My STU build
12-21-2014, 08:15 AM
#1
My STU build
I started competing at national events ~2yrs ago in random vehicles (as a tire-warmer) with decent success...but have never ran my own car at a national SCCA event.
For the 2015 season, I decided to prep my Z for STU and run it nationally. STU is, after all, exactly what I asked for years ago so I thought I should make the effort to run in the class:
https://my350z.com/forum/autocross-r...ire-class.html
The Brian Peters all-out-prep thread was very helpful, but not a direct fit for the compromises I needed to make with my build.
Here's my build in the approximate order that the parts went on:
A Quaife differential has been on the car for almost a decade so it wasn't a change for me, but I highly recommend it for people with the stock diff.
1) Removed JWT flywheel/clutch and went back to stock. (My rev-matching skills took a hit in the absence of the JWT flywheel)
2) Removed SPL UCA's and installed Kinetix UCA's and modified them. (shortened the threaded part of the arm to get more negative camber than in OTS form)
2) Replaced sub-frame because I had an SPL aluminum diff bushing welded into the old one.
https://my350z.com/forum/maintenance...-subframe.html
Bobby from CIN Motorsports hooked me up with a new-to-me sub-frame and Whiteline bushing kit.
2) Enkei RPF1 18X10.5 +15 all around. (The "me too" wheels...I got them used) I removed my staggered 17" SSR setup.
3) BFG Rivals 275/35 18 (they were on sale at the time)
4) Berk HFC's and Borla TD exhaust installed and tuned by HP logic. (Borla TD wasn't my first choice, but I got an awesome deal on a used system) ..Also run a K&N drop in FWIW.
5) Koni "yellow" sport shocks, re-valved and sleeved by ProParts. Jeff was very helpful, and sent the shocks back as a complete system. (although no coil-over wrenches)
-1000lb front, 800lb rear springs. *EDIT* Changed rear to 700lb springs*
-Top hats for the front shocks and adjustable perches+helper springs+ collars for the rear.
-6" springs front and rear.
-Hotchkis 4-hole sway bar up front.
-Whiteline adjustable endlinks **need washers when you install them on Hotchkis sway bars...they are not included**
-No sway bar in the rear.
7) Kinetix rear camber arms
6) Corner balanced
7) Semi-aggressive alignment:
2.9 negative camber up front
2.2 Negative camber rear
.1 deg toe out front
.1 deg toe in rear
Now for the little things I learned in the process so far:
The first 3 items rendered no gains in speed for the car.
The stuff that did make a difference:
-Square wheel tire combo: Going from my dialed-in, staggered SSR 17" wheel setup to the 18" Enkei square setup made much more of a change than I anticipated:
First, the combination of 3 extra rotating lbs at each corner and slightly taller-overall wheel/tire combo, hurt acceleration. I expected this, but was surprised that I could actually feel it.
Second, the square setup also moved the car's balance to oversteer in a big way. The old setup was 255F/275R I expected the the extra 20mm up front to increase front grip but I think the matching offsets added more still. I didn't see the need for stiffer front spring rates relative to the rear until I ran this square setup at a couple events. The throttle was almost unusable out of corners until I made drastic changes to the OTS Koni "yellows" I was running and the Hotckis sway bars. (I basically went way stiff on the front and way soft on the back to get by until the new suspension went on)
Horsepower: The Borla TD exhaust, Berk HFC's, K&N drop-in and tune from HP logic, netted me all of 12HP up top and 20HP "under the curve". The car feels as "peppy" as it did with the 17's up top, and even stronger whilst digging out of corners.
The guys at HP logic were great. I race the car regularly, so I needed a tune that I could safely beat on, over and over. I told them that dependability and smooth power-delivery were far more important to me than the numbers themselves, and they delivered exactly what I wanted.
The car pulls, strong and smooth across the tach, and remains strong all the way to the new redline.
They bumped the redline 400 RPM's which helps me avoid third on some of the faster local courses. They also increased the throttle response, which has brought my rev-matching back to almost where it was with the lightweight flywheel.
Oh, and the Borla TD/Berk HFC's combo sounds great!
Suspension: My old setup felt so good on the track, for so many years, that I forgot how much of a PITA it was to get it dialed in years ago. I basically played "Marco Polo" for a year or two until this "blind squirrel" finally found a nut...and then only made minor adjustments for different tires over the years. Now the process has started all over.
