eric_marsh

eric_marsh

Well Known Member
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.
 
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!
 
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.
 
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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.

fb7.jpg


fb16.jpg
 
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N941WR said:
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.
Click to expand...

I'd be sensitive to the TBO issue. Beyond that, it seems like $1000 for 10% more power is a bargain.
 
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.
 
I for 1

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
 
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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.
 
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eric_marsh said:
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.
Click to expand...

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.
 
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
 
Eric,

I too am a "gearhead"... As you get more involved in aviation I suspect that like me, you will find a lot of things lacking. However, you don't need to look very far under the cowl to find things that are choking the engine. Just like with cars, most gains can be had in the induction and exhaust systems. Even "good" homebuilt exhausts are still a compromise between weight and space requirements. You will see very few true "tuned" 4-1 headers on aircraft - yet they are worth between 10-15 HP on a 180 Lyc. Based upon a great study by CAFE and EAA a few years ago, I built a true 4-1 header with 40" primaries for my airplane and it works great. Following exhaust, a good induction system, allowing high pressure recovery, as well as "tuned' induction tubes are worth gains. On my next engine, I'm doing tuned exhaust, and a custom tuned "cold" induction. It's simply a lot of work, because there is not a lot of aftermarket products supporting this aspect of aviation. It's much like the good old days of hot rodding; before you could order a NHRA spec engine out of the Summit catalog. The difference is, we have decades of auto racing development for guidance.

I would say beyond a light port cleanup and careful assembly and perhaps higher compression pistons, little needs to be done to the basic Lycoming engine. In other words, the biggest gains are exhaust, induction and ignition.
 
eric_marsh said:
...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?...
Click to expand...
This is what you are looking for:
http://www.rotaryaviation.com/eficont.html

eric_marsh said:
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...
Click to expand...
Eric,
My business partner in the EICommander and I have designed one for the Reno racers but due to the limited production run, it is VERY costly. Thus, we haven't sold many.

We have found that the O2 sensors last about 200 hours each for the wide bands and less for the narrow bands due to the leaded fuel.

Don't discount the EICommander coupled with a pair of E/P-mags as a great advance in racing performance as it gives you the ability to tune your ignition on race day and in flight. In addition, it can continuously monitor the condition of your ignition (114 series required) and let you know if you have either a fouled plug or broken plug wire. (That's an upgrade we have under going user testing right now that looks very promising.)
 
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I've noted a number of comments about the benefits of improved ignition. Sounds like one of the challenges is just lighting the mix. That's one of the reasons EFI came to mind - I thought it would provide better atomization of the fuel, not to mention that fuel injection can be used with larger bodies than a carb with venturi.

Most hot rodding gains performance by increasing engine speed which would be the wrong approach. I'm thinking that what one would want to do everything possible to maximize volumetric efficiency at the designed operational speed. It may be that the current designs are pretty well optimized in which case this is a moot point. Toolbuilder, your suggestions sound about right to me.

This conversation may just be academic. But it's interesting to me anyway. I'm going to do some digging and see if I can find some junk heads to look at. There are some good engine modeling programs out there and if I could get a cam profile, head flow and so forth it would be interesting to see what they have to say.
 
eric_marsh said:
...It may be that the current designs are pretty well optimized in which case this is a moot point. Toolbuilder, your suggestions sound about right to me...
Click to expand...

It's not that I think the current designs are optimized as much as I think there is significant "low hanging fruit" to pick before you have to start looking for the optimum port shape, cam profile, etc. The basic engine is a good baseline for external modifications because it is a durable, known configuration. Just like with a production car, the biggest, easiest gains are had when throwing away the restrictive exhaust and intake system and replacing it with something optimized for the engine installation and mission. I certainly encourage you to play with some junk cylinders though? I would just steer you toward the ?obvious? fixes in aircraft engine installations first? There?s plenty of ?em.

Your comments on ignition are on the right track - getting the fire lit is part of it, but the hotter spark of the electronic systems are only part of the solution. With their fixed timing, magnetos are at a severe disadvantage in a variable speed engine. This is because the flame front moves across the piston at essentially the same speed regardless of RPM, and as you know, start of the combustion event must be altered to ensure the peak cylinder pressure is reached at the same point in crankshaft rotation. With fixed timing, there is no way to alter the start (and peak) point of the combustion event. This problem is compounded in a big bore aircraft engine because the flame front has much farther to travel than a car or motorcycle. This is the primary reason for running two plugs in an aircraft cylinder - so that the flame front has only half the distance to travel. The other part of the EI is, as you say, getting the fire lit in the first place. This is not too much trouble in thick air and a rich mixture, but at altitude and running LOP, you need a fat spark to reach out and convince every fuel atom to burn. On a recent flight, I could not get the mixture any leaner than 35 LOP on the magneto equipped -8 I was in without significant stumbling, roughness and speed loss. I suspect that once we get the P-Mags installed, it will run smooth and fast at 50 LOP.
 
