Backstop

Hi all,

I have a 73 coupe (seen here) that's been a slow project for a few years. New paint, new interior parts, shoulder belts, getting the brakes and headlights working, that kind of thing.

The car came to me with a 1972 L48 under the hood with Holley DP, and headers, and a 4.11 rear end mated to the stock 4-speed. It's got stainless brake lines. Currently running 265/50-15 tires on stock wheels.

What I want to do is take this car and make it my autocross/track car (more of a focus on autocross). I currently use my GTI for this but I think a Vette would be more fun and I don't like risking my daily if I go off track or something. Also it's just not getting used much so this would get her out of the garage more often.


My plan is to take it in stages:

1. Switch to 17 or 18" wheels (maybe these)and 255/40/18 tires. Put on better brake pads (car does not have power brakes).
2. Replace the chambered exhaust with an X-pipe setup and a pair of Magnflow/Flowmaster mufflers
3. Upgrade suspension, possibly VB&P's Street & Slalom kit all at once.
4. Better seats with side bolsters
5. Later on, a top-end rebuild to get the motor up to the ~300-HP range.

Does that sound right, taken in that order?

ignatz

Been there, here's my list

1 - bigger and stickier tires like Hoosiers on 18" by at least 9" wheels
2 - a good alignment with increased caster and camber
3 - better seats
4 - SS hoses, good bleed for stiff pedal and I liked the Hawk pads
5 - increased front and rear sway bars
6 - smaller diameter steering wheel
7 - get rid of all your old sloppy bushings, replace with poly. Research your suspension mods a bit more, there are a lot of choices

After you get the car handling better, then go for the power adders. With the exception of 5, you can probably do all the other stuff at once. You will want to play a bit with the sway bars to see what you like. With 4.11 gears you will probably be in 2nd a lot. I would go numerically lower. Oh yeah, did I mention a rev limiter? Best stop here, the list goes on and on.

Backstop

Yeah I know it's a long and expensive road. I would probably take it in stages slowly because the household Office of Accounting and Bill Payment doesn't take kindly to large hits to the credit card.

Probably sticking with CAM classes so tires like RE71Rs rather than Hoosiers.

69autoXr

Stuff as much wheel and tire under there that you can-you'll need it to run CAM-S.

Everything Ignatz said is on the right track, although I like your gearing (assuming wide ratio trans). I run 4.56 with close ratio trans, which is very similar to 4.11/wide ratio. Most all courses I run in second gear.

Do try to get to events at the Toledo Express Airport next year, it's the best site in the MI/IN/OH area.

Backstop

I'll check Toledo out, my home club around Cleveland is hurting for pavement.

Have you been to the new setup at Dragway 42? They set up a sort of grid of pavement and the organizers set the turns and chicanes up with cones. It's almost a road race situation. I probably will stick with them next year unless Cleveland comes up with a lot.

69autoXr

Never heard of Dragway 42, but it sounds similar to West Michigan events at US 131 Motorsport Park.

Frankenvette

I auto-crossed my vette once. It was about 3 weeks after separating from my ex, needed something to do to. Took my 15 year old with me and made it father/son time.

I had the absolute best time. Came in dead last and proud of it. Did not not check my oil, brake fluid, coolant, tire pressue... nothing. Just showed up and drove her hard in 2nd gear.

Lost fuel flow to my carb on one particular turn which caused fuel starvation thus killing my time.

I'm now slowly rebuilding the car for light autocross events. Added Borgeston steering box, rebuilt front end with poly bushings, spreader bar, larger front/rear sway bars, 550 lbs coil springs and just completed a 5 speed tranny swap. Future plan is to add fuel injection to get away from fuel starvation to the carb.

Already added C5 seats, rebuilt rear suspension, 17" C5 wheels with summer high performance Z rated tires.

cagotzmann

The items listed by others covers everything, but the order may vary.

I look at it like this, safe & reliable first.

So what does this look like for me.

Car started as a 78 L48 stock auto TH350. Main use is road course track days, no autocross.

