Shock installation
Finally got the rear shocks all buttoned up-
Not a ton to mention that isn’t obvious from the pictures. Shocks are mounted inverted, which helps reduce unsprung weight a tiny bit. In this case it also means the remote reservoir hose doesn’t move as the suspension moves through its travel, which should be a good thing for the life of those components.
Since the rear swaybar is a no-go at this ride height, was able to re-use the swaybar mount holes for little canister mount brackets. Really happy the length of hose to the remote cansiters, and the way it bends around the frame rails without touching anything – worked out perfectly.
The rear shocks have four adjustments, in two locations. Rebound and “shaft” (better come up with a better name for that, too likely to be the target of jokes) adjustments are in the window where the lower shock eyelet mounts to the leaf spring plate (as an aside – note this shock mount plate puts the shock in double-shear – most run the crummy single-shear plates) and adjustments for low and high speed compression are those two knobs at the top of the canister – not the easiest to get to but reachable if you lie beside the car.
Up front, the shocks are so buried, there isn’t much to see. These things were a packaging nightmare!
Here too they are inverted, which provides the same benefits as the rear. Though in this case it’s more a matter of packaging necessity, than preference.
Since one of the advantages of these sorts of shocks is the bling factor, and the fronts are basically totally hidden, here’s a couple pics before they went on the car:
Complete shock – 8760 body with 8300 canister
T-bar
Staubli quick disconnect
And on the car, buried as can be-
Thank goodness I chose the smaller 45mm bodied 8760s – they just barely clear the rear spring adjustment cup at full droop. To provide room for the remote reservoir nonsense, had to run a 1″ horseshoe-shaped spring spacer up top, which for now meant completely removing the ride height adjuster at bottom. To regain that ability, will need to get shorter springs, or cut these ones down a little.
The canister is in a super-temporary spot until I figure out how to mount it in the engine compartment.
Front adjustment of compression will require opening the hood to turn the knob on the canister. Rebound will require tools, as the “window” with the knob inside is buried in the lower control arm. I’m going to change the way it attaches from this draft (which is approximately version 4.7) to allow the adjustment to be made with only one tool, and not require raising the car or any other disassembly. I probably won’t change front rebound that often anyway, leaving it at max and hoping it’s enough. The front shocks are capable of really big forces, but those forces drop off very quickly as the adjuster is moved away from full.
Speaking of those forces, here is a dyno of the front shocks, or at least, a portion of what they can do – note the x axis ends at 2in/sec. 🙂
Bigger battery and cutoff switch installed + weight placement musings
In the process of getting the car wired I must have left things in a slightly draining state overnight, which killed the Odyssey PC680 battery originally installed:
Which is a bummer, I’d hoped that thing would last a while. I let it charge for a long time using a good charger, but it failed to come back to life, and had difficulty getting the motor to turn over back on the day I first drove it.
Not wanting to have those kind of hassles when it “matters”, at an actual event, or somewhere out on the street, elected to get a much larger battery, until something like Nationals, when the 34lb. weight savings will be most meaningful.
So in went an Odyssey PC1200, a substantially higher-capacity unit. Still the same AGM technology allowing it to be mounted in any orientation.
Not quite enough room to mount it up on the “shelf” where the PC680 went, it ended up a little further back, to the right, and lower.
Also installed a battery cut-off switch. This will ensure the battery isn’t being drained when the car is not in use.
Left the old battery hold-down in place, this way I can swap to the 4lb. battery in about 5 minutes if desired.
Where should I put my battery?
Anybody building a car for a class that allows one to move the battery, likely ends up asking themselves this question at one time or another.
In some cases, advances in modern battery technology have allowed for such compact and lightweight batteries, you almost don’t even need to worry about it. There are batteries out there literally under 2 pounds, that can start small 4-cylinder engines. If the other needs of the electrical system can tolerate a battery like this, there is little to gain from moving it from wherever it was stock, assuming it is already pretty close to the starter.
For cars with bigger engines, or cars that have more demanding electrical requirements, the battery will end up having a significant impact on the static front:rear weight distribution of the car.
Let’s take an example 3000lb. car with front weight of 1600lbs. (53.33%) and rear weight of 1400lbs. (46.66%). Say this car has a 30lb. battery right at the front axle line, and we move it to the rear axle line.
