J-Rho's '67 Camaro Z28 STX build Jason Rhoades builds a 1967 Camaro Z28 clone for SCCA STX autocross

29Nov/100

Ahh the 302

For us car people there's a lot of different ways to find automotive pleasure.  For some it's all about the driving experience on a nice day.  For serious competitors, it's the thrill of  a close and tight race.  Plenty of folks enjoy "car porn", a collection of shiny TIG-welded go-fast parts laid before a car like in a preview for the new "Fast and the Furious" movie, and the romance of bolting those parts on the car.

For me, a lot of the fun is the brainstorming and bench-racing that goes on around the question of "How would car X do in class Y?".  In this case, that question, is "How would a '67 Z28 clone do in STX?".

There's a lot you can find out on the Internet, and with that information, you can start to form a halfway decent picture of how the car is going to perform.  Here are some things you can find out pretty easily, to help in the evaluation process:

Dimensions - Length, width, wheelbase, height, ground clearance

Engine - Displacement, peak power, peak torque, redline

Gearing - 1st, 2nd, 3rd, final drive ratio(s) available

Wheel/tires - sizes, width, diameter

Weight - total and front/rear distribution

Suspension - type at front and rear, adjustability

These are the things usually comprising the "paper" looked at when people say "Car Z looks good on paper ".  However, there's a lot more to find out, and this information can take some digging to find:

Weight of the car in a trim like yours - both the total weight, and the contribution of your weight-reducing efforts to both front and rear axle weights.  For Street Touring for instance, your front seats and mounts should weigh 25 pounds each - how much weight will be saved there?  How much in headers, exhaust, lightweight battery?  Are there any options you can remove?   How low can the car be run on fuel?  You have to look at published weights, or weights from people that have weighed their cars, then offset from those figures to account for the modifications you'd make.

How much wheel/tire can the car fit within your rules?  How much of it can go inboard from stock?

Dyno pull of the engine with modifications made for your class.  This may just be a cat-back exhaust, or that plus a CAI, headers, and a tune, or maybe even more extensive mods.  You also have to take into account the different types of dyno (Mustang, Dynojet, Dynapack, direct engine dyno) and build in some correction factors amongst the dyno types and operators.  Some massaging to do here, but a dyno is MUCH more valuable to evaluating autocross acceleration, than peak numbers.

In a future post I'll maybe go into some detail into the thinking used to take all that information and try to apply it to autocross, to see what cars will be faster than others, where on course.  But for now, that last bullet - engine dyno - is something I was missing somewhat in the pre-purchase planning stages of the build.  I figured an 11:1 compression 5 litre V8 should be able to make more power than a 2.8 litre BMW or normally-aspirated RX8 rotary, but how much more, and where in the powerband?  There's all kinds of legend out there on the 302's real power output, but not a lot of good hard data.  You end up reading through a lot of threads like this:

http://www.camaros.net/forums/showthread.php?t=13864

And not really figuring much out.  Like stock Z28 quarter mile times, you get numbers all over the place, but most are either wrong or completely unsubstantiated.  I did find this dyno:

I happen to know the DTS4000 is an engine dyno, so this was done out of the car, likely without accessories and definitely without any drivetrain loss.  That's about 345hp - certainly more than the factory's 290hp rating, substantiating many's claims of the factory having underrated the engine.  However we still don't know the details of the build - whether the motor was fresh or high mileage, if it had headers or stock manifolds, whether it was tuned at all, etc.  Assuming the reading is correct the air/fuel ratio seems on the lean side, over 14:1, not quite ideal for power.

So for me, the engine's power was a really big question mark when it fired up for the first time this past Friday, 11/26.

J-Rho's 302 is born, first startup

The smells coming off this thing were fantastic, it brought me back to the days as a young teen watching the cars go down the 1/4 mile at the now-defunct Carlsbad Raceway.  I attribute the smell largely to the fuel used - we didn't have any of the Sunoco GT100 fuel I plan to run on hand, so we made a mix of 91 octane pump gas and 110 octane leaded fuel.  No fancy widgets here to foul up from the lead, just my brain to intoxicate with carcinogens, yummy!  🙂

There's a lot of myth and legend about this motor out there, perhaps more than about any other small-block Chevy.  The components used to make the engine changed from 1967 to '68, and again in '69.  They made way more '69 302's than the other years, but in some ways, the '67 engine is easier to reproduce.  This is because there really isn't anything special about the 302 motor in '67, it was all parts-bin stuff - the same 4" bore, small-journal block used by the 327 and 350; the forged crank from a 283; "fuelie" heads with 2.02/1.60 valves from the Corvette, along with its "30-30" cam.  The carb is the same used on the SS396.  There really wasn't anything unique or special in the '67 Z28 engine, which made piecing together a reproduction, possible.  It took a few months, but my chosen engine builder (some may recognize the engine dyno room from these videos) has excellent connections in the vintage and A-Sedan racing circles, having built many smallblock Chevys under varying, but always strict, rulesets.