1. replaced all the suspension bushings with poly and installed the complete VB&P street & slalom kit.

What I learned after using the combo at the track.
1. the brakes suck.
2. tires suck.
3. transmission sucks.
4. engine sucks.

next upgraded the better brake pads.
Result: much better braking, but calipers started to fail. Stock calipers (new or rebuilt) don't have great quality seals in the pistons that take the heat.

Next replaced the motor with a ZZ383, this added more speed and the brake problem became very noticeable. I gave up on the factory calipers and replaced them all with wildwood D8-4 calipers. Brake problem is no longer a problem. I am on season 2 without a single brake failure / leak / problem. I also replaced the MC with wilwood since I still had the original MC from 1978.

Added 18" wheels and a T56 6-speed.

So now with poly everywhere, NT01 tires 275 40R18 ZZ383, 6speed, the factory steering is taking a beating. Started with hose failures to power valve leaks etc. This is going to be replaced this winter with a r&p steering of some sort.

My order of suggested upgrades.

1. suspension complete with poly.
2. brakes
3. tires
4. transmission
5. engine
6. steering.
7. seats < this can be done at any time.

this assumes their are no mechanical problems on the factory parts.

The nice thing about doing it in steps, you will learn which upgrade provides the best performance.

My car started as 1 1:51 sec laptime and now down to a 1:32.8 sec laptime.

The 3 items that provided the best improvement was

#1 engine but this also required additional upgrades to keep it reliable.
#2 tires
#3 transmission.

Changing brakes to wilwood only provided reliable upgrade. You would need bigger brakes / rotors to improve past the factory brakes.

Enjoy it's fun to drive these cars for these type of events.

Backstop

Yeah safe and reliable is where I've got the car now, at least in terms of street use. It starts, stops, and turns correctly and isn't an eyesore which is an improvement from when I bought it.

I'm going to go with the wheels and tires first because it's got some pretty old rubber on it and 15" tires are not great unless you're drag racing.

I was thinking engine upgrades last because I want to work on my turning skills before I get ahead of myself and end up on the green.

Frankenvette

Another thought... what type of track will you be running on? The track in the video above is very different from what I ran. Are you going to be on a dedicated, large, long track like in the video?

The track I ran was in a large parking lot, so you never were able to build up much speed before being slammed into a turn. That was by design to keep the speeds down.

The fastest timed cars where not necessarily the high powered cars. They were the better handling cars with superior drivers behind the wheel.

cagotzmann

Well if you are looking for tires / wheels take your time and do a lot of research.

I would suggest get the widest wheels you can afford and tolerate modifications to the suspension.

Also it will be helpful if you have a square setup to allow tire rotation front to back and left to right. This adds to the problem of what is the widest you can safely go but allows you to max the short tire life due to extreme use.

For track days I have 2 sets of wheels.

Wet rain days 18x8 4" BS running Michelin Super sports.
Dry days 18x9.5" 4.75" BS running Nitto NT01.

To give you an idea on the difference with the 2 tire combo's on the dry is about 3.2 sec a lap 1:36 vs 1:32.8

So also check the tire dia for the given wheels. this will effect clearance problems with the front. Bigger dia wheels on the front will have more problems with full turn rubbing on the frame.

anything using 18x8" wheel 4"bs should just work with anything since this is factory specs. But not wide enough for best lap times.

when going wider you need to consider everything.

Backspacing has the biggest effect on what else needs mods.

Points of interest on the rear.

1. parking brake cable / brackets
2. rear sway bar.
3. spring ends
4. brake caliper
5. outside fender

Points of interest on the front.

1. tierod spindle
2. brake calipers
3. full turn frame rubbing
4. spoiler rubbing
5. outside fender.

The good thing is there are many threads covering "what is the widest tire" and the problems each combo has.

PeterC3

What I learned the first time I tracked my 'vette:

"Don't stress an old drive train"...:-)

69autoXr

Bringing this back up, I'm going to try to be at the Dragway 42 autocross with my C3 on October 28.