Homebrew Head Porting: Attempting the dark art .....
 

I am chasing 300hp on my ’78 3.0 Sc engine on somewhat of a limited budget as per this thread and will be doing the head porting myself, initially to save money, but now more to try and test the below views on the topic from a home DIYer's point of view, and ultimately have the satisfaction of having ported my own heads.

There are various different views on this and other forums on home brew “porting", mostly that it is just a hack and does not make power through a reasonable RPM range.

My mission is to see if I, as a DIYer with limited skill, knowledge and tools, and with a lot of time for research and testing , can do a home brew head “porting job” that can make good Hp and Tq through a resonalbe RPM range

( I am not sure how to measure the performance of the heads other than to make an assessment of the before and after average flow numbers, make the target as planned above on the dyno as other engine builds with a similar build sheets came short of 300Hp, and compare flow numbers with other known ported heads although I am not holding my breath on this)

Here is how I mapped things out:

1) Do a lot of research and get as much as possible literature on the subject
2) Get (build) a flow bench and test equipment
3) Flow measure one of my stock heads to get a baseline with manifolds and carbs
4) Make mold of the port and a plaster copy of the head
5) Make changes and optimize as far as possible and compare average to stock heads
6) Transfer changes to one of the heads “port match” manifolds and do final optimization
7) Make a mold of the ported head
8) Transfer to other heads
9) Equalize flow between heads
10) Dyno test to see how close I got to 300hp.

1st update to follow.

Velocity of air is much more important than volume of air. Remember that before you start hogging out a head and end up with a powerless lump. Having seen good and bad port jobs at the same size, the difference is dramatic. Start by looking at these for what "good" looks like: http://www.early911sregistry.org/forum/showthread.php?t=22220

Thanks for the link Kenik,

Wow those look great have been looking for good visuals on ported Porsche heads to start forming some initial ideas for a while but with limited success.

You are right, from the research i have done up to now, port velocity is one of the key components to make the head work especially with big cams (reversion, bad low RPM response etc. ) There is not a lot of port velocity data available for Porsche heads but a fair amount on Honda, Harley(hemi heads) and various V8 heads which will provide some ballpark parameters to work with.

It will be an interesting exercise to get the velocities up on the big port SC heads, but thats part of the goal.

Part 1 Flow Bench (update1)
 

I have been doing research for the last month on the whole porting deal and looked at various non commercial flow bench designs and came across this forum that is into flow benches and engine dynos. I decided to build the one shown in the Plans Area as there has been a lot of development done around the design.

This is not the least expensive by any means but will provide results comparable to other commercial flow benches. The alternative is to do a simple shopvac based flow device with a simple water manometer, this will provide data on the effect of flow changes made fairly accurately but will

1) Will not be comparable to other's flow results and
2) Will not flow enough to test port flow and velocity at high depressions.

The selected bench is a simple (well relatively simple) orifice design with no moving parts other than a divider plate to change the direction of flow. It uses 8* 100 CFM vac motors of which 2 will have electronic speed control. The orifice plates are calibrated and precision machined for specific flow rates and are changed manually. I will be using a digital manometer connected to my notebook for flow and velocity measurements.

The bench's tested accuracy is within 1% of an SF600 commercial flow bench which is seen as the leading commercial flow-bench. .

Attached are some pictures of flow bench construction so far....


http://forums.pelicanparts.com/uploa...1233873680.jpg

It’s nice when you have the equipment to test the changes you want to make, but often it’s just not feasible to buy professional equipment for limited home use. Building your own Flow Bench is a great solution for the serious DIY like yourself. Some Nay Sayers might chime in about the accuracy of homebuilt equipment but really this is not an issue. There are successful examples of home build flow benches online that work very well and I’m sure yours will to. It establishes a Base Line that you can work from and this important piece of equipment will provide you with all the data you need to determine the success of your porting.

It’s pretty well a one-way street when you start removing material so go slow and take it easy when you get into the actual porting. It would be nice to have a few scrap heads to play with first. That way you can always putty up the ports and try different things without risking your good ones.

Also Check out what Porsche is doing with the new intake plenum designs, the runners taper down to increase the velocity

Have fun and enjoy what your doing

I wish you well and commend you for doing it!


While doing some research a while back, I ran across the following and saved it, hope it’s helpful. Sorry I did not think to save the link at the time.

