Which is better? Help class my '90 Corvette please!

[Kubs]

I am trying to build a '90 Corvette in TTA. For the most part it is the stock weight. I removed the AC and put lightweight race seats in but added a rollbar, accusump, and oil cooler. I will be building the L98 shortblock as much as I can with out going under the 8.7:1 weight to power ratio. Since I am taking points for heads, intake, exhaust, suspension, etc. I am right at 79 points, any more will put me in TTS. Heres my delema, I cannot use the factory shocks without taking points because I have the FX3. If I disable it and use a non adjustable shock my choices are softer shocks for base model C4s and would probably not be the best for my Z51 springs. However, if I go down one tire size I will have 3 extra points in which I can use the stiffer shocks (ie Bistein Sports vs HD). I will be getting 18" wheels to use because scrub tire sizes are all over and easy to come by. I also want to use Hoosier so I qualify for the tire contingency. If I run a 315 width I am maxed out on points and have to use the softer shocks, if I use a 305 I can use the stiffer shock, but Hoosier doesnt have a 305 just 295 or 315. Which would benefit me more, a softer shock but a wide 315 tire? Or, a stiffer shock that works with my suspension and a narrower 295 tire?

 

Sorry for being long winded, I hope I explained my situation clearly.

[AZELISE]

If the car won't be ready till 2010, don't do anything till the rules come out. If the car is ready for the end of the 2009 season, then run whatever tires you can find cheap and run with the shocks on the car in TTS. I know it will not be as competitive, but really it will only be for shakedown and testing till next season. If you absolutely have to be competitive (and win some Hoosiers) in 2009 and considering that the shock rules will probably change in 2010, I would follow the least expensive route. If you can find base shocks at a low price, go with 315's and base shocks. If you can get some aftermarket shocks cheap, then run 295's with the aftermarket shocks.

 

I hope some Corvette experts can help since one of the two mentioned options might be much faster than the other.

[drivinhardz06]

If I run a 315 width I am maxed out on points and have to use the softer shocks, if I use a 305 I can use the stiffer shock, but Hoosier doesnt have a 305 just 295 or 315. Which would benefit me more, a softer shock but a wide 315 tire? Or, a stiffer shock that works with my suspension and a narrower 295 tire?

 

agreed on waiting for 2010 shock rules

 

but my .02 (which is worth about .01 in this economy) is given the same wheel width, (within reason) - tire width is over rated.

 

assuming you are running a 11" wheel (17x11 GS for your C4?) a 295 would fit very well on it. also take a look at the actual hoosier specs (tread width/measured rim width, etc). the 295/17 has a 10.8" tread width, almost spot on perfect for a 11". 315 would fit as well, but NASA has pretty generous pts kickbacks for going 20+mm under.

 

I would run CCW 17x11" wheels on 275 or 295 if I had the $$ ( vs 18" - TTA C5Z here). I like sidewall and I Iike tucking the barrel of the wheel in closer to the axle centerline (MOI). The OEM GM GS 17x11 is a good wheel if you've got a set already, ~22 lbs. however folks want your first born for a used set, and for that $$ I'd go ahead and pony up for new CCW 17x11. What keeps me on the OEM C5Z Speedline 18x10.5's is the cheap cost and insane weight, lighter than virtually any same sized aftermarket wheel, at any price.

 

find some cheap scrubs (315/295) and do some track day testing

[Kubs]

Well, long story but, the car actually probably wont be ready until 2011. I am trying to piece it together as the budget allows. I have a set of aftermarket (heavy) 17x11 GS wheels for sale to help pay for my wedding (this and Im finishing college is reason the budget is low at the moment). I am saving for 18x11 CCWs cause I see many more scubs in 18s and its getting hard to find 17s. Once I graduate I will have more time/money to spend on the car, which is why Im waiting till 2011 to start TTing. I want to take my time and build the car right first.

 

What kind of rule changes would they be making to shock rules? Would it help or hinder? Since the car is not a powerhouse Im leaning towards the 295s and stiffer shocks, but maybe something else would be better with new rules?

[Aardwolf]

I would use the better shocks. I've been planning to use either 275 or 285 for mine. You don't have to use 315's to do well.

 

How are you getting so many points? I'm only at 58 with top tier tires in 275, I'd need 60 to hit TTA.

