So you just bought your new smallblock C3 Corvette and have been less than enthused with the performance of it? Well, first thing first, you need to bring it back to baseline specs. Your C3 has been sitting around for years, possibly rotting away. Start by performing a thorough test of the entire car and make sure everything is up to snuff. You can find links for this here: [One] [Two] and [Three]. If you want a good original driver C3, then go through this list and replace anything that seems worn out, etc, as specified.
Now this is all fine and dandy if you want a stock-performing Corvette. But you most likely didn't find this page because you wanted a stock Corvette.
There are a number of ways to beef up your Vette. Do you want more power, more handling, more comfort? Or all of the above? Read on for details on common upgrades performed by C3 Vette owners. Of course there are limitless options available and there is no one right way to upgrade your Vette. Use these as only general guidelines or a basis for experimentation. If you have anything to add, please email me suggestions. I do not claim to be an expert by any means - I am still learning myself. I hope this document can be used to clear up many initial questions on the forum and in emails to me.
Drivetrain This document is geared more towards the small block Vettes (as that is what I own). If you have a big block and would like to contribute, please email me. There seems to be two different mindsets for engine upgrades that I have seen. Those who need smog equipment to pass emissions and those who do not need to pass emissions. You need to carefully study your local emissions requirement before you touch your Vette's engine and exhaust. And even if you determine that you don't have to worry about emissions, it is a good idea to hold on to your emissions equipment as laws may change.
Exhaust. If you have a 75-82 Vette, the best upgrade you can do to gain horsepower is to work on the exhaust. Previous years (68-74) do not have cats or the infamous 2-1-2 exhaust. The 2-1-2 exhaust goes from dual manifolds to a single cat, and back out to 2 mufflers. Not only are the pipes really small and restrictive, but the ancient catalytic converter is old tech and most likely clogged over the years. Read this link for more info on exhaust upgrades: [Ganey Exhaust Post]. If you need to worry about emissions, the best thing to do for more performance is to get a 2.5" 2-1-2 exhaust setup from Ecklers or MidAmerica, etc. They usually aren't cheap ($500+) but they give you a high flow catalytic converter as well. With this, you will still be legal and have a better flowing exhaust. If you want to bend the laws, some people go with true duals with dual catalytic converters. This is essentially illegal, but you will pass a sniffer test and get more flow since you will be losing the 2-1-2 setup. When emissions aren't a problem, people go with true dual exhaust with no cats. Even better flow. And it is recommended that people [install an X] or H section in exhaust connecting the duals at a single point. The thinking behind this is that after the X or H there is a wider exit point(s) for the exhaust to escape. Plus it supposedly mellows out the sound as well. Many types of mufflers are used and this is largely a personal preference for sound. See the Ganey post above for Horsepower comparisons with different mufflers. While dealing with the exhaust, it would be a good idea to consider headers as well. If you just plan on upgrading exhaust and nothing else, it probably isn't a good idea to install headers. Headers will cost you low RPM torque as they do not supply adequate backpressure in low-rpm situations. But if you plan on upgrading cam/heads/intake/etc, then consider headers. The emissions folks tend to go with the Hedman Headers #68301 which have AIR attachments for your smog equipment. But they aren't cheap - about $250. The non-smog folks go with the Dynomax headers which (uncoated) go for a little over $100. Not a bad price. Add coating to cut underhood temps and you're up to $200 or $250.
Intake & Carb. OK, so you opened up the exhaust. Now what? Intake. There are a number of different options here as well, depending on smog legality. Popular choices are the Edelbrock Performer and Edelbrock Performer RPM. The RPM version is not smog legal, the Performer is, and includes the EGR port for this purpose. With the Edelbrock manifold you will lose weight (at least if going from L48 350 motor) and you will get better flow. Even with the EGR version. With intakes, you will need to worry about hood clearance if you have a stock hood. Be sure to measure everything out and consider that you may need to change your hood. Edelbrock Performer fits fine under my stock 77 hood. Many people also swap out their carbs, but this is not necessary for mild upgrades. Reference this post: [Ganey Carb Comparo]. And there is a lot of information on tuning carbs, check out the stuff from Lars in the Intake section of this site. Of course there are plenty of other options out there for intake and carb and if you have anything else to add, please let me know.