First, some pics of some things I learned for the rear setup. (the front was pretty straight forward)
I saw some pics from someone else's setup that seemed to have the bottom perch adapter placed in the spring bucket metal-on-metal. It may have just been the pic, but I *think* this is the correct way to install the bottom perch, using the stock rubber "gasket":
I placed that^ metal/rubber sandwich into the bucket...
The three tabs that held the top (stock) rubber "guide" in place, can be used to hold the new threaded perch in place. This makes putting in the helper spring,sleeve, and main spring easier:
My choice of putting the helper spring on top also differes from one of the pics I saw from another build:
I was concerned that the front setup didn't have helper springs, but the front sway bar does a good job of keeping the spring in contact with both the top and bottom of the assembly when one side is lifted off the ground.
Basically, a helper spring is not needed on the front unless you either don't run a sway bar up front, or go all "Dukes of Hazzard" with your Z and get airborne with both front wheels at the same time.
Corner balancing: I didn't even understand what corner balancing was until I borrowed my club's scales and and spent a weekend in my garage with google and youtube:
My results, with me in the car and 1/2 tank of gas.
Corner balancing is apparently more like "leveling" a dinner table than "balancing" weight distribution. The weight at each corner of a car, on a level surface, is more of an indicator of the suspension's length/height at each corner than an "end" unto itself.
A car with poor corner balancing is similar to 4-legged dinner table that can rock back and forth when two opposing corners' legs are longer than one or both of the other two. But, whereas a table will rock back and forth over the long-legged axis, and alternately lift the two shorter leggs off the ground, making the issue obvious, the springs on a car will keep all four tires in contact with the ground and mask the issue.
The 4 individual scales, and the resulting weights, show how much force each tire is putting on the ground while at rest.
Less force (weight) on a cross-weight (DF+PR vs PF+DR) means one or both of the "table legs" are too short relative to the heavier cross weight. Or, conversely, the heavier cross-weight has a "leg" or "legs" that are to long.
This exercise also showed me how evil sway bar pre-load is. The sway bar tries to make both sides the same and resists any difference between the two sides. So as soon as you sit in the car, the sway bar starts transferring force from one side to the next. After balancing the car without the sway bar connected and then connecting it, I found the sway bar added ~60-70lbs (can't remember exactly) to a single corner once I sat in the car....Now I have adjustable endlinks, which I installed while my weight was in the driver's seat.
Alignment: This is a compromise. I am trying to go as aggressive as possible while still being able to make road trips on the very tires I compete with. (I don't trailer my car, or my tires) The specs I am running now (listed above) are my starting point.
I'll use the next post to share results of the setup over the 2 outings I have made on the new setup.
For the 2015 season, I decided to prep my Z for STU and run it nationally. STU is, after all, exactly what I asked for years ago so I thought I should make the effort to run in the class:
https://my350z.com/forum/autocross-r...ire-class.html
The Brian Peters all-out-prep thread was very helpful, but not a direct fit for the compromises I needed to make with my build.
Here's my build in the approximate order that the parts went on:
A Quaife differential has been on the car for almost a decade so it wasn't a change for me, but I highly recommend it for people with the stock diff.
1) Removed JWT flywheel/clutch and went back to stock. (My rev-matching skills took a hit in the absence of the JWT flywheel)
2) Removed SPL UCA's and installed Kinetix UCA's and modified them. (shortened the threaded part of the arm to get more negative camber than in OTS form)
2) Replaced sub-frame because I had an SPL aluminum diff bushing welded into the old one.
https://my350z.com/forum/maintenance...-subframe.html
Bobby from CIN Motorsports hooked me up with a new-to-me sub-frame and Whiteline bushing kit.
2) Enkei RPF1 18X10.5 +15 all around. (The "me too" wheels...I got them used) I removed my staggered 17" SSR setup.
3) BFG Rivals 275/35 18 (they were on sale at the time)
4) Berk HFC's and Borla TD exhaust installed and tuned by HP logic. (Borla TD wasn't my first choice, but I got an awesome deal on a used system) ..Also run a K&N drop in FWIW.
5) Koni "yellow" sport shocks, re-valved and sleeved by ProParts. Jeff was very helpful, and sent the shocks back as a complete system. (although no coil-over wrenches)
-1000lb front, 800lb rear springs. *EDIT* Changed rear to 700lb springs*
-Top hats for the front shocks and adjustable perches+helper springs+ collars for the rear.
-6" springs front and rear.
-Hotchkis 4-hole sway bar up front.
-Whiteline adjustable endlinks **need washers when you install them on Hotchkis sway bars...they are not included**
-No sway bar in the rear.
