A Tale of a Race Winning Rx7 Chassis

During the past Pandemic Christmas holiday, I decided to retrofit a decades old slot car race track for the digital age. My young son had been absolutely captivated with it nearly two decades ago and one day there might be grand kids to continue the tradition. I had to convert each analog car to digital by soldering in a Bluetooth enabled circuit board so that each car could be controlled wirelessly and up to 6 cars could race at once on a pair of slotted tracks. Now with lane changing and pit stops and computer controlled pace cars to provide traffic.

I have the Le Mans winning Mazda 787B in slot car form. But not a first generation racing Rx7. They never made one in 1:32 scale. I would have to make my own and I got a head start buying a vintage radio controlled toy Rx7 that happened to be in 1:32 scale. But what race version of the Rx7 should I make it? In the 1980s the Rx7 was a highly successful race car and there are many versions to choose from.

With the announcement of the exciting new Rx7-SA model, the Mazda factory sent two race prepped Rx7s to the 1979 Daytona 24 Hours Race.   Car #7 would be driven by the Japanese team of Katayama, Terado, and Yorino and Car #77 by the American team of Walter Bohren, Jim Downing and Roger Mandeville.  Car # 7 finished 5th overall and took the GTU class1, while #77 came in 6th overall.  Shocked at the Rx7’s performance, the IMSA officials immediately reclassified the peripheral port engine with a 458 lb weight penalty by changing the car weight allowance from 0.9 lb/cc displacement to 1.1 lb/cc.2 The factory cars were sold to Mandeville and Downing  and a #79 Rx7 built by Dave Kent of Creative Car Craft in Hawthorne, California for the Sports Limited Racing Team and driven primarily by Bob Bergstom.   As the 1979 season wore on, the weight penalty ruling was reversed but not before Don Davendorf’s Datsun 280ZX clinched the GTU Driver’s and Manufacturer’s Championship.  Although Bergstrom DNF at Daytona, he did score a 3rd at Road Atlanta 75 Miles GTU, 4th at Laguna Seca GTU,  2nd at Sears Point GTU, 5th at Portland GTU, 9th at Road America (1st in GTU), and 4th at Winston GT Road Atlanta to secure the second place in the GTU championship as did Mazda as a manufacturer. 

79Rx7

Bergstrom did not fare as well in 1980 but Rx7s from many other teams did win all but three races in its GTU class and Mazda easily took the GTU Manufacturer’s Championship.  #79 was sold to the new Dave Kent Race Team for 1981 season to become #92 and repainted white while retaining her original name that Dave had given her in 1979, Lulu.   A sister car #98 was painted red and driven primarily by Walter Bohren while #92 was driven by Lee Mueller3Kent Racing dominated 1981 and won 11 of 16 races.  #92 won at Laguna Seca, Bainerd, Portland, Mosport and Road America and gave Mueller the GTU Driver’s Championship and Mazda once again the Manufacturer’s GTU Championship. 

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Dave Kent himself working on the Lulu (actually named by his youngest daughter, Candis) chassis! The widebody kit would be manufactured and sold for many years to other race teams and Rx7 owners wanting a boy racer look. Creative Car Craft had a long history of modifying and custom building cars for a wide variety of customers. Indeed, the dominance of the 1981 season by the Kent Racing team is due to their many engineering innovations. #92 and #98 were virtually identical cars except #98 had an advanced aerodynamic ground effects package with an inverted wing behind the front spoiler and a smooth underbelly pan to facilitate the creation of a vacuum. David Benson Kent died in 1999 at the young age of 57.

 

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The legacy Kent Racing widebody kit is still available for purchase today but is custom made when ordered. The “cassette tape” opening in the front air dam is made up of a square cold air intake and a rectangular opening for the radiator.

 

KentRacersComparedtoStock
Kent Racers as compared to the stock Mazda Rx7. Described as impressive, brutal and sensual, I missed experiencing this era of racing first hand as I was just entering highschool but the Rx7 still made an impression because my extremely cool English teacher drove one, a standout in a parking lot of otherwise miserable vehicles.
KentRacers
The rotary engine has been relocated 6 inches rearward (right against the stock firewall) and 2 inches lower, intake and exhaust porting shape changed to regain lost horsepower after IMSA denied fuel injection to rotaries for 1981, power is nearly 300 bhp. Dave Kent learned from racing at sand infused Daytona that the rotary can only tolerate clean intake air since any ingested particulate will score the chrome surfaced combustion chamber walls and reduce compression. In a long race, gasoline seepage past the rotor seals will dilute engine oil so Kent designed a quick dump dry sump oil system allowing 2 minute oil changes. Kent is considering replacing the plain bearings in the eccentric shaft to needle bearings to allow reliable rpm over 11,000. Front and rear suspension is totally modified although the location of the rear axle remains stock but the differential is not and a carbon fiber driveshaft is used being much lighter and stronger than steel. Finally 11 inch wide (front) and 12 inch wide (rear) three piece alloy Hayashi wheels are used.