More HP, same redline...

requires raising BMEP. Take a careful look at the way the cylinders are attached to the crankcase (at their base). Consider that the crankcase is two crude aluminum halves bolted together and that DivCo makes a good living welding cracked crankcsases. Consider that the crankshaft is supported by 3 main bearings and the displacement per cylinder is 90 cubic inches.

Reno air racers fly their aircraft to the races on stock engines and then put their race engines in. Many of the engines don't survive the length of a race, which is about 15 minutes.

In my humble mechanical engineering opinion (IMHMEO), go with cubic inches if you want more power, like a Rocket or a Super 6. I am absolutely certain that one can "hot rod" a 360. I am just as absolutely certain that one will trade durability for more power. In another life I raced Super Late Models. Hot rodding the small block Chevrolet engine resulted in power gains that reached the point where main bearing webs were being jerked out of the block!

Larry
 
Agreed.

more power; same RPM redline...

LarryT said:
requires raising BMEP. Take a careful look at the way the cylinders are attached to the crankcase (at their base). Consider that the crankcase is two crude aluminum halves bolted together and that DivCo makes a good living welding cracked crankcsases. Consider that the crankshaft is supported by 3 main bearings and the displacement per cylinder is 90 cubic inches.

Reno air racers fly their aircraft to the races on stock engines and then put their race engines in. Many of the engines don't survive the length of a race, which is about 15 minutes.

In my humble mechanical engineering opinion (IMHMEO), go with cubic inches if you want more power, like a Rocket or a Super 6. I am absolutely certain that one can "hot rod" a 360. I am just as absolutely certain that one will trade durability for more power. In another life I raced Super Late Models. Hot rodding the small block Chevrolet engine resulted in power gains that reached the point where main bearing webs were being jerked out of the block!

Larry
Click to expand...

Hey Fellas:

I have raced at Reno, and I flew there, raced, and flew home (1400 miles) on the same engine. This particular engine was very close to stock, with induction system mods (cold air sump as a start). Piece o cake...with a stock engine...

Suggestion: if you want more power, and you can't/won't fit a larger displacement engine, then you will need to raise BMEP by another means. I would suggest that, for the money & time spent, the forced induction path is the most practical method. Tom Shpakow at G3 (I do not use any of his products -- yet) is probably the point man for such mods. Check out his website, specifically the details of his supercharged 540. I have no idea if he has such as could be fitted on a 4 cyl Lyc...but I think he'd be the man to ask.

Carry on!
Mark
 
LarryT said:
requires raising BMEP. Take a careful look at the way the cylinders are attached to the crankcase (at their base). Consider that the crankcase is two crude aluminum halves bolted together and that DivCo makes a good living welding cracked crankcsases. Consider that the crankshaft is supported by 3 main bearings and the displacement per cylinder is 90 cubic inches.
Click to expand...

I don't think we are talking about going nuts here, just looking at possibly improving on some inefficiencies. Besides, isn't more displacement just doing the same thing, i.e. increasing the pressure on the crank? 90 inches per cylinder - those are big puppies.

Your point about pulling the main webbing out is an interesting one though. In an inline or V engine configuration the main webbing is carrying the full load. Is that also true with a boxer design? Seems like the firing order would have an effect.
 
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Rivethead said:
Give LyCon a call. Ken, the owner of the place is a horse power fanatic. I took a tour of the shop and they do it all. I paraphrase 'We make an IO-360 that makes 250 horse power all day long. It's all good'. When I was talking to Ken he told me they were making 10.5/1 heads on a CNC machine out of billet Aluminum. It's a very impressive operation.
Click to expand...

X2 on Lycon.

When I was there last summer, they were making a cold air sump out of a big old chunk of solid alum------amazing work.
 
Rivethead said:
Give LyCon a call. Ken, the owner of the place is a horse power fanatic. I took a tour of the shop and they do it all. I paraphrase 'We make an IO-360 that makes 250 horse power all day long. It's all good'. When I was talking to Ken he told me they were making 10.5/1 heads on a CNC machine out of billet Aluminum. It's a very impressive operation.
Click to expand...

I bet he's an interesting guy to talk to and I'd love to see his operation. But a big part of the satisfaction of hot rodding is solving problems by one's self. And of course for those of us who can't afford the really nice parts that the big guys manufacturer there's the benefit of doing things on a tight budget. I imagine that a lot of guys are home building aircraft for just those reasons.

As a case in point I've been tinkering with my dragbike for years now just for the satisfaction of experimenting and trying to learn something new. Here's a link to my blog.

