I just purchased my first corvette. It is a 1986 z51 with 4+3 manual transmission. It has the bronze interior with silver beige exterior. It has yet to be delivered and I have not seen the vehicle except via pictures and over Zoom. It is very clean overall, especially the interior. It has around 65k miles and is a two-owner vehicle. I am extremely excited and will post pictures once the car arrives. (This will take a while as I live overseas)

The overall plan for the car is to make a stock-reversible streetcar. I want the car to handle and drive like stock but with more reasonable horsepower/torque ratings. The following are the changes I wish execute:

Interior:
1. No planned changes at the moment, the interior is fully stock with the upgraded audio system, and it is in extremely good condition.

Exterior:
1. Change the color to my favorite color.
2. Purchase a new bronze glass targa top panel. I will still keep the original and also paint that as a second option.

Wheels:
1. Upgrade to 18x9.5-inch wheels with 275/40R18 tires. I am thinking something like the c6 z06 wheel in black to match the black trim that goes around the body of early c4 corvette body styles. Also, I will order a custom black center cap with the c4 logo in black as well. This setup should make the wheel diameter be 0.6 inches larger than stock. This will raise the car by 0.3 inches without changing the suspension and hopefully should be fine. The wheel that I choose will have an offset similar to the stock so I do not require any spacers. (stock offset = +38mm)

Engine:
1. (Bottleneck) Keep the TPI system, but maximize efficiency within the system (porting, etc.) I found a company out of New Jersey that does this. I really enjoy the stock look of corvette engines and plan on maintaining that look. (except for smog system delete, etc.)
2. Camshaft. I am looking for much more power; however, I do want the idle to be clean and not choppy like a drag car.
3. Heads.
4. Pistons + Rods (Maybe)
5. Larger Injectors, upgraded spark plugs, etc.
6. Upgraded chip (OBD2 chip maybe that allows for easier tuning)
7. K&N Air Filter (Maybe) With the TPI system being a major bottleneck, I am not sure if the increased air flow through the air filter will be necessary or even do anything other than allow more particles into the engine)

Transmission:
1. Keep the Doug Nash 4+3 Manual Transmission. Rebuild. I am hoping with my power gains, this transmission should still be adequate. *hopefully*

Differential:
1. Keep the Dana 44. Change fluid and rebuild if necessary.

Exhaust:
1. Long tube headers.
2. High-flow cats (probably depending on the local emission requirements as I am not keen on having to change the exhaust during an inspection. But, for older cars, I believe the emission standards are not too bad.)
3. Mufflers (I am looking for a clean idle with a nice purr. I am looking for some good v8 sounds, but nothing too insane loud. If I am correct, the year I bought was the last year that allows up to 104db where I live, so I think it can still be pretty loud and sound good)
4. Exhaust Tips I am looking to go 4 black exhaust tips. The color idea is to match the black trim, wheels, and rear black corvette logo. I think it should look pretty clean.

That is about it at the moment. Also, if you are reading this and are thinking, this guy doesn't seem to have any mechanical knowledge, you are correct. I will definitely need a lot of assistance to plan and complete this project.

My extremely limited experience with vehicles is very limited. I have done the following:

1. Body work (the pic of the motorcycle was originally all black and cracks in the fairings that I watched YouTube and fixed up.
2. Switched out motorcycle exhaust.
3. Oil Change
4. Brake Fluid Change plus bleed.
5. Changed rear-sets on a motorcycle. Learned the importance of Loctite.
6. Rear fender elimination kit on motorcycle. Ordered the proper plug on the eliminator kit side so that I did not have to cut any stock wiring that allows for the next person that has to work on it to not lose their sanity.
7. Custom headlights with custom wiring.

I feel rather confident with electrical work, but mechanically I have almost no experience. I have watched a lot of videos recently of people working on the exact engine and also general theory of how engines function. I have access to a full garage that I can rent extremely cheaply with a lift along with a friend that has a lot of experience working as a mechanic and transmission specialist. (apparently, he worked for Nissan repairing CVT transmissions for many years) Hopefully I can work alongside him to learn much of this.

Anyways, as said it will be a while before the car arrives and I will post pictures. Then I plan on doing threads for each section of work that I do on the car. Wish me luck, I am going to need it.

