Chris Isaacs Race Cars and Spencer Tramm have teamed up to construct and campaign a twin-turbo 1970 Plymouth Duster in the prestigious MSA British Pro Modified Championship. This page details the buildup of this exciting race car.
We are endeavouring to update this page every 10 to 14 days, so check back regularly. The most recent updates are at the top, so if you are new to this page, start at the bottom and work upwards!
The aluminium seat has now been fabricated and fitted into the support frame on Dzuses. This seat pan is made using our own technique which rolls the whole seat out of a single piece of aluminium.
The Lenco sliders are now fabricated.
CIRC fabricated aluminium wing with adjustable flap.
The support structure for the wing and dual spring-launcher chutes is now made.
The chrome-moly driveshaft tunnel with integral front propshaft loop has been fabricated and installed. The front, cylindrical section of this is rolled from 0.050" moly as per FIA/NHRA rules. The rear, round-to-oval section is constructed from thinner material to save weight whilst maintaining a good level of protection.
As the screen area and sill of this body are not linked, and the body is to be removable for maintenance, we have fabricated this section of tin which both ties the screen and sill together, and forms the bulkhead seal at the leading edge of the door.
The completed seat frame. The thin steel sheet is wrapped around two small diameter chrome-moly tubes for a light (10 oz) but strong support for the driver.
Driver's eye view of the CS2 Lenco cases dummied into position for mounting purposes.
The forward part of the seat frame has been installed.
The carbon wheeltubs being fitted. CIRC's Jedd Guy is seen here handling the tub installation.
The whole bodyshell will be removable for ease of access, so the door latches are mounted to the chassis and the door shut area Dzus-fastened into place for quick 'unbuttoning'.
The driver's side exhaust manifold has been tacked up. The rather complex routing allows for as close as possible to equal length primary pipes within the fairly limited space available, with the pipes feeding into the collector in firing order.
Early stages of exhaust manifold construction. Material is 304 stainless steel with 321 stainless double-slipjoint collectors.
The main turbo mounts use a 4130 strap bolted through the turbo oil-drain flange bolt holes. Although the turbo appears to be bolted solid to the short mounting tubes, the detail design of those mounting spigots allows it to 'float' a small amount in the horizontal plane to allow for header growth due to heat.
The door hinges have also been fabricated.
The turbo position has been finalised, and a simple fixture made to hold them in place. One of the few downsides of the Duster body, for a turbo application at least, is the relative lack of space between the wheel and the A-post, necessitating the turbos to be turned quite a bit inwards. There will be a 6" diameter, aluminium bend fixed to the compressor opening which will bring the intakes parallel with the car centreline and inboard from any debris which may be thrown up by the front tyres.
It makes the turbine exit side quite simple though!
The CIRC designed twin-wishbone track locator. A vertical wishbone from the rear of the axle drops to a rod end on the horizontal wishbone...
...which runs underneath the axle housing...
... and attaches to the chassis on the under-axle rails. This setup gives the same location characteristics as a sliding A-frame but without having to use a wear-prone sliding joint.
The chassis is now stripped down for the big weld-up session.
The axle case hung in position on the 1 3/8" OD fourlink bars.
The right-hand photo shows the beginnings of the front anti-roll bar we will be using on this car. Still a relatively unusual feature on drag race cars, we believe there are benefits to be had under certain on-track circumstances.
The axle housing is almost complete, requiring a fill and drain plug plus the housing tubes boring out to take the floater spindles.
With the strut and steering mounts in place, we were able to break down one side of the strut jig and try a front wheel on... all looks good!
The 4-link chassis brackets have been cut and fitted, along with some triangulation in the double-rail area and the strut mountings.
The strut top mounts are under way, and the A-arms made and mounted. The rack mount is completed, plus the steering arms have had a vertical brace added to increase their rigidity.
The chrome-moly sheetmetal axle housing has also been started.
The top chassis rails are in place, as are some of the upright tubes between the rails.
The bulkhead-area tubes can be seen here.
The project has taken a major step forward with the arrival of our engine! A 521 ci BAE with stage 5 heads, this was one of two engines previously run by the Lindberg brothers of 'Rockstar' '68 Firebird fame. We will be using the blower intake manifold shown here, with a fabricated plenum chamber bolted on top for the throttle bodies. This is a cost-effective alternative to a complete sheetmetal intake, and a similar combination in Sweden has shown good power on the dyno.
The main rails are now installed, plus the strut jig has been fixed in position. We are now able to put the front end on properly, and get a sneak preview of how the car will look.
The funny car cage is completed, as are the floor tubes.
The roof x-braces are in place, and the funny-car cage is under way.
The rear chassis tubes in place. The two holes bored in the vertical tubes just behind the axle centreline will eventually carry bosses for the rear damper chassis mounts.
Main hoop of rollcage now installed.
Upper 4-link crossmember in place, as is the start of the rear frame assembly.
The A-post tubes, windscreen bar and dash bar in place.
Set up on the jig with the first chassis tube in place.
Sill bars and forward crossmember in place. Note how the sill bars run 'uphill' towards front, this is to give space for the exhaust from the turbos.
Rear wheels are Weld Magnum Pro double beadlocks, to SFI 15.3. When these were ordered, the black/machined centres were so new that Weld did not yet have a photo available, and our set were among the first they made in this configuration.
Blocked up at ride height with the wheels under the body.
This shot shows why most Pro Mod wheeltubs reach almost up to the roof!
The body is a fibreglass Pro Mod '70 Duster from Andy McCoy Race Cars in the USA, the original Plymouth shape has been extensively modified for high-speed aerodynamics and low drag, yet its origins are still instantly recognisable.
The first job was to plot out all the main components on paper and create a chassis design. Most CIRC customer cars also start out this way, it gives a good insight into where packaging issues might lie and allows them to be addressed before any metal is cut. This particular design uses SFI spec 25.2 for the driver safety cell.