[jimbow]

I would use the better shocks. I've been planning to use either 275 or 285 for mine. You don't have to use 315's to do well.

 

How are you getting so many points? I'm only at 58 with top tier tires in 275, I'd need 60 to hit TTA.

 

I'd keep the fx3 if they are not shot, otherwise go to something like the tokico D-spec or other high quality adjustable. They are all inexpensive enough that they only cost the 3 points. I found a set of rebuilt/revalved FX3's that I'm using. Based on Jason's results you don't need 315's. My plan is to find another set of C5 rims (not z06, I have one set already) use the 18" rims for 275 or 285, the other set for 245 rain tires. I also have to take points for the front sway bar.

 

I dont have to take points for "29) Non-OEM driver/cockpit adjustable sway bar or suspension settings +4" because I have the controller disconnected and the adjusters disconnected at the shock. Because I start in TTC + 14 (plus mod points so far) leaves me 15 points to work with to get to TTA, if I want to run TTB Street tires leaves me 5 points to work with.

 

Since I also run NCCC events and I don't want to mod the engine I have to keep it to the group 2 rules. Which further limits what mods I can make. I need to research the lightweight flywheel and see if it still keeps me in grp2, its the only "free" mod I've got left.

[Aardwolf]

TTC +14 = 15 points to TTA? It looks to me like TTC +14 = 45 points to get to the top of TTA points. That's TTC +7 and your +7 from mods.

 

I'm running four rear C5 rims, the 18x9.5" thin spokes. They are very light, 18 lbs on my junky scale. 44 lbs with some worn down sport cups. They can be had for a song, plus they look nice.

 

 

There are polished versions as well.

[Kubs]

I would use the better shocks. I've been planning to use either 275 or 285 for mine. You don't have to use 315's to do well.

 

How are you getting so many points? I'm only at 58 with top tier tires in 275, I'd need 60 to hit TTA.

 

Well I start with 14 in TTD plus 10 for running DOT race tires (most likely will be 295s +13?). I am accounting for points in cam heads, intake, relocating throttle body and air cleaner, non OEM injectors, headers, full exhaust, modified cat, heim jointed trailing/control arms, and metallic bushings, and non OEM calipers in the front (C6), modified OEM springs (lowered front), larger Z51 sway, and points for shocks. I may have missed something, and some of these mods I havnt done yet but Im accounting for everything. I got 79 points for everything Ive done/ want to do.

[Kubs]

 

I'd keep the fx3 if they are not shot, otherwise go to something like the tokico D-spec or other high quality adjustable. They are all inexpensive enough that they only cost the 3 points.

 

I thought they could not be adjustable shocks for the 3 points?

 

Since I also run NCCC events and I don't want to mod the engine I have to keep it to the group 2 rules. Which further limits what mods I can make. I need to research the lightweight flywheel and see if it still keeps me in grp2, its the only "free" mod I've got left.

 

No in NCCC Group 2 you cannot change the flywheel. It has to be the heavy duel mass. I ran NCCC for the past three years and got bored so Im getting into NASA. Im told for the money its 10x the seat time and a lot more fun.

[Aardwolf]

I would use the better shocks. I've been planning to use either 275 or 285 for mine. You don't have to use 315's to do well.

 

How are you getting so many points? I'm only at 58 with top tier tires in 275, I'd need 60 to hit TTA.

 

Well I start with 14 in TTD plus 10 for running DOT race tires (most likely will be 295s +13?). I am accounting for points in cam heads, intake, relocating throttle body and air cleaner, non OEM injectors, headers, full exhaust, modified cat, heim jointed trailing/control arms, and metallic bushings, and non OEM calipers in the front (C6), modified OEM springs (lowered front), larger Z51 sway, and points for shocks. I may have missed something, and some of these mods I havnt done yet but Im accounting for everything. I got 79 points for everything Ive done/ want to do.

 

How many points did you give yourself for the heads? Mine are ported stock units so I take six for that. Are you running AFR?

 

A ride height adjustment isn't charged points but you have a Z51 so you have to take points for the spring since it wasn't on a base model.

 

What fuel injectors are you using? Depending on your power level you may be able to use stock. You also may want to go back to a stock cam, taking six points for the ZZ4 cam is a lot for a cam that isn't much better then stock.

 

I'm getting 68 points with no points for shocks and 275 tires. Leaving you with 11 points to spare.

