Porting heads for more power

[JBrady]

Staff,

Ok, not to be a doubter or critic off hand... I must say that polishing intake passages to a mirror finish has not been advocated by any professional head porter that I have ever spoken with or read about in the 30 years that I have been fooling with engines. That said I am always interested in seeing people test ideas and theories as long as they do so objectively.

Now, regarding the leading edge of the port divider... virtually all aerodynamic models suggest that a sharp edge is not the most efficient shape. This is why airplane wings are not shart on the leading edge but rather on the trailing edge.

Your power claims are impressive. Do you have the dyno sheets for baseline and post mods? You say you gained 40rwhp. Is this combined with intake and exhaust mods or heads alone? Your math above suggests 30-48 horsepower for a good exhaust and intake filter modification. What exhaust mods are you running.

I guess the bottom line is... obviously you have put in a great deal of effort. Your ports are certainly shiny. Please post your actual test results, theories, modeling, dynos, comparisions and so forth so that we can intelligently discuss your efforts. Without such information I am concerned that others will attempt to duplicate your results and end up spending time and money and only loosing power

Wurf, the stock heads are not the first restriction. The exhaust is the biggest bottleneck. Remember here that bigger is not necessarily better and in fact with only 4 liters to move the roughly 4000lbs that most of these cars weigh... your goal should be maximizing mid RPM torque and not loosing low RPM torque. This is best accomplished with a high velocity exhaust system including manifolding. Unfortunately proper headers are not sold anywhere and therefore need to be fabricated. You may wish to weigh the cost of this with the supercharger/turbocharger systems Lextreme is working on. Another mod highly recommended would be a higher stall torque converter. David can help you there as well.

10/07/05 UPDATE: Headers are now available from S&S Headers, www.ssheaders.com

 

[SCV8]

WOW! I just looked at those pictures, nice work.I've done that once before on another engine, and it does take a bit of time to acheive that level of finish.
On that car,an older VW Rabbit, it also made a huge difference in the performance/torque.The car could do some great burnouts afterwards!
So you're into airplanes JBrady?

 

[Lexurious]

Polishing can actually decrease airflow. Just look at a golf ball, the dimpled balls fly twice as far as a smooth ball for the same power drive. perhaps a dimpled intake is the way to go

 

[crunchy]

i agree that porting to a chrome finish isnt the best way to go, on heads i do i normally finish the intakes with 80 grit paper and same on exhaust. fuel can turn into droplets and thats not good for fuel distribution plus after a couple of hundred km's the exhaust port is covered in souty carbon, shame it looks too good to use

 

[deathblow]

hey guys im very interested in port and polishing my head. i never thought about doing it. Do u guys know is i might have the same gains in hp & torque on my 92 sc400 with 190k on the engine? any info would be great.

 

[staff]

Port & polishing Lexus sc400

Polishing can actually decrease airflow. Just look at a golf ball, the dimpled balls fly twice as far as a smooth ball for the same power drive. perhaps a dimpled intake is the way to go

Polishing decreases resistance. The smoother the surface, the more minimal resistance becomes. Lowering or eliminating resistance will always increase your air flow.


Dimples on the ball control trajectory, flight, spin rate, wind bore rate. A golf ball is designed for it's trampoleen effect. It's not really speed but rather a funtion of compression and decompression. A golf club compresses it a golf ball. The balls ability to compress and how it acts as it releases off the club moving at a specific club head speed is quite different than air induction.

Anyway, your argument is comparing apples and oranges.

 

[staff]

i agree that porting to a chrome finish isnt the best way to go, on heads i do i normally finish the intakes with 80 grit paper

To rough.. will eventually accumulate carbon in the grit marks.

after a couple of hundred km's the exhaust port is covered in souty carbon, shame it looks too good to use

Using 80 grit I'm suprised you even get that.
This is not a problem when polished out properly as I have shown.

The smoother the better. At no point can you be to smooth.
Air slow is a funtion of minimizing resistance.

Reason why shops don't do it like I did is a funtion of costs and time.
It's grunt hand work that is painstakingly slow.
I have 85 hours in mine.

You could pay $6000- $8000 to have a shop take it the the level I took it to.

 

[staff]

I am concerned that others will attempt to duplicate your results and end up spending time and money and only loosing power

If you polish alone you cannot lose power. The gains were achieved without headers but after losing the stock muffler setup. Headers added only 8HP when added. Sharp or round is not the issue but rather what air flows are created using one or the other.
Though the exhaust manifold looks crude, it is actually more efficient than most for the 4.0 engine. I would not waste money on headers unless you are planning on doing a supercharger upgrade.

 

[TundraEddie]

I put 85 hours this past winter to port & polishing the heads and intake manifold , throttle body etc. for my SC400. This was what I call my extreme P&P and why it looks chrome plated

You weren't kidding about the chrome look...how'd you get the buffing wheel into those really tight areas?

 

[Mcgee]

smooth walls

"Polishing decreases resistance. The smoother the surface, the more minimal resistance becomes. Lowering or eliminating resistance will always increase your air flow."


Problem is in tube flows, like an intake or exhaust is that a polished wall increases the boundary layer thickness the further down the tube you go and hence reduces effective cross sectional area the mainstream flow ie full velocity flow has to travel through. Although for this short distance it should be a problem.

Dimples or a rough surface is used to induce turbulent flow, which is more energetic than laminar (Smooth) flow, this is used on a golf ball because turbulent flow will separate from the back of the ball later than laminar flow and hence reduces Drag.

IMHO it wouldn't matter if its polished or not, there are a lot of other flow restrictions that would negate any effect of polishing the inside, a greater Cross-sectional area would be of benefit as it can pass a greater mass flow rate (volume) at the same pressure.