Cam. Another popular upgrade is the cam. Especially in the L48, more cam is needed to fully take advantage of the exhaust. Popular smog options are the Comp Cams 268h and Comp Cams 260h. The 260h gives you more torque but less horsepower than the 268h. The 260h is also less lopey. Its a personal preference. If you have no emissions to worry about and can tolerate more lope to the cam, the sky is the limit. 274h seems to be a popular choice but I haven't studied the options very much. When changing the cam, you also need to change the lifters.
Heads. This is where all the power comes into play. Porting of stock heads is a popular relatively inexpensive option. I could talk a lot about heads here, but I think it is done best here: The [GoodWrench Quest]. If you plan to go with budget horsepower Vortec (non-smog) heads, you will need a Vortec intake. AFR 190 and Trick Flow 23 degree seem to be popular aluminum head choices for the smog-concious.
Bottom End. There are a ton of options and you need to investigate what is best for your application. Smog legality can limit you. But as long as you have smog exhaust, heads, intake, cam, and all smog equipment in place you should be ok. I see people building up ZZ4 bottom ends, 377 strokers, 383s, 406s that pass smog with the proper equipment in place.
Crate motors. Check out [Scroggin Dickey] to see what GM motors are available. If you're looking for a smog motor, you got the GM Goodwrench and thats about it. Unless you want to look into LS1 or LT1 upgrades. [LS1] and [LT1] are possible. But they aren't cheap. If you don't have to worry about smog, you can go hog wild. ZZ4s are popular as are 454s and 502s even. They will all fit, though you might need to worry about hood clearance.
Transmissions. Depends on what you have now. Though some have gone [auto -> manual] or manual -> auto, most stick with what they got. Popular upgrades for those with the TH-350 or TH-400 automatics are the [700r4] and the [200-4r] autos. These simply give you an extra overdrive gear. This in turn will also allow you to upgrade your rear-end gears as well if you desire more off-the-line power and still retain good highway cruising rpms. After doing these upgrades, many will go up to 3.55 -> 4.11s in the rear as well. If you have a manual transmission, a popular upgrade is the [Richmond 5 or 6-speed]. There's even been a Tremec T-56 6-speed install.
Cooling. Many people are running electric fans in their setup, combined with aluminum radiators to keep underhood temps down. You can find information about the Spal dual electric fans [here]. Others have fitted F-Body fans [here] and [here]. Another bonus with doing this modification is that you can ditch the obnoxious fan shroud. And this gives you room to install one of Vette Brakes trick front braces.
Suspension
Before doing suspension work, you need to think about how the car is going to be driven. If its going to be raced it needs a stiffer suspension. If its going to be street driven, then a tamer suspension would be in order. Another important thing I learned is that it is wise to buy the suspension as a package so that you can be assured that all the parts will work together harmoniously and make for a well setup car. Before doing any suspension work on your C3, it would be wise to read John Greenwood's [Vette Improvement Program]. He is the master.
Vendors. The primary vendors for our C3s are [Vette Brakes and Products] and [Guldstrand Engineering]. Looks through their catalogs and find packages that fit what you want to go with. A popular package is the Vette Brakes Street and Slalom setup for those who want a stiffer ride. The Touring package seems to be popular with the street cruisers. There are many who swear by the [Corvette FE7 performance package] as being the best suspension to run on the C3.
Springs. 550lb and 460lb front coils seem to be the most prevalent. 460lb will not lower your car. 550 lb will lower the front a little. 550 produce a stiffer ride wheras 460 is very close to stock. Some take 460s and chop them to reduce ride height. My car has the 550s up front. There are the hardcore few, who go with the front leaf spring, but many think that the added cost isn't worth the performance gain (if any). For the rear, many looking for more performance tend to go with the steel 7 leaf spring as appeared in the FE7 package. Others (like myself) prefer to shave off some pounds and go with the fiberglass rear spring. Whatever you choose for springs, it is vitally important you get shocks that match the setup. If you want to lower the rear end of the car, Vette Brakes and Guldstrand both sell lowering kits that feature extended length spring bolts.
