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jkopp
10-02-2004, 10:16 AM
1996 NEWSLETTER ARCHIVE

SAFETY RECOMMENDATION - WHEEL CHOCKS


This may seem mundane, but good wheel chocks are an incredibly important safety item to have. Remember how your trailer lurches when you load the car? It needs wheel chocks during loading. Ever need to immobilize your car on the trailer while you tie it down? You need wheel chocks. Even worse, ever had a car roll off of a floor jack? You NEED wheel chocks. The best I've found are from "American Van Equipment" at 1-800-526-4743. Nice 10 pound solid rubber wheel chocks with handles - part # WC-10L at $15.95 each.

CRANKSHAFT RECOMMENDATIONS

I am one of several A/S racers who has catastrophically lost a motor due to a broken cast crankshaft, causing a major expensive motor replacement. As many of you have heard me say, I believe in Smokey Yunick's Circle Track column on cast cranks, when he said that "I'd rather pay $1000 for a (steel) crank and build my house around it. You don't stand near the chance of destroying a whole engine and maybe losing a race." (Circle Track, May 1992, page 148). Since it costs about five times more than that for each time a junk cast crank breaks and destroys a motor, I am definitely against them. I also believe that our motors are rev limited by the minimal spec valve lift, unported heads, small carburetor, and fragile block webbing; and knowledgeable folks have said that there is little or no horsepower to be made in a legal motor above 6200 anyway because of the restricted air flow. Moreover, my cast crank broke in less than one full season despite being always run well below an installed 6400 rev limiter, which echoes the experiences of others that have catastrophically lost motors at well below 6400. BUT, until a rule change occurs that would allow us the option of using a reliable steel crankshaft, we must figure out how to make cast iron crankshafts live. Since both Ford and GM racers have lost motors to a broken cast crank, I offer the following list of ideas that have been discussed in several forums over the past year concerning this sometimes perplexing question of building a reliable race motor with a cast crank:
Needless to say, balance is absolutely critical so choose your machine shop wisely. Stock Car Racing magazine published an article entitled "The Cast Crank Blues" (Sept 1992, pp 90-99) that described in detail the care needed in balancing a race engine using a cast crank. In addition, there are very strong feelings on both sides of the Fluidamper issue, so that there recommended use is unclear. Every engine builder seems to harbor their own strong pro- or con- Fluidamper feelings, or have a favorite alternative harmonic balancer to recommend. Find someone you trust and follow their advice.
Smokey Yunick mentions in his article that you should limit any cast crank to 6500 RPM max, no matter how good it is or how well it is balanced. So remember that statement when you plan your cam power band and rev limiter.
Bad gas (contaminated or too-low octane) and/or too much timing advance causing detonation is hard on the pistons and crankshaft.
Lugging the motor at low RPM (especially when putting the car on the trailer) is hard on the crankshaft.
Hitting the rev limiter repeatedly, even with a "soft touch" rev limiter, causes stress on the crankshaft that you want to avoid. Use a rev limiter, but use self-discipline to shift before you hit it.
Missing gearshifts spins the crank hard. Missing an upshift and getting neutral will cause the motor to at least be constrained somewhat by the rev limiter; but shifting into 2nd when you were aiming for 4th (as can happen in sweeping corners when there are g-forces on the driver) can cause the motor to skyrocket in RPM into serious danger zones. It only takes a moment to damage that crank. Pay special attention and care to your shifts when you are driving at anything other than straight ahead.
Overheating and/or lubrication failure can cause bearing and crankshaft stress. Don't race without a pressure-tested cooling system with a well-fitting radiator cap, and a functional oil cooler. We have learned some interesting things by installing one oil temperature gauge for the sump and another gauge reading the oil temperature exiting the oil cooler before the oil goes back into the block.
Never put the throttle hammer down with oil temp less than about 180 degrees.
Change these cast crankshafts for a new one after a predetermined number of hours, or at the end of every season. Some A/S racers are putting engine-hour meters in their cars for this purpose, and that is probably a real good idea. This is also probably why I am so fond of the proposed steel crank option - this type of "maintenance" rebuild is very expensive and inconvenient for those of us without fully-equipped professional shops. I would much rather build a bullet-proof bottom end once, and then forget about it, except for bearing checks.
Footnote: There has been some discussion about allowing steel cranks in A/S as long as rev limiters are required by the rules and enforced. There are inexpensive instruments that can check a rev limit on the car at impound. However, I have also spoken to many people now that have told me that there is no rev limiter that can't be cheated around. Since we really do not need or want some addition to the rules that opens up a can of worms in enforcement, the rev limiter idea at least at this time appears dead. Plus some Ford racers complained that the better revving Ford motor would require a higher rev limit than the GM motors to be fair, which would cause more clouds in the soup. As mentioned above, I still personally think the restricted breathing of a legal motor and the fragile block webbing and two-bolt mains are good inherent rev limiters already, and a steel crank option still makes sense. But under the current cast crank requirement, pay heed to the recommendations above! We want as many reliable A/S cars finishing races as we can possibly get!



