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.
The most recent updates are at the top, so if you are new to this page, start at the bottom and work upwards!
(photo courtesy Julian Hunt)
.. And we're up and running! The CIRC Duster debuted at Easter 2014 Festival of Power at Santa Pod, and steady progress has seen the car work down to 6.59 secs at 222 mph. Much more to come yet!
The wiring and plumbing is under way - quite a large task on a turbo EFI car!
The titanium driver's shield, carbon tubs and permanently attached areas of tinwork have now been finish-fitted.
The exhaust system has been finish welded. Back-purging the tubes during the welding process ensures a nice, clean, fully penetrated weld with a tidy bead on the inside of the tube as shown in the RH photo.
From left to right: the powder-coating has been completed, the trans cooler fitted and an aluminium cover for the brake master cylinder reservoir has been fabricated.
Body and paint is under way at Przym Painworks, and here is a sneak preview of the detail work as Paul Przybyl applies the decals.
In the midst of stripdown for the final welding session before the car goes to paint.
Left-hand photo shows the rod operated throttle linkage with fabricated pivot on needle roller bearings.
Centre photo shows the finished Bruno overflow tank.
Right-hand photo shows how the billet aluminium control handles made for us by Tom Atkinson flow with the rest of the interior.
The throttle pedal and adjustable stop has been constructed. Still to add is one more small bracing tube from the chassis pivot to the firewall, this will be added once the firewall has been welded in place.
Shown above is the CIRC-fabricated titanium shield fitted to the rear of the funny car cage. Though this is not a mandatory requirement in Pro Mod, for an additional 3 lb or so in weight we feel it is a very important safety item to have on the car.
We are making a custom cowl hood for the Duster - shown here is the beginnings of the steel pattern. The plan shape of the original Duster cowl has been preserved, but the whole thing raised and reprofiled to clear the Moran Motorsports intake manifold and throttle bodies.
The overflow tank for the Bruno has been fabricated and mounted on the passenger side of the dash bar. The Bruno units can 'breathe' quite heavily, and this tank will be plumbed into the top of the Bruno so any trans fluid can vent into the tank whilst on a run, then afterwards the fluid can gravity-drain back into the Bruno case. A breather tube will run from the top of the tank through the firewall, and be capped with a small filter.
The left-hand photo shows the front part of the aluminium bellypan, which runs from the rear of the tanks to the engine midplate. Whilst the diaper is a mandatory item in Pro Mod the belly pan is not - however, for less than 5lb of weight we feel that it is a good safety item for catching any stray drips outside of the engine's bottom end.
The other two pics show the vented cover which fits over the breather tank tray in the trunk lid area. This Dzus-on cover will be painted body colour to blend in with the rest of the trunk lid.
The fuel and oil tanks are now finished and mounted.
The upper section of the firewall has been fabricated.
The Racepak dash and shift light are mounted on the swing-away steering column.
This aluminium panel will mount the BigStuff3 and Racepak systems. The panel will be Dzus-mounted for ease of access and, if necessary, removal.
The left-hand photo shows the exhaust wastegate location as well as the beginning of the w/g outlet pipe. The other two photos show the aluminium intake pipes with the intake wastegates fitted. Also visible here are the tank support straps, and the various filters and electrical components mounted around the front of the chassis and motorplate.
The exhaust manifold tubes have now been completed, plus the turbo outlet pipes have been fabricated. In the LH photo you can also see the start of the intake pipe emerging from the turbo compressor.
The project takes another big step forward with the arrival of the custom billet intake manifold from our turbo & EFI partners Moran Motorsports. We are very pleased with this piece!
The 96" single wheelie bar has been fabricated and mounted. The centre photo shows the central 'turnbuckle' which allows the wheel height to be quickly adjusted by slackening off the rod end locknut, turning the tube it is screwed into, then tightening the locknut, a process which only takes a few seconds.
The fire bottles and CO2 bottle are mounted to a tubular frame, which in turn is bolted to the chassis in front of the passenger side wheeltub. The ECU and datalogger panel is planned to be in a similar area, keeping everything out of the way of any converter/transmission work whilst being easily accessible, and also partially offsetting the mass of the driver.
The window frames and door handle mechanisms have been fabricated. The door handles have been designed to mirror the chute release lever, and the RH photo shows how the handle will be accessible through the window via this carbon 'teardrop' trim panel.
The brake pedal and FIA-mandated foot transbrake pedal in place. The centre photo shows the heavy-duty spring loading of the transbrake pedal which makes it feel somewhat like a road car clutch pedal. This mechanism is then covered by the footpad shown on the right to give a nice, clean appearance. This footpad is a 2-piece design using thinner aluminium for the folded frame structure with a 3mm thick tread-plate panel fixed to it, giving a lightweight but stiff foot support. The whole unit will eventually be Dzus-fastened in place to the floor and chassis.
The almost-completed fuel and oil tanks sitting in place in the chassis.
The oil tank under construction.
The breather tank under construction. The centre photo shows how the breather outlets have been enclosed in a catch-tray which, when the tank is mounted at the rear of the chassis, vents out in the rear deck-lid area. The outlet pipes will be finished with small filters, whilst the tray will be covered by a Dzus-on, louvered panel which will follow the profile of the existing deck.
The tinwork has now been started. The bulkhead and driver's side floorpan will be in steel as per the FIA/MSA regulations, everything else will be in aluminium.
First time on its wheels - 4th Feb 2012.
Close-ups of the column mount and chute pull arrangement. The column mount is fabricated from moly tube and sheet. The actual outer column is only a few inches long, the inner shaft runs on needle-roller bearings in this outer column, plus a spherical bearing mounted into a bracket at the firewall by the steering U/J.
Two views of the driver compartment showing the swing-away steering column, the airshift buttons for the Lenco and - between the handbrake lever and the airshift mount - the small handle which will eventually release and lock the steering column.
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.