Pacific Raceway tech help
I am planning on running at next years road race with SOVERN at Pacific Raceway in seattle. I'll be running my 64 FI car in the road race . I haven't run there before and am wondering what rear differential ratio to use. Have any of you run there before? I run a 4:10 at laguna and a 3:90 at Portland if that provides any perspective. Jerry
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Re: Pacific Raceway tech help
I assume you can get a schematic of the course. I always told the guys in SoCal that if they ever ran at Kent, which is "only" 2.25 miles, they needed to install at least a ten percent taller gear than they ran at the 2.54 mile Riverside "short course" and the same length Willow Springs or they would run out of revs on the straight, which effectively starts at the exit of Turn 9 and ends at the entrance of Turn 2. It's probably something near a mile long. I think most big bore production guys run a ten percent shorter gear for Laguna than Willow and Riverside.
Back in the sixties when I hot lapped my 340 HP SWC at Kent, after figuring out Turn 1 and using a traffic cone and broom to mark the apex I was able to do it flat at about 140 MPH on 6.70-15 Michelin X radials. With my 3.08 axle, running out of revs was not an issue. With a 3.70 I would have been at the 6500 redline.
Turn 1 is just a "kink", but you approach it on about a 0.5 percent upgrade, and it drops off beyond the apex, so it's somewhat blind, and it's tough to pick out the apex, which is why on my second and subsequent visits to Kent I brought the traffic cone and broom to mark the apex. It was my aiming point, and I learned to turn in early due to the understeer caused by the front end lift at that speed. Above 130 a C2's response to the helm is about equivalent to the Titanic! There were also some ripples in the pavement at the apex, which caused the car to skitter a bit sideways, which was a bit scary until I became accustomed to it.
This was all pretty thrilling and educational for a 17-year old whose "driving instructor" was Phil Hill's articles in the pages of Road & Track!
From the Turn 9 apex at about 50 MPH in second, I accelerated at WOT through the exit and the bend that leads onto the dragstrip. I shifted to third (about 100 MPH) about the time I straightened out on the dragstrip. This part of the straight is flat. I shifted to fourth (about 130 MPH) at the dragstrip start finish, which is also the start/finish line for the road course. At this point acceleration trailed off due to being in fourth and the upgrade, which is the drag strip shutdown area, but there is still nearly another half-mile to the entrance of Turn 2.
The last time I was at Kent was 1993 as a spectator at a vintage race. There were concrete barriers from the exit of 9 to the drag strip, which weren't there is the sixties. I think these would be intimidating and probably affect visibility down the track. They certainly don't leave any margin for error. Back in my day it was all open, but a couple of guys lost it in this area and crashed into the paddock. I think those barriers were installed sometime in the seventies after I left Seattle in the late sixties.
Turn 2, which I took at about 80 MPH in second gear is similar to Riverside's Turn 9. At the exit you go down a fairly steep hill which leads to the reverse hairpin turn set. The first is decreasing radius and you can trail brake. The second it much tighter, and I was down to about 30 MPH at the apex. I took these two turns in first gear.
Exiting the second hairpin you can accelerate at WOT through the slight bends on the bottom of the course to the chicane. Approaching the chicane near the top end of second/100 MPH, I braked and was able to to use WOT from the exit of the chicane, up the hill to the brake point for Turn 9. So after the upshift to second after the second hairpin, it was second gear all the way back to the transition to the drag strip.
During that '93 vintage race I told my buddy who is a life-long Seattleite that the chicane looked tighter than it was back in the sixties. He thought I was nuts, but I was able to confirm from an old racer that there was a slide in that area some years before. The track had been rebuilt, and, yes, the new chicane is tighter.
Almost every course I have run has one "pucker turn" that separates the men from the boys and makes a big difference in lap time if you perfect it. At Riverside, it was Turn 2 and Turn 9 at Willow. For me it was Turn 1 at Kent. Most of the other turns are relatively low speed or kinks that you can accelerate through flat. I love tracks like this where you come out of a low speed turn and can then can accelerate flat out though the gears through a series of kinks or mild bends to the next brake point. Pure point to point "straights" can be boring, but they give you a few seconds to relax and check the gages.
Given your car's power and weight, I would suggest that you gear for about 160 MPH at peak revs, which is about what I think you can achieve at the brake point for Turn 2 if you can do Turn 1 flat. I figure given your tire revs/mile and 7200 revs, nothing shorter than a 3.70, and maybe even a 3.55. Also, given the speed range from below 40 MPH to over 150, an engine with good torque bandwidth works best, and you should consider using first gear through the reverse hairpins.
In 1967 Mark Donohue set the first Trans-Am lap record (in qualifying) at 1:29.9. I could hot lap consistently in the mid 1:40s. Kent is a very fun and challenging track with a variety of turns and elevation changes, and I'm sure you'll enjoy it if you're geared right.