Front weight is now 1570 (52.33%), rear weight 1430 (47.66%). That’s a whopping 1% shift in static weight distribution, just by moving the battery!
The reality too, with a car like this Camaro, is the battery starts out about 18″ in front of the front axle, and ends up a bit behind the rear, having more than a 1% effect (assuming those weights are about right).
A lot of people fuss over engine setback, and go to great lengths with firewall modification, custom motor and trans mounts, driveshafts, etc., to get the motor back another 1-2″. While those aren’t necessarily bad ideas for classes that allow it, moving 600lbs. rearward 1-2″, is only about 1/6th as helpful, as moving the battery to the trunk (11 feet or more in a Camaro).
If moving it rearward is good, why do I have it where it is, just about as far forward in the trunk as possible? There is room to go rearward another 2 feet or so?
While doing so would improve the appearance of the static weight distribution numbers, the picture above tells the tale.
Weight placed beyond the axles (ahead of the front, behind the rear) has some negative effects, at least for a car that expects to turn corners.
While placing the battery further back does put more weight on the rear tires (a good thing, especially at launch time), it takes load off the front tires – without actually reducing the amount of mass the front tires have to haul around the corner. The rear axle acts like the fulcrum in a teeter-totter; the further away from the fulcrum, the more leverage the battery’s weight has in “lifting” the front axle. This is a very important thing to keep in mind – while we might feel good about the lower registered front axle weight on a set of corner balancing scales as we move the battery further and further behind the rear axle, what we’re really doing is taking away some of the load those tires deserve to get, load which would add to front grip. While it is true (harken back to the CVD series for more on this) that a tire is more efficient (more grip per unit of load) when more lightly loaded, it still produces less total grip when more lightly loaded.
This is one of two reasons why weight/mass located outside of the vehicle’s wheelbase is a bad thing. The other, is that it tends to increase the polar moment of inertia – which may be okay for a Bonneville car that needs to be arrow-stable, but autocross is at the other end of the extreme, where a car’s ability to quickly rotate is paramount.
With this in mind, there are lots of micro decisions about where to place things in a car. Obviously there are requirements that things be usable, and reliable, and serviceable, but beyond that – when you have some genuine freedom on where to place things – here’s what I use to take creativity and aesthetics out of the equation:
- It should be as low as possible. This minimizes CG height which aids in cornering and braking.
- It should be as far rearward as possible, without being behind the rear axle. This puts more weight on the drive tires (for RWD), and helps unburden the front, without introducing the teeter-totter/lever effect described above. Some already heavily rear-biased cars, like a Porsche 911, may be exceptions to this.
- It should be as close to axle center line as possible. This helps reduce polar moment further. If you imagine looking at a car from above, it would be easier to rotate a car with its mass centered at the shifter, vs. one where the mass is all in the doors.
Obviously few things are as heavy as the car’s battery, but a lot of what makes a really fast car fast, is the incremental contribution of a large number of very small things. In this case, placing every other little thing you can a bit lower and a bit further back, could end up leading to that extra thousandth or hundredth of a second that separates first from second.
In the case of this Camaro, with ultimate freedom, I’d probably run the 4lb. battery where the passenger’s feet go (allowing for super-short cables), and with the big battery, would run it where the right rear seat bottom is. But since we can’t have the battery in the “passenger compartment” in Street Touring, instead chose to mount it just about as far forward in the trunk as possible. It could have gone more rearward which would have the benefit of making it lower and improving the appearance of static weight distribution, but the negative effect on front tire loading is something I wished to minimize, particularly in light of these cars’ known penchant for push.
The other big question mark is fuel level – the difference between full and low fuel levels is probably 80lbs., and it’s all back behind the rear axle. If I can find a way to run it with a low tank, it could have benefits on handling well beyond the pure weight saving element.
Oh, since I know everyone is anxious to see the Rhoades Camaro out dodging cones, here is the young Rhoades showing dad how it’s done 🙂
Quick data from a tire test
My buddy Jeff Cawthorne ran a best-effort tire test this past weekend of two new tires in the Extreme Performance Summer category – the BFGoodich G-Force Rival against the Dunlop Direzza ZII. The test was conducted in his “Stock-prepped” (extra front camber, lightened exhaust) 2013 Scion FRS. For those that don’t know him, Jeff is a veteran racer who would likely have a few National Championship jackets hanging in his closet, if any of us could ever convince him to come to Nats…;)
Upon hearing word of the test I offered Jeff my DL1 data acquisition system, to get a peek at how these new tires are really working. My Camaro will be making its maiden voyages on previous-gen tires, the Yokohama Advan Neova AD08. Both of the tires tested are newer and quite probably better than the Yokohamas.
