Extrude Hone
More to it than you may think – Guaranteed!Extrude Hone power gains are there to be had but sometimes the route toward achieving it is not so obvious!
As performance enthusiasts I doubt there are many of us who have not heard of Extrude Hone. The companies name pretty much describes what they do. Essentially extrude honing is a process where a relatively thick paste-like compound having a lot of abrasive material in it is forced through passages, just like those in cylinder heads and intake runners, to smooth them out. As such the process can, with a fine media, be set up to remove little more than just a mildly rough surface finish or using a course media significantly more material. As simple as this process is it does not replace the need for any heavy porting that may be called for to make gross corrections of a port. What it can do is to rework the surfaces and any rough/jagged edges of an otherwise inaccessible port runner. A good example of this is the runners of a stock 5.0 Mustang. But if it is only the surface finish one could ask just how much can this be worth in terms of added output. At the end of the day it has to be said that the answer depends on whether or not the engine is carbureted or fuel injected and just how in-accessible the intake runners of the induction tract may have been.
First A starting point here is for us look at why a different fuel delivery system may affect the end result of an Extrude Hone ‘before and after’ test. You only have to visit our readers thread on ‘In cylinder Combustion and Turbulence’ to realize that wet fuel flow from re-coagulated fuel delivered by a carb is a really hot topic. Raw fuel simply running past the intake valve into the cylinder can cut combustion efficiency dramatically. Usually some kind of surface irregularity or roughness is required to help break up fuel streams and re-introduce fuel into the air-stream. So it would seem that the glass smooth finish produced by Extrude Hone would be detrimental to a carbureted engines output. Well there may be some truth to that but, as we shall see, like anything, there is more to it than at first seems to be so. But first let’s deal with a fuel injected engine where the proximity of an injection nozzle to the intake valve and 45 plus psi do a significantly better job of ensuring the fuel is better distributed into the air entering the cylinder.
The Stock 5.0 Mustang Intake.
When first introduced the fuel injection intake of a 5.0 Mustang was heralded as a step into the brave new world of exotic intakes. Many of the press write up’s claimed it was really hi-tech and helped deliver all kinds of advantages including more low speed torque from the long runners. The reality is a lot different. I’m sticking my neck out here because I don’t have an editor looking over my shoulder nor do I have to answer to Ford Motor Company. The bottom line is if I had a designer walk into my office with an intake design like that I would be hard pressed not to fire them on the spot! That intake cannot be justified in terms of cost, performance or emissions. The only asset it may have is that it was a talking point for journalists when it first came out. And that’s a sadly weak point on which to justify it’s existence.
So what is wrong with this intake? First, it is the worst aluminum casting on the face of the planet in terms of surface area to volume ratio. The very design industriously collects heat from the engine and it’s under hood surroundings and proceeds to dump it directly into the incoming intake charge. Any advantage the long runners may (and I mean may here) have had will be largely countered by the drop in air density by the time the intake charge arrives at the cylinder head.
It would be hard to design a worse intake in terms of it’s ability to conduct heat from it’s surroundings into the intake charge.
This manifolds capability as a heat sink already justifies my claim that the design was a waste of time. But there is more. The sharp bend and the resulting shoulder left in the intake passage just before entering the cylinder head port on half the runners is simply lack of care on the part of the designer compounded by the pattern maker not questioning it at the final step toward manufacture. This means five of the cylinders are starved of air relatively early on in the rpm range. Then there is the way the throttle body runner enters the plenum. Take a look at this from above. To feed the port runner either side of the throttle body runner the air must make a hard 180 degree turn to go in entirely the opposite direction and there is no real rounding of the edge the air must travel around to make that 180 degree turn. This move defies all logic and the worst of it is you cannot get in there to modify the situation without hacking the manifold apart then welding it back together after it has, as far as possible, been corrected.
The first step toward improving this intake is to establish just how bad it is in the first instance. This means a trip across the shop to the flow bench. First the bottom half was flow tested.
The results were far from good here as the figures we will look at a little later show. Part of the problem, and about the only one we can easily access, is the dog leg in several of the runners just at the intake to cylinder head manifold face. The dog leg is of such proportions that, though it may make things considerably better, Extrude Honing won’t actually fix it.