 

I also forgot to mention in the original post that my horsepower target is around 375 - 400. This may not be obtainable with the stock TPI system, but hopefully with cam, heads, tune, etc. it could get close. My torque target is around 425. Any advice or comments, good or bad, are very welcome as this is unknown territory for me.

Thanks again for reading.

 

Congrats on the new car! Now for the harsh reality check.up, lol.

You have like $15k worth of work you want to do,.maybe more, depending on the color change costs. The 4+3 is kind of a crap transmission,. especially if you want to put serious power through it.

IMO, you are far better off buying something closer to what you actually want vs spending more money to make this otherwise average car.onto what you want. And this is coming from a pro.modding guy, lol.

For what you're going to sink (and lose) into this car to get what you are talking about, you could get a ZR1 that's already there and will retain some value if you want a C4, or get into a C5 or C6 that's way more modern and turn key.

 

Your goals are lofty.... good luck with your project.

 

FAUEE is correct. You'll jump through a lot of hoops getting that car to where you want it to be...if you can get there at all. And being in Japan, it may be even more costly. Not really trying to discourage you here, but rather save you some money.

 

It honestly sounds like a nice car and the color combination is fairly uncommon. If you meet your power goals, the car will definitely be a very fast car! I would love to see pictures of the car whenever its delivered!

 

Thank you guys for all the good warnings and advice! It does sound like I should likely take this in steps and see if I want to proceed further down the list of goals. With that in mind, out of the list, I definitely want to do the exterior paint/weather stripping and wheels at the minimum. So, I will start with that and drive the car and see if the stock horsepower and torque is suffice for the time being. Then, if I want to increase power, etc. I can start with the mind that none of that money will ever come back. This is my only planned project car for my life, so sinking some money just as a hobby shouldn't be too bad.

To other good points brought up in the thread, as to why the 1986 c4 vs zr1, c5 or c6. I choose this one for styling. I really love the 84-90 c4 corvette rear lights, I think it is my favorite rear look of a corvette. Funny enough, I do not feel the same about the front of the c4. Also, I really like the bronze interior option that was only available until 1987. Those are the primary two reasons that I went with the year and model. In Japan, the c5's and c6's aren't too overpriced like the older corvettes and I was considering buying one. But, in Japan, manual transmissions are very rare on non-special edition Corvettes. (This is due to the way that import laws work here where foreign cars have to undergo an insane inspection that is not technically a tax but behaves like one. So, importers import these cars in lots of 10, etc., and ALL specs have to be the exact same. Since automatics are more common, almost all corvettes are automatic. When they do these inspections for a LOT, they only have to pay the inspection price once, which saves them a lot of money. While the handling, horsepower, etc. of the c5 and c6 is much better, I really enjoy the styling of the c4 a little more and want a manual transmission. Side note, the c6 also has a great rear light look, but the front is not the best.

One question for FAUEE regarding the 4+3 manual transmission. About how much HP and torque can it likely handle if I was just using it as a 4 speed manual? As for the overdrive, I would only engage in 4th gear when cruising to save gas. Thanks to anyone who might have this information.

One other point. Even though I do reside in Japan, I do have access to an American shipping address over here, so that should help a bit.

In conclusion, I will take these really good warnings to heart and prioritize the exterior look of the car. If I want to go further, then I will proceed with caution.

Thanks! I will definitely post pictures once the car has arrived in this thread.

 

Sometimes it’s not about the money, but the journey and the fun…the sense of accomplishment that you had a vision and you achieved it.

If you have the financial means, does it matter?

Sounds like a great project. Probably don’t see many 86 Corvettes in Japan.

Looking forward to seeing the pics when you get it.

 

I am definitely excited to finally own a corvette and whether I reach all the goals listed in the original post, the journey should be fun!

No, there are not many corvettes in Japan, but the most common ones are c5's and c6's. I have only seen one c4 so far and it was a 1996 grand sport. The early body style c4's are almost non-existent, and one's with manual transmissions are very rare.

Financially, I am very stable, I have no debt at all (including house). So, none of this money will be precarious to everyday life.

I looked at your profile and see that you have a 2004 z06. That is an awesome car! Do you mind linking a picture or posting one on this thread, I am curious to see what it looks like.

 

Welcome to the asylum...

 

425 lb ft "target" X 2.84 1st gear ratio is 1207 lb ft being put into the input of the OverDrive (OD) section of the trans. When in Direct, the torque goes through a sprag clutch and a spring-loaded clutch pack. The sprag conducts torque in the Forward direction (engine driving the wheels) and the clutch conducts torque in the Reverse direction (rear wheels driving engine, ie "engine braking"), or in Reverse gear.