Here's a video of a full pull, the only one where we went over 7 grand:

302_dynopull

Those awful red boxes are covering the dyno operator's readout showing instantaneous torque and horsepower figures, it also showed oil and water temps.  Hopefully Randy Chase will forgive me, I can't imagine he ever envisioned his Dashware software being used in this manner, especially in so crude a fashion.

In case you're wondering, I won't be publishing the numbers it made.  They'll go to the car's next owner, whenever that is, but won't otherwise be released until then.  Same goes for some final details of the suspension (spring rates, alignment, shock settings) once I have it sorted.  It's not like I expect a dozen other Z28 clones to get built next week, where I'd be giving up some kind of competitive advantage.  Perhaps to some extent, a goal in providing all the information in this blog isn't to provide all the answers I find on a silver e-platter; rather, it is to help make some of my fellow racers more informed in the critical thinking of competition car building/tuning, and empower them to figure more things out on their own.  Perhaps by doing so, some will be inspired to try new things or come up with some new ideas of their own, from which I can learn something in return.  By making my competition better, it forces me to get better, which ups the overall ability levels of everyone involved.  IMO there's not enough innovation and outside-the-box thinking in autocross, which I hope to try to improve.  And you don't have to have an oddball car, or spend a ton of $ to innovate - I see innovations pretty much every year in the ST Civics, even though their rules have been essentially stagnant for over five years.  It just takes effort.

So I don't come across as a total tease, I will share this - I went in with a pretty well formed set of expectations of what the motor would do based on all the research I'd done.  It didn't quite meet my expectations at the top end - I'd read enough stories of people revving these motors to 7500rpm or higher, as delivered from the factory, to believe this sort of thing would be possible.    After the dyno session, I plan to set the rev limiter at 7000rpm, well below the 7500+ I thought it would be good for.  Anybody revving one of these things much past 7k rpm successfully, is either floating the valves something huge, or isn't doing it with stock/ST-legal valvesprings.

At the same time, I was pleased by what it made in the midrange.  We dyno'd with 1 5/8" primary 4-1 headers, with a Y pipe into a single big 3.5" muffler.  I may retain a similar exhaust config on the car to reduce weight, or go with a dual 2.5" exhaust.  Bigger primaries or a larger OD header-back (note I didn't say cat-back, ha!) might help top-end power, but the midrange does tend to be more important in autocross.

One advantage of a dual system, is it should be able to package more muffler longitudinally underneath the car.  There's also a 93db sound limitation at my local lot in San Diego, which I'd like to meet.  Not sure yet if it'll be possible to run the exhaust all the way out the rear of the car or not, with the rear suspension still being worked on.

So, it's good to have the motor built, and home.  It will be tuned again next year, after I have it in the car, with the air cleaner and header/exhaust system in place.  There really isn't much tuning to do anyway, just adjusting the distributor advance.  Fortunately the air/fuel ratio was okay with the carb freshly rebuilt to stock specs- there's definitely more power to be had with some tuning there, but I have no allowances to do so.  Something I'll have to keep working on with the rulesmakers - the fuel injected guys can adjust their ECUs to produce whatever sort of fueling they'd like, would be nice if the old-school carb'd cars were given the same freedom.

29Nov/100

Phase 2 begin

Couple updates for 11/29.  Took the day off work today to get the car up to the aforementioned John Coffey at his shop, Beta Motorsports :

In preparation, thrashed late into the night yesterday putting the back end of the car together enough to get it rolling.  Last minute run to the auto parts store for some bearings, and together went the diff.

Here it is floating out in space, just like the stock one that came out.  But notice here, the Hyperocoil composite leafs, and the once-horrendously filthy 12-bolt, now cleaned up to only moderately filthy, with fresh wheel studs.

Car sits a "little" high on the springs - should come down a little with time as things settle, not to mention the weight of many components like the fuel tank, trunklid, back seats, etc.  Still, I worry I'm going to need to have some custom fiberglass leafs made, as the car is about 4-5" too high here and with 250lb. springs, should only come down a couple inches with the weight.

