I took SWCDuke's advice and purchased a set of Firstone PV41's for my '69 L46 Coupe. Took off a set of 20 y/o GY's that were a real hazzard and probably ready to blow. The tires aren't pretty to look at, but already I can feel a world of difference. Funny thing - I bought them from TireRack, and had them mounted at a local GY shop. The manager/resident expert asked me why I bought such "cheesey" tires. He went on to tell me his H rated MS "perfomance" tires would run circles around the PV's. Didn't wan't to argue with him when he was balancing the tires at the time. Tempted to drop-off a copy of Duke's Restorer artilce to help educate him. Advice to those buying tires - Do your own research and don't rely on a salesperson! Anyway...

Just curious how the handling charicteristics RE grip, ride, etc. will change has the tires get broken-in. With 100 miles on the tires, they already provide 10X more road feel and stick, but seem a little stiff/slick. The car has a medium duty TRW fiberglass rear spring and HD performance Delco gas shocks. I inted the take her out on the track at Pacific Raceways for a track day sometime in the future, and I'd like to get the car set-up to enjoy the experience.

 

New tires have mold release on the surface and need about 100 to 200 miles of normal driving to scrub them in. At that point, full grip should be available.

I ran at Kent in the sixties, and I could do Turn 1 flat at 140 MPH on 6.70-15 Michelin X radials. Back then there were no concrete barriers as you transition onto the drag strip from Turn 9, which looked pretty intimidating when I attended a vintage race there in 1993. I used to exit Turn 9 in second gear at IIRC about 50-60 and accelerate through the gears. I shifted to fourth gear at about the drag strip finish line (about 130 MPH @ 6500, 3.08 axle) and stayed flat to the braking point at Two, which I took in second at about 80. First gear through the hairpins, then to near the top of second (about 100 MPH) before the kink on the bottom of the course. If your L-46 has a 3.70 gear, you may run out of top gear revs.

Come to think about it, once I shifted to second out of the second hairpin on the bottom of the course I was in second all the way around and shifted to third at the end of the transition onto the drag strip.

My lap times were about 1:45.

For track work I recommend negative 1 degree rear camber, and negative 1 at the front with hard urethane bushings in the front anti-roll bar end links. Since I don't know your rear spring rate, I can't say much except most aftermaket springs have higher rate, so they will promote more understeer than the OE spring.

Damping has a big impact on track handling, and unless the track is very smooth adequate street damping rates are usually inadequate for the track.

Replace/Flush your brake fluid with DOT 4 like Castrol LMA and make sure your pads have a least half the OE friction material thickness. The OE and OE equivalent organic pads should be okay for occasional track work, but if you turn into a track time junkie, you might want to consider semi-metallics depending on how the OE/OE equivalents perform.

Also, run your oil level between full (which is MINIMUM for track work) and a half quart overfull. Check the oil a few minutes after shutdown from each session and add oil as required to maintain it at NO LESS THAN FULL!!! I think your engine just has the "small" four quart pan with no baffles or windage tray. Even with the "big", baffled five quart SHP pan with windage tray, the trick is to run it a quart over full to avoid oil starvation in high dynamic loading situations, which can spin a bearing in a matter of seconds!

Also, be aware that full-treaded street tires have more tendency to overheat on tracks, which is why racers shave them down, and a novice driver can actually be harder on tires even though they aren't turning quick lap times. If you're a novice track driver concentrate on "smooth" and don't worry abut your lap times, and make sure you pick out good brake reference points.

Don't be in too low a gear. Once you learn the track you will find that what you thought was a second gear corner can be a third gear corner once you get the braking point and line down to optimum. If you're a novice, ALWAYS take advantage of experienced instructor drivers and LISTEN TO THEM!!!

Best lap times with street tires are usually in the morning or late afternoon sessions. In the middle of the day track and tire temperatures are at their highest, which can get the tires beyond their optimum temperature for maximum grip and it can feel like you are driving on slime. Since these tires are "all-season high performance" they probably will loose grip beyond about 150 degrees tread temperature if not before. Summer high performance tires are usually tood to about 160-180 and DOT legal racing tires from 180-200, but the later two categories are not available in OE or equivalent 15-inch sizes for vintage Corvettes. If the gods are with you it will be a cloudy day - not unusual in Seattle unless its August.