To get this job done some welding on the outside of the offending runners is necessary. Once this has been done the next op will be to use a carbide cutter and rid the port of the dog leg as per the above drawing.
Here the weld added to the inside turn of those ports with a dog leg approach can be seen. This added material allows the ports to be rough cut to a much more appropriate shape.
So what can extrude honing do for an intake like this? Well for sure it cannot completely fix the dog leg in the intake just before the port runner. But by effecting a change in shape with a carbide at this point to a more appropriate form the Extrude Hone can take over from there. Also the process can effectively tackle those area’s that are inaccessible, Casting irregularities along the entire length of the runners can smoothed out and the turn into the runners from the plenum considerably improved.
For the port runners either side of the throttle body runner the air must make a 180 degree turn. The radius on the edge of the port runner on the inside of this turn is critical. It must have as large a radius as possible within the confines allowed by material thickness and be smooth. As seen in this photo the Extrude Hone process will achieve this.
The way the Extrude Hone process works means it attacks corners in the flow path more aggressively than it does surfaces that are part of a straight line path. This is good for most situations where the intent is to increase flow and especially the case for the stock style 5.0 intake manifold being considered here. Below are the before and after figures for the intake upper section as seen on our flow bench.
Bearing in mind the very minimal amount of material removed by the process the gains in flow are very worthwhile. What we are essentially seeing here is an average increase of 21 cfm per runner or a 12.2% increase for the top alone.
At this point we can see that the Extrude Hone process is looking good for an intake with port runners that are otherwise inaccessible. With the dog leg side of the lower half of the intake welded and dressed out and then Extrude Honed the before and after results below were achieved.
As can be seen the results were very favorable. Flow increased by an average of 39.5 cfm which represented an increase of 21.2%.
On the Dyno.
The flow figures for the reworked intake look good but remember the engine produces results based on a combination of parts. This first test was with an engine that was stock other than a cold air kit. This means it had a stock set of heads which don’t flow that well so the heads themselves will ultimately act as a limiting factor in terms of just how much extra air the engine will ingest. Likewise the stock throttle body and a stock short duration low lift cam. OK, now your are aware of the other limiting factors toward making HP take a look at the figures seen below.
Other than the fact the peak power rose by 15 hp there are a few other things these numbers are telling us. First the big gain of 25 hp at 5250 rpm tells us that in spite of poor heads and a lowly cam this intake in stock form was starving the engine. Secondly there is the increase in low speed output. This bears looking at in depth here as it has some significance beyond just airflow improvements. At low speed (1500 to 2500 rpm) the engines demand for air is also low. This means that the stock manifold should have been up to supplying the engines demand and then some so no increase in output should have been seen. But, as the figures show between these two rpm points the engine (as measured at the rear wheels) produced 5 to 6 lbs-ft more torque. So where did that come from? Remember I went on at length as to how bad the Ford 5.0 intake is in terms of surface area to volume as a heat sink. Well the Extrude Hone process has actually improved that. A cast finish is really good for transferring heat from one medium to another. By removing the casting irregularities within the runners the ability to transfer heat into the intake charge has been effectively reduced. Our measurements of the intake charge temperature at the intake/cylinder head interface showed typically a 12 degree drop in intake temperature. This just about accounts for the increased low speed output where the manifold’s airflow is not the main issue toward making torque. What we have then is a process that not only improves flow but also cuts heat transfer from the ambient conditions outside the intake to the air within the intake.
The EH Intake on a Modified Motor.
After what looked to be a successful test on the stock motor our EH intake was later tried on a 5.0 that had previously been equipped with a set of Edelbrock Performer heads. Although these heads punch the power upward a very respectable amount as the sole modification of any magnitude it was felt that the intake would now be starving the engine of air to a much greater extent. We were in the process of running a test on the stock GT intake on this engine and felt before installing the GT intake a test of the Extrude Honed intake would be a good idea. It was! On this test, instead of 16 lbs-ft peak torque rose by 22 lbs-ft. In similar fashion peak hp, which rose by 15 hp in our original tests went up by 25 and the gain at peak rpm (5250) was 36 hp. When the GT intake was installed in out-of-the-box form we actually saw a small drop in output. What this is telling us here is that it was cheaper, per HP gained, to go with the Extrude Honed intake even if it did involve (in this case) some welding on the lower half.