This morning, went and rented a trailer.  Loading a car with no engine or brakes on a trailer sure can be fun!  Ratchet straps make decent winches in a pinch...

Was yet another beautiful day in southern California.  Cold, but clear.  Took this in honor of the recently passed Leslie Nielsen:

And finally, car made it to Beta Motorsports.  I have about a dozen different projects for John, which will take him through most of December.  Fine by me, plenty to do on the side while he works.  As he completes things, I'll post pics and explain what was done with each sub-project.  John will be fixing a few things wrong with the car, modifying a few of my aftermarket parts to work better, and fabricating a few things from scratch.  When he's done, the chassis and suspension will be "done" from a fab perspective.  I still expect to do a lot of suspension tuning, the fruit of this work will be a solid and highly adjustable platform upon which to tune.  It'll also be done from a welding/fab perspective to I can then take the car to get body and paint done.

Filed under: Chassis No Comments
24Nov/100

Phase 1 just about done

If we break this down into five phases,

1. Disassembly/teardown

2. Fabrication

3. Body/paint

4. Assembly

5. Tuning

Phase 1 is pretty much complete.  There isn't much more I can take apart, and still be able to roll the car on a trailer.  As it is I need to get the rear end back in the car.

Car looks low here, mostly because the rear is still way up in the air.  There's actually 6 inches of ground clearance in this pic, at final ride height it'll be about 2" lower than this.  Those upper control arms are from SPC, which I chose for their adjustability.

Next week the car is headed to Beta Motorsports where owner John Coffey will be doing all the difficult fab work and Phase 2 officially begins.  I've known John for years, since we ran the Open Track Challenge back in 2003.  He's done a lot of really nice work for a number of roadracers and autocrossers in California.  If you're in So Cal and need some fab work done, give John a buzz - just please wait till he's done with my car first if you don't mind...:)

Check out the BetaMotorsports Youtube video

I've been chatting with John for several weeks on the project, and what started as 2-3 things for him to do, has grown to 10-11 things.  It's not that I've thought up a ton of new things, it's just that as I've collected some parts and studied the car more closely, I've better realized the extent to which the aftermarket's offerings aren't up to snuff.   There's a lot of parts out there that are "close", that just need a little welding to be made right, a couple other things will be almost scratch-built.  Even those SPC upper control arms shown above, I believe we'll need to modify to increase their adjustment range.  Nothing worthwhile is easy!

Rear brakes got here recently - from before, the stock (awful, worn-out) rear drums weighed 43 pounds.  Was hoping to save weight with my aftermarket brakes but it looks like I didn't-

This pile of brake parts, everything needed for the rears, weighs 48 pounds.  There may be a few pounds in packaging there, but at best, my rear brakes will be a wash from a weight perspective.

I worked out what I'm hoping is a good first stab at the piston areas for the rear calipers.  They have to be "just right" in proportion not only to the front caliper piston area, but also to the master cylinder bore, taking into account pedal ratio and everything else.  Fortunately with a company like Wilwood, I have a few different caliper options with this mounting style and dimension, so I can swap calipers relatively inexpensively if I did this really wrong.

Rotor diameter is 12.19 to start with.  I know that's really disappointing from a bling-bling perspective, but my justification is thus:

1. For autocross, you really don't need monster brakes, there's not enough braking to overheat a reasonably sized system

2. Lighter is better, and the larger options will add weight.  I'm already several pounds over where I'd hoped to be.

3. This is the largest I can run and still hope to fit 15" wheels.  While I don't plan to run 15" wheels while autocrossing, the vintage Trans-Am cars always ran 15's, so I thought it would be cool to be able to slap on some old Minilite-style wheels or whatever, if I'm ever at an event where I want the car to look even more like the classic Trans Am cars.  Plus you never know what new tire sizes might come out some day - if somebody decides to build a radical tire that only comes in an ideal size for the car in 16" diameter, I wouldn't want to feel screwed out of that tire, or have to change the brakes to fit them.  The more wheel diameter options you have, the more tire options you have, and tires are the most important part of the car.

Speaking of important parts of the car, I hope to be picking something up this weekend that is certainly a very very important part of the car.  More to come there, maybe Sunday if it's ready.

In that pic above, the car is sitting on 9.5" long 5"OD springs,  a size Hypercoil and others label as "conventional" springs in their catalogs.  Below is one of those springs, next to a stock spring.  The stock spring is almost twice as long!

Happy Thanksgiving everyone!

