Krogdahl Cylinder Heads

Ever since i was a kid i was interested in cars and engines, i think i brought my first car magazine at around 7 years old i borrowed books from the library and found myself reading car magazines, Street Machine & Van Wheels, Performance Street Car, Custom Rodder, Vans Utes & Trucks, Street Rodding just to name a few. As well as technical books related to cylinder heads, engine performance, cams and valves, superchargers the list went on.

One issue that i do remember was about a guy in Townsville who had designed, refined and built his own DOHC, hemispherical, crossflow design twin spark plug cylinder head that could be used on a few different inline 6 cylinder engines. That guy was Bob Krogdahl, It was in 2014 after trying to track Bob down for a few years that we first made contact and after many phone calls regarding the tooling, patterns, core boxes and specialised machining tools some of which have been destroyed or gone missing a meeting was arranged. Bob is in his 70s and has been retired a few years and has many other interests now outside of automotive. Bob flew down to Adelaide and after some idle chit chat a large packaged was put up on the bench and there it was, an early casting that had many imperfections and was not able to be used on an engine. I had finally got to see a Krogdahl cylinder head in the flesh and to meet the man that made it all happen.


Page one from street Machine Magazine. Click on the picture to enlarge.


Page two of the street machine magazine, click on the image to enlarge.

It took Bob 20 years from when he first started the cylinder head to getting the first engine running, As Bob said the first head was fitted to a Holden red 6 cylinder engine fitted to a 6 cylinder sprint car. To start with they laughed and mocked Bobs idea but it wasnt long until people started to change there mind as more development and refinement was done and the sprint car be come a front runner.


On Sunday the 21st of October at 5.15pm in 1990 the first Krogdahl cylinder head took its first breath, Bob tried to get it published in the birth notices in the local paper but wasnt allowed so it was put in the general notices. So it was 20 years in the development, untold amounts of money and no one kept a record of the hours spent over the 20 years.

The Video is of a later Holden 6 cylinder fitted with motec fuel injection and a Krogdahl cylinder head. This engine was one of the later engines built after many of the refinements had been done on earlier engine fitted with the Krogdahl twin cam cylinder head.

The knowledge, experience and theories of somethings that i was lucky enough to talk about in the time i spent with Bob was one of the highlights  of my time in the performance industry. Bob retired around 2004 and with only around 12 completed engines built the engines are some thing i would classify as rare.


We have over 2000 photos and a few videos of the development and processes related to the Krogdahl head that we will be adding to these pages.


aussiespeed manifolds rocker covers carb scoops performance speed equipment


Aussiespeed Blower to manifold adapters

With so many different superchargers available and so many different engines that customers want to fit a blower that wont blow the bank the basic bolt pattern on most of the Aussiespeed supercharger manifolds are based on the Weiand 142 or slightly larger Teflon rotored Weiand 144 .


Ford 6 cylinder EA to AU sohc manifold with the base plate mounting for the Weiand 142 and Weiand 144. From this standard bolt pad Aussiespeed have a range of adapter plates to fit other superchargers.


This is the casting to fit the larger Eaton M112 to the Aussiespeed range of manifolds that will accept the 142/144 Weiand supercharger, the scooped area allows the bypass valve that is built into the supercharger to be fully operational.


The Eaton M112 supercharger can be fitted with the Aussiespeed AS0512 adapter, For fitment of the M90 GM style supercharger Aussiespeed AS0510 is the part number.


The rear top entry was designed for fuel injection, we have a few intake systems also under development.


The M112 dummy fitted up to an AS0038 Chevy inline supercharger manifold, We hope soon to have the proto type supercharger drive snout finished that will be available in various lengths and will be made right here in Australia.

Supercharger component update

We have really pushed forward on getting the proto types done, Our crank shaft hub is done and has the added feature of a steel outer flange that covers the external ring of the balancer, the balancer needs a small shoulder machined to locate the hub adapter then its 3 bolts to bolt it up then another 4 to secure the crank pulley.


We have decided on steel pulleys and hubs for our supercharger drives.


The supercharger balancer crank hub is available to suit different width harmonic balancers. There are 4 bolts to bolt the pully to the hub and the centre of the hub and pulley are both predrilled in the centre for people wanting to thread the end of the crank to fit a retaining bolt. From the balancer face the hub and pulley extend around 50mm


We want to use as many off the shelf parts in the Aussiespeed supercharger kits so replacement parts can be purchased just about any where. The bracket we had used previously with the Terra Charger had a much smaller diameter drive snout . We have modified the tensioner we had and mounted it on the other side of the supercharger belt adjustor.


We tried to incorporate the standard factory weiand sprung tensioner but because we need the tensioner run on the slack / non drive side the spring rotates the arem the wrong way around. We are still negotiating with a local spring maker to make the reverse spring so the Weiand supplied tensioner can be used.