Below is a screen capture from the Race-Technology data analysis software, showing a comparison of the best Rival run (red) v. the best ZII run (blue).
The main graph in the center here is an X-Y graph I do sometimes when I’m not looking to do any driving analysis, but instead see if a setup change made any difference in the car’s limits. The outer edges of this graph shape is sometimes called the “envelope” though to me the shape a lot of the time looks more like an acorn. (More details on this here in CVD Part2)
This was Jeff’s first time on these tires, in a car that was new to him, and using a DL1 for the first time – all at an event that wasn’t really designed to let him execute a careful test plan in the way anyone would have wanted to. As such, he wasn’t able to get all the data he’d like, or take as many runs, under the sorts of conditions he would’ve liked.
On this day, the Rivals were a lot – 1.4 seconds on a ~65 second course – faster. So there’s not much to see in the data, the Rivals were faster everywhere, in all sectors of the course, and in all phases of the corner. The limits appear a little higher, and the data indicates to me, Jeff had an easier time keeping the Rival at or near its limit.
However – the very next day, Jeff did something of a repeat test at a regular local championship event, and was a little faster on the Dunlop. Didn’t get data from that day unfortunately, but the actual differences are likely quite a bit smaller than the first day’s results bore.
There’s another event this weekend on a grippier surface, hope to get more data from it.
Rear Shocks
This week both front and rear shocks arrived for the Camaro.
Despite my history of nothing but satisfaction and success with the 28-series Koni shocks, for this car, I have chosen to give the Penske platform a try, for a few reasons-
- They offer some more modern valving options not available in the typical 2812Mk2 bodies I’ve run. Will explain that below.
- I do have some experience on Penske triple adjustable shocks – the Lexus IS300 owned by Jason Uyeda I drove a bit in 2005 had them, and they worked great. Also, Doug Hayashi’s Honda S2000 we ran in the 2003 Open Track Challenge had a set built and valved by Erik Messley, and that car was sweet too.
- The people I use to build my shocks, ProPartsUSA, has experience with Penske, and would be able to help me out. I wouldn’t have tried this were it not the case.
- I need *some* excuse to run some kind of Penske sticker on the car. The classic Trans-Am cars always had “Penske-Hilton Racing” or “Penske-Godsall Racing” on the front fenders – if I put “Penske Racing Shocks” in the same spot, should give it the look without being totally illegitimate. Of course advertising for people when you don’t have to (not like anybody is cutting me deals) is kinda silly IMO so who knows what will go there.
What actually got me started down this path was ProParts mentioning they had a set of very high-end 8765‘s sitting on a shelf that they’d used for a test but never on a car, that they could pass on for a very good price. Their dimensions put them in range for the rears, so they proceeded to build them.
Not having built/tuned a live axle car before, many aspects of what comprises an “ideal” rear shock valving are at this time a mystery to me. Some things are known – spring rate, ride frequency, and motion ratio – which, unlike so many aspects of this chassis, actually isn’t a problem. It is basically 1:1 in bump, and close to it in roll. I also know my own preferences – which in general, are to run the rear shocks fairly soft. Too much rear compression, and you risk “blowing the tires away” with a rapid throttle press. Too much rear rebound ups the chances of losing the rear end in a transition type maneuver.
Of course, too little, the car feels dead, and difficult to make “dance” through tight spaces, of which we have plenty in autocross. In my experience if you have a fairly well balanced RWD chassis (either naturally like a Viper or with freedom over bars and springs like an STS 240sx), softer rear shocks are something that makes a car easier to drive, helping you minimize the frequency and magnitude of mistakes, even if maybe it sacrifices ultimate potential a little.
All that said, here’s a few dynos of the rear shocks-
On the rebound side, we have modest forces, and a mildly regressive curve. This shock will be operating around 3in/sec for typical (non-bump) autocross maneuvers. I would have like a slightly wider range of adjustment with another 20% available both below and above this range, but all told it’s probably about where it needs to be anyway.