7) Kinetix rear camber arms
6) Corner balanced
7) Semi-aggressive alignment:
2.9 negative camber up front
2.2 Negative camber rear
.1 deg toe out front
.1 deg toe in rear
Now for the little things I learned in the process so far:
The first 3 items rendered no gains in speed for the car.
The stuff that did make a difference:
-Square wheel tire combo: Going from my dialed-in, staggered SSR 17" wheel setup to the 18" Enkei square setup made much more of a change than I anticipated:
First, the combination of 3 extra rotating lbs at each corner and slightly taller-overall wheel/tire combo, hurt acceleration. I expected this, but was surprised that I could actually feel it.
Second, the square setup also moved the car's balance to oversteer in a big way. The old setup was 255F/275R I expected the the extra 20mm up front to increase front grip but I think the matching offsets added more still. I didn't see the need for stiffer front spring rates relative to the rear until I ran this square setup at a couple events. The throttle was almost unusable out of corners until I made drastic changes to the OTS Koni "yellows" I was running and the Hotckis sway bars. (I basically went way stiff on the front and way soft on the back to get by until the new suspension went on)
Horsepower: The Borla TD exhaust, Berk HFC's, K&N drop-in and tune from HP logic, netted me all of 12HP up top and 20HP "under the curve". The car feels as "peppy" as it did with the 17's up top, and even stronger whilst digging out of corners.
The guys at HP logic were great. I race the car regularly, so I needed a tune that I could safely beat on, over and over. I told them that dependability and smooth power-delivery were far more important to me than the numbers themselves, and they delivered exactly what I wanted.
The car pulls, strong and smooth across the tach, and remains strong all the way to the new redline.
They bumped the redline 400 RPM's which helps me avoid third on some of the faster local courses. They also increased the throttle response, which has brought my rev-matching back to almost where it was with the lightweight flywheel.
Oh, and the Borla TD/Berk HFC's combo sounds great!
Suspension: My old setup felt so good on the track, for so many years, that I forgot how much of a PITA it was to get it dialed in years ago. I basically played "Marco Polo" for a year or two until this "blind squirrel" finally found a nut...and then only made minor adjustments for different tires over the years. Now the process has started all over.
First, some pics of some things I learned for the rear setup. (the front was pretty straight forward)
I saw some pics from someone else's setup that seemed to have the bottom perch adapter placed in the spring bucket metal-on-metal. It may have just been the pic, but I *think* this is the correct way to install the bottom perch, using the stock rubber "gasket":
I placed that^ metal/rubber sandwich into the bucket...
The three tabs that held the top (stock) rubber "guide" in place, can be used to hold the new threaded perch in place. This makes putting in the helper spring,sleeve, and main spring easier:
My choice of putting the helper spring on top also differes from one of the pics I saw from another build:
I was concerned that the front setup didn't have helper springs, but the front sway bar does a good job of keeping the spring in contact with both the top and bottom of the assembly when one side is lifted off the ground.
Basically, a helper spring is not needed on the front unless you either don't run a sway bar up front, or go all "Dukes of Hazzard" with your Z and get airborne with both front wheels at the same time.
Corner balancing: I didn't even understand what corner balancing was until I borrowed my club's scales and and spent a weekend in my garage with google and youtube:
My results, with me in the car and 1/2 tank of gas.
Corner balancing is apparently more like "leveling" a dinner table than "balancing" weight distribution. The weight at each corner of a car, on a level surface, is more of an indicator of the suspension's length/height at each corner than an "end" unto itself.
A car with poor corner balancing is similar to 4-legged dinner table that can rock back and forth when two opposing corners' legs are longer than one or both of the other two. But, whereas a table will rock back and forth over the long-legged axis, and alternately lift the two shorter leggs off the ground, making the issue obvious, the springs on a car will keep all four tires in contact with the ground and mask the issue.
The 4 individual scales, and the resulting weights, show how much force each tire is putting on the ground while at rest.
Less force (weight) on a cross-weight (DF+PR vs PF+DR) means one or both of the "table legs" are too short relative to the heavier cross weight. Or, conversely, the heavier cross-weight has a "leg" or "legs" that are to long.
This exercise also showed me how evil sway bar pre-load is. The sway bar tries to make both sides the same and resists any difference between the two sides. So as soon as you sit in the car, the sway bar starts transferring force from one side to the next. After balancing the car without the sway bar connected and then connecting it, I found the sway bar added ~60-70lbs (can't remember exactly) to a single corner once I sat in the car....Now I have adjustable endlinks, which I installed while my weight was in the driver's seat.