This is the style tenisoner we look like we will go with, it is a bolt on style that uses an off the shelf spring loaded bolt on tensioner that can be used with either a flat or ribbed pulley.


Sorry about the picture quality, with the pieces bolted up you can use the standard alternator position and mounting bracket and v belt this also drives the water pump.


Aussiespeed manifold castings

We will try to explain the work involved and what happens after a pattern is made. Checks that have to be completed of the sand mold and the core to ensure metal thickness is right in the void that is filled with metal. There are many other factors that have to do with castings like contraction, runner system, venting the core, metal temperature, speed the metal is poured into the mold, flow offs and riser sizes. We cant explain it all in the one post but have included some pictures to show you just some of the processes involved. A pattern that is used to make the external shapes of many of the Aussiespeed Performance Product may differ in size but the same amount of work goes into each and every product. The  Aussiespeed pattern shown is what we call the top box, It is a Hemi 6 cylinder long runner manifold with the part number AS0089 it is a solid timber, plastic or aluminum shape that is normally in 2 halves. When a pattern is made you have to add contraction. A pattern has to be larger in size than what you want your final casting to be. Different metals have different contraction rate some are 1mm in 70mm some 1mm in 50mm and others 1mm in 100mm. An easy way to explain it is if a casting is 700mm long say a rocker cover the over all length could contract 10mm. You are thinking well thats easy we just make the pattern 710mm in overall length. Wrong the casting will shrink back to 700mm but every dimension changes. The distance between each bolt hole, the height, width, crossways depth the lot.


Note on top of the carby pad you will see a square block, it is the print and matches up to the print on top of the corebox. The dept on both pieces must line up to hold the core in the right place to give clearance or “wall thickness” to the job. It also locks in to the mold to hold it in position the same as the print bar on the ports.


This is the sand mold that makes the outer bottom of the manifold, note the 2 large round holes, these are the locators that are a sand solid round shape that fit into the location holes to align the top and bottom of the pattern. When you look at a casting and see miss match on the out side it does not always mean that the internal doesnt line up as the internal core has its own location in the mold.


The locator is made on this Aussiespeed manifold from its own core box, The print that is in the sand mold must be exactly the same deepth and size to drop in to give perfect alignment of the top and bottom of the outside of the casting.


This is the core of the manifold, you can see the solid sand bar on the ends of the sand core. This print as it is called does 2 things, it is a locator for the front of the manifold ports so it can not move backwards or forwards and also makes the long legged core easier to handle.


With the core in position there is a print that locks the carburetor pad in place that also has to be set to the right height to give the correct gap to allow for metal thickness on the top of the external casting.


Its hard to tell from the angle that the photo has been taken but the gap you can see between the large outer sand mold and the internal “core” sand mold is where the aluminum flows to give you the casting.


Another picture of the internal core, it is because the manifold has an internal and external shape it allows us to make changes to the internal that have nothing to do with the outside shape of the manifold. So the port can have fins cast in the runner to boost velocity that simply can not be seen.


This was a trial fit and you can see the core has broken on the tie bar across the port face, the internal core has broken off sand which if it was cast would become areas of metal. There is so much more involved in making a manifold but we hope this gives you an idea of some of the processes.


So after all the work and it is assembled with a runner system to allow the metal to get into the pattern and vents to let the gas get out this is what we are left with.


So after all that work we have a casting that the metal did not flow to all areas and we have a hole in the runner that is the second on the left and what we call flash which is the metal that is in the outside of the pattern.


So once you get the the tooling, runner system for the casting, make the machining fixtures then there is the hours of doing changes to the internal design and shapes on the ports and then its time to further improve performance on the dyno.

Be sure to check out the range of Aussiespeed manifolds in our online store. To View Our Range Click Here






Ford Crossflow Magnuson m90 eaton supercharger

We had a customer who had purchased a supercharger kit that was fitted to a Ford 4.1 aluminum headed crossflow engine in a cortina. The engine used a 2 barrel manifold that had been modified to accept the supercharger.


As the carburetor was mounted a long way from the supercharger we suspect that pooling could have been a problem as the draw through system had the carburetor placed a fair distance from the supercharger.


There are many superchargers that have been designed with an internal bolt pattern that can be difficult to bolt on to manifolds where access to all 4 corners to bolt down the blower. The AS0068 is bolted to the internal holes in the base of the supercharger and has 4 external mounting lugs.


The AS0016 Aussiespeed Cross flow 4 barrel manifold has had the angled carb pad machined flat so it is at 90 degrees to the crankshaft and will also allow the mounting of the supercharger as low as possible. The AS0067 wedge adapter can be bolted or welded in position so the supercharger can be mounted to the intake manifold with the 4 external hold down bolts. We dont have the supercharger and the drive as the customer is in another state, we have done all the machining that is required and it will be a case of getting the alignment right then drilling the holes for the hold down bolts and adapter. We manufacture steel spacer rings to move pulleys for the crankshaft if the alignment needs adjusting.


