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bogle's 1991 mild build thread

23 May 2020
SF Bay Area
Hey everyone! I'm a new owner and I've been lurking around here since buying the car. The forum has been super valuable already!

Here's the car. I haven't taken any great pics yet, so pics courtesy the seller:



I bought this car from BaT in mid May. I had been searching for the right fun car for a couple years, mostly looking at S2000s, E46 M3s, 996 turbos, and thinking about maaaybee splurging for a 996 GT3.

I'm a Honda fanboi at heart. I've had a number of EF Civics and a DA Integra. Many moons ago I spent all of my time and what little money I had on a pretty crappy-looking EF sedan, turning it into a still crappy-looking but locally competitive Street Mod autox car. I made parts for it, I had a couple different junkyard B-series engines in it, I reverse engineered the ECU. I occasionally beat the tube frame prepared cars at autox events (usually the very short courses), I took it to a couple HPDEs and bounced off the revlimiter down the back straight (it went 115; 6500rpm + short gears). It was a lot of fun, and I miss it.

I really wanted an NSX, but everything I saw on the internet seemed too expensive. NSXs also felt a little precious--the kind of thing you keep stock, baby it, and watch it appreciate. I didn't want to spend $50k+ on a stock NSX then let it chill in the garage.

I wanted something I could modify and tinker with. And I would feel _bad_ if I bought a nice stock one then messed with it.

So this one came up, and it was The One (provided it didn't go over my $$ limit!). It felt like it had the right combination of mods, but not "done". It also seemed like there were some factors that weren't crazy difficult to deal with, but might turn other people off and keep the price within reason: registered non op, very loud, and no cats / doesn't pass smog. It isn't perfect, but that makes it so I can tinker with it and feel like I am improving it rather than devaluing it.

It has a lot of aftermarket things already on it, the big chunks being:

* CTSC (9psi) on a motor refreshed by Hilltop Auto and tuned by Driving Ambition
* AEM Series 1 ECU
* Tein Circuit Master RA coilovers
* Dali / brembo front BBK
* Sparco seats & steering wheel + a million gauges inside
* Test pipes (OMG it smells)

I have a couple goals:

* Make it comfortablyish streetable: not so loud and not smelly. I guess I'm old now
* Restore or improve all the old / missing / jank / rusty stuff
* Understand even all the things that have been done to it
* Be able to take it to an occasional track day without worrying about reliability
* Have a outlet for tinkering

Right now, I want to keep this pretty mild. But who knows, build threads can get out of hand. First page is always like "yo, what % tint should I get?", then page 15: "Ok, car made 934hp on pump gas and I finally finished the homemade carbon body panels."

More pics from the seller:





Engine / Exhaust

[x] Install quieter exhaust (SoS endura lite)
[x] Install cats
[x] [maintenance] TB / WP (currently 12 years, 20k miles)
[x] [maintenance] Replace fuel lines & fuel filter
[x] [maintenance] Look into and maybe replace supercharger bypass elbow
[x] Gauge setup for both widebands (GaugeART CAN gauge)
[x] Add a second wideband controller
[x] IAT sensor post blower (turns out the stock sensor is post blower)
[x] Better IAT sensor
[x] [maintenance] Replace crank pulley with new OEM part
[x] Add timing belt shield
[x] [maintenance] Replace LMAs with new Honda springs
[x] Tune it for partial throttle
[x] SoS Big bore throttle body
[x] Tune accel fuel
[x] Upgrade current LSU 4.2 controller to an LSU 4.9 sensor to match new controller
[x] Baffled oil pan (cedar ridge)
[x] New radiator (MASiV)
[x] [maintenance] Replace all coolant hoses
[x] OEM coolant tank with R condom
[x] SoS catch can
[x] Water injection
[x] Route oil pressure sensor to the ECU
[x] Route fuel pressure sensor to the ECU
[x] Oil Temp sensor
[x] Griptec supercharger pulley
[x] High output alternator
[x] Rebuild supercharger
[x] Phenolic plate under supercharger
[x] Replace every rusty bolt and bracket
[x] Delete EGR
[ ] Modern ECU (Link G4x)
[ ] OMG tune it again
[ ] Take it to the dyno for WOT
[ ] Turn on ECU O2 feedback
[ ] Replace clutch mc and slave