21Nov/100

Q:was wondering if you could use the camber kit allowance to use an aftermarket lower control arm with the shock attachment located closer to the spindle attachment point, effectively improving your motion ratio

Not a bad idea, unfortunately the rules makers thought of this and restricted it.  From here:

http://www.rhoadescamaro.com/build/?page_id=260

Under 14.8.I.4:

"Intermediate mounting points (e.g. shock/spring mounts)
may not be moved or relocated on the arm, except as incidental
to the camber adjustment."

So, if I were to "spend" the camber kit allowance on lower arms, and I lengthened the lower arm by 1" for instance,  I could choose to add that inch inboard of the spring/shock mount.

This would improve the motion ratio from 9/16 (.5625) to 10/17 (.588), less than 5% improvement.  There'd be about a 10% increase in wheel rate, which would allow for a softer spring.

Of course, anything that helps is welcomed, but after weighing the possibilities, I've decided to stick with the stock lower arms (though they'll get some special bushings) and go with a replacement upper control arm.  I'll explain the reasoning behind that one later...

Filed under: Q&A No Comments
21Nov/102

Why are old Camaros always so slow?

Them be fightin' words in some circles but since this is my blog, it's a fair question to ask.  The context of the question today, is around why they're slow in autocross, when seen from the eyes of a typical die-hard SCCA competitor.

One of the more interesting aspects of this project, has been the speculation and conjecture on why the car is going to be slow in STX.  As a car builder, one ought to understand their platform, and in leveraging available allowances, do everything possible to minimize the impact of any deficiencies, while accentuating the strengths.  We all *know* these Camaros are slow at dodging cones - but what specifically makes them so slow?  Some are convinced it's the axle-tramping rear suspension; others are sure it's the front suspension, still others think the car won't really be making good power vs. its competition because of optimistic 60's SAE Gross vs. today's Net HP ratings.  Or maybe it's way too big and heavy, maybe the brakes can't be made to work, maybe the steering is too slow.

Well, I am sure there are many possible reasons, and until I've got it running and tuned as well as I think I can, we won't know which of the above are true.  Maybe none of them apply if the car is built right; maybe all of them are true, regardless of all you do (at least within ST rules).

Though I haven't gotten too far with it yet, there are two Very Big Things I see holding these cars back in the majority of cases, that I'll address in this post.  Hopefully with my advance knowledge of these shortcomings (queue G.I. Joe) and some efforts made in mitigating them, I can overcome.  Here they are below, in no particular order-

BIG THING THAT MAKES EVERY AUTOCROSS CAMARO YOU SEE SLOW #1:

The person tuning and driving that Camaro you see, doesn't know what they're doing and/or didn't build their car to "go fast".  Now, I understand that statement comes across as horribly arrogant, but let me explain-

We all (or most guys, at least) tend to think we know what we're doing the first we get behind the wheel.  "Of course I'm an excellent driver", and we continue to believe it until we see the times of somebody who really is fast.

To use one of my favorite memes in illustration,

First I was like-
so I was like,
but then I was like-

You just don't tend to see the really fast guys driving old Camaros at SCCA events, and you almost never see the really fast guys at non-SCCA events.  They're often running more modern and closer to stock Miatas or Corvettes, or whatever the hot car is that year.  The best drivers tend to flock to the platforms that are believed to be competitive, because they want to win!  It's super rare to see somebody really good (and please, don't for a second take that to mean I think I am) driving an oddball platform.  What this means is the general Good Driver rule still applies to Camaros- a "really good" autocrosser could hop in the driver's seat of a "beginner/intermediate" Camaro autocrosser, and usually beat them by a few seconds on 50-60 second course.  In some ways the non-competitiveness of Camaros, and many other interesting cars, is a self-fulfulling prophecy,  as those who own them are likely to get discouraged by their early results and lack of any evidence they'll ever be competitive, leading them to to not stick with the sport long enough to get any good at it.  Who knows, perhaps with some success maybe I can change that - I sure see more Nissan 240sx's out there today than I saw before 2006.

So there's the driving element - if the person driving that Camaro wouldn't be competitive in the Miata or Corvette or whatever, there shouldn't be any expectation they'll be fast in the Camaro.  Subtract a few seconds for a really great driver, and maybe the car looks a bit less bad?

The other aspect of this relates to tuning and preparing the car to go fast in autocross, and skill in this area almost exactly parallels driving, though most people seem a little more willing to admit their shortcomings in this space.