This GT 40 intake looked really slick but unless it’s looks you are after the cost did not justify the results. Our Extrude Honed stock intake had the edge on it by a small margin and for a lot less money.
From our experience here we can see that Extrude Hone should, for sure, be something to consider for a fuel injected intake that has runners with die grinder access problems. Being as we have tested with a fuel injection induction system we have avoided the possibility of creating an intake that is too smooth for a carbureted system. Just as a reminder here surface finish can adversely affect wet fuel flow of such. Does this mean that Extrude Hone is only for fuel injected engines? No – in actuality there is at least one situation for a carbureted engine where Extrude Hone could be said to be tailor made for the job.That is what follows.
Small Block Chevy Two Plane Intake Test.
Although known for some 50 years prior the intrinsic advantages of a two plane intake manifold for a V8 have only been seriously exploited for high performance use since about ’92. The fact that they divide off cylinders into sets of four so there is no inter-cylinder robbing as there is in a single plane means better idle, more vacuum for accessories, better mileage and most of all, significantly better low speed output. The down side is the more tortuous route the intake runners have to take to make the intake into a two plane design mean that top end output, compared to a single plane, is compromised. The latest batch of air gap hi-rise style intake manifolds from Edelbrock, Dart, Weiand, and Professional Products are all attempts to get the best airflow possible from this style of intake. As a matter of reference all these companies have produced manifolds that are literally a quantum leap from the old style two plane manifolds that preceded them. In spite of being nothing short of excellent the very nature of the runners in these intakes make it extremely difficult to equal the flow potential of a single plane intake. Porting them by any conventional means for better results is do-able but extremely complex as it requires opening up large holes in the intake, porting the runners then welding the holes shut. This type of porting exercise looks like it is just the job Extrude Hone can take on and deliver results.
Here is an externally polished version of professional Products Crosswind intake. Although primarily polished for looks that shiny finish actually contributes toward the production of power by reflecting heat away from the intake charge. It shows up way more on the track than on the dyno.
Because of the repeatedly good results seen with intakes from the companies just mentioned making this move has been in the back of my mind for some time. I have spent much dyno time trying to get a two plane intake ever closer to the top end output of a single plane without sacrificing the attributes that make this style of intake the best for true street performance on any sanely budgeted engine.
What I really needed here was a little nudge to do a back to back test of an out-of-the-box two plane intake versus the same model but Extrude honed. That nudge toward doing a test came in the form of story about a late model circle track team cheating (Imagine that!). It seemed that the driver was a consistent bottom half of the field finisher and the tech guys never tear down tail end Charlie motors. Well this team sent their intake to Extrude Hone who did their thing with it. It was rumored the results were as much as 20 hp increase. Now that may or may not have been so but what is for sure is that the car started placing consistently in the top 5 and it became only a matter of time before the tech guys took notice of this and began to wonder. So the team decided to put the old intake back on and drop back in the field rather than get caught cheating.
Well that late model stocker story decided the issue right there. Since the ‘air gap’ style two plane intakes had shown so much promise in past dyno testing, especially at low speed I really wanted to explore avenues for improving their already excellent top end capability. My choice of hardware for the tests was the Professional Products Crosswind two plane intake. This is a highly functional intake out of the box and it is a lot less money than most intakes. I put in a call to Professional Products and had them ship me one intake and another to Rick Miller at Extrude Hone. When the Extrude Hone example arrive back at our shop I set about photographing both the stock intake and the Extrude Honed intake. I had the shots done of the stock intake in literally five minutes. The Extrude Hone intake, which looked really good, was another matter altogether. With light bouncing off the runners at all angles glare from over lighting in certain spots was a real problem. Getting the shots you see below took several hours of experimenting with lights. I figured if light will go through this manifold so much easier the air is sure too! Shown below are the visual differences between the two intakes.
On the left we see a stock pair of runners on our Professional Products Crosswind two plane intake. The casting finish is typical for an intake manifold of this type. On the right are the same pair of runners (different manifold) after Extrude Honing. The finish is every bit as smooth as it looks in this shot.
I did not bother showing a before shot of the intakes runners taken at this angle. The finish is so obviously beyond anything that is cast there seemed no need.