RACING TECH - BRAKES IN AMERICAN SEDAN RACING

(This article is contributed by Scott Griffith and concerns the advantages and disadvantages of the stock brake castings versus the allowed A/S alternate of a separate hub and rotor. Thanks, Scott!)

The separate hub is a very big advantage, not a disadvantage. There may be problems with individual hub designs (as everybody who ran the original JFZ hubs knows!), but conceptually the separate hub/rotor wins hands down. Here's why.

First of all, the unicast (one-piece) rotor/hub has got some major thermal problems. The OD of the rotor will run at up to 1300-1400degF, and it conducts this heat directly into the hub if the whole assembly is a single casting.

This causes two problems: the biggest is that the massive thermal stresses due to the temperature differential between the hot rotor and the somewhat cool hub leads to most of the rotor warping problems that the unicast cars face. Unfortunately, the connection to the rotor hub is only on one rotor face, so the other expands more- which leads to the entire rotor distorting into a cone, rather than the flat planar surface that you'd want. If there are any chilled-in stresses, or worse yet gas bubbles, sand inclusions, or whatnot, the rotor will not adopt a smooth cone, but will warp, or crack, or worse.

The second problem is the fact that cast iron is a fairly lousy conductor of heat (as metallic solids go). So, while you aren't dumping enough heat into the hub to make a material difference in the peak rotor temps (in terms of heatsinking capacity), you're dumping more than enough in there to get the wheel bearing temps up *way* over 500degF (according to the Tempilabels I've always run). And I've never yet seen a grease that would live for long at those temps, so your wheel bearings face a nasty, brutish, and extremely short life. I ran unicast rotors for many years. Then, for a couple of years, I ran cut-down stock rotors as hubs, and my own fully custom hats and rotors. Now I use the SN95 Mustang hubs (or my own custom tapered-bearing hubs that are somewhat stiffer), and rotors-on-hats.

The magic of the rotor-on-hat system is that it relieves a lot of the stresses that a one-piece unicast setup cannot avoid. The annular rotor can expand radially, as the aluminum hat has a very high tempco and moves along with it, rather than attempting to constrain it. The bolted joint between the rotor and the hat serves as a very effective thermal barrier (I've still never seen hat temperatures over 300degF, despite seeing peak rotor temps over 1400degF!), and the wheel bearings run at no more than 260degF for the tapered rollers, or 220degF for the much more efficient double-row ball bearing used in the SN95's unit-bearing hub.

In my not so humble opinion, a rotor on hat arrangement is best. A separate hub (either aluminum or steel) supporting a one-piece rotor/hat (like the F-body and Mustang PBR setup) can be nearly as good if the rotor is carefully designed. A unicast rotor/hub setup is a disaster for racing, even if you know a really good heat-treat shop that will stress-relieve the rotors before you machine them true. Unicast rotors are dinosaurs, thank Gawd. If you can avoid them, you should.

The PBR rotors are very cleverly cast to have a nice stress-relief undercut between the hat and rotor sections. I believe that this is there to accommodate some of that differential expansion caused by the huge temperature differential between the rotor OD and the hat. It certainly seems to work, as the 1.1" PBR rotors are much, much harder to hurt than the old unicast Fox junk was...

-skod Scott Griffith email: skod@sun.COM

(Note - And I may add, the separate hub and rotor allows you to only buy and replace rotors, not the entire assembly. Although I always carry a set of stock 1.1" Camaro rotors with me for emergency use. Separate rotors and hubs are available from several sources such as Ground Control Suspensions, Baer Racing, etc. The new size 12 x 1-1/8" rotors are available from several sources including Coleman Racing Products. - Charlie)

RACING TECH Part 2 - BRAKES IN AMERICAN SEDAN RACING

(This article is also contributed by Scott Griffith and concerns brake fluid and pedal feel).

Question: "I had a problem toward the end of the season with the brakes "vapor locking". I had a very hard pedal and no stopping and the fluid was boiling something awful. Does "vapor lock" exist for brakes?"

I don't think it exists, at least in the sense of old-style fuel percolation lockup, where the fuel vapor pressure overcomes the output pressure of the fuel pump. I'd be much more inclined to think that you were running out of vacuum, which can be a real eye opener. I had to install a separate vacuum reservoir to get around that problem (in the past), but I don't think that's a legal mod for A/S.