Things start to get really interesting on the bump side, and this is where the 8765 separates itself from the more-common 8760. Note in the legend at the upper right, there are four dimensions given for each dyno:
- HSB
- LSB
- Rb
- Shaft
Aaaack! Four adjustments?!?!?! In the picture above notice there are two wheels in the eyelet at the end of the shaft, and there are two knobs at the end of the canister. At the other end of the canister is the Schrader valve for gas pressure, which one could even consider a fifth adjustment – oiy.
For those that haven’t seen it, here is what I consider an excellent, clear and concise guide to shock tuning by Neil “Fireball” Roberts:
http://www.ozebiz.com.au/racetech/theory/shocktune1.html
There are some people who will feel that aspects of this are incorrect, but for me, it has worked, and it fits in well with what my gut/intuition tells me is happening at each tire in different phases of the corner.
Now, when Neil talks about bump and rebound, he is talking about their low-speed elements. High-speed shock tuning doesn’t usually come into play for tuning handling – it does change how the car works over bumps though.
On the compression side you can see these shocks have an unusual shape – the compression force actually drops at a certain point. This is known as “regressive” valving and was pioneered in F1, to help keep their chassis from getting upset when the cars hit curbs. This allowed them to continue to have big low-speed compression forces to manage the aerodynamics better, but then have a chassis that became super soft and compliant (relatively speaking) when presented with a big obstacle.
We don’t have curbs in autocross but our sites do occasionally have bumps, and in theory this approach should help keep that big heavy rear axle more compliant over those bumps, while still providing a good measure of traditional low-speed control.
The additional adjustment (“Shaft” on the shock dyno) interacts with the High-Speed-Bump settting, to determine at what shock velocity things “blow off” into regressive mode.
Part of what made me interested in this capability in conjunction with a live rear axle car, is the shock’s contribution to axle torque management. The car depends on its leaf springs to control axle wind-up under acceleration and braking. In ’67 the rear shocks were laid out in a “non-staggered” arrangement, with both lower mounts ahead of the rear axle. These cars were notorious for bad axle tramp, and as a partial remedy, in ’68 the shocks were “staggered”, with one lower mount of the shocks ahead of the axle, with the other behind. So, in a ’67, both rear shocks are in bump under acceleration, and rebound under braking.
When a car is accelerating, the front of the diff wants to rotate upwards, which wants to twist the springs in side view. The much-stiffer-than-stock (approx. 3x) springs I’m starting with will help this somewhat, but the big (1.5″) spacer block hurts, as do the high-grip tires and increased horsepower.
Axle tramp or hop is a violent condition when a wheel/tire begin to bounce, suddenly becoming loaded then unloaded. Not only does it kill acceleration off the starting line or out of a corner, it can also destroy the beefiest of parts. For an example of how it can look, check out the 1:13 mark of this Mustang driver being a hooligan on the streets of San Francisco – granted that was in reverse, but the principles are the same.
Axle tramp can be cured with 75lb. torque arm setups, but I’m hoping that with this range of valving characteristics, it can be sufficiently mitigated with the right shock settings. Sometimes, stiffer valving isn’t the solution.
Sorry not much picture content at this time – have the rear shocks mounted on the car, but the remote reservoir canisters are dangling loose. Darn those canisters!!!
Dash Replacement
The Race-Technology DASH2 was a purchase I’d made early on in this build (back in 2010) when I saw a basically new one come up for sale for a good used price. It sat in a box for about two years, until I was ready to get it mounted in the car and wired in (covered here, in the second half).
The Race-Technology DL1 data acquisition system has served me well since 2006 – never a fault or hiccup in what has to be 100+ events, many times crammed into the center console of baking hot cars. Race Technology’s analysis software has always been good, and they’ve made continuous improvement over the years, both for general purpose and closed-circuit autocross-type events. The DL1 offers amazing bang for the buck, and at no point had I come close to maxing out its capabilities to datalog many analog signals simultaneously.
Unfortunately I found myself having lots of problems with the DASH2 paired with the DL1. It required a strange sequence of button pushes to start displaying data, and sometimes it would just freeze while in action. Any time the car stalled or had to be restarted, you had to repeat the sequence – which served to compound the already aggravating scene of trying to start a finicky high-compression carbureted musclecar with a dying battery. I spent a lot of time (time that could have been spent advancing other elements of the car) playing with different data speed settings for the serial interface, turning off unused channels, all to no avail.
