ninety4formula

Hey guys and gals, I am in need of some guidance. I autocross with a couple different clubs. One being the NCCC and the other being the SCCA. I need some help on some mods I can do and stay in both of my current classes. For the NCCC I am a group 2 car and for the SCCA I am in BSP.

This is my current setup:
1990 corvette w/ Z51 suspension
6 speed
dana 36 with 3.07
C6 Z06 replica wheels with nitto NT-555 fronts (275/40R17) and Nitto Invo rears (295/35R18)
K&N filter with modified lid
Hawk HPS pads front and rear
Aftermarket short shifter
custom chip
muffler eliminators/no cats
throttle body airfoil
180 degree thermostat
air pump delete

I would love to get some slicks on my factory wheels (275/40R17) because I know that would help a lot, but I am having a problem finding out what else I can do to help myself out. If I get used tires then that would be great because I also need to get a trailer and a hitch to transport them to the race. What other things would people here suggest? I have been being beat by a 2009 WRX with suspension and possibly a tune. He isn't beating me by much either so I'm pretty confident that I can beat him just by getting slicks but I am curious what other options I might have that would be a lower cost. Any input is welcome here.

Brian

jaa1992

What alignment specs are you using?

Consider going to the HTC Hawk pads or Carbotech.
Do you have the J55 brakes?

Is this Autocross only?

ninety4formula

I do have the J55 brakes. The car isn't a specific autocross car but that is the main racing that the car sees. I do about 8-10 events a year so far, but I drive the car when the weather is nice out on the street. I don't have my alignment specs on me but I know I am running a little more camber than stock. I think we (my stepdad and a family friend) got the specs from a magazine for C4's that wasn't the street setting but the next setting up. I think my front camber is as much as I'm going to get using the stock suspension without modification.

froggy47

Replica wheels are always pounds heavier than stock and race wheels. Gets some lighter wheels.

Adam@Amp'dAutosport.com

All that said I would look at a break pad up grade to Carbotrech AX6.

The AX6™ takes the place of the Panther Plus™ compound that was so successful. AX6™ was specifically engineered for Autocross applications. A high torque brake compound delivering reliable and consistent performance over a very wide operating temperature range (50°F to 1150°F +). Advanced compound matrix provides an excellent initial “bite”, high coefficient of friction, and very progressive brake modulation and release characteristics. AX6™ offers high fade resistance, rotor friendliness at all temperatures, excellent cold stopping power, and non corrosive dust. As a result, AX6™ is an excellent choice for Autocross & AX6™ has gained tremendous popularity with SCCA Prosolo/Solo2 competitors for its fantastic bite, release & modulation. Many drivers use the AX6™ for street driving as well, even though Carbotech doesn’t recommend street driving with AX6™ due to possible elevated levels of dust and noise. AX6™ is NOT a race compound, and should not be used as such. AX6™ shouldn’t be used by any intermediate or advanced track day drivers, and should not be used with “R” compound tires (racing tires).


F $160 R $140 less 7% forum discount add $40.00 for pre bed. I will be happy to answer questions or place an order for you contact info is below.

ninety4formula

I'm sure that light weight wheels aren't that cheap. I'm looking at $1,000 total that I can put towards upgrades. If it is something that I can do myself that might just take some time, I'm all about it. Funds are just a little tight right now so I am trying to get the most bang for my buck which I believe would be a set of used A6's. I believe my stock wheels are lighter than my other replica wheels I have that are the same size so I will probably just use them for racing. What kind of time difference would you expect to see using light weight wheels on an autocross course anyways?

froggy47

you really have 3 different classifications of weight.

sprung weight

unsprung weight

rotational weight

sprung weight is anything that is on the car that is carried by the shocks/springs. so trunk, seats, engine, etc...

unsprung weight is everything that touches the road before the springs. so wheels, brake rotors and calipers, hubs, and half of the shock itself.

rotational weight is the stuff that rotates. here there is a bit of a mix between sprung and unsprung weight. your driveshaft is rotational weight, but it is also sprung. your wheels are rotational and unsprung.

ideally, your suspension will work best with the least amount of unsprung weight (quicker response, less inertia), so better handling. your car will accelerate best with the least amount of rotational weight. so wheels, brake rotors, drive shafts, light weight clutch, etc. reducing sprung weight helps everything, but not quite to the effect that the other two will.

so if you look at it that way, taking rotating, unsprung weight off the car will help the most. wheels, brake rotors, lug nuts, tires. there is no set number like a lot of people pass around like "1lb of rotating mass is like 5lbs of regular mass". thats just not easily quantifiable because if you take a pound out of a tire, its going to have a much bigger effect then taking a pound out of a driveshaft. the reason is the tire has a much higher moment of inertia then the axle does.

Above from another forum, and all true if simplified. Light rims are HUGE in performance gain vs. most everything else & good ones are not cheap.

BTW the rims will last the life of the car usually, A6 not as long. Look past initial cost to total cost over how long you will participate. If you are only going to dabble in this for a few months & move on (many do) then buy the used a6 & skip the rims. Used a6's could shred in one event if you lack the camber and/or over drive them.

JiminVirginia

First, Hoosier A6s mounted on the wheels you have. Get an autocross trailer, like the one I have from Harbor Freight. And a hitch, obviously.

Your pads, HPS, are good enough for autox.

The second thing I'd do is consider shocks (Konis or Pfadt adjustables).

Third, a stiffer front sway bar. Pfadt has an adjustable but there are others.