Add the Inertia of the larger wheels and tires to increased torque output may exceed the mechanical limits of the OD section, regardless of whether the OD is in Direct or Overdrive. Torque always goes through the OD section. And in lower gears, the engine output torque is multiplied by the transmission gear ratio. It is a common misconception that the 4+3 behaves like a normal 4-speed if the OD is not "engaged". Not at all, it can be broken while in Direct.

We can't get parts for the OD here because there aren't any, at any price, anywhere. I wouldn't modify the power output and I would drive the car like the overdrive is made of glass. And when it does break, which it will eventually, be prepared to spend the money and effort to change the trans to one of the aftermarket solutions. Seriously, you should have bought an automatic. Even in Japan, I'll wager that parts and expertise are available for the 700R4, 4L60.

Best of luck with your ownership of a 40 year old obsolete transmission in Japan.

 

I agree with this.


Are there interesting roads in Japan for the Corvette to "exercise?"

 

Photo from last weekend where it was "warmer" (Slightly above freezing. It snows A LOT where I live and the weekend had a slight opening)


Unfortunately, I lost the data in my phone, and I had a lot of great routes saved on there I used to ride my motorcycle on. I just moved to northern Japan for work, so still getting used to the area. As for areas to "exercise" in Japan, the speeds here are much lower than the states, but if you like winding mountain roads, there are a lot of great places. For higher speeds, there are the highways and the countryside roads. Most people in urban areas will go out at night with less traffic. As for the countryside, there are some amazing highways in the mountains, just choose a point and time where there is no traffic on the road.

In Japan, the best thing is to go to the various circuits they have. I used to go to a large racetrack called Okayama International Circuit. It really was an amazing track. Since I am not a member of the circuit, I was only able to ride on a "once a month" event. The price was very good, but only two 20-minute rides. The rules were stricter too since it was not separated into the experience of the rider and size of motorcycle. But you could still pass in the straights, etc. I plan on taking my corvette to the track here and letting it fully lose. I know it's an old car, but it should still be an absolute blast for me and I am curious how the older z51 suspension will hold up.

 

This is really good information, and I appreciate the detailed explanation! This definitely is a big issue that needs to be addressed. It looks like my options are:

1) Upgrade to an Aftermarket Manual Transmission (Regarding this, are there any kits that do not require any cutting of the body and are for the most part bolt on and good to go?)

2) Overdrive Delete Plate (Remove the OD Unit and Install a Delete Plate. It looks like this would require a slightly longer driveshaft, etc. Anyone know if the stock 4 speed transmission portion of the Doug Nash is durable enough up to 425 pounds of torque? Also, if anyone has any experience with this, feel free to chime in. I have not looked up costs etc, for this, so could be just better to get a brand new aftermarket transmission)

3) Gut out the Overdrive Unit (I don't think I want to go this route, as it seems it requires a lot of machining)

4) Replaceable Parts??? (I am assuming the main three would be the sprag clutch, spring-loaded clutch, and OD drum? Just from quick searching, it seems that parts do not exist as you mentioned)

Here is a rebuilt kit (no parts, just bearings, gaskets, etc.) and 3rd clutch sprag (not sure if this is for the OD portion of the transmission)

https://cobratransmission.com/doug-n...kit-50010006-1
https://www.transmissionpartsdistrib...s-borg-warner/
https://www.transmissionpartsdistrib...s-aftermarket/

Thanks for the heads up again regarding this issue, and any advice is well appreciated.

 

Haha thanks!

 

I love the digital dash c4s, 89 and prior. So when I bought my first c4 I rushed in and bought an 84, which I fixed up cosmetically, but did not touch the crossfire. I then wanted a manual but heard not so great things about the 4+3, so I decided to find a 6 speed 89, which was a complete pain. The guy I bought it from said he likes his 4+3 more than the 6 speed and maybe that’s true.

I guess all I’m saying is a manual c4 to me will always be fun no matter the hp. Working on these cars is some of the best and most frustrating things as a small project can turn long just from the car being so old.

Show some pics

 

Early c4 white corvettes have always looked great! Especially the back with the solid black Corvette badge. Blue interior must be a rather rare combination with a white exterior. That is clean looking as well!