Cold street pressure of 32 all around should be a good starting point and somewhere in the range of 32-36 for the track. Expect an 8-12 psi rise after a typical hot lap session. Try to find the best hot pressure, then measure them cold to get your starting pressures for the next event, but due to changing track and tire temps, this can be a moving target.

Don't do more than about 10-12 laps per session and carefully inspect the tires after each session for chunking, especially the outside shoulder. If they do show evidence of chunking on the outside shoulder you need to either reduce body roll, add more negative camber, slow down, or develop a smoother driving style.

BTW, for C2 owners the PV41 is my pick of the V-rated 225/70R-15 "police pursuit tires", but it probably won't fit C2s without fender interference, which I why I recommend the 215/70R-15 Pirelli P4000 Super Touring for C2s.

I doubt if your GY guy has any idea of what the PV 41 is, has never seen one, and will never see one again. It's only available in three sizes that have been used on OE police pursuit packages in the last then years, and the other two are 235/70R-15 and 225/60R-16.

They are very rare tires. I've never even seen any on a police vehicles in California (or anything else - I've actually never seen one in the "flesh"). Just about all CA police cars have GY Eagle RSAs, due to a volume CHP purchase contact that local agencies can ride.

If you tell me your trans/axle combination, I can probably tell you the shift points on the track.

Duke

 

Thanks for the pointers, Duke. You've answered many questions that have been lingering in the back of my mind as I contemplate how to run the course - all good stuff to know BEFORE taking a single lap at Pacific. I have done a few parade laps in both my '69 L46 Coupe and my '66 L36 coupe (equiped with Pirelli P4000's, thank you very much). Even though speeds were limited by a thankfully spirited pace car, it was a different experience in each Corvette, from straights to curves. I can see why BB Corvettes are considered tough to handle on a course like Pacific. Tended to plow a bit in the hairpin! As for Axle ratios - It'd be great to get shift points on the track for both the Cars:

'69 L46, M21, 3.70
'66 L36, M20, 3.36

The track surface there is really choppy, and from what I've heard from drivers, it eats-up tires pretty quickly. They get hot fairly easily as compared to the smooth course at Portland International. Looks like a few passes at 120+ is worth it to me! As for your 140mph into the sweeper after the straight - whoa... And I mean WHOA!

THanks in advance for the advice. It'd take me a couple dozen laps to figure out half of what you've shared.

 

A L-46 with a CR trans and 3.70 axle is a bit short for Kent. For reference here are the speeds/revs in each gear for 760 rev/mile tires(775 for the 215/70 P4000s), which is the spec for the 225/70VR-15 PV41s and also the OE and Michelin 6.70-15s I had on my SWC back in the sixties.

'69 L-46 CR/3.70, 760 rev/mi tires

2.20 - 58@6000
1.64 - 78@6000
1.28 - 100@6000
1.00 - 128@6000

SWC L-76, CR/3.08, 760 rev/mi tire

2.20 - 76@6500
1.64 - 102@6500
1.31 - 127@6500
1.00 - 154@6000

'66 L-36 WR/3.36, 775 rev/mi tire

2.56 - 50@5500
1.88 - 67@5500
1.46 - 87@5500
1.00 - 127@5500

You can use this data to draw gear charts by plotting lines from the origin on X-Y graph paper to the max speeds using revs for the X-axis and speed on the Y-axis. As you can see, the L-46 second, third, and fourth gear have about the same max speed as my first, second, and third, so I would be a gear lower in many parts of the course.

If you haven't developed a heel and toe technique to do double clutch downshifts while on the brakes, start working on this in street driving.

Let's take a hot lap begining with the point where you shift 3-4, which will probably be about the end of the transistion back onto the drag strip, heading for start/finish. Once you pass start/finish acceleration will slow because the grade goes from flat to about 0.5 percent up. You will probably achieve 6000 revs well before Turn 1 (The jog to the right off the dragstrip). The apex is tough to see because the road slopes back down slightly beyond. When I first ran Kent in the summer of '63 I had to back off because I couldn't see the apex as I approached the turn. The next time I went out I put a broom in the traffic cone to mark the apex, and then I could do Turn 1 flat.