Shocks. Bilstein seem to be regarded as one of the better brands to get. They are available at Vette Brakes. If you go with a fiberglass rear spring, it is important that you get specially valved shocks or you will hate the ride quality. I learned this firsthand. Once I picked up the specially valved shocks for the rear, I was very pleased with the fiberglass rear spring ride quality.
Bushings. Most people tend to worry about bushings when they do a front end rebuild kit or get a rear spring, etc. Most likely your car has rubber bushings from the factory. They can be a real pain to remove (cutting or burning). Installing new rubber bushings requies a press and you will retain the stock ride quality with the rubber. If you want a little more road feel, consider poly bushings. They add a little more harshness, but not much more compared to rubber and do not require a press to install. They can squeak however and it is key that you lubricate them properly. I recommend a good marine grease for this.
Sway Bars. There is a lot of contention concerning these. Some prefer to stick with stock FE7 which is very good. Others prefer the biggest bars they can get. Those with big blocks enjoy large rear sway bars. With small block, I find it better to run no rear bar. I originally got the biggest front and rear bars I could find (cause I'm just that way). :) I was not pleased with the handling. I stepped the rear down from 7/8" to 5/8" and it was better, but not very much. I then removed the rear bar entirely and am very pleased with the handling. I think if you are not happy with your Vette's handling after adding a suspension kit, you should do some experimentation with sway bars as they greatly affect turn-in.
5/6 Link. If you goto Guldstand's site, you see he offers a good 5-link rear suspension. Its gotten good reviews from those who have installed it, but at a cost of over $2000, its over the budget of most C3 owners. Another option is a 6-link setup such as [this one]. Check the corvettefaq suspension section for pics of Aaron Main's 6-link as well.
Coilovers. There are a few people running coilover setup on the C3s, but we haven't heard very many good testimonials or any package deals available. Corvetteforum member RedTurbo has a front coilover and you can find full coilover conversion on [this site].
Brakes. There are a number of options available here. If you have a street driven car, I would highly recommend sticking with the stock brake system. It is really *very* good. You just need to refurbish the entire system. Check with [Vette Brakes] for this. Make sure your calipers are not leaking, or go with Stainless Steel Calipers. Get new rotors; resurfacing seems to be hit or miss - mostly miss. For a bit firmer pedal, go with the Stainless Steel Braided Lines. Go with stock pads again, or for more bite, try the Hawk street pads offered by Vette Brakes. I went with those and they REALLY grab and will literally put you through the windshield on my car if you want it to. But the Hawk pads can be a bit squeaky sometimes. So if you hate squeak, stick with stock pads. Other brake options, if you must are Aluminum Stock Calipers, Wilwood Caliper Conversion (lighter, same performance as stock), and [Porsche Brakes] (very expensive). Supposedly Vette Brakes also offers a "NASCAR" setup that is better too. Drilled or slotted rotors look cool, but don't do much if anything for you on the street.
Steering. If your steering is very loose, the way to go is a complete refresh of your steering system. The stock system is pretty darn good. Find info for that here on corvettefaq in Jim Shea's section. If you want something more exotic, check out a Steeroids Rack and Pinion conversion [here].
Wheels. It is getting very difficult to find decent performance tires that will fit our stock 15x8 wheels. Its time to step up the wheel size to 16 or 17 inch. Some people report clearance problems with 18 inch wheels. Merlin is running 19 inch wheels on his monster Vette. Mandatory reading for wheel/tire upgrades is [More Bite for Older Sharks].
Interior
Seats. 68-77 Seats are heavy. By upgrading to 78-82 seats, you can get more side bolster support and shave about 20 pounds a seat. They are a direct bolt on and can be had fairly inexpensive. Others have put [C5 seats], C4 seats, Fiero seats, Supra seats, [Sparco racing seats], etc.
Rollcage. Some have had [custom] rollcages installed. While others have gone for [drop-in ones].
Further Study
Where to go from here? A good place to look is CorvetteFAQ. Lots of good links to tech articles and ideas here. The best place on the internet is undoubtedly the [Corvette Forum]. Good luck and enjoy Corvette ownership!