Suspension / Chassis

[x] NSX-R front chassis braces
[x] NSX-R front sway bar
[x] Cedar Ridge compliance clamps
[x] [maintenance] New steering rack + new tie rod ends
[x] Quaife short ratio steering rack kit
[x] Cedar Ridge rear toe links
[x] New coilovers (MCS)
[x] Wheel bearings all around
[ ] Alignment
[ ] Get it weighed / corner balanced out of curiosity
[ ] [maybe] Type-S rear sway bar
[ ] Rear beam bushings


[x] [bug] New rotors to fix crazy rattle
[x] [maintenance] New brake pads (carbotec)
[x] Upgrade ABS system
[x] Stainless lines (Goodridge)
[ ] Rear bbk


[x] Lower seat position for driver
[x] Lower seat position for passenger to match driver
[x] Lower driver position even more with short seat pads
[x] [bug] Fix horn: really actually use the steering wheel’s horn button!
[x] [bug] Disable SRS light
[x] [maybe] Lighter seats? Evo2 seats are 26lbs each… (Evo 2 seats actually 17lbs)
[x] Shift boot + e-brake boot
[x] Move gauges around to free up space for a Navpod
[x] Add navpod with RealDash
[x] Remove all gauges
[x] Replace weirdly painted interior pieces (garnishes mostly)
[x] NSX-R pillars and visors
[x] Reupholster ivory hardliner
[ ] Fix super broken knee bolster
[ ] [bug] Fix windows slow rollup with Hugo’s window kit
[ ] [maintenance] Get cluster capacitors fixed
[ ] Replace jank nsxcarpets carpet with OEM black carpet
[ ] New or maybe carbon door panel switch stays
[ ] [maintenance] Get CCU capacitors fixed (was replaced in 2012; punting for a couple years)
[ ] New carbon console

Exterior / Underhood

[x] Replace engine hatch shocks
[x] [bug] Convert to 134a
[x] Replace dumb 40lb battery with Li-ion
[x] [bug] Replace AC compressor, drier, get it charged
[x] Get it detailed so I’m working with a cleanish car
[x] Replace every rusty bolt and bracket, every dirty connector
[ ] Fix faded b-pillars

Wheels / Tires

[x] Thoroughly clean the current wheels
[x] Figure out wheel situation, maybe just rear CE28N 18’s? +28??
[x] New tires (RT660)
[x] Buy 10 sets of wheels I don’t need, ha
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Hello and welcome.

I remember seeing this one on BaT. Yes, you are right, it does have a lot of goodies installed. It's nicely built and setup.
Nice to see the car is still in the CA.

If I recall correctly, it wasn't setup to pass smog. I hope that was an easy fix.

Your goals is similar to what mine are. Have fun!
Thanks! Yeah, it was kind of a pain and took a while, but the seller helped me through getting it smogged. It is smogged & registered, and now lives in a zipcode that requires smog only if it changes hands, not even every 2 years. High-flow cats, here I come!
Welcome and congratulations on your new NSX. The seller did take some great pictures.

You live in CA so I feel bad for all the hoops you have to jump through to get it smogged. I can run with open headers if needed here in GA since 25+ year old cars don't need emissions and are mileage exempt. Hopefully you can find some CARB certified high flow cats or similar.

There should be plenty to discover so looking forward to further updates :^).
Replace those fuel lines immediately. They will leak and could cause fire. Call Schad at driving ambition and get the newer black ones
Thanks! Yeah, the CARB stuff is a total pain. It doesn't make any sense, If the car passes the sniffer test, it should be fine. I'll post something later with all the things I learned. Basic gist is there are no high-flow totally compliant CARB cats for this car.

Replace those fuel lines immediately. They will leak and could cause fire. Call Schad at driving ambition and get the newer black ones

Ah, noted, thanks. I'll add that to the immediate list. Does driving ambition make them, or are they some aftermarket brand that they sell? Are they specific to the supercharger setup?
Schad who owns driving ambition and comptech used to be with comptech who made them as part of the supercharger kit
One of the first things I tackled on the car was a frontend rattle. It was a pretty nasty hollow rattle over every little bump.