BTW, I may have some heads showing up in a few weeks.
 
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Zero4Zulu said:
My engine was built here. www.performanceengines.com

My cylinders were flow matched and have a five angle valve grind to assist flow. 10:1 forged pistons and a custom ground cam.

I hope to fly with this engine this summer when the plane rebuild is finished.
Click to expand...

Lycon or Barrett if you want a big name. We use Pacific Continental Engines here at KWHP for our racing engines, and was very pleased.
 
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Aircraft Engine Performance

eric_marsh said:
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.
Click to expand...

Hi Eric,
Great topic, When you get your bench set up, don?t be surprise when you find out that on a stock head max CFM comes in @ about .380? to .400? valve lift. I?ve been on the flow bench with a Lycoming parallel valve over the past few weeks working on different type of configurations. Implementing techniques that I have learned over the pass years in my racing experience. This month 01/17/10 we will be testing these theories on a RV7 with an aspirated IO-360. We will be conducting static thrust pulls with a digital tension meter to measure pounds of thrust on the ground. When we determine the amount of thrust increase, then we will go test fly for actual in-flight data. I have many hours into this project and I?m excited to see the favorable results. Data will be posted on my facebook group that I just started Aircraft Engine Performance (New @ this & join if you like). Have fun with the bench, its a great learning curve.

Thomas Shpakow
www.g3ignition.com
 
One thing I would like to know is if at 2700 RPMs and the stock valve lift do the heads flow at the needed rate to match the pumping capacity of the piston. Trying to decide if porting/polishing is worthwhile.

Glenn Wilkinson
 
G3i Ignition said:
Hi Eric,
Great topic, When you get your bench set up, don’t be surprise when you find out that on a stock head max CFM comes in @ about .380” to .400” valve lift. I’ve been on the flow bench with a Lycoming parallel valve over the past few weeks working on different type of configurations. Implementing techniques that I have learned over the pass years in my racing experience. This month 01/17/10 we will be testing these theories on a RV7 with an aspirated IO-360. We will be conducting static thrust pulls with a digital tension meter to measure pounds of thrust on the ground. When we determine the amount of thrust increase, then we will go test fly for actual in-flight data. I have many hours into this project and I’m excited to see the favorable results. Data will be posted on my facebook group that I just started Aircraft Engine Performance (New @ this & join if you like). Have fun with the bench, its a great learning curve.

Thomas Shpakow
www.g3ignition.com
Click to expand...

Thomas,

Can you give me a link to Aircraft Engine Performance? I'm interested in seeing what you've got going on there.

Are you using a constant speed prop on your dyno?

This looks like it should be very interesting. I'm especially looking forward to trying to do some modeling.

Eric
 
glenn654 said:
One thing I would like to know is if at 2700 RPMs and the stock valve lift do the heads flow at the needed rate to match the pumping capacity of the piston. Trying to decide if porting/polishing is worthwhile.

Glenn Wilkinson
Click to expand...

That's one of the questions I'd like to know myself, but it's probably going to take a while to get to that point. I imagine that air density will play into that too.
 
To answer the last question...

...an IO-360 parallel valve engine is doing just a nad over 10 Bar BMEP at 2700rpm (180hp). Since many good engines are doing much better than 11 Bar and some over 13 Bar (at peak torque), it's safe to assume that "things could be done" to improve volumetric efficiency of the parallel valve head.

One thing that can be done is to replace them with an angle-valve head. Here, BMEP leaps to 11.2 Bar, which shows you what dramatic changes are needed to make any meaningful improvements.

A
 
Aircraft engine performance & G3i FaceBook links

eric_marsh said:
Thomas,

Can you give me a link to Aircraft Engine Performance? I'm interested in seeing what you've got going on there.

Are you using a constant speed prop on your dyno?

This looks like it should be very interesting. I'm especially looking forward to trying to do some modeling.

Eric
Click to expand...

Hi Eric,
Just started the group, Here's the links:
Aircraft Engine Performance
http://www.facebook.com/help/?ref=pf#/group.php?gid=252683466347

G3i:
http://www.facebook.com/home.php?filter=pp#/pages/G3i-Ignition/243104229291?ref=ts

Thomas
www.g3ignition.com
 
Static dyno pull equipment

Ground testing for static thrust is a simple device. A 2000 lb load sensing digital scale that I purchased off of ebay. It has many in-put and read-out programs, the read out can be fine tuned down to 1/10 lbs. with peak and hold options. The constant speed prop works great as the absorber for the hold RPM at different MP. Also works well with fixed pitch also, just keep RPM data in final calculations.
Thomas
www.g3ignition.com
 
I've been looking at photos of Lycoming engines. I don't have a good photo but from what I've seen it appears that some filling at the short turn radius would be beneficial.

