Hot Rod Techniques

eric_marsh · #1 01-05-2010, 07:40 PM

I've been involved in ground based motor sports and engine development for a long time. Now that I'm learning about aircraft I'm especially curious about the state of engine development.

It would seem to me that a very carefully developed cylinder head would be of great benefit to a normally aspirated aircraft engine, especially as the air density becomes less. Do people experiment with things like porting the heads and perhaps putting oversized valves? Are there guys that specialize in performance work for private aviation or do FAA regulations dictate a hands off policy?

Just curious.

Geico266 · #2 01-05-2010, 07:46 PM

With the experimental category it's up to you. It might interesting to see what tricks you can apply to aircraft engines. Remember, the bores are much bigger than what you are used to though. Measureing the performance after improvement is the most challenging, but I'm sure you'll think of something!

N941WR · #3 01-05-2010, 07:48 PM

Eric,

P&P's are common as is exhaust manifold matching. The risk is that you reduce TBO when grinding on cylinder heads.

Check out LyCon, Eagle Engine, Barrett, and others. Most quote between 15 and 20 hp gains with a light port and polish job. LyCon charges $250 a cylinder so it isn't cheap. I have also been told by one engine builder that adding dual EI will increase hp by 6%, regardless of engine or ignition.

BTW, this is not something you want to do yourself as it is easy to trash a cylinder, from what I have been told.

eric_marsh · #4 01-05-2010, 08:03 PM

At this point I'm just asking questions and trying to learn. But I'm just finishing a computerized home built flow bench that in theory ought to be good for some 400 cfm at 28" of vacuum. It would be cool if I had some junk heads to play with.

I can see that an optimal engine design is different for an aircraft than for other applications, especially if a gear reduction isn't used. But it would seem to me that with a relatively small cam it would be more important than ever to try to get lots of flow moving as soon as possible (which usually means valves with large circumferences or multiple valves) and a port designed to achieve a high velocity yet good flow for maximum cylinder filling. My gut instinct is that with reduced ambient pressure the engine would respond to this sort of thing even better than at increased pressures, i.e. good volumetric filling would be especially beneficial at higher altitudes. But then again I might be completely off base on that one.

As for testing the results a small dyno ought to do the trick just fine. Would it be possible to restrict the intake flow to simulate high altitudes? Just thinking aloud here.

Here's a pic of my flow bench before I put the blowers in and another one of the interface.

eric_marsh · #5 01-05-2010, 08:11 PM

Quote:

Originally Posted by N941WR

Eric,

P&P's are common as is exhaust manifold matching. The risk is that you reduce TBO when grinding on cylinder heads.

Check out LyCon, Eagle Engine, Barrett, and others. Most quote between 15 and 20 hp gains with a light port and polish job. LyCon charges $250 a cylinder so it isn't cheap. I have also been told by one engine builder that adding dual EI will increase hp by 6%, regardless of engine or ignition.

I'd be sensitive to the TBO issue. Beyond that, it seems like $1000 for 10% more power is a bargain.

SHIPCHIEF · #6 01-05-2010, 10:30 PM

Eric:
You go boy!
If you have the experience that you say, then you already know what it takes in terms of invested time, $ and what you may or may not get as a result.
In direct drive aircraft engines that only turn about 2700 RPM max, there is twice as much time for cylinder filling than an equivalent engine turning twice the RPM. On the other hand, these are pretty big cylinders, so factor that in too.
Air cooled cylinder/head assemblies are prone to cracking from high local temperatures, so a lot of exhaust port grinding can remove metal that might be there by design to transfer heat out to the fins.
I'm sure you understand all this, so if you can get someone to donate a red tagged cylinder assembly, you can get started with no harm to anyone.
Maybe someone on this forum has such a cylinder, or you could ask around at the local airport.
Just don't infer that any cylinder you take will ever be run on an engine in a certified aircraft.
Meanwhile, other people have gone this route before. You can learn from some of them....what they think is good or bad, what is FAA legal for certified engines and why.
This is a Van's Aircraft forum, so the airframe is mostly the topic, but there are some gearheads here in the "Fire Wall Forward" section too.