Alignment: This is a compromise. I am trying to go as aggressive as possible while still being able to make road trips on the very tires I compete with. (I don't trailer my car, or my tires) The specs I am running now (listed above) are my starting point.
I'll use the next post to share results of the setup over the 2 outings I have made on the new setup.
Last edited by Z1NONLY; 04-08-2015 at 05:16 PM.
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lufkom (08-09-2016)
12-21-2014, 08:24 AM
#2
Florida State Championships: The first event I attended on the "complete" setup, (as apposed to "dialed-in" setup). I ran in the wet on both days. (test and tune and competition day)
Settings: Front shocks in the middle of their adjustment range, rear shocks, one "swipe" softer than the middle of the adjustment range. Front sway bar, full soft.
Cleaned up and ready to go:
On test and tune day, the car felt surprisingly good, for a stiff suspension, on the wet pavement. Grip was low of course, but break-away was smooth and predictable. Transitions were very well-behaved.
More importantly, I was comparing well to one of my benchmarks. David Marcus (in an STX car) and I had only one car between us in our rotation, so we were getting pretty much the same course. I was consistently in the ballpark with his times.
On race day, all of my benchmarks were in heat 3 on dry pavement, and I was in heat 1 with a wet track again.
(It dried up during heat 2) Still, David Marcus, who won STX with high-caliber talent competing, (Seltzer, Merideth, Disimo, Ruggles etc) was ~1.5 seconds faster on dry pavement than I was on wet pavement. I wouldn't normally be happy with such a big gap, but dry vs wet...I'll take it.
I won STU against a handful of AWD cars, but I was stuck in second place until putting it together on my third run.
After a weekend of racing in the rain:
GCAC December event:*Dry pavement* I put down my new PB on the test and tune track by a few tenths and was able to back up the runs without any drama. (My previous PB seemed like a fluke run since I was unable to get within 3 tenths of it until beating it with the new setup)
My only benchmark that day was my brother, who got within a couple tenths of my time while driving my car. This was all nice, but I was further off my "benchmark drivers" previous best times on that course than I expected to be after state. I think my Rivals were starting to heat-cycle before state and the wet pavement masked the problem.
Race day was ugly, I was way off the pace by >1.5 seconds with both my benchmarks and me getting dry pavement.
I was so far off, after taking all my runs, that I sought out one of the fast guys to take his last two runs in my car. He was slower than me by a wide margin after his first run and complained that the suspension was way too stiff for the available grip of the tires. He had me take 3 PSI out of each tire and soften both the front and rear shocks all they way.
He was then only a little over half a second off my time, and the data-logger showed him actually faster around most of the course than my best run on the tighter settings. (He just made a couple costly mistakes)
I flipped the tires on the wheels after the event but they are pretty much done at this point. I want fresh-ish tires for Dixie so I'm going to finish off the Rivals at the next event and put fresh RS-3's on for February's event. I *hope* I can get everything relatively "dialed-in" by Dixie.
A note on the re-valved Koni "yellows":
Only the rebound was revalved, the compression stayed stock. The rebound adjustment has a ridiculously wide range of adjustment now. The ***** and swipes still have the same range of motion, but if the OTS rebound allowed, say a 30% adjustment, the re-valved rebound has something crazy like 200% adjustment.
Full soft feels almost stock over bumps, the middle feels pretty harsh, and I have yet to try full stiff.
I will continue to work on this system and get top talent to drive my car whenever possible. (and hopefully give advice on setup too) I want to nail down how effective this setup actually is/can be.
Settings: Front shocks in the middle of their adjustment range, rear shocks, one "swipe" softer than the middle of the adjustment range. Front sway bar, full soft.
Cleaned up and ready to go:
On test and tune day, the car felt surprisingly good, for a stiff suspension, on the wet pavement. Grip was low of course, but break-away was smooth and predictable. Transitions were very well-behaved.
More importantly, I was comparing well to one of my benchmarks. David Marcus (in an STX car) and I had only one car between us in our rotation, so we were getting pretty much the same course. I was consistently in the ballpark with his times.
On race day, all of my benchmarks were in heat 3 on dry pavement, and I was in heat 1 with a wet track again.
(It dried up during heat 2) Still, David Marcus, who won STX with high-caliber talent competing, (Seltzer, Merideth, Disimo, Ruggles etc) was ~1.5 seconds faster on dry pavement than I was on wet pavement. I wouldn't normally be happy with such a big gap, but dry vs wet...I'll take it.I won STU against a handful of AWD cars, but I was stuck in second place until putting it together on my third run.