Given the time that has passed, the difference in car configurations, and changes to the track, you should definitely find a BP driver whose "home track" is Kent and hope he will give you an honest assessment of how you should set up your car.
Duke -
Re: Pacific Raceway tech help
Thanks Duke. Sounds like you had fun. I wish more of us would get the trailer queens out and let em run.
It look like the longest portion of the tack is about 3000 feet with a high speed entrance. I think i would run out of gear with a 3:90. As I recall my tire diameter is 84 inches. My rev limit is 7000 with occasional non planned excursions to 7300. I definitely need to talk to a racer from seattle. I have contacted SOVERN but haven't heard back yet. If anyone knows a vintage racer from the Seattle area please let me know. jerryComment
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Re: Pacific Raceway tech help
I think you mean the circumference is 84", which would be a diameter of 26.73, which seems pretty tall.
If we use the Goodyear 6.00-15 (G7) or 5.50-15 (G12) vintage Blue Streak as an example, the catalog states the diameter for both is 25.5" , which is a circumference of 80.1". Using rigid body physics, it would turn about 791 revs/mile, but since tires are not rigid and have higher than rigid body revs/mile due to deflection and slippage, multiply this by about 1.03, and the result is about 815 revs/mile which is about seven percent more than the 760 revs/mile of my 6.70-15 Michelins that I had back then.
Come to think of it, you may want to go with a 3.36 or even 3.08 axle, and definitely use first gear in the hairpins.
I think a lot of first timers at Kent screw up their gearing unless they do some good analysis and talk to some experienced (and honest) guys in their class, preferably running the same type of car.
The question is whether you can run flat from the Apex of 9 to the brake point at 2. I could back then, but given your better power to weight ratio and changes to the track maybe not, but then you've got more grip and probably as not as much front lift.
I still think the key to Kent is doing Turn 1 flat, but I don't know if a current BP vintage race car is capable. This is certainly something you want to get into with a BP vintage racer who currently runs Kent, but you know racers when it comes to talking about those "pucker turns".
One more thing. Back in the sixties the course from the exit of 9 to the transistion to the drag strip was mostly a very gradual turn that allowed me to accelerate flat out all the way through, and with no barriers and considerable runnoff area, visibility all the way was excellent, the line was wide, and it wasn't too hairy, although I sometimes might have had to modulate the throttle a bit just before finally straightening out on the drag strip.
The barriers that were there in 1993 changed the whole perspective, but it's possible that the course was modified to yield a short straight out of 9 and a smaller radius transistion onto the drag strip, which may preclude doing it flat, and this would definitely slow you at Turn 1.
Like I said, back in the sixties the effective "straight" was all the way from the exit of 9 to the entrance of 2, and that was definitely more than 3000 feet, but that may not be the case today due to changes in the course to slow the cars down.
All I can say is that I definitely liked the layout in the sixties better than I did in the nineties, even though I only got a spectator's rather than a driver's point of view, and I sure loved holding the throttle to the floor as I drifted through Turn 1 at 140 MPH!
DukeComment
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Re: Pacific Raceway tech help
Jerry,
What ratio did you use at Road America?
The track you describe sounds a little like RA. I think we used a 3.70 there with the small block car. Didn't used 1st gear.Comment
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Re: Pacific Raceway tech help
I've run RA many times but never with this motor/tire configuration. THe RPM limit of stamped steel rocker configuration really changes the equation. I suspect that a 3:70 is about right. This puts me around 150MPH top speed which for a long track and 7000 RPM max is about right. JerryComment
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Re: Pacific Raceway tech help
What tire are you running now, and what are the published specs?
DukeComment
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Re: Pacific Raceway tech help
Jerry,
Here's a map/configuration of the track...
And a few laps around the track...
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Re: Pacific Raceway tech help
I'm running a Goodyear 6.00X15 BiasComment
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Re: Pacific Raceway tech help
Well, I guess you can forget everything I said about Kent and gearing back in the sixties and even 1993.
What is now labeled Turn 8 was Turn 9 in the sixties, and the gradual transistion from the exit of this turn to the dragstrip was not a numbered turn back then. It appears that the exit azimuth from what is now called Turn 8 is several degrees to the left resulting in a "real turn" to the dragstrip, and obviously this section is no longer flat out.
So lot's has been done to slow top speed including that hokey chicane just before start/finish that was not there in 1993. Road racers still had the whole width of the dragstrip at that point in time. I'd say a 3.70 would be a conservative choice and a 4.11 may not be too short. The highest speed will still be at the brake point for Turn 2, but it will only be 130-140 MPH.
As far as I'm concerned they've ruined this great track, but I guess they had to make the changes to limit top speed in the name of safety.You would have loved the sixties configuration, especially the balls-out WOT run through the gears from the exit of Turn 9 (now 8) to the brake point for Turn 2 - no barriers, plenty of runnof area, no roll bar, no helmut - just the production lap belt.
Those were the days!
DukeComment
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