Flow Bench Fallacies: Our era is often referred to as the Information Age, but not all of the information is necessarily useful. I am beginning to think flow benches should come with a government warning:
"Caution! Excessive reliance on flow numbers may be harmful to your engine!"
I'm kidding of course. Used wisely, a flow bench can be a useful tool in engine development, just like a timing light or a dynamometer. Unfortunately, some racers believe that a flow bench is the ultimate answer machine. When the subject is cylinder heads, the four words I dread to hear are, "What do they flow?" Novice racers and magazine writers share a fixation about airflow.
Their mistaken belief that "more is better" is often the false assumption that produces an under-performing engine. A flow bench measures air movement in a very rudimentary way - steady-state flow at a constant depression (vacuum). Obviously, the conditions that exist in a running engine are quite different.
The flow bench can't simulate the effects of pistons going up and down, the reversion pulses as the valves open and close, the sonic waves that resonate inside the runners, the inertia of fuel droplets, and all of the other phenomena that influence engine performance in the real world.
When you flow test a cylinder head, you are simply measuring how far you can move the liquid in a manometer. The bigger you make the port, the more it flows. That's hardly shocking news. Bolt a sewer pipe on to a flow bench it will generate terrific flow numbers.
So should we use ports as big as sewer pipes on our racecars? The flow bench says we should - the time slip says something completely different.
If airflow were everything, we would always use the longest duration cams we could find after all, more duration means more airflow. In fact, we know that there is a finite limit to how long the valves can be open before performance suffers. That is because the valve events have to be in harmony with the rest of the engine. That same principle applies to cylinder heads. Simple airflow capacity should never be the first consideration in evaluating cylinder heads. Characteristics that are far more important include air speed, port cross-section, port volume and shape, and the relationship between the size of the throat and the valve seat.
If these attributes are wrong, you can work forever on the flow bench and not overcome the fundamental flaws.
Here's a do-it-yourself example: Turn on a garden hose and the water dribbles out a couple of feet. Now put a nozzle on the hose and the water will spray across your backyard. The water pressure and volume haven't changed, but the velocity has increased dramatically. Now think about air and fuel going into your engine's cylinders. Which would you prefer: slow and lazy or fast and responsive?
An engineer will tell you that an engine requires a prescribed amount of air and fuel to produce's "x" amount of horsepower. In a perfect world, that may be true - but we race with imperfect engines. The shape and cross sectional area of the runners is absolutely critical to performance. For example, I have two sets of Pro Stock cylinder heads that produce nearly identical flow numbers, yet one pair produces nearly150 more horsepower at 9200 rpm than the other. The flow bench can't tell the difference between them, but the engine certainly can.
There are software programs that claim to be able to predict an engine's performance based on airflow numbers. Unfortunately, a critical shortcoming of many of these programs is that they are based on inaccurate information or false assumptions. A computer is an excellent calculator, but it is not an experienced engine builder. The software doesn't know if the short-turn radius is shaped properly, whether the flow is turbulent at critical valve lifts, or whether the flame speed is fast enough. Racers have a tendency to believe that computers are infallible, so they accept the software solutions as gospel when in fact they be badly flawed. Textbooks would have you believe that an exhaust to intake flow ratio of 80 percent is ideal - yet a typical Pro Stock head has exhaust posts that flow less than 60 percent of the intake runners, (Bruce here, YES!)
You can improve the exhaust flow tremendously with about 40 minutes of work with a hand grinder, but the supposed improvements will just about kill the engine's on-track performance. I know because I've been there. We also have learned that the low-lift flow, (meaning anything below .400 valve lift in a Pro Stock engine with a .900 lift camshaft) is relatively unimportant.
Think about the valve events in a racing engine: From the point when the valve is first moves off its seat until it reaches mid-lift, the piston is either going the wrong way, (that is, it is rising in the cylinder) or it is parked near Top Dead Center. The piston doesn't begin to move away from the combustion chamber with enough velocity to lower the pressure in the cylinder until the valve is nearly halfway open.
Consequently, it is high-lift flow that really matters in a drag race engine. The shape of the combustion chamber also has a significant impact on performance.
A conventional chamber with deep reliefs around the valve seats and a relatively flat valve seat angle can produce terrific flow at .200 - .300 valve lift. Today, a state-of-the-art chamber typically has 55-degree valve seats and steep walls that guide the air/fuel mixture into the cylinder to enhance high lift flow. This doesn't mean that every racer needs state-of-the-art Pro-Stock cylinder heads - along with the high maintenance they require.
The heads have to match the application. Conventional combustion chambers and 45-degree valve seats are just fine for a dependable, low-maintenance racing engine that will run a full season between overhauls.
The classic Hemi combustion chamber is capable of producing impressive flow numbers, but it's not going to make impressive power. Engine technology in all forms of motorsports is converging around smaller, high-efficiency combustion chamber designs. You can see the result in lower brake specific fuel consumption (BSFC) numbers, which indicate improved engine efficiency. Twenty years ago, a racing engine with a .48 BSFC was considered

Thanks for the post great info, I will be doing most of the initial work on plaster copy of the head before i touch the real heads. think this was an interview with one of the Reher-Morison head porting guru's.

Gert

I think this is great. My concerns would be:

1) You may increase the flow of the head but it may not correlate to better performance on the dyno; and

2) You may see better performance on the dyno but it may not correlate to better performance on the track.