There is an unbelievable quantity of parts out there for these cars, as they've been undergoing speed tweaks for over 44 years now.  While as best I can tell the majority of effort into these cars for decades was around drag racing, the idea of making them go fast around corners has become very hot in recent years and the parts variety reflects this.  The "handling" renaissance begat a staggering quantity of suspension parts but not a lot of good guidance on what to do with them.  Individuality, limitless modification options with no rules boundaries, and differing levels of willingness to sacrifice street manners on the altar of speed, have prevented the crystallization of a "spec" setup for the Camaro.  A good example of a spec setup, is that for the super-popular Street-Touring 1989 Civic Si, published by Chris Shenefield about 8 years ago:

http://www.redshiftmotorsports.com/RedShift%20Tech%20Page.htm

With no spec setup to start from and no prior experience assembling a proper-handling autocross car, it's no mystery so many of these cars end up not working very well, driving aside.  The Camaro as a platform is a deep dark hole to climb out of, too difficult to expect anyone to succeed with as their first autocross tuning project.  You can put your faith in what your suspension vendors tell you, but their answers are going to be targeted to the middle of their demographic, who may care more (or less) about a comfortable cruising ride, than you do.

There are some people floating around out there in the old-Camaro world who kinda know what they're doing around the cones, I think, but since there isn't really any sort of rules in the old-car specific events, it's impossible to tell who's doing a lot with a little (bit of modification), or who's doing less, with a whole lot more.  Structure and rules are frowned upon in those circles, which is a shame because it makes results impossible to use in drawing conclusions.

I guess as a message to all my fellow old Camaro owners out there - if you really want to be fast in your Camaro at the autocross (and largely also, the track) - the best thing you could probably do, is park the Camaro for a while.  Get a Miata, or an S2000, or a Corvette, and go run a ton of events (SCCA preferably).  Figure out who the fast guys are in your region and track your times against theirs.  Even better if you get a similar car.  By getting a car that's great out of the box, you can forget about setup and focus on driving.  This will teach you the importance of driving, while at the same time familiarizing you with the characteristics of a proper-handling car.  When you're ready, then go back to the Camaro - I suspect the experience gained in a "good" car will better illustrate how far you have to go with your Camaro.  It should also help you better understand the importance of different modifications, and get you to spend the next few bucks on tires or shocks, instead of a supercharger.

How am I going to avoid this common problem?  By drawing on my experience as a driver and a tuner from many other cars, to dig this thing out of the deep dark hole it starts out in.  I don't have any success stories to look to, but that's part of the fun/challenge.

BIG THING THAT MAKES EVERY AUTOCROSS CAMARO YOU SEE SLOW #2:

The stock front suspension really is as bad as you've heard.  There's a lot of things wrong; below I'll attempt to explain just one facet of the wrong-ness 🙂

Most of the old Camaros you see at the autocross look awful - they are too soft, and the front suspension looks like it's doing the opposite of what it should.

Not trying to pick on this car or driver here - this photo pulled from http://www.milesspeed.com/ - a neat site I stumbled across in researching these cars.  Car is owned/driven by cool chick Liz Miles, and this was taken very early on in the car's development.  Using it just to illustrate some of what's wrong with the car's front end; odds are if you've seen an old Camaro on an autocross course, it looked a lot like this.

Here's another one from a 1967 magazine article on the original Z28:

That thing has no grip on the crap OE tires, but it still manages to showcase how utterly whacked its front suspension is.

Front grip is tremendously important in autocross.  At the track if you've got way more power than everyone else, you can maybe get away with a pushy (understeering) car, heck, it's more stable.  But not in autocross.  You need to generate big yaw/rotation, and you need to be able to change direction quickly.  The front tires do all this work and it's the front suspension's job to keep the tires as happy as it can.

Pretty much nobody with one of these old cars is giving them enough front tire.  I've seen cars with $10k+ in aftermarket grafted-on C6 subframes, uber expensive shocks, and mega-$ forged wheels ... wrapped in 245 width tires!  With 335s out back!  That sort of stagger might work on a 911, with over 60% of its weight on the rear axle, but it's a recipe for terminal understeer (and a frustrating/boring driving experience) in a 55% front-weight Camaro.  If you want one of these things to turn, you need to give it all the front wheel/tire you can, and nothing made today with a DOT stamp is "too much".  My Viper had about the same front weight as most of these Camaros, and it had 335s up front!  At that size things were just starting to work right. 🙂  Obviously packaging is a problem but with all the effort put into everything else, I don't see why more of those guys aren't running at least 285s up front.