I did a bunch of reading on the forum and, at first, I was convinced it was the steering rack. I found a couple threads explaining their steering rack rattle, and found out about http://nsxrackrepair.com.

The issue with the racks is that the bushing on the passenger side between the shaft and housing wears out, the shaft has some lateral play: rattle, rattle.

I did some tests and found some lateral play in the rack. But only a veeery small amount. Seemingly too small to account for the gnar rattle I had on both sides.

After a couple more drives, I realized it doesn't happen when I was on the brakes!

It has a Dali/Brembo BBK and, turns out, the 2 piece rotors rattled. A lot.


The hardware is tight (like the bolt to the nut) but there is crazy play. The nuts dug into the hats, and the wear was uneven: the nuts dug harder into the hat toward the front of the car (when on top of the rotation). Makes sense, each time you’d grab the brakes the ring would slow and the hat would slam forward on the hardware :/


The ring dug pretty hard into the hat too:


Some other pics of the old. I’m not sure who made them. Could they be an old version of the racing brake? Are they brembos?




Racing brake makes replacement rotors for the Brembo / Dali setup (https://racingbrake.com/standard-iron-brake/acura/2156), they confirmed the rotors would fit, so I picked up a set:





The new hats (0.273”) are much thinner (.19”) than the old (0.463”).


Aaand mounted:


I was a little worried it would locate the disk differently in the calipers, or the .2” / 5mm less offset would make my wheels hit the calipers. But it’s all good (17x8 ce28n +38).
your old set look like the comptech kit...
bogle said:
Hey everyone! I'm a new owner and I've been lurking around here since buying the car. The forum has been super valuable already!
I have a couple goals:

* Make it comfortablyish streetable: not so loud and not smelly. I guess I'm old now
* Restore or improve all the old / missing / jank / rusty stuff
* Understand even all the things that have been done to it
* Be able to take it to an occasional track day without worrying about reliability
* Have a outlet for tinkering

Right now, I want to keep this pretty mild. But who knows, build threads can get out of hand. First page is always like "yo, what % tint should I get?", then page 15: "Ok, car made 934hp on pump gas and I finally finished the homemade carbon body panels."

Welcome to our little corner of the NSX world! That's a cool NSX you found and I think you are being really smart about how to tackle the project. I agree that you should address those fuel lines asap and it looks like Shad is already on the case. Setting aside the issue of the supercharger, here are some things to consider:

* To make it more "streetable" I would get rid of the Tein suspension and replace it with OEM springs on new Bilstein shocks. It will ride MUCH more comfortably and still have enough firmness for the occasional track day. You are fortunate in the sense that the RA was the only suspension Tein made for the NSX that was any good. But, being an aluminum shock body, it's probably in need of a rebuild and even if freshened, it's going to be quite harsh (it's a racing spec).
* Also in the name of "streetable," I would ditch the center exit exhaust and replace the rear valence with the Honda genuine piece. The Gen 1 Comptech exhaust is a great option, as is the Gen 2. The king of all NSX exhausts is the Fujitsubo Super Ti, but it is expensive. Not sure how they will stand up to boost, though. You may also want to check with SoS, as they used to make a FI exhaust that was pretty good. I would also put some high flow cats back on to tame the stink and soot on the bumper.
* Things like rebuilding the brake calipers and refreshing the steering rack can make your NSX feel like a new car and it isn't that expensive to do. All of these cars, being so old, have a rats' nest of aftermarket wiring for stereos and crappy 90's alarms. I'd spend a week or two over the winter ripping all that stuff out and sorting it properly. OEM connectors and harnesses are available cheap and can really clean things up. It will also save you from future electric gremlin hunting.
* I noticed that someone quite cleverly welded an oil catch can into your coolant overflow tank. I really like the concept, but it's not routed in an ideal way. I would have Shad take a look at it and see if he can improve the routing. It might be ok, but most race NSX oil catch systems draw fresh air from the intake and have individual connections for each head.

Now let's talk about the supercharger. :D I would have Shad refresh the blower by replacing the seals, bearings and oil. Forced induction adds stress on the engine system mostly in the form of extra heat, which must be managed by the water pump/radiator/oil cooler, but it also stresses the NSX fuel pump, which runs in high setting almost all the time to maintain enough fuel pressure to deliver enough gas through those little 240cc injectors. I would therefore add a larger capacity radiator and replace the fuel pump with something a little more robust. Shad can help you with both of those things. Fixing these two issues will help ensure trouble free running for years to come, especially if you plan on going to the track. Tracking a supercharged NSX with a crusty old OEM radiator is asking for trouble- like $20k repair bill trouble. The cooling system on your NSX is probably its most critical component- take care of it and it will take care of your car.