Bob Axsom · #7 01-06-2010, 01:32 AM

I would like to track the experimental work of someone in the propulsion system arena. I do race my RV and additional power would certainly be welcome. There are many problems such as the danger associated with engine failure in an airplane - the $1,000 price for a significant increase in power is almost trivial but the cost of a single engine failure is incalculable. In the recently released movie "Air Racer: Chasing the Dream" Daryl Greenamyer says some revealing things about the engine in his Lancair Legacy but the most sobering is "I have about 175 hours on the airplane and this is the 4th engine." It is also said about his engine in the movie that in its normal configuration it puts out 300 horse power but his is developing between 600 and 700 horsepower. His example shows that it not only can be done but it is being done in spite of the cost and risks. I admire the risk taker and the innovator and wish you well.

The Sport Air Racing League (www.sportairrace.org) currently has two classes devoted to RVs described under the mission link at that site. Basically any RV with a 320 cu. in. engine can fly in the RV Red class and any RV with a 360 cu. in. engine can fly in the RV Blue class. Three years of racing has just ended and all of the speeds for every airplane in every race are listed. SARL is currently considering another RV class open to larger engines and it may be called the RV Gold class. The race schedule for 2010 now includes 12 races heavily focused in Texas but there are races in Alabama, Arkansas, Colorado, Pennsylvania, Tennessee and Ontario, Canada. They are listed under "Calendar of Events" at www.sportairrace.org. It would seem to me that there is a "proving ground" to demonstrate the improved performance if you have the resources and the ability to produce the "better engines". Some periodicals and e-mail publications are just starting to publish results so getting the word out will not be as effective as it would be if reported in EAA Sport Aviation for example. Again, I wish you well and I would like to see Eric Marsh be one of those iconic names that come to mind when people think of aircraft engine performance.

Good Luck,

Bob Axsom

eric_marsh · #8 01-06-2010, 06:15 AM

Well, I most certainly wouldn't want to get ahead of myself. As much as anything I'm just curious about how well what I've learned over the years would be applicable to aircraft. I understand that the very most important thing is reliability.

There is a certain ratio of intake to exhaust flow that's considered to be more or less standard. In fact a lot of the race car guys are moving to very small exhaust valves in order to facilitate larger intake valves and more flow on that side. If the exhaust side is prone to developing cracks then it would likely be best just to leave them alone. The piston will always force the gas out of the cylinder - the real benefit comes from making sure the cylinder is as full as possible. That doesn't necessarily mean going nuts with a grinder. Often relatively small changes in the right place can bring significant benefits. The photos I've seen show some really big bosses around the intake guide. I'd think that some shaping there would help without adversely affecting reliability. Bigger valves are pretty much always a good thing but if the intake seats are cast in that will be the limiting factor. Perhaps a nice radius valve job?

Are there any EFI conversions available? Of course with EFI if you lose electrical power that would be a bad thing. Perhaps a system that could fall back to the carb in the event of a failure?

I would think that wide band o2 exhaust gas sensors would be useful. Knowing the damage that can be caused by an overly lean mixture the idea of adjusting fuel/air ratios by feel sounds kind of scary.

Again, please remember that I'm just tossing out ideas based on my past experience which may turn out to be not very useful in this application.

n468ac · #9 01-06-2010, 06:38 PM

Quote:

Originally Posted by eric_marsh

I would think that wide band o2 exhaust gas sensors would be useful. Knowing the damage that can be caused by an overly lean mixture the idea of adjusting fuel/air ratios by feel sounds kind of scary.

I too have thought about a wide band o2 sensor and gauge ... but I would think the lead in av gas would cause the o2 sensor to fail in unpredictable ways.

DEWATSON · #10 01-06-2010, 06:59 PM

Eric,

I, like you, have some experience hot rodding automobile engines. Honestly, the things that you and I are used to doing to create more power usually result in higher engine RPM to realize the power increase. Aircraft engines are pretty much limited to their operating RPMs. Propeller tip speed limitations are another consideration. Porting and polishing, etc. will help some with these slower turning engines, but I believe the best research should be done with ignition timing and more efficient fuel injection systems. No doubt there is a lot that can be accomplished. Get after it man!!!!! Post your thoughts and keep us up to date.

David
49FD