by Barry Schonberger with Bob Jardine and Tom Patton
In 1975 STOA reprinted an article by L.C. (Bud) Bohrer, the 1974 SCCA Solo II “B” Prepared National Champion on “How to Autocross a Prepared Tiger.” To this day, that article (see attached) remains an excellent reference for preparing a Tiger. In the 14 years since that article was published, SCCA Solo II rules have changed considerably (they even let us run tube frame cars), so a few comments are in order. My reference points for this article are two MK I A’s and an MK II that have won consecutive Divisional Championships in competitive SCCA Divisions and one SCCA National Championship. Preparing a car is like climbing Mt. Everest; the goal is to get to the top, but there can be a wide variety of successful paths taken to get there.
Start here before you invest big dollars in your engine. All of the power that money can buy won’t get you around the course unless you can get the power to the ground and make the car handle. Starting with the front end, don’t hesitate for a minute to reinforce and rebuild the cross member as to the specs in Tom Hall’s and Torn Ehrhart’s tech tips. The stress that the front of the car will take when you bolt on race rubber is well beyond the original design. Pay special attention to the welds around the shock tower and A arm bushing sleeves. Check the threaded plates where the lower A arm attaches. Don’t hesitate to tack weld the upper ball joints in place. Also, you must reinforce the sway bar clamp bracket slot in the lower arm. (Tom Patton failed to defend a Divisional Championship one year because of this failure). A strip of metal welded across the top will do the job. All inner A arm bushings should be replaced with a solid material impregnated with a lubricant. The solid bushings give the driver a much better feel for the road and eliminate the suspension settings changing as a result of the rubber bushing flexing. ‘The upper A arms may be lowered at the shock tower to obtain an improved roll center and improved camber gain. A 1″ solid or preferably hollow front sway bar set in solid bushings seems to do the job. I would recommend Koni shocks on the front set full hard. Because of the front wheel spring rate on a Tiger, the springs need all the help they can get a spring rate of 250 lbs. and custom 70/30 shocks would be optimum.
Concerning front springs, I found the CAT replacement springs acceptable when used with the rubber seats. I have known people to run them without the rubber seats to lower the car. A hard to get item, but one that makes a world of difference, is a quick steer rack and pinion as offered by Bill Miller in the 70’s. This unit reduces the lock to lock from 3.2 to 2.6 turns, providing a real asset in Solo. (This rack is no longer produced). Front-end alignment was 1.5 degrees negative camber, 3.5 degrees castor and 1/16″ toe out. Toe out helped the car turn in faster.
Current Solo II rules allow 12″, 13 “, or 14″ x 10″ wheels or 14”, 15 “, 16″ x 8″ wheels. The only two wheel sizes that are even up for consideration are 13″ x 10″ or 15″ x 8″. The reason for that is the availability of race tires from the major manufacturers. The current situation is not good. The 13″ tires are still being developed, but not for cars in the Tiger’s weight class. Only two companies have 15″ tires available with a third possible in the future. However, limited development is taking place in this area. The big advantage of the 15 ” wheel is the possibility of running bigger brakes. If you choose that route, however, you will be considered a GT spec car, rather than production, and may have to run the 10% weight penalty (not a good idea with a production car). The best answer seems to be a 13″ tire, 9″ to 10.0″ tread face by 20″ or 21 ” tire circumference. This tire is available from a number of manufacturers. When considering wheel offset, remember the stock front suspension geometry win only accept a 3.5″ backspace before the rim hits the rack and pinion arm. Most applications are only 8″ rims in the front because of this clearance problem. With a 10″ front wheel the offset is to the outside, causing scrub problems because of the design of the spindle and Akerman angles. (Look for new rules allowing 16″ X 10″ wheels in 1992.)
The rear suspension can take on a number of different configurations. I found that the forward spring mount needed to be reinforced. It’s very common for this area to be rusted and cracked. I used the CAT springs in their hardest arrangement. Bob Jardine uses stock springs with additional clamps on the front half of the spring to prevent spring windup. I tried a number of different approaches to traction bars before I discarded all of them and went to Ford Mustang quad shocks. Talk about eliminating wheel hop and being able to launch a car, these babies do the job! Brackets were fabricated for the inside of the frame rails and the axle tubes. Credit for this application goes to Bill Miller, who was familiar with the use of shocks as a torque reaction device on the Hollywood car. The rear axle was raised in the chassis using 1 ” blocks at the spring pads. Blocks could be eliminated by de arching the rear springs. This, in relationship to the front ride height made the car just a hair higher in back. Under acceleration, the suspension would even out. A new panhard rod running from driver’s side to passenger side was fabricated to allow for rear roll center adjustment. A 3.73 LSD with the MKII wide ratio transmission allowed for the car to be driven in only 2nd gear on most courses. Shocks were Sprax Adjustable, set on three clicks or in Bob and Tom’s case, Koni’s set full soft. The softer setting allows the power to get to the ground. I didn’t install a rear sway bar. The car only pushed in tight off camber turns and I would compensate by braking deeper in those comers and getting the rear end to come around. Both Bob and Tom used a 5/8″ rear bar. Stock springs and a bar just might have the same roll stiffness as the CAT springs. Bob likes the stock springs with a 5/8″ bar, because it “gives me a little more compliance on the rear with rough surfaces.” I ran a disc brake conversion on the rear, and Bob ran the LAT disc option, but we’re not confident that it helped in the Solo application. My rear wheels were 13″ x 10″ with a 4″ backspace. The car did have Gremlin metal flares on all four comers.