*edit* I would also have Shad take a look at the tune and make sure you are running safe. He can tune the AEM and is quite familiar with the CT supercharger and its quirks.
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Hey Honcho! Thanks for the feedback. I'll try to address each item:

* I'm going to stick with the Teins for now. They actually aren't that bad. It does seem weird that it's a rear stiff setup on a RWD car. From what I understand the RAs are 10k/12k rates, though I found no markings on the springs. I ran similar spring rates on my 2k lbs EF and they were fine on the street.... It seems like a few people have sourced 10k springs for the rear. That could be a thing here.

* Yeah, I knew I was going to swap the exhaust from the minute I bid on it, and an SoS exhaust + SoS cats were the first thing I bought for the car. I actually have the exhaust almost entirely sorted now; I was planning on doing a post on it very soon. There was some weirdness with the o2 sensors in the test pipes, so it took me a little while to get the cats on cause I wanted to understand what was going on and how things were setup. Diffuser wise, I actually like the diffuser, the exhaust fits with it, and I don't really want to source & probably paint a stock valence, so I'll stick with it for now.

* The rack rebuild is still on the list along with new tie rod ends, just less dire now cause there isnt that much play, and it isn't the source of the gnar rattle.

* Noted rebuild on the calipers and coilovers, yeah, I don't know how many miles are on them.

* Interesting bit about the catch can, I'll look into it. I bet that combo tank was a Dali or SoS piece from long ago. I dont think he had anything really custom made for the car.

* Supercharger rebuild wise, how often do they need to be rebuilt / refreshed? The seller did have the supercharger oil changed as part of a refresh of all the fluids. But i'm sure this thing has never been rebuilt. It probably has in the 20k miles range on it.

The fuel system has been upgraded. It has RC550s and an aftermarket fuel pump (though I dont know which pump). It was tuned twice by Driving Ambition / Shad (is Driving Ambition only Shad?), once on the 6lb pulley, and once on the 9lb pulley. The AFR gauge in the car shows mid - low 11's at WOT.

Another streetability concern is that it runs pretty rich in partial throttle situations. It varies between mid 12s and mid 14s, but rarely in the mid 14s when I would expect it to be. I pulled the tune off the ECU and it's open loop all the time: o2 feedback is turned off (I realize this is confusing with the previous o2 statement; I was confused too). Makes sense cause there is only one wideband installed, seems dangerous to adjust the rear bank with only the front bank feedback. So my plan here is to basically upgrade the current wideband controller to a LSU 4.9 setup, add a second one to the rear bank, then take it to Driving Ambition for a tune in the hopes we can get it sorted such that the o2 feedback can be turned on. At that time, I'll def have him make sure the WOT is all good.

In the mean time, I plan to experiment with the AEM's logging features to see where things are at. I obviously now can connect to the ECU with the laptop, but I want to get the internal logging pulling the values I want too.

For reliability at a track day: the cooling + 9lb pulley makes me totally nervous. I have been eyeing a koyorad, so good to know that would be a big help. I'm also considering getting it tuned for the 6lb pulley and only running that. I mean, that extra 30 - 50hp isn't something I need. This car's so new to me, and it's been so long since I've driven on a track, I'd probably be better off with no boost.

Though if anyone has experience on the track reliable setup at 9psi with only a radiator upgrade, I am super curious. I see the water injection and after coolers for sale, and I don't think I ever want to add the complexity / expense if I can help it.
I avoided mentioning it as I did not want to offend you, but I would go back to the 6lb pulley. It's easier on the engine. Shad can definitely tell you about the service interval on the blower. The Koyo gives you about a 20% improvement in coolant capacity, but honestly it's not going to be enough, especially in California summers. I was thinking more of the dual pass radiator Shad (yes he is Driving Ambition- used to be at Comptech) offers. You should PM [MENTION=20915]RYU[/MENTION]. He spent years chasing heat soak on his supercharger at the track. I think he ended up going with the Masiv radiator and that finally solved it. Don't neglect your cooling hoses either- they should be replaced if it's been more than 10 years. I know a lot of the old school NSX guys swapped the Tein RA springs to be 12/10. But 10/10 would probably work too. You're definitely on the right track with this NSX. I'd probably ditch all those aftermarket gauges and invest in a Gauge Art display or something similar. It would really clean up the look of the interior.
An update! tl;dr:

* The exhaust is sorted now. It's quieter, it has cats, it fits with the diffuser ��
* The car is at Hilltop Auto getting a TB/WP + 134a AC conversion
* I added a TODO list to the first post with all the planned items

The car was way too loud for me with the center exit exhaust + test pipes. After I took delivery, I drove it one time for a short distance, felt like a jerk driving through the neighborhood, then came home and researched exhausts.

I landed on the SoS Endura Lite. It seemed quiet enough, had a good note, seemed like a good choice flow-wise for the supercharger, and looked like it would maybe fit with the downforce diffuser.


I was most concerned with the fit. I wasn't able to find any pictures of someone who had tried the Endura Lite with the diffuser. Most people had either the Taitec exhaust, or something totally custom. Before I pulled the trigger, I guestimated the silencer size (it's 9" in diameter FWIW) and its location, then took a whole bunch of measurements between the bumper and diffuser. All my measurements pointed to yes, but figured if it didn't I could move to a stock lower valence.

Wellll, it fits! Yay! It is also quiet enough, and super quiet when not under much load, e.g. on the freeway.


It turned out to be very close fit, though. There is a fair amount of room above the muffler, but only about a 1/2" between the muffler and diffuser at the the closest point. I replaced all the hangers with Cedar Ridge adjustable hangers. It still needs some adjustment, but fits pretty well. Some day, i'll get a pic of the gap between the can and the diffuser......

For the cats, I ended up with SoS FI cats. As with everything from them SoS so far, these are nice pieces:


They are really Gesi G-Sport metal substrate cats (part number 50025, 300 cell, "support up to 500hp each").


I really agonized over this decision. Ideally I'd have a set of CARB cats, but 1️⃣ no one (that I could find) makes a bolt-on CARB cat setup for the NSX, and 2️⃣ the only fully CARB legal converters that are reasonably available is either Magnaflow part 332304 or 3321304.

I could get a set of converters for a V8, like part #441125, but technically the CARB EO needs to list the specific car, then of course, I'd still need to get someone to make them work for the NSX. Also, all these CARB approved parts are ceramic substrate, and I was concerned that they would have a pretty limited lifespan with the car running kinda rich.

Too many things, so I bit the bullet and went with the SoS pair. I'll deal with smog again if/when it comes up. Right now, the car is registered in a zip that does not require a smog test every 2 years, so things should be ok unless we move. At which point I'll get a set of stock cats.

Installing them was a bit of a pain because of the o2 sensor setup: 2 narrowband o2 sensors were screwed into the test pipes and plugged into the harness.

Why were the stock o2 sensors in there? I still don't know. It was kind of a process to ultimately determine that I can just straight up unplug them and take them out. The AEM ECU does not use them, one of the O2 inputs is occupied by the wideband, and O2 feedback is turned off.

All good now. It runs exactly the same and has no smell! Here they are bolted up:


Now the car is at Hilltop Auto in Daly City (near San Francisco) getting a spanking new timing belt and water pump. The belt had 20k on it, but was last last replaced in 2008.


It was kind of a rush deal. I was planning on accumulating a bunch of maintenance parts, then taking it in to get everything installed / replaced at once. But about 2 weeks ago we were evacuated due to the CA fires. We evacuated to SF, and I figured that since I was there with the car, I might as well take it in to get the most pressing things done: TB/WP + general inspection.

Don at Hilltop did the engine refresh 20k miles ago along with a bunch of other maintenance in 2008, 2012, and 2013, so I wanted to talk to him about what was done and get any insight he had on the car. The main thing I learned: it has JE forged pistons. Unfortunately, he didn't remember the alloy (probably 4032?) or compression ratio (probably close to stock?). Also it has an SoS clutch with 2k miles on it, and my CTSC apparently doesn't have the rubber bypass elbow that can crack (it is the OG version?).