The Aussiespeed AS0067 is cast as a wedge and can be machined to get your desired height and to get the blower at 90 degrees to the crank. it can be mounted with counter sunk bolts or welded to the manifold.


The 2 adapter plates sitting on the manifold. Additional grinding of the plenum to remove the internal lip may be required once the adapters have been positioned to match the drive length.


All supercharger manifolds should be fitted with a backfire valve to help prevent damage to your supercharger or intake manifold incase of a misfire. The AS0016 has been machined on the side of to keep the backfire valve in close as engine bay room on the cortina is a bit tight.

Dual 4 barrel Carbs

Aussiespeed is always looking at new products and to complement our range of performance intake manifolds and supercharger manifolds a new range allows inline 6 cylinder and at a later day V6 and V8 guys to fit twin 4 barrel carbs to most engines. Part number will be AS0139


Some will say why would you want to drown an inline 6 with dual 4 barrel carbs ? An engine needs air and fuel needs to be metered to match the airflow and 2x 600 Holley vacs set up with the secondries either disconnected or with ultra heavy springs the engine will only draw what it needs. Sure this set up isnt for a stock 161 Holden engine but with the right engine combo it can be tuned and give you a wild looking intake set up.


Holden 9 Port 2×4 barrel Aussiespeed intake manifold will accept Holley 390 upwards squarebore carbs in north south or east west mounting.

Ford 250 crossflow manifold

With 5 different manifolds in the dual 4 barrel range for the Ford 6 plus the blower intakes and 2 and 4 barrel carb intakes Aussiespeed have the largest range of Ford 6 cylinder manifolds.


Chevy inline dual quad intake manifold


With 6 of the best manifolds for Ford Alloy head crossflow engines from 2 barrel street manifolds Aussiespeed has most of your induction needs covered.

In the Aussiespeed 2×4 intake manifold range we currently have or will soon have available.

Holden Red Motor 9 Port

Holden 12 Port Black/Blue Motor

Chevy rectangular port 250/292 inline 6

Ford 250 2V cast iron head

Ford Crossflow alloy head

Ford 3.9 and 4.0 SOHC

Ford Barra DOHC 6 cylinder

Ford 240, 300 Big six

Slant 6 short runner 170 & 225

Hemi 6 cylinder short runner

Holden 253, 308 B cast Heads

Holden VN onwards 5.0L

Chevy 4.3L 1986 onwards Vortec heads

These manifolds will also accept the Weiand 142 or Weiand 144 supercharger when fitted with an Aussiespeed back fire valve kit.

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Supercharger Intake Manifolds

Its been super busy down here working on our new range of blower manifolds to suit a very large range of inline 6 cylinder engines.


We have our test fit engine an old Chevrolet 250 Cubic incher that was removed from a Chevy pick up. Once we remove the brackets and extra pulleys give it a wash and a coat of paint we can start the puzzle. We plan on 3 options supercharger wise. The Weiand 142 or Weiand 144, M90 Eaton from the L67 V6 Buick or super charged Commodore if you are in Australia and the M112 Eaton that was fitted to engines around 5.0L.


A semi machined manifold casting.

Our Products in the USA

We shipped 2 Aussiespeed Endurance go karts to the Briggs & Stratton Motorsport facility in Milwaukee in the USA. The karts are to be used for engine testing and for displays at trade fairs and go kart events through out the USA and Canada. It was great to see our Aussiespeed banner hanging in the Briggs & Stratton Racing testing station along side outher great companies and brands like Summit racing who are also distributors of Briggs & Stratton Racing engines to the Junior Dragster Fraternity, Amsoil manufactures of Briggs 4T Amsoil 4 stroke small engine racing oil available @

The Briggs & Stratton 4T is now available in Australia.


Aussiespeed AS0139 Carb adapter

With so much going on here at Aussiespeed we have decided to bring all areas of the business to one central location. With an expansion into the supercharger market for not only early model Holden, Ford, Valiant inline 6 cylinder engines over the next 12 months you will see many other new products to suit some of the later model engines also being added to the Aussiespeed performance product range.


This is the top of the pattern for the new AS0139 2×4 barrel carb plate. It mounts dual 4 barrel carbs on to the Aussiespeed supercharger manifolds or any of the Weiand or B&M manifolds that accept the 142 or 144 supercharger. The patterns are at the foundry and we hope to have castings back at the end of the week. The other thing that may appeal to inline 6 cylinder owners is for that look of twin 4 barrels on your inline 6. When set up and run with dual 465 vac or 600 vac Holleys in either north south or east west position with very heavy secondary springs the engine can be tuned to operate like a single 4 barrel engine. More updates soon.


Aussiespeed High Performance and Racing Engine Products