There have been some data acquisition advancements since 2006. One is an increase in available GPS frequency – the DL1 MK2 I have is 5hz, and there are now 10 or 20hz options. The other thing is the availability of combined dash/datalogger units in a single box. In general I don’t like the proliferation of “magic boxes” and other add-ons inside an interior, preferring things simple and “clean”.
Despite 7 years of nothing but positive experiences (until just recently), outstanding software that might be the most advanced and in-depth *for autocross use*, and excellent responsiveness and attempts to make things right through good service, I decided to punt on the R-T gear. So what now?
Definitely leaning toward an integrated dash/logger. I enjoy nerding out on data, diving into deep analysis on the nights between and days after a race – so I need very good software. It’s got to be of a quality commensurate with the rest of the build, and available in time to have it here and on the car in advance of the SD Tour later this month.
With those parameters in mind, there are really only two other choices – AiM and Motec.
AiM is coming out with their MXL2 very soon now, which appears to offer the combined data/dash capability present in the DL1+DASH2 Race-Technology combination, at a reasonable and competitive price…but it’s not out yet, and retailers weren’t sure exactly when it would be. They have the Pista dash which does these things, but it is getting very long in the tooth now, and if I went that way, I’d be installing something that is basically already outdated.
That left Motec. The problem with them isn’t quality or capability or even availability – it’s price. Their ADL3 (Advanced Data Logger) system used in most professional race cars is amazingly robust and powerful – with a price tag to match. The ADL3’s cost of entry makes sense when you’ve got big-name sponsors and are vying not just for first, but also for TV time during your race. Besides being way too much $$$, the ADL3 is also way more than the Camaro needs. They have a lower-priced SDL3 (Sport Data Logger) which cuts out a lot of the super-high-end features of the ADL3, and about halves the price. That puts it much closer, but the thing about Motec is they get you with add-ons – the GPS is $$, additional I/O capability is $$, and even turning on the built-in data logging capability is $$. So, even if the SDL3 started out within the realm of reason, by the time the needed add-ons are tallied, it is back into unreasonable-land.
Fortunately there is one step further down their food chain, the CDL3 (Club Data Logger). This is a relatively recent unit, introduced at the end of 2011. Designed for the weekend warrior club racer type, it includes even few features than the SDL3 – but even then, it still does more than I need.
Well, there she is. Bracketry was a bit rushed, as I’m getting the looming sense time is running out; the impetus is on getting it in (done) and wired (not yet done). Excited to get some data collected and begin to use their software.
Couple videos of first drive
The family was kind enough to come outside and do some camera work as I maneuvered the Camaro out onto the street:
http://www.youtube.com/watch?v=kmWIYpJrp8A
and around the block:
http://www.youtube.com/watch?v=ET-FRcrcH-w
for the first time.
Fortunately the car made it off the crazy curb we have without scraping anything…not sure the story would have been the same with the subframe connectors still in place.
In the first video it is amusing to see how freely the rear axle articulates as the car descends the curb/gutter. That’s what having zero rebound will do for you! 🙂
Embarrassingly, I did stall the car on the driveway (mostly due to a small wheel interference issue I’ll soon fix) – and the lesson there, was it needs a new battery. I’d let the PC680 in it now run down a couple times, and while it will rise to and hold a normal voltage, it doesn’t deliver diddly-squat when it comes time to turn over the motor. Even with a plug-in battery tender/jump-starter at its max 80A setting, the motor wouldn’t turn over after the stall. I thought this was some kind of dreaded starter heat-soak issue, but as soon as I supplied a battery-based jumpstarter multi kit (which is also an air compressor, light, and 12V DC/110V AC power source) it turned right over and fired.
Given how much a pain getting it going in that situation was, I’ve decided to go to a much larger (and unfortunately, heavier) battery for the time being – an Odyssey PC1200. At 38 lbs. it’s about 2.5x the weight of the PC680, but delivers over 3x the reserve and more than 2x the cold-cranking-amps needed to get this high compression motor turning. Will have to save the 4lb. lithium-ion PC680 equivalent for Nationals.
