left in it (bearings and synchros are good to 200,000+ miles with regular fluid changes and proper driving technique). Just change the fluid with Honda MTF and it's good for another 2 years.

For just a fun driver, you don't really need much more than an exhaust (even headers are kind of pointless if you just want it to sound good/fun). There are tons of options available and it's really what your friend prefers for sound. I always tell people to go to a NSX meet and listen to exhausts before deciding. Another cheap and fun mod is the LeMans GT2 style intake scoop. ATR makes a nice one and it directs a lot of VTEC induction noise to the driver compared to the factory snorkel.

There are plenty of tires available for the 15/16 wheels and the phat fives are coming back in vogue in terms of style. Most guys on the fives run the RE-71R.

AFAIK, iLift is the only system developed for the NSX and it can work with the KW and BC Racing suspension kits. @SakeBomb Garage is a vendor here on Prime and they offer the Ohlins NSX kit- you may want to contact them to see if they can set up a lift kit. The NSX doesn't really like too much lowering. The geometry of the control arms means that you cause more and more problems the lower you go- it looks cool, but it compromises handling and ride quality. There are partial solutions like eccentric camber correction bushings, but I generally recommend not going lower than 20mm below stock height. For a fun driver/cruiser, the Ohlins and KW are way overkill, but I understand you need adjustable ride height for the driveway.

Hope this helps.
Just my personal antidote to add to Hondo's thorough advice. I have only put on 20k onto a 4k 92 over 31 years. IF the car was driven just a bit once a year you may not see many of those issues. Of course i have done all fluids every few years and done all hoses and lubed my window tracks and installed aftermarket follower tabs. I have not done all engine block seals and have no leaks other than valve covers, cam seals and oil pan. No electrical issues from old age except for the bose amps(and owner induced mod's issues he-he). I have purchased electrical spares just in case and had MITA overhaul my cluster just in case. I did have to flush my gas tank because of using gas stabilizers (a big mistake IMO). Rubber seal life varies a ton. There are folks out there in vintage racing running 80 year old rubber seals still going strong. Is that smart? Of course not, only saying that you may not have to address every single issue at once to make your buddy safe, at least from my one example. Ditto on keeping the 5-spd, you already have an LSD. For wheels, why not simply go to the OE second generation 16/17? You should be able to find some reasonably, they are light and they FIT nicely he-he. He is going to let you borrow it now and then, right? No one drives my car. Enjoy your wrenching.
The only consideration I might add to Honcho's comment about keeping the original cast iron manifold is that at some point you or the owner will likely have to deal with an ageing O2 sensor failure. My recollection is that on the early cars with the cast iron manifold the front O2 sensor has a bit of a reputation for becoming 'one' with the mounting bung leading to snap-offs during O2 replacement attempts. This may or may not require complete removal of the manifold to fix depending on the nature of the 'snap off'. If that happens, at that point you might want to consider replacing the cast iron manifold with a tube style header. The later cars came with OEM tubular headers and these will fit the engine; but, require adapters / modifications because they are not a drop in fit with the rest of the exhaust system unless you also replace all of that with the later design. I expect that there are drop in place aftermarket headers for the na1; but, can't advise on what is good or not so good. Maybe the O2 sensor will play nice and come out easily and you don't have to address this problem. If not, and you have to remove the manifold to extract the remains of the sensor then something to consider.

The other issue that has not been raised is the 1991 ABS system. Aside from being dated in the technology, the 1991 modulator will (not may) have maintenance issues and it may be increasingly difficult to deal with those maintenance issues. Aside from outright deletion of the ABS, the technically easy replacement solution was to fit the ABS mechanism from the 2000+ NSX. Because of supply issues, that may no longer be easy or possible to do. I believe an ABS modulator from a salvaged Honda S 2000 will also fit / work. If you want to consider this, then start your hunt for a replacement system now. If I were going to spend discretionary money, I would spend it on the ABS system before I spend it on a 5 to 6 speed upgrade.

In terms of the 6 speed transmission, I have a 2000 with the 6 speed. I have driven two early cars with the 5 speed, so not a statistically significant data set. My observation is that once the 6 speed is stinky hot it shifts wonderfully. When it is cold, mine shifts like a box of rocks. I frequently drive my car when the overnight temperatures drop to 0 - 5C and I have to be very deliberate with shifts until the transmission gets hot and it does take a fair amount of time for it to get hot. The two five speeds that I have driven did not seem to display this cold sensitivity. If this car is going to be a recreational / non track car I would not spend big coin to replace the 5 speed with a 6 speed.
Whoa. In California, headers need to be CARB approved. Otherwise OEM 97+ required.

IMHO The ALB should just be electronically bypassed and left in place. Takes 5 min and looks great.

Keep all the original parts, modifications greatly diminish the future value.

Has the driveway been addressed? It is hard on the fenders and condensers. I put in a new driveway, aprons, and sidewalk in one of houses so my NSX would not scrape. This is probably where OP should concentrate efforts first...plan it all over a holiday week and have it done before the City can react. It's just not very sexy.