To alleviate both concerns, I would start by COPYING the known porting solutions in the Porsche community. While the real secrets are still secret, there is enough information in the public domain, including here on the forum, to get you started. Then you can iterate from there.

You seem like a technical guy, how will you replicate the port shape from cylinder to cylinder? I wonder if there are any shops with a digital Coordinate Measuring Machine that could digitize your successful port shape, which would then allow you to replicate it across all the cylinders with a CNC milling machine? That is the modern approach.

But enough caveats which you know, I admire your DIY approach and will be watching this thread closely for ideas.

Talk about a Labor of Love, 2 weeks of Clean up work on my own 3.2 heads :)

Wish the pictures turned out better, they don't do justice to the results.

http://forums.pelicanparts.com/uploa...1233944992.jpg


http://forums.pelicanparts.com/uploa...1233945040.jpg


http://forums.pelicanparts.com/uploa...1233945081.jpg

Eh! once you get your flow bench up and running, if possible could you flow test a Motronic (barn door) AFM? It would be nice to know the restriction of this unit when calculating boost. Thanks

Buy a used camera off of Ebay with "super macro" feature. Works wonders.

I just use a cheapy because someday its going to get dropped into the wash tank!

http://i30.photobucket.com/albums/c3...1/100_7844.jpg

Craig, that looks like a Georgia O'Keefe painting.

SOLD

I take paypal:D

OK, but only if you will deliver it and hang it on the ceiling.

What was this thread about anyway? :)

subscribed

The stock Porsche inlet and exhaust ports are pretty nice right out of the mold. But I love what you guys do to them...

I wonder what the cost vs. time graph would look like for die grinding by hand next to CNC?

Has someone done this?

Mark

Can't say's I have, but.......

A CMM to digitize a stock ports (or one of your choosing) as a baseline.
A CATIA work station to model it, reshape, then program for the mill.
A 5 axis mill.

There's about 600-700K.

You may find someone that has the necessary equipment/personnel with a labor rate of under 150 per hour.....but I doubt it. Couple hundred man hours for the first attempt.

Reinventing the wheel costs money. :D

Better to find a sucessful undertaking (with proof of the pudding) and pay to have yours done.

JP,
I didn't mean to compare a start-up from scratch! That is always big bucks. But now that there are some shops out there that have made the committment, like Rennsport Systems, the per unit cost should come down. Probably never approaching the DIY cost, but who knows?

Mark

You can do a "street port" job yourself where you're just smoothing out the origonal casting lines and marks and the abrupt and unsmooth factory machine marks where it transitions to the valve seat.
If you don't overdo it and screw up the shortside radius that might give you around 5-8 horsepower up top, maybe a little more.

You can get a generous supply 80 grit sandpaper cones and flaps and arbors in a little $25 kit at harbor freight.
You use them on an air powered straight die grinder, but you better have some experince and have excellent hand~eye coordination and feel.

You want a course finish on the intake ports to create surface turbulance on the surface of the ports, and a polished smooth finish in the exhaust ports so carbon won't stick as well.

Update Flowbench
 

John, Craig interesting views :)

John, you are right these are some of my main concerns, i dont have a mega budget and time to test every change on the dyno and track and this is where i think some of the real secrets are created. ;) I have collected as much as possible visuals and plan to use that as a starting point. There are some literature on the subject and a lot of information on the net (Mostly American hot rodders and drag racers). In my situation i will have to do a lot more research before making changes and hope to uncover the secrets as i go along, the key being research both on and off the flowbench and a lot of help from knowldeable folks in this and other communities.


I am going to try and stay away from new technology and stick to purely "home brew " porting that anyone should be able to do with a dremel or die grinder and some hand tools. I am planning on making a positive mold of the final product create 1/4" or 1/2" measurement segments and transfer the measurements / shape to the other heads and finally balance them from a flow point of view.


Dynamohum: did your labor of love yield any positive results? and yes i will flow test your AFM.


Here is sone updates on the flowbench:

I have been working mostly on completing the flowbench which is taking a lot longer than anticipated. MDF sucks, this stuff gets in everywhere is as bad as sanding drywall.

I completed the trail construction and will be knocking it down to the core again to start sealing and painting the inside. By the end of the week i should be done with the construction and will start installing the vacuum motors and wiring.


http://forums.pelicanparts.com/uploa...1234275503.jpg


http://forums.pelicanparts.com/uploa...1234275578.jpg

http://forums.pelicanparts.com/uploa...1234275615.jpg

Cheers
Gert

Ps: Spell check didnt work

Hey Kenik, you mentioned the velocity #s can you share those? It would be interesting to compare them to the stock heads once i get the flowbench rigged up.

Have you already completed the engine?

Thanks
Gert