So to the subject of analysis here - the motion ratio - and boy is it TERRIBLE!  To many that may not mean anything, so let me attempt to explain.  Below is a photo of a stock '67 Camaro lower control arm.  At the far left, the rod illustrates the axis upon which the arm pivots.  At a bit past 8.5 inches down the tape measure, are the two bolts that hold the shock.  When installed, the spring sits concentrically around the shock.  At the far end, just under 16 inches, is the lower ball joint's pivot point.  Though you can't see it here, there's a hole for the stock swaybar attachment at about 13.5 inches.

So what's the motion ratio, and why do I care?  Well, the motion ratio, is the ratio between how far the wheel moves, compared to how far the shock absorber (or spring) moves.  The further out on the arm the spring/shock attach, the higher (and better) the motion ratio.  To calculate the motion ratio, you take the distance from the inner pivot to the spring/shock attachment, and divide it by the distance from inner pivot to lower ball joint pivot.  If we round the pictured measurements a bit, we get:

Motion Ratio = 9/16 = .5625

This means, for every inch of wheel movement, we only are going to see .5625" of spring/shock movement.   Okay, so why's that bad?

It's bad because we depend on our shocks to damp the motion of both our unsprung (wheel/tire, 1/2 our suspension) and sprung (the rest of the car) weight.   The better a job the shock can do, the more consistently loaded our tires will be, the more grip we'll have, the faster the car will go around the corner, the lower our laptimes.  This motion ratio is about 30% lower than the motion ratio of a good modern car.

Below is a pic of a Viper's front corner - look at how the spring and shock attach waaaaay out on the arm, right next to the lower ball joint:

The Viper enjoys a much much better motion ratio than the Camaro.

Shocks depend on velocity to do their job - if they are not moving, they are not displacing fluid, which means they aren't doing anything.  The more shock travel we can get per unit of wheel travel, the better we can control every microscopic bit of that wheel travel.   This also allows us to control things with lower shock forces, which makes it easier to find reasonably priced units.

In an autocross car with a good motion ratio, we're generally looking for what the shock does at about 3 inches/second on a force vs. velocity graph (explained somewhat here: http://farnorthracing.com/autocross_secrets20.html ).  Most of the movements the suspension sees on an autocross course are in this speed range, so that's where we care about what our shocks are doing.  Shock velocities above that speed (bumps) are important too but somewhat less so, they'll be a subject for a later day.

So getting back to the Camaro - with a motion ration of .5625, we're only getting about 2/3 the shock travel or velocity, of a "good" suspension car.  So whereas they get to build their shocks to work at 3 in/sec, ours have to be doing the same quality of control, with 2 in/sec.  The problem is, accurate control and large forces at these low shaft speeds, are very hard to come by - any of the common shocks available over-the-counter just aren't going to get it done, at least not very well.  But wait, it gets worse!

Spring rate by itself is a not very good indicator of how stiff a car is - what's more useful is the "wheel rate", or maybe the "natural frequency" of a suspension.  Here's an online calculator if you're interested to find out yours: http://www.racingaspirations.com/?p=292

Those that have ever ridden in an unladen 1-ton pickup truck, and been bounced all around, have experienced a high wheel rate, and a high natural frequency.  The high natural frequency is caused by a very high wheel rate, combined with not much weight on the spring (an empty truck bed).  If you've ever then loaded up that bed with a few thousand pounds and noticed the truck suddenly rode much more comfortably, it's not because the wheel rate went down (in some leaf systems, it might actually have gone up) - it's because the natural frequency has gone way way down due to the weight/load in the bed.

We arrive at wheel rate by taking the motion ratio, and multiplying it by itself - "squaring it", in math terms, then multiplying it by our regular spring rate.  In the Camaro's case, .5625*.5625=.316.  That means that for every 1 pound of spring rate, we are going to have .316 pounds of wheel rate.

Wheel rate and natural frequency are concepts you can use to compare the stiffness of any two cars, regardless of suspension type.  You'll often see sliding scales where 1hz is "comfy street car", 1.5hz, "sporty car", 2.0hz "race car", 3.0+hz "race car with aero downforce" - something like that.  Those are really just broad generalizations and by no means limits on what you can do with your car.