Use a soft street Datsun Z car pad. No metallic or semi metallic, because they don’t heat up fast enough. Datsun pads give you a little extra pad area. Braided brake lines with an adjustable brake bias in the rear line were installed. Bob kept his brake booster, because “It is a lot easier to modulate the brakes if you don’t have to stand on the pedal!!” Bob also suggests “looking at Datsun for rear wheel cylinders that are direct replacements for the Sunbeam, but of different diameters.”
With the new rules, you can run a 302 bored out .047″ over with any head. This appears to be the hot ticket in the Tiger vs. small block Corvette game. A number of Tiger owners have installed SVO aluminum heads with success. Other full comp heads could be a problem when it comes to headers. For Solo purposes, you want your torque range to be very broad, i.e. low duration, high lift and possibly a split profile. Unless you use a roller cam, it is difficult to get this profile. Big dollar item, but could make the car very drivable in one gear. As a starting point, I found the General Kinetics Co. “Redline” hydraulic cam with 290 Duration 438 lift strong (this area needs more discussion). Because of the RPM range involved and the torque needed, the Edelbrock Torker II with a 600CFM double pumper was used, and time was spent timing the carb (see reference book at end of article). A good electronic distributor with a computer ignition will do wonders in Solo because of the ability to keep the plugs from fouling. If you want to save a little weight on the front of the car, use an early timing cover with the exposed impeller aluminum water pump. A bigger radiator core is a must, along with an electric fan upfront and 6 blade behind. An electric water pump drive comes in handy also to cool things down between runs. You are very limited when it comes to headers. The lack of space is your problem. A set of headers from CAT or J.C. Whitney will do the job.
Don’t go too radical with your compression ratio if you intend to drive’ on the street. Ratios in the 10 to 1 range give you the power without excessive heat and octane problems. Compression does help torque however. Oil control in comers is a problem with the small block Ford. For Solo purposes, a Boss pan and windage tray will solve most problems. However, the investment in an Accusump system is recommended. For Solo, you might have your engine builder set the engine up with pretty wide main and rod clearances. You don’t get much of a chance to warm the oil, and the clearance helps. Bob recommends a good oil cooler to help in cooling.
Engine and Transmission Mounts
Drill an extra hole and add a 5/16″ bolt to the driver side mount. Weld up a solid mount on the passenger side. Bob says enlarging the plate on the tubular transmission mount can control wheel hop. This restricts the movement of the rubber mount.
The Dana 44 rear end is plenty tough for Solo. The Power Lock LSD is as tough as they get with its four spider gears. You might consider shimming up the LSD so that the release pressure is higher. Use a gear lube additive to control clutch chatter.
Quick acceleration and engine braking are important elements to a successful Solo car. For Solo II, a double or triple disk, racing clutch is essential. With its lightweight (18 21 lbs.) and small diameter (7 9 inches), the racing clutch will make a significant difference. McCleod makes one of the best, followed by RAM and Quarter Master. The down side of this clutch is its in/out characteristic. There is very little feel. Starts can be a problem, it is not streetable and for a Pro Solo launch, you lose the weight of the flywheel. Use a soft diaphragm spring if available with not too high a ratio.
You might also consider an internal throwout bearing slave cylinder. Manufactured by Tilton, QuarterMaster and others, this item has proven to do the trick. Alignment and spacing are critical in the setup. Certain models only work with certain clutches because of clutch finger design.
A good Carter, Holley, etc. fuel pump with a constant 5 – 6 lb. pressure is what you need. Install a good, large capacity fuel filter because the Tiger fuel tanks will peel their lining. If you’re in a hot climate, consider a cool can to chill your fuel. It can be located where the brake servo once lived. The stock metal fuel lines are acceptable.
For additional information, don’t hesitate to contact me.
(812) 985 9592
Does anybody have a copy of this article by L.C. (Bud) Bohrer, the 1974 SCCA Solo II “B” Prepared National Champion on “How to Autocross a Prepared Tiger.”
Use the contact form and let us know. We’d love to be able to reprint it here.