1982 started well at Daytona-24 Hours with #98 placing 6th overall but winning GTU, #92 placed 7th overall.   #98 was driven by Kathy Rude, Lee Mueller and Alan Moffat.  Both Kathy and Alan were Canadians, with Kathy born and raised in Victoria, British Columbia. She became the first female driver to win an IMSA race and the first woman to win a major professional road race in the US.  Then Dave Kent received a far too enticing offer from Toyota to run their GTU team with a pair of Celicas.  Unfortunately the move away from Rx7s did not go well and Toyota terminated the relationship at the end of September.   #92 made one final appearance in the Daytona Finale at the end of the season and DNF.

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1981 Road America race with #92 finishing 8th overall to take first in GTU. Seen leading #11 BMW M1 which finished 9th and took first in GTO. Even in 12A engine form the Rx7 punched well above its weight class.

This is a short 8mm film transfer of the 1981 Pocono IMSA race showing #18 winner Porsche 935 of infamous4 father/son team John Paul Sr/John Paul Jr passing #92.   #98 won the GTU class with #92 just behind it.

Kent Racing no longer had Mazda factory backing so they found a new sponsor with Firestone Tires and ran their performance S-660 H rated street tires for racing!! #92 redeemed herself at 1983 Daytona -24 Hrs with a 12th overall place (1st in GTU) but the last time #92 was seen with Kent Racing was at Riverside in April with a 28th place finish and a new red livery.   #92 was apparently sold to Dick Greer Racing and she amazingly soldiered on until early 1989 (and had her number changed to #82 in 1985) but without victories.

Red92Rx7

FirestoneAd
You can see how happy Firestone was with #92’s Daytona win in January 1983 with their full spread 2 page ad in Popular Mechanics. It is impressive that a street tire rated at only 130 mph could endure 160 mph speeds, 2000 miles of race torture and provide enough grip in the dry when others were running racing slicks. Sadly this was Firestone’s last hurrah as the company was hemmorhaging money from its disastrous 1970s era radial tire and the company was sold for a fraction of its worth in 1988 to Bridgestone.

#92 was reacquired in 2017 by IMSA driver Kelly Marsh who drove #98 rebadged as #93 and repainted teal for the Mid O Race Team.  #92 was thoroughly restored and painted in her 1983 Firestone Red livery and was awarded the most historically significant IMSA car at the 2020 Amelia Island Concours.    The first generation Rx7 won 8 straight GTU driver’s and manufacturer’s championships from 1980-1988 and won over 100 class race victories and is regarded as the most winning car model in professional racing history. 

AmeliaIsland92Rx7

  1. GTU – Grand Touring cars under 2.5 L. 13B engined cars contested in the GTO category. GTX was the top class.
  2. For the 12A engine, each rotor has a combustion chamber displacement of 573 cc. To convert rotary displacement to a conventional 4 stroke piston engine we see that a complete combustion cycle takes 720o of crankshaft rotation in a 4 stroke. In the rotary, 720o exposes only 4 of the 6 rotor surfaces to combustion so 573 cc x 4 = 2.292L engine. At a 0.2 lb/cc weight penalty = 2292×0.2 = 458 lbs
  3. There is some confusion as to whether the Bergstrom #79 chassis ended up being #92 or #98. Despite the conflicting sources, I’d like to think that #79 became #92 became #82 and then was saved, restored and honored in 2020.
  4. John Paul Sr had a near psychopathic level of rage and was charged with marijuana smuggling and then later with attempted murder as he shot a federal witness in the case. He fled the US and was recaptured, served 11 years of a 20 year sentence and then disappeared after a woman he was dating was found dead. Without a real sponsor for his expensive Porsche 935 Turbo, he had to finance his race career with alternative methods.

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1:32 slot car build progress of the 1981 Kent Racing #92 Mazda Rx7. You would think that Rx7’s race history alone would earn the respect of motor heads everywhere, but there is still the stench that an Asian designed and built car is somehow inferior. How many road going models of Ferraris, Lambos, or Maseratis have an equivalent race history? ZERO.

If you want to see how the finished car turned out, you can check out my Instructables entry here:

https://www.instructables.com/Making-a-132-Scale-Mazda-Rx7-Slot-Car/

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