If you're setting up a car to handle well, 2.0hz isn't a terrible place to start.  If you've driven other prepared-suspension cars that you really liked, that were of a similar layout (RWD, FWD, AWD), it might be worthwhile examining that car's frequencies and consider it as a baseline.  For instance, my 240sx used a 550lb. front spring when it was in STS (street tire) trim.  It had a bit over 700lbs. of total weight per front corner, about 55lb. unsprung.  It used a strut front suspension which granted a motion ratio of about .96.  Its 550lb. spring netted a ~500lb wheel rate, and with the car's weight, its natural frequency was around 2.7hz.  While this was way higher than anybody is likely to recommend for a daily driver, it wasn't terrible on the street, but more importantly, it wasn't so stiff that the street tire wasn't working well.  The car worked great!

A similar calc on the rear of an STS Civic I built, puts the frequency around 3.5hz!  Some guys I know are running springs up in the 4-5hz range on the rear of those cars.

So getting back to the Camaro, now knowing the 240's numbers (500lb. wheel rate, 2.7hz) as a ballpark.  With our Camaro's motion ratio, to get a 500lb. wheel rate, we'd need (500/.316)=1582lb. springs!  Even at that rate, our frequency is only going to be a bit over 2.5hz, in some ways softer than the 240sx.  To get to the same frequency I'd need springs up around 1820lb./in!

Ugg, now we've got not much shock velocity to control our wheel motion, and on top of it, we're going to have to run crazy stiff springs to get this thing to the stiffness level we want.

There are a lot of things "less than ideal" about the Camaro's front end geometry - bump steer, camber curves, etc., that I can't really fix in ST, and that you can't really fix with the stock subframe.  In an earlier post I mentioned my plan for dealing with these was to set the static numbers good and "not let it move much".  You can see now why people hadn't really tried that approach before - they couldn't!  No normal shock you could buy off the shelf would damp a 4-digit spring given an equal motion ratio; things that stiff were just outside the bounds of people's thinking.  About the stiffest I've seen anyone run is 800lb. springs, for a 250lb. wheel rate, about half what I've depicted above.  It's no wonder people were so concerned with bump steer and camber curves - at that low a wheel rate, the suspension would experience large (double to triple) the quantity of travel as the more stiffly sprung version, so the negative effects of bad bumpsteer/camber curves would also be doubled or tripled.  It also means they had to run their cars a lot higher, which is a Big Bummer for them, we'll explore later.

So to bring this home-

Bad motion ratio gives shocks poor control of sprung/unsprung motions, leading to inconsistent tire loading

Bad motion ratio creates a lot of suspension travel at "normal" spring rates, exacerbating the problems with the stock suspension's camber and bumpsteer curves and necessitating higher front CG

How am I going to avoid letting this screw me up?  Simple answer - great shocks!  The 28-series Konis I have, were originally designed a few years back for high-downforce Indy cars, where there are very large forces needed at very small suspension displacements.  Even though an autocrossing '67 Camaro is a long ways from a recent Indy car, the characteristics needed end up being quite similar.  There are many other high-end brands (Penske, Ohlins, Moton, AST, JRZ, Sachs, and more) than can get this done too, Koni just happens to be the one I'm most familiar with.  With a little bit of revalving, they are going to allow me to run these really high spring rates, while maintaining good wheel control, something a lower-end shock wouldn't.

Lots more wrong with front suspension, more to come on that later...

15Nov/100

John Purner and Complete Custom Wheel

Spoke with John Purner of Complete Custom Wheel today.  Not quite ready to order anything yet but had a good chat with him about the project and bounced around some ideas.  I ran CCW wheels on both my SM 240sx and on the SS Viper.  While I haven't received any sponsorship or special deals from CCW, I always look to them first.  Their wheels offer a tremendous value in custom-sized forged wheels, part of why so many racers run them.  I also think the "Classic" style they offer would look good on the Camaro-

John was having, as he put it, an "average" day.  Well, I don't know if I could have handled him on a good day - he had me laughing so hard I was practically falling out of my chair.

Turns out John and I share a lot of the same viewpoints on things related to these cars.  It was refreshing to find someone else who not only thought like I do, but also felt so free to vocalize those thoughts without a Political Correctness filter.  Doubly so, as he's a guy who has a business selling parts to the public, oftentimes people in that position are so reserved in what they say to preserve their "image".

I don't know if I'll be running CCWs on the Camaro.  I don't get anything if you decide to buy some.  But you owe it to yourself to at least consider these wheels at the time of your next purchase, the guy is just that cool.

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7Nov/100

Caswell zinc plating and blue trivalent chromate

One enjoyable aspect of working on cars is taking something funky and making it nice and clean again.  With plastic stuff that usually means throwing out the old and buying a new, but with metal, especially decent metal, there's usually something you can do to "bring it back", without having to buy a new part.  Plus it's fun to use as much of the original car as possible.

