Manifold Porting


If you have, or are thinking of buying an Aussiespeed manifold and then spending time porting it or giving the manifold to your engine builder and getting them to port it, please get them to read this article before they go near it with a die grinder or stones.


Brads 265 6 cylinder recently ran a 9 second 1/4 mile pass using an AS0265 manifold. Many hours of r&d go into our products as we want to help you to go faster and make your engine more efficient.

This is not a personal attack on any other manufacturer of manifolds, individual or engine builder, but some info we think may help our customers with understanding the reasons we would rather our customers not port our manifolds.


With this being said, there are engines that may find improvements from porting our manifolds. Our experience has shown this is not the case, with a turbo charged Hemi 265 making over 500 rear wheel horsepower with an AS0265 manifold out of the box, 250 crossflows making over 350+HP and Slant 6 and Holden sixes also making figures that shouldn’t be sneezed at. Some may disagree with what is written in this article and are entitled to there opinion. Being the founder of Aussiespeed Performance Products, I still have the same passion for my products as i had on day 1 and want to give our customers and users information straight from the horses mouth and not from the horses arse. If you are reading this you might have already purchased an Aussiespeed Manifold and this may give you more confidence in our products, as we want you to get the best results from using Aussiespeed Performance Products




AussieSpeed manifolds differ in design from manifolds designed by other manufacturers. We have spent many, many hours grinding, cutting, welding, adding shapes and removing shapes when we design our manifolds. On a few occasions we get phone calls from guys or there engine builders or tuners with problems they are having tuning an engine. The conversation normal starts with ” Hi or G’day” we have one of your manifolds on a ” crossflow, Holden 6 or 4 litre” and numbers 1 and 5 are running rich” Then we say has the manifold been ported? The response normally is ” we just match ported it” or gave it a bit of a grind or tickle ” At this point the conversation can go either of two ways. We get the story that “they have been building engines since before they could walk”, my mate or my mates uncle said he had an engine that pulled to 10,000 rpm and it had dome top pistons, was fully ported and the head flowed that well that the numbers were more than the flow bench could handle and all the other bullshit that goes with it. Or we get the guy who is deeply concerned and says have we done something wrong.


Aussiespeed Manifolds are designed to deliver high velocity, an even as possible charge of fuel and air to all cylinders. Different port shapes have shown different characteristics with our development over the years, We have developed manifolds that have never made it to our stock list to be added to the Aussiespeed range as they haven’t worked the way we try to design our manifolds to work.

 where-to-cut-hemi cain-manifold lr

A Ford crossflow round port responds different when reshaped to a rectangular port of a Holden 6 red, black or blue 6 cylinder. A square port slant 6 or Hemi six port is totally different again. We will look at these 3 engine types here and explain what we have learnt over recent years while developing the range of Aussiespeed street and race manifolds.


The first manifold we will look at is a Holden 6 cylinder 202 black and blue motor. The manifold is a Aussiespeed supercharger manifold to suit the m90 Eaton style supercharger, the AS0009 looks very similar to the AS0002 red motor manifold. The blue, black motor is taller in the port and the manifold has been designed the same way. Inside the plenum on the inside closest to cylinders 3 and 4, you will notice centre divider and the unusual shape how it points towards the inside closest to the cylinder head. We tried filling it in to a flat section and it didn’t like it, It upset balance of flow to all the cylinders so it is advised not to touch it.


The Plenum floor with the plenum “PIG” filler, This is cast into the manifold so it can not be removed this was done to stop guys from unbolting it and ending up with an engine that wont pull from a moderately low rpm and can also cause pooling of fuel on the port and plenum floor, removing it slows air speed and velocity and also makes engines boggy. The shape was designed to increase the performance and not reduce to much volume, at higher RPM it also directs air and fuel. The shape was changed many times and the correct location, height and tail length along with the centre divider all work together to deliver optimal port flow and velocity.


If you start grinding any of these areas you have undone the many hours we have spent perfecting the manifold.


 As the AS0009 was cast to obtain optimum port and plenum size to deliver good torque over a wide rev range, shown is the Aussiespeed east west carb adapter that allows the carb to be run eastwest


Picture of a manifold that was modified by a engine builder, We were told our manifold didn’t work. as the engine was sluggish down low, fouled plugs and had fuel dropout on the port floor. This is normally caused by incorrect power valve sizing & when the cross sectional area of the manifold has been increased and is to large.


You may notice the different tail lengths on the plenum pig, this is done for a reason, If you are going to compete in a 500 mile reversing race, please contact us.. so please do yourself a favour and don’t change it..

 We were horrified when we received this manifold back from an engine builder. Had the power valve sizing been correct and jetting sorted and it not have been attacked with a die grinder it would have saved a lot of time.