Also, why is the plenum in the sump? Because of space constraints?

I would really like to get my hands on a disassembled engine.
 
eric_marsh said:
Also, why is the plenum in the sump? Because of space constraints?
Click to expand...

It was to prevent intake freezing, and to keep the fuel atomized well. Needed on carb engines, not much of an issue with FI.

Basic safety thing, keeping the engine running is pretty much a high priority in an aircraft engine, lots of things will look a bit screwy to folks whose engine knowledge is derived from the automotive world, and even worse if that was the hot rod side of the automotive world.

Bit different mission that that air gap manifold you are used to.
 
Yea I can appreciate that when dealing with aircraft as a general rule keeping them in the air tends to be a priority.

I've got three parallel valve heads and one angle valve head on their way here. Should have some preliminary numbers before long.

Once I've got the head flowed there are three things that I need before I can try to model the engine. One is the connecting rod length and the second is the camshaft profile degreed out. I guess that the third would be the specs of the intake runner tubes.
 
eric_marsh said:
Yea I can appreciate that when dealing with aircraft as a general rule keeping them in the air tends to be a priority.

I've got three parallel valve heads and one angle valve head on their way here. Should have some preliminary numbers before long.

Once I've got the head flowed there are three things that I need before I can try to model the engine. One is the connecting rod length and the second is the camshaft profile degreed out. I guess that the third would be the specs of the intake runner tubes.
Click to expand...

Getting the cam info should be easy but the intake tubes vary with the sump used and there are a number of different sumps. A few examples are forward facing horizontal, rear facing horizontal, forward facing horizontal cold air, vertical, and with the vertical, there are a few different locations of the carb opening on the sump.

How much time and money do you have?

One suggestion, take one model and "model" that, see what you can do, and then move to the other variants.
 
I've got a lot more time than I have money - I'm curious as to how the pipes affect intake air flow. So it's a matter of mocking up one one with about the correct length and diameter or for that matter playing with those variables.

I'm not familiar with GT Power - guess I'll have to look it up. Initially I'm thinking Pipe Max (http://www.maxracesoftware.com/pipemax36xp2.htm). I've also got a 1 cyl version of the engine analysis software written by Lotus (http://www.lesoft.co.uk/index1.html) though I've not yet completely figured it out yet.
 
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I've got three parallel valve Lycoming heads now and one angle valve. Unfortunately I didn't get valves or retainers with the heads so I'm looking for those now.

Just for giggles I put one of the heads on my bench, blocked of the bores of the valve guides, plugged the plug holes and exhaust port and flowed it with no intake valve at all. It looks like it's pulling about 205 CFM at 28" of water.

Interestingly enough there is a place about 3/8" in from the left wall of the port where there is no air velocity at all.

I really need valves to come up with more realistic numbers. I'm trying to get some now.
 
100% Volumetric efficiency

is 286 cfm @ 2750 RPM if I did the math right. I don't think the engine turns fast enough to be able to exceed 100% volumetric efficiency, but I've been wrong before. With roller cams and high revving V-8s, most race car engines were well above 100% V.E.

360 cu. in. / 2 x 2750 RPM / 1728 cu. in per cu. ft. = 286.46cfm

Not being a cam designer, I don't know enough about the affect of the valves at low opening heights. During my racing days, I bought some stuff from Diamond Racing products. Jim Cavilaro told me that his partner Butch Elkins devoted a lot of time to improving flow at partial valve opening positions. (I still have a new-in-the-box set of aluminum small block heads that Butch did for a "stock-block" Indy engine. Apparently I never throw anything away.)

LarryT

eric_marsh said:
I've got three parallel valve Lycoming heads now and one angle valve. Unfortunately I didn't get valves or retainers with the heads so I'm looking for those now.

Just for giggles I put one of the heads on my bench, blocked of the bores of the valve guides, plugged the plug holes and exhaust port and flowed it with no intake valve at all. It looks like it's pulling about 205 CFM at 28" of water.

Interestingly enough there is a place about 3/8" in from the left wall of the port where there is no air velocity at all.

I really need valves to come up with more realistic numbers. I'm trying to get some now.
Click to expand...
 
There's is a difference between the bulk flow required by an entire engine and the numbers that a flow bench will give. To do the job right it's necessary to calculate how long the valve is open, the mean lift and then use those numbers to determine how much flow is required. The head has peak flow when the valve is open all the way but in an engine the valve is open all the way for the shortest amount of time. Low lift flow is important because that's what gets the air moving through the port. The valve is open somewhere between these two points most of the time.

To really do it right probably takes a computer though and the valve lift profile (well cam profile) needs to be calculated against against the profile of the flow through the cylinder head.

So all I need is some valves. :rolleyes:
 
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