With the 240sx I had a lot of the suspension components powdercoated.  Powdercoat is a much more durable finish than paint , available in a variety of colors and textures.  Being a thick coating, it adds a little weight, and won't work anywhere you have tight tolerances, like in a fastener or on two tightly mated surfaces.  I plan to have several things on the Camaro powdercoated.  RW Little is a place in San Diego I've gone to many times that has good prices and reliably quick turnaround.

Since building the 240 I've learned about how DIY'ers can apply other sorts of finishes to their metal parts at home.  Another very popular coating in automotive applications is cadmium plating.  This is often seen in brake boosters but also in some suspension components, on fuel pumps, or carburetors.  The cadmium plating offers excellent corrosion resistance, and a neat yellow sheen when new.

Caswell plating has a range of kits to do all sorts of platings and coatings and anodizing at home.  Standard cadmium plating involves some very toxic chemicals and is pretty much banned in CA.  Caswell has a good alternative, their "Copy Cad" kit.  With it, you apply a standard zinc coating, then dip the parts in a trivalent chromate, leaving the parts with a nice sheen.  The most popular is the yellow chromate, which ends up leaving the parts looking just like a freshly cad plated part.

The plating kit arrived last Friday so I got to work-

For all of this, you need distilled water.  Needed to go to Target anyway, so we loaded up the cart with 15 gallons.

There's four buckets you need to do this-

One is a degreaser bucket, orange bucket in the pic below.  The degreaser is supplied as a powder to get mixed with distilled water.  Parts go in this after they've been prepped as a final cleanup stage.  This stuff needs to be heated up over 110 to work its best.

Next is a rinse bucket.  You use this to rinse the parts after degreasing, and any time you're moving parts between the other buckets.  Mostly you just hold parts over this bucket while spraying them with water to rinse between stages.  You can see the edge of the black bucket there, my rinse bin/bucket.

After that they go in to the plating bucket, the white bucket with brown water in it.  This bucket gets a bunch of a different powder, and some gnarly brown liquid mixed in.  All this stuff is supposed to be pretty safe as far as plating operations go, but note the large box fan to the side. 🙂

The plating bucket gets heated also to about 140.  It also gets an agitator pump to keep the fluid circulating within the bucket, which helps the plating process.

The last bucket and step (after another rinse) is the chromating process.  Again, this stuff mixes with distilled water.  Instead of the old-hat yellow, I opted to go with a blue chromate.  It is a little bit less blingy, and a little bit less resistant to corrosion (not that the car is going to see much bad weather ever again), but I like the more understated end result.

To get plating, you suspend the part you wish to plate by a wire.  Inside the bucket you place a large-ish sheet of zinc, which you connect to the positive terminal of your power supply.  To the negative side, you connect the wire holding the part(s), and away you go.  The power supply I'm using goes a bit over 5 amps and is of a constant-current design.  Parts stay in the bath for 20-30+ minutes, depending on the size of the part and the desired thickness of the coating.

I decided to start off with a few small parts that aren't really visible, the three "hangers" for the steering column.  Mine were filthy and rusty when I pulled them out of the car-

(Sorry for the cell phone pic, left regular camera inside that night)

In with them are a brake bracket, and the underbody emerbency brake assist hanger thing.

Before the plating process can begin, you need to get the parts down to bare metal.  For most of this I used a wire wheel on a bench grinder.

They actually look ok at this point, but left alone, would be back to a rusty funk in very short order.

So into the degreaser, then a rinse, then into the plater.  These are some of the clutch mechanism parts I decided to do later, never got a photo of those things in the plating bucket.

Once out of the plating bucket, the parts have a dull gray zinc coating.  There is a "brightener" additive available but I didn't use much of it, didn't want the parts too shiny.

From there a rinse and into the chromate bucket for 30-60 seconds.  A final rinse and hung in front of the fan to dry-

Overall I am pleased with the end results.  I don't quite have the power supply...power to plate the big clutch lever as well as I would have liked.  I also didn't get every last fleck of paint off the original parts, using a bead blaster or sand blaster might have been more effective there than my wire wheel.  The pictures don't capture very well the subtle iridescence of the  blue chromate, but it looks quite cool in person.

Here's some before, during, and after pics of a few parts

This update isn't totally car related, but other progress is being made, just have to wait  for progress updates in other areas.  Can see some clues based on doodads visible in some of these pics.

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