You'll probably want to back off or feather the throttle at about 6000 and through Turn 1 and to the brake point at Turn 2. Take Turn 2 in third (I used second) and accelerate out down the hill to the first hairpin, shifting to second as you brake for entry ( I downshifted to first). Carry second around the second hairpin, accelerate out and shift to third at 6000, and you should be able to stay flat to the right/left kink at the end of the bottom of the course. Brake for the kink and accelerate out in third all the way around through Turn 9 and shift to fourth after the transition back on the drag strip, which is where we began. I was in second all the way from the upshift point out of the second hairpin to the transition back to the dragstrip, but you will be in third.

When I spectated at Kent in '93 the kink on the bottom of the course looked different, and I found an old hand who said there was a landslide years ago, and confirmed that the rebuilt kink is tighter than it used to be, so you may want to downshift to second, but I would recommend third until you can take the kink as fast as possible, then decide if a downshift to second is necessary.

As you can see, you don't have to do a lot of shifting. Fix this pattern in your mind and use it. Some gears may be seem too high as you are learning the course, but as you get faster, you will realize they are correct. The only open question is whether you need to use second at the "new" kink on the bottom of the course.

Since you have a restricted capacity oil pan you want to use the highest gear possible, as the higher the revs and dynamic loading, the tougher it is for the oil to get back to the pan. The highest sustained dynamic loading is from the Turn 2 brake point and through that turn, which is the longest period of braking followed by the longest sustained turn. Catch a peak of the oil pressure gage. and make sure it is steady. If it fluctuates, raise your oil level! Try to catch a peak of the gage in the hairpins and also Turn 9.

If you have a basic plan for both the car and your driving, you'll be better off, and be sure to listen to the experienced instructors. A lot of novice drivers spend too much brain power on what gear they should be in an not enough learning the braking points and lines. If you fix your gear selection BEFORE you run the course (assuming you have some good guidance on what they should be from someone with a similar car) then you can devote all your brain power to learning the course, since gear selection is "preprogrammed".

Another mistake that novices make is trying to enter a turn too fast. This will just set the car into understeer, then you drift wide, can't hit the apex right and accelerate out of the turn. The entire field then passes you. The key is to enter the turn a little conservative so the car doesn't go into terminal understeer. If you hit the apex right, you should be able to then start adding power to accelerate out of the turn and the car should go into a nice neutral drift. Small block Corvettes are very neutral - mild understeer on turn-in and they should transition to near neutral as you power out, as long as you don't get on the power too early or quickly. This can also get you into heavy understeer. The rear ends can be a little twichy - especially under trail braking or trailing throttle, which is another reason to not try to enter a turn too hot, as the rear can get away quickly and spin the car quicker than you can say boo!

Turn entry is somewhat a function of the dynamic response of a car, but as a rule (with a fairly neutral car) you want to follow a decreasing radius line to the apex either by trail braking or letting the car scrub off speed after you start to turn in. At the apex start smoothly adding power and follow an increasing radius out of the turn. There are exceptions. Some turns (like kinks) or even fairly long turns may require a fairly rapid "pitch-in" depending on the entrance geometry.

Another thing to remember is that most turns are "late apex". The apex defines the boundary between entering and exiting a turn. If you apex a turn too early, you can run out of room at the exit and go off course. Ask anyone who's ever run Willow Springs what happens when you apex Turn 9 too early. This is the turn at Willow that separates the men from the boys! Most courses have a "key turn". Riverside was Turn 2. I think the key turn at Kent is the kink at the bottom of the course. If you loss too much speed there it's tough to get back since you go uphill at the exit, but Turn 1 is key on a very high powered car. The guys that don't lift are going to be a lot quicker around the course.

Gear use in the '66 BB would be about the same although you might want to just keep it in fourth through Turn 2. The overall first through third is about the same as your '69, but not as many useable revs, and then there is a big gap to fourth. Overall, the '69 will probably be a much better track car, but the '66 should be able to achieve more speed on the straight if you're willing to let it rev over 5500.

Kent is a great course, and someday I'd like to run it again. Remember, I ran this course with J-65 metallic drum brakes and mid-sixties vintage first generation Michelin X radial tires, but back then the pavement was probably a lot better. The extreme front end lift of the C2 at 140 MPH made it somewhat reluctant to turn in to Turn 1 flat at 140, and I recall there were some ripples in the pavement that made the car skitter a bit sideways, but, hey, back then I was immortal!