If you're boiling the fluid, you'll get a long, soft pedal, not a high, hard one. The vapor bubbles will expand and force fluid back into the reservoir, resulting in the need to pump fluid back into the resulting compressible voids. Boiling fluid will always result in a soft, long pedal - there's no circumstance that I can think of that introducing gas into the system will result in a hard pedal. Also, it almost never happens that the pedal "comes back" to full hard after a fluid-boiling episode *without* bleeding the brakes. Gases forced out of solution by overheating the fluid tend not to get reabsorbed. It's not as simple as steam condensing back into a fluid, I'm afraid. So once the fluid boils and the pedal goes away, it'll stay partially gone until you bleed them down yourself.

If the pedal was really hard, you were out of vacuum. This often happens when you heel/toe to downshift and you're actively modulating the brakes. There's a nasty phenomenon where you exhaust the vacuum reservoir with the pedal well down, so that if your foot hangs on the throttle and holds it partially open, you don't get enough vacuum produced for the servo to "recharge" and work linearly (as your braking muscles expect it to). The pedal feels like a brick, but "the car: she no slow down." This is No Fun. It feels just like green fade, but doesn't smell as bad. Worse yet, it is intermittent. For me, the turn where this always used to happen the worst was the downhill, left hand Turn 2 at Laguna, where I was hard on the brakes for a long time, modulating like mad. I fixed it partially by rearranging the pedals to prevent that accidental hangup on the throttle, and completely by adding more vacuum capacity.

(Charlie's side note: This also assumes that the questioner was not running-in and smelling green (new) brake pads fading away to nothingness. You can also push on a hard pedal with the brake pads faded out and the car will not stop as you would expect).

There is one other possibility, but it's a remote one- I've only seen this once. A friend had an '87 Mustang that had a "haunted" brake booster. Under certain circumstances of cornering and braking force, the booster body itself would flex enough that the servo valve would jam up and go nonlinear- suddenly, no boost at all, despite having good vacuum. A booster swap cured that problem, but that's the only time I've ever heard of that happening. He still owes me that booster from his junk box so that I can dissect the dadgum thing and figure out just how this happened. He chased that problem for 2 seasons. Everyone tends to think of them as immortal, but those boosters aren't actually very tough at all. The plastic servo valves can be cracked (resulting in vacuum leaks) or killed outright in handling. Might be worth checking.

Question: "Could my problem be the booster loosing vacuum? It was somewhat repeatable in only one corner at the Glen."

Betcha this was happening in old 10, coming up out of the Boot, right? You'd be developing a little side force there and be hard on the brakes, so you could well be hanging on the throttle a bit.

Question: "Our ducts flow to the center of the rotors and pull the air out through the fins. We have directional wheels, but that race, one was on backwards! Do you think its a problem not to have the air blasting the pad contact surface of the rotor?"

In my humble opinion, no. Do everything you possibly can to keep the rotor's peak temperature down, and the most efficient way to do that is to push large quantities of air though the center eye, out through the wheel spokes, and get rid of it in the free stream. You can do a surprising amount for brake flow by rigging little pseudospoilers at the leading edges of the wheelwells to provide a little more negative pressure outboard of the wheels- the NASCAR boys pull the front fenders in front of the wheel wells out noticeably wider at places like Martinsville, partially for improved front downforce, and partially for improved brake cooling. (Note - this would not be legal in American Sedan racing).

Squirting cold air at the working surfaces is not as efficient as pushing it through the vents. You want surface area, and the vents give you that in spades. Bleeding off a little flow to direct at the caliper body can help in really extreme fluid-boiling cases, but basically you want to shove everything you possibly can through the vents and out. Dropping the peak rotor temps 100deg can really extend your pad life, and obviously reduces the risk of fluid boiling while you're at it.

Directional wheels are great. I used to have a set of those old Kelsey-Hayes 16" 3-spoke "blower" wheels that were all the rage in Firehawk in about 1985. I didn't have good instrumentation back then, but those things were good enough to double my pad life all by themselves... Whatever you can do to increase the volume of air into the rotor eye, and then exhaust the heated air into the free stream, *do it*.

Brian Kelley then added two important points to this discussion:

Obviously, the amount of vacuum available is limited by your camshaft.

It is also very important that your brake booster vacuum line can't be pulled off due to the engine torquing around, etc.

Charlie adds: Don't overlook the condition of the hose that connects the back of the Holley carburetor to the vacuum brake booster. That rubber hose gets yanked every time you remove the carburetor for changing jets, etc., and the condition can deteriorate and leak vacuum.