As far as other maintenance items that I would have liked to have installed at the same time are: a new crank pulley, pulley shield, and updated LMAs. Those things are all on their way now. I don't want to do the LMAs myself, so I made an appointment with Trackspec in Fremont in a couple months.

Been slowly accumulating more parts as well, pics on the way!
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That's great to *hear*. haha more dad jokes to come. Glad you are happy with your exhaust. Yes, not having drone on the freeway is a blessing. The fitment looks spot on.

After your big maintenance job, you can be worry free on your up coming drives.

You mentioned about the evacuation. Scary stuff. I was in a similar situation and thankful for all the fire fighters and their efforts.
Great update and nice TO DO list. Just a couple of thoughts...

If you do the Type-S rear sway why not do the Type-S front sway as well? I have both NSX-R chassis braces (upper and lower) in the front, the Type-S front and rear sway bars and the 02+ R engine chassis brace on my 1991 and I love the setup...to be fair I am running the OEM Type-S suspension.

For the interior upgrade to 02+ R headliner and bits, as far as I’m aware, the A pillars, B pillars, visors, and dome lamp are still available...the headliner has been on back order for about 14 months now

Sent from my iPhone using Tapatalk
Why do you have the supercharged by basch on your rear tail light. Your car has a comptech (different company) supercharger and basch supercharging doesn’t A good reputation for Nsx’s. Their design was centrifugal (good for high end, not low end power) but they has numerous engine failures due to their selection of engine management hardware / software
Bring on the dad jokes! Yeah looking forward to not stressing about the timing belt & harmonic balancer.

Definitely thankful for the firefighters! Glad you guys made it out of the fire situation unscathed. It was pretty stressful for a few days while the wind was moving directly in our direction and the fire was only a couple miles away :/

The sticker on the taillight was apparently from the install, I was told that Mike Basch installed the CTSC and put the sticker on at the same time. I guess I haven't thought about it, but it makes sense to remove it.

As for the sway bars, I went with the front R sway for 2 reasons: fitment with the lower NSX-R brace, and a balance change.

I am under the impression the Type-S front sway is the same size as stock (18.3mm), and I assumed it was the same shape as stock. If it is the same shape as stock, I'm surprised you don't have issues with the sway bar resting/rubbing on the brace. My stock sway was resting on the brace with quite a bit of tension, no bueno as it would affect the front spring rate (it couldn't rotate when both front wheels hit a bump!) and act like a way stiffer sway bar. The NSX-R bar is shaped a little different from the stock bar to clear the brace. I actually have it installed now and it has all the clearance. I took a bunch of pics of the shape differences I'll share in another post.

Did the Type-S have the R chassis braces stock? I wonder if the S and R bars are shaped the same...

Balance wise, the car already has rear-stiff spring rates and it doesn't need to be any looser for me right now. The Type-S full set would make it _more_ rear stiff and tend more toward oversteer. The plan is to see how I feel about the front R + stock rear. If I feel it is understeering too much, I'll add the Type-S rear bar. I bought both the R front and S rear at the same time, so it's chilling in the garage, but I'll only install it if I feel like I need it.

Noted on the headliner, I did see mita isn't selling the whole package anymore. I'm probably realistically a year or more out on it anyway. There is a lot more to do before it feels necessary.
The thickness of the Type-S front sway is probably the same as the stock ‘91-94 bar but it is shaped differently. The ‘91-‘94 stock front sway ends in 010 but all ‘97-‘05 coupes (not R’s) had the same front sway bar which ends in 003.

You can see mine clears the brace:


The Type-S (‘97-‘99 nor 02+) did not have an engine chassis brace but the S Zero did. I’m only running it since the ‘91 had one and I don’t know what effects not running one will have since the car was designed for one.
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Ah awesome. That’s good to know it clears and is shaped like the R sway. Thanks for the pic.

I feel like this stuff should be in the wiki or something. It took me a long time to find confirmation on the forums that the type R bar was shaped such that it cleared no problem. Also it seems many people are running the stock 91 sway with the lower brace, but don’t report problems.
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wow that pic of hilltop brought back memories of my conference visit 22 years ago...It looks the same...I had a good time visiting Dr. Steve and Andre...