Look at the size of the plenum, it is big but has areas inserted to balance the manifold so it can work on a hottie street engine to an all out strip stormer. This same manifold out of the box is used in 6 cylinder ski race boats that must run a single carb. Current model Aussiespeed manifolds have had the plenum floor modified as you will notice the cast lines in the bottom

 Note the blue marks on the calipers, these were pre set to the first port and not changed for any of the pictures taken below

Note the bell mouth on the port on the left hand side also the extra distance the calipers go into the port, We didn’t even check the height of the port the evidence of the width was bad enough. Plus the removal of material from the port floor


The middle runner on the AussieSpeed Holden 6 manifolds are different size than runners 1,2,5 and 6 for a reason, It is important that they are left this way. Match porting & polishing looks good when you show people or at a bench racing session but does more harm than good with our Holden 6 manifolds


A huge amount of material has been removed, the customer said they only gave them a “tickle”. I would hate to see what a good grind was…


 Abracadabra they even hit the port floor on this one and look at the amount removed to the left port side wall.

 So in short after seeing the pictures of the manifolds above here are some important points

The ports on the Aussiespeed Holden 6 manifolds differ in size on the port mouth for a reason.

This is done to balance cylinder fill to give good velocity and an even flow on all cylinders

 The dividing wall in the plenum in front of cylinders 3 and 4 and the runners are matched to the port sizes on cylinders 1, 2, 5 and 6.

The reason the Aussiespeed 2 and 4 barrel manifolds can deliver high levels of performance is due to the balance of flow on all 6 cylinders.

When picking your carb and manifold be sure to not go to big. We had a customer ring and complain that his engine went real hard with his old carb and manifold, after installing our manifold and a 750 vac Holley it went backwards. When asked what was the old carb and manifold he replied ” stock single barrel Stromberg on a factory manifold” with a  “standard head standard cam”. So please do your self a favor and select a car and manifold suited to your combo..

Ford Crossflow AS0016, AS0015 manifolds & horror port jobs

The Aussiespeed crossflow 2 and 4 barrel 6 cylinder Ford performance manifolds have been used on hundreds of engines with results that even impressed us. Our first model crossflow manifold was the AS0128. This manifold has been used on a very quick Queensland car run at 1/8 and 1/4 mile tracks. The car has done many 11 second passes with some real good top end speeds. After the AS0128 we introduced the AS0137 this was way to big for street engines and after seeing the amount of guys wanting to run Aussiespeed Manifolds we decided to bring out another model that was between the AS0128 and AS0137 The AS0016 was released. This new manifold offered a slightly taller plenum with angled floor to reduce total volume, a wide tapering runner that is 6mm taller than any other manifold. If you look at all the new style engines port and valve angles have changed to reduce the angle that enters the short turn on the cylinder head. We couldn’t change the valve angle but by closing the end of the port the hole way round we picked up a few gains. The venturi affect of fuel and air entering the cylinder head port at a higher speed, the charge enters the head port at a higher angle and flows along the top of the port roof rather than the floor. The smaller port also stops any reversion, as the manifold is smaller than the head port for a short distance. A Cortina recently ran at western Sydney Drag Strip and ran a low 12 with no gas first time out. After a bit of fine tuning the car ran mid 11s with an AS0016 out of the box…

please-do-not-port-it lr

The ports pictured above have been enlarged by a small amount by around 2mm on a 4.0 Litre AU Falcon speedway car this small modification did increase top end performance with a drop off of in torque at the bottom. Even though 2mm was removed it increased the port exit by 4mm total & moved the RPM range by 1600 RPM


The only tool required to remove material from the conical designed port on an Aussiespeed 6 cylinder Ford manifold

 ford-factory-manifold-on-flow-bench lr

Many hours of research has gone in to developing our range of manifolds, we have many different ways we like to test manifolds in which has caused some critics to disagree.

A customer from Perth ran his old banger Cortina with a brand of manifold that has been around for a long time. With the help from an engine builder from Perth they took the Cortina to the drags on a test & tune night and ran the car as it had been run for the last 11 months the combo totally as was the times had been 13.4 to 13.7.On the night with the manifold they had been using it ran 13.6. The Aussiespeed AS0016 was pre-fitted before the night so an easy swap over could be done. The guys did a manifold change in the pits and with the AS0016 fitted a quick rejet and power valve change for the 2nd run of the night with the new Aussiespeed AS0016 being used for the first time on the engine the car dropped from a 13.6 second pass to a 12.98. This calculates to over a 30HP gain. This was using a AS0016 straight out of the box with no porting and replacing the other brand manifold that had had extensive internal work done.. So there are a few examples of Out of the box gains.. So you have read about why not to port of an Aussiespeed manifold is likely to result in an unbalanced flow and  a loss in velocity and can possibly result in a loss of horsepower and torque. The reason our manifolds are smaller on the port to cylinder head face is to increase air speed. Think of a garden hose, with the end of the hose with no restriction water will either dribble or run out depending on the amount of pressure at the tap end & the length of the hose. If you stick your finger over the end or fit a sprinkler, the water picks up speed  and sprays much faster now the size of the hole in the sprinkler or the amount of  restriction with your finger placed over the hose end is important to the volume that can still flow. A venturi works in a similar way.





Aussiespeed Manifolds & Old School Speed Equipment Co.

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