So much for looks – indeed if looks alone equated to performance I could de-stroke one of my small block Chevy’s down to 2.4 liters and expect it to be competitive in F1! Since we all know that not to be the case it’s time to start testing. First the flow bench. The results below show what was seen in the way of increased air flow.
The numbers in the ghosted red area under the heading CFM+ show the gains after Extrude Honing. The column to the right of those shows the percentage gain. Overall, the average gain is right around 8% - a very promising figure to go to the dyno with.
Certainly the above results look promising for sure. The question now is just how well this increase in flow translates to an increase in power. Remember it’s not just about airflow here. It’s also about mixture preparation and we have seen many times with single plane manifolds that too good a finish just makes the problem of fuel coagulating and streaming into the cylinder rather than breaking up and entering in a more burnable fashion. However the two plane intake is a different cat. It’s split runner setup produces a stronger pulse at the carb boosters than seen by the boosters of a carb on a single plane intake. This of it’s self means better atomization. The question now is will the increase in flow more than compensate for a possible (but not certain) drop in mixture quality. Only the dyno will tell and that is our next step. At this time (03/03/08) we have just finished a hot 350 to dyno test each of the two Professional Products intakes. One being stock the other Extrude Honed. As you can see from the following shot it looks a sharp motor.
Well it took a few weeks but we finally got on the dyno and tested the extrude hone intake vesus an as-cast one. Here are the results.
Now before you absorb these numbers and say - so that's the way it is - there are a few factors I need to throw in for your consideration here. First, in hindsight, Dusty's screaming 350, though it made some big numbers for a muffled two plane euipped engine, may have not been the most optimal unit to test on. Maybe it was the fuel we were using, the weather or who knows but the run-to-run reapeatablity was not as good as one would wish. That said with averaging, the trends were pretty clear cut.
Before going into results here I want to make a few points concerning manifold finish. As a rule of thumb the smoother the finish the more likley the charge entering the cylinder will have a greater proportion of fuel in wet or rivulet form. If this is so then this would mean the shiny smooth finish such as our Extrude Hone intake has should be worse at low rpm. At high rpm a worse quality mixture may be offset by greater airflow. On the other hand if the carb has good atomization charactoristics at reletivly low speed the wet flow situation may not be the big adversity we might suppose. If this were a fuel injected engine such as the 5.0 tested earlier then wet flow would not be an issue. It would be a simple case of more flow equals more power.
The carb we were testing with here was an AED of some 825 cfm. Our 900 CFM AED was back at AED for a rebuild after I screwed it up re-assembling it after a photo shoot at about 1 am.
From experience we know that our AED carbs is good on fuel managment in every quarter. The question is would the test carb used here be good enough to allow us to tap into the Extrude Hone finished intake to get positive results.
At low rpm the induction system can pass all the air the engine will need so the extra flow won't figure into the equation here. What will be a factor is that the shiny surface will put less heat into the intake charge so it should be denser. By the same token the cooler charge will mean less fuel is vaporized. What we need to know here is which faction will win out at low speed. Check the results. These results were a suspected possibilty but no more than just that. What we see here is a meaurable gain in torque at 3000 rpm from the suspected cooler charge. By the time the rpms are up to the mid range the effect of a cooler charge is lost. This happens because there is now so much air and fuel passing through the system that the temperature of both the before and after intakes is about the same. Also about this time the intake manifold is starting to be a resitance to the volume of air the engine needs. What now happens is that the higher flowing Extrude Hone intake starts to show it's legs because it can pass more air. At this point it became obvious that what we really wanted was a bgger carb - like the 900 cfm AED - remember where that is - right - it's at AED because yours truly screwed up!
So what have we learned here? The bottom line is that Extrude Honing an intake can not only be a benifit to a fuel injected engines intake manifold but, uinder the right circumstance, it can also pump up a carburated engines output.
After our carburated tests we are encouraged to the extent that we will conduct more tests to extract the full potential of this process. Other than to run a test on a Honda engine, our next move is to do some pre-porting on an intake then apply the final touches with the Extrude Hone process. Also we are looking at the possibilty of a fuel injected two plane as we know, going in, that the Extrude Hone will deliver on that.