Oh! I have slipped the surly bonds of … the garage
This pic is funny to me, because of how much I like seeing the reverse lights. How they worked was actually a mystery until the last couple weeks, when suddenly a curious hole in the filewall, a lonely connector under the dash, and a few parts I hadn’t yet ordered, all came together. It’s a good feeling to be closing out all the remaining mysteries I had for how one of these things goes together, and given the amount of head-scratching that went into it, I’ll never take reverse lights for granted again.
Once out on the driveway took a few shots…leaving a little of the blue tape on for a while since the door glass isn’t done yet, it detracts somewhat. But I think finally, the ride heights are at a pretty good place, a decent starting point anyway.
Had some help of course!
Did get a couple little videos, will get them posted soon.
Watt a pain in the…eye?
Well, that was an awful weekend last weekend.
Thought I’d gotten through all the really gnarly work, but prep for the Watts turned out to be one of the toughest weekends yet, for a few reasons.
One, it was unusually cold in San Diego – not that it ever gets really that cold here, but there was a frost advisory with overnight lows in the 30’s. Enough to make lying on the garage floor feel a bit like lying on a hockey rink…
Two, it was a bit challenging psychologically. With composite leaf springs in the rear, the car has to have some kind of dedicated lateral axle locating device. I set out to cut away a perfectly good one, that somebody had worked really hard on, to do something else that might be only a little bit better. And if I ran into some kind of bad gotcha, that could delay things significantly.
But lastly and most of all – it was the crap! The crap that flew everywhere as I cut away all the metal for the panhard – off the axle, off the chassis. Went through about 15 cutoff wheels on my 4.5″ angle grinder.
It seemed like no matter how I positioned myself under the car, how I set the tool’s guard, and what direction the shower of sparks was flying, it all landed on me. In my face, in my hair, and on several occasions, the searing hot crap seemed to find its way behind my tightly-strapped unvented goggles, right into my eyeballs. On several occasions I had to stop and dig out what landed there. Next time I’ll have better face/eye protection!
John had done a very nice and thorough job ensuring the panhard had a solid base to work from….which means it took a ton of effort to get enough of it out of away, for the Watts to go in cleanly. Once the panhard was out of the way, the Watts was pretty straightforward.
The unit bolts in, consuming the space behind the rear axle, where the factory originally packaged the muffler. (Overall exhaust packaging beyond where it is now, is going to be difficult. Will need to do something more, under-car dumps are kinda ghetto, and the car is a bit too loud still.)
The propeller for the Watts has 12 positions of possible adjustment, comprising roughly a 6″ range of rear roll center heights. Fays2 recommends starting at 4 up from the bottom for “most people”; I started 8 up from the bottom, seeing as my car is 1-2″ lower in the rear than most people run.
They recommend installing the center pivot bolt from the rear of the unit – problem with that, is you can’t fit it in (except maybe on the lowest adjustment hole) with the fuel tank in place. Even if you put it in the car with the bolt already pushed through, you wouldn’t be able to adjust the roll center height later without either pulling the Watts unit, or the fuel tank.
It’s funny too – in the early part of the instructions there is no mention of fuel tank removal, just wheels and normal stuff. But then later around step 8 there’s a “now you can reinstall the fuel tank” line…seems like some selective editing.
Anyway it worked out ok for me – the propeller comes with a number of spacers allowing you to move it forward if needed, and defaults to one. I ended up taking out that one spacer, which puts the center pivot bolt through the Watts frame on the shank of the bolt (instead of the threaded portion), so it should be just as good. And this way I can adjust if needed!
On the driver side, the propeller runs to a new plate sandwiched below the spring and the factory lower spring plate. On the passenger side, it runs to a new axle-clamping tube. With these things, it’s important to get the angles and lengths identical from side to side; otherwise you end up introducing lateral movement, or other weirdness, into the suspension motion. I ended up with link length of 16.5″ and an angle of 9.6 degrees from horizontal, running “downhill” away from the propeller.
Bounced the suspension a whole bunch (easy to do, still no shocks) and there is no perceptible lateral motion or bind in the system. Will be interesting to see how it holds up to the world of autocross!
First race entry
The SCCA San Diego National Tour is coming up March 30-31 – this is my home event on the SCCA National Tour series, and will probably be the car’s first live autocross. That only leaves 7 and a half weeks to get this thing together!