 

If your taking one point for a cut lid on the air cleaner you could use a stock lid as there's very little gain there if any.

[Kubs]

 

How many points did you give yourself for the heads? Mine are ported stock units so I take six for that. Are you running AFR?

 

A ride height adjustment isn't charged points but you have a Z51 so you have to take points for the spring since it wasn't on a base model.

 

What fuel injectors are you using? Depending on your power level you may be able to use stock. You also may want to go back to a stock cam, taking six points for the ZZ4 cam is a lot for a cam that isn't much better then stock.

 

I'm getting 68 points with no points for shocks and 275 tires. Leaving you with 11 points to spare.

 

If your taking one point for a cut lid on the air cleaner you could use a stock lid as there's very little gain there if any.

 

Well the heads I am not sure of. If I port mine it will be 6 points, if I go with aftermarket I will need to be evaluated for an engine swap. If I can still be in TTA after that I will go AFR or something.

 

The way my car sits with the heim jointed suspension, springs, and metallic bushings I am about 2 points over TTB into TTA, so instead of being on the low end of TTA I decided to start to build an engine and max out my points in TTA to be more competitive. I am not staying with the ZZ4 cam I am going with something more aggressive for the 6 points, and to better work with my combo. I am replacing the stock intake manifold with a single plane EFI with an elbow and LSX throttle body, which is why I am taking points for non OEM throttle body, non OEM intake, and relocation of air filter. The injectors are ones I got cheap to replace the leaking stock ones, 30# SVT injectors. I understand I can get by without taking points for all the intake changes, but doing anything to the TPI, ie porting or increasing runner size, is the same amount of points and just seems worthless. I can build an engine with a much stronger power curve and having a single blade throttle body give better throttle response. I have heard the difference is night and day over the twin setup. I emailed the TT director for my region just to make sure Im not violating any of the rules, but I think with the exception of aftermarket heads Im OK.

 

Edit: As far as springs I took points for having cut the rubber pads off to lower it (modify OEM spring), before realizing I had to take points for it being a Z51 anyway.

[jimbow]

Maybe I wasn't clear

I start out in TTC +14

Shocks, springs, swaybar (remember Z07) - +7

Exhaust (by what I've been told Headers, new cats and catback) +5

275 street tires +4

Modified Air filter housing +1

= +31pts = TTB (8pts left)

 

245 Hoosier/Khumo = +36 still TTB

 

275 Hoosier/Khumo = +41 = TTA

315 Hoosier/Khumo = +53 = TTA

 

So if I found another set of C5 fronts I could run 245 sticky tires and still be TTB

Don't think that would be any faster than 275 streets though.

 

OBTW - I reviewed the NCCC rules and the poster is correct I can't go lightweight FW without moving to grp 3. So I will wait until the OEM flywheel bites the dust to replace it. I only run 2 or 3 NCCC events a year. Do need a tow vehicle and truck first, thats the next things on the "spend funds on". Once I have those I'll be caging and modding to the edge of TTA. Spec C5Z's will still be faster

[Kubs]

Maybe I wasn't clear

I start out in TTC +14

Shocks, springs, swaybar (remember Z07) - +7

Exhaust (by what I've been told Headers, new cats and catback) +5

275 street tires +4

Modified Air filter housing +1

= +31pts = TTB (8pts left)

 

245 Hoosier/Khumo = +36 still TTB

 

275 Hoosier/Khumo = +41 = TTA

315 Hoosier/Khumo = +53 = TTA

 

So if I found another set of C5 fronts I could run 245 sticky tires and still be TTB

Don't think that would be any faster than 275 streets though.

 

OBTW - I reviewed the NCCC rules and the poster is correct I can't go lightweight FW without moving to grp 3. So I will wait until the OEM flywheel bites the dust to replace it. I only run 2 or 3 NCCC events a year. Do need a tow vehicle and truck first, thats the next things on the "spend funds on". Once I have those I'll be caging and modding to the edge of TTA. Spec C5Z's will still be faster

 

You would be much faster on a R-comp tire that is a bit narrower than on street tires. The grip is night and day. Also, check Hoosiers spec on tire sizes and compare them to your 275 street tires. I bet they are closer than you think.

 

Edit: a 245/40/18 Hooiser has the same tread width as a 275/40/17 Goodyear street tire, plus the extra grip. I would take the points and run the Hoosiers in TTB if thats what you want.