April 3, 2018

1966 – 1969 Mopar B-Body Radiator Upgrade

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Project 22” b‐body upgrade started with an inquiry about an “original owner, numbers matching” ’68 Road Runner owned by a fellow named Charlie in Sacramento, Calif.. Charlie stated he bought the car in ’68 when he returned from Viet Nam and will have this car until he dies. Over the years the car has gone through a lot of transformations with upgrades to the original 340 horse 383, suspension, and chassis components and has always “run warm since day one”, in his words. About 10 years ago the engine was bored 30 over and a .545 cam installed to go rally racing and an original air conditioning unit from a donor car was installed. Over the years he’s tried several versions of a 22” radiator to keep this monster cool to no avail and asked if we could help. The correct way to approach a project like this would be to change the core support to a 26” which is how this car would have come from the factory with “factory air”, and install a 26” wide radiator to complete the upgrade. In uni‐body cars that’s a fairly labor intensive and expensive path for most vintage Mopar owners to go unless doing a comprehensive restoration. Charlie stated, “I don’t care what you do or how long it takes as long as I can drive the car without overheating” so we set out to do just that in hopes of creating several bolt in product’s to deal with 60’s cooling system engineering issues we were aware of.

The first step was to test all aspects of the cooling system to see where improvements could be made including the actual design of the radiator and mounting efficiencies/deficiencies as it relates to “air‐flow”. Throughout the 60’s Chrysler radiators were produced with a “bucket header” design on all 22” wide units and a “flat header” design on 26” wide units used on big blocks with air and Hemis. During the same time period Ford used the same top tank bucket header design on most of their small to medium horse power and wheel base cars as well. However, by 1970 Chrysler discontinued the use of bucket headers and changed the 22” radiator top tank to mount to a stronger flat header design thus preventing top tank seam failure from the higher pressure created by coolant expansion at higher temperatures. Ford made the change in ’67 on big block cars and by 1970 the bucket header design was no more.

Knowing the better style radiator for high horse power and performance began in the 70’s we began by building a 70’s style radiator, both in 22” and 26”, to mount in a 66‐69 B‐body 22” core support for big block’s and high horse power cars. By doing so we were able to move the radiator and core closer to the core support which not only created some additional room between the radiator and engine but more importantly created greater airflow through the radiator by reducing the gap between the condenser and radiator core. Other problems we found with air flow on this car was the mounting of the pusher and puller electric fans and re‐circulating engine compartment heat rather than pulling ambient air through the grille.

Once we designed the Chrysler styled radiators (22” and 26”) to fit the original 22” core support and center on the manual fan, along with an electric fan kit and available shrouds for both if desired, we focused on maximizing air‐flow at all performance ranges and came up with an upper grille to support air dam that increased through the grille ambient air by 18%. The overall tests were VERY GOOD and the pictures pretty much tell the story step by step.

Project Car:
1968 Road Runner
383 cu in. bored 20 over
.545 Comp Cam
Crane Fireball Hi-6 ignition
Holley Terminator EFI
Estimated 400-500 HP
Non air car with 22″ core support
Aftermarket 22″ 3 row radiator core
Flow Kooler water pump
180 Mr Gasket thermostat

Initial Air Flow and Coolant Temp Tests:
1.0-1.3 MPH @ 1000 RPM idle air flow with unshrouded 16″ electric puller and pusher
200 degrees at radiator inlet holding
50 MPH @ 3000 RPM (2nd gear)
225+ degrees and climbing

Final Air Flow and Coolant Temp Tests 22″ and 26″ Radiators @ All RPM Range (160 stat):
5.0 MPH idle air w/ shrouded dual 11″ electric pullers
6.0 MPH idle air w/ 17″ 7 blade shrouded manual fan
18% air gain on both with a grille to core support air dam
175-180 degrees w/ electric fan and shroud 22″ radiator
155-165 degrees w/ manual fan and shroud 26″ radiator
Replace 180 degrees stat

1) Air flow and temp test to get a starting point.
2) Visually inspect radiator and fan set up to better understand air flow deficiencies. Un‐shrouded puller fans and pushers only utilize a small amount of the radiator core and the design of the bucket header radiator pushes the core away from the core support which will increase gap turbulence between condenser and radiator. The owner agreed to allow us to change to a later 70’s style Chrysler 22” radiator and narrow that gap and minimize air flow around the core at speed.
3) Remove radiator, condenser, and dryer to gain passenger side space for larger 26” unit. Moved dryer forward of core support.
4) Visually inspect existing radiator for blockage and found some debris but adequate flow which confirmed inadequate heat transfer for this engine with air conditioning. At this point we decided to build a 4 row Optimum (1/4” fin) core and “Triple Flow” with tank baffles to replace original unit and install a 160 degree stat to get everything working earlier. This plan would also require an add on trans cooler mounted to the condenser.
5) Once we made the necessary bracket changes to mount the shroud and later style 22” radiator all tests indicated we had solved the overheating problem with little or no changes to the original core support. Slight modifications to the shroud where it meets the new style top tank were made and we moved on to our original goal.
5) Once we made the necessary bracket changes to mount the shroud and later style 22” radiator all tests indicated we had solved the overheating problem with little or no changes to the original core support. Slight modifications to the shroud where it meets the new style top tank were made and we moved on to our original goal.

6) The ultimate goal was to design a 26” radiator to match the original appearance and performance of a big block w/ air that’s easily mounted on to a 22” support, center on the exiting manual fan with shroud, and allow for height clearance with the hood. Several changes were made to the radiator and bracketry but once the unit was aligned with the engine and manual fan and clamped in place only four ¼” mounting holes were all that was need to complete. Note: the stock Chrysler 26” unit when clamped in place with clearance on the bottom of 22” core support and centered on the fan the hood would not close.
7) Once mounted and tested we moved on to finalizing air flow efficiencies by making and installing an air dam over the air box in front of the core support. This one simple step increased air flow by 18% at idle by minimizing recirculating engine compartment heat and forcing grille air to flow through the condenser and radiator at speed.
8) The final touch was making a 1‐quart aluminum overflow bottle to maintain a sealed system to handle engine‐off expansion and eliminate air from entering the system at cool down and mounts to shroud mounts on Passenger side.
22″ square tank radiators for 66-69 B-bodies can be found here.
26″ radiators for 66-69 B-bodies with 22″ core supports can be found here.