Duke

P.S. Suggest you install a set of AC R43 or equivalent heat range plugs the day before the event. They should not foul out with just one cold start and drive to the track. You can then swap them back out after you get home. Street heat range plugs are too hot for serious track work. They can overheat and get the engine into detonation, and with open exhaust (I ran cutouts) you can't hear it. The OE AC "4" heat range is too cold for the street, but probably too hot for the track. I ran AC43s at the track and AC 45s on the street.

 

Coming out of 9 on the back stretch, the course no longer cuts immediately all the way over to the drag strip. Think this was revised 3 or 4 years ago. After exiting turn 1, the course now parallels the drag strip well past the staging lanes for about 150-200 yards, then dog-legs left back onto the drag strip.

As you mentioned, the etrance to turn 1 is the best place to watch races as the cars come out of 9 jamming gears and drifting as they jocky for position going into the first straight stretch. This is where the track takes a slight right before paralleling the strip. This corner sometimes puts their outboard tires in a gravel/weed patch that runs inbetween this portion of the track and the drag staging lanes. I'm surprised they haven't paved over that patch as it's the only asphalt-locked gravel patch on the track. Looks to me like a roll-over hazard. Yikes - but makes spectating that much more exciting.

Anyway, having toured the track with both Corvettes and using your advice, I can run through the gears in my mind's eye. The first hairpin feels definately like a 2nd gear corner to me - it's very, very tight, all the while dropping downhill directly into the next hairpin that exits uphill. The first hairpin certainly generates a lot of outward inertia - and spins the most cars on the track.

Regardless the speed, I love the sound of the 427's N11 when down-shifting heading toward the hairpin! This is going to be a blast... Thanks again. And I'll muster a report when I've gotten around to driving it for real.

PS- And next time you come on up to Seattle - take your pick of a '69 or a '66 and we'll go for a spin around the track!

 

I'll take you up on your offer if I ever get back to Seattle. Last time was 1993. I recall in a race back in the sixties a car spun on the transition out of Niine to the dragstrip and ended up in the pits! They put up concrete barriers after the last time I ran Kent in '68, and now it sounds like they've changed the course in that area to slow it down, which make sense.

If you now transition onto the drag strip at lower speed, then you won't be approaching One as fast, so maybe your gearing is just right. I know back in the sixties the length from the exit of Nine to the brake point at Two was effectively "straight" as you could accelerate at WOT out of Nine, throught the sweeping transition onto the drag strip and flat through One until you reached the brake point for Two. Believe me, that section was one hell of a Z-ticket ride 40 years ago - like a combination of an autocross and a one-mile drag race. That's why I love road racing!

The second hairpin is a bit tighter than the first, but the first has what is effectively a decreasing radius entrance. That combined with the fact that the entry is downhill can make the rear end light and it's probably the most common place where guys spin - or if you know you're too hot, you can just take the escape road if it isn't coned off. Like I said - in easy - out hard! BTW, I never spun at Kent - in fact, never spun in probably something between 5000 and 10,000 miles of race track hot lapping and SCCA racing. I spun on the street twice - not far from the house where I grew up in Magnolia. Once on a wet Magnolia Blvd. (1964) and once I was wet (Viewmont in 1966). That was my last spin and both were in the SWC, but neither resulted in damage.

One other thing I'll mention is about shifting. Novice driver's - especially those who have drag raced - have a tendency to use "drag race shifts" on road courses. This is both unecessary and undesireable. Each engine-trans combination has a "natural shift speed" based on gear spacing and how quickly the revs drop. With a CR trans and the OE 30 pound flywheel the revs should drop off fast enough to make reasonably quick shifts, without shockloading the drive train. Find this pace and stick with it.

In road racing, you want to develop both an upshift and downshift technique that results in 100 percent absolute positive engagement of the next gear. Trying to speed-up shifting at the risk of missing a gear is not worth anything timewise and is tough on the drivetrain. The key to quick road course times are nailing the braking points properly and using the proper lines through the turns.

Yeah, let us know how it turns out!

Duke