To put extra pressure on its completion, went ahead and registered now – so here is the car’s first appearance on an autocross entry list–
Entries are still a little light as of today – most people register in the few weeks just before the event. There are 30 registered at the moment, should be 300+ by the time registration is complete. The 2 entrants in the STX (“Street Touring Extreme”) class should be 12 or so come race day.
Still a lot to do, though the to-do list is slowly shrinking.
Watts up with the Camaro?
A long time ago there were some posts on the panhard rod I had built for the Camaro:
http://www.rhoadescamaro.com/build/?p=793
http://www.rhoadescamaro.com/build/?p=866
The reality is, if that had been the last project before the car’s completion, I probably would have gone with it and been perfectly happy.
But lots of time has passed, and I’ve had more time to think about it, and some of the imperfections of the idea chipped away at me.
One thing bugging me, which isn’t the panhard’s fault, is it was tied to this axle with its welded-on components. It hadn’t occurred to me back then, but I’ve since realized, it might be nice to be able to swap out complete rear ends to change final drive ratio. This could be for damage repair, or between venues like autocross and track. By keeping the lateral locator bolt-on, it enables easier swapping between rear ends.
Another, totally my fault, is I probably had John build the panhard rod backwards. The way it was built, mounting to the axle on the left and the chassis on the right, improves grip in left-hand turns, but worsens it in right-hand turns. Totally the right thing to do for circle track, but not necessarily autocross – autocross tends to be fairly neutral in left/right turn distribution, but there are other things about a live-axle car that make it favor left-hand turns (to the detriment of right-handers) and this mounting approach amplifies this disparity. Should have mounted it to chassis on left, axle on right.
The last thing, is I’d always had in the back of my mind, might like to change to a Watts later at some point. The car will be headed into the exhaust shop soon, and I’ve decided it’s better to have the rear in a more final state, for that part of the process. Don’t know if I’ll be able to get the exhaust to exit the rear of the car, but if it can, want to have it do so now, with what is more likely the final rear lateral location solution.
So I bought a Watts. Fortunately this was a pretty easy choice in the aftermarket, there appears to only be one standalone pure bolt-in Watts kit, made by Fays2. Very reasonably priced.
It’s pretty straightforward – the red (only color offered) crossmember piece bolts to the rear frame rails. A central propeller rides in one of the overlapping holes in the center of the unit, allowing ride height adjustability over a ~6″ range, in 1/2″ increments.
Total weight is a little higher than the panhard setup, though fortunately the weight isn’t in a terrible spot (low and rearward) and the crossmember portion should theoretically add some stiffness to the chassis. And of course, it should bring the innate benefits of a Watts over the panhard – elimination of axle lateral movement through suspension travel, and more consistent handling behavior in left and right turns.
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Since switching from the panhard is going to be a bunch of work – requiring removal of the rear end, cutting away all the nicely welded-on work John did (I’m sure he’ll be laughing at me when he reads this!), and installing the Watts, might as well make a couple other little changes while it’s apart for the umpteenth time.
One plan is to modify the front spring eye bushings – they are mostly as they arrived from Flex-a-Form, and in their provided design, they offer quite a bit of lateral stiffness to the spring, not allowing the end to move at all. This comes at some cost, they also bind the end of the spring a little bit as it looks to rotate in normal suspension travel. With a good lateral locator like a panhard or watts, you no longer need the leaf springs themselves to provide the lateral location. Once could argue you could even go to spherical bearings in the spring eyes, but I won’t be going that far. Will just be trimming the bushings, so they still provide good longitudinal location of the spring eye, so they still transfer drive, brake, and wind-up forces quickly and securely to the chassis, but remove the lateral pieces. This should reduce/eliminate bind in the front, and maybe save an ounce or so!
The other plan is to “adjust” the rear ride height lower. Since the rules disallow changing to coilovers, have to manage ride height through leaf spring spacer blocks.
The car has 1″ units on it now – on the left are 1.5″, 2″ on the right. Will be going to the 1.5″ to see how that looks/feels, that way can go up or down a little as needed.
With larger spacers, the axle gets “further away” from the spring, which makes it more difficult for the spring to control axle wrap-up forces under acceleration and braking. I’m hoping the relatively modest grip from street tires, modest rear tire size, and a relatively stiff/thick rear leaf spring, will keep those motions under control.