After a weekend of racing in the rain:
GCAC December event:*Dry pavement* I put down my new PB on the test and tune track by a few tenths and was able to back up the runs without any drama. (My previous PB seemed like a fluke run since I was unable to get within 3 tenths of it until beating it with the new setup)
My only benchmark that day was my brother, who got within a couple tenths of my time while driving my car. This was all nice, but I was further off my "benchmark drivers" previous best times on that course than I expected to be after state. I think my Rivals were starting to heat-cycle before state and the wet pavement masked the problem.
Race day was ugly, I was way off the pace by >1.5 seconds with both my benchmarks and me getting dry pavement.
I was so far off, after taking all my runs, that I sought out one of the fast guys to take his last two runs in my car. He was slower than me by a wide margin after his first run and complained that the suspension was way too stiff for the available grip of the tires. He had me take 3 PSI out of each tire and soften both the front and rear shocks all they way.
He was then only a little over half a second off my time, and the data-logger showed him actually faster around most of the course than my best run on the tighter settings. (He just made a couple costly mistakes)
I flipped the tires on the wheels after the event but they are pretty much done at this point. I want fresh-ish tires for Dixie so I'm going to finish off the Rivals at the next event and put fresh RS-3's on for February's event. I *hope* I can get everything relatively "dialed-in" by Dixie.
A note on the re-valved Koni "yellows":
Only the rebound was revalved, the compression stayed stock. The rebound adjustment has a ridiculously wide range of adjustment now. The ***** and swipes still have the same range of motion, but if the OTS rebound allowed, say a 30% adjustment, the re-valved rebound has something crazy like 200% adjustment.
Full soft feels almost stock over bumps, the middle feels pretty harsh, and I have yet to try full stiff.
I will continue to work on this system and get top talent to drive my car whenever possible. (and hopefully give advice on setup too) I want to nail down how effective this setup actually is/can be.
Last edited by Z1NONLY; 12-25-2014 at 06:18 AM.
12-21-2014, 04:05 PM
#7
Damn. I could shave another ~15lbs by removing my aftermarket amp, but I would go nuts with a bone stock system on road trips.
I already removed my 45lb JL sub/box and went to a removable 6.5 inch sub.
Not really sure where else to get real weight savings.
Oh, and I had a half tank of gas....however much that weighs.
I already removed my 45lb JL sub/box and went to a removable 6.5 inch sub.
Not really sure where else to get real weight savings.
Oh, and I had a half tank of gas....however much that weighs.
Last edited by Z1NONLY; 12-21-2014 at 04:07 PM.
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12-25-2014, 06:09 AM
#12
Last edited by Z1NONLY; 12-25-2014 at 07:58 AM.
12-25-2014, 06:16 AM
#13
Come to think of it, I didn't even get an official parts list or anything. I'm not complaining because the hardware he sent back was complete. (Minus coil-over wrenches) But I don't know the name brands or the part numbers of any of the red anodized parts.
If you contact pro parts and ask for Jeff, he sounded like he is very familiar with this Z conversion kit. He probably knows the part numbers from memory.
01-02-2015, 03:21 PM
#19
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Good thread, keep it going.
I recently picked up an 03 with 15,000 miles and starting a build. Have the 10.5" rfp1's with rs3's siting in the garage (thanks Scott!). Also have the kinetic upper arms and rear camber arms sitting on my garage bench. Waiting to do my taxes before I plunge on the shocks. Need sway bar still for the front. Probably will not do to much more this year. Brakes, diff, intake/exhaust will probably be next year. My goal is to have a locally competitive car that could take FTD and beat Scott S, lol! And is more fun than my NB STR Miata was. Not sure about nationally competitive, will watch the C5 developments.
Should get the fender roll and timing advance this weekend.
I recently picked up an 03 with 15,000 miles and starting a build. Have the 10.5" rfp1's with rs3's siting in the garage (thanks Scott!). Also have the kinetic upper arms and rear camber arms sitting on my garage bench. Waiting to do my taxes before I plunge on the shocks. Need sway bar still for the front. Probably will not do to much more this year. Brakes, diff, intake/exhaust will probably be next year. My goal is to have a locally competitive car that could take FTD and beat Scott S, lol! And is more fun than my NB STR Miata was. Not sure about nationally competitive, will watch the C5 developments.
Should get the fender roll and timing advance this weekend.