The fourth step might be a front spring from VBP. 1100 pounds or so.

Jim

RX7 KLR

Any particular reason you are using a diff from an AT car? Changing to a Dana 44 with a 3.45-3.54 would make a big difference when digging out of slow turns.

Get some weight out of the car... Pull the AC, small battery, race seats and a lightened flywheel.

btw, slicks are not allowed, the tires being used are DOT legal R compound tires.

jaa1992

I really love the Carbotech brakes. I can brake almost at the same marks as a C5z06 on the road courses - and I always over brake.
I loved the Panther pads when just Autocrossing. That .1 sec later breaking for a turn could be all you need.

I hear you on the front camber, before I put poly bushings on the best I could get was +0.1, now I'm at 0 and since offset bushings are 0 points in NASA (check legality fro grp II NCCC) those are going in over the winter.

Check to see what tire compunds you can run Khumo V710 and Hoosier A6 are popular DOT R compounds. On the road courses I run 275 on all 4 corners for competition, haul out the 315's for all corners for HPDE only and NCCC events. I don't know - I'm kinda digging the 275 square setup. I don't autocross anymore - never seems to fit in the schedule.

BrianCunningham

Most drivers in BSP are running offset bushings to get as much camber as they can, so there's only so much you can do with a street car.

I'm running some pretty big wheels (18x12f, 17x12r) but they weigh less than stock ones with the Hoosiers mounted.

Shocked valved for autocross help, these can be adjustable so you can dial them back for street use.

Mike P

A set of A6 tires could take SECONDS off your times. Street tires vs. DOT race tires is a huge difference.

And to take the most advantage of the tires, the alignment has to be at least close to what the tires need. You'll want close to 2 degrees of negative camber in the front, and 1 to 2 in the rear. Combine that with 3/16" toe-OUT in the front, and 1/16" toe-IN in the rear.

See Vette Brakes guide...
http://www.vbandp.com/index.php?opti...man&Itemid=170

Mike P

Solofast

The biggest thing you can do is to get the front end hooked up. What you have is basically a stock setup in classes that allow you to fix what is basically wrong with the car. You are bringing a knife to a gunfight.

First of all get a set of offset bushings for the lower control arms. This will allow you to get some negative camber in the front end. Get about -2 degrees of negative camber in the front end and set the rear at about -1.5 degrees. Also make sure you have at least 7 degrees of caster, and more is better.

Toe out is great for the track, but with 2 degrees of camber and toe out it's going to eat tires on the street. Better to set it at zero or a bit of toe in and crank some toe out (one full turn of the tie rods towards toe out) before each event. Mark your tie rods with a streak of paint across the tie rod and the end link and just move in full turn increments.

After that the next thing is a serious set of tires.

At this point all you have bought tires.

The Dana 44 is a good thing. Not only is it stronger, it has a much tougher limited slip. If your limited slip is slipping the car will have a lot more oversteer and it won't put the power down coming out of corners. You will have to replace the batwing to put in the 44, but it's a long term thing.

Less weight is good, but if it's a street car first, taking out the AC and going to lighter weight is a lot further down the list.

ninety4formula

I am running a dana 36 because I bought my current car without a rear end so I had to install the one from my wrecked 90. I would like to get a dana 44 with a 3.45 seeing as how I do a good amount of street driving, but I can't afford the dana 44 and A6's. I have been keeping my eyes out for a good deal but I haven't really found any. I am hoping to make some more money off of parting out my car to help with my mod fund. The ideas that everyone listed sound good to me. I will probably hold off on weight reduction right now. My region doesn't have a big BSP class, but I need a little bit of an edge seeing how I am essentially a stock 21 year old car running against the newer technology. I do well with it though and have a blast I just want to win more haha.

How much are those offset bushings? I could probably fit those in there. Will they eat up my street tires more with daily driving? My one method of justifying the A6's is that my street tires would last for a couple more seasons so I don't necessarily want to negate that.

Solofast

VB&P has them for $110 for the lower control arms (all you need). A bargin at twice the price.

With about 2 degrees of negative camber you will wear out the front tires on the inside, but it's not that bad so long as you don't toe it out on the street. If you run 1/8 of an inch of total toe in you will need to flip the tires on the rims at about 10,000 street miles. Depends on how aggressive (soft) a tire you are using on the street, but it is toe out that eats tires, camber less so. Also if you go to A6's and don't get the camber right you are going to eat the outside of the A6's in just a few weekends. Considering the cost of A6's and the speed at which you eat them without a good alignment, the small loss of street tire mileage is a good trade.

Aardwolf

You can save the money and trim the conical spacers too. There is a huge benefit to more camber, the car will really turn! I have 888's on there and the front camber is wearing off the inside pretty fast. The rear is wearing on the outside though so I've been rotating them. This is street and track driving.

BrianCunningham

C4's are not that hard to align.

You can make up a plate that you pull out before autocrossing and pop it back in for the street.

for toe, just mark it with some tape

l98tpi

You could get a 3.73 ratio ring and pinion installed in the D36 carrier. That would definantely help. Your ratio now is probably a 2.59. That is killing you with the 6spd.

RX7 KLR

Not legal in BSP.

RX7 KLR

The rear end ratio is not free in BSP, it must be a factory offered ratio for that model (C4), and must be done as a complete unit. You can only use GM gears, and they must be in the correct case, a Dana 44. LSD is open. It can't be that hard to find a 44 for a decent price.