 

[JBrady]

If you polish alone you cannot lose power. The gains were achieved without headers but after losing the stock muffler setup. Headers added only 8HP when added. Sharp or round is not the issue but rather what air flows are created using one or the other.
Though the exhaust manifold looks crude, it is actually more efficient than most for the 4.0 engine. I would not waste money on headers unless you are planning on doing a supercharger upgrade.

Again, I ask for before and after data preferably including dyno numbers. Your porting theory goes against aerodynamic theory and conventional applications. While going against prevailing theories can occasionally find new and improved ways to do things your statements by themselves are tough to agree with.

Regarding the stock exhaust manifolds... you have GOT to be KIDDING.

 

[racingbrett]

As far as polishing goes all the latest information tends to prove that allthough a nice shiny mirror/chrome finish will give better results on the flow bench, when put into use on an engine it will not always yield a greater increase over a rougher finish, in fact it will often decrease performance, the fuel will tend to cling to the shinyer surface and build up, to be dispersed as larger fuel droplets causing unwanted fuelling effects, the fuel doesnt cling to the rougher finish so easy and the turbulent effects from the rougher finish actually aid in supplying a better air/fuel mix by the bouncing n buffeting effect around the outer extremes of the rougher finish.. Theres also a theory that in polishing the exhaust side once the carbon has started to build it is able to build up and cling to the metal fatser and easyer for the same reason as stated in the intake and also the fact that there will be no trapped air/water/gasses under the carbon which would be present in the ruffer casting which actually aids the carbon to break up, although i have yet to see this theory proved on the exhaust side.

 

[Toranamat69]

I have often wondered about which is the best finish to do on the inside of ports and have heard the tales from the old racers from the Carby days about how highly polished ports cause fuel droplets and lose power - this I can at least visuallise with large (low velocity) ports and the carburettor pouring fuel down the holes.

What I am not conviced of is if this is still true with fuel injection and high velocity intakes. To me it sounds like it could be one of those things that hangs over from the old technology and no-one challenges the idea.

I am in this situation as I plan to port match and extrude hone the plenum and injector housings on my engine in the next few months. I really don't want to go the effort of polishing to mirror finish if there is no gain or infact a power loss. If there is a gain - even very small I certainly would go the extra effort.

The only way to really tell would be to do a before and after comparison on the same engine but I really can't seem to find anyone who has done this. Everyone has an opinion but it always seems to be based on something they have 'heard'.

Would be interresting to know how they prepare the ports on an F1 car or a group A touing car as these blokes do a lot of development.

Has anyone seen comparative flow figures for polished vs say an 80 grit type finish on a port.

 

[racingbrett]

the experienced head porter i use for my A-series race engine has tested both (both in injection and carbed engines including cars prepped for the btcc) if anything the shiny port method is a hangover from the olden days, my race headed mini isnt polsihed to such a high extent on the intake by my builder and as a result of his advice none of my own porting work recieves such a high level of polishing.... While a flow bench is of great importance so is knowledge and esperience with working on a particular head, flow figures can mean nothing if u mess up the characteristics of the head,,, case study was a 1600 Xflow head, it recieved extensive porting and flowed the largest figures seen by this particular shop, however when put on the motor power was way down, seems although it could flow more, the flow pattern/ swirl caused for the burn to be weaker n hence less power was made, its now widley known in Xfow tuning that one section which causes a flow restriction is essential and not to be removed.
Just a little to add on the exhaust mirror finish, how we see it is yes, this side of things a mirror may be of benefit but not for a road car, my mini head is polished on the exhaust in an effort to squeeze every last bit of power from the engine, but after every race meet the heads stripped, rebuilt and re polished, yes it carbs up that quick... for a normal road car its not really worth all the effort of stripping and polishing every couple of weeks as it will not give you a noticable gain.

 

[Dreamkiller]

What i believe with respect to carby'd engines, is a rougher inlet tract is better because it allows the air fuel mixture to swirl around somewhat and mix better. Whereas with fuel injection, the injector "sprays" not "squirts" the fuel in and would reduce the need for a rougher surface.

 

[racingbrett]

even so the fuel molecules bond/stick better to the shinyer surface, which u dont want to happen

 

[Trvln Nalzmn]

Long time listner first time caller.

The more turbulant the flow once inside the cylinder = more power due to better burning chracteristics. To make the air turbulant you'd have to restrict the flow somehow, so the diameter and surface finish could only be tuned for a certain engine RPM. Its a balancing act I think.

I'd say that the best intake manifold would have a ribbed surface that too would probably only be good for a certain air velocity.

I too have heard that a polished finish is not the best.

Look at a things in nature that travel at high speed through fluids. I can't think of anything that has a mirror finish.

 

[xirforever]

Dolfins are pretty close...... as close as they can possibly be, i have touched them and when wet they are extremely slippery to the water for a higher velocity of speed....

 

[Trvln Nalzmn]

Dolphins distort their skin when moving making riblets that while greatly increasing surface area act to decrease overall drag. I think that it is only effective when the flow is turbulant. Sharks have the same tech but its a permanent fixture. Thats why their skins appears to be like sand paper, but under a microscope it appears as VVVVVVVVVVVVV.

 

[Zuffen]

Americas Cup boats actually have a finish on them like a Dolphin or shark. small ribs in the finsh to improve water flow.

This was first used in the Challenge against a Australia by the Yanks in the mid 80's.

Why do footballers use shark skin (foot) balls in the wet?

Because they are rough and help them hold the ball.

I don't think sharks would have skin designed to slow them down. I know there are a few swimmers who have wished they did!